Urinary System Flashcards

1
Q

State the seven major functions of the
kidneys.

A
  1. Excretion of metabolic waste products
    * Urea, creatinine, bilirubin, hydrogen
  2. Excretion of foreign chemicals
    * Drugs, toxins, pesticides, food additives
  3. Secretion, metabolism & excretion of hormones
    * Erythropoetin
    * 1,25 dihydroxycholecalciferol (Vitamin D)
    * Renin
    * Most peptide hormones
  4. Regulation of acid-base balance
  5. Gluconeogenesis
    * Glucose synthesis from amino acids
  6. Control of arterial pressure
  7. Regulation of water & electrolyte excretion
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2
Q

Describe the mechanism of moving urine from kidneys into bladder

A

Urine formed in the nephron collects into the renal pelvis of the kidney .
Urine then travels down the ureter due to gravity but
aided by peristalsis into the bladder, acheived by smooth muscle.the pacemaker activity of the smooth muscle in the ureters also contain
mechanosensitive channels that increase the rate of depolarization when they encounter stretch.

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3
Q

Micturition Reflex (At Rest)

A

Internal sphincter is
contracted (passively)
* External sphincter is
contracted (skeletal
muscle)
* Toxic discharge of
somatic motor neuron
* Higher CNS input, also

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4
Q

Micturation

A

Stretch receptors on
bladder send afferent
signal to the spinal cord;
leads to:
* Parasympathetic neurons
activating bladder muscle
* Bladder smooth
muscle contracts,
pulling internal
sphincter open
* Inhibition of somatic motor
neuron
* External sphincter
relaxed
* Can be inhibited by CNS

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5
Q

Explain the process of urination and the micturition reflex

A

the bladder is innervated by the sympathetic nervous system only to control blood flow to the bladder.
The parasympathetic nervous system innervates the bladder, the neck, and the sphincters (Md: somatic motor neuron]
At rest, the internal sphincter is contracted passively and the external sphincter is contracted through skeletal muscle by toxic APs down the somatic motor neuron.
During the micturition reflex, stretch receptors on the bladder send afferent signals to the spinal cord.
This will lead to parasympathetic motor neurons activating the bladder smooth muscle, causing contraction + opening of the internal sphincter.
It also leads to inhibition of the somatic motor neuron l
pudendal) to relax the external sphincter

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6
Q

Excretion

A

Filtration-Reabsorption+Secretion

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7
Q

Filtration

A
  • Somewhat variable
  • Not selective (except for proteins)
  • Averages 20% of renal plasma flow
  • Takes place at
    glomerulus
  • Substances must
    cross filtration
    membrane
  • Glomerular filtrate
    composition is about
    the same as plasma,
    except for large
    proteins
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8
Q

Reabsorption

A

Highly variable and selective
* Most electrolytes (e.g. Na+, K+, Cl-) and nutritional
substances (e.g. glucose) are almost completely
reabsorbed
* Most waste products (e.g. urea) are poorly reabsorbed

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9
Q

Secretion

A
  • Highly variable and selective
  • Important for rapidly excreting some waste products (e.g. H+),
    foreign substances (including drugs), and toxins
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10
Q
A
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11
Q

Define filtration , reabsorption,
and secretion .

A

Filtration is the process the Bowman’s capsule uses to remove waste from the blood. It is somewhat variable and not selective, except concerning proteins. ~ 20% of renal plasma flow is filtered, the remaining 80% continues to the peritubular capillaries.

Reabsorption is the process of putting some components of solute in the nephron back into the blood. It uses energy that is highly variable and selective. Most electrolytes Na+,k+, and nutrients (glucose) as almost completely reabsorbed.
Most waste products are not reabsorbed at all.

Secretion is the process of components of blood being put into the nephron. It is highly selective and variable and uses energy for action. Secretion is important for rapidly excreting waste products.

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12
Q

Glomerular Filtration Rate (GFR)

A

GFR = 125 ml/min = 180 liters/day
* Plasma volume is filtered 60 times per day
* Filtration fraction (GFR / Renal Plasma
Flow)
= 0.2 (i.e. 20% of plasma is filtered)

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13
Q

Filtration Coefficient of
Glomerular Capillaries

A
  • Kf describes permeability
  • In glomerular capillaries, Kf = GFR/NFP
  • Normally not highly variable
    Using normal values:
    Kf = 125ml/min / 10 mmHg
    = 12.5ml/min/mmHg
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14
Q

Bowman’s Capsule
Hydrostatic Pressure (PBC)

A

Normally changes as a function of GFR
* Affected by
* Tubular Obstruction
* Kidney stones
* Tubular necrosis
* Urinary tract obstruction
* Prostrate hypertrophy
* Cancer

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15
Q

Glomerular Capillary Osmotic
Pressure (Pi G)

A

Affected by
* Arterial plasma oncotic pressure (Pi A)
* increase in Pi A causes increase Pi G
* Filtration fraction (FF)
* increase in FF causes increase Pi G

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16
Q

Glomerular Hydrostatic Pressure (PG)

A
  • Influenced by
  • arterial pressure (effect is buffered by
    autoregulation)
  • afferent arteriolar resistance
  • efferent arteriolar resistance
  • PG is GFR determinant most subject
    to physiological control
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17
Q

Renal Blood Flow (RBF)

A

Kidneys get ~22% of
CO
* To maintain GFR
* Much more than O2 or
nutrient demand
* Kidneys consume ~2X
as much O2 as brain
(per gram weight)

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18
Q

Determinants of RBF

A

RBF = P / R
* P = renal artery pressure – renal vein pressure
* R = total renal vascular resistance
* Sum of resistances of all renal vessels

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19
Q

Control of GFR and RBF

A

Neuralhormonal/Paracrine
1. Sympathetic Nervous System
2. Angiotensin II
3. Endothelin
4. Prostaglandins
5. Endothelial-Derived Nitric Oxide
* Local/intrinsic

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20
Q

Sympathetic Nervous System/
catecholamines

A

(strong innervation)
Increase in RA + Increase RE -> decrease in GFR & decrease in RBF

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21
Q

Endothelin

A

(released by damaged vessels)
Increase in RA + Increase RE –> decrease in GFR & decrease in RBF

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22
Q

Angiotensin II

A

(helps prevent GFR)
Increase RE <——-> GFR & decrease in RBF

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23
Q

Prostaglandins/Bradykinin

A

Decrease in RA + Decrease RE -> Increase in GFR & Increase in RBF

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24
Q

Endothelial-Derived Nitric Oxide (EDRF)

A

Decrease in RA + Decrease RE -> Increase in GFR & Increase in RBF

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25
Local Control of GFR and RBF
Autoregulation of GFR and RBF * Myogenic regulation * Macula densa feedback (tubuloglomerular) * Angiotensin II
26
Reabsorption Rate
Filtration Rate – Excretion Rate
27
Filtration Rate
GFR x Plasma Concentration
28
Excretion rate
Urine Concentration s x V (V = urine flow rate)
29
Transport Maximum (Tm)
Maximum rate of reabsorption or secretion * Some substances have this due to saturation of carriers, limited ATP, etc. * When Tm of reabsorption is reached for all nephrons, further increases in tubular load are not reabsorbed and are excreted
30
Renal Threshold
Tubular load at which Tm is exceeded in some nephrons * This is not exactly the same as the Tm of the whole kidney because some nephrons have lower transport maximums than others
31
Loop of Henle
Thin descending limb * Very permeable to H2O * Thick ascending limb * Reabsorbs ~25% filtered loads of Na+, Cl-, K+ * Also reabsorbs Ca++, HCO3-, Mg++ * Secretes H+ * Impermeable to H2O
32
Early Distal Tubule
Like thick loop * Not permeable to H2O * Reabsorbs ~5% filtered loads of Na+ * Also reabsorbs Cl-, Ca++, Mg++ * Impermeable to H2O * Contains macula densa
33
Late Distal Tubule & Cortical Collecting Duct
Reabsorbs H2O (w/ADH) * Principle cells * Absorb Na+ and Cl- * Secrete K+ * Type A intercalated cells * Absorb K+ and HCO3- * Secrete H+ and Cl- * Type B intercalated cells (not shown) * Secrete K+ and HCO3- * Reabsorb H+ and Cl-
34
Medullary Collecting Duct
Reabsorbs H2O (w/ADH) * Reabsorbs Na+, Cl-, HCO3-, and urea * Secretes H+
35
Regulation of Tubule Reabsorption
Glomerulotubular Balance * Peritubular Capillary Starling Forces * Arterial Pressure (pressure natriuresis and pressure diuresis) * Hormones * Aldosterone * Angiotensin II * Antidiuretic hormone (ADH) * Natriuretic hormones (ANF/ANP) * Parathyroid hormone (PTH) * Sympathetic Nervous System
36
Peritubular Capillary Reabsorption
Reabsorption = Net Reabsorptive Pressure X Kf = 10 mmHg X 12.4 ml/min/mmHg = 124 ml/min
37
Aldosterone – Collecting Duct
Increases Na+ reabsorption (and H2O) * Increases K+ and H+ secretion
38
Increase aldosterone secretion
Angiotensin II * Increased K+ * ACTH
39
Decrease aldosterone secretion
Atrial natriuretic factor (ANF) (aka ANP) * Increased Na+ concentration/osmolarity
40
Angiotensin II
Increases Na+ reabsorption (and H2O) * Proximal tubule, thick ascending limb, collecting tubule * Increases H+ secretion * Stimulates aldosterone secretion * Constricts efferent arterioles * decreases peritubular capillary hydrostatic pressure * increases filtration fraction - which increases peritubular colloid osmotic pressure
41
Angiotensin II Blockade
Decreases Na+ reabsorption (and H2O) * Proximal tubule, thick ascending limb, collecting tubule * Decreases MAP * Medications * ACE inhibitors (captopril, benazipril, ramipril) * Ang II antagonists (losartan, candesartin, irbesartan) * Renin inhibitors (aliskirin) * Effects * Decrease aldosterone * Directly inhibit Na+ reabsorption * Decrease efferent arteriolar resistance  All lead to natriuresis, diuresis, and decreased BP
42
Antidiuretic Hormone (ADH/AVP)
Increases H2O reabsorption * Target cells are distal tubule/collecting duct * Regulates ECF osmolarity * Allows differential control of water and solutes Stimulus: increased osmolarity * Receptors: osmoreceptors (hypothalamus) Also integrating center * Output signal: ADH
43
Atrial Natriuretic Peptide
Stimulus: Atrial stretch * Detected by myocardial cells * ANP (or atrial natriuretic factor, ANF) released by myocardium * Peptide hormone * Half-life of 2-3 minutes * Targets: brain, adrenal medulla, kidney
44
ANP Effects on Kidneys
Increases GFR * Dilates afferent arteriole and constricts efferent * Increases vasa recta flow * Decreases Na+ and H2O reabsorption * Less Na+ channels in apical membrane * Decreases sympathetic activity * Inhibits renin Has other effects elsewhere in body All lower blood volume/pressure
45
Parathyroid Hormone (PTH)
* Works on thick ascending limb/distal tubule * cAMP GPCR
46
Sympathetic Nervous System Regulation of Absorption
Decreases Na+ and H2O excretion * Causes constriction of arterioles * Lowers GFR * Increases Na+ reabsorption along tubule * Increases renin & angiotensin II
47
Clearance
Clearance describes the rate at which substances are removed (cleared) from the plasma. * Renal clearance of a substance is the volume of plasma completely cleared of a substance per min by the kidneys. C s =Urine [s] X Urine Flow Rate / Plasma [s]
48
Effects of Countercurrent Multiplier
More solute than water is added to the renal medulla * solutes are “trapped” in the renal medulla * Fluid in the ascending loop is diluted * Most of the water reabsorption occurs in the cortex * in the proximal tubule and in the distal convoluted tubule, rather than in the medulla * Horizontal gradient of solute concentration established by the active pumping of NaCl is “multiplied” by countercurrent flow of fluid.
49
Reasons for Concentrated Medulla
Active transport of Na+, Cl-, K+ and other ions from thick ascending loop of Henle into medullary interstitial fluid * Active transport of ions from medullary collecting ducts into interstitial fluid * Passive diffusion of urea from medullary collecting ducts into interstitial fluid * Diffusion of only small amounts of water into medullary interstitial fluid
50
Urea Handling
Urea is passively reabsorbed in proximal tubule (~ 50% of filtered load) * In the presence of ADH, water is reabsorbed in distal and collecting tubules, concentrating urea in these parts of the nephron * The inner medullary collecting tubule is highly permeable to urea, which diffuses into the medullary interstitial fluid * ADH increases urea permeability of medullary collecting tubule by activating urea transporters (UT-1)
51
ADH
Stimulus for release * Increased osmolarity * Decreased blood volume (cardiopulmonary reflexes) * Decreased blood pressure (baroreceptor reflexes) * Angiotensin II * These things also stimulate thirst * Opposite factors decrease release Guyton, 13th Ed., Fig. 29-10
52
Mechanisms of H+ Regulation
Body fluid chemical buffers (rapid but temporary) * bicarbonate - ammonia * proteins - phosphate 2. Lungs 3. Kidneys
53
Body fluid chemical buffers (rapid but temporary)
* bicarbonate - ammonia * proteins - phosphate
54
Bicarbonate
most important ECF buffer H2O + CO2 <-->H2CO3 <--->H+ + HCO3 -
55
Phosphate
important renal tubular buffer HPO4-- + H+ <--->H2PO 4 -
56
Ammonia
important renal tubular buffer NH3 + H+<---> NH4+
57
Proteins
important intracellular buffers H+ + Hb <---> HHb
58
Lungs
(rapid, eliminates CO2) Increase H+-> Increase ventilation -> Increase loss in CO2
59
Kidneys
(slow, powerful); eliminates non-volatile acids * secrete H+ * reabsorb HCO3- * generate new HCO3-
60
Acidosis
pH < 7.4 - metabolic: decrease HCO3 - - respiratory: increase PCO2 - increased H+ excretion - increased HCO3- reabsorption - production of new HCO3-
61
Alkalosis
pH > 7.4 - metabolic: Increase HCO3 - - respiratory: Decrease PCO2 - decreased H+ excretion - decreased HCO3- reabsorption - loss of HCO3- in urine
62
ANP Effects on Other Tissues (Hypothalamus)
Less vasopressin released
63
ANP Effects on Other Tissues (Medulla Oblongata)
Decreases sympathetic output
64
ANP Effects on Other Tissues (Adrenal Cortex)
Less aldosterone secreted
65
Factors that Decrease Renal Excretion/ Increase BP
* Angiotensin II * Aldosterone * Sympathetic Activation
66
Renin Angiotensin System
Increases blood pressure by several mechanisms * Renin released in response to ↓ BP * Directly causes granular cells of afferent arteriole to produce renin * ↓BP causes ↓GFR, which causes ↓NaCl transport. Macula densa sense ↓NaCl and release paracrines that cause granular cells to release renin * ↓BP activates medulla oblongata to increase sympathetic activity, which causes granular cells to release renin Renin is released into blood * It is an enzyme that converts angiotensinogen (secreted into blood by the liver) into angiotensin I (ANG I) * ANG I in the blood is converted to ANG II by angiotensin converting enzyme (ACE), which is produced by vascular endothelium
67
Angiotensin II (ANG II)
Increases blood volume and pressure * Peptide hormone * Dissolved in plasma * Half life ~1 min * Receptor: AT receptors * AT-1: GPCR, coupled to Gq/11 and Gi/o
68
Effects of Angiotensin II (Kidneys)
Causes ↑ Na+ absorption in proximal tubule * Receptor is GPCR that results in ↑Na+ pumps and channels increase volume (and BP) and maintain osmolarity
69
Effects of Angiotensin II (Adrenal cortex)
* Causes release of aldosterone * ↑ Na+ absorption in distal nephron increase volume (and BP) and maintain osmolarity
70
Effects of Angiotensin II (Hypothalamus)
* Increases thirst * Increases ADH release * Increases volume * Increases BP
71
Effects of Angiotensin II (Arterioles)
Directly causes vasoconstriction (lead to increased blood pressure )
72
Effects of Angiotensin II (Medulla oblongata)
Increases sympathetic response (lead to increased blood pressure )