Histology for Pathologist

Question 1

What are the three embryologic kidney progenitors? WHen do they form?

Answer 1

Pronephros (3rd week of gestation)

Mesonephros (4th week of gestation)

Metanephros (5th week of gestation)

Question 2

What does the mesonephros form in men and women?

Answer 2

Men: Epididymis

Women: Epoophoron, paraoophoron, Gartner duct

Question 3

What is blastema?

Answer 3

Metanephric mesenchyme, which becomes the mature kidney parenchyma due to interaction with the mesonephric duct.

Question 4

When do fetal lobations form and regress?

Answer 4

Form at 6-7 weeks, regress starting at 28 weeks (but may persist)

Question 5

Recite the layers of the renal cortex.

Answer 5

Inner (juxtamedullary) and outer (superficial).

“Cortex corticis” is a glomerulus-free area just under the renal capsule.

Question 6

What are medullary rays of Farrein?

Answer 6

Groups of tubules that extend to the cortical surface, dividing the kidney into lobules.

Question 7

What is the normal glomerular basement membrane thickness? What is it composed of?

Answer 7

Around 310-380nm, thicker in men and older patients. Composed of type IV collagen, laminins, and glycosaminoglycans.

Question 8

How many nephrons are in a typical kidney? When do they form?

Answer 8

Usually between 600,000 and 1.2 million. All develop in utero, though maturation continues into childhood.

Question 9

What are ectopic glomeruli?

Answer 9

Glomeruli found usually in the renal sinus which regress in infancy.

Question 10

What is a typical kidney weight? Are they the same size?

Answer 10

Around 140g (men > women).

The left kidney is usually slightly larger.

Question 11

How many pyramids are found in the typical kidney? What separates them?

Answer 11

8-18, separated by the septa of Bertin.

Question 12

Why do Wilm’s tumors usually invade through the renal sinus?

Answer 12

There, the capsule does not enclose the renal parenchyma.

Question 13

What are the normal components of the glomerulus?

Answer 13

Mesangium (mesangial cells)

Capillaries with endothelial cells

Podocytes, parietal and visceral epithelium

Basement membrane

Question 14

How large is the normal glomerulus?

Answer 14

Normally around 200 microns, can be larger in hypertrophy.

Question 15

How can normal age-related global glomerulosclerosis be calculated?

Answer 15

(age/2) - 10 %

Question 16

Describe the appearance and functions of glomerular endothelial cells.

Answer 16

Oval nuclei within the capillary lumina.

Expresses polyanionic glycoproteins (Podocalyxin), has fenestrations (induced by VEGF), and synthesizes NO and endothelin.

Question 17

Describe the appearance and functions of glomerular mesangial cells

Answer 17

PAS/GMS+ structural support cells that also express actin and myosin to confer contractile function. Also reparative.

Question 18

What are the layers of the glomerular basement membrane?

Answer 18

Lamina rara externa

Lamina densa

Lamina rara interna

Question 19

Describe the appearance and functions of podocytes.

Answer 19

Large hobnailed cells. Synthesize GBM, provides filtration via foot processes & filtration slits. WT1+, desmin-.

Question 20

What are the three components of the glomerular filtration barrier? What size of filtration do they confer?

Answer 20

Fenestrated endothelium (70-100nm)

Glomerular basement membrane

Filtration slit (30-40nm)

Question 21

Describe the appearance and functions of parietal epithelial cells.

Answer 21

Hobnailed cells lining the outsides of glomeruli. Synthesizes type IV collagen. Expresses CK8, Pax2, and cadherens.

Question 22

Describe the structure and function of the juxtaglomerular apparatus.

Answer 22

A region in the vascular pole which regulates the RAAS axis. Composed of granular cells especially in the afferent arteriole, and extraglomerular mesangium (Goormaghtigh cells).

Question 23

Describe the structure and function of the macula densa.

Answer 23

Specialized cells in the distal convoluted tubule which detect NaCl concentration to regulate afferent arteriolar flow and regulate renin release.

Question 24

Describe the morphology of proximal tubule epithelium.

Answer 24

Cuboidal to low-columnar cells with eosinophilic granular cytoplasm with round, usually basally-located nuclei. Luminal PAS+ brush border of microvilli.

Question 25

Describe the morphology and function of thin limb loop epithelium.

Answer 25

Flat/simple epithelium with bulging nuclei. Water-permeable in the descending portion, salt-permeable in the ascending portion.

Question 26

Describe the morphology of distal tubular epithelium.

Answer 26

Eosinophilic and cuboidal cells with round, usually apically-located nuclei.

Question 27

Recall the two cells of the collecting duct. Which is more common where?

Answer 27

Principal cells (increases distally) and intercalated cells (decreases distally)

Question 28

Describe the structure and function of principal cells.

Answer 28

Cells with light/clear cytoplasm which express ENaC, a sodium channel. Also sensitive to vasopressin to express aquaporins. Chief role is salt/water exchange.

Question 29

Describe the structure and function of intercalated cells.

Answer 29

Darkly staining cells which regulate acid-base (contain carbonic anhydrase). Alpha cells secrete acid, beta-cells secrete base.

Question 30

What is the normal volume and composition of the interstitium?

Answer 30

Around 5%, but increases with age. More in the medulla. Contains type I/III collagen and fibronectin.

Question 31

Recall the progressive designations of the renal arterial supply.

Answer 31

Segmental

Interlobar

Arcuate

Interlobular

Afferent arteriole

Question 32

What nerves can be found in the kidney?

Answer 32

Adrenergic nerve fibers from the celiac plexus, which run along with arteries.

Question 33

Where are the renal lymphatics located?

Answer 33

Embedded in periarterial connective tissue in the renal cortex. None in the medulla.