Osmoregulation
Biology: AQA A Level, topic 6.4.8
Osmoregulation
Water is vital to the normal functioning of the body so it is important that water potential of the blood is carefully controlled. Osmoregulation is the control of the water potential in the blood.
The kidneys
- Osmoregulation takes place in the kidneys.
- The kidneys absorb more or less water according to the water potential.
High water potential
- If blood water potential is too high, more water must be lost by excretion to return the water potential to normal.
- The blood reabsorbs less water from the kidneys.
- The urine is more dilute and water potential in the blood decreases.
Low water potential
- If blood water potential is too low, less water must be lost by excretion to return the water potential to normal.
- The blood reabsorbs more water from the kidneys.
- The urine is more concentrated and water potential in the blood increases.
Structure of the Nephron
Osmoregulation takes place in the nephron. The nephron is the functional unit of the kidney and each kidney has several million. The structure of the nephron is important for osmoregulation.
Structure
Bowman's capsule
- The Bowman's capsule is the beginning of the tubules that make up the nephron.
- The capsule surrounds a network of capillaries. This network is called the glomerulus.
- The first step of filtration of the blood to form urine takes place in the Bowman's capsule. This step produces the glomerular filtrate.
Afferent and efferent arterioles
- Blood flows into the glomerulus through the afferent arteriole and out of the glomerulus through the efferent arteriole.
- The afferent arteriole is much wider than the efferent arteriole. This means that the blood pressure in the capillaries is very high.
Proximal convoluted tubule (PCT)
- The PCT is the site of selective reabsorption.
- After the glomerular filtrate has been produced in the Bowman's capsule, glucose and water are reabsorbed into the bloodstream through the PCT.
Loop of Henle
- The loop of Henle produces a low water potential in the medulla of the kidney.
- The loop of Henle consists of an ascending limb and a descending limb.
- The ascending limb is impermeable to water.
- The descending limb is permeable to water.
Collecting duct
- Water is reabsorbed into the blood through the collecting duct.
- The amount of water that is absorbed depends on the water potential of the blood.
- If blood water potential is low, more water is reabsorbed.
- If blood water potential is high, less water is reabsorbed.
- This is osmoregulation.
Test yourself on Osmoregulation
Where does osmoregulation take place?
Which of the following statements about osmoregulation are true?
Which of the following statements about nephrons are true?
Where does osmoregulation take place??