Kidney Histology Flashcards
renal corpuscle
-marks the beginning of the nephron
-encompasses bowman’s capsule and glomerulus
bowman’s capsule
-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
afferent arteriole of bowman’s capsule
ushers unfiltered blood into the glomerulus
efferent arteriole of bowman’s capsule
ushers filtered blood out of the glomerulus
glomerulus
filtration apparatus composed of fenestrated capillaries, glomerular mesangial cells, and podocytes
fenestrated capillaries
-responsible for filtering blood, creating urine, and reabsorbing nutrients
-lined with fenestrated endothelial cells
glomerular mesangial cells
-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
podocytes
-unique visceral epithelial cell type
-provide extensive processes that completely enclose glomerular capillaries
-create barriers of filtration slits and maintain glomerular basement membrane
glomerular filter
-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
proximal convoluted tubules (PCT)
-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
epithelial cells of the PCT
-large
-eosinophilic cytoplasm
-form a simple cuboidal epithelium
features of the PCT cells for reabsorption
-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
loop of henle
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
loop of henle: thin descending limb
-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
loop of henle: thin ascending limb
-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
loop of henle: thick ascending limb
-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
distal convoluted tubules (DCT)
-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
function of DCTs
-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
ureter
-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
collecting duct
-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
macula densa
-abundance of epithelial cells located in the juxtaglomerular apparatus
-responds to NaCl concentrations that are out of the optimal range
juxtaglomerular apparatus (JGA)
-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
JGA components
-macula densa cells
-juxtaglomerular cells (granular cells)
-extraglomerular mesangial cells (lacis cells)
macula densa cells
-“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)
juxtaglomerular cells (granular cells)
-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
extraglomerular cells (lacis cells)
-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
renin and blood pressure homeostasis
-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
JGA and blood pressure control
-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
renin-angiotensin-aldosterone system (RAAS)
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
external collecting system and urothelium
-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
umbrella cells
-most apical layer of cells forming a single layer
-often binucleated
-width can range from 25-250um long
-specialized disk shaped vesicles
urinary bladder
-urothelium is more than 6 cells thick
-thin submucosa
-muscularis: 3rd circular layer present (collectively detrusor)
-superior portion of adventitia is mesothelium
urethra
-3rd layer of muscle called the external urinary sphincter (EUS)
-skeletal muscle
-along its length transitions from urothelium —> pseudostratified columnar —> non-keratinized stratified squamous
chronic kidney disease (CKD)
-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
CKD causes
diabetes, high BP, heart problems or stroke, obesity, family history, tobacco use, and over the age of 60
CKD symptoms
dry and itchy skin, tiredness or weakness, bubbly or foamy pee, puffy eyes, trouble sleeping, loss of appetite, need to pee more often
diabetic nephropathy
-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
nodular sclerosis
kimmelsteil-wilson lesions
hypertension
-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
hypertension pharma treatments
induction of diuresis and vasodilation
diuretics
-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
classes of diuretics
-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
renin inhibitors
-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
nephrotic syndrome
-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
