Excretion Flashcards
What is excretion?
The removal of metabolic waste from the body.
CO2 when we breathe out
Nitrogenous waste in the urine
Why is excretion important for homeostasis?
It prevents build up of substances that could cause tissue damage.
What are the functions of the liver?
Breaking down amino acids into urea
Detoxifying the blood
Storing glycogen
Producing bile.
what is the process where liver converts excess amino acids to urea?
Deamination
Ornithine cycle
What is the ornithine cycle?
Metabolic pathway where amino acids are deaminated to form ammonia and organic acids
Ammonia is converted into urea by reacting with CO2
Urea is released into the blood stream
How does urea get excreted?
Urea is released into the bloodstream
Filtered by the kidneys and excreted by the body in urine
What vessels are involved in liver function?
Hepatic artery - oxygenated blood
Hepatic vein - deoxygenated blood
Hepatic portal vein - liver to intestines
Bile duct - liver to gall bladder
What is the structure of the liver made up of?
Liver lobules which are cylindrical structures made of hepatocytes
What are sinusoids in the liver?
Special capillaries that connect the central vein to hepatic artery and portal vein
Allows blood to flow through liver
What is the role of Kupffer cells in the liver?
Break down old red blood cells and remove bacteria from blood stream
What are the 2 main parts of the kidney?
The Medulla - inner part
The Cortex - outer part
How does blood flow to and from the kidney?
Blood is carried to the kidney via the renal artery
Filtered blood is taken away by renal vein
What are nephrons?
Individual structures in the kidneys that filter the blood and remove waste products.
What substances do our kidneys remove from the blood?
Excess water
Excess ions
Urea
What processes are involved in the removal of substances from the blood stream?
Ultrafiltration and selective reabsorbtion
What happens during ultrafiltration?
Blood is placed under high pressure in the glomerelus
the efferent arteriole has a smaller diameter than the afferent arteriole
Small molecules are pushed out the blood into the Bowman’s capsule
What are the 3 layers that small molecules pass through?
The capillary endothelium
The basement membrane
The epithelium of the Bowman’s capsule - podocytes
What is glomerular filtrate?
Substance formed when small molecules are pushed out of the bloodstream
What happens to larger molecules during ultrafiltration?
large molecules remain inside the capillaries during ultrafiltration
What is the proximal convoluted tubule (PCT)?
In the PCT, useful substances are reabsorbed back into the blood
How is glucose reabsorbed in the PCT?
Na+ is actively transported into the capillaries
Na+ concentration decreases in the PCT epithelial cells
Na + moves from PCT lumen to epithelial cells down a concentration gradient
Na+ is co-transported with glucose into the epithelial cells
Glucose diffuses into the blood
What structures in the PCT aid in reabsorbtion?
The PCT has microvilli that provide large surface area
How is water reabsorbed in the kidneys?
At the top of the ascending limb, sodium ions are pumped into the medulla
this lowers the water potential of the medulla so water moves out of the nephron by osmosis from the descending limb
More water moving out means filtrate becomes more concentrated so sodium ions diffuse out ascending limb
Water potential in medulla is lowered more and water moves out by osmosis
What is ADH?
ADH controls the water content of urine by increasing the reabsorption of water from the collecting duct.
It is released by the pituitary gland when water levels are low
Explain the negative feedback mechanism of ADH
Osmoreceptors in the hypothalamus detect a drop in blood water potential
Hypothalamus signals the posterior pituitary gland to secrete ADH
ADH causes the walls of the DCT to become more permeable to water
More water moves out of the DCT by osmosis and reabsorbed into the blood - DCT water potential increases.
Smaller volume of concentrated urine produced
How does the DCT become more permeable to water?
Incorporation of more aquaporins into the membranes of the cells that line these parts of the nephron
What is kidney faliure?
Kidney faliure occurs when the kidneys stop filtering toxic substances out of the blood
What causes kidney failure?
Infection - inflammation in kidney which damages cells so the nephron cant reabsorb substances
High blood pressure - damages the glomeruli so large substances like proteins can pass into the nephron
How is kidney failure diagnosed?
Measuring glomerular filtration rate (GFR) - the rate at which blood is filtered from the Bowman’s capsule
Low GFR = kidney failure
Problems of kidney failure
Build up of waste products - urea
Ion imbalance - acidic blood, brittle bones and water retention
Accumulation of fluids in tissue - swelling
Anaemia - low blood haemoglobin
Mortality
What is dialysis?
Connecting patients blood supply to a dialysis machine
Blood passes through partially permeable membrane surrounded by dialysis fluid
Urea is removed and glucose, water and salts are maintained
Negatives of dialysis
Multiple hospital visits
Long sessions connected to machine
Expensive
Patients must maintain a controlled diet
What are some alternative treatments to kidney failure?
A kidney transplant
Major surgery which comes with the risk of organ rejection
requires immunosupressant drugs
How are drugs detected in urine?
Detected using test strips with antibodies that bind to the drug, causing a color change
confirmed by gas spectrometry/ mass spectrometry
How do pregnancy tests work?
Pregnancy tests detect human chorionic gonadotropin (hCG) in the urine
Test stick contains monoclonal antibodies bound to coloured beads that attach to hCG
Urine moves up test strip and immobilized antibodies capture the hCG
