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HAP > UROGENITAL (PART 2) > Flashcards

UROGENITAL (PART 2) Flashcards

1
Q

Why do the kidneys need a high blood flow rate?

A

Filter all blood waste products
Maintain electrolyte, pH, fluid, and blood pressure balance
High energy requirements for cellular function

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2
Q

What is the name of the small arteries that enter the kidneys and branch into glomerular capillaries?

A

Afferent arterioles

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3
Q

What factors contribute to the filtration pressure gradient?

A

Glomerular hydrostatic pressure (blood pressure in glomerulus) pushing fluid out
Capsular hydrostatic pressure (pressure of filtrate) pushing fluid back in (usually negligible)
Glomerular osmotic pressure (blood protein concentration) pulling fluid back in

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4
Q

What happens during glomerular filtration?

A

Blood is filtered into the glomerulus, allowing water and small solutes to pass into Bowman’s capsule

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5
Q

What is the net filtration pressure (EFP)?

A

EFP = (glomerular hydrostatic pressure - capsular hydrostatic pressure) - (glomerular osmotic pressure - capsular pressure)
A higher EFP increases glomerular filtration rate (GFR)

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6
Q

Why are plasma proteins important for glomerular filtration?

A

They are large and don’t pass through the glomerular membrane easily
Their presence in the blood creates an osmotic pressure that pulls water back into the bloodstream, opposing filtration

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7
Q

What is a typical value for net filtration pressure (EFP)?

A

Around 10 mmHg
An EFP of 1 mmHg is thought to produce a GFR or 12.5 ml/minute

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8
Q

Why is glomerular filtration so rapid?

A

Glomerular capillaries have many pores (fenestrations) for high permeability
Higher glomerular hydrostatic pressure due to efferent arteriole resistance

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9
Q

What is glomerular filtration rate (GFR)?

A

The rate of fluid filtered from the glomerulus into the Bowman’s capsule

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10
Q

What factors affect GFR?

A

Net filtration pressure (EFP) - higher EFP increases GFR
Diameter of afferent and efferent arterioles
Systemic blood pressure (indirect effect)
Glomerular membrane permeability (stress, disease)

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11
Q

How does systemic blood pressure affect GFR?

A

GFR generally increases with increased blood pressure, but afferent arteriole constriction limits this rise

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12
Q

How can GFR be estimated?

A

By measuring the renal clearance of a substance like creatinine or inulin
Renal clearance: volume of plasma cleared of a substance per minute

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13
Q

Why is creatinine a good substance for GFR estimation (assuming normal muscle mass)?

A

Produced at a constant rate in the body
Not reabsorbed by the kidneys

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14
Q

Summarise the factors influencing glomerular filtration rate (GFR).

A

Net filtration pressure (NFP)
Total surface area of the glomerulus available
Filtration membrane permeability

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14
Q

What are advantages and disadvantages of creatinine and inulin clearance for GFR estimation?

A

Creatinine clearance:
Easier and cheaper to measure
Less accurate (affected by muscle mass)
Inulin clearance
More accurate
More expensive and complicated

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15
Q

Where does the renal tubule start and end?

A

Starts at the renal corpuscle and ends at a collecting duct shared with other nephrons

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15
Q

What is the general structure of the renal tubule?

A

A winding tube with epithelial cell walls, containing a single cilium for sensing fluid flow and composition

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16
Q

What are the main sections of the renal tubule?

A

Proximal convoluted tubule (PCT): closest to glomerulus, with microvilli brush border for increased surface area
Nephron loop (Henle loop)
Thin descending limb
Thin ascending limb
Thick ascending limb
Loop length affects urine concentration
Distal convoluted tubule (DCT): carries filtrate to collecting duct
Collecting duct: formed by merging tubules, collects urine from nephrons

17
Q

Where does urine exit the kidney?

A

Through openings in the renal papilla into minor calyces

18
Q

What is reabsorption in the renal tubule?

A

The second step in urine formation, where filtered substances are actively or passively moved from the tubule back into the bloodstream
This maintains blood plasma composition and returns water to the body

19
Q

What is the importance of sodium reabsorption in the kidney?

A

Maintains blood plasma composition and regulates blood volume

20
Q

Where does most sodium reabsorption occur?

A

Proximal convoluted tubule (PCT) by Na-H exchange (60%)

21
Q

How is glucose reabsorbed?

A

Reabsorbed with sodium in the PCT via SGLT-2 cotransporter
Essentially all filtered glucose is reabsorbed

21
Q

How is sodium reabsorbed in the renal tubule?

A

Sodium moves from the tubule lumen into the cells (down a concentration gradient) via co-transporters and exchangers
Na/K-ATPase pump actively transports sodium out of the cells into the bloodstream

22
Q

How are amino acids reabsorbed?

A

Cotransported with sodium in the PCT
Amino acids exit the cells by passive or facilitated diffusion

22
Q

How is chloride reabsorption regulated?

A

Some reabsorbed with sodium and potassium in the thick ascending limb
Exact mechanism for other chloride reabsorption is not fully understood

23
Q

Why does the fluid become hypotonic in the ascending limb of Henle’s loop?

A

Sodium, potassium and chloride are actively pumped out (co-transport) but water stays in, diluting the remaining fluid

23
Q

Why is water reabsorbed in the descending limb of Henle’s loop?

A

The descending limb is permeable to water (aquaporin-1) and water moves out to the hypertonic medullary interstitium

23
Q

How is sodium reabsorbed in the thick ascending limb of Henle’s loop?

A

Na-K-ATPase pump actively moves sodium out of the cells
Co-transporter moves sodium, potassium, and two chloride ions into the cells from the lumen
Potassium leaves the cells back into the lumen or goes into the interstitium

24
Q

What is the role of ADH in water reabsorption in the collecting duct?

A

ADH makes the collecting duct permeable to water, allowing reabsorption into the bloodstream when present
Without ADH, the collecting duct is impermeable, and hypotonic fluid is excreted as urine

25
Q

What is the role of urea in the medullary interstitium?

A

Urea diffuses out of the collecting duct, further increasing the osmolarity of the medullary interstitium, which helps reabsorb water

26
Q

What is countercurrent multiplication?

A

A mechanism in the kidneys that creates a concentration gradient to reabsorb water and make concentrated urine

27
Q

What hormone is required for countercurrent multiplication?

A

ADH (antidiuretic hormone)

28
Q

How does the loop of Henle contribute to the concentration gradient?

A

The thick ascending limb actively pumps out sodium chloride, increasing the osmolarity of the surrounding medullary tissue

29
Q

What happens to the thin descending limb of the loop of Henle?

A

Water passively moves out of the thin descending limb due to the high osmolarity of the surrounding medullary tissue, increasing urine concentration

30
Q

What is the role of the collecting duct in countercurrent multiplication?

A

Becomes permeable to water in response to ADH, allowing water reabsorption
In the inner medulla, it allows urea to passively diffuse out, further increasing the osmolarity of the medullary tissue

31
Q

What is the consequence of countercurrent multiplication?

A

A high concentration gradient in the medulla (increasing from outer 300 mOsm/kg to inner 1200 mOsm/kg), allowing for efficient water reabsorption and concentrated urine production

32
Q

What happens to blood in the descending limb of the vasa recta?

A

Water moves out, and solutes move into the blood, equilibrating with the surrounding medullary fluid

33
Q

What is the solute concentration of blood at the bend of the vasa recta?

A

Similar to the concentration of the medullary interstitial fluid

34
Q

What happens in the ascending limb of the vasa recta?

A

The opposite of the descending limb: water moves in, and solutes move out of the blood

35
Q

Why are the vasa recta arranged in a countercurrent flow pattern?

A

To create a countercurrent exchange where water and solutes move in opposite directions between the two limbs

36
Q

What is the overall effect of the vasa recta on the medullary tonicity?

A

The vasa recta help maintain the high medullary tonicity created by the countercurrent multiplier system, although some water and solutes are exchanged

37
Q

What are the main characteristics of the thin descending limb of the nephron loop?

A

Reabsorbs water (H2O) passively
It is impermeable to sodium (Na)
It allows the urine to be concentrated, the urine in the TDL is hypertonic

38
Q

What are the main characteristics of the thick ascending limb of the nephron loop?

A

Na, K and Cl are actively reabsorbed
It is impermeable to H2O
This segment makes the urine less concentrated
The loop of Henle reabsorbs 10-20% Na+ and Cl- and 10% of the filtered water

HAP (12 decks)

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