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Physiology 2130 > Module 11 > Flashcards

Module 11 Flashcards

1
Q

List the organs involved in the renal system

A

Kidneys, ureters, bladder, and urethra

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2
Q

List the principal functions of the kidneys

A

Regulation of water balance, electrolyte levels, pH of the blood, and long-term regulation of arterial pressure

Basic function is to remove nonessential substances from plasma (waste metabolites, excess water, electrolytes), recover any essential substance (like glucose), elimination of waste or foreign substances (drugs, food additives, vitamins), and endocrine hormone production (erythropoietin, renin, vitamin D, stanniocalcin)

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3
Q

Name the different areas within the kidney

A

Renal cortex and medulla

Nephrons drain into collecting ducts, draining into calyces that connect to the renal pelvis then to the ureter

Renal pyramids with renal papillae at their tips

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4
Q

Describe the flow of blood through the kidney

A

Enters through renal artery, branches into interlobar arteries (between renal pyramids) then arcuate arteries (top of pyramid in cortex), then interlobular arteries that supply the nephron capillaries. After the nephron, flows into interlobular vein, arcuate vein, interlobar vein, then large renal vein

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5
Q

List the functions of the nephron

A

Filter blood, reabsorb essential substances, and excrete nonessential molecules and waste

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6
Q

Describe the structure of a nephron, starting at the blood source

A

Glomerular capsule surrounds glomerulus, collectively called the renal corpuscle, followed by tubes: proximal convoluted tubule, descending and ascending limbs of the loop of Henle, distal convoluted tubule, and collecting duct

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7
Q

Describe the blood supply surrounding the nephron

A

Blood in afferent arteriole leads to glomerulus, then leaves via the efferent arteriole to peritubular capillaries, a dense network that surrounds tubes of the nephron, which drains into the interlobular vein

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8
Q

Define filtration

A

The movement of fluid through the glomerular capillary due to hydrostatic pressures

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9
Q

Define filtrate

A

The solution created by filtration, composed of water plus all dissolved solutes in the blood (except large proteins too big to be filtered)

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10
Q

Define reabsorption

A

The movement of substance from the lumen of the nephron back into the blood

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11
Q

Define secretion

A

The movement of a substance from the blood into the lumen of the nephron

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12
Q

Define excretion

A

The removal of substances from the body

Excretion = Filtration + Secretion - Reabsorption

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13
Q

Define glomerular filtration

A

The bulk flow of fluid from the blood into the glomerular capsule, where the filtrate contains the same substances as plasma except for large proteins and RBCs

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14
Q

List the factors affecting glomerular filtration

A

The permeability of capillaries in the glomerulus (many fenestrations in glomerular epithelial cells), larger diameter afferent arteriole and smaller diameter efferent arteriole, podocytes (special epithelial cells surrounding capillaries, have large filtration slits formed between pedicles), and Starling Forces

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15
Q

Explain Starling Forces in the glomerular capsule and name the different forces

A

They cause bulk movement of fluid across capillaries due to combination of hydrostatic and colloid osmotic forces

Two hydrostatic pressures (blood hydrostatic pressure and capsular hydrostatic pressure) and one colloid osmotic force (colloid osmotic pressure due to plasma proteins, none in glomerular capsule because few proteins are filtered)

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16
Q

Describe the blood hydrostatic pressure in the glomerular capsule

A

Pressure due to the difference in diameter of the afferent and efferent arterioles

Causes filtration

Approx 60mmHg (almost 2x a regular capillary)

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17
Q

Describe the colloid osmotic pressure in the glomerular capsule

A

Due to plasma proteins in the glomerulus

Causes reabsorption

Approx -32mmHg (shown as negative to show direction)

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18
Q

Describe the capsular hydrostatic pressure in the glomerular capsule

A

Pressure due to the confined space of the glomerular capsule as it fills with filtrate

Causing reabsorption

Approx -18mmHg (shown negative to show direction)

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19
Q

Describe the equation for net filtration pressure (NFP) in the glomerular capsule

A

NFP = BHP - COP - CP

If positive, net filtration, if negative, net reabsorption

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20
Q

Define glomerular filtration rate (GFR)

A

The volume of fluid filtered by the glomerulus during a certain time period

Roughly 180L/day

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21
Q

Describe the equation for filtered load

A

Filter load = GFR x plasma concentration of the substance

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22
Q

Define urine concentration

A

The amount of solute excreted per unit volume of urine (g/L)

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23
Q

Define amount of solute excreted and describe the equation

A

The actual amount (in grams) of solute excreted in urine

Amount excreted = Urine Concentration x Amount of water excreted per day (1.8 L/day)

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24
Q

Define amount reabsorbed and describe the equation

A

The amount of filtered substance that is taken back up by the kidneys

Amount Reabsorbed = Filtered Load - Amount Excreted

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25
Q

Describe the equation for fraction excreted

A

Fraction Excreted = (Amount Reabsorbed/Filtered Load) x 100%

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26
Q

List the substances reabsorbed and secreted in the proximal tubule

A

Reabsorbed: glucose, amino acids, Na+, K+, Cl-, HCO3-, H2O

Secreted: H+

66% of total filtrate is reabsorbed

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27
Q

List the substances reabsorbed and secreted in the descending limb of the loop of Henle

A

Reabsorbed: H2O (15% of filtered water)

Secreted: nothing

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28
Q

List the substances reabsorbed and secreted in the ascending limb of the loop of Henle

A

Reabsorbed: Na+, K+, and Cl- (20% of the filtered Na+, and 25% of all Na+, K+ and Cl- due to co-transporter)

Secreted: H+ and K+

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29
Q

List the substances reabsorbed and secreted in the distal tubule

A

Reabsorbed: Na+, HCO3-, and H2O (12% of Na+ filtered at glomerulus)

Secreted: H+ and K+

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30
Q

List the substances reabsorbed and secreted in the collecting duct

A

Reabsorbed: H2O and Na+ (10% of filtered Na+ and water)

Secreted: H+ and K+

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31
Q

List the transport routes taken for reabsorption in the nephron

A

Paracellular transport and transcellular transport

Also secondary active transport using the Na+/K+ pump

32
Q

Describe paracellular transport

A

Tubular cells are joined together by tight junctions that generally don’t allow substances to cross, but along nephrons, they vary and can be leaky, allowing some substances to diffuse between cells

Generally non-regulated (no hormonal control)

33
Q

Describe transcellular transport

A

Some substances are transported across the tubular cell membrane from the lumen into the cell, then into the interstitial fluid and into the blood

Can be regulated by hormones, but most of the time are non-regulated

34
Q

Describe secondary active transport for reabsorption in the nephron

A

Na+ concentration gradient established by the Na+/K+ pump used to power other transporters. As Na+ moves down its concentration gradient, other substances either move with Na+ or move out in exchange with incoming Na+

35
Q

List examples of secondary active transporters in the nephron

A

Na+/Glucose co-transporter and the Na+/H+ exchanger, both on the luminal side of tubule cells

Na+/Amino acid co-transporter

36
Q

List the areas of the nephron where Na+ is reabsorbed, and whether it is regulated or unregulated

A

Proximal tubule, ascending limb of the loop of Henle, and the early distal tubule

Mostly non-regulated, can be regulated in proximal tubule by AngII and in distal tubule by aldosterone

37
Q

List the areas of the nephron where water is reabsorbed and whether it is regulated or non-regulated

A

Proximal tubule and descending limb of the loop of Henle (non-regulated) and in the late distal tubule and collecting duct (regulated by ADH)

38
Q

List the areas of the nephron where K+ is reabsorbed

A

Proximal tubule and the ascending limb of the loop of Henle

39
Q

List the areas of the nephron where K+ is secreted and whether it is regulated or non-regulated

A

In small amounts in the ascending limb of the loop of Henle (non-regulated) and in larger amounts in the late distal tubule and collecting duct (regulated with aldosterone)

40
Q

List the areas of the nephron where H+ is secreted and whether it is regulated or non-regulated

A

Proximal tubule and ascending limb of the loop of Henle (regulated and non-regulated) and in the late distal tubule and collecting duct (complex mechanisms)

41
Q

List the areas of the nephron where glucose and amino acids are reabsorbed

A

All glucose and amino acids filtered at the glomerulus is reabsorbed in the proximal tubule in a healthy individual

42
Q

Describe how glucose and amino acids are reabsorbed in the proximal tubule

A

Na+/Glucose co-transporter (can be regulated by AngII) and Na+/amino acid co-transporter

43
Q

Describe how Na+ is reabsorbed in the proximal tubule

A

Due to Na+/K+ pump, the Na+ concentration gradient allows Na+ to be reabsorbed by simple diffusion

44
Q

Describe why glucose in urine is a sign of diabetes mellitus

A

Diabetes is a disease affecting the production of insulin, which stores glucose after a meal, so without it glucose concentration builds up in the blood. When lots of glucose is filtered at the glomerulus, it saturates the Na+/glucose co-transporter, so not all cal be reabsorbed and some is excreted in urine

45
Q

Describe how water is reabsorbed in the proximal tubule

A

After reabsorbing Na+, glucose and amino acids, filtrate has a lower solute concentration and higher water concentration compared to cell and interstitial fluid, so with this osmotic gradient and aquaporins (special water channels), water moves down concentration gradient by osmosis (simple diffusion)

Reabsorbed both by paracellular and transcellular transport, and only takes place after solutes have been reabsorbed

46
Q

Describe how K+ and Cl- are reabsorbed in the proximal tubule, and whether it’s regulated or non-regulated

A

Through 2 types of paracellular transport, both non-regulated: solvent drag and simple diffusion

Cl- is also reabsorbed by transcellular transport

65% of all filtered K+ and Cl- are reabsorbed in the proximal tubule

47
Q

Define solvent drag

A

The reabsorption of K+ with movement of water being reabsorbed by osmosis; as it moves between cells, the water carries with it some dissolved substances in the filtrate

48
Q

Describe how reabsorbed substances return to circulation from the proximal tubule

A

Starling Forces, with pressures different than around regular capillaries

In kidney, capillary hydrostatic force (Pc) is 13mmHg, interstitial hydrostatic force (PIF) is 6mmHg, osmotic force due to proteins in plasma (πp) is 32mmHg, and interstitial osmotic force (πIF) is 15mmHg

Equation: NFP = (Pc - PIF) - (πp - πIF)
Results in -10mmHg back into the capillary

49
Q

Describe reabsorption of ions and water in the descending limb of the loop of Henle

A

Descending limb is very permeable to water and not very permeable to any ion, so water will move out by osmosis into interstitial space, and very few ions will diffuse out

End result is water loss from filtrate, increasing concentration of filtrate from 300mOsm/kg water to almost 1200mOsm/kg water

50
Q

Describe reabsorption of Na+, K+, Cl- and water in the ascending limb of the loop of Henle

A

Ascending limb is not permeable to water, so no water movement, but very permeable to Na+, K+ and Cl-, and their movement depends on the Na+/K+ pumps in tubule cells, creating a concentration gradient for Na+ to drive a specific cotransporter, the Na+/K+/Cl- co-transporter

Due to both the pump and co-transporter, K+ concentration increases in tubule cells dramatically, so some will be secreted back out into filtrate by simple diffusion

Filtrate concentration decreases from 1200mOsm/kg water to 100mOsm/kg water

51
Q

Describe reabsorption of Na+ and water in the distal tubule

A

Reabsorption of water is controlled by ADH, depends on hydration of the individual, amount varies from 0-15% of the original filtrate

Na+ is reabsorbed in early distal tubule by simple diffusion due to concentration gradient, but in late distal tubule, is regulated by aldosterone, which increases the activity of the Na+/K+ pump, decreasing concentration of Na+ in the cell, and causes cell to manufacture more Na+ channels to allow easier diffusion

52
Q

Describe secretion of K+ in the distal tubule

A

Aldosterone causes secretion of K+ into the lumen by increasing the number of K+ channels in the luminal membrane

53
Q

Describe the reabsorption of water and Na+ in the collecting duct

A

Always regulated by hormones

Na+ reabsorption by aldosterone
Water reabsorption by ADH

Increase in either hormone increases reabsorption

54
Q

Describe the secretion of K+ in the collecting duct

A

Takes place due to aldosterone

Increases Na+/K+ pump activity on basal side of collecting duct cells, increasing intracellular K+ concentration, manufactures more K+ channels, allowing K+ to leak out down concentration gradient into lumen of collecting duct

55
Q

List the mechanisms by which Na+ is handled by the nephron

A 
Proximal tubule:
Na+/glucose co-transporter
Na+/amino acid co-transporter
Na+/H+ exchanger
Simple diffusion of Na+

Ascending limb:
Na+/K+/Cl- co-transporter

Distal tubule:
Na+ under influence of aldosterone

All reabsorption

56
Q

List the mechanisms by which glucose and amino acids are handled by the nephron

A

Proximal tubule:
Na+/glucose co-transporter
Na+/amino acid co-transporter

All reabsorption, in a healthy individual all of both is completely reabsorbed

57
Q

List the mechanisms by which water is handled by the nephron

A

Proximal tubule:
Non-regulated osmosis

Descending limb:
Non-regulated osmosis and aquaporins

Distal tubule and collecting duct:
Regulated by ADH

All reabsorption

58
Q

List the mechanisms by which K+ is handled by the nephron

A

Proximal tubule:
Solvent flux/drag and simple diffusion (reabsorption)

Ascending limb:
Na+/K+/Cl- co-transporter (reabsorption)
Simple diffusion (secretion)

Distal tubule and collecting duct:
Regulated by aldosterone, creating more K+ channels (secretion)

59
Q

List the mechanisms by which H+ is handled by the nephron

A

Proximal tubule and ascending limb:
Na+/H+ exchanger, activity increased by AngII

Distal tubule and collecting duct:
Complex mechanism

All secretion

60
Q

Describe the concept of water balance

A

In order to have water balance, water lost must be balanced by water gained to maintain homeostasis of body fluids

61
Q

List ways that water is gained

A

Drinking, eating, and by metabolism of energy stores

62
Q

List ways that water is lost

A

Through urine, sweating, lungs, and feces

63
Q

Describe how kidneys regulate water balance

A

Kidneys don’t produce water, only reabsorb it, and that is regulated by ADH (produced in hypothalamus, released from posterior pituitary) by negative feedback using osmoreceptors

64
Q

Describe osmoreceptors and their function

A

Sensors to detect changes in body fluid concentrations, located in the hypothalamus, and will determine the release of ADH

Osmoreceptors will shrink or swell depending on osmolarity of body fluids, which signals the release or inhibition of ADH

65
Q

Describe how dehydration will affect release of ADH

A

Dehydration concentrates body fluids, increasing osmolarity, causing osmoreceptors to lose water by osmosis and shrink, signalling posterior pituitary to release ADH, which causes kidneys to reabsorb more water from distal tubule and collecting ducts, resulting in lower blood volume and pressure

66
Q

Describe how overhydration will affect release of ADH

A

Overhydration dilutes body fluids, decreasing osmolarity, causing osmoreceptors to swell, less ADH is released, less water reabsorbed in distal tubule and collecting duct, more water excreted in urine, resulting in increased blood volume and pressure

67
Q

List the receptors detecting changes in body fluids to influence ADH release

A

Changes in blood volume are detected by volume receptors in the walls of the left atrium, and lower blood volume causes release of ADH

Osmoreceptors in the hypothalamus detect osmolarity of body fluids, and high osmolarity (causing them to shrink) causes release of ADH

68
Q

Describe how ADH affects cells

A

Causes water reabsorption in distal tubule and collecting duct by acting directly on cells in the regions

Stimulates cells to manufacture aquaporins, which insert into the luminal membrane

This leads to more water reabsorbed by osmosis and less excreted in urine, due to the existing concentration gradient across luminal cells (low solutes outside, high solutes inside)

Reabsorbed water enters peritubular capillaries due to Starling Forces

69
Q

Explain how alcohol affects ADH

A

Alcohol inhibits the release of ADH from the pituitary gland, causing people to urinate more after drinking alcohol, due to less aquaporins in the distal tubule and collecting duct, less water reabsorbed and more excreted in urine

70
Q

Name the system that regulates Na+ levels in the body

A

The renin-angiotenson system (RAS) and aldosterone, which combined are the renin-angiotensin-aldosterone system (RAAS)

71
Q

Describe aldosterone and its purpose

A

A steroid hormone produced by the adrenal glands, secreted into circulation when blood Na+ levels are low or blood K+ levels are high to help return ion concentration to normal

It is secreted in response to AngII and in small amounts by ACTH

72
Q

Describe how aldosterone functions

A

Returns Na+ and K+ concentrations to normal by causing Na+ reabsorption and K+ secretion in distal tubule and collecting duct, by causing tubule cells to manufacture more Na+ and K+ channels for the luminal membrane, so they move down their concentration gradients

Also increases Na+/K+ pump activity

73
Q

Describe the RAS’s function

A

Regulates Na+ balance in the body by increasing reabsorption of Na+ in the proximal tubule, by converting inactive protein angiotensinogen into active hormone AngII

74
Q

Describe how the RAS functions

A

Angiotensinogen (produced by liver) reacts with renin (produced by juxtaglomerular cells in walls of afferent and efferent arterioles)

Renin is released when blood pressure or plasma Na+ levels are low, and converts angiotensinogen to AngI, which is converted to AngII by angiotensin converting enzyme (ACE, produced in lungs)

The final product AngII increases reabsorption of Na+ in proximal tubule and ascending limb

75
Q

Describe the effects of angiotensin II to reabsorb Na+

A

Acts directly on proximal tubule and ascending limb cells to increase Na+/H+ exchanger activity, reabsorbing more Na+ and secreting H+

AngII also stimulates secretion of aldosterone from the adrenal gland, which will act on distal tubule and collecting duct cells to reabsorb Na+ and secrete K+

76
Q

Describe the effects of angiotensin II on the rest of the body

A

Released when blood pressure is low

AngII is a potent vasoconstrictor, constricts vessels, increasing total peripheral resistance, which increases blood pressure

Stimulates sensation of thirst to trigger drinking to increase blood volume and blood pressure

Stimulates release of ADH from posterior pituitary, causing reabsorption of water by kidneys and absorption of water and Na+ from the digestive tract

Physiology 2130 (16 decks)

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