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Physiology Block 3 > 2 - Renal > Flashcards

2 - Renal Flashcards

1
Q

What is the fundamental unit of the kidney?

A

The nephron and it’s vascular structure.

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2
Q

What is the initial step in urine formation? What is the speed of this?

A

Bulk filtration in the glomerulus.

This process filters ~100 ml/min of plasma in the normal human.

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3
Q

What happens to the fluid once it is filtered by the glomerulus?

A

It undergoes net reabsorption in the tubule.

This returns ~99% of the filtered fluid to the ECF.

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4
Q

What happens once the ~99% of fluid is returned to the ECF?

A

Some substances are transported from the ECF into the tubular lumen in a process called secretion.

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5
Q

What are the common parameters of renal blood flow?

A

Blood flow: Renal art flow (RBF) = 20-25% of CO ~1200 ml/min

Renal Art plasma flow (RPF = RBF(1-Hct) ~700 ml/min

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6
Q

What are the common renal parameters for filtration?

A

Glomerular filtration rate (GFR) ~ 125 ml/min

Filtration fraction (GFR/RPF) = 125/700 = 18% : Range: 15-25%

Filtered Load (GFR x plasma concentration = mass / time)

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7
Q

What is the common renal parameter for reabsorption?

A

99% of filtered solute and water ~124 ml/min

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8
Q

What is the common renal parameter for excretion?

A

Urine flow ~ 1ml/min

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9
Q

What is the common renal parameter for venous blood flow?

A

~1199 ml/min

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10
Q

What is secretion?

A

Transport of solutes from blood into tubular lumen?

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11
Q

Where are the kidneys located? How much of the body weight are the kidneys? How much CO do they recieve?

A

On the posterior wall of the abdomen, outside of the peritoneal cavity.

Approx 0.5% body weight, yet they receive 20-25% of CO.

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12
Q

How is the kidney divided?

A

Into 8-18 pyramids consisting of cortex, medulla, and inner medulla.

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13
Q

What is the nephron composed of?

A

Bowman’s capsule - which combines with the glomerular capillaries to form the glomerulus, the proximal tubule, the loop of henle (thin descending, thin ascending limb, and thick ascending limb), distal tubule (early distal tubule), connecting tubule (late distal tubule), and the collecting duct system (cortical, outer medullary, and inner medullary segments)

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14
Q

Describe the arterial blood flow to the kidneys. What is the purpose of these vessels?

A

Abdominal aorta > large segmental arteries > interlobar arteries > arcuate arteries > interlobular arteries.

Serve primarily as conduit to deliver blood to the high resistance afferent arterioles.

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15
Q

How does pressure change in the afferent arterioles?

A

They provide a large resistance to blood flow and the pressure drops about 60 mmHg.

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16
Q

What percentage of the nephrons are superficial cortical nephrons? Describe the blood flow and the hydrostatic pressure.

A

90% of the nephrons.

Blood flows through a second major vessel, the efferent arteriole, and leads into the peritubular capillaries that surround tubular structures in the renal cortex. Then to venous system.

Hydrostatic pressure is relatively low (20mmHg).

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17
Q

The other ten percent of nephrons are what type? Describe the blood flow. What is the hydrostatic pressure?

A

Juxtamedullary (deep) nephrons.

Blood flows through a second major resistance vessel, the efferent arteriole, and leads into the vasa recta capillaries that surround the renal medulla.

Hydrostatic pressure is relatively low (20mmHg).

18
Q

Describe the structure of juxtamedullary (deep) nephrons.

A

Have long loops of henle that extend into the inner medulla and also have a thin ascending and descending limb.

19
Q

What is the function of the postglomerular peritubular capillaries (cortical nephrons) and vasa recta capillaries (juxtamedullary nephrons)?

A

To reabsorb fluid to the ECF.

20
Q

The renal circulation has two capillary beds in _________?

A

Series

21
Q

What is the difference in pressure in the glomerular capillaries compared to the postglomerular capillaries (vasa recta and peritubular)?

A

Glumerular have higher hydrostatic pressure that favors glumerular ultrafiltration (net filtration from capillaries)

Postglomerular capillaries have lower hydrostatic pressure which favors reabsorption.

22
Q

Where are resistance vessels located? What happens in these vessels?

A

Because and after the high pressure glomerular capillaries: afferent arteriole and efferent arteriole.

There is the largest drop in pressure in them.

23
Q

What is the initial step in urine formation? What is the net filtration pressure?

A

Glomerular filtration, which is a bulk process.

Approximately 100-125 ml/min

Net filtration pressure is 10mmHg (hydrostatic -glomerular oncotic - bowman’s capsule pressure).

24
Q

What is the second step of urine formation?

A

Reabsorption, which is approx 99% of the filtered load (amount of solute and volume filtered).

25
Q

What is the third step of urine formation?

A

Secretion of some solutes by the tubules in the tubular lumen.

26
Q

What is the fourth step of urine formation? How would you calculate this?

A

Excretion!

Excretion = Filtration + secretion - reabsorption

27
Q

What is glomerular filtrate? What is its composition?

A

An ultrafiltrate of plasma formed by the net effect of starling forces to move fluid out of the capillaries into bowman’s space.

Same concentration of most salts and organic substances found in plasma. Large proteins and cellular elements are excluded from filtrate.

28
Q

What is another way that GFR can be expressed?

A

Flux (Jv) equation

Jv = Ultrafiltration coefficient (Kf) X sum of all forces opposing and favoring filtration

29
Q

In the 70 kg man, what is the normal renal plasma flow (going into the afferent arteriole)? How much of this is filtered and how much of this goes through the efferent arteriole?

A

Renal plasma flow (RPF) in through the afferent arteriole is 700 ml/min.

The GFR is 125 ml/min so what’s not filtered, 575 ml/min is the plasma flow through the efferent arteriole (EffPF).

30
Q

What are the three layers of the filtration barrier in the glomerulus?

A
  1. Capillary wall: 700 A fenestrations - permeable to small molecules, neg charged glycoproteins on surface
  2. Basement membrane: porous matrix of ECF proteins including type 4 collagen, laminin, fibronectin and other - charged proteins
  3. Podocytes: finger-like processes with negatively charged proteins and slit pores ~40 x 140 A
31
Q

What does the filtration barrier select by?

A

Size: more permeable to small molecules

Charge-selective: more permeable to positively charged molecules

32
Q

What is the structure of the proteins covering slit pores?

A

A molecular lattice of proteins including nephrin, P-cadherin, and other cytoskeletal proteins form a membrane.

33
Q

What happens when nephrin is absent in the slit pore?

A

The molecular lattice bridging the split pore is altered, making it larger (10 nm as opposed to the normal 5nm).

Excess albumin and proteins are filtered, leading to albuminuria and proteinuria (protein in the urine).

34
Q

How does filterability change with size? What about charge?

A

Filterability decreases as molecular size increases.

Compared to neutral compounds, positively charged molecules have a high filterability and negatively charged molecules have a low filterability.

35
Q

What are factors that could alter the GFR?

A

Anything that alters ultrafiltration coefficient: change in hydraulic permeability or surface area of glomerular capillary membrane.

Or anything that changes the driving force: Glom capillary hydrostatic pressure, bowman’s space hydrostatic pressure, or glomerular capillary oncotic pressure

36
Q

How is GFR primarily regulated physiologically?

A

By alterations in vascular resistance that leads to changes in glomerular capillary hydrostatic pressure and renal blood flow.

37
Q

How does Ohm’s law apply to renal blood flow?

A

Flow = Driving pressure / Vascular resistance

Perfusion is kept constant.

Vascular resistance is both upstream in the afferent arteriole and downstream in the efferent arteriole of the glomerular capillaries.

38
Q

How does glomerular colloid pressure pressure and Hct change based on distance along the glomerular capillary?

A

Near the afferent end, there is a lower colloid pressure and Hct.

Near the efferent end, there is a higher colloid pressure and a higher Hct.

39
Q

What are some pathophysiological causes of decreased GFR?

A

Renal disease, diabetes, hypertension.

Urinary tract obstruction.

Increased plasma protein.

Decreased MAP (minimal effects due to auto-regulation.

Preglomerular constriction, and postglomerular dilation.

40
Q

How does protein concentration change in the glomerular capillaries?

What effect does this have on colloid osmotic pressure?

A

Since large, neg charged molecules are not filtered across the glomerular membranes, the concentration of protein in the plasma in the glomerular capillaries must increase.

There will be a greater colloid osmotic pressure in the plasma in the efferent end than the afferent end.

41
Q

What effect would changing the filtration fraction have on the change in glomerular colloid osmotic pressure?

A

An increase in the filtration fraction results in a bigger increase in colloid osmotic pressure.

This makes sense because more fluid being filtered means that there more proteins in the plasma that exert the colloid pressure.

42
Q

What is the filtration fraction?

A

Glomerular Filtration Rate / Renal Plasma Flow

Physiology Block 3 (17 decks)

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