US Lecture 2 - Structural Basis Of Kidney Function

Question 1

What is the function of the kidney?

Answer 1

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)

Question 2

How are the kidneys stimulated?

Answer 2

Sensitivity to body needs via hormone, nerves

Question 3

What is the structure of the kidney? FITB

Answer 3

Question 4

Which part of the kidney dies first and why?

Answer 4

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

Question 5

What is the mechanism for urine production?

Answer 5

Filtration, reabsorption, creation of hyperosmotic extracellular fluid, adjustment of ion content of urine, concentration of urine

Question 6

What is the structure of the glomerulus? FITB

Answer 6

X

Question 7

What are the components of the renal capsule?

Answer 7

Bowman’s capsule, glomerulus consists of capillaries, podocytes associated with glomerulus

Question 8

What are the structural features of the proximal convoluted tubule?

Answer 8

Cuboidal epithelium, sealed with tight junctions, aquaporins, lots of mitochondria, membrane area increased to max rate of resorption

Question 9

What occurs in the filtration stage of urine production?

Answer 9

Blood passes through glomerulus and is filtered - filtrate consists of all components less than 50,000 molecular weight

Question 10

What occurs in the reabsorption stage of urine production?

Answer 10

Material to be retained is reabsorbed in proximal convoluted tubule - inc. ions, glucose, amino acids, small proteins, water, etc

Question 11

What occurs in the creation of hyperosmotic ECF stage of urine production?

Answer 11

Main function of loop of Henle and vasa recta, countercurrent mechanism

Question 12

What occurs in the adjustment of ion content in urine stage of urine production?

Answer 12

Principally a function of distal convoluted tubule, controls amounts of Na, K, H, NH4+

Question 13

What occurs in the urine concentration stage of urine production?

Answer 13

Occurs at collecting tubule, movement of water down osmotic gradient into ECF, controlled by vasopressin

Question 14

What occurs in the descending tubule of the loop of Henle?

Answer 14

It maintains a passive osmotic equilibrium, formed of simple squamous cell epithelium

Question 15

What are the adaptations of the glomerulus that allow to build up pressure and for filtration to only filter out the unnecessary molecules?

Answer 15

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

Question 16

How is the fluid that enters the Bowman’s Capsule adapted?

Answer 16

It is isotonic, so there is no harm to the cells in the capsule

Question 17

What happens when hypertension occurs to the kidneys?

Answer 17

Nephropathy occurs as the thin vessels become damaged

Question 18

Where does the renal corpuscle get its blood supply?

Answer 18

Vascular pole of corpuscle, from afferent arteriole exit to efferent arteriole - so glomerular capillaries are at high pressure NB: NO veins/venules

Question 19

What does the filtration barrier of the renal corpuscle consist of?

Answer 19

Fenestrae in capillary endothelium, specialised basal lamina, filtration slits between foot processes of podocytes - allows passage of molecules less than 50,000

Question 20

Where is the filtrate drained from the renal corpuscle?

Answer 20

At urinary pole of corpuscle and drains to proximal convoluted tubule

Question 21

What are the adaptations of the proximal convoluted tubule for reabsorption?

Answer 21

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

Question 22

What is the function of the proximal convoluted tubule?

Answer 22

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

Question 23

What are some adaptations of the loop of Henle to help with creating the hyperosmotic environment?

Answer 23

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

Question 24

What occurs in the ascending thick limb of the loop of Henle?

Answer 24

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

Question 25

What is the Vasa recta?

Answer 25

Blood vessels arranged in a loop, blood in rapid equilibrium with ECF - loop structure stabilises hyperosmotic [Na+]

Question 26

What is the function of the distal convoluted tubule?

Answer 26

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)

Question 27

How does the urine concentration phase work at the medullary collecting duct?

Answer 27

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

Question 28

How is the AQ-2 in apical membrane controlled?

Answer 28

Content is varied by exo/endocytosis mechanism Under control of VP

Question 29

What is the structure of the medullary collecting duct?

Answer 29

Simple cuboidal epithelium, cell boundaries don’t interdigitate and there is little active pumping so less mitochondria

Question 30

Where does the urine drain into after the medullary collecting duct?

Answer 30

Into minor calyx at papilla of medullary pyramid Minor/major calyces and pelvis have urinary epithelium

Question 31

How does the kidney regulate BP?

Answer 31

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

Question 32

What is the function of the juxtaglomerular apparatus?

Answer 32

Endocrine specialisation - secretes renin to control BP via Ang, senses stretch in arteriole wall and [Cl-] in tubule

Question 33

What are the cellular components of the juxtaglomerular apparatus?

Answer 33

Macula densa of distal convoluted tubule and JG cells of afferent arteriole