US Lecture 2 - Structural Basis Of Kidney Function Flashcards
What is the function of the kidney?
Production of urine: filtration of blood plasma, selective reabsorption of contents, tubular secretion of some components, concentration of urine as necessary Endocrine: signals to rest of body (hormone: renin, erythropoietin, 1,25 OH vit D)
How are the kidneys stimulated?
Sensitivity to body needs via hormone, nerves
What is the structure of the kidney? FITB
Which part of the kidney dies first and why?
Papillary - necrosis leads to papillary cells in the urine Cortex of kidney has the most blood supply so the papilla would have the least, hence would be more prone to ischemia, thus necrosis
What is the mechanism for urine production?
Filtration, reabsorption, creation of hyperosmotic extracellular fluid, adjustment of ion content of urine, concentration of urine
What is the structure of the glomerulus? FITB
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What are the components of the renal capsule?
Bowman’s capsule, glomerulus consists of capillaries, podocytes associated with glomerulus
What are the structural features of the proximal convoluted tubule?
Cuboidal epithelium, sealed with tight junctions, aquaporins, lots of mitochondria, membrane area increased to max rate of resorption
What occurs in the filtration stage of urine production?
Blood passes through glomerulus and is filtered - filtrate consists of all components less than 50,000 molecular weight
What occurs in the reabsorption stage of urine production?
Material to be retained is reabsorbed in proximal convoluted tubule - inc. ions, glucose, amino acids, small proteins, water, etc
What occurs in the creation of hyperosmotic ECF stage of urine production?
Main function of loop of Henle and vasa recta, countercurrent mechanism
What occurs in the adjustment of ion content in urine stage of urine production?
Principally a function of distal convoluted tubule, controls amounts of Na, K, H, NH4+
What occurs in the urine concentration stage of urine production?
Occurs at collecting tubule, movement of water down osmotic gradient into ECF, controlled by vasopressin
What occurs in the descending tubule of the loop of Henle?
It maintains a passive osmotic equilibrium, formed of simple squamous cell epithelium
What are the adaptations of the glomerulus that allow to build up pressure and for filtration to only filter out the unnecessary molecules?
Afferent arteriole is larger than the efferent arteriole to generate pressure Modified endothelium and basement membrane have fenestrations present in the walls Podocytes have little feet, all of which form 3 meshes and a fine filter which allows selected molecules through
How is the fluid that enters the Bowman’s Capsule adapted?
It is isotonic, so there is no harm to the cells in the capsule
What happens when hypertension occurs to the kidneys?
Nephropathy occurs as the thin vessels become damaged
Where does the renal corpuscle get its blood supply?
Vascular pole of corpuscle, from afferent arteriole exit to efferent arteriole - so glomerular capillaries are at high pressure NB: NO veins/venules
What does the filtration barrier of the renal corpuscle consist of?
Fenestrae in capillary endothelium, specialised basal lamina, filtration slits between foot processes of podocytes - allows passage of molecules less than 50,000
Where is the filtrate drained from the renal corpuscle?
At urinary pole of corpuscle and drains to proximal convoluted tubule
What are the adaptations of the proximal convoluted tubule for reabsorption?
Many vesicles and mitochondria, as they are very active so high amount of energy is required SA is increased by brush border at apical surface and interdigitations of the lateral membrane
What is the function of the proximal convoluted tubule?
Reasorption of 70% of glomerular filtrate, Na uptake by basolateral Na pumps followed by water/anions Glucose uptake by Na/glucose co-transporter and A.a. by Na/a.a. co-transporter Protein uptake by endocytosis
What are some adaptations of the loop of Henle to help with creating the hyperosmotic environment?
Desc. tubule is very thin, asc. tubule has many mitochondria Vasa recta needed to remove the liquid so that there isn’t a build up and the concentration gradient can be maintained
What occurs in the ascending thick limb of the loop of Henle?
Na+, Cl- actively pumped out of tubular fluid, with impermeable (water) tight junctions, no aquaporins, resulting in hypo-osmotic tubular fluid and hyperosmotic ECF, cuboidal epithelium, few microvilli, prominent mitochondria
What is the Vasa recta?
Blood vessels arranged in a loop, blood in rapid equilibrium with ECF - loop structure stabilises hyperosmotic [Na+]
What is the function of the distal convoluted tubule?
Not many vesicles, invaginations with Na pumps to adjust ion conc (controlled by aldosterone) Site of osmotic reequilibration (control by VP) Cuboidal epithelium, not many microvilli, numerous mitochondria Specialisation at macula densa (part of JGA)
How does the urine concentration phase work at the medullary collecting duct?
Passes through medulla w/hyperosmotic ECF, so water moves down osmotic gradient to concentrate urine, rate depends of AQ-2 in apical membrane AQ-3 is on basolateral membranes, not under control
How is the AQ-2 in apical membrane controlled?
Content is varied by exo/endocytosis mechanism Under control of VP
What is the structure of the medullary collecting duct?
Simple cuboidal epithelium, cell boundaries don’t interdigitate and there is little active pumping so less mitochondria
Where does the urine drain into after the medullary collecting duct?
Into minor calyx at papilla of medullary pyramid Minor/major calyces and pelvis have urinary epithelium
How does the kidney regulate BP?
Kidney knows BP drops, so renin secreted, causing Ang->AngI which then with ACE turns into AngII which causes release of more aldosterone (^ Na/H2O reabsorption) and causes vasoconstriction
What is the function of the juxtaglomerular apparatus?
Endocrine specialisation - secretes renin to control BP via Ang, senses stretch in arteriole wall and [Cl-] in tubule
What are the cellular components of the juxtaglomerular apparatus?
Macula densa of distal convoluted tubule and JG cells of afferent arteriole
