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Systems Phys 2022 > Renal I > Flashcards

Renal I Flashcards

1
Q

What is the main function of the kidney?

A

maintain constant body fluid volume
maintain constant fluid composition
endocrine organ
acid-base balance

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2
Q

Define: Osmosis

A

the movement of water across cell membranes

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3
Q

What is the driving force for the movement of water?

A

the osmotic pressure difference across the cell membrane

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4
Q

Define: Osmotic Pressure

A

determined solely by the number of solute particles in the solution

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5
Q

Define: Osmolarity

A

concentration X number of dissociable particles

the ability of a liquid to undergo osmosis

mOsm/L = mmol/L X number of particles/mol

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6
Q

How does liquid flow?

A

Liquid flows toward the more concentrated compartment

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7
Q

Define: Oncotic Pressure

A

the osmotic pressure generated by large molecules such as proteins (has symbol π )

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8
Q

Why is oncotic pressure important in the kidneys?

A

it regulates fluid movement across the glomerulus and peritubular capillaries

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9
Q

How is body fluid organized?

A

it is compartmentalized in extracellular and intracellular compartments

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10
Q

Body Fluid: Intracellular Compartment

A

⅔ total body fluid

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11
Q

Body Fluid: Extracellular Compartment

A

⅓ total

further divided into → plasma (¼) and interstitial compartments (¾)

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12
Q

Body Fluid: Extracellular Compartment: Plasma Compartment

What is regulated in the plasma compartment?

A

sodium and water

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13
Q

What do the kidneys maintain volume of?

A

Extracellular fluid and plasma fluid

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14
Q

What would happen if you drank gatorade (isoosmotic)?

A

Extracellular volume would increase

osmolarity would stay the same

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15
Q

What happens to intracellular fluid if you change extracellular fluid?

A

intracellular volume will also change

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16
Q

What causes an increase in EC/IC fluid and a decrease in EC/IC osmolarity?

A

drinking water

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17
Q

What causes an increase in EC fluid and EC/IC osmolarity and a decrease in IC fluid?

A

drink/injected with hyperosmotic solution → goes immediately to EC and pulls fluid from IC

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18
Q

What causes a decrease in EC/IC fluid and an increase in EC/IC osmolarity?

A

dehydration

lose volume, water, ions → increase osmolarity

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19
Q

What causes an increase in EC/IC fluid and a larger decrease in osmolarity than drinking water?

A

being injected with a hypoosmotic saline

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20
Q

How does fluid drain in the kidney?

A

Cortex → medulla → minor calyces → major calyces → renal pelvis → ureter

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21
Q

What is the functional unit of the kidneys?

A

nephron

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22
Q

What makes up the nephron?

A

renal corpuscle

tubule

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23
Q

Define: Renal Corpuscle

A

glomerulus (glomerular capillaries)

The glomerulus of all nephrons is found in the renal cortex

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24
Q

What are the segments of the Renal Corpuscle (Glomerulus)?

A

Bowman’s space and Bowman’s capsule

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25
Q

Where do nephrons extend?

A

some nephrons extend only to the outer region of the renal medulla while others reach far down into the renal medulla

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26
Q

What are the tubular segments the nephron is divided into?

A

Proximal convoluted tubule

Descending thin limb of Henle’s loop

Ascending thin limb of Henle’s loop

Thick Ascending limb of Henle’s loop

Distal convoluted tubule

Cortical collecting duct

Medullary collecting duct

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27
Q

What is the main function of the nephron?

A

it elaborates the fluid within them to produce different amounts and composition of urine depending on the individual’s status

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28
Q

Which nephron segments are found in the cortex of the kidney?

A

Afferent and efferent arterioles

glomerulus

Bowman’s capsule

Proximal Convoluted Tubule

straight portion of proximal tubule

Macula densa

Distal Convoluted Tubule

Connecting Segment

Cortical collecting tubule

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29
Q

Which nephron segments are found in the medulla of the kidney?

A

Thin descending limb of loop of Henle

Thin ascending limb of loop of Henle

Thick ascending limb of loop of Henle

Medullary collecting tubule

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30
Q

Define: Juxtaglomerular (JG) apparatus

A

portion of tubule where the late thick ascending limb of Henle’s loop courses between the arterioles

Made up of 2 cell types: granular cells (JG cells) and macula densa cells

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31
Q

Define: Juxtaglomerular Cells (granular cells)

A

differentiated smooth muscle cells in the walls of arterioles

secrete renin

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32
Q

Define: Macula densa cells

A

contributes to control of glomerular filtration rate and to the secretion of renin

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33
Q

How is blood supplied to nephrons/the kidneys?

A

Blood enters each kidney via the renal artery → subdivides into smaller branches till it reaches afferent arterioles → lead to glomeruli → through glomerular capillaries and combine to form efferent arterioles → subdivide into peritubular capillaries → distribute throughout the length of the nephron

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34
Q

What are Vasa recta?

A

a type of peritubular capillaries which are long and straight and drape (like hair-pin loops) along the lope of Henle

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35
Q

Renal Innervation

A

afferent and efferent arterioles are richly supplied with sympathetic noradrenergic neurons

noradrenergic neurons act on both afferent and efferent arterioles via α-adrenergic receptors to cause constriction of both sets of arterioles

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36
Q

Define: Filtered Load

A

mass of material filtered through glomeruli

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37
Q

Define: Reabsorption

A

process by which material is transported from lumen to peritubular capillaries

38
Q

Define: Secretion

A

process by which material is transported from capillaries to lumen

39
Q

Define: Excretion

A

process by which material moves through the length of the nephron and is the combination of reabsorption and secretion

filtration - reabsorption + secretion

40
Q

Define: Filtration

A

movement of fluid from glomerular capillaries to Bowman space

41
Q

Define: Glomerular Filtration Rate (GFR)

A

rate at which material/substances are filtered through the glomerular capillaries

index of kidney function

volume of filtrate formed per unit time

42
Q

Define: Glomerular Filtration

A

bulk flow of fluid from glomerular capillaries into Bowman’s capsule

43
Q

Define: Glomerular filtrate

A

fluid within Bowman’s capsule normally doesn’t contain cells, essentially protein-free and contains most inorganic ions and low molecular weight organic solutes

44
Q

Filtered substances go through:

A
  1. Fenestrae in the glomerular-capillary endothelial layer
  2. Basement membrane
  3. Slit diaphragms between podocyte processes
45
Q

Physical aspects (of filtrate) that regulate filtration of substances:

A

Substances Sizes > 70,000 Daltons mwt., is not filtered

Electrical Charge: negatively charged molecules are less filtered

46
Q

Why are negatively charged molecules less filtered?

A

the surfaces of the filtration barrier are coated with polyanions which tend to repel negative charges

47
Q

Physical aspects of glomerulus-endothelial cell barrier that regulate filtration of substances: Permeability

A

Size of space/fenestra between endothelial cells

Size of spaces between epithelial podocytes of Bowman’s capsule

48
Q

What is normal GFR?

A

approximately 180L/day ( 125 mL/min)

49
Q

What are direct determinants of GFR?

A

rate of filtration = permeability X surface area X Net filtration pressure (NFP)

Kf = permeability X surface area

GFR = Kf X NFP

50
Q

Define: Kf

A

ultrafiltration coefficient

51
Q

How is permeability determined?

A

by size of space/fenestra between capillary endothelial cells and size of pores between epithelial podocytes of Bowman’s capsule

52
Q

How is surface area determined?

A

by mesangial cell status and number of viable nephrons (lose as you age)

53
Q

What happens if mesangial cells relax?

A

surface area increases

Kf increases

54
Q

What happens if mesangial cells contract?

A

surface area of glomerular capillaries decreases

Kf decreases

GFR decreases

55
Q

How is Net Filtration Pressure (NFP) determined?

A

NFP = (PGC + πBC) - (PBC + πGC)

56
Q

Define: PGC

A

glomerular-capillary hydrostatic pressure

57
Q

Define: πBC

A

oncotic pressure of fluid in Bowman’s Capsule

taken as zero (negligible) because there is virtually no protein n Bowman’s Capsule

58
Q

Define: PBC

A

hydrostatic pressure in Bowman’s Capsule

59
Q

Define: πGC

A

oncotic pressure in glomerular-capillary plasma

60
Q

What is the overall equation for GFR?

A

GFR = Kf X NFP (PGC - PBC - πGC)

61
Q

How does filtration of essential protein effect πGC and NFP?

A

filtration of essential protein free fluid concentrates protein n glomerular capillary increasing πGC and decreasing NFP

62
Q

Kf: increased glomerular surface area (mesangial cells relax)

A

increased GFR

63
Q

PGC: Increased renal arterial pressure, decreased afferent-arteriolar resistance (arteriolar dilation), increased efferent arteriolar resistance (efferent constriction)

A

Increases GFR

64
Q

PBC: Increases intratubular pressure (obstruction of tubular or extrarenal urinary system)

A

Decreases GFR

65
Q

πGC: increased systemic oncotic pressure, decreased renal plasma flow

A

Decreased GFR

66
Q

Renal Blood Flow (RBF)

A

the flow from the renal artery, interlobular artery, through afferent and efferent arterioles, peritubular capillaries, veins and renal vein

in typical adult approx. = 1.1 L/min

20-25% of CO

67
Q

Equation for RBF

A

RBF = (arterial pressure - renal venous pressure) / renal vascular pressure (R)

R = resistance

68
Q

How is RBF regulated?

A

mean arterial pressure

contractile stat of renal arterioles

a given change in arteriolar resistance produces the same effect on RBF regardless of whether it occurs in the afferent or efferent arteriole

more constriction = more resistance = decrease in RBF

69
Q

How does arteriolar caliber affect RBF?

A

arteriolar caliber affect RBF independent of whether afferent or efferent arteriolar caliber is altered

70
Q

How does arteriolar caliber affect GFR?

A

arteriolar caliber affects GFR in a way that depends on whether afferent or efferent arteriolar caliber has been altered

71
Q

What happens if the afferent arteriole is constricted but the efferent arteriole isnt?

A

PGC, GFR, and RPF decrease

72
Q

What happens if the afferent arteriole is relaxed but the efferent arteriole constricted?

A

PGC, GFR increase

RPF decrease

73
Q

What are the functions of RBF?

A

Indirectly determined GFR (decrease in RBF, decrease in GFR)

modifies the rate solute and water reabsorption by the proximal tubule

participates in the concentration (and dilution) of urine

delivers oxygen, nutrients, and hormones to nephron cells; returns CO2 and reabsorbed fluid and solutes to circulation

delivers substrates for excretion in urine

74
Q

Regulation of GFR: Factors that influence afferent and efferent arteriolar caliber (how constricted)

A

Renal sympathetic nerves

Renin-angiotensin system

Autoregulation
Prostaglandins

75
Q

Regulation of GFR: Renal sympathetic Nerves

A

Arterioles are richly supplied with sympathetic nerves which release norepinephrine

circulating norepinephrine also causes renal vasoconstriction

76
Q

What effect does renal vasoconstriction have?

A

renal vasoconstriction causes a large decrease in RBF and small initial increase in PGC

results in NET decrease in NFP and small decrease in GFR

if filtration continues with constricted arterioles over time, PGC decreases and there is a significant decrease in GFR

77
Q

Why is regulation of GFR important?

A
  • regulates the amount of fluid going into nephron tubules which helps regulate:
    • amount of fluid being excreted/reabsorbed
    • clearance of specific molecules (e.g. toxins, drugs, certain metabolites)
  • these function to help control fluid volume and composition
78
Q

Regulation of GFR: Renin-Angiotensin System

A

Renin produced from JG cells converts angiotensinogen to angiotensin II → angiotensin I converted to angiotensin II by action of angiotensin converting enzyme (ACE)

levels of angiotensin II dependent on levels of renin

79
Q

Angiotensin II

A

powerful vasoconstrictor → constricts both afferent and efferent (more effective on efferent) → increases PGC

decreases RBF → decreases PGC, increases πGC

decreases Kf by acting on mesangial cells

has greater effect on RBF than GFR

80
Q

How does angiotensin II effect GFR in normal situations?

A

Ang II tends to decrease GFR

81
Q

How does angiotensin II effect GFR in pathological situations?

A

Ang II tends to maintain GFR

82
Q

Where is renin produced?

A

by granular cells in afferent arteriole of the JG apparatus

83
Q

What controls renin secretion?

A

Intrarenal baroreceptors

macula densa

renal sympathetic nerves

Ang II (negative feedback inhibition)

84
Q

Autoregulation of RBF and GFR

A

myogenic response → similar to one found in vascular smooth muscle beds

tubuloglomerular feedback

mechanism by which the kidneys regulate RBF and GFR in the face of changes in BP → fine tuning of arteries

85
Q

Autoregulation: Myogenic response

A

intrinsic property of vascular smooth muscle → tendency to contract when it is stretched

86
Q

Autoregulation: tubuloglomerular feedback

A

goal is to maintain a relatively constant GFR in the face of changes to mean arterial pressure

intrinsic mechanism

doesn’t rely on hormones

works if BP is within the “autoregulatory range”

87
Q

How does tubuloglomerular feedback regulate GFR?

A

Increases in arterial pressure cause increases in GFR → increases in GFR raises flow through tubules → increased flow increases delivery to the macula densa → increase is detected → adenosine (vasoconstrictor) generated by JGA constricts afferent arteriole → increases resistance, decreases PGC and GFR

88
Q

Define: Prostaglandins

A

local metabolites of arachidonic acid which are produced by both renal sympathetic stimulation and Ang II

ensure there isnt too much constriction

89
Q

What are the 2 major prostaglandins produced in endothelial cells of renal arterioles?

A

PGI2 (prostacyclin)

PGE2

vasodilatory agents which are particularly important to prevent excessive vasoconstriction during cardiovascular stress

increase sympathetic nervous activity → significant constriction of arterioles

90
Q

Define: Nitric Oxide

A

important vasodilator in control of RBF

counteracts Ang II and catecholamines

when blood flow increases → greater shear force acts on endothelial cells → increases production of NO

91
Q

Define: Dopamine

A

vasodilator produced by proximal tubule

serves to increase renal blood flow and inhibit renin secretion

Systems Phys 2022 (25 decks)

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