Homeostasis- Controlling Blood Water Potential Flashcards
Why does the amount of water in the blood need to be kept constant?
As water is essential to keep the body functioning
How is water lost in mammals?
Through excretion and through sweat
What is osmoregulation?
The kidneys regulate the water potential of the blood so the body has the right amount of water
What happens when the water potential of the blood is too low (the body is dehydrated)?
More water is reabsorbed by osmosis into the blood from the tubules of the nephrons- urine is more concentrated so less water is lost during excretion
What happens when the water potential of the blood is too high (the body is too hydrated)?
Less water is reabsorbed by osmosis into the blood from the tubules of the nephrons- urine is more dilute so more water is lost during excretion
Where is water reabsorbed into the blood?
Along almost all of the nephron
Where does regulation of water potential take place?
Loop of Henle, DCT and collecting duct
What controls the volume of water reabsorbed by the DCT and the collecting duct?
Hormones
Where is the loop of Henle located?
In the medulla of the kidneys
What is the loop of Henle made up of?
The descending limb and the ascending limb
What do the limbs in the loop of Henle control?
The movement of sodium ions so that water can be reabsorbed by the blood
What happens near the top of the ascending limb?
Sodium ions are pumped out into the medulla using active transport
Why does water stay inside the tubule of the ascending limb?
It is impermeable to water
What does water staying inside the ascending limb create?
A low water potential in the medulla because there’s a high concentration of ions
Why does water move out of the descending limb into the medulla by osmosis?
Because there’s a lower water potential in the medulla than the descending limb
What happens near the bottom of the ascending limb?
Sodium ions diffuse out into the medulla which further lowers the water potential
What happens after sodium ions diffuse out?
Water moves out of the distal convoluted tubule by osmosis and is reabsorbed into the blood
How is water potential of the medulla lowered?
The ion concentration in the medulla is massively increased
What does lowered water potential of the medulla cause?
Water to move out of the collecting duct by osmosis
How is the water in the medulla reabsorbed into the blood?
Through the capillary network
What is water potential of the blood monitored by?
Cells called osmoreceptors in the hypothalamus (in the brain)
What happens when the water potential of the blood decreases?
Water will move out of the osmoreceptor cells by osmosis which causes the cells to decrease in volume
What is caused when osmoreceptors decrease in volume?
A signal is sent to the hypothalamus which sends a signal to the posterior pituitary gland which causes the posterior pituitary to release antidiuretic hormone (ADH) into the blood
What does ADH do?
Makes the walls of the DCT and collecting duct more permeable to water
What does the DCT and collecting duct walls becoming more permeable do?
More water is reabsorbed from these tubules into medulla and into blood by osmosis- small amount of concentrated urine is produced so less water is lost from the body
When do blood ADH levels rise?
When you’re dehydrated
What happens when you’re dehydrated?
- Water content of blood drops so water potential drops
- Detected by osmoreceptors in hypothalamus
- Posterior pituitary gland stimulated to release more ADH into blood
- More ADH means collecting duct and DCT become more permeable so more water is reabsorbed into blood by osmosis
- Small amount of highly concentrated urine produced and less water is lost
When do blood ADH levels fall?
When you’re hydrated
What happens when you’re hydrated?
- Water content of blood rises so water potential rises
- Detected by osmoreceptors in hypothalamus
- Posterior pituitary gland releases less ADH into blood
- Less ADH means collecting duct and DCT become less permeable so less water is reabsorbed into blood by osmosis
- Large amount of dilute urine produced and more water is lost
