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Physiology II > renal > Flashcards

renal Flashcards

1
Q

functions of kidneys

A

regulate ECF water (and thus long-term arterial pressure), ECF concentrations of many inorganic ions, and (together with the lungs) regulate ECF acid-base balance

remove metabolic wastes from ECF (urea from protein catabolism, uric acid from nucleic acids, creatinine from muscle creatine, end products of hemoglobin breakdown

removes some foreign chemicals (e.g. drugs, pesticides) from ECF

gluconeogenesis

produces hormones (renin, erythropoietin, and 1,25-dihydroxyvitamin D)

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2
Q

gluconeogenesis (occurs in kidneys but primarily in liver)

A

during fasting, synthesis of glucose from other molecules such as amino acids and release it into the blood

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3
Q

nephron (functional unit kidney) is comprised of:

A

renal corpuscle - the filtering component

(renal) tubule - extends out from the corpuscle and is surrounding by peritubular capillaries

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4
Q

renal corpuscle consists of

A

a tuft of capillaries called the glomerulus or GLOMERULAR CAPILLARIES

a balloon-like hollow Bowman’s capsule (BC) into which the capillaries protrude the fluid-filled space within which is called Bowman’s space

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5
Q

fluid from the capillaries filters into Bowman’s space across

A

the thin membranes of the capillaries and of Bowman’s capsule

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6
Q

kidney has an outer cortex and a deeper medulla; all renal corpuscles are

A

within the cortex

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7
Q

juxtamedullary nephrons have corpuscles

A

near the cortex/medulla junction

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8
Q

cortical nephrons have more superficial corpuscles nearer

A

the kidney surface

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9
Q

renal tubule: its lumen

A

is a continuation of the space in Bowman’s capsule

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10
Q

proximal tubule

A

first section of the tubule; it drains Bowman’s space (has a convoluted portion and a straight portion)

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11
Q

loop of henle

A

next section of the tubule (after proximal tubule); it has a descending limb followed by an ascending limb

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12
Q

distal convoluted tubule

A

next section of the tubule (after loop of henle)

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13
Q

collecting duct

A

final section formed by union of many distal tubules

composed of a cortical collecting duct followed by a medullary collecting duct

contains the fluid that will be transported to the bladder and eventually eliminated

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14
Q

the tubules of most (not all) nephrons

A

loop down into the medulla, sometimes deeply

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15
Q

afferent arteriole

A

carries blood (from a branch of the renal artery) into a tuft of glomerular capillaries

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16
Q

the glomerular capillaries recombine to form another arteriole, the ______ arteriole, through which

A

efferent

blood leaves the capillaries

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17
Q

the efferent arteriole divides into another set of capillaries, the _______, which

A

peritubular capillaries

branch to form a network surrounding the tubule

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18
Q

kidney function overview:

the low-molecular weight substances (_________) in glomerular capillary plasma are filtered ________, which is called ________

A

water, glucose, urea, ions

across the thin membranes of the capillaries and of Bowman’s capsule into Bowman’s space

glomerular filtration

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19
Q

glomerular filtration forms the glomerular filtrate (also called ultrafiltrate) which contains the same substances in _____ concentrations as their plasma concentrations

A

the same

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20
Q

what is not included in the filtrate and why?

A

cells or proteins

because they’re too large to cross

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21
Q

as the filtrate moves from BC into and through the tubule, its composition is altered by two general processes

A
  1. tubular reabsorption

2. tubular secretion

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22
Q

tubular reabsorption and secretion occur because

A

the tubule is very close to the peritubular capillary network, and substances can be transferred in either direction between peritubular capillary blood and the lumen of the tubule

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23
Q

filtration, tubular reabsorption, and tubular secretion combine to allow the kidneys to excrete

A

all, some, or non of a given substance in the blood

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24
Q

total excretion

A

substance that is filterable, cannot be reabsorbed, and undergoes 100 percent secretion

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25
Q

partial excretion

A

substance that is filterable, undergoes partial reabsorption, which only allows partial secretion

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26
Q

no excretion

A

substance that is filterable, undergoes 100 percent reabsorption, and cannot be secreted

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27
Q

not all substances undergo all 3 processes (filtration, reabsorption, and secretion); the rates at which the 3 processes proceed are often subject to

A

physiological control, and thus allow control of the concentrations of substances in body

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28
Q

where the ‘inner’ walls of BC abut the glomerular capillary walls, the BC cells are called ______ and contain many extensions (foot processes). spaces between foot processes are called _______

A

podocytes

filtration slits or “slit pores”

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29
Q

pathway of substance during filtration

A

a substance moves across the single layer of (or between the cells of) epithelial cells (called endothelium) forming the capillary walls –> across a layer of noncellular materials (basement membrane) –> and between foot processes into Bowman’s space

these filtration membranes serve only as a filtration barrier and have no energy-requiring function

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30
Q

the process of filtration involves using pressure to force a filtrate of plasma through the glomerular pores into Bowman’s space; except for being essentially protein-free, the filtrate is thus almost identical to plasma and contains:

A

water, glucose, urea, sodium, chloride, potassium, etc in their plasma concentrations

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31
Q

the force driving filtration is mostly

A

glomerular capillary fluid (blood) pressure, which is high (60 mmHg) relative to pressure in other capillaries. filtration is driven mostly by a fluid pressure gradient not a diffusion (concentration) gradient

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32
Q

filtration is opposed by two relatively small forces

A
  1. fluid pressure in Bowman’s space

2. osmotic force caused by proteins in plasma that are not present in Bowman’s space

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33
Q

the net pressure favoring filtration is

A

10 mmHg (or a bit more)

34
Q

the glomerular capillaries are much more permeable to fluid than most other body capillaries, resulting in massive filtration of about ______ per day

A

180 L/day or 45 gallons

35
Q

massive filtration by kidneys allows kidneys to regulate

A

some components of the internal environment very precisely

36
Q

of the 900 liters of plasma entering the kidneys per day 180 liters are filtered into Bowman’s space and the rest passes into the

A

efferent arterioles and then into the peritubular capillaries

37
Q

glomerular filtration rate (GFR)

A

the volume of fluid filtered into the combined Bowman’s spaces per unit time

38
Q

total amount of a given substance filtered per unit time (the filtered load of the substance) =

A

GFR times the plasma concentration of the substance

39
Q

if less of a substance is excreted than is filtered per unit time, _______ has occurred

A

tubular reabsorption

40
Q

if more of a substance is excreted than is filtered per unit time, _____ has occurred

A

tubular secretion

41
Q

GFR is not a fixed value but is subject to physiological control, achieved mainly by

A

neural and hormonal inputs to the afferent and efferent arterioles

42
Q

impact of constriction of the afferent arteriole on net glomerular filtration pressure

A

decreases glomerular capillary blood pressure by increasing the pressure drop between arteries and capillaries

43
Q

impact of constriction of the efferent arteriole on net glomerular filtration pressure

A

increases glomerular capillary blood pressure by causing blood to dam up in the capillaries

44
Q

percent reabsorption of water

A

99

45
Q

percent reabsorption of sodium

A

99.5

46
Q

percent reabsorption of glucose

A

100

47
Q

percent reabsorption of urea

A

44

48
Q

filtered loads are huge, and filtered amounts of some substances would quickly

A

deplete body stores if reabsorption ceased

e.g. total plasma water would be urinated in 30 minute

49
Q

rapid excretion of wastes (e.g. urea) can occur because quantities excreted are

A

sizable fractions of the filtered amounts

50
Q

useful plasma component (e.g. organic nutrients, ions, water) undergo relatively complete reabsorption, so excreted amounts are

A

small fractions of the filtered amounts

51
Q

the reabsorption process for some filtered substances (e.g. most organic nutrients) is not

A

physiologically regulated; these substances are typically completely reabsorbed at all times

52
Q

reabsorption rates for other substances (water and many inorganic ions) are regulated

A

according to the body’s needs

53
Q

can reabsorption regulate plasma glucose levels (minimize changes from a set point): assume ideal level is 80 mg glu/100 ml plasma

if plasma concentration is 100mg/ml (or 60 mg/ml) and complete reabsorption occurs, ____ glucose is lost from the body, and the plasma level remains at 100 (or 60)

thus, the kidney _____ set and regulate the plasma glucose concentration

A

no

does not

54
Q

can reabsorption regulate plasma water levels?

the kidney does not always reabsorb all (or even 99 percent) of the total amount of water filtered; instead, the water reabsorption rate is

A

constantly subject to physiological control

55
Q

increase water intake –> ____ reabsorption –> ____ excretion –> restoration of plasma water level to normal

A

decreased

increased

56
Q

tight junction exist between the _____ borders of the tubular epithelial cells

A

luminal

57
Q

transcellular path (into and out of the tubule lumen) is through the plasma membranes forming the luminal borders and thus through cells; occurs by

A

diffusion or active transport

58
Q

paracellular path (into and out of the tubule lumen) is through the tight junctions and thus between cells; occurs by

A

diffusion

59
Q

a substance need not be actively transported across both the _____ and ______ membranes to be actively transported (actively reabsorbed)

A

luminal

basolateral

60
Q

substances move from the renal interstitial fluid into the _____ by

A

peritubular capillary plasma

a combination of diffusion and bulk flow

61
Q

substances are reabsorbed by _____ and/or ______ transport mechanisms

A

diffusion

carrier-mediated

62
Q

carrier-mediated transport mechanism

A

glucose is reabsorbed by secondary active transport (sodium cotransport) and thus uses energy and can occur against the glucose concentration gradient

63
Q

steps in glucose carrier mediated transport

A
  1. Na/K pump pumps Na out of cell and into rental interstitial fluid (creating Na concentration gradient favoring Na into the cell)
  2. Na/glucose cotransporter moves Na with its concentration gradient (into the cell from tubule lumen) and takes glucose with it
  3. GLUT transporter transports glucose out of cell and into interstitial fluid
64
Q

when considering glucose reabsorption, because a carrier protein is involved, a very high glucose concentration in blood (and thus in interstitial fluid) can exceed the capacity (called the transport maximum) of the carrier, in which case glucose will appear

A

in the urine (diabetes mellitus)

65
Q

urea is reabsorbed by

A

diffusion

66
Q

since urea is filtered at the renal corpuscle, its concentration in the first portion of the tubule is equal to its concentration in the interstitial fluid around the tubule and in the peritubular capillary plasma.

as the filtrate flows along the proximal tubule, water reabsorption occurs, thus ______ the tubular concentration of urea

urea then diffuses passively down its concentration gradient from ____ to ____

A

increasing

tubule to peritubular capillary

67
Q

most ____ and ____ in urine enters the tubules by secretion; thus renal regulation of these is accomplished primarily by controlling the rates of their

A

K+ and H+

tubular secretion

68
Q

some organic ions (e.g. creatinine) and foreign substances (e.g. penicillin) are

A

secreted

69
Q

secretion is by ______ or ______ , and the secretion of many substances is coupled to

A

diffusion or carrier-mediated transport

sodium reabsorption

70
Q

secretion from the renal interstitial fluid into the filtrate within the tubule draws substances from the peritubular capillary plasma, is a way to increase the kidney’s ability to excrete substances at a higher rate than if the kidneys depended solely on the

A

filtered load

71
Q

clearance

A

describes the rate at which substances are removed (cleared) from the plasma by the kidneys

72
Q

renal clearance of a substance is the

A

volume of plasma completely cleared of a substance per unit time by the kidneys (units are volume of plasma/unit time)

73
Q

Cs =

A

Us*V / Ps

74
Q

example of clearance:

40 mg or a substance S shows up in each liter of urine (urine concentration of S = 40 mg/L)

during an hour, 0.5 L of urine is produced (this half liter of urine contains 20 mg of S– the kidney are getting rid of 20 mg of S per hour)

Cs =

A

(40 * 0.5) / 5

75
Q

urinary excretion rate of substance S =

A

Us * V

76
Q

Clearance rate of inulin =

A

GFR

77
Q

creatinine is an endogenous filtered substance that undergoes 0 reabsorption and almost 0 secretion (similar to inulin), so clearance rate of creatinine =

A

GFR

low GFR is hallmark of kidney disease

78
Q

hypothetical situation:

have a patient in which GFR decreased by half: only half as much creatinine will be filtered and thus excreted (but change is transient). creatinine will start accumulating – its plasma concentration rises. this will cause the filtered load eventually to increase because there is so much creatinine in the blood. excretion eventually returns to normal and a balance is re-established between creatinine production and excretion, but this only occurs when the plasma creatinine concentration is about _____ what it was before

A

double

79
Q

a blood test for creatinine levels is commonly used as an indicator of _____

A

GFR

80
Q

high creatinine is an indicator of a _____ GFR, which is one hallmark of kidney disease

A

low

Physiology II (16 decks)

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