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BIO > The Urinary System: Renal Physiology > Flashcards

The Urinary System: Renal Physiology Flashcards

1
Q

During the formation of urine

A

20-25% of resting cardiac output is delivered to the kidney
◦Every minute ~ 1.25 L of blood passes through
the kidneys (roughly half is plasma)
◦From this, 125 ml is filtered across the
glomerulus (~20% of plasma) and becomes filtrate (most is reabsorbed into the body)

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2
Q

Filtrate contains

A

Almost everything found in plasma (excluding proteins)

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3
Q

Of the 180 L of filtrate that is formed each day:

A

◦< 1% (1.5 L) leaves the body as urine
◦>99% is reabsorbed

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4
Q

The first process in urine formation & adjustment of blood composition is

A
  1. Glomerular filtration
    ◦ Produces cell- & protein-free filtrate
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5
Q

The 2nd process in urine formation & adjustment of blood composition is

A
  1. Tubular Reabsorption
    ◦ Selectively returns 99% of substances from filtrate → blood in renal tubules & collecting ducts
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6
Q

The 3rd process in urine formation & adjustment of blood composition is

A
  1. Tubular secretion
    ◦ Selectively moves substances from blood → filtrate in renal tubules & collecting ducts
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7
Q

A passive process in which hydrostatic pressure forces fluids & solutes through filtration membrane

A

Glomerular filtration
◦ Not energy requiring
◦ Non-selective (water & any solutes smaller than plasma proteins pass through)

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8
Q

The filtering out of blood cells is prevented by

A

The fenestrated endothelium of glomerular capillaries

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9
Q

The filtering out of negatively charged molecules (e.g., plasma proteins) is inhibited using

A

Negatively charged glycoproteins in the basement membrane (forces like opposing magnets)

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10
Q

Filtration of medium sized proteins is inhibited by

A

Filtration slits formed by the podocytes in the visceral layer of glomerular capsule

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11
Q

Pressure that is
◦Essentially glomerular blood pressure
◦The primary force pushing water & solutes out of
blood and across the filtration membrane

A

Glomerular hydrostatic pressure

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12
Q

Pressures that oppose GHP; try to move fluid back
into the glomerulus

A

Capsular hydrostatic pressure and blood colloid osmotic pressure

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13
Q

Positive net filtration pressure (NFP) is formed from

A

Fluid (blood plasma) moving from glomerulus → glomerular capsule

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14
Q

Glomerular filtration rate (GFR) is

A

The volume of filtrate formed each minute by all the glomeruli of the kidneys combined

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15
Q

Glomerular filtration rate (GFR) is directly proportional to

A
  1. Net filtration pressure – sensitive to hydrostatic pressure in glomerulus (controlled by the diameter of the afferent arteriole)
  2. Total surface area available for filtration
  3. Permeability of the filtration membrane
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16
Q

GFR is tightly regulated for two crucial, sometimes opposing needs:

A

◦ the need for a constant GFR to maintain extracellular homeostasis
◦ the regulation of blood pressure (↑GFR = ↓BP; ↓GFR =↑BP)

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17
Q

GFR is controlled by

A

changing glomerular hydrostatic pressure (GHP is controlled by the diameter of the afferent arteriole & renal blood flow)
◦↑afferent arteriole diameter =↑blood flow =↑GFR
◦↓afferent arteriole diameter =↓blood flow =↓GFR

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18
Q

Intrinsic controls regulating GFR

A

◦are renal autoregulation
◦act locally within kidney to maintain GFR

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19
Q

Extrinsic controls regulating GFR

A

◦are neural & hormonal regulation
◦nervous and endocrine systems maintaining BP
◦Take precedence over intrinsic controls when extreme changes in BP occur

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20
Q

The afferent arteriole smooth muscle is

A

stretch-sensitive & responds to changes in systemic blood pressure

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21
Q

During increased systemic blood pressure the intrinsic myogenic response is

A

◦Vascular smooth muscle stretches → contraction → afferent arteriole constriction →↓blood flow into nephron
◦ Reduced blood flow into nephron protects the glomeruli from damaging high blood pressure

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22
Q

During decreased systemic blood pressure the intrinsic myogenic response is

A

Vascular smooth muscle less stretched → relaxation → afferent arteriole dilation →↑blood flow into nephron
◦Increased blood flow into nephron helps maintain GFR

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23
Q

In tubuloglomerular feedback (intrinsic) the response of the macula densa cells of juxtaglomerular complex to filtrate NaCl concentration reflects

A

GFR
◦ As GFR↑, NaCl in filtrate↑

24
Q

In tubuloglomerular feedback (intrinsic) high filtrate NaCl:

A

Macula densa cells release vasoconstrictor chemicals → afferent arteriole constrict →↓blood flow to nephron & GFR

25
Q

In tubuloglomerular feedback (intrinsic) low filtrate NaCl:

A

Inhibited release of vasoconstrictor chemicals from macula densa cells → afferent arteriole dilate →↑blood flow to nephron & GFR

26
Q

The baroreflex acting to increase BP when blood pressure is low is

A

extrinsic regulation via sympathetic nervous system controls

27
Q

In SNS extrinsic regulation increased sympathetic activity via increased blood pressure leads to

A

increased norepinephrine & epinephrine causing vasoconstriction of systemic arterioles
◦ ↑ total peripheral resistance to ↑ systemic blood pressure

28
Q

In the kidneys increased sympathetic activity (extrinsic) leads to

A

◦ vasoconstriction of afferent arterioles →
↓ blood flow to nephron → ↓ GFR ◦ ↓ urine output to ↑ blood volume → ↑ systemic BP ◦ blood flow redirected to other vital organs

29
Q

Extrinsic regulation
Renin-angiotensin- aldosterone mechanism is:

A

hormones released in response to decreased systemic BP/blood volume in effort to increase

30
Q

in regulation via the (extrinsic)
Renin-angiotensin- aldosterone mechanism aldosterone increases BP/volume via

A

increasing Na + & H2O reabsorption

31
Q

in regulation via the (extrinsic)
Renin-angiotensin- aldosterone mechanism angiotensin II increases BP/volume via

A

peripheral vasoconstriction

32
Q

The three pathways that activate the renin that is released from
juxtaglomerular cells in reponse to low systemic BP

A

◦ Sympathetic nervous system – as part of baroreflex
◦ Activated macula densa cells (low Na+ in filtrate
representing low GFR)
◦ Reduced stretch (due to low BP)

33
Q

Different regions of the nephron tubules & collecting ducts secrete or absorb different molecules because there are

A

different specific transport proteins & channels in
the epithelial cell membranes at different parts of the nephron

34
Q

Excretion is

A

the solutes & fluid that drain into the
minor & major calyces & renal pelvis and are excreted
as urine

35
Q

Tubular reabsorption begins when

A

The filtrate enters the proximal convoluted tubule

36
Q

In which tubule is nearly all organic nutrients (e.g., glucose & amino acids) reabsorbed

A

proximal convoluted tubule

37
Q

processes included in tubular reabsorption in the PCT are:

A

◦ Transcellular (across/through) or paracellular (through spaces between cells) routes
◦ Active & passive tubular reabsorption

38
Q

healthy urine does not contain

A

amino acids, proteins, glucose

39
Q

◦ Transport across apical membrane → diffusion
through cytosol → transport across basolateral membrane

A

Transcellular (through cells) route in tubular reabsorption

40
Q

◦ Solute moves between tubule cells through
leaky tight junctions
◦ Particularly in PCT some charged molecules that can’t get across charged cell membrane (H2O, Ca2+, Mg2+, K+, & some Na+)

A

Paracellular (in between cells) route in tubular reabsorption

41
Q

Passive tubular reabsorption is

A

◦ Not energy requiring
◦ Molecules move down their electrochemical gradients via diffusion, facilitated diffusion, or osmosis

42
Q

Active tubular reabsorption is

A

◦ primary active transport: Direct use of ATP
◦ secondary active transport: Indirect use of ATP

43
Q

the most abundant cation in filtrate; most energy is used to actively reabsorb it via transcellular mechanism

A

Na+

44
Q

Na+ is transported via

A

◦ primary active transport across basolateral membrane with Na+-K+-ATPase
◦ Bulk flow of H2O sweeps it into the adjacent peritubular capillary

45
Q

Active pumping of Na+ out of cell creates a gradient for

A

Na+ to diffuse into cell across apical membrane
◦ secondary active transport for cotransport of glucose, amino acids, some ions, & vitamins

46
Q

H2O is reabsorbed via

A

◦ osmosis (gradients created by reabsorption of Na+ & other solutes)
◦ passive tubular reabsorption

47
Q

Aquaporin water channels for H2O reabsorption are abundant in the

A

PCT
◦ Obligatory water reabsorption

48
Q

The collecting duct contains inactive aquaporins stored in cytoplasm that are activated by

A

Antidiuretic hormone (ADH)
◦ Facultative water reabsorption

49
Q

Passive tubular reabsorption of solute occurs due to

A

higher solute content as H2O is reabsorbed
◦ Creates concentration gradients for solutes to
move into tubule cell & peritubular capillaries (fat-solubles, ions, & urea)
◦ allows fat-soluble drugs & environmental pollutants
to be reabsorbed as well

50
Q

Reabsorption via transport proteins is limited by

A

Transport maximums: when concentration of solute in urine exceeds the saturation point of the transporters, excess is lost in the urine
◦ E.g., water soluble vitamins – taking more doesn’t mean you “get” more

51
Q

Tubule most active in tubular reabsorption:

A

PCT
◦ Nearly all glucose, amino acids, & vitamins; 65% of
H2O & Na+

52
Q

In the nephron loop/loop of Henle absorption of H2O takes place in the

A

Descending limb
◦ permeable to H2O but not ions

53
Q

In the nephron loop/loop of Henle absorption of ions takes place in the

A

Ascending limb
◦ impermeable to H2O but passive &
active transport of ions

54
Q

In the DCT & collecting duct – Na+ & H2O permeability is regulated by

A

Hormones
◦ aldosterone: monitors Na+ content
◦ ADH: adds/removes aquaporins

55
Q

Tubular secretion (reabsorption in reverse) is most active in the

A

PCT (also occurs in other areas of nephron)

56
Q

Purpose of tubular secretion is to dispose of

A

Unwanted solutes and reabsorbed solutes
◦ Protein-bound substances (such as drugs &
metabolites)
◦ Urea & uric acid
◦ Excess K +
◦ Excess H + or HCO3- to control the blood pH

BIO (12 decks)

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