Functional Histology of The Kidney

Question 1

What are the functions of the urinary system?

Answer 1

Blood homeostasis

Question 2

What role does the urinary system play in blood pressure homeostasis?

Answer 2

Using renin

Question 3

What role does the urinary system play in plasma homeostasis?

Answer 3

Excretion of water, ions and organic waste products into the urine

Question 4

What role does the urinary system play in RBC homeostasis?

Answer 4

Synthesise and secrete erythropoietin

Question 5

Briefly, describe the nephron.

Answer 5

Functional unit of the kidney

Question 6

Describe the function of the nephron.

Answer 6

Where blood is filtered to produce urine while retaining cells and large proteins.

Question 7

What is the function of the renal tubule?

Answer 7

• Adjusts the composition of the ultrafiltrate to recover nutrients, water, etc.
• Regulate plasma composition.

Question 8

What is the function of the proximal convoluted tubule?

Answer 8

Reabsorption from the ultrafiltrate

Question 9

Give examples of molecules reabsorbed by the PCT using active transport.

Answer 9

Na+
Glucose
Amino acids

Question 10

Give examples of molecules reabsorbed by the PCT using pinocytosis.

Answer 10

Macromolecules i.e proteins

Question 11

What happens to molecules reabsorbed by pinocytosis?

Answer 11

Hydrolysed by lysosomes and returned to blood

Question 12

Give examples of molecules reabsorbed by the PCT using passive flux

Answer 12

Water
Chloride ions

Question 13

Describe the adaptations of a cell of the proximal convoluted tubule. Give a brief explanation why it has these adaptations.

Answer 13

• Microvilli - high surface area for reabsorption
• Lytic enzymes on the surface - hydrolyse macromolecules.
• Lysosomes - hydrolyse recycle macromolecules.
• Mitochondria - fuel active transport

Question 14

What are the functions of the Loop of Henle?

Answer 14

• Reabsorption of water and salts from the filtrate
• By passive flux across the epithelium, by osmosis and concentration gradients.

Question 15

Describe the structure of an epithelial cell in the thin Loop of Henle.

Answer 15

Thin, squamous epithelium to allow passive fluxes

Question 16

What are the functions of the distal convoluted tubule and the thick ascending Loop of Henle?

Answer 16

Homeostasis by regulated active transport and exchange of ions

Question 17

Describe the structure of an epithelial cell of the distal convoluted tubule. Give brief explanations why they have these structural features.

Answer 17

• Cuboidal epithelium - reduce passive fluxes and accommodate organelles.
• Few, short, microvilli (unlike the PCT).
• Many basal mitochondria to fuel active transport

Question 18

What are the functions of the collecting duct and the collecting tubule?

Answer 18

• Transport of urine to the ureter.
• Water homeostasis as the passive reabsorption of water, regulated through epithelial permeability.

Question 19

Describe the structure of an epithelial cell of the collecting duct. Give brief explanations why they have these structural features.

Answer 19

• Cuboidal to columnar epithelium - prevent the passive flux of water (and urea, etc.).
• Specialised dense membranes at cell contacts (red) - possibly to prevent passive flux.

Question 20

What does the macula densa do?

Answer 20

• Senses [Na+] in the DCT fluid.
• Signals to juxtaglomerular cells.

Question 21

What do juxtaglomerular cells do?

Answer 21

• Release renin - more so in response to lower [Na+] in the DCT.

Question 22

What does renin do?

Answer 22

• Increases vascular tone and sodium reabsorption

Question 23

What do Lacis cells do?

Answer 23

We don’t know what they do.

Question 24

What are Lacis cells known as?

Answer 24

Extraglomerular mesangial cells

Question 25

Describe the transitional epithelium.

Answer 25

• Specialised stratified epithelium found only in ureters and the bladder.
• Specialised to be impermeable to urine.

Question 26

What structural changes occur to transitional epithelium upon stretching?

Answer 26

• Large apical cells
• Apical cytoplasm

Question 27

There are plaques in specialised (urine-resistant) plasma membrane in the apical cells of the transitional epithelium.
Describe their function in a distended bladder.

Answer 27

Protect apical cells from the toxic urine.

Question 28

There are plaques in specialised (urine-resistant) plasma membrane in the apical cells of the transitional epithelium.
Describe their function in a contracted bladder.

Answer 28

• Plaques are invaginated, forming pits and vesicles in the cell
• Allows the cell surface area to decrease.

Question 29

What is cystitis?

Answer 29

Inflammation of the bladder
- Usually caused by a bladder infection.

Question 30

Why are UTIs (urinary tract infections) quite common?

Answer 30

• Transitional epithelium is highly impermeable
• Leukocytes cannot readily penetrate it.

Question 31

Why are UTIs commoner in females?

Answer 31

• Female urethra is shorter
• More risk of contamination

Question 32

What is the most common advice doctors give regarding UTI prevention?

Answer 32

Increase fluid intake

Question 33

What is the glomerulus the site of?

Answer 33

Ultrafiltration

Question 34

What is ultrafiltration?

Answer 34

→Filtration of blood through a molecular filter

Question 35

What capillaries are there in the glomerulus?

Answer 35

Fenestrated capillaries

Question 36

What happens during nephrotic syndrome?

Answer 36

→Glomerular basement membranes become damaged
→Proteins lost in the urine (proteinuria)

Question 37

What happens to glomeruli during high pressure?

Answer 37

Some glomeruli are destroyed and replaced by masses of hyaline material

Question 38

As you go down the collecting duct what happens to the cells?

Answer 38

→ cells become more impermeable to the water crossing them

Question 39

Where is the juxtaglomerular apparatus found?

Answer 39

→Is found where the DCT loops back to meet arterioles of the same nephron