histology of the kidney

what is the filtrate flow from the kidney to the urethra

kidney → ureter → urinary bladder → urethra

what 5 structures are included in the cortex of the kidney

• renal corpuscles

• proximal tubules

• loop of Henle

• distal tubules

• collecting ducts

what 4 structures are included in the medulla of the kidney

• renal pyramids

• collecting ducts

• thick and thin limbs of loop of Henle

• medullary rays

medulla structures all represent invasion of…

ureteric bud tissue in the metanephric kidney tissue

the loop of Henle can also be referred to as…

loop of the nephron

when filtrate enters the collecting tubule, it is now called…

urine

what are the two parts of the collecting tubule

• connecting tubule

• collecting duct

what and where is the connecting tubule

an initial arching which drains a single nephron; will lead to the collecting duct

what is a collecting duct

drains many nephrons and will extend uninterrupted through both the cortex and the medulla carrying the urine down the renal papilla to the minor calyx

what are the two types of nephrons

• cortical nephron

• juxtamedullary nephron

main funx of the cortical nephron

reabsorption of water and small molecules

main funx of the juxtamedullary nephron

concentrates urine

what are medullary rays

appear as streaks in the cortex running toward the medulla; each ray consists of one collecting duct plus the parallel loops of the many nephrons that empty into that duct

what is a cortical labyrinth

substance between medullary rays; has renal corpuscles and the associated convoluted tubules of the nephrons that empty into the collecting duct of a ray

______________ + _____________ = the renal corpuscle

glomerulus (capillary tuft) + glomerular (Bowman’s) capsule enclosing it

at what pole do arteriole enter and leave at the renal corpuscle

vascular pole

what pole is the proximal convoluted tubule start in the renal corpuscle

urinary/tubular pole

what are the three major layers of Bowman’s capsule

• outer parietal layer

• inner visceral layer

• intervening capsular space

histologically, what is the outer parietal made out of

simple squamous epithelium

histologically, what is the inner visceral layer of Bowman’s capsule made out of

octopus-shaped cells called podocytes (on the glomerulus capillaries)

in order, how is blood filtered from the glomerular capillaries to Bowman’s space

1. through fenestrae in the endothelial cells

2. through the basement membrane

3. through filtration slits between pedicels of the podocytes

what is the capillary tuft of the glomerulus supported by

mesangial cells and ECM = mesangium (green)

what is the mesangium

an extra-cellular matrix of collagen IV, proteoglycans, and glycoproteins that support the capillary loops

where are podocytes found

they surround glomerulus capillaries- they form the simple epithelium of the inner visceral layer

what are podocytes

have primary processes and secondary processes that aid in filtration

what are the primary processes of podocytes known as

arms

what are the secondary processes of podocytes known as, what is their funx

pedicels- interdigitate to give support for capillaries and form filtration slits

filtrations depends on what three things…

• high blood pressure (45 mm hG)

• fenestrated capillaries

• membrane channels- aquaporins

peritubular capillaries receive _________ molecules and give up ______________ molecules

reabsorbed; secreted

describe histologically what the proximal convoluted tubules look like

cuboidal cells that are large and stained pink, are wider than the DCT and have fewer nucelli

how does the PCT cells inc the apical surface area

have densely packed microvilli that form an apical brush border and almost obliterate the tubule lumen → gives them a fuzz-filled appearance in histological sections

CD

collecting ducts

A

thick-walled ascending limb

T

thin-walled descending limb

*

vasa recta capillaries

describe what the distal convoluted tubules look like histologically

have fewer and shorter microvilli, lack brush border, fewer mitochondria- less acidophilic than PCT → lighter pink, higher number of nuclear profiles

brush border or no- is it PCT or DCT

no brush border- DCT

brush border or no- is it PCT or DCT

brush border- PCT

what are the collecting ducts lined by

simple cuboidal epithelium changing to columnar in larger ducts; epithelial cells have round apical surfaces and distinct intercellular boundaries that can be seen w a light microscope

1

renal corpuscle

2

PCT

3

the loop of henle/nephron

4

DCT

5

collecting tubule

6

collecting duct

7

papillary duct

8

minor calyx

C

the cortex

M

medulla

what are the two types of epithelial cells in the collecting ducts

• dark cell- intercalated

• light cell- principal

funx of dark/intercalated cell in the collecting duct

secreted H into lumen and reabsorbs HCO₃

funx of light/principal cells in the collecting duct

reabsorbs Na and secreted K

left arrow

dark/intercalated cell of the collecting duct

right arrow

light cell- principal cell

where is the juxtaglomerular apparatus located

against the afferet arteriole near the vascular pole of each glomerulus

what cells make up the JGA

• macula densa

• juxtaglomerular cells

• extraglomerular mesangial cells

what “zone” is this

inner zone of the renal medulla

P

papillary ducts

MC

minor calyx

AC

area cribrosa of the renal papilla

U

urothelium that lines the minor calyx

from the renal calyces through the urinary bladder, is the structure similar or different

similar

describe histologically how the structure from the renal calyces through the urinary bladder look

• mucosal layer w transitional epithelium (urothelium) and lamina propria

• transitional epithelium stretches

• muscularis mucosae and submucosal layers are absent

the urothelium has abundant ___________ and folds to allow for distension

elastin

describe the structure of the ureter

• hollow tubes of smooth muscle

• urothelium can be from 3-5 layers

what are the layers of the urinary bladder wall

• mucosa of urothelium and lamina propria

• submucosa

• muscularis

• adventitia

what are we looking at here

bladder

U

urothelium

LP

lamina propria

S

submucosa

bracket

muscularis (smooth muscle)

A

adventitia

the urothelium resists stretch and is impermeable to water, solutes and toxic agents, why is this important

prevents interstitial water in the bladder wall from diffusing into the hypertonic urine, and prevents urea and other toxins in urine from poisoning the bladder wall

stretched or unstretched bladder

unstretched- is relaxed

stretched or unstretched bladder

stretched- distended state

what is the urethra of a male lined by

pseudostratified columnar to stratified epithelium, becoming stratified squamous epithelium in the glans near the tip of the pp

what is the urethra of a female lined by

transitional and pseudostratified epithelium, then stratified squamous toward the opening to the exterior- vulva