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SP1 Physiology/Microanatomy 2 > Lecture 33 4/5/24 > Flashcards

Lecture 33 4/5/24 Flashcards

1
Q

What are the main functions of the kidney?

A

-control blood volume and electrolyte composition
-renin-angiotensin II pathway
-rid body of waste material
-acid-base regulation
-regulation of erythrocyte production
-regulation of calcitriol production
-glucose synthesis

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2
Q

What does the rate of glomerular filtration depend on?

A

-rate of kidney blood flow
-properties of the glomerular capillary membranes

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3
Q

How does urine formation begin?

A

large amount of fluid that is virtually protein-free is filtered from glomerular capillaries into Bowman’s capsule

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4
Q

What is the concentration of glomerular filtrate in Bowman’s capsule similar to?

A

plasma

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5
Q

What happens to the filtrate as it passes from Bowman’s capsule through the tubules?

A

-modified by reabsorption of water and specific solutes into the blood
-modified by secretion of substances from peritubular capillaries into the tubules

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6
Q

What is net excretion the result of?

A

what is filtered - what is reabsorbed + what is secreted

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7
Q

How does filtration impact reabsorption?

A

increased filtration leads to increased reabsorption

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8
Q

What are the types of filtration and reabsorption patterns in the kidney?

A

-filtration only: creatinine
-filtration and complete reabsorption: glucose, AAs
-filtration and partial reabsorption: Na, Cl, bicarb
-filtration and secretion: K+, H+, organic acids/bases

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9
Q

How do the rates of filtration, reabsorption, and excretion compare to one another?

A

the rates of filtration and reabsorption are extremely large compared to the rate of excretion

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10
Q

What are the characteristics of the glomerular basement membrane?

A

-has proteoglycans with a strong neg. charge
-prevents certain proteins like albumin from filtering out
-epithelial layer is not continuous; has “slit pores”
-epithelial layer also has neg. charge to repel plasma proteins

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11
Q

Which characteristics of molecules determine their filterability?

A

-size
-electrical charge

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12
Q

Which molecules are most readily filtered?

A

-those with a small molecular size
-those with a positive charge

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13
Q

What is the clinical correlation of the glomerular filtration barrier?

A

proteinuria/albuminuria can occur with changes in glomerular filtration barrier permeability

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14
Q

What does glomerular filtration rate represent?

A

the flow of plasma from the glomerulus into Bowman’s space over a specified period; chief measure of kidney function

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15
Q

What is the importance of a high GFR?

A

allows the kidneys to control the volume and composition of body fluids precisely and rapidly

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16
Q

What determines the GFR?

A

-sum of the hydrostatic and colloid osmotic forces across the glomerular membrane (net filtration pressure)
-glomerular filtration coefficient Kf
-GFR = Kf x net filtration pressure

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17
Q

Why does Bowman’s capsule not have an oncotic pressure?

A

no protein should be passing the filter

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18
Q

Why do the glomerular capillaries have a high filtration rate?

A

-higher hydrostatic pressure
-high Kf

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19
Q

What is filtration fraction?

A

-the portion of plasma entering the kidney that ends up as filtrate
-GFR/RPF

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20
Q

What percent of the plasma flowing through the kidney is filtered through the glomerular capillaries?

A

20%

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21
Q

Which factors affect the GFR?

A

-glomerular hydrostatic pressure
-glomerular oncotic pressure
-renal plasma flow
-filtration coefficient Kf
-balance between afferent and efferent resistance

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22
Q

Why does the glomerular oncotic pressure gradually increase through the glomerulus?

A

filtration of water concentrates the proteins since they are not filtered, which elevates the oncotic pressure

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23
Q

What is the average colloid oncotic pressure of the glomerular capillary plasma proteins?

A

32 mmHg

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24
Q

Which two factors influence the glomerular capillary colloid osmotic pressure?

A

-arterial plamsa colloid osmotic pressure
-fraction of plasma filtered by glomerular capillaries

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25
Q

How does increasing the arterial plasma colloid osmotic pressure impact GFR?

A

decreases GFR

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26
Q

How does increasing the filtration fraction impact GFR?

A

decreases GFR

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27
Q

What happens when there is a reduction in renal plasma flow with no initial change in GFR?

A

-increase in filtration fraction
-raise glomerular capillary colloid osmotic pressure
-leads to reduced GFR

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28
Q

What happens when there is an increase in renal blood flow?

A

-decrease in filtration fraction
-slower rise in the glomerular capillary colloid osmotic pressure
-less inhibitory effect on GFR/potential increase in GFR

29
Q

What is the primary means of physiological regulation of GFR?

A

changes in glomerular hydrostatic pressure

30
Q

How does a change in glomerular hydrostatic pressure impact GFR?

A

-increased pressure raises GFR
-decreased pressure lowers GFR

31
Q

Which variables impact glomerular hydrostatic pressure?

A

-arterial pressure
-afferent arteriolar resistance
-efferent arteriolar resistance

32
Q

How does increased arterial pressure impact GFR?

A

raises glomerular hydrostatic pressure, which increases GFR

33
Q

How does increased resistance of afferent arterioles impact GFR?

A

reduces glomerular hydrostatic pressure, which decreases GFR

34
Q

How does constriction of efferent arterioles impact GFR?

A

increases resistance to outflow, which raises glomerular hydrostatic pressure and increases GFR slightly (as long as resistance does not reduce renal blood flow too much)

35
Q

What happens if constriction of efferent arterioles is severe?

A

-rise in colloid osmotic pressure exceeds increase in glomerular capillary hydrostatic pressure
-net force for filtration decreases, reducing GFR

36
Q

Why is the renal blood flow to the kidneys about 22% of the cardiac output?

A

-to supply the kidneys with nutrients and remove waste products
-to supply enough plasma for the high rates of glomerular filtration necessary for precise regulation of body fluid volumes and solute concentrations

37
Q

What is the equation for renal blood flow?

A

(renal artery pressure - renal vein pressure)/total renal vascular resistance

38
Q

What determines the total vascular resistance through the kidneys?

A

the sum of the resistances in the individual vasculature segments

39
Q

Where does the majority of renal vascular resistance reside?

A

-interlobular arteries
-afferent arterioles
-efferent arterioles

40
Q

What controls the resistance in renal vasculature?

A

-sympathetic nervous system
-hormones
-local internal control mechanisms

41
Q

How do increases and decreases in vasculature resistance impact renal blood flow?

A

-increases in resistance decrease blood flow
-decreases in resistance increase blood flow

42
Q

What is the function of autoregulation?

A

allows the kidneys to maintain renal blood flow and GFR at a relative constant over a range of arterial pressures

43
Q

Which region of the kidney receives the majority of the blood flow?

A

cortex

44
Q

Which portion of the peritubular capillary system supplies blood to the medulla?

A

vasa recta

45
Q

What happens when there is strong activation of the sympathetic nervous system?

A

-constriction of the renal arterioles
-decrease in renal blood flow and GFR

46
Q

What happens when there is mild/moderate activation of the sympathetic nervous system?

A

-little influence on blood flow and GFR
-stimulates renin release and increased tubular reabsorption
-decreased sodium and water excretion

47
Q

What is an autacoid?

A

physiologically active substance produced by the body that typically has a localized effect of brief duration

48
Q

What are the effects of epinephrine/norepinephrine on the kidneys?

A

-constrict afferent and efferent arterioles
-reduce GFR and renal blood flow

49
Q

What are the characteristics of endothelin?

A

-peptide released by damaged vascular endothelial cells of the kidneys
-may contribute to hemostasis
-powerful vasoconstrictor

50
Q

What are the characteristics of endothelial-derived nitric oxide?

A

-autacoid that decreases renal vascular resistance
-released by vascular endothelium
-important for maintaining vasodilation

51
Q

What effect do drugs that inhibit nitric oxide formation have?

A

-increase renal vascular resistance
-decrease GFR and urinary sodium excretion
-cause high blood pressure

52
Q

What are the functions of prostaglandins and bradykinin?

A

-cause vasodilation
-increase renal blood flow and GFR
-may dampen the renal vasoconstrictor effects of sympathetic nerves and angiotensin II

53
Q

What are the characteristics of angiotensin II?

A

-powerful renal vasoconstrictor
-formed in kidneys and in systemic circulation
-receptors present in virtually all blood vessels of the kidneys

54
Q

Which vessels are protected from angiotensin II, and how?

A

-preglomerular blood vessels, especially afferent arterioles
-protection is due to release of vasodilators (nitric oxides, prostaglandins) which counteract the vasoconstrictor effects of angiotensin II

55
Q

Which vessels are highly sensitive to angiotensin II, and why?

A

-efferent arterioles
-increased angiotensin II levels raise glomerular hydrostatic pressure; prevents decreases in glomerular hydrostatic pressure and GFR
-decreased blood flow caused by constriction increases sodium and water reabsorption to restore blood volume and blood pressure

56
Q

What is the importance of autoregulation?

A

prevent potentially large changes in GFR and renal excretion of water that would otherwise occur with changes in blood pressure

57
Q

Why does arterial pressure exert a lesser effect on urine volume?

A

-renal autoregulation prevents large changes in GFR
-additional adaptive mechanisms cause an increase in reabsorption when GFR rises

58
Q

What are the two components of the tubuloglomerular feedback mechanism?

A

-afferent arteriolar feedback mechanism
-efferent arteriolar feedback mechanism

59
Q

What are the components of juxtaglomerular complex?

A

-macula densa cells in distal tubule
-juxtaglomerular cells in walls of afferent and efferent arterioles

60
Q

How does a decreased GFR impact the Loop of Henle?

A

-slows flow rate of LOH
-increases reabsorption of sodium and chloride ions delivered to ascending LOH
-reduces concentration of sodium chloride at macula densa cells

61
Q

What effects do the macula densa cell signals have when NaCl conc. is decreased?

A

-decreases resistance to blood flow in the afferent tubules
-increases renin release from juxtaglomerular cells; leads to angiotensin II causing efferent arteriole constriction

62
Q

How does high protein intake impact renal blood flow and GFR?

A

increases blood flow and GFR

63
Q

Why is it important that amino acids and sodium are reabsorbed together?

A

increased amino acid reabsorption stimulates increased sodium reabsorption when protein intake is high

64
Q

How do large increases in blood glucose levels impact renal blood flow and GFR?

A

increases blood flow and GFR

65
Q

What happens when proximal tubular reabsorption is reduced?

A

-ability to reabsorb sodium chloride is decreased, leading to large amounts of sodium chloride reaching the distal tubule
-can quickly cause excessive volume depletion without compensatory mechanisms

66
Q

Why is it important that an increase in reabsorption of NaCl prior to the macula densa increases renal blood flow and GFR?

A

helps return distal sodium chloride delivery to normal in order to maintain normal rates of sodium and water excretion

67
Q

What is the importance of the myogenic reflex?

A

-prevents excessive stretch of the vessel
-raises vascular resistance
-helps prevent excessive increases in renal blood flow and GFR
-protects kidney from hypertension-induced injury

68
Q

What are the characteristics of creatinine?

A

-byproduct of muscle metabolism
-freely filtered while not being reabsorbed or secreted
-used to measure glomerular filtration
-increased serum creatinine indicates decreased renal clearance

SP1 Physiology/Microanatomy 2 (50 decks)

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