excretion-liver/ kidney Flashcards
(27 cards)
what is excretion
process of removing metabolic wastes
e.g carbon dioxide & nitrogen-based byproducts to maintain metabolism
enables organisms to maintain ph balance & regulate osmotic pressure
describe the gross structure of the mammalian liver
liver lobules : cylinders of hepatocytes arranged in rows & connected at the centre - are connected to:
hepatic vein: takes deoxygenated blood away from the liver & is attached to- hepatic portal vein: contains products of digestion & hepatic artery: supplies oxygenated blood via sinusoid capillaries
and bile duct transports bile to gall bladder for storage
outline the functions of the mammalian liver
~site of gluconeogenesis, glycolysis, glycogenesis
~stores glycogen
~deaminates excess amino acids, forming ammonia & organic acids. acids can be respired or converted into glycogen. ammonia is detoxified by addition of CO2 in ornithine cycle
~detoxifies chemicals e.g converts alcohol to ethanal then acetic acid
describe the gross structure of a mammalian kidney
fibrous capsule: protects kidney
cortex: outer region consists of bowman’s capsules, convoluted tubules, blood vessels.
medulla: inner region consists of collecting ducts, loops of henle, blood vessels
describe the blood vessels associated with a nephron
wide afferent arteriole from renal artery enters renal capsule & forms glomerulus: branched knot of capillaries which combine to form narrow efferent arteriole
efferent arteriole branches to form capillary network that surrounds tubules
describe the sections of a nephron
bowman’s capsule at start of nephron: cup shaped, surrounds glomerulus, inner layer podocytes
proximal convoluted tubule: series of loops surrounded by capillaries, walls made of epithelial cells with microvilli
loop of henle: hairpin loop extends from cortex into medulla
distal convoluted tubule: similar to pct but fewer capillaries
collecting duct: from several nephrons empty into collecting duct, which leads into pelvis of kidney
Describe osmoregulation
-coordinated by the hypothalamus in the brain which contains osmoreceptors that are sensitive to changes in water potential of blood
-adh( antiduretic hormone ) is synthesised in the hypothalamus and then transported to the posterior pituitary gland where it is stored
-collecting duct has receptors specific to adh and water channels (aqua porins ) when water potential decreases more adh is realised this binds to the receptors and cause the aqua porins to be opened increasing the amount of water reabsorbed reducing volume of wee
-hypothalamus also creates feeling of thirst
describe the process of ultrafiltration
occurs in bowman’s capsule
- high hydrostatic pressure in glomerulus forces small molecules ( urea, water, glucose, ions) out of capillary fenestrations against osmotic gradient
- basement membrane acts as filter blood cells, plasma, platelets to large to pass through so remain in capillary
how are the cells of the bowman’s capsule adapted for ultrafiltration
-fenestrations ( small pores) between epithelial cells of capillaries
-fluid can pass between & under folded membrane of podocytes
state what happens during selective reabsorption and where it occurs
useful molecules from glomerular filtrate e.g glucose are reabsorbed into the blood
-occurs in proximal convoluted tubule
how does kidney produce urine
-after selective reabsorption, filtrate passes through loop of henle, which acts as counter current multiplier & then through distal convoluted tubule, where water & mineral ions are reabsorbed
-more water is reabsorbed in collecting duct. remaining fluid (urine) contains only waste materials & water.
what happens in the loop of henle
- active transport of NA+ and cl- out ascending limb
-water potential of interstitial fluid decreases
-osmosis of water out of descending limb( ascending limb is impermeable to water)
-water potential of filtrate decreases going down descending limb: lowest in medullary region highest at top of scending limb
explain the role of the distal convoluted
reabsorption:
a. water via osmosis
b. of ions via active transport permeability of walls is determined by action of hormones
define osmoregulation
control of plasma water potential via negative feedback homeostatic mechanisms
explain the role of the hypothalamus in osmoregulation
- osmosis of water out of osmoreceptors in hypothalamus causes them to shrink
- this triggers hypothalamus to produce more antidiuretic hormone (ADH)
explain the role of the posterior pituitary gland in osmoregulation
stores and secretes the ADH produced by the hypothalamus
explain the role of ADH in osmoregulation
forms hormone-receptor complex on surface membrane of cells in collecting duct
triggers activation of cAMP as secondary messenger
triggers cellular processes that increase reabsorption of water.
urine becomes more concentrated
how does ADH increase reabsorption of water
-make cells lining collecting duct more permeable to water
binds to receptor - activates phosphorylase- vesicles with aquaporins on membrane fuse with cell-surface membrane
-makes cells lining collecting duct more permeable to urea; water potential in interstitial fluid decreases
what can cause kidney failure
-kidney infections cause inflammatory damage= change in glomerular filtration rate
-kidney stones
-uncontrolled diabetes
-high blood pressure damages capillaries of glomeruli = larger molecules pass into urine
describe the effects of kidney failure
-build up of toxic waste products e.g urea causes symptoms such as vomiting
-if kidneys cannot remove excess water from blood, fluid accumulation leads to swelling
-disruption to electrolyte balance can make bones more brittle or increase water retention
name the potential treatments for kidney failure
~renal dialysis: haemodialysis/ peritoneal dialysis (short term solution repeated several times a week so toxic waste products don’t accumulate )
~kidney transplant : ( long-term solution, but difficult to find suitable donor with same blood/ tissue type & patient requires immunosuppressants
describe haemodialysis
removes blood from body & pumps it through a machine
-blood runs countercurrent to dialysis fluid. artificial membrane separates fluid = diffusion gradient enables molecules to move
-add blood thinning agent to avoid clotting outside body
describe peritoneal dialysis
dialysis fluid is put into body cavity. exchange of molecules happens across the body’s own peritoneal membrane
fluid must be drained and replaced
how can urine samples be used to test for pregnancy
monoclonal antibodies bind to the hormone human chorionic gonadotropin (hcg) in the urine of pregnant women
