Kidneys and Homeostasis Flashcards
What are the main functions of the kidneys?
Control water content of the blood
Removal of urea from the blood
Removal of excess mineral salts from the blood
Why do we produce urine?
It is a mixture of urea (made by the liver from proteins not needed in the body) and water, excreted because urea is poisonous and cannot be allowed to build up in the blood
What do kidneys control?
Water levels
Ion levels
What is urine concentration affected by?
Amount drunk
Temperature (if we sweat or not)
Describe the structure of the excretory system
Blood enters kidney through RENAL ARTERY Blood leaves kidney through RENAL VEIN URETER carries urine from kidney to bladder BLADDER stores urine URETHRA carries urine out of the body
What are the 3 main areas of the kidney?
Outer cortex (outer layer) Inner medulla (inner layer) Pelvis (where urine drains)
What is the role of nephrons?
To remove urea, excess mineral salts and excess water from the blood to make urine
What is the first stage of urine production in a nephron?
Ultrafiltration:
The blood capillaries form a tightly knotted cluster, squeezing out small particles from the blood and into the Bowman’s capsule
The blood is filtered and all water, urea and salts are removed from the blood.
Blood cells and proteins remain in the blood as they are too big to move across the capillary walls.
What is the second stage of urine production in a nephron?
Selective reabsorption: Useful molecules (e.g. glucose, salts and most water) are reabsorbed in the bloodstream. The remaining mixture forms urine which passes into the collecting ducts
How many nephrons are in each kidney?
Around 1,000,000
How does the capillary knot inside a nephron work?
Arterioles from the renal artery become very narrow and form a tight knot of capillaries. The arteriole leading into the knot is wider than the arteriole leading out the knot which increases blood pressure. Under this pressure, small molecules are filtered into the Bowman’s capsule.
Describe the journey of molecules through a nephron
Capillary knot -> Bowman’s capsule -> Tubule -> Collecting ducts (urine) OR Capillary network (useful substances)
What does presence of blood or cells in urine indicate?
Kidney disease
How do useful substances get back into the bloodstream from the tubule during reabsorption?
Through the walls of the tubule and into the capillary network than travels alongside it
What is another name for the capillary knot?
Glomerulus
What osmoregulation and what is it controlled by?
Concentration of water in the blood - controlled by anti diuretic hormone (ADH)
What path does ADH take?
Released by the pituitary gland in the brain, carried in the blood to the kidneys
What happens when too little water is detected? (Concentrated blood)
Brain triggers release of ADH which increases permeability of nephron tubules, meaning more water is reabsorbed into the bloodstream.
Result is small volume of concentrated urine
What happens when too much water is detected? (Dilute blood)
Brain signals to stop release of ADH which decreases permeability of nephron tubules, meaning less water is reabsorbed into the bloodstream.
Result is large volume of dilute urine
Why is blood in urine a sign of kidney disease?
Blood cells and proteins are normally too large to pass through the capillary walls when the blood is filtered in the Bowman’s capsule. This means the nephron is damaged.
What is glucose in urine a sign of?
Diabetes.
Blood glucose levels are so high that all of the glucose in the filtrate can’t be reabsorbed from the nephron tubules, so some glucose ends up in the urine.
What are the two treatments available for kidney disease?
Kidney dialysis
Kidney transplant
What is kidney dialysis?
Where a patient is attached to an artificial kidney machine which removes wastes and restores the balance of salts and water in their blood
How does dialysis work?
- Blood from patient taken from blood vessel in arm and pumped into machine.
- Dialysate also put through machine, a fluid which contains the same concentration of glucose and salts as blood plasma.
- Blood passes over a partially permeable membrane designed to replicate kidney tubules, with dialysis fluid on the other side.
- A concentration gradient is established, allowing excess ions and urea to diffuse from an area of high concentration in the patient’s blood to an area of low concentration in the dialysis fluid.
- Blood returned to body
