Control of blood water potential Flashcards
What is osmoregulation?
Osmoregulation is the control of the water potential of the blood.
Describe the process of ultrafiltration:
Blood enters the kidney via the renal artery at high hydrostatic pressure. The renal artery divides into the afferent arteriole and the glomerulus. Water and soluble components are forced out of the efferent arteriole through the basement membrane into the renal capsule down the pressure gradient. The pressure gradient is aided by the efferent arteriole being narrower than the afferent arteriole. Glomerular filtrate is formed.
What is the purpose of the basement membrane?
Acts as a filter to prevent large protein molecules into the glomerular filtrate.
Name some adaptations the proximal convoluted tubule has for selective reabsorption:
- Microvilli - increased surface area
- Co-transporter proteins - increased surface area and each one is complementary to a specific solute
- A high number of mitochondria - more ATP for active transport (sodium-potassium pump)
- Tightly packed cells - prevents fluid from passing between cells.
Describe the selective reabsorption process of glucose:
Glucose is reabsorbed by co-transport from the epithelial cells of the PCT to the blood capillaries. This is because Na+ is actively transported out of epithelial cells into the blood creating a diffusion gradient for Na+ in the PCT lumen to move in by facilitated diffusion. Glucose is co-transported with this. Higher concentration of glucose in epithelial cells so the diffuses into blood down the concentration gradient.
How does the loop of Henle maintain a sodium ion gradient in the medulla?
Na+ ions are actively transported out of the ascending limb creating a low water potential in the medulla. The ascending limb is impermeable to water so water only moves into the interstitial space by osmosis. This creates a high water potential so water moves into the blood by osmosis.
Where on the loop of Henle do sodium ions move out by diffusion?
At the base of the ascending limb as the interstitial space is very dilute due to all the water moving in from the descending limb.
How is even more water reabsorbed in the distal convoluted tubule and the collecting duct?
Due to all the sodium ions being actively transported out of the PCT when it reaches the top it is very dilute. This then moves into the DCT and collecting duct and the section of the medulla surrounding these two parts is very concentrated (low water potential). Therefore even more water moves out by osmosis. What remains transported to and forms the urine.
In what conditions is increased ADH released:
The blood water potential is low therefore osmoreceptors in the hypothalamus shrink as the solution is hypertonic to it so water moves out by osmosis. This leads to more ADH being produced and secreted by the posterior pituitary gland.
Which gland secretes ADH?
Posterior pituitary gland.
How does ADH increase the blood water potential?
ADH travels to the kidneys and binds to receptors on the surface of the collecting duct and activates the enzyme phosphorylase causing more aquaporins to be formed. This increases water permeability so more water leaves and is reabsorbed back into the blood.
What are aquaporins?
Aquaporins are protein channels for water to pass through.
What does the enzyme ADH activates phosphorylase do?
Phosphorylase causes the vesicles containing aquaporins to fuse with the cell surface membrane and the aquaporins embed.
