Histology

Question 1

What are the functions of the kidney and urinary tract?

Answer 1

Maintain water and electrolyte homeostasis, body fluid osmolarity and acid-base balance.

Excrete toxic metabolic waste products (mainly urea and creatinine).

Act as an endocrine gland, producing renin and erythropoietin.

Question 2

What is the kidney covered by?

Answer 2

Strong capsule of dense collagen fibres.

Question 3

What is the renal hilum?

Answer 3

Site of entry of renal artery and exit of renal vein and ureter.

Question 4

What is the renal medulla composed of?

Answer 4

Medullary pyramids (8-18 per kidney) with apices pointing toward the hilum (called papillae) ending on the minor calyces.

Question 5

What is considered a kidney lobe?

Answer 5

A medullary pyramid and its associated cortical tissue.

Question 6

What is the kidney capsule made of?

Answer 6

Collagenous fibres that are continuous with the connective tissue lining the renal sinus.

Question 7

What is a nephron?

Answer 7

The basic functional unit of a kidney.

Question 8

What is a nephron composed of?

Answer 8

Renal corpuscle.

Renal tubules.

Question 9

What is the function of the renal corpuscle?

Answer 9

Production and collection of the glomerular filtrate.

Question 10

What is a renal corpuscle composed of?

Answer 10

A tuft of capillaries (the glomerulus) surrounded by a cup of simple squamous epithelium at the blind end of the nephron which the capillaries invaginate into (Bowman’s capsule).

Question 11

What are the 2 cell layers that separate blood from glomerular filtrate in the renal corpuscle?

Answer 11

Capillary endothelium.

Specialised epithelium that lies on top of the glomerular capillaries made up of podocytes.

Question 12

What is the mesangium?

Answer 12

A specialised connective tissue, composed of mesangial cells, which sits at the core of the renal corpuscle.

Question 13

What are the 3 components of the glomerular filter?

Answer 13

Fenestrated endothelium of the capillary wall.

The thick basement membrane (shared by endothelium and podocyte).

Filtration slits between pedicels.

Question 14

What is the function of the proximal convoluted tubule?

Answer 14

Reabsorption of water, proteins, amino acids, carbohydrates and glucose.

• 70% of sodium (active transport) and water (diffusion) is reabsorbed.*
• Almost all glucose and amino acids reabsorbed (by co-transport).*

Question 15

What is the function of the loop of Henle?

Answer 15

Creation of a hyperosmotic environment in the medulla.

Question 16

What is the function of the distal convoluted tubule?

Answer 16

Acid-base and water balance (absorption of water, sodium and bicarbonate; excretion of potassium and hydrogen ions).

Question 17

What is the renal medulla composed of?

Answer 17

Parallel tubules.

Loops of Henle.

Collecting ducts.

Looping vascular network.

Question 18

What is the composition of a loop of Henle?

Answer 18

A thick descending limb.

A thin descending limb which makes a hairpin turn and journeys back out of the medulla as a thin ascending limb.

Thick ascending limb.

Question 19

What are the thick limbs of the loop of Henle lined by?

Answer 19

Simple cuboidal epithelium.

Question 20

What are the thin limbs of the loop of Henle lined by?

Answer 20

Simple squamous epithelium.

Question 21

What are vasa recta?

Answer 21

Loops of thin-walled blood vessels that dip down into the medulla from above and then climb back up to the cortex to supply the loops of Henle.

Question 22

What are the main histological differences between the proximal and distal convoluted tubules?

Answer 22

Distal convoluted tubules (DC) are slightly smaller and have a more obvious luminal margin because they have only sparse apical microvilli.

Question 23

What is the role of aldosterone in the distal convoluted tubule?

Answer 23

Reabsorption of Na+ in the DCT is controlled by the hormone aldosterone which is secreted by the adrenal cortex and results in greater Na+ and water retention and therefore it increases blood pressure.

Question 24

What is the function of the collecting ducts?

Answer 24

Reabsorption of water under the control of ADH.

Question 25

What are the medullary rays?

Answer 25

Bundles of collecting ducts, proximal and distal tubules that run parallel together perpendicular to the surface of the kidney.

Question 26

What is the role of ADH on the collecting duct?

Answer 26

ADH from the posterior pituitary increases the permeability of the collecting duct to water.

Thus in the presence of high ADH (e.g. hot day with low water intake) permeability of the duct is high during passage through the medulla and, because of the high salt content in the surrounding tissue, water passes out of the lumen and a concentrated urine results.

Question 27

What epithelium lines the conducting parts of the urinary tract?

Answer 27

A special epithelium called transitional epithelium (urothelium).

It is stratified and forms an impermeable barrier.

Question 28

What are umbrella cells?

Answer 28

Cells at the luminal surface of the bladder.

These cells face the luminal space of the bladder.

Question 29

What are the cell layers of the bladder?

Answer 29

Epithelium.

Lamina propria.

2-3 layers of smooth muscle.

Question 30

What epithelium lines the ureter?

Answer 30

Transitional epithelium (urothelium) backed by a lamina propria.

Ureter also has an inner longitudinal and outer circular layer of smooth muscle which is surrounded by adventitia/serosa.

Question 31

What epithelium lines the urethra of females?

Answer 31

Initially lined by transitional epithelium which transitions to stratified squamous near its termination.

Question 32

What epithelium lines the prostatic urethra of males?

Answer 32

Transitional epithelium.

Question 33

What epithelium lines the membranous urethra of males?

Answer 33

Transitional epithelium changes to stratified columnar.

Question 34

What epithelium lines the penile urethra of males?

Answer 34

Lined by stratified columnar epithelium which near the tip of the penis becomes stratified squamous.