Histology Of Urinary System Flashcards
Bowman’s capsule (tissue slide)
- vascular pole
- urinary pole
- glomerular filtrate–>tubular filtrate–>urine(minor calyx)
What is the pathway of venous drainage of the kidney
1) interlobular vein
2) arcuate vein
3) interlobar vein
- -no segmental vein
4) renal vein
***lymphatic drainage most likely follows the veins
Loop of Henle
- made up of simple squamous epithelium, divided into 4 parts:
- thin descending limb
- thin ascending limb
- thick ascending limb
- cortical thick ascending limb
Filtration of blood (kidney)
- kidneys receive 21% of cardiac output
- each kidney filters 600 mL of blood every minute
- both kidneys filter the entire blood every 5 min
Urination (micturition)
-stretch receptors in bladder send impulses to spinal cord (200-400 mL of urine)
What kind of epithelium forms thick segments of loop of Henle
Simple cuboidal epithelium
Anti-diuretic hormone (ADH)
- makes the DCT, collecting tubule, & collecting duct permeable to water and urea
- stimulates reabsorption of water
- concentrates urine
Medullary rays
- loops of Henle
- collecting ducts
Internal urethral sphincter
- continuous with the middle muscular layer of the bladder near its neck
- involuntary
What is the effect of aldosterone on distal convoluted tubule
- it stimulates Na+/K+ ATPase pump to transport Na+ and Cl- from filtrate in lumen into renal interstitium
- K+ and H+ into lumen
- impermeable to water
Ammonia
Metabolic byproduct of aa metabolism
Mesangial cells
- specialized cells around the glomerulus that keep it free of debris
- provide physical support
- phagocytosis
- maintenance of basement membrane
- contraction of efferent arteriole in response to angiotensin II
Thin ascending limb of loop of Henle
- impermeable to water
- permeable to ions (solutes get reabsorbed)
Juxtamedullary nephrons
- have loop of Henle deep in medulla
- renal corpuscle is near medulla (juxtamedullary) but still in cortex
What 3 hormones act on the distal convoluted tubule
- aldosterone: stimulates reabsoption of Na+
- atrial natriuretic factor: inhibits aldosterone
- parathyroid hormone: stimulates reabsorption of Ca+
Vitamin D synthesis
1) UV converts precursor vit D to vit D3 in skin
2) liver converts vit D3–> 25OH vit D3 (precursor)
3) kidney converts it to 1,25-(OH)2 vit D3 (active form)
Glomerulus
- Capillary tuft that receives its blood supply from an afferent arteriole
- glomerular blood pressure is driving force for water and solutes out of blood and into bowman’s capsule
What happens with decrease in blood pressure
–>decreased glomerular filtration rate (GFR)–> decreased sodium concentration in fluid of DCT–> macula densa –> indirect release of renin
Macula densa
- tightly packed simple columnar epithelium (osmoreceptors)
- tall, narrow cells with centrally-located nucleus
- senses any increase in Na+ and Cl- concentration in the distal tubule of the kidney
- secretes paracrine vasopressor which acts on adjacent afferent arteriole to decrease GFR
- decreases renin release from juxtaglomerular cells of the afferent/efferent arterioles
Pathway of action of renin
- released by juxtaglomerular cells and converts angiotensinogen in blood to angiotensin I
- angiontensin I (blood) travels to lungs and is converted to angiotensin II by ACE
- angiotensin II is a potent vasoconstrictor
- renin also increases aldosterone secretion (increase in Na+ and Cl- reabsorption in DCT)
Components of urinary system
- 2 kidneys
- 2 ureters
- 1 bladder
- 1 urethra
- 2 renal arteries
- 2 renal veins
Thin descending limb of loop of Henle
- reasonable permeability: Na+, Cl-, and other ions
- high permeability: water (water channels) due to concentration gradient
- urea enters lumen of tubule
Renal cortex (tissue slide)
- skip pattern
- cortex= cortical labyrinth (renal corpuscles plus convoluted tubules) + medullary rays (straight part of tubules)
Renal capsule
- made of 2 layers
- outer: dense irregular CT; fibroblasts and collagen fibers
- inner: myofibroblasts
Uric acid
Formed from nucleic acid catabolism
Thick ascending limb of loop of Henle
- pumps Na+ and Cl- from the lumen into renal interstitium eventually to vasa recta
- Na+ and Cl- are responsible for maintenance of concentration gradient in outer medulla
How does urine travel through the ureter
Peristalsis-like muscular contractions
Collecting duct
- simple cuboidal epithelium
- collecting duct carries ultrafiltrate from DCT of nephron to renal papilla
- impermeable to water (normally)
- in response to ADH, collecting ducts become permeable to water
- site of acidification or alkalization of ultrafiltrate
What kind of tissue forms the thin segments of the loop of Henle
Simple squamous epithelium
Creatinine
Formed from creatine phosphate catabolism
What is the pathway of arterial supply of kidneys
1) renal artery
2) segmental artery
3) interlobar artery
4) arcuate artery
5) interlobular artery
6) afferent arteriole
7) glomerulus (capillaries)
8) efferent arteriole
9) vas recta
Renal papilla
Apex of renal pyramid
Minor calyx
- area cribosa at tip of renal papilla empties ultrafiltrate into minor calyx
- called urine in minor calyx
Proximal convoluted tubule
-lies in the cortex and lined by simple cuboidal epithelium w/ brush borders -brush border increases area of absorption
Glomerular basement membrane/basal lamina
- made of endothelial cell (glomerulus) and podocyte basal laminas
- lamina densa: filters by size
- lamina lucida (2): traps (-) charged molecules like albumin
Renal tubule
- portion of the nephron containing tubular fluid
- proximal convoluted tubule, loop of Henle, distal convoluted tubule
Urethra
- crescent-shaped lumen w/ folds
- drains urine out of body from bladder
Glomerular filtration
- 180 liters of filtrate produced each day
- about 1% of filtrate or 2 liters is excreted as urine daily
Layers of the urinary bladder
1) transitional epithelium
2) tunica musclaris (3 layers)
3) adventitia: CT and adipose tissue
Ureter layers
1) transitional epithelium
2) basal lamina
3) lamina propria: dense, irregular fibroelastic CT
4) tunica muscularis
5) adventitia
Juxtaglomerular apparatus
1) mucula densa of distal convoluted tubule
2) justaglomerular cells of efferent arteriole
3) mesangial cells
Ureteric orfices
- ureter openings into bladder
- have valve-like flap which prevents regurgitation of urine from bladder back into ureters
- also have diagonal course through wall (helps prevent back-flow)
External urethral sphincter
- formed by skeletal muscle fibers
- voluntary
Renal corpuscle
- comprised of:
- glomerulus
- Bowman’s capsule
- beginning of the nephron
- initial filtering component
Ureter
- begins as inferior extension of renal pelvis
- ends at the posterior aspect of urinary bladder
- carries urine from kidney to bladder, star-snapped lumen when empty
Parasympathetic innervation during urination
Contraction of detrusor muscle and relaxation of internal urethral sphincter
What is the effect of parathyroid hormone on the distal convoluted tubule
Calcium absorption into the interstitium
What are the functions of the urinary system
1) filter blood
- secrete metabolic waste products
- regulates blood pressure & conserves body fluid
- maintains acid-base balance
2) part of vitamin D synthesis
3) stimulates RBC production via erythropoietin
Cortical nephrons
- all nephrons have renal corpuscle located in cortex
- have loop of Henle in renal medulla near junction with cortex
Vit D stimulates
1) calcium and phosphate absorption in small intestine
2) calcium and phosphate release from bone
Distal convoluted tubule
- portion of kidney nephron between loop of Henle and collecting ducts
- lined with simple cuboidal epithelium, few short microvilli, numerous mitochondria
Transitional epithelium of the urinary bladder
- acts as an osmotic barrier
- large, round, dome-shaped w/ empty bladder (flattened when distended)
- **inferiorly adjacent is lamina propria
Proximal convoluted tubule is sight of reabsorption of:
- Na+/K+ ATPase on basolateral cell membrane
- Na/K pumped into extracellular space
- Cl- follows Na+ (electroneutrality)
- water follows Na+ to maintain osmotic equilibrium
- Ca+, 99% of bicarb
- glucose, small proteins & AA, creatine
Bowman’s capsule
- 2 layers (visceral and parietal); beginning of tubular component of nephron
- v: inner layer, podocytes
- Bowman’s space
- p: outer layer, simple squamous epithelium
- fluids from blood filtered through podocytes resulting in glomerular filtrate
Conscious part of brain (urination)
-allows for relaxation of external urethral sphincter
Cortical thick ascending limb
-drains urine into the distal convoluted tubule
Urethral epithelium
1) transitional epithelium near bladder
2) stratified squamous non-keratinized epithelium along most of urethral length and near external urethral orifice
3) pseudostratified columnar epithelium interspersed throughout its length
Parts of the kidney
- renal capsule
- cortex
- medulla (pyramids + columns)
- renal column
Compare proximal convoluted and distal convoluted tubules
1) nuclei: DCT close to luminal surface and bulge into the surface while PCT nuclei more central
2) PCT has more epithelial cells per cross-section due to smaller size of cells
3) more PCT than DCT, PCT cells are longer than DCT
4) lumen of PCT looks “messier” than that of DCT
5) DCT cells have less cytoplasm
6) DCT has larger lumen than PCT
Proximal convoluted tubule
- simple cuboidal epithelium with nucleus located basally
- a lot of long microvilli on luminal border
- numerous mitochondria
What is the effect of high ADH on the distal convoluted tubule
-water and urea leave the lumen to enter the renal interstitium eventually into blood vessels
Renal sinus
Comprised of adipose tissue +loose (areolar) CT
Urea
Liver converts ammonia to urea, less toxic version
Renal column
Cortical tissue contained within the medulla
