5.1.2 (c) the Kidney Flashcards
what 2 homeostatic roles do the kidneys play in the body?
excretion
osmoregulation
how are the kidneys involved in excretion?
they filter nitrogenous waste out of the blood
how are the kidneys involved in osmoregulation?
by helping maintain water balance and the pH of the blood
what vessel carries blood into the kidneys?
the renal arteries which branch off of the aorta
which vessel carries blood out of the kidneys?
renal vein which drains into the vena cava
what are the kidneys composed of?
nephrons which are filtering units
what liquid is produced by the kidney tubules?
urine
what does the urine leave the kidney in?
the ureter
what does the ureter lead to?
the bladder
how does urine leave the bladder?
through the urethra and out of the body
what are the 3 main areas of the kidney?
cortex
medulla
pelvis
what happens in the kidney cortex?
site of ultrafiltration
what happens in the kidney medulla?
selective reabsorption and osmoregulation
what happens in the kidney pelvis?
where the urine collects and then passed into the ureter
what are the 5 regions of a nephron?
bowman’s capsule
proximal convoluted tubule
loop of Henle
distal convoluted tubule
collecting duct
what is the bowman’s capsule?
contains the glomerulus which is where ultrafiltration takes place
what is the proximal convoluted tubule?
coiled region following the bowman’s capsule where selective reabsorption begins
what is the loop of Henle?
long loop with an ascending and descending loop where selective reabsorption takes place
what is the distal convoluted tubule?
second coiled region following the loop of Henle where osmoregulation occurs with its wall’s permeability affected by ADH levels
what is the collecting duct?
moves urine down the medulla and into the pelvis as well as more osmoregulation
what are the 3 functions of the nephrons?
ultrafiltration
selective reabsorption
osmoregulation
what supplies the glomerulus with blood?
afferent arteriole
what forces blood out through the capillary walls of the glomerulus?
the greater pressure created by the efferent arteriole
blood moves from a high pressure to a low pressure through fenestrations in the glomerulus
what does the blood leave the glomerulus in?
efferent arteriole
which is narrower and therefore creates greater pressure
what are the three layers between the capillary and Bowman’s capsule?
capillary endothelium
basement membrane
podocytes
what are found in the capillary endothelium to control entry of blood?
fenestrations to prevent large molecules from passing through
what is the basement membrane?
acts as a second sieve by filtering out the plasma contents
what cannot pass through the basement membrane and why?
plasma proteins and red blood cells
they are both too large to fit through…
what effect does the plasma proteins remaining in the blood have on the capillaries?
this creates a low water potential which allows for water to move back into the blood later
what are podocytes?
specialised cells which wrap around the capillaries and form slits to prevent large molecules from passing through
what do podocytes filter out?
any cells, platelets or large plasma proteins which have managed to get through the epithelial and basement membrane
order of 3 part filter
glomerulus endothelium
basement membrane
podocytes
what does the filtrate after the bowman’s capsule contain?
salt
glucose
urea
water
why does selective reabsorption occur?
to bring back necessary substances which have been removed from the blood, back into the blood
where does selective reabsorption occur?
at the proximal convoluted tubule
what is reabsorbed at the proximal convoluted tubule?
sodium chloride
water
glucose
amino acids
how are glucose and amino acids removed from the filtrate at the proximal convoluted tubule?
by active transport
how are sodium ions removed from the filtrate at the proximal convoluted tubule?
pumped out by active transport
how are chloride ions and water removed from the filtrate at the proximal convoluted tubule?
passively down a concentration gradient
what are the adaptations of the proximal convoluted tubule?
- covered with microvilli which increase the SA so more substances can be reabsorbed
- have many mitochondria to provide ATP for active transport
- epithelium lines walls
where do the reabsorbed materials go after being reabsorbed?
they diffuse into extensive capillary network which has a steep concentration gradient between them which is maintained by a constant flow of blood
what does Loop of Henle act as?
acts as a countercurrent multiplier by using energy to produce a concentration gradient that allows for the movement of substances
what happens to Na+ and Cl- ions in the descending loop?
they stay in the filtrate as the walls are impermeable to Na+ and Cl-
makes the filtrate very concentrated
what happens to Na+ and Cl- in the ascending limb?
Na+ and Cl- ions are pumped out into the medulla at the top
Na+ and Cl- ions diffuse into the medulla at the bottom
this makes the water potential in the medulla lower
filtrate leaves very dilute
as the water potential of the medulla is lower what happens at the top of the descending limb?
water moves into the medulla by osmosis from high water potential to low water potential
water is reabsorbed into the blood via capillaries
as the water potential of the medulla is lower what happens to the collecting duct?
water moves out by osmosis and then reabsorbed into the blood via capillaries
what stops water and ions re-entering the Loop of Henle at the ascending loop?
it is impermeable to water
what is the role of the distal convoluted tubule?
site of water balancing
controls the pH levels
what hormone are the walls of the DCT affected by?
ADH
what organelle is found in excess in the DCT and why?
contain a lot of mitochondria to power active transport
what is pumped out of the filtrate at the DCT when salt conc is low?
Na+ ions and Cl- ions are actively pumped back into the blood to restore salt conc
what is the function of the collecting duct?
more osmoregulation
walls effected by ADH
water moves out by diffusion
why cant podocytes underogo mitosis?
they are specialised so remain in G0
therefore formation of spindle fibres and mitosis cannot occur
features of glomerulus
efferent arteriole more narrower than afferent
causes a high hydrostatic pressure
forces filtrate to form in bowman’s capsule
fenestrations in the endothelium are small
prevent large plasma proteins and RBCs from entering
