Summary
Summary Unit 3.7 - Homeostasis and the kidney
- Institution
- WJEC
Notes on homeostasis, ultrafiltration, selective reabsorption, osmoregulation, secretion, loop of henle adaptations and nitrogenous wastes
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3.7 Homeostasis and the kidneyHomeostasis:
Homeostasis = constant internal environment
Homeostatic processes require a detector/sensor which monitors the factor being controlled
Detector senses change -> informs controller which is a coordinating system
Controlled communicates with one or more effectors e.g. endocrine glands which correct
change
Factor returns to normal and detector switches off – this is called negative feedback
Kidney:
Two main functions: Removal of nitrogenous waste and osmoregulation
If there’s too many amino acids in the body, they are deaminated by the liver. This reaction
produces ammonia in humans which is converted to urea and found in urine.
This process is called the Ornithine cycle
See booklet for kidney and nephron structures
Kidneys are made up of many nephrons
At the beginning of each nephron is a knot of capillaries (glomerulus) which is supplied with
blood by the afferent arteriole and blood is removed by the efferent arteriole
From the glomerulus, there are two capillary networks in each nephron
One serves the PCT and DCT and the other runs alongside the loop of Henle and is called the
Vasa recta
Nephrons have three different processes:
1. Ultrafiltration
2. Selective reabsorption
3. Secretion
Ultrafiltration:
Filtration that happens when blood is put under pressure in the glomerulus
Purpose -Separates small, soluble products from blood plasma e.g. salts, glucose, minerals,
water, urea, amino acids and vitamins
White blood cells, red blood cells and plasma proteins are too large to be filtered so they stay in
blood
Structure of glomerulus allows ultrafiltration through basement membrane which forms a
selective barrier and acts like a molecular sieve
There needs to be high pressure in the glomerulus for this to work which is achieved in two
ways:
1. Afferent arteriole has a wider diameter than the efferent arteriole so blood builds up in
pressure as it’s waiting to leave
2. Water potential on blood produced by plasma proteins – presence of proteins lowers
the water potential in the glomerulus, so water moves into glomerulus by osmosis
increasing its pressure
Podocytes increase surface area for contact with filtrate
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