Kidney Histology

Question 1

renal corpuscle

Answer 1

-marks the beginning of the nephron
-encompasses bowman’s capsule and glomerulus

Question 2

bowman’s capsule

Answer 2

-a hollow sphere formed by a simple layer of squamous epithelial parietal cells
-vascular pole = afferent and efferent arterioles
-urinary pole = beginning of proximal convoluted tubule (PCT)
-PCT- tube that ushers filtrate out of the nephron

Question 3

afferent arteriole of bowman’s capsule

Answer 3

ushers unfiltered blood into the glomerulus

Question 4

efferent arteriole of bowman’s capsule

Answer 4

ushers filtered blood out of the glomerulus

Question 5

glomerulus

Answer 5

filtration apparatus composed of fenestrated capillaries, glomerular mesangial cells, and podocytes

Question 6

fenestrated capillaries

Answer 6

-responsible for filtering blood, creating urine, and reabsorbing nutrients
-lined with fenestrated endothelial cells

Question 7

glomerular mesangial cells

Answer 7

-responsible for: turning over the basal lamina, controlling capillary diameter, and secreting vasoactive compounds and cytokines
-mesangial cell type provides structural support to glomerular tuft
-dispersed b/w capillary branches

Question 8

podocytes

Answer 8

-unique visceral epithelial cell type
-provide extensive processes that completely enclose glomerular capillaries
-create barriers of filtration slits and maintain glomerular basement membrane

Question 9

glomerular filter

Answer 9

-3 components: fenestrated epithelium, thick basal lamina, and pedicles (filtration slits between podocytes’ processes)
-functions to stop the passage of proteins 68 kDa or larger

Question 10

proximal convoluted tubules (PCT)

Answer 10

-first element where the filtrate from the renal corpuscle is modified
-longest section of the nephron tubule —> more opportunity to absorb ions and molecules from the lumen
-follows a twisting convoluted path in cortex —> when a PCT enters the medulla, it becomes proximal straight tubule, which is parallel to the other elements

Question 11

epithelial cells of the PCT

Answer 11

-large
-eosinophilic cytoplasm
-form a simple cuboidal epithelium

Question 12

features of the PCT cells for reabsorption

Answer 12

-apical surface: microvilli for a brush border, Na-dependnet cotransporters to import specific molecules from the lumen into epithelial cells (Ex. glucose, amino acids, Na)
-basolateral surface: basolateral invagination, Na-K pumps, channels for molecules absorbed from the PCT lumen to exit the cells
-cytoplasm with densely packed mitochondria

Question 13

loop of henle

Answer 13

entering medulla:
1. thin descending limbs come from the PCT
2. make a 180 degree turn at the bottom
3. becomes thin ascending limb
4. transitions into the thick ascending limb
exits the medulla, back into the cortex

Question 14

loop of henle: thin descending limb

Answer 14

-function: allows water to move out of the tubule into the interstitial space, contains passive transporters like aquaporins, and concentrates filtrates
-histoloy: lined with squamous epithelium and no apical brush border

Question 15

loop of henle: thin ascending limb

Answer 15

-function: reabsorb Na and Cl from filtrate into the interstitial flud, contains passive Na and Cl channels, impermeable to water, and dilutes the filtrate
-histology: lined with simple squamous epithelium and no apical brush border

Question 16

loop of henle: thick ascending limb

Answer 16

-function: actively transports Na, Cl, and K into interstitial fluid, contains active pumps, impermeable to water, further dilutes the filtrate
-histology: lined with simple cuboidal epithelium, no apical brush border, and uniform luminal space

Question 17

distal convoluted tubules (DCT)

Answer 17

-follow the thick ascending limb
-have a coiled path similar to the PCT found mainly in the cortex —> LESS convoluted and SHORTER than PCT
-DCT always occupy less space than PCTs —> DCT cells are smaller and are tall, simple cuboidal epithelium
histology: short blunt apical microvili, elongated mitochondria, densely packed, and basolateral invagination

Question 18

function of DCTs

Answer 18

-fine tuning of Na reabsorption (<5%)
-apical surface: Na-dependent cotransporters and sodium channels to import the Na into the epithelial cells
-basolateral surface: Na-K pumps to transport the Na from the filtrate (urine) into the interstitium
-cytoplasm: densely packed mitochondria

Question 19

ureter

Answer 19

-urothelium: stratified epithelium cells with umbrella cells that are bi- or multi-nucleated cells
-lamina propria: connective tissue
-muscularis: smooth muscle and connective tissue that is arranged in two layers of longitudinal and circular layers with a third circular layer closer to the bladder —> smooth muscle does peristaltic contractions
-adventitia: loose connective tissue providing a structural support to the ureter as well as blood supply

Question 19

collecting duct

Answer 19

-cortex and medulla of the kidney
-several collecting tubules —> one collecting tubule in the cortex —> medullary collecting ducts
-composed of simple cuboidal epithelial cells —> simple columnar epithelial cells
-stained pale with distinct borders around the cells
-site for fluid reabsorption and acid-base balance

Question 20

macula densa

Answer 20

-abundance of epithelial cells located in the juxtaglomerular apparatus
-responds to NaCl concentrations that are out of the optimal range

Question 21

juxtaglomerular apparatus (JGA)

Answer 21

-anatomical unit in nephron located in the vascular pole
-tubuloglomerular feedback system that controls renal blood flow
-controls glomerular filtration rate (GFR) by sensing the amount of fluid in the ascending limb
-tubular control of renin secretion

Question 22

JGA components

Answer 22

-macula densa cells
-juxtaglomerular cells (granular cells)
-extraglomerular mesangial cells (lacis cells)

Question 23

macula densa cells

Answer 23

-“dense spot” in thick ascending limb
-monitor NaCl concentration in filtrate through membrane transporters
-too high —> slow down GFR (signal afferent arteriole to constrict through adenosine)
-too low —> speed up GFR (signal juxtaglomerular cells to release renin —> angiotension —> causes arterioles to constrict and other systemic effects of angiotensin)

Question 24

juxtaglomerular cells (granular cells)

Answer 24

-in tunica media of afferent arteriole at the entrace of the glomeruli
-modified smooth muscle cells
-produce, store, and secrete renin
-sense blood pressure in arteriole through baroreceptors and if increased, secrete renin
-respond to signals from macular densa cells and the sympathetic nervous system —> highly innervated

Question 25

extraglomerular cells (lacis cells)

Answer 25

-within pyramid between afferent and efferent arterioles and macula densa
-modified smooth muscle
-function not fully known —> possibly involved in stimulating renin secretion and removing trapped residue from the glomerular basement membrane

Question 26

renin and blood pressure homeostasis

Answer 26

-renin = enzyme produced by juxtaglomerular cells
-regulates blood pressure via renin-angiotensin-aldosterone system (RAAS)
-release inhibited by atrial natriuretic peptide (ANP), from stretched atria in response to increases in blood pressure

Question 27

JGA and blood pressure control

Answer 27

-produced by juxtaglomerular cells in response to:
1. low blood pressure (hypotension)/reduced extracellular fluid volume —> detected by baroreceptors in the afferent arteriole
2. low NaCl concentration (hyponatremia) —> detected by macula densa cells in the distal convoluted tubule
3. sympathetic nervous system activation —> beta-1 adrenergic receptors on JG cells

Question 28

renin-angiotensin-aldosterone system (RAAS)

Answer 28

renin converts angiotensinogen (produced by the liver) to angiotensin I —> angiotensin I converts to angiotensin II by angiotensin converting enzyme (ACE) —> angiotensin II has widespread effects to raise blood pressure and volume

Question 29

external collecting system and urothelium

Answer 29

-urine is toxic waste
-urothelium has specialized protective epithelial cells that provide chemical resistance and prevent leakage
-urothelium has three regions: umbrella cells, intermediate cells, and basal cell layer
-other tissue layers include the lamina propria, muscularis, and adventitia

Question 30

umbrella cells

Answer 30

-most apical layer of cells forming a single layer
-often binucleated
-width can range from 25-250um long
-specialized disk shaped vesicles

Question 31

urinary bladder

Answer 31

-urothelium is more than 6 cells thick
-thin submucosa
-muscularis: 3rd circular layer present (collectively detrusor)
-superior portion of adventitia is mesothelium

Question 32

urethra

Answer 32

-3rd layer of muscle called the external urinary sphincter (EUS)
-skeletal muscle
-along its length transitions from urothelium —> pseudostratified columnar —> non-keratinized stratified squamous

Question 33

chronic kidney disease (CKD)

Answer 33

-damage to kidney —> can’t perform their functions like filtration
-“chronic” and progressive- occurs slowly over long period of time
-leads to waste buildup in your body

Question 34

CKD causes

Answer 34

diabetes, high BP, heart problems or stroke, obesity, family history, tobacco use, and over the age of 60

Question 35

CKD symptoms

Answer 35

dry and itchy skin, tiredness or weakness, bubbly or foamy pee, puffy eyes, trouble sleeping, loss of appetite, need to pee more often

Question 36

diabetic nephropathy

Answer 36

-diabetes: chronic condition characterized by high blood glucose levels due to insufficient insulin production or use
-blood vessel damage: high blood glucose causes the vessels of the kidney to become narrow and clogged
-nephron damage: thicken and scar causing proteinuria
-nerve damage: bladder cannot signal to the brain when full —> high pressure damages kidneys
-increased risk factors include smoking, not following diabetes plan, high salt diet, inactive, obesity, family history
-treat it by managing diabetes

Question 37

nodular sclerosis

Answer 37

kimmelsteil-wilson lesions

Question 38

hypertension

Answer 38

-condition where pressure within the vessels is consistently high
-hypertension bp: 130/80 mmHg, 140/90 mmHg
-second leading cause of kidney failure in the US
-dangerous cycle of hypertension —> kidney function inhibition —> more hypertension

Question 39

hypertension pharma treatments

Answer 39

induction of diuresis and vasodilation

Question 40

diuretics

Answer 40

-MOA: increase urine production by influencing the kidney to excrete extra water and sodium
-several classes of diuretics exist with varying efficacy and act on various parts of the kidney nephron unit

Question 41

classes of diuretics

Answer 41

-carbonic anhydrase inhibitors: increase bicarbonate, Na, Cl excretion in PCT
-loop diuretics: inhibit the Na/K/2Cl cotransporter and Na reabsorption in the loop of Henle
-thiazide: inhibit Na/Cl cotransporter in DCT and reabsorption of Na
-K sparing: aldosterone receptor antagonists, ENaC blockers, both types act on the collecting duct ENaC channels

Question 42

renin inhibitors

Answer 42

-MOA: bind to active site of renin molecule to prevent it from binding to angiotensinogen and the subsequent conversion of angiotensin I to angiotensin II
-not used as primary pharma treatment

Question 43

nephrotic syndrome

Answer 43

-tetrad of manifestations that indicate disrupted functioning of the kidneys like proteinuria, hypoalbuminemia, hyperlipidemia, and edema
-symptoms: swelling, foamy urine, weight gain, loss of appetite
-complications: severe infections, blood clots, hypertension, difficulty breathing, CKD
-increased permeability of glomeruli due to kidney diseases or systemic diseases