1. Homeostasis of body fluid
Text: Chapter 8
Human Biology Stage 3

2. Keywords Hypothalamus Osmoreceptors Thirst centre ADH Adrenal glands
Aldosterone
Nephron
Bowman’s capsule - glomerulus
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collection duct
Ureter
Bladder
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3HBS

3. Renal function: osmoregulation (6 min)

4. Fluid balance – water in
Food ml
Fluids ml
Metabolic water (from respiration) 300 ml
TOTAL ml
Anthea Sieveking, Wellcome Images

5. Fluid balance – water out
Urine ml
Sweating ml
Lungs ml
Faeces ml
TOTAL ml
Anthea Sieveking, Wellcome Images

6. Regulation of body fluids
The kidneys regulate the level and composition of body fluids
Functions
Fluid balance
Salt balance
Removal of wastes (urea)
pH balance
interdependent
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7. The kidney Proximal convoluting tubule Glomerulus Capsule Cortex
Distal convoluting tubule
Medulla
Renal artery
Collecting duct
Renal vein
Loop of Henle
Renal pelvis
Capillaries
Ureter
KIDNEY
A NEPHRON

8. The kidney Renal medulla – loops of Henle Renal artery Renal vein
Renal cortex – Bowman’s capsules
Ureter –
to the bladder
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3HBS

9. The kidneys The functional unit of the kidney is the nephron
It filters waste products out of the blood
Each kidney contains about 1.2 million nephrons
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10. The kidneys
Blood enters the glomerulus (Bowman’s capsule) under high pressure.
Water and small molecules are forced out of the blood vessels
This filtrate is collected and passes through several tubules
Some water and useful substances are reabsorbed
The rest passes through to the ureters and is stored in the bladder for excretion
Renal cortex
Renal medulla
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3HBS

11. Fluid regulation
There are 2 hormones that regulate the body’s fluid composition:
Antidiuretic hormone (ADH)
Water reabsorption
Pituitary gland
Aldosterone
Salt reabsorption
Hypothalamus & adrenal glands
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3HBS

12. Selective water re-absorption
The second stage of water re-absorption is important if we become dehydrated.
It can be divided into two phases (though both are interdependent).
The first phase involves the re-absorption of salt under the influence of the hormone aldosterone.
The second phase involves the re-absorption of water under the influence of the antidiuretic hormone (ADH).

13. Fluid regulation
ADH acts by increasing the permeability of the walls of the distal convoluted tubule and the collecting duct
Aldosterone acts by increasing the activity of the sodium-potassium pumps in the loop of Henle and the distal convoluted tubule
ADH – water reabsorption
aldosterone – salt reabsorption
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3HBS

14. Selective reabsorption
Process
Structure
Substance
Active/passive
Reabsorption
PCT
Water (60-70%)
Salts (60-70%)
Glucose (100%)
Amino acids (100%)
Vitamins (100%)
Passive (osmosis)
All active
Loop of Henle
Water (25%)
Na+/Cl- (25%)
Active
DCT
Water (5%)
Na+/Cl- (5%)
Collecting duct

15. Tubular secretion Tubular secretion PCT & DCT Active H+
Process
Structure
Substance
Active/passive
Tubular secretion
PCT
&
DCT H+
NH4+ (ammonium)
Creatinine
Toxins
Drugs
Neurotransmitters
Active

16. Reabsorption of salt - aldosterone
Stimulus
Decreased blood volume → reduced blood pressure
Receptor
Baroreceptors in Renal artery

17. Reabsorption of salt - aldosterone
Transmission
Several chemical messengers ending with release of aldosterone from the adrenal cortex
Effector
Sodium pumps in DCT and loop of Henle
Response
Sodium reabsorbed increasing ion concentration in interstitial fluid (creates osmotic gradient)

18. Negative feedback – aldosterone
Pressoreceptors in
renal artery
Decreased blood volume → reduced blood pressure
Stimulus
Receptor
Hypothalamus & adrenal glands –(aldosterone)
More water is reabsorbed because of increased osmotic gradient
Negative feedback
Regulation
Response
Effector
Sodium reabsorbed
Sodium pumps in loop of Henle and distal convoluting tubule

19. Reabsorption of water - antidiuretic hormone
Stimulus
Decreased blood volume → reduced blood pressure → increased osmotic pressure
Osmotic pressure is the minimum pressure which needs to be applied to prevent the inward flow of water across a semipermeable membrane or
The tendency of a solution to take in water by osmosis.
Receptor Osmoreceptors in hypothalamus → (activates thirst reflex)

20. Reabsorption of water - antidiuretic hormone
Transmission
nerve signal to posterior pituitary gland ADH released into bloodstream
Effector
DCT and collecting duct
Response
Increases permeability of above structures water (approx 10%) reabsorbed

21. Negative feedback – ADH
Decreased blood volume → reduced blood pressure → increased osmotic pressure
Osmoreceptors in hypothalamus
Stimulus
Receptor
ADH from posterior pituitary gland
Osmotic pressure maintained or reduced
Thirst reflex
Negative
feedback
Drink
Regulation
Water reabsorbed
Response
Effector
Increases permeability of DCT and collecting duct
DCT and collecting duct

22. Deamination Definition The stripping of nitrogen from amino
acid and nitrogen bases (RNA)
Deamination occurs in the liver
Nitrogen occurs in the amino (NH2) part of an amino acid.
Nitrogen is toxic to the human body and must be removed.
The amino group
Alanine

23. Deamination – chemical reaction
Amino acid → ammonia + organic compounds (used for respiration)
Ammonia (very toxic) + CO2 → urea (H2NCONH2)

24. Nitrogen wastes Nitrogen compound Source Amount Relative Toxicity Urea
Amino Acids
21 g/day
Moderate
Creatinine
Muscle metabolism
1.8 g/day
High
Uric acid
RNA
480 mg/day
Weak