5.1.2 excretion as an example of homeostatic control Flashcards
What is excretion?
Excretion is the removal of the waste products of metabolism from the body.
What are the main metabolic waste products in mammals?
Carbon dioxide= waste product of respiration and excreted by the lungs.
Bile pigments= waste product of breakdown of haemoglobin from old red blood cells in the liver and excreted in bile.
Nitrogenous waste(urea)= formed from breakdown of excess amino acids by the liver and excreted by kidneys in urine.
What are three main blood vessels in the liver?
Hepatic artery (oxygenated blood to the liver).
Hepatic vein (removed and returned to the heart).
Hepatic portal vein (blood loaded with products of digestion).
What is the structure of the liver?
Made up of hepatocytes-large nuclei, prominent Golgi Apparatus, and lots of mitochondria (metabolically active).
Blood from hepatic artery and hepatic portal vein mix in sinusoids which are surrounded by hepatocytes-increase the oxygen content of the blood from the hepatic portal vein.
Sinusoids contain Kupffer cells which act as resident macrophages of the liver.
Hepatocytes secrete bile into canaliculi, from these the bile drains into the bile ductules taking it to the gall bladder.
What are the roles of the liver?
Carbohydrate metabolism (glycogen storage)- hepatocytes convert glycogen into glucose under the influence of glucagon.
Deamination of excess of amino acids.
Detoxification.
What is the process of deamination of excess amino acids in the liver?
The amine group (NH3-ammonia) is removed from the amino acids.
The ammonia is added to ornithine with CO2-makes citruline removing H2O.
Ammonia is added to citruline-makes arginine removing H2O.
Adding H2O to arginine-makes urea.
(converts highly toxic ammonia into less toxic urea)
What is transamination and deamination?
Transamination=the conversion of one amino acid into another.
Deamination=the removal of an amine group from a molecule.
What does the liver detoxify?
Hydrogen peroxide is broken down into H2O and oxygen with the help of catalase.
Ethanol is broken down to ethanal and then ethanoate with the help of alcohol dehydrogenase.
What is the structure of a kidney?
Three main areas:
Cortex- dark outer layer, where filtering of blood happens and has dense capillary network carrying blood from renal artery to nephrons.
Medulla- lighter colour, contains tubules of nephrons that form pyramids of the kidney and collecting ducts.
Pelvis- central chamber where urine collects before passing down the ureter.
What is the structures and functions of the nephron?
Bowman’s capsule= cup-shaped structure that contains the glomerulus (tangle of capillaries). More blood goes into the glomerulus than leaves due to ultrafiltration.
Proximal convoluted tubule= first coiled region of tubule, found in cortex of kidney, many substances reabsorbed into the blood.
Loop of Henle= long loop of tubule that creates a region with a very high solute concentration in tissue fluid.
Distal convoluted tubule= fine-tuning of water balance of the body takes place. The permeability of the walls to water varies to levels of ADH in the blood. Further regulation of the ion balance and pH of blood.
Collecting duct= urine passes down the collecting duct through the medulla to the pelvis.
What is the process of ultrafiltration in the kideny?
Ultrafiltration is the first stage in removal of nitrogenous waste and osmoregulation of blood.
Blood is forced through capillary wall- and passes through the basement membrane.
Water, glucose, salt, amino acids, and urea all leave the blood (small enough to pass through) into glomerulus filtrate.
What is the glomerular filtration rate?
The glomerular filtrate rate is the volume of blood which is filtrated through the kidneys in a given time.
90-120 (normal range)
What is the process of reabsorption in the kidneys?
Glucose, amino acids, and salt are reabsorbed by diffusion and Active Transport (water potential of filtrate rises).
What are the adaptations of the cells lining the proximal convoluted tubule?
They are covered in microvilli-increasing the surface area over which substances are reabsorbed.
They have many mitochondria- provide ATP needed in active transport systems.
What is the process of osmoregulation in the kidneys?
- Osmoreceptors detects the need for more or less water, then ADH is produced by the hypothalamus and stored in the posterior pituitary.
- ADH is released and binds to the ADH receptor-doesn’t go inside the cell, just binds.
- cAMP is made from ATP (when ADP binds to receptor), cAMP acts as a secondary messenger to move the vesicle and aquaporin to the membrane.
- cAMP causes vesicle to fuse with the membrane which increases permeability for H2O.
- Water enters the cell using the aquaporin (leaves the filtrate).
- More ADH is produced when there is a higher need for water, and less when there is a lower need for water.
