E1: Human Physiology Ehozfeesoi# Mmmmphysiology Notes My

Home , Reabsorption, Ultrafiltration (kidney)

E1: Human Physiology EhoZfEEsoI# mmmmPhysiology Notes my

Deﬁnition Keep water potential of blood and tissue ﬂuid stable, so cells function properly to sustain life

Ultrafiltration Ch1 Osmoregulation * High blood pressure (not diffusion or other form of transport, strictly pressure) forces water and other small soluble molecules in the plasma through the thin wall of glomerulus and the Definition Bowman’s Capsule * Filtrate is glomerular filtrate, which is similar to plasma with no plasma particles and blood cells Keep water potential of blood and tissue fluid stable, so cells function because they are too large to pass through properly to sustain life

Reabsorption (prevent loss of useful substances) Ultrafiltration * Occurs in proximal convoluted tubule, features include: * High blood pressure (not diffusion or other form of transport, strictly 1. Long and highly coiled: increase surface area and time for reabsorption 2. Single layer of epithelial cells (one cell thick): shortens distance for reabsorption of pressure) forces water and other small soluble molecules in the plasma substances from filtrate into blood through the thin wall of glomerulus and the Bowman’s Capsule 3. Many mitochondria: provide cells with lots of energy for active transport * Filtrate is glomerular filtrate, which is similar to plasma with no plasma 4. Dense capillary network: rapid transport of substances away from site of reabsorption, thus maintaining a steep concentration gradient for efficient absorption particles and blood cells because they are too large to pass through

Osmoregulation Reabsorption (prevent loss of useful substances) * The amount of water reabsorbed is controlled by ADH which is released from the pituitary gland * Occurs in proximal convoluted tubule, features include: * Hypothalamus contains osmoreceptors to detect water potential, thus controlling release of 1. Long and highly coiled: increase surface area and time for ADH 1. Hypothalamus detects water potential and releases ADH from the pituitary gland reabsorption 2. Pituitary gland releases ADH 2. Single layer of epithelial cells (one cell thick): shortens distance for 3. ADH is transported to all parts of the body by blood and exert effects on collecting duct reabsorption of **ADH increases permeability of collecting duct so larger proportion of water is reabsorbed substances from ﬁltrate into blood 3. Many mitochondria: provide cells with lots of energy for active *When water potential is higher than normal transport 1. Water potential higher than normal 4. Dense capillary network: rapid transport of substances away from 2. Hypothalamus detects change and cause pituitary gland to release less ADH 3. Wall of collecting duct become less permeable to water site of reabsorption, 4. Smaller proportion of water reabsorbed thus maintaining a steep concentration gradient for eﬃcient 5. Larger volume of dilute urine produced absorption

Osmoregulation * The amount of water reabsorbed is controlled by ADH which is released from the pituitary gland. * Hypothalamus contains osmoreceptors to detect water potential, thus controlling release of ADH 1. Hypothalamus detects water potential and releases ADH from the pituitary gland 2. Pituitary gland releases ADH ADH is transported to all parts of the body by blood and exert eﬀects on collecting duct **ADH increases permeability of collecting duct so larger proportion of water is reabsorbed** When water potential is higher than normal Water potential higher than normal Hypothalamus detects change and cause pituitary gland to release less ADH Wall of collecting duct become less permeable to water Smaller proportion of water reabsorbed Larger volume of dilute urine produced When water potential is lower than normal Water potential lower than normal Hypothalamus detects the change and stimulate pituitary gland to release more ADH Wall of collecting duct becomes more permeable to water Greater proportion of water reabsorbed Smaller volume of concentrated urine produced * When water potential is lower than normal 1. Water potential lower than normal 2. Hypothalamus detects the change and stimulate pituitary gland to release more ADH 3. Wall of collecting duct becomes more permeable to water 4. Greater proportion of water reabsorbed 5. Smaller volume of concentrated urine produced

Excretion VS Egestion Excretion: Removal of metabolic waste from the body

Waste produced by body cells Excretion VS Egestion Substance CO2 Urea Bile Pigment Excretion: Removal of metabolic waste from the body Site of formation Cells Liver Liver Process Respiration Breakdown of excess Breakdown of Wastes produced by body cells amino acids haemoglobin is (x protein) Substance CO2 Urea Bile Egestion: removal of undigested or unabsorbed food substances Pigment Site of formation Cells Liver Liver Kidney & Liver Process Respiration Breakdown of excess * Kidney: excreting urea (urea x accumulates) Breakdown of - Carried out continuously amino acids - ↓blood urea concentration haemoglobin * Liver: deaminating excess amino acid (x protein) (x protein) - Carried out continuously -↑blood urea concentration Egestion: removal of undigested or unabsorbed food substances

* Normal = rate of urea production = rate of urea excretion Kidney & Liver * Kidney: excreting urea (urea x accumulates) Water balance - Carried out continuously Water gain Water loss Preventing water loss Drinking Urination 1. Kidney reabsorbs most of the H2O from urine - ↓blood urea concentration Eating Sweating 2. Human seek shade Respiration Exhalation 3. Human lungs are sunken deep inside the body C6H12O6 + 6O2 -water ﬁlm (air sac) 4. Human skin and oil on the skin is imperious to water * Liver: deaminating excess amino acid (x protein) ⇐-> 6CO2 + 6H2O - outermost layer of epidermis of waterproof - Carried out continuously - Sebaceous gland -↑blood urea concentration

* Normal = rate of urea production = rate of urea excretion

Water balance Water gain. Water loss. Preventing water loss Drinking. Urination. 1. Kidney reabsorbs most of the H2O from urine Eating. Sweating 2. Human seek shade Respiration C6H12O6 + 6O2 -> 6CO2 + 6H2O Exhalation -water ﬁlm (air sac) 3. Human lungs are sunken deep inside the body 4. Human skin and oil on the skin is imperious to water - outermost layer of epidermis of waterproof - Sebaceous gland Urinary System https://www.google.com/url? sa=i&url=http%3A%2F%2Ftrinitykck.org%2Furine-ﬂo Urinary System

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Flow in blood vessels: renal artery > afferent arteriole > glomerulus > efferent arteriole > blood capillary > renal vein

Flow of fluid: renal artery > afferent arteriole > glomerulus > Bowman’s capsule > first coiled tubule > loop of Henle > second coiled tubule > collecting duct > renal pelvis > ureters > urinary bladder > urethra Formation of urine 1. Blood pressure in glomerulus is high (∵ pumping action of the heart) 2. The pressure in glomerulus is higher than that in Bowman’s capsule 3. The walls of glomerulus and Bowman’s capsule are porous which form a filter 4. The presence of hydrostatic pressure gradient and filter results in ultra-filtration of blood 5. Some plasma (including useful materials & wastes) except plasma protein are forced from glomerulus into Bowman’s capsule, forming glomerular filtrate 6. Useful materials (glucose, amino acids and some salts) are reabsorbed actively from glomerular filtrate back to the surrounding blood capillaries but not waste (urea) 7. After reabsorption of useful materials, the remaining materials is called urine.

* Simpliﬁed Model

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Blood – red blood cell – plasma protein = glomerular filtrate Blood – red blood cells = plasma Plasma – fibrinogen = serum Composition of different fluid

1. Plasma proteins are present in plasma, but not in glomerular ﬁltrate ∵ too large —> can’t pass the walls of glomerulus and Bowman’s capsule

2. Water content % in glomerular ﬁltrate > plasma ∵ protein can’t pass the walls of glomerulus and Bowman’s capsule

3. Glucose & amino acid are present in glomerular ﬁltrate, but not in urine ∵ all reabsorbed back to the surrounding blood capillaries by active transport & diffusion

4. Some salts in glomerular ﬁltrate are reabsorbed back to blood capillaries. The amount depends on the amount of salt in our body.

5. The solute concentration of fluid in the 1st coiled tubule remains unchanged as the fluid flows along the tubule ∵ amount reabsorbed from the fluid is proportional to the amount of solute reabsorbed

6. Urea is not actively reabsorbed, moves back to blood by diffusion

7. Concentration of urea in urine > glomerular filtrate ∵ % of water reabsorbed from glomerular filtrate is greater than that of urea Adaptations for reabsorbing useful materials effectively 1. Numerous nephrons surrounded by blood ↑ rate of reabsorption of useful materials from glomerular filtrate back to blood 2. Kidney tubules are vascularised with blood capillary ↑ rate of reabsorption 3. Blood circulation transport reabsorbed materials away from kidney tubules ↑ rapid reabsorption 4. Kidney tubules are very long ↑ time for more reabsorption 5. Kidney tubules are highly coiled ↑ surface area to volume ratio for more reabsorption 6. Walls of kidney tubule & blood capillaries are thin, one-cell thick ↓ distance for rapid reabsorption 7. Kidney tubules & blood capillaries are in close contact ↓ distance for rapid reabsorption 8. Presence of microvilli on the inner wall of kidney tubule ↑ surface area to volume ratio for rapid reabsorption 9. Presence of a large number of mitochondria —> provide energy for active transport 10. Most substances are reabsorbed back into blood in 1st coiled tubule, so epithelial cell of 1st coiled tubule has more microvilli & mitochondria than 2nd coiled tubule

Reabsorption Limit Filtered = Reabsorbed + Excreted

Filtered A glucose Rate of handling glucose minute mg per Executed glucose

- ±µ - reabsorbed glucose Plasma glucose ¥ concentration reabsorbed mmol 1dm? Diabetes mellitus 1. Liver can’t convert excess glucose in blood into glycogen 2. Blood glucose level (BGL) can’t drop to normal after carbohydrate is ingested 3. When the glucose in glomerular filtrate is greater than the upper limit for complete reabsorption, glucose appears in urine 4. Glucose in glomerular filtrate decreases water potential (Ψ) of glomerular filtrate 5. Ψ of glomerular filtrate is lower than normal 6. increase in glucose in glomerular filtrate decreases Ψ. This decreases water reabsorbed from glomerular filtrate to blood, causing osmotic diuresis (larger volume urine + glucose)

Diabetes insipidus Pituitary gland fails to release sufﬁcient ADH or kidney tubules don’t respond to ADH. So large volume of dilute urine is produced, leading to danger of dehydration

Antidiuretic hormone (ADH) Use Decrease the amount of urine produced

Origin Produced by hypothalamus pituitary gland Process - Hypothalamus controls the pituitary to adjust the amount of ADH secreted to blood - ADH travels via blood to reach 2nd coiled tubule and collecting duct - ADH increases the permeability of walls of the 2nd coiled tubule & collecting duct to water - Larger proportion of H2O reabsorbed from glomerular ﬁltrate to blood

Dialysis machine Dialysis tubing: differentially permeable, allows small molecules to pass through only —> helps to remove urea from blood while retaining large blood components like plasma proteins and blood cells in blood

Dialysis ﬂuid: water potential similar to blood, concentrations of nutrients similar to blood, no metabolic waste —> prevents loss of water, prevents loss of nutrients and allows metabolic waste to diffuse into the dialysis ﬂuid

Process of dialysis machine operation 1. Blood pumped out from body 2. Metabolic waste like urea diffuses from blood into dialysing fluid along concentration gradient through selectively permeable dialysis tubing 3. Nutrients like glucose are retained in blood (no net movement of nutrients) as their concentrations in dialysing fluid are similar to blood and no loss of nutrients 4. Plasma proteins and blood cells are retained in blood as they are too large to pass through 5. Cleaned blood returns to body 6. Urea carried away by the dialysis fluid for removal