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Histology > Renal Physiology > Flashcards

Renal Physiology Flashcards

1
Q

the kidneys manage the outflow of ___, and the retention or expulsion of various components of the ___

A
  • urine
  • serum
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2
Q

the kidneys are regulators of what?

A
  • blood pressure
  • blood plasma constituents
  • pH
  • this regulation is provided by what is kept (returned to circulation) vs what is expelled (as urine)
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3
Q

what are the 4 body fluid compartments that physiological fluid is distributed across? where is the majority of the fluid?

A
  • plasma
  • intracellular fluid (majority is found here, but it can easily traverse cell membranes [tonicity])
  • interstitial fluid
  • transcellular fluid
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4
Q

generally, for alterations in the overall fluid volume, the ___ is the point of entry

A

plasma

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5
Q

how many liters of physiological fluid are in the body on average at any one time?

A

42 liters

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6
Q

how many liters per day of fluid do the kidneys dispose of?

A

0.5-2 liters

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7
Q

what ways other than renal is physiological fluid excreted from the body?

A
  1. 700 ml/day lost from skin (not sweat), insensible water loss from skin/respiratory tract
  2. 100 ml/day up to 1-2 L/hour in heavy exercise
  3. Around 100 ml/day in feces.
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8
Q

what is blood volume?

A

the fluid in the plasma and the fluid contained in RBCs

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9
Q

the circulatory system is a ___ system

A

closed

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10
Q

substantially increased volumes of fluid would substantially increase pressure. how do the kidneys function in managing this?

A
  • control of urine volume can rapidly shed excess pressure
  • restriction of urine volume in dehydration can conserve pressure
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11
Q

the kidneys regulate ___ balances and ___

A
  • electrolyte balances and tonicity
  • the kidneys control retention or excretion of these ions, thus can help regulate plasma levels
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12
Q

T or F:

the kidneys serve to excrete metabolic waste products an foreign chemicals

A

true

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13
Q

describe renal regulation of pH

A
  • excretion or retention of acid or base
  • so, urine can be either acidic or basic
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14
Q

T or F:

the kidneys deal with volatile acids

A

false

the kidneys deal with nonvolatile acids

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15
Q

the kidneys produce ___, which creates RBCs

A

erythropoietin

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16
Q

the kidneys are a site of ___, particularly during a fasting state

A

gluconeogenesis

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17
Q

what glands are located on the kidneys?

A

adrenal glands

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18
Q

the outser layer of the kidney is called the ___, and the inner layer is called the ___

A
  • renal cortex
  • renal medulla
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19
Q

within the ___, there are specialized regions of tissue called ___, which are composed of many individual filtration units called ___

A
  • medulla
  • renal pyramids
  • nephrons
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20
Q

each renal pyramid is connected to the ___, or urine drainage tube, by ___

A
  • renal pelvis
  • papilla
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21
Q

describe the general flow through the kidneys

A
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22
Q

where does filtration occur in the kidneys?

A

nephrons in the renal pyramids

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23
Q

filtrate passes through each ___ and is modified by ___ and/or ___ of water, ions, metabolites, etc.

A
  • nephron
  • reabsorption
  • secretion
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24
Q

what is the nephron?

A

the basic functional unit of the kidney where filtration occurs

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25
Q

about how many nephrons are in all of the renal pyramids in a single kidney?

A

1 million

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26
Q

each nephron is fed by a small cluster of ___, often referred to as a ___, which is covered by epithelial cells and encased in ___.

A
  • glomerular capillaries
  • glomerulus
  • bowman’s capsule
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27
Q

describe the flow of plasma through the nephron

A
  1. plasma containing solutes passes out of the glomerulus and into bowman’s capsule
  2. proximal tubule
  3. loop of Henle (longer loop = more concentrated urine)
  4. distal tubule
  5. collecting duct
  6. renal pelvis
  7. ureter
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28
Q

describe the 2 types of nephrons

A
  • Cortical nephrons (around 70%) are located primarily within the cortical region of the kidney, with only the loop of Henle penetrating the medulla. They are more superficial.
  • Juxtamedullary nephrons (around 30%) are located primarily within the medullar region of the kidney. They have very long loops of Henle that penetrate deeply into the medulla.
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29
Q

describe how the blood supply differs between the two types of nephrons

A
  • cortical nephrons - peritubular capillaries are tightly associated with the loop of henle
  • juxtamedullary nephrons - the efferent arterioles extend part of the way down the loop of henle and form specialized peritubular capillaries called vasa recta; allows these nephrons to form highly concentrated urine
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30
Q

around what percentage of the blood plasma presented to the glomerulus enters the proximal tubule via bowman’s capsule?

A

20%

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31
Q

what is the equation for urinary excretion rate?

A

(filtration rate - reabsorption) + (secretion)

32
Q

describe the 5 possible net filtration scenarios

A

5th scenario is no filtration

33
Q

T or F:

kidneys secrete most of what they filter out

A

false

they reabsorb most of what they filter out

34
Q

generally, ___ are very efficiently filtered but tend not to be reabsorbed. thus, a high ___ ensures rapid removal from the blood

A
  • waste products
  • glomerular filtration rate
35
Q

what is a normal total GFR?

A

180 L/day

we only have about 3L of blood plasma, so it is filtered about 60 times per day

36
Q

for most substances, filtration rates and reabsorption rates are very ___ compared to the proportion which is ___

A
  • high
  • excreted
  • thus, relatively small changes in filtration or reabsorption rates translate into relatively large changes in secretion
37
Q

describe the membranes of glomerular capillaries

A
  • slightly specialized to make it selective for relatively small positively charged molecules
  • glomerular capillaries are capable of filtering several hundred times the amount of water and solutes as a normal capillary
38
Q

describe the 3 layers of glomerular capillary membranes

A

1) Endothelium: Fenestrated, negatively charged
2) Basement membrane: Collagen/Proteoglycan mesh, negatively charged
3) Specialized epithelial cells called ‘podocytes’

39
Q

describe the endothelium of glomerular capillary membranes

A
  • has small fenestrae
  • endothelial wall is negatively charged and thus repels large negatively charged albumin proteins
40
Q

describe the basement membrane of glomerular capillary membranes

A

•The basement membrane serves to fuse the endothelium to the the podocyte cell layer

41
Q

describe podocytes of the glomerular capillary membrane

A
  • form slit pores which restrict filtrate based on size and charge
42
Q

describe the glomerular filtration rate

A

GFR = (Kf)(net filtraiton pressure)

  • Kf = glomerular capillary filtration coefficient; a measure of the surface area and hydraulic conductivity
  • net filtraiton pressure = the sum of the colloid and hydrostatic pressures across the glomerular capillaries
43
Q

describe the profiltration and antifiltration pressures of the glomerulus/bowman’s capsule

A
44
Q

describe how alteration of afferent arteriole diameter alters GFR

A
  • alteration in diameter of afferent and efferent arterioles (controlled by sympathetic nervous system)
  • constriction: increase pressure on glomerulus, forcing blood out of bowman’s capsule, decreasing GFR
  • dilatation: opposite effect
45
Q

describe how alteration of efferent arteriole diameter alters GFR

A
  • Minor constriction of the efferent arterioles increase resistance for blood to leave Bowman’s capsule, thereby increasing GFR.
  • HOWEVER major constriction traps proteins in the Bowman’s capsule circulation, raising colloid osmotic pressure and actually decreasing GFR.
  • Dilatation decreases GFR.
46
Q

describe systemic regulation of GFR

A
47
Q

in the steady state, is renal blood flow and GFR relatively constant?

A

yes

48
Q

what is tubuloglomerular feedback?

A
  • autonomic regulation of GFR
  • links the sodium chloride concentration in the distal tubule with the constriction state of the afferent and efferent renal arterioles
49
Q

describe the significance of the macula densa

A
  • located in the distal tubule, and forms the juxtaglomerular complex with the walls of both the afferent and efferent arterioles
  • can detect a decrease in NaCl concentration in the distal tubule, which indicates a decreased renal flow (GFR)
50
Q

what is the role of the macula densa after a decrease in NaCl concentration in the distal tubule is detected (decreased GFR)?

A
  • the macula densa initiated dilatation in the afferent arterioles and causes an increased release of renin
  • renin increases angiotensin I and II levels, causing constriction of the efferent arterioles
  • GFR is restored
51
Q

describe diabetic alteration of GFR

A

*pay attention to blue line, not black

note the effect of antihypertensive therapy

also note that this is representing someone who has poor control of their blood sugar

52
Q

once the glomerular filtrate enters the proximal tubule, it is very similar in composition to the blood plasma, minus the ___

A
  • protein
  • reabsorption is selective and quantitatively large, so filtrate will be modified
53
Q

what do the relative reabsorbed amounts of water and solutes depend on?

A
  • osmolarity (or hydration state) of the body fluid
  • when osmolarity is high (body water is low), the kidney will form a more concentrated urine
  • when osmolarity is low (body water is high), the kidney will form a more dilute urine
54
Q

___ are generally poorly absorbed, whereas ___ and ___ are very well absorbed

A
  • waste products
  • glucose and electrolytes
55
Q

the proximal tubule is heavily involved with the reabsorption of ___ through ___, which is linked to active ___ gradients

A
  • water
  • passive diffusion
  • Na+
56
Q

around 65% of water and Na+ are reabsorbed where?

A
  • the proximal tubule
  • a significant amount of Cl- is reabsorbed along with the Na+
57
Q

describe the cells bordering the proximal tubule

A
  • have a huge capacity for active transport and passive reabsorption
  • lots of mitochondria
  • brush border with large membrane surface area
58
Q

what is preferentially reabsorbed at the more proximal end of the proximal tubule? distal end?

A
  • proximal end: glucose, amino acids, HCO3-, and Na+
  • distal end: glucose and amino acids are depleted, so it is mainly Cl- that is reabsorbed
59
Q

why are waste products not well reabsorbed?

A
  • due to tubule permeability
  • drugs/drug metabolites are often the same
60
Q

what happens to the amount and concentration of Na+ as you proceed along the proximal tubule?

A
  • amount decreases
  • concentration stays the same
61
Q

describe the thin descending segment of the loop of henle

A
  • highly permeable to water (aquaporins)
  • not very many active transporters
  • about 20% of filtered water is reabsorbed here
62
Q

describe the thick ascending segment of the loop of henle

A
  • not permeable to water
  • lots of active transporters
  • reabsorption of Na+, Cl-, K+ (around 25% of these ions are reabsorbed here)*
  • Ca2+, Mg2+, and HCO3- are also reabsorbed here

*in contrast to the proximal tubule, Na+ primarily moves out of the lumen via Na+, Cl-, and K+ co-transporter, because there is not much glucose/amino acids left

63
Q

what is the main function of the loop of henle?

A

control the concentration of the urine

64
Q

describe the general mechanism of renal counter-current exchange

A

water permeability of the thin descending segment works in conjunction with the active transporter capabilities of the thick ascending segment

65
Q

describe osmolarity of the interstitial fluid in deep tissues of the renal medulla

A
  • osmolarity is maintained at a very high level compared to that in the rest of the body
  • around 1200-1400 mOsm/L vs 300 mOsm/L
  • this gradient allows more water to be drawn out of the descending limb, while the structural nature of the ascending limb prevents it from getting back in, thus concentrating the urine
  • **the transporters in the thick ascending segment only have a capacity to maintain a 200 mOsm/L difference
66
Q

the distal tubule contains the ___ and thus, the ___

A
  • macula densa
  • juxtaglomerular apparatus
67
Q

T or F:

the kidneys are involved in the metabolism and excretion and secretion of systemic hormones

A

true

68
Q

what are 4 common metabolic waste products that the kidneys serve to excrete?

A
  • urea (protein metabolism)
  • uric acid (nucleic acid metabolism)
  • creatinine (muscle metabolism)
  • bilirubin (hemoglobin metabolism)
69
Q

what are 4 common foreign substances excreted by the kidney?

A
  • pesticides
  • food additives
  • toxins
  • drugs
70
Q

is the retention of HCO3- more or less important than H+ excretion in terms of renal control of pH?

A
  • it is more important
  • excreting 1HCO3- is basically the same as adding 1H+
  • the kidneys can also produce “new” HCO3- by metabolizing glutamine, which makes ammonium and bicarbonate
71
Q

describe the blood supply of the kidneys

A
  • supplied by renal artery which enters via the hilum
  • branches into afferent arterioles
  • branch into glomerular capillaries (supply nephrons, site of filtration)
  • glomerular capillaries feed into efferent arterioles
  • form peritubular capillaries (reabsorption/secretion occurs)
  • these ultimately return to the renal vein which passes back out of the hilum
72
Q

describe the hydrostatic pressure in the glomerular capillaries

A
  • it is much higher than in the peritubular capillaries (60 mmHg vs. 13 mmHg)
  • this is regulated by changes in the afferent/efferent arterioles
73
Q

describe filtration in the different segments of the nephron loop

A
74
Q

describe the transporters in the tubules

A
  • Na/K ATPase - primary active transporter
    • sets up gradients for secondary active transport
    • active transport of Na+ is linked to the reabsorption of many things, including glucose and H+ ions
  • co-transporter
    • brings glucose into the cell from the tubule with Na+ and it can diffuse out the other side back into the blood
  • counter-transport
    • H+ ions are excreted with Na+
75
Q

how does water traverse the proximal tubules?

A
  • it traverses the proximal tubule tight junctions in response to the osmotic force generated by Na+ and can drag some small solutes along with it
76
Q

T or F:
Na+ reabsorption is independent of the reabsorption of other things

A

false:

Na+ reabsorption is highly linked to the reabsorption of many other things

77
Q
A

Histology (5 decks)

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