Excretion- Biology F214

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  • The liver is split into cylindrical lobules.

Blood is provided from two sources:

-Oxygenated blood: comes from the heart via the hepatic artery. 

-Deoxygenated blood: comes from the digestive system via the hepatic portal vein.

Blood leaves the liver through the hepatic vein.

Bile duct carries bile from the liver to the gall bladder.

Alcohol detoxification: Competes for NAD, ethanol --> Ethanoate --> Acetyl CoA

Sinusoid: blood from the hepatic artery andportal vein joins = intra-lobular vessel

Liver cells: Remove and add molecules to blood in sinusoid, produce bile (bile canaliculi)

Kuppfer cells: specialised macrophages break down old red blood cells to form bilirubin.

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Substances Excreted

Carbon Dioxide

  • Reduces oxygen transport as H+ ions are formed (enzyme= carbonic anhydrase). Thede H+ ions combine with haemoglobin.
  • CO2 can bind to haemoglobin to make carbaminohaemoglobn which has a lower oxygen affinity.
  • Excess CO2 causes respiratoty acidosis:

CO2 + H2O -->   H2CO3

H2CO3 -->  H+   +   HCO3-

Nitrogenous Compounds

  • Body  can't store proteins or amino acids, so they are deaminated and converted to urea.
  • Remaining keto acids are used for respiration.

2NH3 +  CO2 -->  CO(NH2)2  +  H2O

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Pressure of glomerulus > Bowman's Capsule

Basement membrane consists of collagen and glycoproteins- contains podocytes



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Selective and Water Reabsorption

Proximal Convoluted Tubule: This is where 85% of the filtrate is reabsorbed, mainly glucose and amino acids.

FACILITATED DIFFUSION of H2O. Na+, glucose and amino acids through sodium-potassium channels into capillary. PCT cells have microvilli to increase surface area. WATER MAY BE REABSORBED.

Loop of Henle

Thin descending limb: permeable to water, so water potential lowers as water lost by osmosis. Na+ and Cl- enter by diffusion.

Thick ascending limb: impermeable to water, water potential increases as Na+ and Cl- diffuse out. Higher up, they are actively transported out. 

Distal Convoluted Tubule: Active transport used to adjust levels of different salts.

Collecting Duct: Water is moved by osmosis back into surrounding tissue. Carried to pelvis, then away.

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  • Controlled by the hormone ADH

Water potential is monitored by osmoreceptors in the hypothalamus:

1. Water potential in the blood lowers.

2. Osmoreceptors shrink, detected by the hypothalamus.

3. Neurosecretory cells in the posterior pituitary gland secrete ADH (anti-diuretic hormone).

4. Collecting duct walls become more permeable,so more water is reabsorbed.

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Haemodialysis: When the blood froma vein is passed through a dialysis machine.

- Blood and dialysis fluid are separated by the dialysis membrane.

- Heparin used to avoid clotting, and bubbles must be removed beforeblood returned.

Peritoneal Dialysis: Dialysis fluid is pumped into thebody cavity.

-The exchange occursacross the body's own partially permeable membrane.

- Permanent tube is inserted to the abdomen, and dialysis fluid is poured through this tube, then drained.

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Pregnancy Tests

  • When pregnant, the embryo secreteshCG (human chorionic gonadotrophin).
  • Pregnancy tests use monoclonal antibodies which bind to hCG.

1. If hCG molecules attach to the antibodies,the antibodies are tagged with a blue bead.

2. These move up the ***** until they reach a wall of immobilised antibodies.

3. hCG complex sticks to the band forming a blue line.

A control blue line exists to use for comparisonto check if it is working.

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