Section 3 - Excretion:

Excretion - removal of metabolism waste products from the body

The liver:

Functions of the liver:
- Deamination of amino acids - removal of the amine group from amino acids, forming ammonia and organic acids. Organic acids can be used for respiration to give ATP or be converted to carbohydrates. Ammonia + carbon dioxide occurs in the ornithine cycle.
- Breaks down alcohol into ethanal, into acetic acid. Excess alcohol causes cirrhosis of the liver (scar tissue blocks blood flow).
- Breaks down paracetamol, and excess insulin.
- Stores glycogen
Structure of the liver:
- Hepatic artery supplies the liver with oxygenated blood, the hepatic vein takes deoxygenated blood away.
- Hepatic portal vein brings blood from the duodenum (small intestine), which is full of products of digestion. Any harmful products are broken down.
- Bile duct takes bile (emulisfies fat) to the gall bladder to be stored.
- Liver is made up of lobules, which are made of hepatocytes
- Each lobule has a central vein, and branches of hepatic artery, vein, and hepatic portal vein
- Hepatic portal vein and hepatic artery are attached to the central vein by sinusoids
- Kupffer cells remove bacteria and break down old red blood cells
- Bile duct is connected to the central vein by the canaliculi

The kidney:

Main function is to excrete waste products, and regulate water potential
Structure:
- Blood enters via the renal artery, through the afferent arteriole, to the glomerulus, through the proximal convoluted tubule, to the loop of henle, back out the distal convoluted tubule and out the collecting duct
Ultrafiltration:
- In the glomerulus, blood goes three layers to get into the bowman's capsule (capillary membrane, basement membrane, podocytes).
Selective reabsorption:
- Takes place in the PCT, loop of Henle and DCT.
- The walls of the PCT have microvilli that have a large surface area for reabsorption. Useful solutes like glucose, AAs, vitamins and salts are reabsorbed due to active transport and facilitated diffusion
Controlling water potential:
- Near the top of the ascending limb, Na and Cl ions are actively pumped into the medulla, lowering the water potential in the medulla.
- The lower water potential means water diffuses out of the descending limb by osmosis. This water is then reabsorbed back into the blood
- Near the bottom of the ascending limb, Na and Cl ions diffuse out as they are in such high concentration
- Water potential is controlled by the anti-diuretic hormone, they are released when you're dehydrated. Osmoreceptors in the hypothalamus detect this. the posterior pituitary gland releases more ADH which makes the collecting duct and DCT more permeable, so more water is reabsorbed back into the blood.
Kidney failure:
- Can be detected by measuring the glomerular filtration rate
- Caused by kidney infections, that mean swelling of the kidneys stops filtering at the bowman's capsule or reabsorption
- High blood pressure damages the glomeruli, large molecules can get into urine
- Causes many problems: urea is toxic in the body, fluid accumulates and parts of the body swell, blood may become to acidic, long term kidney failure leads to anaemia
- Renal dialysis:
  - Using a machine to filter blood, by passing it by a partially permeable membrane with dialysis fluid on the other side. It takes 3 to 5 hours, you feel ill between sessions, expensive, less risky that surgery
- Kidney transplant:
  - Cheaper, convenient, major op, may be on immune system suppression drugs
Detecting chemicals:
- Pregnancy tests:
  - Stick with an application area that contains antibodies for hCG bound to coloured beads. When any urine is applied with hCG in, it will bond to the antibodies and move up the strip. The test strip has antibodies attached to it also, if the strip turns blue, the hCG has bound to the strip with the coloured beads
- Steroids:
  - Gas chromatography/mass spectrometry is used to see if there are steroids in the urine of an athletes

	Created by Hannah Stephens about 6 years ago

A level Biology Note on Module 5, created by Hannah Stephens on 19/02/2018.

Module 5