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Summary Notes on Osmoregulation - AQA A Level Biology
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3.6.4.3 Control of blood water potential – AQA A Level BiologyOsmoregulation – homeostatic control of the water potential of the blood
The structure of the nephron
The kidney has two primary roles: excretion of metabolic waste from the body and control
of blood water potential
Nephrons
- Functional units of the kidney
- Straddle across the cortex and medulla of kidney
, The nephron’s role in the formation of glomerular filtrate (GF)
First process is ULTRAFILTRATION when blood enters the nephron
- Leads to formation of liquid called GLOMERULAR FILTRATE in Bowman’s capsule (renal)
1) Blood arrives into glomerulus via renal artery, which divides into smaller vessels called
arterioles
2) AFFERENT arteriole enters Bowman’s capsule and divides further to form capillaries of
glomerulus
3) Capillaries rejoin to form EFFERENT arteriole which leaves Bowman’s capsule
AFFERENT arteriole has a larger diameter, which helps increase the blood pressure in the glomerulus
- High pressure forces liquid and small molecules in the blood out of the capillary and into the
Bowman’s capsule
Larger molecules and blood cells cannot pass through so stay in blood
- Some of these larger molecules are soluble so affect the osmotic properties of the blood
Liquid and small molecules pass through 3 layers to reach renal capsule (Bowman’s):
- Blood capillary endothelium (gaps between cells so blood can pass out)
- Basement membrane (from collagen fibres and glycoproteins which act as filter for larger
molecules)
- Epithelium of renal capsule made of PODOCYTES with specialised shape
Describe how ultrafiltration occurs in a glomerulus (marking points)
1) Small molecules arrive under high hydrostatic pressure
2) Glucose and water pass out
3) Through fenestrations in the capillary endothelium
4) And through the capillary basement membrane
5) Then fluid is collected in Bowman’s capsule called GF
Rate at which glomerular filtrate is generated is called Glomerular Filtration Rate (GFR)
- GFR is dependent on blood pressure, higher BP = increased GFR
- Impaired kidney function is associated with low GFR
The nephron’s role in the reabsorption of glucose and water by the proximal convoluted tubule
Once GF is formed “useful” substances eg glucose, water and amino acids must be reabsorbed into
the blood, whilst “waste” eg urea and excess water will stay in the filtrate (which will eventually
leave as urine)
= carried out by PCT and is called SELECTIVE REABSORPTION
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