Histology: Renal

Question 1

What are the main roles of the kidneys in homeostasis?

Answer 1

Water/electrolyte balance maintenance, acid-base balance maintenance, excretion of toxic products such as creatinine and urea, endocrine functions to produce renin (increase BP), EPO (stimulates erythropoiesis) and convert calcidiol to calcitriol (regulates calcium levels)

Question 2

What is the renal papilla?

Answer 2

The pointed, central oriented part of the medullary pyramid; this is surrounded by the minor calyx

Question 3

What are the papillary ducts (Ducts of Bellini)?

Answer 3

These are the collecting ducts that then extend back into the medulla and then merge to form the largest ducts that open into the calyces

Question 4

What histological features characterise the renal cortex?

Answer 4

Contains renal corpuscles, PCT, DCT and medullary rays (collecting ducts)

Question 5

What histological features characterise the renal medulla?

Answer 5

contains the straight thick and thin portions of the loop of Henle, collecting ducts and vasa recta

Question 6

What are the four main branches of the renal artery as it enters the renal hilum?

Answer 6

Segmental branches - there is one posterior branch and 2/3 anterior branches
Interlobar arteries - these run between the medullary pyramids
Arcuate arteries - these run laterally where the renal cortex meets the medulla
Interlobular arteries - these run upwards into the cortical tissue

Question 7

How do the efferent arterioles provide blood supply to the kidney parenchyma?

Answer 7

The efferent arterioles give rise to two secondary capillary plexi:

Vasa recta - these arise from the efferent arterioles of the glomeruli where this system runs straight down into the medulla and then drains into the veins of the corticomedullary junction to supply the renal medulla.

Cortical capillary network - these capillaries arise from the efferent arterioles in the rest of the cortex and allow exchange between the cortex and cortical tubules

Question 8

Describe the blood supply from the vasa recta to the kidney parenchyma

Answer 8

Vasa recta arise from juxtamedullary glomeruli and run straight into the medulla and drain into veins at the corticomedullary junction to supply the medulla and generate a high osmotic pressure for the generation of concentrated urine

Question 9

What is the renal corpuscle?

Answer 9

This consists of the Bowman’s capsule and the glomerulus within it; this is the site of plasma filtration

Question 10

Describe the structure of the Bowman’s capsule (visceral and parietal walls)

Answer 10

The bowman’s capsule consists of two continuous layers of epithelial cells with a urinary space between:

Visceral layer - this consists of the podocyte layer of cells

Parietal wall - this is formed by capsular simple squamous epithelium

Question 11

What makes up the visceral wall of the Bowman’s capsule?

Answer 11

Podocytes

Question 12

What makes up the parietal wall of the Bowman’s capsule?

Answer 12

Simple squamous epithelium

Question 13

What is minimal change nephropathy?

Answer 13

A condition that occurs in children due to the disruption of podocyte architecture which leads to excessive proteinuria and nephrotic syndrome

Question 14

Describe the structure of the glomerulus

Answer 14

The glomerulus is a collection of fenestrated capillary loops that are enclosed by the visceral layer (podocyte layer) of the Bowman’s capsule). The glomerulus is supported by mesangial cells.

Question 15

What type of capillaries are present in the glomerulus?

Answer 15

Fenestrated capillaries

Question 16

What is the role of the mesangial cells in the glomerulus?

Answer 16

They synthesise the connective tissue matrix (mesangium), phagocytose trapped particles on the endothelial side of the filtration barrier, maintains the basement membrane and control glomerular blood flow by contracting or relaxing to make the glomerular capillaries narrowed or wider respectively.

Question 17

What makes up the glomerular filtration barrier?

Answer 17

The podocyte layer (visceral layer of Bowman’s capsule), fenestrated endothelium of the glomerulus and the basement membrane

Question 18

Where does the proximal convoluted tubule originate?

Answer 18

At the urinary pole of the renal corpuscle

Question 19

Describe the histological structure of the proximal convoluted tubule

Answer 19

Lined by simple cuboidal epithelial cells with prominent brush border of microvilli and basolateral interdigitations of the plasma membrane (increase surface area)

Question 20

What is the role/function of the proximal convoluted tubule (PCT)?

Answer 20

• Sodium is reabsorbed via active transport (Na+/K+ ATPase) into the basolateral space between cells and then into the peritubular capillaries
• Reabsorption of water and negatively charged ions – this is driven by the reabsorption of sodium and 70-80% of water, sodium and chloride are reabsorbed in the PCT
• Bicarbonate ions are reabsorbed as H+ ions are secreted (exchange mechanism)
• Glucose and amino acids are reabsorbed completely here by facilitated diffusion (using carrier proteins driven by the co-transport of sodium/Na+)
• Larger proteins and carbohydrates that have managed to enter the filtrate undergo endocytosis into the PCT cells and are then degraded by lysosomal enzymes into amino acids and simple sugars which can then diffuse from the cells.

Question 21

What are the four segments of the loop of Henle?

Answer 21

1) Pars recta (straight portion) - this is the straight portion of the proximal tubule
2) Thin descending limb
3) Thin ascending limb
4) Thick ascending limb

Question 22

What type of epithelia makes up the walls of the thin ascending and descending limbs of the loop of Henle?

Answer 22

Simple squamous epithelia

Question 23

Describe the histological structure of the thick ascending loop of Henle?

Answer 23

This is lined by simple cuboidal epithelia with basolateral interdigitation of the membrane and abundant mitochondria (same as the DCT)

Question 24

What is the function of the loop of Henle?

Answer 24

Acts to increase the osmotic gradient from the cortex to the tip of the renal papilla to increase water loss via the counter-current mechanism

Question 25

Explain the counter-current multiplier mechanism

Answer 25

• Descending limb is permeable to water and urea but less permeable to sodium and chloride water moves into the surrounding tissue down the osmotic gradient and is absorbed by the vasa recta supplying the nephron
• The thin ascending limb is permeable to sodium and chloride but not to water therefore you get NaCl efflux but water cannot follow out of the tubule here due to impermeability
• The thick ascending limb actively transports NaCl out of the tubule whilst limiting diffusion of most other molecules such as water, ions and urea. This generates a high solute concentration in the medullary interstitium and the tubule fluid become hypotonic increased water loss.

Question 26

Describe the histological structure of the distal convoluted tubule

Answer 26

Lined by simple cuboidal epithelium with basolateral interdigitations and abundant mitochondria (same as thick ascending loop of Henle)

Question 27

What’s the difference in the epithelium of the PCT in comparison to the DCT and thick ascending loop of Henle?

Answer 27

All of them have simple cuboidal epithelia with basolateral interdigitations and abdundant mitochondria, but the PCT has extensive brush border microvilli whereas the other two do not have this.

Question 28

What is the function of the distal convoluted tubule?

Answer 28

• Reabsorbs Na+ through coupled secretion (exchange) of H+ or K+ ions into the tubular fluid in the presence of aldosterone balance
• Usually relatively impermeable to water but ADH can increase permeability to permit concentration of urine
• Secretes ammonium ions and some drugs
• Forms part of the juxtaglomerular apparatus

Question 29

Describe the juxtaglomerular apparatus

Answer 29

This apparatus is found at the vascular pole of the renal corpuscle and consists of juxtaglomerular cells, macula dense and extraglomerular mesangial cells (lacis cells) and is important in the control of systemic blood pressure and volume.

Question 30

What is the role of the juxtaglomerular cells in the juxtaglomerular apparatus?

Answer 30

These are modified smooth muscle cells in the wall of the afferent arterioles which can sense changes in blood pressure and secrete renin in response to low detected BP

Question 31

What is the role of the macula densa in the juxtaglomerular apparatus?

Answer 31

This is a region of the distal tubule • that associates with the glomerulus as it loops back into the cortex. The cells of the distal tubule closest to the glomerulus become taller, more densely packed and with more prominent nuclei. The cells of the DCT in this region are thought to be able to detect Na+ concentration changes in the DCT and convey this to the juxtaglomerular cells

Question 32

What is the macula densa?

Answer 32

A region of the distal tubule that associates with the glomerulus as it loops back into the cortex

Question 33

What is the role of the extraglomerular mesangial cells (lacis cells) in the juxtaglomerular apparatus?

Answer 33

These cells support the complex

Question 34

How can you identify the macula densa on histology?

Answer 34

The cells of the distal tubule closest to the glomerulus become taller, more densely packed and with more prominent nuclei

Question 35

Describe the histological structure of the collecting tubules

Answer 35

The collecting ducts are lined by simple columnar cells with distinct lateral plasma membranes due to reduced interdigitations of these membranes with neighbouring cells.

Question 36

What is the function of the collecting tubule?

Answer 36

• Concentrate urine in the presence of ADH
• Regulation of acid-base through secretion of H+ and reabsorption of bicarbonate
• Secretion of ammonium and some drugs
• Maintenance of interstitium solute concentration as it’s permeable to urea, which may diffuse down the gradient in concentrated urine to aid osmotic gradient production.

Question 37

What does the ‘lower urinary tract’ consist of?

Answer 37

Everything below the kidneys; renal calyces, renal pelvis, ureters, bladder, uretha

Question 38

What two factors make the urothelium (transitional epithelium) most suited for it’s function?

Answer 38

The membrane folds (umbrella cells) allow for distension and the presence of tight junctions also creates urine impermeability to allow removal of concentrated urine

Question 39

Outline the four layers of the lower urinary tract wall

Answer 39

1) Mucosa
2) Submucosa (including lamina propria)
3) Muscularis mucosa
4) Adventitia

Question 40

Describe the muscular layer of the lower urinary tract wall

Answer 40

Consists of 2-3 layers of smooth muscle:

1) Innermost longitudinal muscle
2) Circular muscle
3) Outermost longitudinal muscle

Question 41

Does the epithelium of the kidney tubules rest on a basement membrane?

Answer 41

All epithelia rests on a basement membrane

Question 42

When is the outer layer of a wall referred to as a serosa instead of an adventitia?

Answer 42

Serosa is used if the wall is covered by mesothelium, if it is not the outer layer is known as adventitia

Question 43

How does epithelium derive nutrition?

Answer 43

From the underlying connective tissue

Question 44

Where is urothelium/transitional epithelium found?

Answer 44

Kidney calyces, renal pelvis, bladder, urethra (proximal urethra in females and prostatic urethra in males)

Question 45

What two things can lead to thickening of the glomerular capillary walls?

Answer 45

Expansion of the basement membrane or an increase in the mesangial matrix

Question 46

What does a PAS stain highlight?

Answer 46

PAS stains for glycoproteins, which are found in the basement membrane

Question 47

How does the basement membrane play a role in the glomerular filtration barrier?

Answer 47

It is negatively charged and therefore acts to repel negatively charged proteins

Question 48

What is membranous glomerulonephritis?

Answer 48

A condition characterised by thickening of the glomerular capillaries due to autoimmune reaction which leads to glomerular damage which can cause glomerular filtration barrier ‘leakiness’

Question 49

What type of tumour are alanine dye workers more likely to get?

Answer 49

Papillary transitional cell carcinomas