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)
features of the collecting duct?
- act of ADH is most important
- Rate of water movement depends on aquaporin-2 in apical membrane
- Basolateral membrane has aquaporin-3, not under control
- simple cuboidal epithelium
- Cell boundaries don’t interdigitate
- Little active pumping so fewer mitochondria
what is theJuxtaglomerular apparatus?
- Endocrine specialisation
- Secretes renin to control blood pressure via angiotensin
- Senses stretch in arteriole wall and [Cl-] in tubule
what are the cellular components of the Juxtaglomerular apparatus
?
- macula densa of distal convoluted tubule
- juxtaglomerular cells of afferent arteriole