KIDNEY 2 Flashcards
What are the main functions of the kidney?
• filtering waste products out of the blood
• reabsorbing useful solutes (eg. glucose and amino
acids)
• carrying out osmoregulation to control the water
potential of the blood
How is blood passed to kidneys?
Kidney is supplied with blood from a renal artery and is drained by the renal vein. The kidney removes waste products from the blood and produce urine. It then passes through the ureters to the bladder (for storage) and released out of the body through the urethra.
What does the nephron contain?
nephron begins with a cup shaped structure called a renal (Bowman’s) capsule followed by the proximal convoluted tubule (PCT) then loop of Henle which leads into the distal convoluted tubule (DCT) and finally joins to a collecting duct
What does ultrafiltration do?
formation of urine
Where does ultrafiltration take place?
Bowman’s Capsule
How does blood flow into the glomerus?
Blood flows into the glomerulus from the afferent arteriole, which is wider than the efferent arteriole which carries blood away.
This increases the pressure in the glomerulus compared to the pressure in the Bowman’s capsule which forces blood plasma through the pores in the blood capillary, through the basement membrane and epithelial cells of the renal capsule forming glomerular filtrate.
What adaptations are there for ultrafiltration?
- Endothelial cells: narrow gaps allowing blood plasma through.
- Basement membrane: mesh of collagen and glycoprotein fibres which act as the filter only allowing molecules through with a relative molecular mass les than 69 000, which means large proteins and cells are NOT filtered out. The presence of proteins lowers the water potential and ensure some water is retained.
- Epithelial cells of the renal capsule called podocytes: have finger like projections, fluid passes between these processes into the lumen of the Bowman’s capsule.
What does the glomerular filtrate consist of?
- ) Amino acids
- ) Urea
- ) Ions
- ) Water
- ) Glucose
What does selective reabsorption do?
The glomerular filtrate contains many substances that the body still needs. All the glucose, all the amino acids and some salts are reabsorbed as a result of active transport and facilitated diffusion
Where does selective reabsorption take place?
Proximal Convoluted Tube (PCT)
What happens during selective reasbsorption?
- The sodium- potassium pump actively moves Na+ from the cells lining the proximal convoluted tubule into the tissue fluid by active transport using ATP. This lowers the concentration of Na+ in the cell cytoplasm.
- Na+ are transported into the cell of the PCT along with glucose and amino acids by a co-transporter protein by facilitated diffusion.
- Glucose and amino acids then diffuse along a concentration gradient out of the epithelial cells into the tissue fluid and then into the blood capillary (Some water will also pass in this direction due to the water potential gradient.)
What are the adaptaions of PCT?
- Folding of membrane on capillary side to increase surface area and presence of sodium-potassium pump for active transport.
- Membrane on lumen side contains co-transporter proteins for facilitated diffusion.
- Microvilli of the epithelial cells of the PCT provide a large surface are for absorption.
Where does Water Reabsorption take place?
Loop of Henle
How permeable is the loop of Henle to water?
- The ascending limb is impermeable to water
* The descending limb is permeable to water
Loop of Henle’s permebility to ions?
- The ascending limb can actively transport (pump) Na+ and Cl- out (NB. Na+ and Cl- diffuse out near the bottom of the ascending limb)
- Na+ and Cl- ions diffuse into the descending limb
What is hairpin countercurrent multiplier?
one part of the tubule passes close to the other part with fluid flowing on the opposite direction. This allows exchange of material and allows the increase in concentration of ions in the medulla.
How is the hairpin countercurrent multiplier different in other animals?
Desert animals have a very long loop of Henle which allows them to conserve water. The longer the loop of Henle, the more Na+ and Cl- are actively transported out of the ascending limb. Therefore the water potential in the medulla is even lower, so then more water moves by osmosis from the descending limb, DCT and collecting duct into the medulla, and is then reabsorbed back into the blood.
Where does osmoregulation take place?
DCT and collecting tube
What is ADH?
ADH (Anti-Diuretic Hormone) controls water levels in the body
What happens during osmoregulation?
Water potential of the blood is monitored by osmoreceptors in the hypothalamus of the brain.
When water potential of the blood decreases, osmoreceptors cells lose water by osmosis.
They lose volume and send a signal to the posterior pituitary gland causing it to release a hormone called ADH.
When ADH is released and enters the bloodstream, it is transported to the distal convoluted tubule and collecting duct, where it binds to membrane bound receptors and causes protein channels called aquaporins to move into the membranes. This makes the walls of the DCT and collecting duct more permeable to water, as this allows more water to move out of the DCT and collecting duct by osmosis back into the blood causing the urine to be more concentrated.
What happens when blood water content is low?
- water content drops so water potential drops
- detected by osmoreceptors in the hypothalumus
- posterior pituitary gland is stimulated to release more ADH into the blood
- More ADH means that the DCT and collecting duct are more permeable, so more water is reabsorbed into the blood by osmosis
- A small amount of highly concentrated urine is produced and less water is lost
What happens when blood water content is high?
- water content rises so water potential rises
- detected by osmoreceptors in the hypothalumus
- posterior pituitary gland is stimulated to release less ADH into the blood
- Less ADH means that the DCT and collecting duct are less permeable, so more water is reabsorbed into the blood by osmosis
- A large amount of dilute urine is produced and more water is lost
What are the 4 steps that occur in the kidney?
- ) Ultrafiltration
- ) Selectibe Reabsorption
- ) Water Reabsorption
- ) Osmoregulation
