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Physiology (MPP 3202) > Ch. 17 Renal System (Day 1) > Flashcards

Ch. 17 Renal System (Day 1) Flashcards

1
Q

Functions of the Kidneys (6)

A
  1. Regulation of extracellular fluid volume and BP
  2. Regulation of osmolarity
  3. Maintenance of ion balance
  4. Homeostatic regulation of pH
  5. Excretion of waste
  6. Production of hormones
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2
Q

Renal Structure

A

Gross anatomy: three clearly demarcated anatomical areas

Cortex constitutes the major portion of the kidney and receives a disproportionately higher percentage (90%) of the blood flow

Medulla (6-10%)

Papilla (1-2%)

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3
Q

Where does the nephron start? Where does it go?

A

Starts in cortex –> down to medulla –> back up to cortex –> repeats…

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4
Q

Overall path of renal circulation

A

Afferent arteriole –> Glomerulus (capillaries) –> Efferent article –> peritubular capillaries or vasa recta

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5
Q

Afferent vs. Efferent Arteriole

A

Afferent: going to glomerulus

Efferent: exiting glomerulus (to veins)
–Efferent = “E” for exit glomerulus

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6
Q

Renal Blood flow

A

22% of CO

Portal System: afferent articles –> glomerular bed –> efferent articles –> peritubular bed –> veins

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7
Q

Are tubular flow and blood flow the same, or are they 2 different things?

A

2 different things!!!!

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8
Q

Renal Filtration

A

Kidneys receive 22% of CO; unlike other organs, renal blood flow far exceeds metabolic demand

All blood flow is filtered through glomeruli; mechanisms that regulate renal blood flow (RBF) are closely linked to control of glomerular filtration rate (GFR)

(*Don’t worry about these absolute numbers, just get a general idea)

  • Renal blood flow: 1100 mL/min
  • Renal plasma flow: 605 mL/min (hematocrit: 45%)
  • Glomerular filtration rate: 125 mL/min
  • Filtration fraction: GFR/RPF (125/605 = 21%)

Higher GFR allows for precise control of fluid volume/composition and rapid removal of waste

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9
Q

Overall Renal Function

A

Formation of urine involves 3 basic processes:

  1. ultrafiltration of plasma by glomerulus
  2. reabsorption of water and solutes from ultra filtrate
  3. secretion of selected solutes into tubular fluid (active, requires energy)

Plasma filtered into tubular system

Need substances reabsorbed back into plasma, while wastes stay in, eventually excreted in urine

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10
Q

What cannot pass through the filter?

A

Proteins

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11
Q

Nephron Tubules and Associated Blood Vessels

A
  1. Glomerular (Bowman’s) capsule surrounds glomerulus. Together, they make up renal corpuscle
  2. Filtrate produced in renal corpuscle passes into the proximal convoluted tubule (PCT)
  3. Filtrate passes into descending and ascending limbs of Loop of Henle
  4. Filtrate passes into distal convoluted tubule (DCT)
  5. Finally, fluid passes into Collecting Duct
  6. Fluid is now urine and will drain into minor calyx
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12
Q

Glomerulus

A

Capillary bed; filtration

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13
Q

Proximal Tubule

A

Reabsorption (60%)
Secretion
Sodium and water similar

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14
Q

Loop of Henle

A

Descending limb is water permeable

Ascending limb is water impermeable

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15
Q

Distal Tubule/Collecting Duct

A

Water permeable in presence of ADH (vasopressin)

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16
Q

Equation of Secretion (*MEMORIZE)

A

Amount filtered (F) - Amount reabsorbed (R) + Amount secreted (S) = Amount of solute excreted (E)

F - R + S = E

17
Q

Pressure Differences in Nephron

A

Determine net filtration vs absorption

Increase change in pressure in glomerulus favors filtration. Lower pressure in tubules, but still greater than that in interstitial, yet don’t see filtration - see net absorption

Gradient differences are important

18
Q

Starling Forces

A 
Pc = capillary hydrostatic pressure
(pi)i = interstitial oncotic pressure (=0)
(pi)c = capillary plasma oncotic pressure (plasma proteins)
Pi = interstitial hydrostatic pressure

Net Filtration Pressure (NFP)

NFP = (Pc - Pi) - (pi(c) - pi(i)

So… NFP = Pc - Pi - pi(c)

19
Q

NFP in Glomerulus

A

NFP = Pgc - Pbc - (pi)gc

gc = glomerular capillaries
bc = Bowman's capsule

Net filtration from glomerular capillaries into Bowman’s capsule
–yields positive charge/number

20
Q

NFP in Peritubular Capillaries

A

NFP = Ppc - Pi - (pi)pc

pc = peritubular capillaries
i = interstitial fluid

Net absorption from interstitial space into particular capillaries
–yields negative charge/number

21
Q

Glomerular vs Peritubular capillary pressure and processes

A

Glomerular:

  • high capillary pressure
  • process: filtration

Peritubular:

  • low capillary pressure
  • process: absorption
22
Q

Glomerulus

A

Capillaries of glomerulus are fenestrated
–large pores allow water and solutes to leave but not blood cells and plasma proteins

Fluid entering the glomerular capsule called filtrate

23
Q

Which has protein: filtrate or plasma?

A

Plasma has protein (stays in capillaries)

Filtrate has NO proteins
–if protein found in urine, it’s a problem

24
Q

Glomerulus Filtration

A

Filters water and small solutes (ions, glucose, AAs, etc) while restricting passage of large molecules (proteins)
–proteins negatively charged, and so is basement membrane, so they can’t pass through b/c too large and b/c of charge repulsion

Basement membrane: primary barrier to large molecules, being both size and charge selective

Glomerular filtrate is similar to plasma in its composition, except no significant amount of protein

25
Q

Filtrate passes through?

A
  1. Capillary fenestrae
  2. Glomerular basement membrane
  3. Visceral layer of glomerular capsule composed of cells (podocytes) w/ extensions called pedicles
26
Q

Glomerular Filtration Rate (GFR)

A

Volume of glomerular filtrate formed per unit time - 125 mL/min or 180 L/day

Influenced by 2 factors:

  1. Net filtration pressure
    - -> capillary hydrostatic pressure - capillary plasma oncotic pressure - hydrostatic pressure in Bowman’s capsule
  2. Filtration coefficient
    - -> surface area of glomerular capillaries available for filtration (most important aspect of filtration coefficient)
    - -> permeability of interface between capillary and Bowman’s capsule
27
Q

Glomerular Filtration Fraction (GFF)

A

Fraction of renal plasma flow that becomes glomerular filtrate

Normal plasma flow through both kidneys = 650 mL/min

Normal GFR = 125 mL/min

GFF = (125/650) * 100 = 19%

If filtration fraction goes up, filtering out more fluid (protein concentration also increases), higher oncotic pressure/concentration

If filtration fraction decreases, filtering out less fluid (protein concentration also decreases), lower oncotic pressure/concentration

28
Q

Factors Affecting GFR

A

Kidneys can regulate hydrostatic pressure in glomerular and peritubular capillaries, thereby changing the rate of glomerular filtration and/or tubular reabsorption

Factor:

  • -renal blood flow; effect: as increase RBF, increase GFR
  • -constriction of afferent arterioles; effect: decrease GFR
  • -constriction of efferent arterioles; effect: increase or decrease GFR
29
Q

Effect of increasing renal blood flow on glomerular filtration

A

Increased flow rate increase Pgc and causes percentage increase in pi(gc)

Increase in GFR

30
Q

Effect of constriction of AFFERENT arteriole on glomerular filtration

A

Constriction reduces inflow to glomerular capillaries leading to decreased flow and decreased Pgc
–decrease in GFR

Possible causes:

  1. Activation of renal sympathetic nerves, e.g. fight or flight, brain ischemia, severe hemorrhage
  2. Vasoconstrictor substances: norepinephrine, epinephrine, endothelin
31
Q

Effect of constriction of EFFERENT arteriole on glomerular filtration

A

Constriction causes decreased flow through - fluid piles up which increases Pgc

As fluid filteres, get huge increase in (pi)gc which counteracts the increase in Pgc
–increase or decrease GFR

Cause: Angiotensin II

32
Q

GFR Regulation

A

Normally, GFR is fairly constant over a significant range of arteriole blood pressures: auto regulatory response

Myogenic response:

  • -intrinsic ability of vascular smooth muscle to respond to pressure changes
  • -similar to auto regulation in other systemic arterioles

Tubuloglomerular feedback:
–paracrine control

Hormones and autonomic neurons:

  • -by changing resistance in arterioles
  • -by filtering filtration coefficient
33
Q

Tubuloglomerular feedback

A

Macula densa cells sense change in flow rate and ion concentration in tubular fluid

34
Q

Sympathetic Nerve Effects

A
  1. In a fight/flight reaction –> vasoconstriction of afferent arterioles
  2. Helps divert blood to heart and muscles
  3. Urine formation decreases to compensate for drop in BP

Physiology (MPP 3202) (32 decks)

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