15.5 Structure & Function of the Mammalian Kidney Flashcards
What 2 homeostatic roles is the kidney responsible for?
EXCRETION (regulation of waste)
OSMOREGULATION (regulation of water)
Blood ⟶ kidneys using what vessel?
Renal artery
Blood from kidney ⟶ inferior vena cava using what vessel?
Renal vein
Urine from kidney ⟶ bladder using what vessel?
Ureter
What are the 3 main parts within the kidneys?
CORTEX
MEDULLA
PELVIS
What happens in the cortex of the kidney?
Area of dense capillary network
providing blood from renal artery
to nephrons
What is the function of the pelvis of the kidney?
Central chamber
where urine collects before entering ureter
What is a nephron?
TUBULES
making up the main FUNCTIONAL STRUCTURES
of the KIDNEY.
What is the Bowman’s capsule?
CUP-SHAPED structure
containing GLOMERULUS.
Site of ULTRAFILTRATION.
What is a glomerulus?
Entangled capillaries found in each Bowman’s capsule
What is the proximal convoluted tubule?
1st twisted section of nephron
after Bowman’s capsule
What occurs in the proximal convoluted tubule?
SELECTIVE REABSORPTION
What processes occur in the proximal convoluted tubule?
- selective reabsorption
- active transport (Na+ actively transported out of pct cell)
- diffusion (Na+ diffusing into vasa recta, glucose diffusing into vasa recta)
- facilitated diffusion (Na+ & Glucose using cotransport protein moving from filtrate into pct cell)
Outline the process of selective reabsorption in the proximal convoluted tubule:
-
Na+ actively transported out of pct cell by sodium pump into tissue fluid
- concentration of ions in pct cell ￬ -
Na+ & glucose in filtrate move into pct cell by facilitated diffusion using cotransport protein
- concentration of glucose in pct cell ￪ - Glucose diffuses from pct cell ⟶ vasa recta/surrounding capillaries
What are the features of the ascending and descending limb of the loop of henle?
DESCENDING: permeable to water molecules only
ASCENDING: permeable to ions only, Na+ Cl-
What is the role of the ascending limb?
to create a water potential gradient
in the tissue fluid
for water to move out of the descending limb by osmosis.
(Done by active transport of Na+ Cl- out, since permeable to ions.)
Outline the steps of osmoregulation which occur in the loop of henle:
DESCENDING LIMB: permeable to H2O ONLY
- H2O moves out of tubule ⟶ tissue fluid ⟶ vasa recta, by osmosis.
- (due to water potential gradient created by ascending limb actively transporting ions out) - Further down, less water present in tubule, ∴ filtrate increasingly concentrated.
ASCENDING LIMB: permeable to IONS ONLY
-
actively transports ions out ⟶ medulla tissue fluid
- creates low water potential in tissue fluid - Further up, less ions present, ∴ filtrate decreasingly concentrated
What is the name of the system in which the 2 limbs of the loop of Henle function?
Countercurrent multiplier system
Why is the loop of Henle described as a “countercurrent multiplier” system?
COUNTERCURRENT - solutions in each limb travel in opposite directions.
MULTIPLIER - concentration of filtrate decreases while tissue fluid increases. Allows production of urine more concentrated than blood.
At what point in the loop of henle is the filtrate most concentrated?
the bend.
(after the bend, ion concentration of filtrate decreases in ascending limb)
Outline the general process which occurs in the distal convoluted tubule/collecting duct in response to ADH:
(Wall permeability varies with ADH concentration)
- More ADH produced by posterior pituitary gland:
- Tubule walls more permeable to water
- More water reabsorbed
- Urine becomes lower in volume + more concentrated
In the loop of Henle, water is moved by osmosis as a result of…
water potential gradient being created
by the active transport of ions by the ascending limb
What occurs in the Bowman’s Capsule?
Ultrafiltration
What occurs in the proximal convoluted tubule?
selective reabsorption
What process occurs in the loop of Henle/distal convoluted tubule/collecting duct?
osmoregulation
What are the 2 functions of the nephron?
ULTRAFILTRATION
SELECTIVE REABSORPTION
What is ULTRAFILTRATION?
process by which
blood plasma FILTERED through BOWMANS CAPSULE
under HIGH PRESSURE
What is SELECTIVE REABSORPTION?
REABSORPTION of selected substances
those which are needed by the body
in KIDNEY tubules
What 2 factors maintain a high pressure in the glomerulus during ultrafiltration?
- Arterial blood is under high pressure
- The lumen of the efferent arteriole is narrower than that of the afferent arteriole, causing buildup of pressure in glomerulus
Outline the process of ultrafiltration in the Bowman’s Capsule:
- Blood enters Bowman’s capsule through AFFERENT arteriole & leaves via efferent.
- afferent lumen > efferent lumen, so blood in glomerulus is under high pressure. - HIGH PRESSURE in glomerulus >> ULTRAFILTRATION
- Some blood solutes forced through FENESTRATIONS in:
- Capillary walls
- Basement membrane
- Podocyte layer
- Forms FILTRATE
What is a podocyte?
CELLS which form a part of the wall of the Bowmans capsule.
Have PROCESSES called PEDICITES, which wrap around glomerular capillaries, only allowing filtering of small molecules.
What are the layers through which ultrafiltration in the Bowman’s capsule occurs in?
- capillary
- basement membrane
- podocyte layer
Which solutes are NOT filtered out of the blood during ultrafiltration?
large plasma proteins (albumin, fibrinogen, globulins)
red blood cells
What does glomerular filtrate consist of?
urea
glucose
amino acids
hormones
nutrients
other small molecules
Should glucose be found in urine?
no
ALL glucose reabsorbed + any excess is stored as glycogen in liver + muscle cells
Which substance(s) is/are NOT selectively reabsorbed in the proximal convoluted tubule?
urea
How are the epithelial cells of the proximal convoluted tubule specialised?
- Contain many MITOCHONDRIA
- ATP, for active transport of Na+
- Has MICROVILLI on apical side only
- increases surface area for reabsorption, which occurs in 1 direction only
What is the function of the renal artery?
supply oxygenated blood to the kidney
What is the function of the renal vein?
carry deoxygenated blood from the kidneys to inferior vena cava
What is the function of the ureter?
carry urine from kidneys to bladder
In which section of the kidney does ultrafiltration & selective reabsorption occur?
renal cortex
