Excretion: the liver + part 2 of kidneys

what does excretion mean?

• removal of waste products of metabolism from the body such as carbon dioxide and nitrogen

• excreting waste products from the body maintains normal metabolism and homeostasis by helping keep levels of certain substances in the blood roughly constant

Roles of liver: storage of glycogen

liver converts excess glucose into glycogen - glycogenesis and stores its granueles in cells until the glucose is needed for energy

this process is triggered by insulin

glycogen produced during glycogenesis is stored in hepatocytes - glycogen is a compact molecule that allows for release of glucose when needed

Role of liver: deamination

• protein in our diets is broken down into amino acids which are absorbed into the blood and transported into liver via hepatic portal vein

• Amino acids contain nitrogen in amino groups - nitrogenous substances are not normally stored by the body

• this means excess amino acids can be damaging to body so much be used or broken down and excreted

Role of liver: detoxification

• breakdown of substances that are toxic such as alcohol

Detoxification of alcohol:
- inside hepatocytes, alcohol dehydrogenase converts ethanol into ethanal which is then converted into other molecules that enter respiration

• metabolism of ethanol generates ATP so hepatocytes do not metabolise as much fat as usual and instead store fat. Excess alcohol over long time period can lead to cirrhosis of liver - cells of liver die

• paracetamol - broken down by liver and excess can cause liver + kidney failure

• insulin

External liver structure

• oxygenated blood from heart is carried to liver via hepatic artery so liver has a good supply of oxygen for respiration, providing energy

• liver receives blood from digestive system via hepatic portal vein - allows it to absorb and metabolise nutrients absorbed in small intestine

• deoxygenated blood exits liver in hepatic vein and flows back to heart

• bile duct takes bile (substance produced by liver to emulsify fats) to the gall bladder and is stored

Internal liver structure

liver is made up of hepatocytes - cells that carry out most of functions for the liver

liver cells are arranged into liver lobules

each lobule has a central vein in the middle that connects to the hepatic vein. Many branches of the hepatic artery, hepatic portal vein and bile duct are also found connected to each lobule

blood from hepatic artery and portal vein mixes within each lobule inside sinusoid

blood runs through sinusoids, past hepatocytes that remove harmful substances and oxygen from the blood

harmful substances are broken down by hepatocytes into less harmful substances that then re-enter blood

cells called kupffer cells are also attached to walls of sinusoids. they remove bacteria and break down old red blood cells

hepatocytes produce bile and secrete it into bile canaliculi. these tubes drain into bile ducts. the bile ducts from all lobules eventually connect up and leave liver

Histology diagrams + microscopic

on google and in textbooks/revision guide

Kidney failure

• kidney can not carry out normal function because they do not work properly

• detected by measuring glomerular filtration rate (GFR) - rate at which blood is filtered into glomerulus and bowman’s capsule

• rate lower than normal means kidney is not functioning properly

Kidney failure can be caused by many things including:

Kidney infections - cause inflammation of kidneys, which can damage the cells.

High blood pressure - can damage glomeruli. capillaries can be damaged if blood pressure is too high. Large molecules such as protein can get through capillary walls and into urine

Kidney failure can cause lots of problems for example:

• waste products that kidneys would normally remove begin to build up in blood - too much urea in blood causes weight loss and vomiting

• balance of electrolytes in body becomes unbalanced - blood may become too acidic and salt build up may cause more water retention

• long-term kidney failure causes anaemia - a lack of haemoglobin in the blood

• fluid starts to accumulate in the tissues because the kidneys can’t remove excess water from the blood which causes parts of the body to swell.

Renal dialysis

Haemodialysis - patient’s blood is passed through dialysis machine - blood flows on one side of a partially permeable membrane and dialysis fluid on other side

waste products and excess water and ions diffuse across the membrane into dialysis fluid, removing them from the blood

blood cells and larger molecules like proteins are prevented from leaving blood

each dialysis session takes 3 to 5 hours, and patients need 2 or 3 sessions a week, usually in hospital. patients can feel unwell between dialysis sessions since waste products and fluid start to build up in blood

Kidney transplant

A kidney transplant is where a new kidney is transplanted into a patient’s body to replace a damaged kidney

new kidney has to be from a person with same blood and tissue type, often from a living relative as people can only survive with one kidney. They can also come from other people who have recently died - organ donors

Advantages and disadvantages of kidney transplant

Disadvantages:

• immunosuppressant drugs must be taken for the rest of their lives - can have long term side effects and leave patients vulnerable to infections

• not enough donors to cope with demand

Advantages:

• have much more freedom as not tied to a dialysis several times a week in one place

• diets can be much less restrictive than they are when on dialysis

• cheaper than dialysis

• kidney transplant is long term, dialysis can work only for a limited amount of time

Urine tests for glucose

all glucose in glomerular filtrate should be reabsorbed by PCT so no glucose should be present in urine

if glucose is present in urine - something is wrong with person’s homeostatic control of glucose

Urine tests for proteins

• if urine test shows protein is present, suggests the person’s blood pressure may be too high or kidney infection

Pregnancy tests (look at CGP for visualisation)

1. A stick is used with an application area that contains monoclonal antibodies for hCG bound to a coloured bead

2. when urine is applied to application area, any hCG will bind to antibody on beads

3. urine moves up the strip, carrying beads with it

4. test strip has antibodies to hCG stuck in place (immobilised)

5. if hCG is present, the test strip turns blue because immobilised antibody binds to any hCG attached to the blue beads, concentrating blue beads in that area. If no hCG present, beads will pass through test area without binding to anything so it won’t go blue.

Testing for anabolic steroids

• athletes are regularly tested for anabolic steroids as they can be used to rapidly build muscle mass by stimulating protein synthesis

• anabolic steroids are detected in urine via gas chromatography or mass spectrometry

Test for recreational drugs

• urine can be tested to see if people have been using recreational drugs such as cannabis or cocaine

• testing for these drugs usually starts with test strips, containing antibodies that the drug being tested for will bind to. Sample of urine is applied to test strip and if certain amount of drug is present, a colour change will occur, resulting in positive result

• if the first test shows a positive result, sample of urine is usually sent for further testing to confirm which drugs have been used.