By the End of This Topic, You Should Be Able To

By the End of This Topic, You Should Be Able To

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 spermatozoain 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 ovain the ovaries.

2. The production of the hormoneoestrogen 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
calledseminal 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 menstruationbeing 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 secondpart, 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 thatwomen 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.