Histology of the Urinary System - Wright

Question 1

Urinary system consists of:

Answer 1

Kidneys, Ureters, Urinary bladder, Urethra

Question 2

Endocrine function of kidney:

Answer 2

Secretion of renin which helps regulate blood pressure
Secretion of erythropoeitin, which stimulates production of RBCs
Di-hydroxylation of vitamin D, makes it more active
Gluconeogenesis

Question 3

Parts of a nephron, in order:

Answer 3

Renal corpuscle (consists of glomerulus, glomerular capsule), proximal tubule, loop of Henle, distal tubule, connecting tubule

Question 4

After nephron, connecting tubules drain into… and then…

Answer 4

connecting tubules -> collecting tubules -> collecting ducts -> minor calyces via renal papillae -> combine to form major calyces -> combine to form renal pelvis -> drains to ureter -> bladder -> urethra.

Question 5

Renal lobe:
Renal Lobule:

Answer 5

Renal Lobe: made up of one pyramid plus the part of the cortex covering that pyramid.
Renal Lobule: made up of a medullary ray (bundle of collecting tubules in cortex) plus all the nephrons draining to the tubules of the medullary ray.

Question 6

Renal circulation:
Renal arteries originate from abdominal aorta, then divides into ____, which divides into ___, which divides into ___, which give off ___, which gives off ____ that supply each renal corpuscle.

Blood then leaves corpuscle in an ____, gives rise to ____, or gives rise to ____.

Answer 6

Renal arteries -> segmental arteries (at hilum) -> interlobar arteries (between renal pyramids) -> arcuate arteries (corticomedullary junction) -> interlobular arteries (extend into cortex) -> afferent arterioles (renal corpuscle)

Afferent arteriole -> efferent arteriole -> peritubular capillary network, or gives rise to vasa recta.

Question 7

Glomerular (Bowman’s) Capsule: parietal / visceral layer

Answer 7

Parietal: simple squamous
Visceral: Podocytes, cover surface of glomerular capillaries.

Question 8

Vascular pole
Tubular / Urinary pole

Answer 8

Vascular pole: Place where afferent / efferent arterioles enter and exit glomerulus.
Tubular/urinary pole: Site where proximal tubule exits corpuscle

Question 9

Podocytes: branch into

Filtration Slits

Answer 9

Podocytes have elongated processes from which smaller processes branch, called pedicels or foot processes.

Filtration Slits: narrow slit between pedicels. Very small.

Question 10

Filtration apparatus in renal corpuscle:

Major Filtration barrier

Answer 10

Fenestrations of capillary endothelium: Block blood cells/platelets
GBM: restrict large proteins
Filtration slit diaphragms: restrict some small proteins

Major Filtration barrier: GBM (glomerular basement membrane). Restricts proteins larger than 70 kDa.

Question 11

Mesangium

Answer 11

Cells and ECM located between glomerular capillaries.
Enclosed inside GBM
Functions: Keep GBM free of debris. Removes trapped residues / proteins.
Endocytose plasma proteins, including immune complexes
Provide structural support for podocytes
Synthesize / secrete cytokines / growth factors in response to injury
Contractile, hypothesized to affect BP

Question 12

Proximal Convoluted Tubule features

Answer 12

Acidophilic cytoplasm (lots of mitochondria)
Long microvilli forming brush border
Basal membrane folding

Question 13

Proximal Convoluted Tubule Function

Answer 13

Reabsorption of water, electrolytes, glucose, AAs, vitamins
Secretion of organic anions and cations, H+ and NH4+
Hydroxylation of Vitamin D***

Question 14

Tubular Pole -> Loop of Henle

What does loop of Henle consist of?

Answer 14

Tubular Pole -> PCT -> Proximal straight tubule (enters medulla) -> loop of Henle

Loop of Henle consists of thin descending limb -> thin ascending limb -> thick ascending limb

Thin limbs: reabsorb Na+ and Cl-
Thick ascending limb: reabsorb various electrolytes.

Question 15

Distal convoluted tubule

Macula Densa location

Resorption regulated by…

Answer 15

Thick ascending limb of loop of Henle transitions to distal tubule. Straight part of distal tubule passes between afferent / efferent arterioles of same nephron. This is where MACULA DENSA forms, then continues as the distal convoluted tubule.

cells of distal tubule = cuboidal.

Resorption of Na+ regulated by hormone aldosterone

Question 16

Juxtaglomerular apparatus:
3 structures found outside of renal corpuscle

Function of each

Answer 16

Macula Densa function: Monitor NaCl concentration in distal tubule, decrease in NaCl increases blood flow in afferent arteriole and increases renin secretion.

Juxtaglomerular cells function: secrete renin (protease that converts angiotensinogen into angiotensin I)

Lacis Cells (extraglomerular mesangial cells): Same function as intraglomerular mesangial cells. Same as mesangial cells, just on outside.

Function of all: autoregulation of GFR, regulation of BP.

Question 17

Feedback loop: What happens when elevated arterial pressure occurs?

Answer 17

Elevated arterial pressure -> increased Glomerullar capillary BP -> increased GFR.

Increased GFR -> increased Na Cl in thick ascending limb, monitored by Macula Densa

Macula Densa release ATP, adenosine, vasoactive compounds -> lowers glomerular pressure / decreases GFR

Decreased GFR turns off release of vasoconstrictors from macula densa.

Question 18

Feedback loop: What happens when decreased arterial pressure occurs?

Answer 18

Decreased arterial pressure -> increased autonomic stimulation of JG (juxtaglomerular) cells due to baroreceptor function

JG cells -> release renin -> angiotensinogen -> angiotensin I

ACE in lung capillaries cleaves angiotensin I -> angiotensin II (vasoconstrictor) -> secretion of aldosterone by suprarenal gland. -> Na+ and H2O reabsorption in distal convoluted / connecting tubules. raises blood volume, thus raising BP.

Increase of BP turns off secretion of renin by JG cells.

Question 19

2 cells of Collecting ducts

Answer 19

Principal cells: respond to antidiuretic hormone (ADH): stimulates movement of water from urine to interstitium, reducing urine volume but increasing concentration

Intercalated cells: maintain acid-base balance by secreting either H+ ions or HCO3 ions

Question 20

Ureter

Urothelium:

Answer 20

Ureter: looks like esophagus, but has urothelium, no muscular mucosa, no submucosa, no muscula externa. Only muscle mixed with CT and adventitia around outside.

Ureter walls lined with this.

umbrella cells: surface cells of relaxed urothelium look like umbrellas
Uroplakins: Outer phospholipid layer of membrane of umbrella cells contain lipid rafts with proteins called this.

Question 21

Urinary Bladder:

Answer 21

Walls lined by urothelium
Muscularis composed of 3 muscular layers forming detrusor muscle, contracts to empty bladder.

Question 22

Urethra in males: 3 parts:

Answer 22

Prostatic urethra
Membranous urethra: forms external sphincter
Spongy/penile urethra