Structural basis of kidney function Flashcards
what is the standard amount of fluid we should have
2 Litres for a 70 kg Man
How can ADH kill you?
- ADH makes you thirsty
- once you have too much ADH, thirst stops so they become overly dehydrated which kills the person
What are the functions of the kidneys?
Production of urine:
- Filtration of blood plasma
- Selective re-absorption of contents to be retained
- Tubular secretion of some components
- Concentration of urine as necessary
-Sensitive to body needs via hormones, nerves
Endocrine function - signals to rest of body (hormones include renin, erythropoietin, 1,25-OH vitamin D):
State some endocrine functions of the kidneys.
Production of erythropoietin
Hydroxylation of 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol by 1 alpha hydroxylase (in other words: production of calcitriol)
Activation of the renin-angiotension system by secreting renin
Describe the filtration of the blood plasma
- Lots of tubules
- outer cortex is very granulated
- medulla is striated structure
- filteration takes place and end up in the major calyces
- comes out of the ureter.
What part of the kidney dies first if someone is going through kidney failure?
- The kidneys are clinically important because it receives a lot of blood supply.
- When someone is going through kidney failure, the amount of blood is reduced to the kidneys and the bowel.
- The part to die first of the kidney is the pyramid as it receives the most minimum amount of blood and the cortex receives the most.
- This can be seen in people’s urine
What causes the granular structure and the striated structure?
- Granular because it is not a regular structure
- in the medulla: have very straight tubules so the medulla looks very different.
What is the renal corpuscle?
Bowman’s capsule
glomerulus consists of capillaries
podocytes associated with glomerulus
Describe filtration and the components filtered?
-Blood passing through glomerulus is filtered,
-Filtrate consists of all components
-at urinary pole of corpuscle
drains to proximal convoluted tubule
Describe what happens to people with uncontrolled hypertension?
- Renal artery comes off the aorta
- very short distance
- high pressure structure
- these arterioles have a lot of pressure
- hypertension: capillaries get damaged
- proteins in the urine
- because filter is damaged
Describe some features of the glomerulus.
The capillaries are fenestrated. There is a specialised basal lamina that filters the blood.
What are the 3 components of the filter?
- High SA, lots of capillaries
- Inner surface of capillaries is fenestrated endothelium, so acts like a sieve.
- Modified basement membrane allows blood to filter.
How many layers of filtaration on the glomerulus. Describe another feature which is used for filtration?
There are 3 layers of filtration on the glomerulus.
Outside of the capillaries, there are podocytes which provide filtration.
Describe some features of the glomerulus.
The capillaries are fenestrated. There is a specialised basal lamina that filters the blood.
what type of fluid leaves after filtaration
ISOTONIC.
State the five stages of urine production.
Ultrafiltration Selective Reabsorption Creation of hyper-osmotic ECF Adjustment of ion concentration in urine Final adjustments of urine concentration
Where does most reabsorption take place?
Proximal convoluted tubule (70% reabsorbed)
State some features of the proximal convoluted tubule and what happens at this structure
Larger diameter than the distal convoluted tubule
Brush border
Abundant mitochondria
CUBOIDAL epithelium sealed with tight junctions
Aquaporins
Sealed with (fairly water-permeable) tight junctions
Membrane area increased to maximise rate of resorption
brush border at apical surface
interdigitations of lateral membrane
Functions
Reabsorption of 70% of glomerular filtrate
Na+ uptake by basolateral Na+ pump
Water and anions follow Na+
Glucose uptake by Na+/glucose co-transporter
Amino acids by Na+/amino acid co-transporter
Protein uptake by endocytosis
What mechanism creates the hyperosmotic extracellular fluid?
Countercurrent mechanism
Describe features of the descending and ascending limbs of the loop of Henle.
Descending Thin, squamous epithelium Permeable to water Ascending Thick, cuboidal epithelium Few microvilli Prominent mitochondria (for active transport of ions) Na+ and Cl- are pumped out into the ECF Water impermeable
State some features of the distal convoluted tubule. Which features are different from the proximal convoluted tubule?
Smaller diameter than the proximal convoluted tubule
Few microvilli
Numerous mitochondria
Complex lateral membrane interdigitations
Adjusts Na+, K+, H+ and NH4+ under the influence of aldosterone
Macula densa cells
What is the role of the collecting duct?
Final adjustment of urine concentration
Which transporters are involved in the movement of water into the cell via the apical membrane and out of the cell via the basolateral membrane?
Aquaporin 2 - apical membrane
Aquaporin 3 - basolateral membrane (not affected by vasopressin)
What type of epithelium do the calyces and the renal pelvis have and what are its properties?
Urothelium - resistant to urine, ability to stretch, low permeability
What does the juxtaglomerular apparatus respond to? What does it do?
Macula Densa - detects NaCl concentration
Juxtaglomerular Cells - detect stretch in afferent arterioles (renal perfusion pressure)
Leads to secretion of renin resulting in angiotensin II production
describe the mechanism of reaborption?
Material to be retained is reabsorbed in proximal convoluted tubule
Includes ions, glucose, amino acids, small proteins, water, etc
Creation of hyper-osmotic extracellular fluid
Main function of loop of Henle and vasa recta (blood vessels)
Countercurrent mechanism
Adjustment of ion content of urine
Principally a function of distal convoluted tubule
Controls amounts of Na+, K+, H+, NH4+
Concentration of urine
Occurs at collecting tubule
Movement of water down osmotic gradient into extracellular fluid
Controlled by vasopressin (=ADH, antidiuretic hormone)
Describe the countercurrent mechanism for the loop of henle?
Loop of henle becomes thin and there are different lengths of this. In the medulla there are different concentrations, there is a difference in its concentrating ability.
The vasa recta are the capillaries
Descending thin tubule
-not many mitochondria
Passive osmotic equilibrium (aquaporins present)
Simple squamous epithelium
Ascending thick limb
Na+ and Cl- actively pumped out of tubular fluid
Very water-impermeable tight junctions
Membranes lack aquaporins - low permeability to water
Results in hypo-osmotic tubular fluid, hyper-osmotic extracellular fluid
Cuboidal epithelium, few microvilli
High energy requirement - prominent mitochondria
Vasa recta
Blood vessels also arranged in loop
Blood in rapid equilibrium with extracellular fluid
Loop structure stabilises hyper-osmotic [Na+]
What happens in the distal convoluted tubule/corticol collecting duct?
Site of osmotic re-equilibration (control by vasopressin)
Adjustment of Na+/K+/H+/NH4+ (control by aldosterone)
Cuboidal epithelium, few microvilli
Complex lateral membrane interdigitations with Na+ pumps
Numerous large mitochondria
Specialisation at macula densa, part of juxtaglomerular apparatus
`what happens in the medullary collecting duct?
Passes through medulla with its hyper-osmotic extracellular fluid
Water moves down osmotic gradient to concentrate urine
Rate of water movement depends on aquaporin-2 in apical membrane
content varied by exo-/endocytosis mechanism
under control from the pituitary hormone vasopressin
Basolateral membrane has aquaporin-3, not under control
Duct has simple cuboidal epithelium
Cell boundaries don’t interdigitate
Little active pumping so fewer mitochondria
Drains into minor calyx at papilla of medullary pyramid
Minor and major calyces and pelvis have urinary epithelium
Describe the juxtaglomerular apparatus
Endocrine specialisation
Secretes renin to control blood pressure via angiotensin
Senses stretch in arteriole wall and [Cl-] in tubule
Cellular components are
macula densa of distal convoluted tubule
juxtaglomerular cells of afferent arteriole
How much distal is there
There are less distal convuluted tubule as it is shorter so you see more proximal than distal
