By the End of This Topic, You Should Be Able To
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Higher Human Biology
Unit 2: Physiology and Health Learning Objectives
By the end of this topic, you should be able to:
• explain the origin of gametes;
• describe the role of the seminiferous tubules and the interstitial cells;
• describe the role of the prostate gland and seminal vesicles;
• describe the development of the ova in the ovary;
• describe the functions of the follicle in the ovary;
• describe the process of fertilisation
1. Gamete Production in Males and Females All organisms must reproduce to ensure survival of the species. In animals, the gametes are separated from the other body cells and they only mature when the body of the individual reaches a stage in growth at which it can support the offspring.
Gametes are produced from a basic cell type called GERMLINE cells.
REMEMBER! Any cell which is not a gamete is called a SOMATIC cell!
Male Reproductive Organ
The male reproductive organ has 2 main functions;
1. The production of spermatozoa in the seminiferous tubules.
2. The production of testosterone in the interstitial cells to pass directly into the bloodstream. Due to the motility of sperm, it is essential that there is adequate fluid for movement as well as a source of energy.
This is achieved by; 1. Seminal vesicles secreting a fructose rich liquid 2. Prostate gland secreting a lubricating liquid rich in enzymes
Collectively these secretions alongside the sperm is commonly known as SEMEN.
Female Reproductive Organ
The female reproductive organ also has two main functions;
1. The production of ova in the ovaries.
2. The production of the hormone oestrogen from the follicle and progesterone from the corpus luteum. Each ovum in the ovary is surrounded by a follicle which protects the developing egg and secretes the hormone oestrogen to promote proliferation of the endometrium.
After the ovum is released during ovulation the follicle which was protecting it develops into a corpus luteum and secretes the hormone progesterone to promote vascularisation of the endometrium for implantation of a fertilised blastocyst.
As the ovum develops in the ovary it goes through several stages as shown below; Stage 1 - Immature follicle Stage 2 - Follicle starting maturation process, releasing small quantity of oestrogen Stage 3 - Follicle close to maturity, releasing large quantity of oestrogen Stage 4 - Ovulation, follicle moves to surface of ovary and ovum released into oviduct Stage 5 - Corpus luteum after ovulation, releasing progesterone Stage 6 - Corpus luteum degenerating as fertilisation has not occurred
Use the laminate card provided to practice labelling the reproductive organs and the developing ovum. (Match cards for structures and functions also available)
Summary • Sex cells called gametes.
• Gametes are produced from germline cells.
• Sperm are produced in the seminiferous tubules of the testis.
• Testosterone is released from the interstitial cells of the testis.
• The prostate gland and the seminal vesicles secrete fluids collectively called seminal fluid.
• Seminal fluids maintains the mobility and viability of the sperm.
• The ovaries contain many immature ova in various stages of development.
• The ova are contained within follicles.
• The follicles protect the ovum and secrete hormones.
• The release of an ovum from the ovary is called ovulation.
• At ovulation the ovum is released into the oviduct.
• After ovulation the follicle develops into the corpus luteum. • The corpus luteum secretes hormones. Learning Objectives
By the end of this topic, you should be able to:
• explain how hormones cause the onset of puberty
• describe the influence of the pituitary hormones (follicle stimulating hormone and luteinising hormone/interstitial cell stimulating hormone) on the testes and the ovaries
• describe the influence of testosterone on the testes and the negative feedback control of its production;
• describe the influence of the ovarian hormones (oestrogen and progesterone) on the uterus and the pituitary gland;
• explain the changes which take place during the menstrual cycle and the control of these changes through the interaction of various hormones. 2. Hormonal Control
REMEMBER: Hormones are chemical messengers produced by endocrine glands and released into the blood to reach its specific target tissue.
Hormones control the onset of puberty as the hypothalamus secretes a releaser hormone which targets the pituitary gland to start producing 2 specific hormones in boys and girls.
Male Hormone Control
In boys these hormones are:
- follicle stimulating hormone (FSH) to trigger sperm production.
- interstitial cell-stimulating hormone (ICSH) to trigger testosterone production.
Once testosterone is released it builds up in high concentrations in the bloodstream and INHIBITS (prevents) any more FSH and ICSH from being released by the pituitary gland.
Only once the levels have sufficiently lowered is this ‘block’ on the pituitary lifted and activity resumes as normal. This regulatory way of controlling hormone release is called NEGATIVE FEEDBACK CONTROL.
Female Hormone Control
In girls these hormones are:
- follicle stimulating hormone (FSH) to trigger development of each follicle and the secretion of oestrogen.
-luteinising hormone (LH) to trigger ovulation, the development of the
corpus luteum and the secretion of progesterone.
The release of oestrogen promotes the proliferation of the endometrium to ensure that it is prepared for implantation of a fertilised zygote. Oestrogen also promotes the release of LH from the pituitary gland.
The release of progesterone promotes further development of the endometrium into a spongy vascular layer ensuring it is ready for the embedding of the blastocyst if fertilisation has occurred. Progesterone release also inhibits the release of LH and FSH from the pituitary gland in a negative feedback loop. The Menstrual Cycle
The menstrual cycle in humans lasts approximately 28 days, the first day of menstruation being counted as day 1. Menstruation usually lasts about 4 days (but anything from 2 to 7 days is considered normal) and ovulation typically occurs at day 14.
The cycle is split into two phases. The first from menstruation to ovulation, is known as the follicular phase and the second part, from ovulation to the start of menstruation, is the luteal phase.
The following diagram represents the different events working together for the cycle as a way of summarising how each part affects to the next;
THINK! What happens to the hormone levels if fertilisation does NOT occur and what affect does this bring about in the cycle?
______Summary
Onset of Puberty • The hypothalamus triggers the onset of puberty by passing a releaser hormone to the pituitary gland.
• The pituitary responds to this releaser hormone by in turn releasing follicle stimulating hormone (FSH) and luteinising hormone / interstitial cell stimulating hormone (LH/ICSH).
• FSH and LH control the production of gametes throughout the reproductive life of the individual.
• FSH and LH production form part of a negative feedback cycle.
Control of Sperm Production • FSH stimulates the cells lining the seminiferous tubules to produce sperm.
• LH stimulates the interstitial cells to release testosterone.
• Testosterone stimulates the production of sperm by the seminiferous tubules.
• Testosterone activates the prostate gland and the seminal vesicles.
• High levels of testosterone inhibit the production and release of FSH and LH.
• This is an example of negative feedback control.
Control of the Menstrual Cycle • The first day of menstruation marks the start of the menstrual cycle.
• On average a menstrual cycle lasts 28 days.
• The part of the menstrual cycle up to the point of ovulation is called the
follicular phase. • The part of the menstrual cycle after ovulation is called the luteal phase.
Follicular Phase • In the first few days of the cycle, the pituitary releases relatively high levels of FSH.
• FSH stimulates the development of follicles in the ovary.
• FSH stimulates the release of oestrogen by the follicle.
• Oestrogen stimulates the proliferation of the endomentrium in preparation for implantation.
• High oestrogen levels around the time of ovulation cause the production of cervical mucus which is more watery and easily penetrated by sperm.
• The high oestrogen levels of the late follicular phase cause the pituitary
to release a surge of LH into the blood.
• The high level of LH around day 14 triggers ovulation.
Luteal Phase • After ovulation, the high level of LH causes the follicle to develop into the corpus luteum.
• The corpus luteum secretes progesterone and oestrogen.
• Progesterone causes further development and vascularisation of the endometrium.
• This provides an optimum environment for the implantation and growth of the blastocyst.
• During this phase the secretion of both oestrogen and progesterone rise to a maximum and then decline.
• FSH and LH production form part of negative feedback cycle with oestrogen and progesterone. • The high levels of oestrogen and progesterone inhibit the pituitary from
secreting FSH and LH.
• These low level of FSH suppresses the development of further follicles. • The low level of LH causes the corpus luteum to degenerate and progesterone secretion to fall to a minimum.
• The falling level of progesterone at the end of the cycle triggers the start of menstruation.
• The low level of oestrogen at the end of the cycle causes the pituitary to increase secretion of FSH.
• If fertilisation occurs, a hormone from the implanted embryo causes the
corpus luteum to continue producing progesterone for another eight weeks until this function is taken over by the placenta. Learning Objectives
By the end of this topic, you should be able to;
• explain the reasons for infertility treatments and contraception
• contrast the fertile period of males and females
• describe and explain the various treatments for infertility
• explain the basis of the different methods of contraception
3. Human Fertility and Control
Males are capable of producing sperm until the day they die (although production does decrease with age) due to the constant control of the hormones FSH and ICSH in the bloodstream.
Essentially this means that men are CONTINOUSLY FERTILE and can father children at any stage in their life after puberty.
THINK! Are women continuously fertile? Explain your answer: ______
Women only release eggs from puberty until MENOPAUSE (usually around the age of 45-55) and so limits their window of fertility as they get older.
We say that women undergo CYCLICAL FERTILITY due to the delicate balance of hormones which regulate the menstrual cycle - which in turn restricts a woman’s fertility period to only a few days in each month. A woman is fertile immediately after ovulation is triggered. There are 2 physiological indicators which can be used to calculate when this is (particularly for a couple trying to conceive); - Increase in body temperature by around 0.2 to 0.5 - Cervical mucus is secreted (low viscosity to allow sperm easy access)
Infertility Treatments
Use your general knowledge to discuss with your partner what might cause infertility in either males or females. Note your answers below: ______
Statistics show that 1 in 7 couples struggle to conceive within the UK and therefore look to specialists for fertility treatments which are suitable for them.
Treatments for fertility problems could be any of the following: 1. Ovulation drugs 2. Artificial insemination 3. In Vitro Fertilisation (IVF) 4. Intracytoplasmic sperm injections (ICSI)
1. Ovulation Drugs
Ovulation drugs can be given to a woman in order to bring about the normal action of FSH and LH or to prevent the negative feedback of oestrogen on the FSH being secreted.
These drugs can be so effective that they bring about “Super Ovulation” leading to multiple births.
Ovulation drugs are often given to women to collect ova for IVF treatment.
2. Artificial Insemination
Artificial insemination is the procedure of inserting sperm into the female tract without sexual intercourse.
This technique is useful when a male has been diagnosed with a low sperm count as several sperm samples can be collated over a period of time in order to increase the chances of conceiving.
3. In Vitro Fertilisation (IVF)
IVF is one of the most well-known treatments of infertility and overcomes problems occurring due to a blockage of the oviducts as it allows fertilisation to occur outside the body in a culture dish.
There are 6 stages to IVF treatment: 1. Woman is given hormone drugs to stimulate ovulation. 2. Surgical procedure carried out to remove several eggs from the ovary. 3. Eggs are mixed with sperm in a culture dish of nutrient medium to allow fertilisation to occur. (Alternatively ICSI is employed-see next description) 4. Fertilised eggs are incubated in the nutrient medium for 2-3days to allow cell division and embryo formation (blastocyst) 5. Between 2-3 embryos are selected and inserted into the uterus in the hope of 1 egg implanting. 6. The remaining embryos are frozen and stored in case a second attempt at IVF implantation is required.
Practice putting the stages of IVF in order using the match cards provided.
4. Intracytoplasmic Sperm Injections (ICSI)
During IVF when the sperm and eggs are mixed in a culture, there is a good chance of fertilisation occurring due to the large numbers of healthy active sperm.
Intracytoplasmic sperm injections (or ICSI for short) is a technique devised to overcome problems whereby the man’s sperm count is low or many of the mature sperm are defective in some way. The procedure involves directly injecting a single healthy sperm into an egg using a needle to ensure fertilisation. Pre-Implantation Screening/ Diagnosis and Surrounding Ethics
Before an embryo is implanted into the uterus in IVF treatment, one or two cells may be removed and tested for genetic abnormalities. This could be in the form of either: - Pre-implantation genetic screening (PGS) A non-specific test that checks for single gene disorders and common chromosomal abnormalities. - Pre-implantation genetic diagnosis (PGD) A specific test that checks for a known gene of chromosomal defect.
Ethical controversy surrounds these procedures as you can imagine.
THINK: What are the possible arguments for and against the use of these procedures? Discuss your thoughts with your partner and note some points in the table provided below.
Advantages (For) Disadvantages (Against)
Birth Control and Contraception
Contraception is the INTENTIONAL prevention of conception (pregnancy) by either natural or artificial means.
The most common preventatives are in the BARRIER PROTECTION bracket and include: - Condoms - Diaphragm - Cervical cap - Intra-uterine device (IUD) [commonly referred to as the ‘coil’] - Sterilisation procedures.
There are also CHEMICAL methods of contraception which a woman may take in addition to the use of barrier protection: - Combined oral contraceptive pill - ‘Mini’ pill - ‘Morning after’ pill - Implant; Learning Objectives
By the end of this topic, you should be able to:
• describe some of the techniques used to monitor the health of a pregnant woman
and the developing foetus
• describe the background checks which can be made to determine the possibility of an inherited condition in the foetus
• describe routine tests which may be carried out on all pregnant mothers
• describe scanning and diagnostic tests which can be carried out at different stages in pregnancy
• state the conditions which such tests can suggest or identify
• describe the tests carried out after birth and the conditions which they may identify
4. Antenatal and Postnatal Care
Antenatal care is defined as being the routine monitoring and testing carried out with the mother’s permission during the baby’s development in the womb.
Postnatal care is defined as the routine checks after the baby is born.
Antenatal care includes: - Ultrasound imaging - Biochemical tests - Diagnostic tests - Rhesus Antibody tests
1. Ultrasound Imaging
During pregnancy women receive 2 scans using ultrasound technology. The first is carried out between 8-14 weeks and is used to “date” the pregnancy. The second scan is carried out between 18-20 weeks to ensure the foetus is developing normally.
This is a normal 20 week scan of a healthy developing baby, however the image below it shows the anomaly of Downs Syndrome. Can you see any differences between them? 2. Biochemical Tests
Biochemical tests are carried out at various stages throughout a woman’s pregnancy to detect any ‘markers’ (often proteins) which if present at the wrong levels may signify possible abnormalities with the foetus development or a health issue of the mothers.
An example of a biochemical test which is carried out during the early stages of pregnancy is the concentration of the hormone HCG (human chorionic gonadotropin).
This is the basis for many home pregnancy tests as an elevated level of HCG in urine is indicative of a positive pregnancy test. HCG will also be elevated in the blood which is why a blood test is often used to confirm a pregnancy by a doctor.
Another example would be testing for elevated levels of urea in blood plasma and a reduced level of calcium in urine for women who may be suffering from a high risk medical condition during their pregnancy called Pre-Eclampsia.
THINK: What problems might arise if the biochemical tests are carried out at the wrong times during the pregnancy? How do you think health officials overcome this issue? Note your ideas below: ______
3. Diagnostic Testing
A diagnostic test is used to provide a DEFINITIVE result on a suspected condition/ abnormality.
Diagnostic testing is offered to a pregnant woman if she meets any of the following criteria; - Evidence of a potential problem which has already emerged from results of earlier routine tests. - Family history of genetic disorders. - Is classified as being in the high-risk category (over 35 etc.) Diagnostic tests often involve a greater degree of risk of a miscarriage. Two of the most well-known tests include amniocentesis and chorionic villus sampling (CVS).
Details of each test are outlined in the table below:
Amniocentesis Chorionic Villus Sampling Risk Associated Slight increase Drastic increase (miscarriage) Test Carried out Week 14-16 As early as Week 8 Cells Used Amniotic Fluid Placental Cells
4. Rhesus Antibody Testing
REMEMBER! Blood antigens can be ABO but some are (-) and some (+). This is due to the Rhesus D antigen being present or absent.
In a minority of cases, a woman who lacks the rhesus D antigen can carry a baby whom is rhesus D positive.
This poses a dangerous risk to both mother and child if the blood mixes for any reason as the mother’s blood will see the baby’s’ as “foreign” and start to make antibodies to fight them off.
Essentially the mother’s antibodies will attack the baby’s blood resulting in a condition known as haemolytic disease of the new-born.
Blood test typing is carried out in advance of the birth so that preparations of ‘Anti-Rhesus antibodies’ are on standby to give the mother so that her immune system does not have time to create antibodies against the rhesus antigen and thus protect any future ‘incompatible’ pregnancies. Postnatal Care
Diagnostic tests are routinely carried out after birth for metabolic disorders including; PKU, Galactosaemia and Congenital Hyperthyroidism.
Phenylketonuria (PKU)
PKU is an inborn error of metabolism which if left undetected can seriously affect cognitive development amongst other symptoms.
PKU is screened by testing a baby’s’ blood for excess phenylalanine within the first few days of birth.
This condition can be effectively managed by restricting a sufferer’s diet to contain the minimum quantity of phenylalanine required for growth and development thus ensuring as normal a life as possible.
Galactosaemia
Galactosaemia is a rare genetic disorder caused by a mutation which renders one or more of the enzymes required to breakdown galactose dysfunctional. This leads to a toxic accumulation which causes severe adverse health problems. Galactosaemia is treated by eliminating lactose and galactose from the diet entirely, however some sufferers still go on to experience learning difficulties despite this.
REMEMBER! Thyroxin is involved in growth and metabolism and is released by the thyroid gland upon stimulation by TSH from the pituitary.
Use the resources provided or the internet to research the metabolic disorder of Congenital Hypothyroidism and make notes on the condition in the box below.
Genetic Screening and Inheritance
REMEMBER! The X and Y chromosomes are called the sex chromosomes.
All other chromosomes are known as autosomes.
A pattern of inheritance can be created in the form of a family tree (pedigree chart) by a genetic counsellor if a family has a history of genetic disorders to assess the risk of parents passing on the condition to the next generation.
There are 4 different patterns of inheritance you must know about: ~ - Autosomal dominant - Autosomal recessive - Autosomal incomplete dominance - Sex-linked recessive
Autosomal Dominant
Huntington’s chorea is an example of autosomal dominant inheritance as it appears in every generation of the family tree since each sufferer has an affected parent.
The condition is caused by a nucleotide sequence repeat mutation on chromosome 4 and appears when the dominant allele is passed on to the next generation i.e. HH or Hh. Autosomal Recessive
Cystic Fibrosis is an example of autosomal recessive inheritance as it appears relatively rarely and may skip generations in a family tree.
The condition is caused by a frameshift deletion on chromosome 7 producing a non-functioning protein and appears only when the genotype is homozygous recessive i.e. cc.
Any member of the family with a heterozygous genotype is said to be a carrier of the condition.
Autosomal Incomplete Dominance
Sickle-cell disease/trait is an example of autosomal incomplete dominance as the fully expressed form is relatively rare while the partially expressed form is more frequent.
The condition causes red blood cells to become ‘moon’ shaped and thus less efficient at their job in the body. Non-sufferers are homozygous for one incompletely dominant allele i.e. AA, whilst fully expressed sufferers are homozygous for the other incompletely dominant allele i.e. SS.
Carriers of the disorder are heterozygous for both alleles i.e. AS.
Sex-Linked Recessive
Red-Green colour blindness is an example of sex-linked recessive inheritance since the X chromosome is larger than a Y chromosome it contains more genes therefore each of these extra genes is expressed as a phenotype in males all the time (rare in females).
All sufferers of this condition are homozygous recessive and the carriers are heterozygous females.
THINK! Why would a sex-linked condition such as red-green colour blindness be rare in females? ______Summary
Antenatal Screening • Pre-implantation Genetic Diagnosis (PGD) may be carried out as part of the IVF procedure.
• PGD is used to test the DNA of the embryo for the presence of specific
single gene disorders, and for chromosome abnormalities.
• Ultrasound imaging uses very high frequency sound to create images of the foetus in the uterus.
• The first ultrasound scan (dating scan) is carried out between 10 - 14 weeks to determine the age of the foetus and the date when it is due to be born (due date).
• A second ultrasound scan (the anomaly scan) is carried out between 18 - 20 weeks to detect possible physical problems.
• A pregnant woman's blood carries a range of chemicals which can be used to check that the pregnancy is progressing normally.
• The level of these marker chemicals normally varies throughout the pregnancy.
• The timing of these tests must be taken into account in order to avoid false indications about the presence of a disorder.
• A false positive result would be obtained if the level of a marker chemical indicated the presence of a disorder when in fact the foetus did not have it.
• Marker chemicals will be present in the mother's blood during a trouble- free pregnancy, but the presence of a disorder may affect the level of a particular marker.
• Screening tests, like ultrasound scans and blood tests, indicate the likelihood of a disorder being present. • Diagnostic tests, like amniocentesis and chorionic villus sampling, confirm very exactly whether a condition is present or not.
• Diagnostic tests, like amniocentesis and chorionic villus sampling, are invasive and carry a small element of risk of inducing a miscarriage.
• Amniocentesis samples cells from the amniotic fluid.
• Cells from amniocentesis samples are multiplied up in culture and used
to produce a karyotype.
• A karyotype is used to identify anomalies in terms of numbers or structure of chromosomes.
• Chorionic villus sampling (CVS) removes cells from the placenta which can be used immediately to produce a karyotype.
• CVS can be carried out earlier than amniocentesis but entails a correspondingly higher risk of inducing a miscarriage.
Postnatal Screening • A Guthrie heel-prick test is used to collect a blood sample from a newborn child.
• Dried blood from this sample is screened for several inherited disorders.
• Phenylketonuria (PKU) is an autosomal recessive disorder causing an error of metabolism.
• PKU results in high levels of phenylalanine which severely restrict brain development.
• Individuals with PKU are given a restricted diet which lacks phenylalanine. Learning Objectives
By the end of this topic, you should be able to:
• describe the structure and function of the main types of blood vessel.
• explain how their structure is related to their different functions.
• describe the movement of materials in and out of the blood circulation.
• state the substances which move into and out of the blood and tissues.
• state how lymph is formed and what happens to it.
• describe the structure of the heart and the blood circulatory system.
• state what is meant by the terms cardiac output, heart rate and stroke volume.
• explain the calculation of cardiac output.
5. Structures of the Cardiovascular System
The human cardiovascular system is essential in the continuous exchange of substances required for survival such as glucose and oxygen.
REMEMBER! The cardiovascular system itself is composed of; - heart (Cardiac muscle) - blood vessels (Arteries, Veins & Capillaries) - blood (RBC’s, WBC’s, Platelets & Plasma)
The Heart
The heart is responsible for the continuous flow of blood around our entire body. It starts to beat before birth and can sometimes beat even after we have died. REMEMBER! The heart has 4 main chambers; 2 atria and 2 ventricles Label these on the diagram below.
The right half of the heart receives DEOXYGENATED blood from all parts of the body through the veins called the VENA CAVAE, whilst the left half receives OXYGENATED blood returning from the lungs via the PULMONARY VEINS.
Notice the presence of VALVES linking the atria to the ventricles. The purpose of these is to PREVENT the BACKFLOW of blood and keep it moving in one direction.
These are called the atrio-ventricular or AV valves.
The other two valves which are easily observed, are called the SEMI- LUNAR valves and open only during contraction to ensure blood flows in one direction as it leaves the heart.
THINK: Why is the left ventricle wall thicker than the right? Discuss with your partner and note your answer below. ______
There are 3 key terms which are associated with cardiac functioning. Work with your shoulder partner to match each term to its correct definition.
Heart Rate Volume of blood expelled by each ventricle on contraction
Cardiac Output Number of heartbeats that occur per minute
Stroke Volume Volume of blood pumped out of a ventricle per minute
Blood Vessels
The comparison table below highlights the main differences between the arteries, capillaries and veins:
Blood Structure Function Additional Vessel Info. Artery Thick Muscular Layer Carries - High Thick layer of Elastic Fibres blood Pressure away from the heart Vein Thin Muscular Layer Carries - Low Thinner layer of Elastic Fibre blood Pressure towards - Valves the heart Present
Capillaries 1 Cell Thick - - Most Exchange abundant in of body substance - s Microscopic - Connectio n between arterioles to venules
The difference in blood pressure in the arteries and veins is mirrored in the rate of flow and in the distribution of blood between the different parts of the circulatory system.
At any one time, the heart, arteries and capillaries contain about a third of the blood, the other two thirds being in the veins.
REMEMBER! High pressure in the arteries is detected as a pulse Exchange of Materials
The capillaries are the only vessels in which movement of materials between the blood and the tissues occurs.
Their thin wall acts as a filter which allows the liquid fraction of the blood, the plasma, to pass out into the surrounding tissue, where it forms the tissue fluid. This occurs due to the high pressure at which blood arrives at the arterioles and causes pressure filtration within the capillaries.
The diagram below highlights the pressure differences which cause the flow of fluid out of and into the capillaries.
These are measured in mmHg, the standard unit used in medicine for blood pressure;
The tissue fluid diffuses down a concentration gradient towards nearby cells to supply them with their essential requirements.
Due to osmosis 90% of the tissue fluid returns to the capillaries at the venule side of the bed and carries with it the carbon dioxide released by the respiration of the cells, any wastes from their metabolism (e.g. lactic acid, urea), and any products (e.g. hormones). The waste products are then carried around the body until they reach the organs which excrete them (carbon dioxide in the lungs, urea in the kidneys).
For the remaining 10% of tissue fluid, it is absorbed into thin walled lymphatic vessels located in the connective tissue.
The fluid is now referred to as ‘Lymph’. Lymphatic System
The lymph capillaries join to form larger lymph vessels which lead to lymph nodes. (bean shaped filtering stations around the body)
These are dispersed throughout the body, but are especially frequent in the chest, neck, pelvis, armpit, groin and intestinal regions.
The main functions of the lymphatic system are to: Remove excess fluid from tissue. Return protein to cardiovascular system. Remove waste products and toxins. Transport fat. Essential to the immune system.
Use the internet to research the disorders of the lymphatic system: 1. High Blood Pressure 2. Malnutrition 3. Elephantiasis
Use your research to create a short summary of each detailing the cause, symptoms and treatments in the space below.
Disorder Cause Symptoms Treatment Other Info.
High Blood Pressure
Malnutrition
Elephantiasis Summary
The Structure of the heart • The heart consists of four chambers, two (upper) atria and two ventricles.
• Blood enters the heart from the body into the right atrium via the (superior and inferior) vena cava.
• Blood leaves the heart for the lungs from the right ventricle via the pulmonary artery.
• Blood enters the heart from the lungs into the left atrium from the pulmonary vein.
• Blood leaves the heart for the body from the left ventricle in the aorta.
• The atrioventricular valves prevent backflow from the ventricles into the
atria.
• The semilunar valves prevent backflow from the aorta and pulmonary artery into the ventricles.
• The same volume of blood is pumped through each ventricle.
• The blood circulation carries blood from the heart through arteries to the tissues and back through veins to the heart.
• Blood pressure decreases with distance from the heart.
• All blood vessels have a central lumen lined by the endothelium.
Arteries • Compared to veins, arteries have thicker muscular walls
• The outer layer of artery walls is made of connective tissue with elastic fibres.
• The middle layer of artery walls contains smooth muscle and elastic fibres.
• The contractions of the heart create surges of blood under high pressure.
• The elastic fibres in the artery walls allow them to stretch and recoil as these surges of blood pass.
• Contraction of the smooth muscle in the middle layer of the artery wall reduces the diameter of the lumen of the artery. This is called vasoconstriction.
• Vasoconstriction reduces the flow of blood into capillary beds.
• Relaxation of the smooth muscle of the middle layer of the artery wall causes the opposite effect, called vasodilation.
• Vasodilation increases the diameter of the lumen and allows blood to flow into a capillary bed.
Capillaries • Capillaries allow exchange of substances with the tissues.
• The wall of the capillary is very thin, consisting of a layer of endothelium cells and a surrounding layer of connective tissue.
Veins • Compared to arteries, veins have thinner walls with much less smooth muscle.
• Veins contain valves which ensure blood only flows in one direction, back to the heart.
• Blood flow in veins is caused by the contraction of muscles in the vicinity of the vein, so squeezing the vein and causing the blood to move through the valves.
Exchange of materials • The pressure difference between the blood in the capillary and the fluid in the surrounding tissue causes lymph to flow out of the capillary.
• In most capillaries, the escaping fluid consists of water with a variety of
dissolved substances including glucose, oxygen, hormones, amino acids and mineral ions.
• This escaping fluid becomes tissue fluid which is similar to blood plasma but does not contain plasma proteins.
• Tissue fluid returning to the capillaries carries with it carbon dioxide and metabolic wastes for excretion.
Lymph vessels • Ninety percent of the tissue fluid returns to the capillaries.
• Ten percent of the tissue fluid enters lymph vessels.
• Lymph is returned to the veins near the heart. Learning Objectives
At the end of this topic, you should be able to:
• explain how blood is pumped through the heart (the cardiac cycle) and identify the vessels involved
• state the sequence of contraction and relaxation of the muscular walls of the heart during systole and diastole;
• similarly state the sequence and cause of the opening and closing of the heart valves;
• explain the role of the autonomic nervous system in the control of heart rate;
• describe the effect of hormones and exercise on heart rate;
• state the role of the atrioventricular node (AVN);
• state that blood pressure changes in the arteries as a result of the cardiac cycle; and is measured by a sphygmomanometer;
• state a typical blood pressure reading and explain it;
• state that hypertension is a major risk factor for many diseases including coronary heart disease.
6. The Circulatory System
Oxygenated blood is pumped out of the left ventricle into the aorta.
The aorta begins to divide into various other arteries to supply oxygenated blood around the body including:
• Coronary arteries - supplying the heart muscle itself • Carotid artery - carrying blood to the head and brain • Hepatic artery - supplying the liver • Renal arteries - supplying the kidneys Deoxygenated blood is pumped from the right ventricle into the pulmonary artery which carries it to the lungs to be re-oxygenated.
From here the oxygenated blood is carried back to the left atrium via the pulmonary veins.
Work with your partner to try and match the correct veins to the area they are found. Use your previous knowledge about arteries to help you.
Vein Area Found
Jugular Vein Kidneys
Hepatic Vein Intestines/ Liver
Hepatic Portal Vein Head
Renal Liver
Cardiac Cycle
The cardiac cycle refers to the pattern of contraction and relaxation of the heart during one complete heartbeat.
Contraction of the heart is termed as systole while relaxation is known as diastole.
The atria of the heart contract a fraction of a second faster than the ventricles allowing the atrio-ventricular valves (bicuspid and tricuspid valves) to open for blood to rush into the ventricles.
At this point the ventricles are relaxed (in diastole) and the semilunar valves are closed. Only when the ventricles contract do the semi-lunar valves open forcing the blood out of the heart. It is the opening and closing of the heart valves that cause the beating sound which you can hear using a stethoscope.
What Makes it Beat?!
The heart is made of MYOGENIC muscle which means it does not require an electrical stimulus to start contracting and relaxing. Instead the heart is controlled by the sino-atrial node (SA node – commonly called the pacemaker) and the nervous system in synchronisation.
The cells of the SA node, although modified muscle cells, do not themselves contract. They are autorhythmic, sending out between 60 and 100 impulses per minute without any external stimulation! THINK! What is the purpose and function of the AV node? Discuss with your partner and write your answer below.
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Changing Heart Rate
Whilst the pacemaker is responsible for each heart beat it can be altered by activity within your body such as the nervous system or by the release of hormones.
Nervous Control
The heart receives impulses from two nerves: sympathetic nerve parasympathetic nerve
The signals which are received from the sympathetic nerve are excitatory and will increase the heart rate while signals sent from the parasympathetic nerve have the opposite effect. Hormonal Control
Under stressful situations or during exercise, the sympathetic nervous system acts on the adrenal glands to release the hormone EPINEPHRINE (Adrenaline).
When this hormone reaches the SA Node of the heart it brings about a faster rate of impulses and thus an increase in heart rate. (Think Fight or Flight)
Using the resources available to you, find out what an Electrocardiogram shows and explain what is meant by the QRS complex. Create an information poster with your information.
Blood Pressure
Blood pressure is the force caused by blood pushing against the vessels as it travels round your body.
As the heart goes through systole and diastole cycles, the blood pressure rises to a maximum and falls to a minimum. Blood pressure is measured in millimetres of mercury (mmHg) using a sphygmomanometer.
Blood pressure varies greatly from person to person however a typical set of values for a healthy individual would be 120/70 mmHg.
The first number of 120 mmHg is the reading for the systolic pressure while the one below is the diastolic pressure. BP readings are referred to as “120 over 70”.
Hypertension
Hypertension is the term for constant high blood pressure whilst at rest. Indicator levels of hypertension include a BP reading of > 140/90 mmHg.
Hypertension is fairly common in adults over 35 and is a major risk factor for strokes and coronary heart disease. THINK! Hypertension is commonly found in adults with an unhealthy lifestyle. List 5 main factors which put people at risk of developing high blood pressure.
1.______2.______
3.______
4.______
5.______
Summary
The Cardiac Cycle • The cardiac cycle is the pattern of contraction and relaxation of the heart during one complete heartbeat.
• Systole refers to contraction of the muscle and diastole to its relaxation. • Atrial systole starts slightly before ventricular systole, forcing blood through the AV valves into the ventricles.
• Ventricular systole follows, closing the AV valves and forcing blood through the SL valves into the pulmonary artery and the aorta.
• During diastole, relaxation of the muscles of the atria and ventricles causes blood to flow into the atria and through into the ventricles.
• Both atria and ventricles are in diastole for about half of a heart beat.
• During ventricular diastole, backflow of blood under high pressure from
the arteries is prevented by closure of the SL valves.
• The opening and closing of the AV and SL valves cause the heart sounds detected with stethoscope.
The Control of Heart Rate • Heart rate is externally regulated by the autonomic nervous system and by hormones.
• The medulla of the brain raises the heart rate through the sympathetic nervous system.
• The medulla of the brain lowers the heart rate through the parasympathetic nervous system.
• The sympathetic and parasympathetic nervous systems act antagonistically (opposite effects)
• Nerve cells of the sympathetic nervous system accelerate heart rate by
secreting noradrenaline (norepinephrine).
• Nerve cells of the parasympathetic nervous system slow heart rate by secreting acetylcholine.
• The hormone adrenaline and exercise increases heart rate.
The Cardiac Conducting System • Heart muscle cells are myogenic, i.e. they contract and relax to their own internal rhythm without external stimulation.
• Heart beat is regulated by the autonomic nervous system and by hormones.
• The sinoatrial node (SAN), or pacemaker, sets the rate of contraction of the heart muscle.
• The cells of the SAN are autorhythmic, not contracting themselves but sending out impulses which co-ordinate the contraction of the heart muscle.
• Impulses from the SAN travel across the atria, causing them to contract simultaneously, and to the atrioventricular node (AVN).
• The AVN passes the impulses through the ventricles, causing them to contract simultaneously.
• The impulses from the SAN and the AVN generate currents which are detected by electrocardiography and recorded on an electrocardiogram.
Blood Pressure • The contraction and relaxation of the heart muscle during the cardiac cycle cause the variations in blood pressure in the arteries.
• These variations in pressure are detectable in arteries as the pulse.
• Blood pressure is measured by a sphygmomanometer.
• The steps in the use of the sphygmomanometer are: – an inflatable cuff stops blood flow and deflates gradually, – blood flow restarts as systolic pressure is reached, and the pulse is felt, - once blood flows freely, and the pulse is no longer felt, diastolic pressure has been reached.
• Blood pressure is expressed as systolic pressure/diastolic pressure.
• A typical reading for a young adult is 120/70mmHg. • Hypertension is defined as blood pressure above 140/90mmHg.
• Hypertension is a major risk factor for many diseases including coronary heart disease.
Learning Objectives
At the end of this topic, you should be able to:
• explain what cardiovascular disease (CVD) is. • describe the development and effects of atherosclerosis, thrombosis and peripheral vascular disease.
• explain the role of cholesterol in CVD
• explain how the concentration of glucose in the blood is maintained within a narrow range.
• explain the effect of exercise on blood sugar levels.
• describe the contribution of chronically raised blood sugar levels on cardiovascular disease.
• describe the different forms of diabetes and their effects.
• describe the causes and effects of obesity, how it is measured and how it may be reduced.
7. Cardiovascular Disease (CVD)
Cardiovascular disease (CVD) is an umbrella term used for diseases of the heart and blood vessels.
It includes diseases such as coronary heart disease (CHD) which itself includes angina, myocardial infarction (heart attack), sudden death and stroke.
Atherosclerosis
Atherosclerosis is the formation of plaques called atheromas in the walls of arteries.
Atheromas build up over years from deposits of fatty cholesterol, fibrous material, calcium and more cholesterol as shown in the diagram: THINK! We know that calcium is essential for growth and is found in nails, teeth
and bones. If calcium is being deposited in the artery linings as part of a plaque formation, what might you expect the artery to feel like?
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There are 3 main problems which the presence of atheromas cause; 1. Narrowing of the artery’s lumen 2. Restriction of blood flow 3. Increase in blood pressure
Atherosclerosis symptoms often do not appear until later in life when the condition can then lead to the development of CHD or peripheral vascular disease (PVD).
Thrombosis
The plaques which develop in atherosclerosis can be divided into two broad groups; - Stable
- Unstable
The outer cap of an unstable plaque is weak and quite likely to rupture, damaging the endothelium and exposing the fibrous material and cholesterol to the blood plasma. These act as clotting factors which cause the platelets and blood proteins to trigger a cascade of reactions including the conversion of the enzyme prothrombin into its active form thrombin. This enzyme then converts the soluble plasma protein fibrinogen into the insoluble fibres of fibrin which link together to form of a blood clot, or thrombus.
The presence of a thrombus creates further blockage in the vessels but can be even more dangerous if it breaks loose. At this point the free clot is called an embolus and is at risk of blocking off a narrow vessel entirely.
If a thrombus forms in a coronary artery, an ensuing embolus causes a myocardial infarction. A thrombus in a carotid artery taking blood to the head, or in an artery in the brain, may lead to a stroke!
Peripheral Vascular Disorders (PVD)
Peripheral arteries are those OTHER THAN the aorta, coronary and carotid arteries but most commonly affects vessels in the legs. Atherosclerosis affects these arteries in much the same way and narrows the central cavity as shown below;
Deep vein thrombosis -or more commonly referred to as DVT- is a common example of PVD which many people associate with long haul flights. A thrombus forms in a vein (commonly in the calf of the lower leg) causing restricted blood flow and symptoms which include swelling and pain due to the blockage.
THINK! Another very serious example of PVD is called a PULMONARY EMBOLISM. Use your knowledge of the topic so far to discuss with your partner what this is and write your answer in the space below.
PULMONARY EMBOLISM:______The Role of Cholesterol
Cholesterol is a lipid which is a major component of all cell membranes and the precursor for the synthesis of all steroid hormones.
Cholesterol is taken in from the diet but is mainly synthesised in the liver. The liver is also responsible for the elimination of cholesterol, as a component of bile.
There are two important types of cholesterol-carrying proteins in the blood; - low-density lipoproteins (LDL) or ‘bad’ cholesterol - high-density lipoproteins (HDL) or ‘good’ cholesterol.
The summary table below outlines the main differences between these proteins in the body;
Type of % of Total Function in Body CHD risk Cholesterol blood (ratio of cholesterol LDL:HDL) LDL 60-70 Deliver cholesterol to Increased if high body cells for levels of LDL in membrane and blood compared hormone synthesis via to HDL LDL receptors controlled by negative feedback. HDL 20-30 Transports excess Lowered if high cholesterol from body levels of HDL in cells to liver for blood compared elimination. Removal of to LDL cholesterol from atheromas.
Awareness campaigns over the past decade have focused on ways to reduce your cholesterol (i.e. regular exercise, low fat diet etc.) in an attempt to prevent increasing numbers of people suffering from CVD in later life but current treatment for high cholesterol levels rely on drugs called STATINS.
Using the resources available, put together a detailed information leaflet which explains to someone with high cholesterol how these drugs work.
Familial hypercholesterolaemia (FH)
FH is caused by an inherited autosomal dominant gene which decreases the number of LDL receptors present in the cell membranes or changes their structures so that they do not function properly.
This means that cholesterol cannot be unloaded into cells properly by LDL resulting in extremely high levels of cholesterol in the bloodstream which, if left untreated, the individual will suffer from cardiovascular problems at a young age.
The condition can be screened for by a genetic test and treated through a modified lifestyle and use of medications such as statins.
Importance of Glucose Balance
Negative Feedback
Glucose is maintained within the plasma around a constant level of between 4.5-6mmol/l.
This level varies slightly based on the demand for energy from respiring tissues however maintenance of this base level is achieved by storing excess glucose after a meal in the form of glycogen in the liver and skeletal muscles.
This prevents blood glucose levels from becoming too high - hyperglycaemia.
The brain requires a constant supply of glucose, so between meals and after an overnight fast, blood glucose levels are maintained by the liver releasing glucose back into the bloodstream.
This prevents blood glucose from falling too low - hypoglycaemia. Blood glucose levels are controlled by the hormones insulin and glucagon, which are secreted by small clusters of cells scattered throughout the pancreas and known as the Islets of Langerhans.
Beta (β) cells secrete insulin and Alpha (α) cells secrete glucagon.
The control of blood glucose levels by the opposing actions of insulin and glucagon is known as negative feedback and is illustrated below:
Glucose and Microvascular Disease
If a person is suffering from untreated diabetes, their blood glucose levels may increase to an unusually high level i.e. 30 mmol/l.
This can cause severe damage to the endothelial cells which line the blood vessel as they will absorb too much glucose causing their basement membrane to thicken and weaken, leaving the vessel susceptible to haemorrhaging (burst and bleed).
Microvascular disease can cause severe damage to the retina, kidneys and nerves therefore it is important to ensure that the blood glucose level is maintained within a narrow range to avoid such internal damage.
THINK! During exercise or survival responses it is important that our bodies have raised levels of glucose for bursts of energy. We release the hormone epinephrine (adrenaline) into the bloodstream to aid this response.
How do you think epinephrine works on the negative feedback loop to ensure high levels of glucose without damaging blood vessels? Discuss your ideas as class and note some points below:
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Diabetes
A comparison of Type 1 and Type 2 diabetes is summarised below: People suffering from diabetes are unable to control their blood glucose levels. Although there are two types of diabetes a common factor is that if left untreated, a rapid increase in blood glucose is detected after a meal.
The high levels of glucose cannot be reabsorbed in the bloodstream resulting in high levels of glucose being excreted as waste in urine. Due to this, a urine test is often used as an indicator for the condition.
The next stage in diagnosis is a glucose tolerance test.
Simply put, the blood glucose levels of the individual are measured after fasting and subsequently every two hours after drinking 250- 300ml of glucose solution. The results are recorded as a glucose tolerance curve and analysed for diagnosis.
Obesity and Health Risks
Obesity is a condition in which excess fat has accumulated in the body to the extent that it begins to have an adverse effect on health.
It is largely a product of our modern 'Western' way of life and is rarely found in the developing world however genetic, psychological and metabolic factors may also be contributors.
A person is generally classified as obese if they have an excess of body fat compared to their lean body tissues, such as muscle.
The degree of obesity can be estimated by calculating the Body Mass Index (BMI) as: BMI = mass (kg) (height (m))2
BMI values can be used to assign people to body condition categories and associated health risks as shown: BMI range Category Risk of Associated Health Problems < 18.5 underweight Increased 18.5 - 24.9 normal Normal 25 - 29.9 overweight Increased 30 - 40 obese Greatly Increased 40+ very obese Very Greatly Increased
The BMI method is not always an accurate measurement of body fat.
For example, a bodybuilder would wrongly be categorised as obese using this method and so there are some limitations to consider.
To ensure body fat is measured accurately, a measurement of body density is required using any one of the following methods: - densitometry - skin-fold callipers - bioelectrical impedance - waist/hip ratio.
Discuss with your partner ways in which to treat obesity and explain in what ways this will have an effect on reducing the likelihood of CVD. Note your answers in the space provided. ______Summary
Atherosclerosis • Atherosclerosis is the thickening of artery walls by a build-up of fatty material.
• The thickening is in the form of plaques beneath the endothelium consisting of fibrous material, an atheroma of fatty material (mainly cholesterol), and calcified tissue.
• The growth of the plaque reduces the lumen of the artery, reducing the
blood flow and increases blood pressure.
• The growth of the plaque also reduces the elasticity of the artery wall ~ so increases blood pressure.
• Atherosclerosis is the root cause of cardiovascular diseases such as angina, heart attack (myocardial infarction), stroke and peripheral vascular disease.
Thrombosis • Unstable plaques may rupture, damaging the endothelium and exposing the fibrous tissue and atheroma cholesterol to the blood plasma.
• These act as clotting factors which activate the cascade of reactions of
the clotting process.
• As part of this process, the enzyme precursor prothrombin is converted
to the active form thrombin.
• Thrombin catalyses the conversion of the soluble plasma protein fibrinogen to insoluble fibres of fibrin.
• The fibrin threads form a meshwork which traps red blood cells and forms a clot, sealing the wound and allowing the growth of scar tissue.
• When such a clot forms in an artery it is called a thrombus.
• If such a clot breaks loose into the blood stream, it is called an embolus which will travel through the blood circulation and may block a blood vessel.
• In a coronary artery, this leads to a heart attack (myocardial infarction).
• In an artery in the brain, it causes a stroke.
• In these cases, the cells served by the blocked arteries/arterioles die from lack of oxygen.
Peripheral vascular disorders • Peripheral vascular disease (PVD) is atherosclerosis of arteries other than those serving the heart or the brain.
• PVD is most common in the arteries of the legs.
• As elsewhere in the body, the atherosclerosis of PVD deprives cells of oxygen, causing symptoms for mild pain to gangrene leading to amputation.
• Deep vein thrombosis (DVT) is the formation of a clot in a deep vein, most commonly in the leg.
• If the clot becomes detached, forming an embolus, it may pass through
the heart and lodge in a branch of the pulmonary artery.
• If the embolus lodges in the pulmonary artery, this is called a pulmonary embolism.
Cholesterol • Cholesterol is a waxy solid, a steroid and a fat.
• It is synthesised in all body cells, but the liver produces most in the body.
• Cholesterol is present in animal foods, especially dairy products, meat and poultry.
• A diet high in saturated fats may cause increased cholesterol levels.
• It is eliminated from the body in the bile produced by the liver. Functions of cholesterol • It is a component of cell membranes, where it controls permeability.
• It is a precursor of vitamin D and steroid hormones.
Transport of cholesterol • Cholesterol is transported by lipoproteins synthesised in the liver.
• High density lipoproteins (HDLs) carry excess cholesterol from the body cells to the liver.
• High levels of HDLs in the blood can reduce the presence of cholesterol in plaques in the artery walls.
• Low density lipoproteins (LDLs) transport cholesterol from the liver to body cells.
• LDLs become attached to LDL-receptors, found on the cell membrane of most cells.
• The LDL-receptors pass into the cell and release the cholesterol.
• The production of LDL-receptors is controlled by negative feedback.
• Once a cell has sufficient cholesterol, LDL-receptor production is suppressed.
• Excess LDL circulates in the blood and can become absorbed into atheromas in plaques in artery walls.
• A high ratio of HDLs to LDLs lowers the level of cholesterol in the blood and so reduces the development of atherosclerosis.
Controlling cholesterol levels • Regular physical activity raises HDL levels and so reduces cholesterol levels.
• Reducing the content of unsaturated fat in the diet reduces the level of LDLs.
• Reducing the content of animal foods rich in cholesterol reduces cholesterol intake.
• Statins are drugs which reduce cholesterol levels.
• Statins inhibit an enzyme in the pathway producing cholesterol in the liver.
Familial hypercholesterolaemia • FH is caused by an incompletely dominant autosomalmutation of the LDL-receptor gene.
• The mutant allele results in fewer (or altered) LDL-receptors on liver cells.
• This causes high levels of LDL-cholesterol in the blood and the early onset of cardiovascular disease.
• The presence of the FH mutation can be detected by genetic testing.
• FH can be treated by changes to lifestyle such as following a diet low in total fats and saturated fats.
• FH can be treated drugs such a statins which reduce LDL-cholesterol levels in the blood.
Regulation of blood glucose levels • Blood glucose levels are homeostatically regulated by negative feedback.
• Receptors in the pancreas detect the concentration of glucose in the blood.
• High blood glucose levels stimulate the release of insulin by the pancreas.
• Insulin stimulates the liver (and other tissues) to convert glucose to glycogen.
• Low blood glucose levels stimulate the release of glucagon by the pancreas.
• Glucagon stimulates the liver to convert glycogen to glucose. • Exercise and fight/flight situations stimulate the release of adrenaline from the adrenal glands.
• Adrenaline stimulates the liver (and other tissues) to convert glycogen to glucose.
• Adrenaline also stimulates the release of glucagon and inhibits the release of insulin by the pancreas.
Blood glucose levels and diabetes • Diabetes is a common cause of hyperglycemia.
• Diabetics are unable to control a rise in blood glucose levels.
• Chronic vascular disease is a complication of diabetes.
• There are two forms of diabetes called Type 1 and Type 2.
• Type 1 diabetes typically appears in childhood, results from a failure of insulin production, and is treated by regular insulin injections.
• Type 2 diabetes typically develops in adulthood, results from a reduced
cellular sensitivity to insulin caused by a decreased number of receptors on the liver cells.
• Type 2 diabetes is frequently associated with obesity and is mainly treated by adjustments to diet and exercise regimes.
• Both forms of diabetes cause abnormally high blood glucose levels after meals.
• At these high blood glucose concentrations the kidneys are unable to reabsorb all the glucose from the glomerular filtrate, and so glucose is excreted in the urine.
• A positive result for glucose in urine sample test is a strong indicator of diabetes.
• A glucose tolerance test assesses a blood sample taken after an 8hr fast.
• A glucose tolerance test uses two blood samples, one taken before drinking a solution containing 75g of glucose, and a second taken 2hr later.
Blood glucose levels and vascular disease • Chronic high blood glucose levels lead to endothelial cells taking in abnormally large quantities of glucose, so damaging the lining of the blood vessels.
• This may lead in larger blood vessels to atherosclerosis, cardiovascular disease, stroke or peripheral vascular disease.
• In smaller blood vessels this may cause haemorrhaging in the retina, renal failure or peripheral nerve dysfunction.
Obesity • Obesity results from an excess of body fat in relation to lean body tissue (muscle).
• Obesity is a major risk factor for cardiovascular disease and Type 2 diabetes.
• BMI (body mass index) is calculated as mass / height2, where mass is measured in kg and height in metres.
• A BMI in excess of 30 indicates obesity.
• In order to accurately measure body fat, a measurement of body density is needed.
• Obesity is linked to high fat diets and reduced physical activity.
• To counter obesity, the content of fats and free sugars in the diet should be limited.
• Dietary fat should be limited because fats contain twice as much energy per gram as proteins or carbohydrates.
• Free sugars should be limited because their digestion requires no metabolic energy expenditure.
• Exercise increases energy expenditure and preserves lean tissue. • Exercise can reduce the risk of developing cardiovascular disease by helping control weight, reducing stress and hypertension, and raising HDL levels.