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human physiology and exercise > renal system > Flashcards

renal system Flashcards

1
Q

describe the renal system

A
  • in the kidney
  • acts as an integrative system
  • process plasma
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2
Q

what are the functions of kidneys?

A
  • regulate water concentration, inorganic ion compositions, acid base balance and fluid volume
  • excrete metabolic waste products into urine e.g. urea, creatine
  • urinary excretion of some foreign chemicals e.g. drugs, pesticides and food additives
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3
Q

what process is the renal system involved in?

A
  • gluconeogenesis during prolonged fasting
  • kidneys synthesis glucose from amino acids and other precursors and release it to blood
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4
Q

what do kidneys act as? what hormones do they release?

A
  • act as endocrine glands
  • release erythropoietin and dihydroxy vitamin D, renin
  • control blood pressure and sodium balance
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5
Q

what is the main functional unit of the kidney? what does it contain?

A
  • nephron (1 million in kidney)
  • renal corpuscle
  • tubule that extends from renal corpuscle
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6
Q

what is the glomerulus?

A
  • main plasma filtering unit
  • formed by network of small blood vessels enclosed within Bowmans capsule
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7
Q

what gives an added layer of filtration?

A
  • podocytes ; glomerulus very porous so elements such as sodium, glucose, aas further filtered
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8
Q

is efferent or afferent smaller?

A
  • lumen of efferent is smaller therefore high pressure is maintained
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9
Q

what is the driving force of ultrafiltration across glomerulus?

A
  • contraction of left ventricle creates arterial pressure
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10
Q

what is the proximal convoluted tubule?

A
  • site of bulk reabsorption
  • found in cortex
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11
Q

what takes place in proximal convoluted tubules?

A
  • active transport of filtrate occurs and reabsorption of water, amino acids, glucose into bloodstream
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12
Q

what happens in descending and ascending loop?

A
  • water diffuses out of descending loop
  • ascending loop reabsorbs Na+, Cl- and K+
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13
Q

describe the descending limb

A
  • generates hyperosmotic interstitial fluid in medulla; majority of water is removed
  • fluid reaches an equilibrium with adjacent interstitial fluid
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14
Q

describe ascending limb

A
  • where sodium, potassium and chloride is pumped out via net passive diffusion from tubule to interstitial fluid
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15
Q

what does solute removal from ascending limb cause?

A
  • hyperosmolarity of medulla
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16
Q

what limb of loop of henle is permeable to water?

A
  • descending limb is permeable so water diffuses out
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17
Q

what occurs in the distal convoluted tubule?

A
  • more sodium reabsorption occurs
  • increased by aldosterone
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18
Q

what happens in the collecting duct?

A
  • ADH acts
  • reabsorbs water as all remaining fluid enters collecting duct system which runs through hyperosmotic medulla to drain to pelvis
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19
Q

what state is the water in entering the collecting duct?

A
  • hyposomotic
  • due to sodium removal by active transport
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20
Q

what is the renal capsule?

A
  • contains glomerulus and renal tubule
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21
Q

what is the juxtaglomerular apparatus?

A
  • composed of macula densa and juxtaglomerular cells
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22
Q

what are juxtaglomerular cells?

A
  • mechanoreceptors (detect BP change)
  • found in afferent arteriole
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23
Q

what are macula densa cells?

A
  • chemoreceptors responding to changes in NaCl
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24
Q

describe differential handling in the kidney

A
  • substances can enter the tubule and be excreted by urine
  • substances can be completely reabsorbed
25
Q

how do you work out the amount excreted?

A

amount excreted = amount filtered + amount secreted - amount reabsorbed

26
Q

what are the three main processes of the renal system

A
  1. glomerular filtration
  2. tubular reabsorption
  3. tubular secretion
27
Q

what is GFR?

A
  • glomerular filtration rate
  • amount of blood filtered by glomeruli each minute
28
Q

what is the normal GFR for a healthy adult?

A

-120ml/min

29
Q

how do you work out the net filtration pressure?

A

net filtration pressure= change in hydrostatic pressure - change in osmotic force

30
Q

what happens to colloid osmotic pressure along glomerular capillaries?

A
  • it increases
31
Q

how many times a day do the kidneys filter the entire plasma?

A
  • 60 times
32
Q

how is osmotic pressure maintained during filtration?

A
  • through plasma proteins remaining in the plasma
33
Q

what factors affect the GFR?

A
  • capillary permeability
  • surface area of capillary bed
  • hydrostatic pressure that drives fluid out of capillaries
  • osmotic forces within capillaries
34
Q

what does low GFR show?

A
  • signifies a lack of functioning nephrons
35
Q

what law is GFR governed by?

A
  • Starling’s law; hydrostatic pressure difference across capillary wall vs protein difference across capillary wall
36
Q

what changes are GFR controlled by?

A
  • vascular changes
37
Q

why are glomeruli more efficient filters than other capillary beds?

A
  • filtration membrane has a large surface area and is very permeable to water/ solutes
  • glomerular pressure is higher so they produce 180L/day vs 3-4l/ day by others
38
Q

what is it called when blood cells or protein are found in urine? what does this indicate?

A
  • proteinuria
  • indicates a problem with filtration membrane
  • found in diabetes/ hypertension; signals kidney damage
39
Q

why would filtrate become dilute?

A
  • due to imbalance between sodium and water reabsorption in loop of Henle
  • produces hypoosmotic filtrate and more dilute as it flows through distal tubules
40
Q

when does urine have highest osmolarity?

A
  • in the morning
  • we secrete ADH during sleep
  • urine concentrated
41
Q

when does tubular reabsorption begin?

A
  • as soon as filtrate enters tubule cells
42
Q

what is paracellular transport?

A
  • transfer of molecules between adjacent cells
43
Q

what kind of process is tubular reabsorption ?

A
  • can be active or passive
44
Q

describe tubular secretion

A
  • H,ion, potassium and organic anions move from patibula capillaries into tabular lumen
45
Q

what is tubular secretion important for?

A
  • removing excess K+, controlling blood pH, disposing of drugs, excreting undesired substances
46
Q

where does reabsorption occur in tubules?

A
  • mainly in proximal tubule and loop of Henle
  • ensures masses of solutes and volume of water entering distal tubule are small
47
Q

what segment does fine tuning and why?

A
  • distal segments> determines amount of excreted in urine
48
Q

what is renal clearance?

A
  • amount of substance filtered per minute (mL/min)
49
Q

how do you work out renal clearance?

A

RC= (conc of substance in urine x flow rate of urine formation) / conc of substance in plasma

50
Q

what substances are used to determine renal clearance?

A
  • insulin, creatine
  • insulin more effective as creatine partly secreted/ reabsorbed
51
Q

what must the substance be to be useful for GFR?

A
  • not metabolised/ secreted by kidneys
  • nontoxic
  • small
  • easily measured in blood/ urine
52
Q

is clearance of a substance dependent of its plasma conc. ?

A
  • a substance like insulin is independent of its plasma conc.
53
Q

when can renal clearance ratio allow us to estimate GFR?

A
  • if substance is freely filtered
54
Q

what does it show if there is a net reabsorption of a substance?

A
  • clearance is less than GFR
55
Q

what is the filtration fraction?

A
  • proportion of plasma entering the kidneys and is filtered at the glomerulus
56
Q

how do you work out filtration fraction?

A

GFR/ renal plasma flow

57
Q

what is the typical filtration fraction?

A
  • 0.16 to 0.20 so 20 % of the blood entering the kidneys is filtered
58
Q

what happens to RPF and GFR with age?

A
  • declines with age
  • but rate of declines are such that filtration fraction remains constant

human physiology and exercise (18 decks)

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