L20: Histology Of The Kidney And Urinary Tract

Front 1

What does the urinary system consist of?

Back 1

Two kidneys

Two ureters

One bladder

One urethra

Front 2

What happens to the urine produced in the kidneys?

Back 2

Urine produced in the kidneys isconducted by the ureters to thebladder where it is stored untilvoided via the urethra

Front 3

Where does the blood supply originate from?

Back 3

Blood supply: renal arteries arisefrom the abdominal aorta. One ormore renal veins drain each kidneyto the inferior vena cava.

Front 4

How many times is the total blood volume circulated through the kidneys each day?

Back 4

Total blood volume circulatedthrough the kidneys ~ 300 timeseach day

Front 5

What is the hilum?

Back 5

The hilum: site of entry and exitof the renal blood vessels andureter

Front 6

What are the renal papillae and what surrounds them?

Back 6

Renal papillae: multiple medullarylobes (10-18) called pyramids,surrounded by extension of therenal pelvis called the calyx

Front 7

What is the renal cortex?

Back 7

Renal cortex: fused corticalparts of the lobes, extend downbetween adjacent medullarylobes

Front 8

What surrounds the whole kidney?

Back 8

Whole kidney is invested by atough fibrous capsule; alsosurrounded by a thick layer offat – protection against impacttrauma.

Front 9

What are the Arcuate and interlobular vessels?

Back 9

The arcuates give off branches: the interlobular or cortical radial arteries, which are arranged radially over the basal surface of the pyramids

Front 10

What is a nephron?

Back 10

A nephron is the functional unit of thekidney; consists of renal corpuscle andrenal tubule

Front 11

What does the renal corpuscle, the site of plasma filtration consist of?

Back 11

Bowman’s capsule; distended, blind endof the renal tubule

Glomerulus; packed capillaries thatinvaginate Bowman’s capsule derivefrom the afferent arteriole

Front 12

What happens at the renal tubule?

Back 12

Renal tubule – reabsorption. Extends from Bowman’s capsule to thecollecting duct

Front 13

What shape is the renal tubule?

Back 13

Convoluted in shape,four histological-physiological zones

Front 14

What are the four histological-physiological zones?

Back 14

a: proximal convoluted tubule (PCT)

b: loop of Henle

c: distal convoluted tubule (DCT)

d: collecting tubule

Front 15

What does the renal cortex contain?

Back 15

The renal cortex contains the renalcorpuscles

Front 16

What makes up the vast bulk of parenchyma between corpuscles?

Back 16

Tubules make up the vast bulk of theparenchyma between the corpuscles.

Note differences in shape, andinternal diameter of the tubules.Lots of PCT, less DCT and collectingtubule

Front 17

Which vessel enters the Bowman's capsule?

Back 17

Wide afferent enters BC at thevascular pole, branches to form anetwork of capillaries.

Front 18

Why is the efferent arteriole smaller in diameter?

Back 18

Efferent arteriole is smaller indiameter, so to maintain a pressuregradient that drives filtration ofplasma into Bowman’s space.

Front 19

What happens to the plasma filtrate from the glomerular capillaries before it enters the renal tubule?

Back 19

Plasma filtrate from the glomerularcapillaries passes through 3 layersbefore entering the renal tubule

Front 20

What is the first layer?

Back 20

Capillary endothelium – fenestrated

Front 21

What is the middle layer the filtrate passes through?

Back 21

Glomerular basement membrane –thick (~ 300 nm) as formed by 2basal laminae of podocytes &endothelia. Otherwise normalcomposition (collagen IV, laminin,proteoglycan rich in heparinsulphate)

Front 22

What is the third layer the plasma filtrate passes through?

Back 22

Podocytes – interdigitating pedicels(primary and secondary processes).The secondary pedicels attachdirectly to the glomerular basementmembrane.

Front 23

What are the gaps between the pedicels?

Back 23

Gaps between pedicels are filtrationslits.

Front 24

How can you observe podocytes?

Back 24

Scanning electron microscopy revealsthe podocytes.

Front 25

What do the primary and secondary processes resemble?

Back 25

The primary and secondary processes(pedicels) resemble octopus tentaclesthat completely cover the endothelia.

Front 26

What are the features of the podocytes?

Back 26

In low power (A), note that the cellsare flat, with large bulging nuclei (N).Each podocyte has several long primaryprocesses (P1) that can cover more thanone capillary.

Front 27

What can be seen on the pododytes at greater magnification?

Back 27

At greater magnification (B), thesecondary processes (pedicels) can beseen (P2) as lateral extensions of theprimary processes.

Front 28

What does interdigitation give rise to?

Back 28

Interdigitation of processes gives riseto regularly spaced filtration slits ofuniform width (~ 25 nm).

Front 29

What is the proximal convoluted tubule?

Back 29

Longest part of renal tubule

Front 30

What happens at the PCT?

Back 30

Appx 75% of filtrate is reabsorbed at PCT

Front 31

What type of epithelium line the PCT?

Back 31

Simple tall columnar epithelium with large brush border (BB) of tall microvilli.

Front 32

Where do the capillaries around the PCT arise from?

Back 32

Many capillaries (C) arise from efferent arteriole – receive moleculesreabsorbed by PCT.

Front 33

What are the features of the PCT from the EM?

Back 33

EM reveals microvilli (Mv), many vesicles (V) and lysosomes (L). Capillaries (Cap)under the basal lamella (BM) take the reabsorbed solutes after transport acrossthe epithelial cells

Front 34

Why are there a high number of mitochondria?

Back 34

Note the high number of mitochondria (M), indicative of high ATP requirement

Front 35

In which parts of the Kidney is the loop of henle situated?

Back 35

Arise in cortex, dips to medulla (descendinglimb), then returns to cortex as ascending limb.

Front 36

How thick are the walls of the loop of Henle?

Back 36

Mostly thin walled, but ascending limb becomes thick walled during ascent.

Front 37

what other segment of the nephron is found in the medulla?

Back 37

CT collecting tubule: CD collecting duct alsofound in the medulla. Note blood vessels ofvasa recta (V)

Front 38

Where is the distal convoluted tubule and what happens here?

Back 38

Found within the cortex – resorption of sodium ions from tubule lumen(aldosterone control)

Front 39

What type of epithelium is found at the DCT?

Back 39

Simple cuboidal epithelium, no brush border. Many mitochondria

Front 40

What is the juxtaglomerular apparatus?

Back 40

JGA is a specialisation of the afferent arteriole (AA) and DCT of the samenephron

Front 41

How does the Distal convoluted tubule regulate blood pressure?

Back 41

Regulates blood pressure via renin-angiotensin-aldosterone system.

Front 42

What are the macula densa?

Back 42

Macula Densa (of DCT): an area of large closely packed epithelial lining cellsfacing AA

Front 43

What are the juxtaglomerular cells?

Back 43

JG cells (of AA): specialised smooth muscle cells of the AA wall, contain renin.

Front 44

What are the lacis cells?

Back 44

Lacis cells (L), derived from mesangial cells; Erythropoietin synthesis & secretion but function unclear

Front 45

What are the collecting tubules and Collecting ducts?

Back 45

CT is extension of DCT. Several CT converge to form a CD

Front 46

What is the function of the collecting ducts?

Back 46

Concentrateurine by passive reabsorption of water into medullary interstitium followingosmotic gradient created by countercurrent multiplier system of loops ofHenle. Controlled by ADH.

Front 47

What do the CDs descend into?

Back 47

CDs descend as medullary rays towards renal medulla, progressively mergingto form larger ducts of Bellini that drain urine from tip of renal papilla intorenal pelvis.

Front 48

What is the renal pelvis?

Back 48

Forms the apex of themedullary pyramid;projects into the proximalrenal pelvis or pelvicalcealspace (PCS).

Front 49

What do the ducts of bellini converge for?

Back 49

Ducts of Bellini (DB)converge to drain urine atthe tip of the papilla

Front 50

What are the features of the pelvicalceal space?

Back 50

PCS is the very proximalend of the ureter (U) andis thus lined with typicalurinary transitionalepithelium (E). Smoothmuscle in the walls of thepapilla is continuous withthat of the ureter.

Front 51

What is the ureter?

Back 51

Muscular tube that conduct urinefrom the kidney to the bladder.

Front 52

How does urine move along the ureter?

Back 52

Urine moves by peristaltic actionof uteric wall.

Front 53

What are the 2 layers of smooth muscle that bring about peristalsis?

Back 53

Two layers of smooth muscle:Longitudinal (L); inner layer andreally an elongated spiral.Circular (C); outer layer and alsoa (tight) spiral

Front 54

What lines the lumen of the ureter?

Back 54

Lumen of ureter is lined bytransitional epithelium, with deeplamina propria rich in collagen(LP).

Front 55

What surrounds the ureter?

Back 55

An adventitia surrounds ureter:note the arteries and veins

Front 56

What does the wall of the bladder consist of?

Back 56

Wall of bladder consists of 3smooth muscle layers (as doeslower section of ureter) andabundant elastic fibres

Front 57

What does the adventitia contain?

Back 57

The adventitia containsarteries, veins and lymphatics.

Front 58

What does the bladder look like in the relaxed state/

Back 58

When the bladder isrelaxed (void) the transitionalepithelium is thrown into folds.

Front 59

What is the urinary epithelium also called?

Back 59

Also called transitional epithelium

Front 60

Where is the urinary epithelium found?

Back 60

Only found within the conductingpassages of the urinary system, forwhich it is especially adapted.

Front 61

What type of epithelium is the urinary epithelium?

Back 61

Stratified, number of layers greatestwhen not distended. Squamous onlywhen distended.

Front 62

What are the features of the cytoplasm?

Back 62

Superficial cytoplasm is heavilystained and indistinct (U). Consists ofthick inflexible ‘plaques’ with narrowzones of normal membrane betweenacting as ‘hinge’.

Front 63

What does this lead to?

Back 63

Leads to much folding and formationof deep clefts of fusiform vesicles –renders epithelium impermeable tourine, which is toxic.

Front 64

What does the lamina propria contain?

Back 64

Lamina propria (LP) containscapillaries