Kidney and Glomerular Filtration

Question 1

What are the functions of the kidney?

Answer 1

• excretion of metabolic waste products and foreign chemicals
• regulation of water and electrolyte balances
• regulation of RBC production
• synthesis of vitamin D3

Question 2

What are the 2 most important parts of the kidney?

Answer 2

cortex and medulla

Question 3

What is the functional unit of the kidney?

Answer 3

the nephron

Question 4

What does each nephron consist of?

Answer 4

1. glomerulus
2. tubule

Question 5

What is the glomerulus formed by?

Answer 5

the invagination of a tuft of capillaries into the dilated blind end of the nephron (Bowman’s capsule)

Question 6

What is Bowman’s capsule?

Answer 6

the cup-like structure formed when blood vessels form and invaginate in the tubule at the bottom of the basement membrane

Question 7

What does the afferent arteriole do?

Answer 7

enter into the glomerulus and bring in blood before breaking off into capillaries that gather to form an efferent arteriole

Question 8

What are the 2 cellular levels that separate the blood from the glomerular filtrate?

Answer 8

1. capillary endothelium
2. specialised epithelium of the capsule

Question 9

What is the capillary endothelium surrounded by?

Answer 9

the glomerular basement membrane (GBM) and specialised cells called podocytes

Question 10

What do podocytes do?

Answer 10

interdigitate to form filtration slits along the capillary walls

Question 11

Where are mesangial cells located?

Answer 11

between the GBM and endothelium

Question 12

What does the glomerulus open into?

Answer 12

the proximal convoluted tubule

Question 13

What are the 7 components of the renal tubule?

Answer 13

• Bowman’s capsule
• proximal tubule
• descending limb of loop of Henle
• thin ascending limb of loop of Henle
• thick ascending limb of loop of Henle
• distal tubule
• collecting tubule

Question 14

What is the juxtaglomerular complex?

Answer 14

where the efferent and afferent arterioles come together with the distal tubule

Question 15

What does the juxtaglomerular complex consist of?

Answer 15

• macula densa cells in the initial portion of the distal tubule
• juxtaglomerular cells in the walls of the arterioles

Question 16

What is the macula densa?

Answer 16

a specialised group of epithelial cells in the distal tubules that come in close contact with the afferent and efferent arterioles

Question 17

What are functions of the juxtaglomerular complex?

Answer 17

• regulation of BP
• glomerular filtration
• sodium reabsorption
• synthesis of renin

Question 18

What type of nephron is more rare and what do they do?

Answer 18

juxtamedullary nephrons that concentrate and dilute urine

Question 19

What percentage of CO is renal blood flow?

Answer 19

~22% (1100 ml/min)

Question 20

What are the 2 capillary beds of the renal circulation?

Answer 20

• glomerular capillaries
• peritubular capillaries

Question 21

What is the GFR?

value

Answer 21

180L/day

Question 22

What are the 4 degrees of filtration and absorption of the renal system?

Answer 22

• filtration only e.g. inulin
• filtration and partial reabsorption e.g. electrolytes
• filtration and complete reabsorption e.g. amino acids, glucose
• filtration and secretion e.g. certain drugs, creatinine

Question 23

What appears in high and low volumes in the urine respectively?

Answer 23

• high = end products of metabolism e.g. urea, creatinine
• low = electrolytes e.g. sodium, chloride, bicarbonate ions

Question 24

What is completely reabsorbed into the blood?

Answer 24

glucose and amino acids

Question 25

How does the body respond to excess sodium?

Answer 25

- increased rate of sodium filtration - reduced rate of sodium reabsorption

Question 26

What is GFR?

Answer 26

the amount of plasma ultrafiltrate formed each minute

Question 27

What is FF?

Answer 27

the fraction of renal plasma flow filtered across the glomerulus

Question 28

What is the formula for FF?

Answer 28

FF = GFR/renal plasma flow

Question 29

What are the 3 determinants of GFR?

Answer 29

- size of the capillary bed (surface area) - permeability of the capillaries - hydrostatic and osmotic pressure gradients across the capillary wall

Question 30

What does the glomerular ultrafiltration coefficient (Kf) describe?

Answer 30

the ease (or difficulty) with which water migrates across the filtration membrane

Question 31

What is the formula for Kf?

Answer 31

Kf = glomerular capillary permeability x filtration surface area

Question 32

What does contraction of mesangial cells cause?

Answer 32

a reduction in the area available for filtration

Question 33

What regulates mesangial contraction?

Answer 33

angiotensin II

Question 34

What is the glomerular capillary permeable to?

Answer 34

- molecules less than 4nm - positively charged non-proteins

Question 35

What is albumin?

Answer 35

a negatively charged plasma protein repelled by the glomerular capillary despite its small size

Question 36

What is glomerulonephritis?

Answer 36

a condition where immune cells attack and damage the glomerulus; the negative charge is lost and albumin can enter the urine

Question 37

Which forces favour filtration?

Answer 37

- glomerular capillary BP - net filtration pressure

Question 38

Which forces oppose filtration?

Answer 38

- plasma-colloid osmotic pressure - Bowman's capsule hydrostatic pressure

Question 39

What must happen for substrates to filter into Bowman's capsule?

Answer 39

the pressure in the capillaries must be higher than in the glomerulus

Question 40

What is hydrostatic and colloid osmotic pressure generated by respectively?

Answer 40

- hydrostatic = pressure of fluids - colloid osmotic = proteins attracting water

Question 41

What reduces filtration surface area?

Answer 41

- ageing - diabetes - renal diseases

Question 42

What do kidney stones cause?

Answer 42

the Bowman capsule pressure to increase and oppose the filtration forces

Question 43

What are the effects of increased sympathetic activity on GFR?

Answer 43

1. ↑ sympathetic activity e.g vasoconstrictor hormones 2. afferent arteriolar constriction 3. ↓ renal blood flow 4. ↓ hydrostatic pressure 5. ↓ GFR

Question 44

What are the effects of increased angiotensin II on GFR?

Answer 44

efferent arteriole constriction which increases GFR

Question 45

How is GFR maintained at low BP?

Answer 45

angiotensin II constricts the efferent arterioles

Question 46

What is tubuloglomerular feedback?

Answer 46

a special feedback mechanism that links changes in the sodium chloride concentration at macula densa with the control of renal arteriolar resistance and autoregulation of GFR

Question 47

How is blood flow increased to the kidney?

Answer 47

the afferent arteriole dilates to decrease resistance

Question 48

What is plasma clearance?

Answer 48

the volume of plasma necessary to supply the amount of substance excreted in the urine per unit of time

Question 49

What is the formula for clearance rate?

Answer 49

clearance rate = (concentration in urine x urine flow)/concentration in plasma

Question 50

What is the formula for urine flow?

Answer 50

urine flow = urine volume/time

Question 51

When is the rate of excretion in urine equal to GFR?

Answer 51

when a substance is freely filtered and is not reabsorbed or secreted by the renal tubules

Question 52

How is GFR measured?

Answer 52

using the excretion of substances that are non-toxic or metabolised by the body e.g. inulin or creatinine

Question 53

How can an approximation of changes in GFR be obtained?

Answer 53

by measuring the plasma creatinine concentration (PCr)

Question 54

What is the relationship between PCr and GFR?

Answer 54

inversely proportional

Question 55

When is a substance secreted into renal tubules?

Answer 55

when its clearance is greater than GFR

Question 56

When is a substance reabsorbed in the renal tubules?

Answer 56

when its clearance is less than GFR