lecture 2 : The Structural Basis of Kidney Function Flashcards
what are the main function of the kidney?
what are the major actions of the kidney?
is the production of urine
Filtration of blood plasma –
- Glomerulus
- Selective reabsorption of contents – Proximal
convoluted tubule. - Retention of unwanted contents in urine – Loop of
Henle - Concentration selection or urine – Distal convoluted
tubule.
which part of the kidney has the worst blood supply?
the pyramid
what are the 4 overall stages of Urine Production
- filtration
- reabsorbtion
- creation of hyperosmotic extracellular fluid:
- Adjustment of ion content in urine:
explain the filtration process
- Filtration:
- The glomerulus filters the blood that passes through it
- Filtrate ONLY contains molecules that weigh less than 50,000 Da.
all larger structure are sieved out
- the fluid that leaves is isotonic ( same concentration as the blood)
- the capillary is fenestrated
- there is high pressure to force the fluid out
what are the components of the renal corpuscle?
Components
- Bowman’s capsule
- glomerulus consists of
capillaries
- podocytes associated
with glomerulus
Filtration barrier consists of
- fenestrae (“windows”) in
capillary endothelium
- specialised basal lamina
- filtration slits
explain the reabsorption process?
- Material to be retained is reabsorbed in proximal convoluted tubule
Includes ions, glucose, amino acids, small proteins, water, etc
features of the PCT?
- Cuboidal epithelium
- Sealed with (fairly water-permeable) tight junctions
- contains aquaporins
- brush border
- lots of vesicles
- lots of mitochondria
explain the creation of the hyper osmotic extracellular fluid?
- Main function of loop of Henle and vasa recta (blood vessels)
- Countercurrent mechanism
what 3 parts of the loop of henle are involved in the countercurrent mechanism?
- Descending thin tubule
- Ascending thick limb
- Vasa recta
what happens in the Descending thin tubule
?
Passive osmotic equilibrium (aquaporins present)
Simple squamous epithelium
what happens in the 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
what happens in the vasa recta?
Blood vessels also arranged in loop
Blood in rapid equilibrium with extracellular fluid
Loop structure stabilises hyper-osmotic [Na+]
explain the adjustment of the ion content in the urine?
- Principally a function of distal convoluted tubule
- Controls levels of Na+, K+, H+, NH4+
what are the features of the distal convoluted tubule?
- Site of osmotic re-equilibration (control by vasopressin)
- Adjustment of Na+/K+/H+/NH4+ (control by aldosterone)
- Cuboidal epithelium, few
microvilli - Na+ pumps
- Numerous large mitochondria
- Specialisation at macula densa
how does the control of concentration of urine work?
- Occurs at collecting tubule
- Movement of water down osmotic gradient into extracellular fluid
- Controlled by vasopressin (=ADH, antidiuretic hormone)
