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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. .

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PP 3

Excretion in Humans

define excretion
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
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:
  • Pass through / pass into cells and cells use it to make proteins
  • Liver itself uses it (makes fibrinogen)
  • 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


Urine is released here

After it is left the bladder


Inside part

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

Outside part


1. Blood vessels bring blood into tubule

5. Last




Can be


sorbed if

Body need

2. In the renal capsule plasma filtered into tubule

4. Blood vessels take blood away from tubules

3. 1st part of tubule where

Glucose / water / salts are


kidney dialysis
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
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


  • - 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

kidney transplant
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 needed

Positive: - if transplant is successful

– then kidney function is restored