genitourinary

Question 1

• What are the main functions of the kidney?

Answer 1

Excretion of metabolic products such as urea, uric acid, creatinine

Excretion of foreign substances

Homeostasis of bodily fluids, electrolytes and acid-base balance

Regulates blood pressure

Secretes hormones such as erythropoeitin and renin

Question 2

• Where does the urine once formed, travel through in the kidney?

Answer 2

Minor calyx to the Major calyx and then through the ureter

Question 3

• What are the functions of the peritubular capillaries?

Answer 3

Provide oxygen and nutrients to the nephron to allow them to perform their functions

Help in reabsorption of different substances along the nephron and then take it away to the circulatory system

Help in secretion of different substances into the tubular fluid

Question 4

• What is the function of the detrusor muscle?

- What does stretching of the trigone to its limit lead to?

Answer 4

Detrusor muscle - Contracts to build pressure in the urinary bladder to support urination

Signals sent to the brain about the need for urination

Question 5

• Is it the internal or external sphincter that gives involuntary control to prevent urination?

Answer 5

Internal sphincter - must be relaxed for urination to proceed

External sphincter gives voluntary control to prevent urination

Question 6

• What are the 2 different cell type classes in the distal convoluted tubule and the collecting duct and describe their mitochondria density?

Answer 6

Principal cells - Low density of mitochondria, the main Na+ reabsorbing cells and the site of action of aldosterone K+ sparing diuretics

Intercalated cells - High density of mitochondria, regulation of acid-base homeostasis

Question 7

• What are the anatomical differences between the juxtamedullary and superficial nephrons?

Answer 7

The glomerulus of the superficial nephron is in the upper cortex, whereas the juxtamedullary nephron has its glomerulus closer to the medullary border

The Loop of Henle in the superficial nephron only extends to the outer medulla, whereas the juxtamedullary nephron has its one extending into the inner medulla

Question 8

• Why does the cortex have a granular appearance, whereas the medulla has a striated appearance?

Answer 8

Loop of Henle extending through the medulla gives it its striated appearance

Question 9

• What are the main functions of this juxtaglomerular apparatus?
• What forms the juxtaglomerular apparatus?

Answer 9

GFR regulation through tubular-glomerular feedback mechanism
Renin secretion for regulating blood pressure

macula densa on distal convoluted tubule
juxtaglomerular cells
extraglomerular mesangial cells

Question 10

• What are the 4 main renal proccesses?

Answer 10

Glomerular filtration

Reabsorption

Secretion

Excretion

Question 11

• Describe the permeability of the filtration barrier

Answer 11

Highly permeable to fluids and small solutes

Impermeable to cells and proteins

Question 12

• What is the name of the spaces between capillary endothelium and how big are they?
• What substances can pass through these spaces?

Answer 12

Fenestrae
70nm in diameter

Water, ions and small proteins

Question 13

• What substances can pass through the slit diaphragm of the glomerular basement membrane?
• What are podocytes?

Answer 13

Water and small solutes only

Highly specialised cells of the kidney glomerulus that wrap around capillaries and that neighbour cells of the Bowman's capsule

Question 14

• How do you calculate the net ultrafiltration pressure?

Answer 14

Puf = HPgc - HPbw - πgc

Puf - Net ultrafiltration pressure

HPgc - hydrostatic pressure in glomerular capillaries

HPbw - hydrostatic presure in bowman's capsule

πgc - Oncotic pressure of plasma proteins in glomerular capillaries

Question 15

• What is meant by the glomerular filtration rate and how do you calculate it?

Answer 15

Amount of fluid filtered from the glomeruli into the Bowman’s capsule per unit time (ml/min)

GFR = Puf x Kf

Kf - ultrafiltration coefficient (membrane and surface area available for filtration

Question 16

• Describe the myogenic mechanism used to regulate the GFR when arterial pressure is high

Answer 16

Arterial pressure increases, so Afferent arteriole stretches

Ateriole contracts

Vessel resistance rises

Blood flow reduces

GFR stays the same

Question 17

• Describe the tubulo-glomerular feedback mechanism used to regulate the GFR (if increase, converse for decrease)

Answer 17

Increase in GFR

Increased NaCl in Loop of Henle

Change detected by macula densa

Increased ATP and adenosine discharged

Afferent arteriole constricts

GFR stabilises

Question 18

• What is meant by renal clearance?

Answer 18

Number of litres of plasma that are completely cleared of the substance per unit time

Therefore it is only concerned with the excretory role of the kidneys

Question 19

• How would you calculate renal clearance?

Answer 19

C x P = U x V therefore C = (U x V)/P

C = Renal Clearance

U = Concentration of substance in urine

V - Rate of urine production

P = Concentration of substance in plasma

Question 20

• If a substance is only filtered in the kidneys and not reabsorbed or secreted, then what value is the GFR the same as?

Answer 20

Renal clearance

Question 21

• Give an example of a molecule that is only filtered and so it follows this principle?
• Since inulin is not found in mammals, what must be done?

Answer 21

Inulin

Transfuse it

It is a plant polysaccharide so we do not have the enzymese to diffuse it, meaning it cannot be taken orally

Question 22

• How can creatinine be used to assess renal function?

- Why is creatinine not the ideal molecule like inulin and why is it still commonly used despite this?

Answer 22

If renal function is stable, the creatinine amount in urine is stable
Low creatinine clearance or high plasma creatinine may indicate renal failure

It is secreted in small amounts into the nephron
However, the process for estimating creatinine in the blood and urine can account for that to allow for GFR calculations

Question 23

• What is the renal plasma flow?

Answer 23

Volume of plasma that reaches the kidney (afferent arteriole) per unit time

If the total amount of a molecule entering the kidney equals amount excreted, then the renal clearance of this molecule is the same as the renal plasma flow

Question 24

• What molecule is therefore used to measure the renal plasma flow?
• What is meant if a substance is freely filtered?

Answer 24

Para aminohippurate - all of it is removed from the plasma passing through the kidney through filtration and secretion

Means they can be found in the ultrafiltrate and plasma at same concentration

Question 25

- What is meant by the filtration fraction and how is this calculated?

Answer 25

Ratio of amount of plasma filtered, and which arrives via the afferent arteriole is defined by Filtration Fraction FF = GFR/RPF

Question 26

- What is the difference betwen primary and secondary active transport? - Is endocytosis a primary or secondary active transport mechanism?

Answer 26

Primary - Uses ATP directly to transport molecules in and out of the cell Secondary - Movement of one solute along its electrochemical gradient provides energy for the other solute to move against its own electrochemical gradient Primary - small proteins are reabsorbed in the PCT using an ATP molecule

Question 27

- Explain how the Na+Glucose symporter works | - Explain how the Na+/H+ antiporter works

Answer 27

Na+ moves down its electrochemical gradient into the cell This provides the energy to transport Glucose against its electrochemical gradient into the cell Na+ moves down its electrochemical gradient into the cell This provides energy to actively transport H+ against its electrochemical gradient out of the cell

Question 28

- In the epithelial cell layer of the renal tubules, how does water follow the transcellular pathway?

Answer 28

It is transported from tubular fluid → Epithelial cells → blood via aquaporins in the epithelial cells

Question 29

- In the epithelial cell layer of the renal tubules, how does water follow the transcellular pathway?

Answer 29

It is transported from tubular fluid → Epithelial cells → blood via aquaporins in the epithelial cells

Question 30

- How does trancellular Na+ reabsorption occur?

Answer 30

3Na+ is transported from epithelial cells into blood via Na+/K+ ATPase This creates a concn. gradient for Na+ as it is lower in the epithelial cell so Na+ from the tubular fluid diffuses into cell 2 K+ is transported from blood into epithelial cells via Na+/K+ ATPase so this is an active transport as ATP is used

Question 31

- What is meant by the paracellular pathway in the renal tubules? - How does Angiotensin II regulate the Na+ reabsorbed?

Answer 31

Substances such as water, Ca2+, K+, Cl- and urea are transported through the tight junctions between the epithelial cells By increasing the number of Na+/H+ antiporters

Question 32

- How does Na+ and Bicarbonate reabsorption occur in the early proximal convoluted tubule?

Answer 32

Na+/K+ ATPase creates a low Na+ concn. in the epithelial cell CO2 enters epithelial cell by diffusion and binds to H20, catalysed by carbonic anhydrase to form bicarbonate and H+ Na+/H+ antiporter then transports Na+ down its concn. gradient into the cell from tubular fluid and H+ out into the tubular fluid against concn. gradient using the energy from transportation of Na+ Na+/HCO3- symporter transports Na+ down concn. gradient into blood and bicarbonate is transported into blood against conc. gradient using energy from transportation of Na+

Question 33

- How does glucose reabsorption occur in the early proximal convoluted tubule?

Answer 33

Na+/K+ ATPase creates concn. gradient with less Na+ in the epithelial cell Na+/Glucose symporter (SGLT2) transports Na+ from tubular fluid into epithelial cell and this provides energy to transport glucose against its gradient from the tubular fluid into the epithelial cell Glucose transporter (GLUT2) transports glucose into the blood from the epithelial cell via facilitated diffusion

Question 34

- Explain the general processes of reabsorption involving the Loop of Henle occurs

Answer 34

Na+Cl- passively leaves thin ascending limb into the medulla and leaves actively from the thick ascending limb This creates a low water potential in the medulla and so water leaves through the descending limb passively

Question 35

- Describe and explain the osmolarity of the tubular fluid in the different parts of the loop of Henle

Answer 35

At the point where the descending limb enters the ascending limb, the tubular fluid is hyperosmolar as water has been passively reabsorbed from the descending limb however since it is impermeable to Na+Cl-, the fluid is hyperosmolar ( will have a high oncotic pressure) At the tip of the thick ascending limb, the tubular fluid is hypoosmolar as the salt has been reabsorbed far more

Question 36

- How does Na+Cl- reabsorption in the thick ascending limb of the Loop of Henle occur?

Answer 36

Na+/K+ ATPase creates concn. gradient with low conc. in the epithelial cell Na+/K+/2Cl- symporter transports these ions from the tubular fluid into the epithelial cell K+ is recycled back out into the tubular fluid K+/Cl- symporter allows reabsorption of these ions back into the blood from the epithelial cell There is also a passive chorine channel passing through basolateral membrane from cell to blood