2. Structural basis of kidney function Flashcards
(30 cards)
How is fluid lost from the body?
Exhalation
Urine
Sweat
Functions of the kidneys
Production of urine: Filtration of blood plasma Selective reabsorption of contents to be retained Tubular secretion of some components Concentration of urine as necessary
Sensitive to body needs via hormones and nerves
Endocrine function: signals to rest of body (hormones include renin, erythropoietin, 1,25-OH vitamin D)
Appearance of cortex and medulla
Cortex: Granular
Medulla: Striated
What happens to the kidneys if someone goes into shock?
Body will try to reduce blood supply to bowels and kidneys
If someone goes into renal failure because of blood loss: pyramids die 1st as have worst blood supply
Describe filtration in urine production
Blood passing through glomerulus is filtered
Filtrate consists of all components <50 000 molecular weight
How is high pressure maintained in the capillaries of the glomerulus?
Renal artery comes off aorta
Short distance= high pressure
Describe the size of afferent and efferent arterioles. What is the consequence of this?
Afferent arteriole: Big
Efferent arteriole: Small
Creates a pressure gradient, this squeezes the fluid out through the filtration system
3 components that allow filtration in the glomerulus
High SA: many capillaries with fenestrated endothelium
Specialised basal lamina
Filtration slits between foot processes of podocytes: allows passage of ions and molecules <50 000
Composition of fluid entering proximal tubule
Isotonic: exactly the same concentration as the blood (minus the cellular components)
What are the components of the Renal corpuscle?
Bowman’s capsule: collects fluid
Glomerulus consists of capillaries
Podocytes associated with glomerulus
Where does drainage of the renal corpuscle occur?
At urinary pole of corpuscle
Drains to proximal convoluted tubule
Describe reabsorption in urine production
Material to be retained is reabsorbed in proximal convoluted tubule
Includes ions, glucose, amino acids, small proteins, water
Describe the structural features that of the proximal convoluted tubule
Cuboidal epithelium
Sealed with (fairly water-permeable) tight junctions
Many vesicles as reabsorbing and sending things across
High SA to maximise rate of resorption:
Brush border at apical surface
Interdigitations of lateral membrane
Contains aquaporins: membrane protein mediating transcellular water diffusion
High blood supply
Many mitochondria: as requires lots of energy
Function of proximal convoluted tubule
Reabsorption of 70% of glomerular filtrate
Na+ uptake (basolateral Na+/K+ ATPase creates gradient)
Water and anions follow Na+
Glucose uptake by Na+/glucose cotransporter
Amino acids by Na+/amino acid cotransporter
Protein uptake by endocytosis
Describe creation of hyper-osmotic extracellular fluid in urine production
Main function of loop of Henle and vasa recta (blood vessels)
Countercurrent mechanism
Describe the descending thin tubule of the loop of Henle
Sits in hypo-osmotic fluid, so fluid is pulled in
Passive osmotic equilibrium (aquaporins present)
Allows fluid and ions to cross membrane
Simple squamous epithelium
Describe the ascending thick limb of the loop of Henle
Na+ actively pumped out of tubular fluid
Very water-impermeable tight junctions (fluid becoming more concentrated in tubule, don’t want water going back in)
Membranes lack aquaporins: low permeability to water
Results in hypo-osmotic tubular fluid, hyper-osmotic extracellular fluid
Cuboidal epithelium, few microvilli
High energy requirement so many mitochondria
Describe the vaso recta
Blood vessels also arranged in loop
Blood in rapid equilibrium with extracellular fluid
Loop structure stabilises hyper-osmotic [Na+]
Describe Adjustment of ion content of urine in urine production
Principal function of distal convoluted tubule
Controls levels of Na+, K+, H+, NH4+
Describe the distal convoluted tubule
Site of osmotic re-equilibration (controlled by vasopressin)
Adjustment of Na+/K+/H+/NH4+ (controlled by aldosterone)
Cuboidal epithelium, few microvilli
Complex lateral membrane invaginations with Na+/K+ pumps
Numerous large mitochondria
Specialisation at macula densa, part of juxtaglomerular apparatus
Why are more proximal convoluted tubules seen in a slice than distal convoluted tubules?
Distal are shorter in length as it doesn’t have as much work to do
Describe concentration of urine
in production of urine
Occurs at collecting tubule
Movement of water down osmotic gradient into extracellular fluid
Controlled by vasopressin
Describe 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 pituitary hormone vasopressin)
Basolateral membrane has aquaporin-3, not under control
Simple cuboidal epithelium
Cell boundaries don’t interdigitate
Little active pumping so fewer mitochondria
Where does the medullary collecting duct drain?
Drains into minor calyx at papilla of medullary pyramid
