Human Excretory System

What are the kidneys?• 2 Kidneys – supplying oxygenated blood from the aorta, via renal arties.Removing deoxygenated blood by the vena cava, via renal veins.

• Ureter is a tube leading from the kidneys to the bladder.

• Bladder (muscular membranous sac in the abdomen which receives urine and stores it for excretion). Stretchy to hold large quantities.

• Sphincter muscles – when contract, urethra is sealed shut --> no urine out

• Urethra – tube from the bladder to the outside

Kidney3 main parts Cortex – outer partMedulla – inner partPelvis – broadened top part of the ureter

Kidneys are made up of tiny tubules (nephrons) thousands of them"thousands of tiny tubes in the kidney that produce urine from filtered blood"

Filtration• Blood --> in renal artery --> renal capsule (in nephron) [cup shaped with mass of capillaries in the centre (glomerulus)]• High pressure at these capillaries squeezes small molecules (like water,salt,glucose and urea)

out and into the renal capsule.

• This high blood pressure is because the vessels supplying the blood are wider than the ones removing blood, meaning blood can't easily escape

(Filter – only allow certain materials to pass through) Proteins/ RBC too big to pass through

Glomerulus: a tangle of capillaries in the 'cup' of a renal capsule.

Reabsorption• Now, in the renal capsule, is a solution of glucose, salt, urea in water

• Glucose, salt and water are useful for the body, taken back into the blood. Loop of Henle

• At the collecting duct, mainly water, urea and salts (urine)

• Sent to bladder

Kidney DialysisIf a person's kidneys stop working properly (infection, tumor, damaged, obstructions), allows urea to build up in the blood.

• Dialysis = exchange of substances between two solutions through a partially permeable membrane.• Dialysis machines, for treating people with kidney failure.

• Blood flows from a person --> through the machine --> back into the person

• In the machine = dialysis fluid contains glucose, water, salts (like normal blood)• As blood flows through the tubes, substances diffuse along concentration gradients eg. There is no urea

in the dialysis fluid, so urea diffuses out of the blood

• Treatment last several hours and is need 2-3 times a week!

Kidney Transplant• 2-3 times a week• Donor gives kidney to recipient.• The donor and recipient need to be a close match. Their tissue-types need to

match or the immune system will reject it. - attack it recognising it as foreign• But even after transplant, patient needs to take immunosuppressants for life• Stop the immune system (WBC) working efficiently• Problems?• More likely to catch infections