Kidney Structure and Function

Question 1

What are the primary functions of the kidney?

Answer 1

Regulates fluid & electrolyte balance
Controls blood pressure
Maintains acid-base balance
Excretes waste products
Produces hormones (EPO, renin)
Activates vitamin D

Question 2

How does the kidney regulate blood pressure?

Answer 2

By adjusting plasma volume via sodium and water balance
(↑ volume → ↑ BP; ↓ volume → ↓ BP)

Question 3

. What are the three basic processes in urine formation?

Answer 3

Filtration (in glomerulus)
Reabsorption (nutrients, ions, water)
Secretion (active removal of unwanted substances)

Question 4

What is the functional unit of the kidney?

Answer 4

Nephron – composed of a vascular and a tubular component

Question 5

What is the glomerulus?

Answer 5

A ball of capillaries where filtration of plasma occurs

Question 6

What is Bowman’s capsule?

Answer 6

A cup-shaped structure surrounding the glomerulus that collects the filtrate

Question 7

What is the order of tubular structures in a nephron?

Answer 7

Bowman’s capsule → Proximal tubule → Loop of Henle →
Distal tubule → Collecting duct

Question 8

What are the parts of the Loop of Henle and their roles?

Answer 8

Thin descending limb: water reabsorption
Thin ascending limb: passive Na+ diffusion
Thick ascending limb: active Na+/Cl− transport (impermeable to water)

Question 9

What sets up the osmotic gradient in the kidney?

Answer 9

The loop of Henle and surrounding vasculature (countercurrent mechanism)

Question 10

How much plasma is filtered per day?

Answer 10

~180 L/day (125 mL/min), but most is reabsorbed

Question 11

What is the afferent and efferent arteriole?

Answer 11

Afferent: brings blood into the glomerulus
Efferent: carries unfiltered blood out and supplies the rest of the nephron

Question 12

Why is renal failure life-threatening?

Answer 12

Toxic waste products rapidly accumulate → requires dialysis or transplant

Question 13

What are the three main barriers that filtrate must cross in the glomerulus?

Answer 13

Capillary endothelium (with large pores), basement membrane (with negative charges), and podocyte processes (from the inner layer of Bowman’s capsule).

Question 14

What are podocytes and their role in filtration?

Answer 14

Specialized epithelial cells with interdigitating finger-like processes that form a filtration barrier and regulate what passes into Bowman’s capsule.

Question 15

Why don’t proteins usually get filtered through the glomerulus?

Answer 15

Because of size exclusion and negative charge repulsion from the basement membrane.

Question 16

What is the role of mesangial cells in the glomerulus?

Answer 16

They form a ‘plug’ to prevent filtrate from leaking out the top of the glomerular capsule.

Question 17

What is the normal GFR in humans?

Answer 17

Approximately 125 ml/min.

Question 18

Why is it important to measure GFR?

Answer 18

To assess kidney function and detect declines in filtration that can indicate renal disease.

Question 19

Why can’t GFR be measured directly?

Answer 19

Because the filtration process cannot be directly observed or probed; it must be measured indirectly via clearance.

Question 20

: What is the concept of clearance in renal physiology?

Answer 20

The volume of plasma from which a substance is completely removed per unit time.

Question 21

What properties must a substance have to be used to calculate GFR accurately?

Answer 21

It must be freely filtered, not reabsorbed, and not secreted.

Question 22

What is inulin, and why is it used to measure GFR?

Answer 22

: A polysaccharide from plants that is filtered but neither reabsorbed nor secreted—ideal for GFR calculation.

Question 23

What is creatinine and how is it used clinically?

Answer 23

An endogenous product of muscle metabolism, used to estimate GFR, though it slightly overestimates due to minor secretion.

Question 24

What does a clearance of zero (e.g., for glucose) indicate?

Answer 24

Complete reabsorption of the substance by the kidney.

Question 25

What does a clearance of ~62.5 ml/min for urea indicate?

Answer 25

Partial reabsorption—only about half of urea is cleared.

Question 26

What is the clearance equation for GFR?

Answer 26

A: Clearance = U × V P Clearance= P U×V ​ Where: U U = concentration in urine V V = urine flow rate P P = plasma concentration

Question 27

What dilution equation relates concentrations and volumes before/after filtration?

Answer 27

A: C 1 × V 1 = C 2 × V 2 C 1 ​ ×V 1 ​ =C 2 ​ ×V 2 ​

Question 28

What is the renal plasma flow (RPF)?

Answer 28

Around 625 ml/min, based on clearance of substances like PAH (para-aminohippuric acid).

Question 29

What is the filtration fraction (FF)?

Answer 29

The proportion of plasma filtered through the glomerulus, normally about 20%.

Question 30

What does it mean if the FF increases or decreases significantly?

Answer 30

: An increase may indicate glomerular damage (increased permeability); a decrease suggests reduced filtration efficiency.

Question 31

What mechanisms regulate afferent arteriole diameter?

Answer 31

Myogenic response (stretch), tubuloglomerular feedback (via macula densa), local hormones, and sympathetic nervous input.

Question 32

How does afferent arteriole constriction affect GFR?

Answer 32

Reduces glomerular pressure and lowers GFR.

Question 33

How does afferent arteriole dilation affect GFR?

Answer 33

Increases glomerular pressure and raises GFR.

Question 34

What is the role of the macula densa?

Answer 34

Detects NaCl concentration in distal tubule and signals afferent arteriole to constrict or dilate to maintain GFR.

Question 35

What is the main function of tubular reabsorption in the nephron?

Answer 35

To reclaim solutes and water from the filtrate to prevent their loss in urine.

Question 36

What is the primary energy source driving active tubular reabsorption?

Answer 36

The sodium-potassium ATPase on the basolateral membrane.

Question 37

How many barriers must a substance cross to be reabsorbed from the filtrate into the blood?

Answer 37

Five: apical membrane, cytosol, basolateral membrane, interstitial fluid, and capillary wall.

Question 38

What substances are almost completely reabsorbed by the nephron under normal conditions?

Answer 38

Water, sodium, glucose, and amino acids.

Question 39

Which transport mechanism is primarily responsible for reabsorbing glucose and amino acids?

Answer 39

Sodium-linked secondary active transport.

Question 40

Why is urea partially reabsorbed?

Answer 40

It helps establish the medullary osmotic gradient for water reabsorption.

Question 41

What accounts for 80% of the kidney’s ATP usage?

Answer 41

Sodium reabsorption driven by the sodium-potassium ATPase.

Question 42

Which nephron segment reabsorbs the majority of sodium and water?

Answer 42

The proximal tubule (~75% of sodium reabsorption occurs here and in the distal tubule).

Question 43

What is the role of the loop of Henle in nephron function?

Answer 43

It establishes a vertical osmotic gradient in the medulla for water conservation.

Question 44

Which part of the loop of Henle is impermeable to sodium but permeable to water?

Answer 44

The descending limb.

Question 45

What happens in the thick ascending limb of the loop of Henle?

Answer 45

Active transport of sodium and chloride into the interstitium; impermeable to water.

Question 46

What allows urine to be concentrated in the kidney?

Answer 46

The counter-current multiplication system and the vertical osmotic gradient.

Question 47

What is the maximum osmolarity the human kidney can achieve in urine?

Answer 47

About 1200 mOsm/L.

Question 48

At what plasma glucose concentration does glucose begin to appear in urine (threshold)?

Answer 48

Around 200 mg/dL (2 g/L).

Question 49

Why does glucosuria (glucose in urine) cause increased urination?

Answer 49

Glucose acts as an osmotic agent, pulling water into the filtrate.

Question 50

How does the body regulate phosphate reabsorption?

Answer 50

It's regulated by a threshold system and dietary intake; excess is excreted.

Question 51

Which hormone regulates sodium reabsorption in the distal tubule?

Answer 51

Aldosterone.

Question 52

What are the two main fluid compartments in the body?

Answer 52

Intracellular fluid (2/3) and extracellular fluid (1/3).

Question 53

What is the typical osmolarity of body fluids?

Answer 53

About 300 mOsm/L.

Question 54

What part of the nephron is most sensitive to hormonal control?

Answer 54

The distal tubule and collecting duct.