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Human Physiology > Urinary System > Flashcards

Urinary System Flashcards

1
Q

What are the 6 main functions of the kidney

A

Regulating ECF volume and blood pressure, regulating osmolarity, maintaining ion balance (Na+, K+, and Ca2+), regulating pH (H+ and HCO3-), excreting wastes, and producing hormones

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2
Q

What are metabolic wastes excreted by the kidneys

A

Creatinine (from skeletal muscles) and nitrogenous wastes like urea and uric acid (from protein breakdown)

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3
Q

What are xenobiotics

A

Foreign substances like drugs, environmental toxins, saccharin, and potassium benzoate

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4
Q

What is involved in production of hormones in the kidney

A

Renin (enzyme regulating hormones for Na+ balance and BP regulation) and erythropoietin (controls erythropoiesis/ the RBC production in bone marrow)

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5
Q

What are the key functions of the nephron

A

To filter blood by keeping water, sugars, vitamins, amino acids, and other vital substances while eliminating excess water, salts, minerals, urea, uric acid, creatinine, hormone waste, toxins, xenobiotics, etc.

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6
Q

What are the 4 steps that take place in a nephron

A

Filtration (Moving from blood to lumen), reabsorption (from lumen to blood), secretion (from blood to lumen), and excretion (from lumen to outside of body)

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7
Q

Describe filtration

A

First step in forming urine, takes place in a glomerulus (network of capillaries) surrounded by nephron (Bowman’s capsule), creates filtrate, leaving blood cells and most plasma proteins in capillary

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8
Q

What is filtrate

A

Filtered plasma (H2O and dissolved solutes) that is isosmotic with plasma

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9
Q

What is the filtration fraction

A

% of plasma that is filtered into Bowman’s capsule from capillary (~20%)

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10
Q

What would happen if you filtered and removed 100% of plasma from blood

A

Blood would turn into sludge of cells and proteins

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11
Q

What is the renal corpuscle

A

Glomerular capillaries surrounded by Bowman’s capsule

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12
Q

What drives filtration

A

Net filtration pressure (~10mmHg) = hydrostatic pressure - colloid osmotic pressure - capsule fluid pressure

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13
Q

What is hydrostatic pressure

A

Blood pressure (MAP) that pushes water and solutes out of capillaries

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14
Q

What is colloid osmotic pressure

A

Oncotic pressure due to plasma proteins that opposes hydrostatic pressure

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15
Q

What is capsule fluid pressure

A

Fluid within Bowman’s capsule that opposes more fluid movement in

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16
Q

What is bulk flow

A

Mass movement due to pressure gradient

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17
Q

What is glomerular filtration rate (GFR)

A

Volume of fluid filtered per unit time = Filtration pressure * Filtration coefficient, fairly constant over range of MAPs

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18
Q

What is autoregulation

A

Local kidney control process to maintain relatively constant GFR by regulating blood flow through renal arterioles (dilate, increases P(H), increases GFR, increases RBF)

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19
Q

What are the 2 autoregulation mechanisms

A

Myogenic response (Inherent ability of vascular smooth muscle to respond to pressure changes and alter blood flow) and tubuloglomerular feedback (paracrine signaling mechanism caused by changes in fluid flow through loop of Henle)

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20
Q

How does the Myogenic response react due to increased MAP (5 steps)

A

Stretch afferent arteriole smooth muscle opens stretch-sensitive ion channels, muscle cells depolarize opening voltage-gated Ca++ channels, vascular smooth muscle contracts, causing vasoconstriction that increases resistance to flow

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21
Q

What effect does vasoconstriction of the afferent arteriole have

A

Decrease RBF, decreased filtration pressure (because decreased hydrostatic pressure), and decreased GFR

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22
Q

Why is local control in the kidneys possible

A

Because of the twisted configuration of the nephron (ascending limb close to renal corpuscle)

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23
Q

Paracrine signaling occurs between the afferent arteriole and what cells to change arteriole diameter and influence GFR

A

Macula densa cells

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24
Q

What is the function of macula densa cells

A

To sense distal tubule flow and release paracrine that affect afferent arteriole diameter

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25
Q

What cells in the juxtaglomerular apparatus secrete renin

A

Granular cells

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26
Q

Describe the 4 steps of tubuloglomerular feedback response to increased GFR

A

Macula densa cells sense increased tubular flow rate (NaCl), release more ATP and adenosine, and decrease nitric oxide secretion, which binds to receptors on afferent arteriole smooth muscle to cause vasoconstriction

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27
Q

What does nitric oxide do

A

Cause vasodilation of afferent arteriole in the kidney

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28
Q

Reabsorption happens between the nephron and what kind of capillaries

A

Peritubular capillaries

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29
Q

Where does reabsorption occur in a nephron

A

Proximal tubule, the loop of Henle, distal tubule, and collecting duct

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30
Q

Where does most reabsorption of fluid reoccur

A

Proximal tubule

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31
Q

How is H2O reabsorbed

A

Passively via osmosis

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32
Q

Other than osmosis, what other kind of transport is involved in reabsorption

A

Passive and/or active transepithelial transport (depending on solute electrochemical gradient)

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33
Q

How is Na+ resorbed

A

Passive facilitated diffusion (uses NHE and ENaC) from filtrate into ICF, then secondary active transport (Na/K ATPase) from ICF to ECF

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34
Q

What is the main driving force for most renal reabsorption

A

Na+ (99% is reabsorbed)

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35
Q

What percent of Na+ is resorbed in the proximal tubule and what is its role (6 things)

A

67%, it plays role in reabsorbing glucose, amino acids,H20, Cl-, K+, and urea

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36
Q

What percent of Na+ is resorbed in the ascending loop of Henle and what is its role

A

25%, plays key role in ability to produce urine of varying concentrations

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37
Q

What percent of Na+ is resorbed in the distal and collecting tubules and what is its role

A

8%, role varies (based on hormonal control), but helps regulate ECF volume

38
Q

How is glucose reabsorbed

A

Via secondary active transport (Na+-linked secondary active transport / “SGLT transporter) from lumen into ICF, then GLUT passive facilitated diffusion from ICF to ECF

39
Q

Reabsorption of what molecules relies on Na+-linked secondary active transport

A

Glucose, amino acids, ions, etc.

40
Q

What is renal threshold

A

Plasma concentration at which saturation of transporters occurs

41
Q

What is transport maximum

A

The transport rate at saturation

42
Q

How is glucose handled by a nephron

A

Filtration proportional to plasma concentration (can’t saturate), reabsorption also proportional until transport maximum is reached (~300mg/100mL plasma), and only exerted once renal threshold is reached

43
Q

Is glucose ever secreted

A

No

44
Q

What is glucosuria

A

Lots of glucose in the urine

45
Q

Which is selective, filtration or secretion

A

Secretion (uses transporters)

46
Q

Where does secretion occur

A

Proximal tubule, distal tubule, and collecting duct

47
Q

What kind of transport is involved in secretion

A

Active transport

48
Q

What 2 things is secretion important for

A

Homeostatic regulation (K+ and H+) in the collecting duct, and organic anion & cation elimination (hormones and xenobiotics) in proximal tubules

49
Q

What is filtrate referred to after it leaves the collecting duct and why

A

Urine because composition can no longer be altered

50
Q

Where does excretion occur

A

Collecting duct

51
Q

What is renal handling

A

The amount of substance in urine = amount filtered - amount reabsorbed + amount secreted

52
Q

What is clearance

A

Rate at which substance is cleared from the body by excretion (Excretion rate * Concentration)

53
Q

What is clearance used for

A

To determine how a nephron handles a substance that’s filtered into it (drug clearance and non-invasive way to measure GFR)

54
Q

What is another word for micturition

A

Urination

55
Q

What is micturition

A

A simple spinal reflex, under conscious and unconscious control from higher brain centers

56
Q

At rest, describe the sensory input to the bladder, internal sphincter, and external sphincter

A

External sphincter tonically active, internal sphincter passively active, bladder wall inactive

57
Q

What happens when stretch receptors in the bladder wall activate

A

Parasympathetic neurons contract smooth muscle in the bladder wall (in waves) and relax the internal sphincter, urine forces the internal sphincter open, somatic neurons to external sphincter are inhibited and it relaxes

58
Q

What hormone effects blood ECF volume

A

Vasopressin

59
Q

What changes disturb fluid and electrolyte homeostasis

A

Blood (ECF) volume affects blood pressure and osmolarity affects tonicity and membrane potentials

60
Q

What 3 hormone/systems effect osmolarity

A

Aldosterone, atrial natriuretic peptide, and renin-angiotensin system

61
Q

What 3 systems/responses integrate fluid and electrolyte balance

A

Cardiovascular system, behavioral responses, and kidney responses

62
Q

What does vasopressin do and where

A

It is an anti-diuretic hormone produced by the posterior pituitary that controls H2O reabsorption in the collecting duct and distal tubules

63
Q

How do kidneys maintain homeostasis of H2O

A

They can conserve or excrete it but can’t replace it

64
Q

What change does an increased secretion of vasopressin have on the distal nephron and collecting ducts

A

Increases the permeability of the collecting duct epithelium to water so that it is conserved rather than excreted (prevents reabsorption)

65
Q

How does vasopressin change the epithelium’s permeability to water

A

By inserting aquaporins (water pores) through a cAMP secondary messenger pathway that results in exocytosis

66
Q

What are the 3 stimuli to conserve fluid

A

Increased ECF osmolarity, decreased BP (baroreceptor stretch), and decreased blood volume (atrial stretch)

67
Q

What effect does ingested salt (NaCl) have on blood osmolarity

A

It increases

68
Q

What triggers thirst in the hypothalamus

A

Angiotensin II

69
Q

What are the 2 responses to increased blood osmolarity

A

Increased vasopressin release and thirst to conserve and bring in more water (both will also increase ECF volume and blood pressure)

70
Q

What is K+ important for and what is it controlled by

A

Maintaining membrane potentials, controlled by aldosterone

71
Q

What is Na+ important for in electrolyte homeostasis and what controls it

A

Important for ECF volume and osmolarity, controlled by aldosterone, RAS pathway, and ANP

72
Q

What does aldosterone do

A

Acts on principal (P) cells of the collecting duct to increase Na+ reabsorption and K+ secretion in distal nephron

73
Q

What produces aldosterone

A

Adrenal cortex

74
Q

What are the 3 stimuli for aldosterone

A

Increased K+ (hyperkalemia), decreased BP (via RAS pathway), and very high osmolarity inhibits it

75
Q

What does the liver do in the RAS/RAAS pathway

A

Constantly produces angiotensinogen

76
Q

How is ANG I made

A

Renin converts angiotensinogen to ANG I

77
Q

How is ANG II made

A

ACE enzyme converts ANG I to ANG II

78
Q

What are the 5 things ANG II acts on to raise blood pressure

A

Arterioles (vasoconstrict), cardiovascular control center in medulla oblongata (increases BP via CO and TPR), hypothalamus (triggers thirst and vasopressin), adrenal cortex (produces aldosterone), and proximal tubule (increases Na+ reabsorption)

79
Q

What is atrial natriuretic peptide (ANP) and what does it do

A

Stretch of myocardial cells in atria indicates increased ECF and blood volume, has the opposite effect of RAAS pathway (decreases vasopressin, renin, and aldosterone secretion, decreases BP, decrease blood volume, and increases Na+ and H2O excretion)

80
Q

What are 3 consequences of pH disturbances in the blood

A

Disruption of protein shape, disturbance of K+ levels, and effects on excitable tissues

81
Q

What is a normal pH range for plasma

A

7.38-7.42 (<7.38 = acidosis, and >7.42 = alkalosis)

82
Q

Do acidity or basicity have a greater input effect

A

Acids

83
Q

How does the body reduce H+ to neutralize acids

A

Buffers, ventilaiton, and kidneys

84
Q

What is the largest source of H+

A

CO2 (bicarbonate buffering reaction)

85
Q

What is the first line of defense to neutralize acids

A

Buffer system = mixture of two compounds that can remove or produce free H+ as needed, fastest response but only removes H+ from solution, not body

86
Q

What are 2 buffers within cells and plasma

A

Extracellular buffering: Bicarbonate (HCO3-)
Intracellular buffering: Proteins

87
Q

What is the 2nd response to neutralize acids

A

Respiratory compensation (hyperventilate if acidosis, hypoventilate if alkalosis)

88
Q

What is the most important site for renal pH regulation

A

Intercalated disks of distal nephron (secrete H+ and reabsorb HCO3- if acidosis, secrete HCO3- and reabsorb H+ if alkalosis)

89
Q

What are the 2 characteristics of renal compensation for acidosis

A

Type A intercalated cells secrete H+ at apical membrane (H+/K+ exchanger often leads to hyperkalemia) and HCO3- is absorbed at the basolateral membrane

90
Q

What are the characteristics of renal compensation for alkalosis

A

Type B intercalated cells reabsorb H+ at basolateral membrane (H+/K+ exchanger often leads to hypokalemia) and secretes HCO3- at apical membrane

Human Physiology (12 decks)

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