2. The kidneys and excretion Flashcards
describe what occurs during ultrafiltration
-blood enters from the renal artery into the smaller arterioles in the cortex.
-each arteriole splits into a structure called a glomerulus.
-the arteriole that takes blood into the glomerulus is called the afferent arteriole and the arteriole that takes the filtered blood away is called the efferent arteriole.
-the efferent arteriole is smaller in diameter that the afferent arteriole, and so the blood in the glomerulus is under a high pressure.
-this high pressure forces liquid and smaller molecules in the blood out of the caplillary and into the bowman’s capsule.
-the liquid and small molecules pass through three layers to get into the bowman’s capsule, and enter nephron tubule.
-larger molecules like RBC and proteins can’t pass through and so stay in the blood.
-the liquid and smaller molecules, filtrate, pass along the rest of the nephron and useful substances are reabsorbed along the way.
-eventually, the filtrate follows through the collecting duct and passes out of kidney through the ureter.
describe what occurs during reabsorption
-reabsorption of the useful substances takes place as the filtrate flows along the proximal convoluted tubule, through the loop of henle, and along the distal convoluted tubule.
-useful substances leave the tubules of the nephrons and enter the capillary network thats wrapped around them.
-the epithelium of the wall of the PCT has microvilli to provide a large SA for the reabsorption of useful substances from the filtrate and into the blood.
-useful solutes like glucose, amino acids, and vitimins, some salts, are reabsorbed along the PCT by active transport and facilitated diffusion. some urea is also reabsorbed by diffusion.
-water enters the blood by osmosis because the water potential of the blood is lower than that of the filtrate.
-water is reabsorbed from the loop of henle , distal convoluted tubule, and collecting duct.
- the filtrate that remains is urine.
describe what occurs in the loop of henle- the countercurrent multiplier mechanism
- -near the top of the ascending limb, Na+ and Cl- ions are actively pumped out into the medulla.
-ascending limb is impermeable to water (water stays inside the tubule), this creates a low water potential in the medulla due to high conc. of ions. - -because there is a lower water potential in the medulla than in the descending limb, water moves out of descending limb via osmosis.
-this makes the filtrate more concentrated . the water in the medulla is reabsorbed into the blood via the capillary network. - -near the bottom of the ascending limb, Na+ and Cl- ions diffuse out of the tubule into the medulla, further lowering the water potential in the medulla.
4.- the first three stages massively increases ion conc. in the medulla, lowering water potential. - causes the water to move out of the collecting duct by osmosis.
-water in the medulla is reabsorbed into the blood via a capillary network.
what is the role of the osmoreceptors in the hypothalamus?
monitors the water potential levels in the blood. stimulated by either a low water potential in the blood or a high water potential in the blood.
what is the role of the hypothalamus?
sends nerve impulses to the posterior pituitary gland
what is the role of the posterior pituitary gland?
releases the hormone ADH into the blood, or decreases its levels into blood
what is the role of ADH (what do they do) and what are its effects on the walls of collecting duct?
-ADH molecules bind to the receptors on the plasma membranes of cells in the DCT and the collecting duct.
-protein channels called aquaporins are inserted into the plasma membrane.
-these channels allow water to pass through via osmosis, which makes the walls of the DCT and collecting duct more permeable to water.
-this means that more water is reabsorbed from these tubules into the medulla and then into the blood by osmosis.
A small amount of concentrated urine is produced, which means less water is lost from the body.
osmoregulation- what happens when the blood water content is too low?
-water content of the blood drops and so the water potential drops.
- this is detected by the osmoreceptors in the hypothalamus
-the posterior pituitary gland is stimulated to release more ADH into the blood.
-more ADH means that the walls of the DCT and the collecting duct are more permeable so more water is reabsorbed into the blood by osmosis.
-a small amount of highly concentrated urine is produced and less water is lost from the body.
osmoregulation- what happens when the blood water content is too high?
-The water content of the blood rises and so does its water potential.
-this is detected by the osmoreceptors in the hypothalamus
- the posterior pituitary gland is stimulated to release less ADH into the blood.
-less ADH means that the walls of the DCT and the collecting duct are less permeable and so less water is reabsorbed into the body by osmosis.
-a large amount of dilute urine is produced and more water is lost from the body
what is the glomerular filtration rate and what indicates that the kidneys aren’t working properly?
the rate at which blood is filtered from the glomerulus into the bowman’s capsule.
a lower rate than normal than the normal range indicates that the kidneys aren’t working properly.
how can kidney infections cause kidney failure.
kidney infections cause inflammation of the kidneys, which can damage the cells.
this interferes with the filtering in the bowman’s capsule, or with the reabsorption in other parts of the nephrons.
how can a high blood pressure cause kidney failure.
HBP can damage the glomeruli. the blood in the glomeruli is already under high pressure but the capillaries can be damaged if the blood pressure gets too high.
this means that larger molecules such as proteins can get through the capillary walls and into the urine.
what are the problems arising from kidney failure?
weight loss and vomiting- waste products that the kidneys would normally remove begin to build up in the blood.
parts of the body swelling- fluid starts to accumulate in the tissues because the kidneys can’t remove excess water from the blood.
water retention and brittle bones- the balance of electrolytes in the body(ions) becomes unbalanced. the blood may become too acidic, and an unbalance of phosphate and calcium can lead to brittle bones. salt=water retention.
anaemia- long-term kidney failure.
