PP 3

Excretion in Humans

Define excretion

the removal from organisms of toxic materials, the waste products of metabolism (chemical reactions in cells including respiration) and substances (carbon dioxide, urea and salts) in excess of requirements.

the function of the kidney: removal of urea /excess water / the reabsorption of glucose and some salts

Urea:- Made in liver (from excess of proteins / a.a)- A. a. are absorbed into blood and go via the

hepatic portal vein to the liver- AA in liver:1. Pass through / pass into cells and cells use it to

make proteins 2. Liver itself uses it (makes fibrinogen)3. Excess is broken down by the liver – changed to

carbs or fats for storage • This requires the N part of a.a. to be removed*** Alcohol / drugs and hormones are also broken

down in liver

Deamination – removal of Nitrogen from a.a. - N containing part made into urea (nitrogen

excretory product) Urea is carried away from liver in blood to

kidneys Kidney’s filtering system:- Plasma is filtered into kidney- Useful substance (glucose / ions (NaCl) are

taken back to blood (reabsorption)- Urea kept in kidney

Urine – urea in water. Too much water in body is excess – also

removed in urine If there is not enough water in body –

only little water will flow out as urine and the majority of it will be taken back into blood

Urine: water + salts + urea- urea, uric acid, ammonia, hormones,

dead blood cells, proteins, salts and minerals, and toxins

Urine flows through here into Bladder

Urine is released hereAfter it is left the bladder

Outside part

Inside part

Both contain tiny tube = kidney tubules (start in cortex as renal capsule

Kidney

Structure Function

Renal capsule

•Blood is delivered here and flows through a capillaries network •blood plasma is squeezed through wall of capillary wall of capsule into the cavity inside the kidney tubule• Blood plasma passes through filter• It does not pass through: cells / big proteins•Molecules that pass through: water, urea, glucose, ions : sodium & chloride

Renal Tubule

• As fluid flows through tubule - anything useful is reabsorbed into the blood (not lost from body)•Water is removed from the tubule

Ureter • collects excess water / salts / urea = urin

1. Blood vessels bring blood into tubule

2. In the renal capsule plasma filtered into tubule

3. 1st part of tubule whereGlucose / water / salts are Reabsorbed

4. Blood vessels take blood away from tubules

5. Last Portion Where WaterCan beReab-sorbed ifBody need

Kidney Dialysis

Kidney stops working (infection / trauma / genetics) Kidney no longer can remove urea / excess water Feeling ill ->death 2 options : Kidney Transplant or if possible Kidney

Dialysis Dialysis: filtering patients blood (like the kidney

does) using a Kidney Dialysis Machine by passing blood through it.

- The process of diffusion of different molecules each according to its own concentration gradient though a partially permeable membrane

How dialysis works

blood passes through tiny channels in dialysis tubing in machine

Dialysis tubing allows only certain molecules though because of the size of holes (very small – molecule size) that the tubing is made of.

Smalls molecules can pass though – water / urea/glucose can pass through

Large molecules like proteins can not

Dialysis fluid – the liquid outside the dialysis tubing

- This made to have similar composition of healthy human blood plasma (water / glucose / salts – but no urea)

- It is sterile (no germs)- Dialysis fluid flows in 1 direction in the machine- Patients blood passes in the opposite direction - Fluid and blood will diffuse down its

concentration gradient

Therefore: - No urea in dialysis fluid - urea in patients blood will

diffuse out of the patient and into the dialysis fluid If more water in blood than in dialysis fluid then water

will diffuse out of blood of patient If the opposite is true – then water will flow in from the

dialysis tubing into the patients blood (same for salt and glucose)

Problems:- This needs to be done several times a week for several

hours- Can make people feel sick / must be careful of what they

eat / Positive:- cheaper than transplant

How Dialysis works

Kidney transplant

Kidney taken from a donor and placed in a recipient

Problems: - not enough kidneys for number of donors- Must come from healthy donor- Cells or donor kidney must be similar to

recipient’s - Immunosuppressant drugs are still neededPositive: - if transplant is successful – then kidney function is restored