Excretion Flashcards
What is excretion
Removing metabolic wastes e.g. co2 and nitrogen based byproducts to maintain metabolism
Enables organisms to maintain PH balance and regulate osmotic pressure
Whats the structure of the mammalian liver
Liver lobules are connected to:
Hepatic veins which takes deoxygenated blood away from liver and is attached to:
Hepatic portal vein: which contains products of digestion and hepatic artery: supplies oxygenated blood via sinusoid capillaries
and bile duct: transports bile to gall bladder for storage
Outline functions of mammalian liver
Site of gluconeogenesis, glycolysis and glycognesis
Stores glycogen
Deaminates excess amino acids, forming ammonia and organic acids- acids can be respired
Detoxifies chemicals
Describe structure of mammalian kidney
Fibrous capsule: protects kidney
Cortex: outer region consists of bowmans capsules, convulated tubules and blood vessels
Medulla: inner region consisting of collecting ducts, loops of henle and blood vessels
What are the main excretory products
co2, urea, ammonia and bile pigments
Why do we get rid of metabolic waste products
They can alter the pH interfering with cell processes so the normal metabolism is affected, they may also inhibit enzymes
Why is excess co2 a problem
Mostly transported as hydrogen carbonate ions the formation which releases H ions,
Affects the PH of the cytoplasm of the RBC’s changing the bonds and shape of Hb reducing affinity for o2
Why must we excrete nitrogenous compounds
Amino acids cant be stored as they contain a toxic amino group which needs removing
Absorbed by cells and decreases their water potent and they burst
Uric acid may crystallise in joints
Which vessel does blood flow into the liver
hepatic artery (oxygenated from the heart
hepatic portal vein (deoxygenated blood from digestive system)
What is the bile duct
Duct carries the bile secreted in the liver from the liver to gall bladder
In which vessel does blood from the vein and arteries mix
A sinusoid
What is the purpose of blood passing through sinusoids
They put the blood in close contact with liver cells that alter the concentrations of substances in it
What do kupfer cells in sinusoids do
They recycle and break down RBC producing bilirubin as well
What vessels drain blood from the liver
Hepatic vein
What are the metabolic functions of hepatocytes
Protein synthesis
Transformation/storage of carbs
Synthesis of cholesterol and detoxification
How do hepatocytes store glycogen
In granules in the cytoplasm
How might hepatocytes detoxify substances
May oxidise, reduce or combine with another molecule
How is alcohol broken down by detoxification
Ethanol broken down by ethanol dehydrogenase to ethanal which is dehydrogenated by ethanal dehydrogenase to ethanoate which combines with coenzyme A to form acetyl coenzyme .
NAD forms reduced NAD from h ions
Why does alcohol make fat build up
Because NAD is used to detoxify it and it is used up doing this so cannot break down fatty acid
Which part of amino acids make them toxic
Amino group
What is deamination
Amine group and H removed from Amino Acid to form ammonia and a keto acid which may be respired or converted to glucose/fat
What is the ornithine cycle
Ammonia is toxic so it is converted to urea. Ammonia and co2 combined to urea and water
Urea diffuses through the phospholipid bilayer of the hepatocytes and into kidney
What is the role of the kidney
Remove waste products from blood and produce urine
Where is each bowmans capsule
In cortex
Which vessel enters the kidney
Renal artery
What is the glomerulus
Bunch of the capillaries that are the result of the renal artery splitting into afferent arterioles
What is ultrafiltration
When fluid from the blood is pushed into the bowmans capsule
Which three layers act as the filter for ultrafiltration
The endothelium of the capillary, the basement membrane and the epithelial cells of the bowmans capsule
What substances are filtered out of the glomerulus
Water, amino acids, glucose, urea and mineral ions
What substances are not filtered out of the glomerulus and why
Blood cells and proteins because they are too large
What is the basement membrane composed of
Meshwork of collagen and glycoprotein fibres
Water and small molecule can pass through
Proteins too large and are replled by negative charges on fibres
Outline the endothelium of blood capillary in the bowmans capsule
Very thin
Perforated with thousands of pores about 10nm diameter
Provides barrier to cells but not plasma proteins
Outline the epithelium of renal capsule of bowmans capsule
Made of cells modified for filtration
Describe podocytes
Each cell has many foot like extensions projecting from its surface
Extensions wrap around the capillaries of the glomerulus and interlink with extensions from neighbouring cells
Extensions fit together loosely leaving filtrarions slits
Filtered fluid passes through slits
Why is it important that these substances are/are not filtered out
So that the blood is left with a lower water potent which makes reabsorption of water back into blood possible later
What happens in the PCT
Reabsorption of most sugara, mineral ions and some water
How is salt conc established in loop of henle
Descending limb is permeable to water but not salts but the ascending limb is permeable to salts not water
This means that as the loop descends into the medulla, the interstitial fluid becomes more salty and hypertonic as water leaves the tubule by osmosis
Outline the countercurrrent mechanism in the vasa recta as a way of establishing a salt gradient
Vasa recta blood network surrounds the loop of henle flows in the opposite direction (counter current)
Means salts are released from the ascending limb are drawn down into the medulla, further establishing a salt gradient
What happens in the thin ascending limb of henle
As the fluid in the tubule ascends back up towards the cortex, the water potent becomes higher
But can’t leave as the wale is impermeable to water.
Due to counter current from vasa recta, salts are drawn down into the medulla- establishing a salt gradient
What happens in the thick ascending loop of henle
Contains large epithelial cells w specialised transport
- NA/K ATPase pump im membrane pumps 3NA out of and 2k into cell
- Low intracellular Na conc drives the electroneutral Na-K-2cl co transporter at the apical membrane
- K is recycled back into the lumen through k channels in the apical membrane= continued NaCl uptake. Cl leaves through chlorine channels in basolateral membrane.
What happens in the distal convulated tubule
Actively transport finely tunes the conc of various salts in the tubule- water and NaCl are releases
What happens in the collecting duct
When the fluid reaches the collecting duct it has a high water potent.
Collecting duct carries fluid back into medulla which contains a lot of salts ( low water potent)
As fluid passes through, water moves by osmosis, from the tubule fluid into surrounding tissue
Then enters the blood capillaries by osmosis and carried away
How is osmoregulation activated
Osmoreceptors in hypothalamus monitor the water potential of the blood
If osmoreceptors detect a decrease in the water potential of the blood.. ADH causes kidneys to reabsorb more water which reduces loss of water in the urine
What is the effect of ADH on kidneys
ADH causes the luminal membranes of collecting ducts to become more permeable to water by causing an increase in the number of aquaporins in the luminal membranes of collecting duct cells
How does ADH work
ADH molecules bind to receptors which activates a signalling cascade= phosphorylation of the aquaporin molecules
Phosphorylated aquaporins drive fusion of vesicles with the luminal membranes of the collecting duct cells
Water molecules move from the collecting duct through the aquaporins, and into the tissue fluid and blood plasma in the medulla
What is the counter current multiplier mechanism
Divided into three segments: descending, thin ascending and thick ascending
Increases the conc of solute and ions within the interstitium of the medulla
Allows the nephron to reabsorb more water in the same time frame using as little energy as possible
Whats osmoregulation
Loop of henle establishes a salt gradient in medulla
Anti diuretic hormone regulates the level of water reabsorption in the collecting duct
Describe the mechanism of reabsorption in the PCT
Sodium ions pumped out cells lining the tubule, creating a conc gradient of sodium ions towards the cell cytoplasm
Sodium ions diffuse into cell via cotransport proteins carrying glucose or amino acid with them
The glucose and amino acids diffuse into the blood on the other side of the PCT.
A water potent gradient is created in the process so that the water moves into the cell via osmosis
Describe changes in glucose conc throughout the tubule
In the PCT glucose is selectively reabsorbed so the conc of it present is removed
Describe the changes in Na and K ions conc throughout the tubule
Na ions diffuse into the descending limb of the loop of henle, in the desc limb they are pumped out
K ions actively transported into the tubule and when water removed from tubule their conc also increases
Describe the changes in urea conc throughout the tubule
As water is withdrawn from the tubule the conc rises
Actively moved into the tubule
What is osmoregulation
Controlling the water potential throughout the body
How do kidneys alter the volume of urine produced
They alter the permeability of the collecting duct
What is filtered out of the blood into the nephron during ultrafiltration
Water
AA
Glucose
Urea
Inorganic ions
