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Human Physiology 2 > Ch. Twelve: Urinary System > Flashcards

Ch. Twelve: Urinary System Flashcards

1
Q

Kidney Main Function

A
  • primarily responsible for maintaining stability of ECF volume, electrolyte composition, and osmolarity
  • main route for eliminating potentially toxic metabolic wastes and foreign compounds from the body
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2
Q

Kidney Functions

A
  • maintain H2O balance in body
  • maintain proper osmolarity of body fluids, primarily through regulating H2O balance
  • regulate the quantity and concentration of most ECF ions
  • maintain proper plasma volume
  • help maintain proper acid-base in the body
  • excrete end products and foreign compounds
  • produce erythropoietin and renin
  • convert vitamin D into its active form
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3
Q

Consists of

A
  • urine forming organs (kidneys)

- structures that carry urine from kidneys: ureter, urinary bladder, and urethra

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4
Q

Kidneys and Urine

A
  • lie in back of abdominal cavity
  • supplied with a renal artery and vein
  • acts on plasma flowing through it to produce urine
  • outer cortex and inner medulla
  • formed urine drains into the renal pelvis: located at medial inner core of each kidney
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5
Q

Ureters

A
  • smooth muscle-walled duct
  • exits each kidney at the medial border in close proximity to renal artery and vein
  • carry urine to the urinary bladder
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6
Q

Urinary Bladder

A
  • temporarily stores urine
  • hollow, distensible, smooth muscle-walled sac
  • periodically empties to the outside of the body through the urethra
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7
Q

Urethra

A
  • conveys urine to the outside of the body
  • urethra is straight and short in females
  • in males: much loner and follows curving course; dual function (provides route for eliminating urine from bladder, passageway for semen from reproductive organs)
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8
Q

Nephron

A
  • functional unit of kidney
  • smallest unit that can perform all functions of the kidney
  • has vascular component and tubular component
  • outer region (renal cortex)
  • inner region: renal medulla and made up of renal pyramids
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9
Q

Juxtaglomerular Apparatus

A
  • afferent and efferent arterioles
  • distal convoluted tubule (DCT)
  • nephron’s DCT passes between its own afferent and efferent arterioles
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10
Q

Vascular Component

A
  • dominant part is glomerulus
  • ball like tuft of capillaries
  • water and solutes are filtered through glomerulus as blood passes through it
  • filtered fluid then passes through nephron’s tubular component
  • from renal artery, inflowing blood passes through afferent arterioles which deliver blood to glomerulus
  • efferent arteriole transports blood from glomerulus
  • efferent arteriole breaks down into peritubular capillaries which surround tubular part of nephron
  • peritubular capillaries join into venues which transport blood into the renal vein
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11
Q

Tubular Component

A
  • hollow, fluid-filled tube formed by a single layer of epithelial cells
  • components: Bowmans capsule, proximal tubule, loop of Henle, Juxtaglomeruler apparatus, distal tubule, collecting duct or tubule
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12
Q

Nephron (Glomeruli)

A
  • originate in cortex: Glomeruli and Bowman’s capsule give granular appearance of cortex
  • proximal and distal tubules within cortex
  • glomeruli cortical nephrons lie in the outer layer of the cortex (80% of nephrons)
  • glomeruli of juxtamedullary nephrons lie in the inner layer of the cortex (20%): performs most of urine concentration
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13
Q

Nephron: Efferent Arterioles

A
  • juxtamedullary nephrons: peritubular capillaries are long looping vascular loops called vasa recta
  • concentrate and dilute urine
  • cortical nephrons: peritubular capillaries instead entwine around nephrons short loops of Henle
  • perform excretory and regulatory functions
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14
Q

3 Basic Renal Processes

A
  1. Glomerular filtration
    - 20% of plasma
    - protein-free
    - 125ml/min
    - 180L/day
  2. Tubular reabsorption
    - 178.5 L/day
  3. Tubular secretion
    - further route for excretion
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15
Q

Kidney Blood Flow

A
  • receive 20-25% of cardiac output
  • total blood flow through the kidneys > 1L/min
  • CO= 5L/min
  • required so to monitor and control the ECF
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16
Q

Glomerular Filtration Membrane

A
  • fluid filtered from the glomerulus into Bowman’s capsule pass through 3 layers of the glomerular membrane
    1. glomerular capillary wall:
  • fenestrated capillary
  • more permeable to water and solutes than capillaries elsewhere
    2. basement membrane
    3. Inner layer of Bowman’s capsule:
  • consists of podocytes that encircle the glomerulus tuft
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17
Q

Podocytes

A
  • terminate in foot processes
  • surround the basement membrane of the glomerulus
  • clefts between the foot processes are called filtration slits
  • where the filtrate enters the Bowman’s capsule
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18
Q

Glomerular Filtration

A
  • passive process in which hydrostatic pressures force the fluids and solute through a membrane
  • glomeruli are efficient filters:
    1. filtration membrane is a large surface area and very permeable to water and solutes
    2. Glomerular pressure is higher (55mmHg), so they produce 180L vs 3-4L formed by other capillary beds
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19
Q

Forces Involved in Glomerular Filtration

A
  1. Glomerular capillary blood pressure (55mmHg)
    - afferent VS efferent resistance
    - filtration along entire capillary length
  2. Plasma-colloid osmotic pressure (30mmHg)
    - high because of more water filtered
  3. Bowman’s capsule hydrostatic pressure (15mmHg)
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20
Q

Glomerular Capillary BP

A
  • fluid pressure exerted by blood within glomerular capillaries
  • depends on: contraction of heart, resistance to blood flow offered by afferent and efferent arterioles
  • major force producing glomerular filtration
  • 55mmHg
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21
Q

Plasma-colloid Osmotic Pressure

A
  • cause by unequal distribution of plasma proteins across glomerular membrane
  • opposes filtration
  • 30mmHg
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22
Q

Bowman’s Capsule Hydrostatic Pressure

A
  • pressure exerted by fluid in initial part of tubule
  • tends to push fluid out of Bowman’s capsule
  • opposes filtration
  • 15mmHg
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23
Q

Net Flitration Pressure

A
  • Net filtration pressure= glomerular capillary blood pressure- (plasma-colloid osmotic pressure + Bowman’s capsule hydrostatic pressure)
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24
Q

Glomerular Filtration Rate

A

(GFR)

  • depends on:
  • net filtration pressure
  • how much glomerular surface area is available for penetration
  • how permeable the glomerular membrane is
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25
Q

Unregulated influences on the GFR

A
  • pathologically plasma-colloid osmotic pressure and Bowman’s capsule hydrostatic pressure can change
  • plasma-colloid osmotic pressure:
  • severely burned patient (increase GFR)
  • dehydrating diarrhea (decrease GFR)
  • Bowman’s capsule hydrostatic pressure:
  • obstructions ex. Kidney stone
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26
Q

Controlled Adjustments in GFR

A
  • glomerular capillary blood pressure can be controlled to adjust GFR to suit the body’s needs
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27
Q

2 Major Control Mechanisms in GFR

A

1 . Autoregulation (aimed at preventing spontaneous changes in GFR)

  • myogenic mechanism
  • tubuloglomerular feedback (TGF)
    2. Extrinsic sympathetic control (aimed at long-term regulation of arterial blood pressure)
  • mediated by SNS input to afferent arterioles
  • baroreceptor reflex
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28
Q

Mechanisms Responsible for Auto regulation of the GFR

A
  • without auto regulation:
    if increase BP, increase GFR (in direct proportion)
  • undesirable
  • spontaneous, inadvertent changes in GFR are largely prevented by intrinsic regulatory mechanisms:
  • initiated by the kidneys themselves, a process known as regulation
  • GFR kept within a narrow range despite changes in BP
  • auto regulation works through changing the diameter of the afferent arteriole:
  • changes the BP experienced in glomerular capillary
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29
Q

2 Intrarenal Mechanisms Contribute to Autoregulation

A
  1. Myogenic mechanism: common property of vascular SM
    - stretch cause afferent arteriole SM to contract (when increase in BP)
    - less stretch, cause relaxation
  2. Tubuloglomerular feedback (TGF) involves the juxtaglomerular apparatus
30
Q

Glomerular Filtration: Tubuloglomerular feedback

A
  • salt delivery to macula dense regulates ATP release:
  • degraded to adenosine
  • adenosine constricts afferent arteriole
  • increase in salt (due to increased GFR) releases ATP:
  • afferent arteriole constriction, decrease blood flow, decrease GFR
31
Q

Auto regulation of Glomerular Filtration Rate

A
  • autoregulation prevents unintentional shifts in GFR: imbalances in water, electrolytes, and waste products
  • increases in BP that can occur normally e.g.. exercise, do not increase GFR:
  • prevents needless loss of water and solutes
  • low BP does not result in excess of waste products, excess electrolytes in body
32
Q

Extrinsic Control of GFR

A
  • extrinsic sympathetic control
  • aimed at long-term regulation of arterial blood pressure
  • deliberate change in GFR despite normal BP range overrides auto regulation mechanisms
  • mediated by sympathetic nervous system input to afferent arterioles to regulate arterial BP
  • baroreceptor reflex eg. blood loss:
  • effect on heart and blood vessels
  • long term on plasma volume: reduce urine output
33
Q

GFR influence by changes in filtration Coefficient K

A
  • this coefficient is not constant but is subject to physiological control
  • GFR= Kf x net filtration pressure
  • depends on: SA, permeability of the glomerular membranes, both can be modified by contractile activity within the membrane
34
Q

Tubular Reabsorption

A
  • involves the transfer of substances from tubular lumen into peritubular capillaries
  • highly selective and variable process
  • involves transepithelial transport
  • reabsorbed substance must cross five barriers:
  • must leave tubular fluid by crossing luminal membrane of tubular cell
  • must pass through cytosol from one side of tubular cell to the other
  • must cross basolateral membrane of the tubular cell to enter interstitial fluid
  • must diffuse through interstitial fluid
  • must penetrate capillary wall to enter blood plasma
35
Q

Tubular Reabsorption

A
  • all tubular fluid constituents at the same concentration as in plasma (except proteins)
  • reabsorb useful substances
  • waste material remain in tubule
  • passive reabsorption: no energy is required
  • occurs down electrochemical or osmotic gradients
  • active reabsorption: occurs if any one of theses steps in transepithelial transport of a substance requires energy
  • movement occurs against electrochemical gradient
36
Q

Why is Na+ reabsorption so important?

A

Proximal tubule: 67&
- plays a role in reabsorbing glucose, amino acids, water, CL-, and urea
Ascending limb go the loop of Henle: 25%
- plays critical role in kidneys’ ability to produce urine of varying concentrations
Distal and collecting tubules: 8%
- variable and subject to hormonal control; plays role in regulating ECF volume

37
Q

Na+ Reabsorption

A

Na+-K+ ATPase pump

  • on basolateral membrane- essential for NA+ reabsorption
  • of total energy spent by kidneys, 80% is used for Na+ transport
  • Na+ is not reabsorbed in the descending limb of the loop of Henle
  • water follows reabsorbed sodium by osmosis which has a main effect on blood volume and blood pressure
38
Q

Control body Na (and Cl)

A
  • control body water–> control blood volume–> important in BP control
39
Q

Sodium Reabsportion

A
  • Na reabsorption coupled to movement of other substances: glucose and amino acids
  • Na+ is the most abundant cation in the filtrate (and in ECF)
  • Na+ reabsorption is almost always active transport
  • active pumping of Na+ (via Na+/K+ ATPase)
  • generates an electrochemical gradient that couples to passive entrance of other substances (glucose, amino acids etc.) via co-transporters
40
Q

Na+ Reabsorption Fine-tuning

A
  • carried out in distal tubule
  • if too much body Na+, then less reabsorbed (eg. excreted in urine)
  • if too little body Na+, then more is reabsorbed
  • important to remember: Na+ load reflects ECF volume (90% of ECF osmolarity due to NaCl)
  • ECF volume changes affect BP
41
Q

Na+ Reabsorportion and RAAS

A
  • Renin-angiotensin-aldosterone system
  • most important for Na+ regulation
  • granular cells of JGA
  • renin release: Barorecptors (decrease BP), NaCl load (macula dense), and sympathetic drive (decrease BP)
  • most important and best known hormonal system involved in regulating Na+
  • renin converts angiotensinogen into angiotensin 1
  • angiotension 1 is converted into angiotensin 2 by angiotensin-converting enzyme
  • angiotension 2 stimulates secretion aldosterone
42
Q

Functions of the RAAS

A
  • increases Na+ absorption, promotes water retention
  • acting in a negative-feedback fashion, alleviates the factors that trigger initial release of renin
  • angiotension 2 is a potent constrictor of systemic arterioles and stimulates thirst and vasopressin secretion
43
Q

Aldosterone

A
  • acts on last portion of distal convoluted tubules and collecting ducts
  • increase apical membrane Na channels
  • more basolateral Na+/K+ ATPase pumps
44
Q

Low ECF volume/decrease BP effect

A

–> renin released–> more aldosterone–> more Na reabsorption–> less body volume lost in urine

45
Q

High ECF volume effect

A

–> less renin released–> less aldosterone–> less Na reabsorption–> more body volume lost in urine

46
Q

Atrial Natiuretic Peptide (ANP)

A
  • inhibits Na+ reabsorption
  • secreted by atria in response to:
  • being stretched by Na+ retention, expansion of ECF volume, increase in arterial pressure
  • ANP release promotes: natriuresis (loss of Na), diuresis (increase urine production), hypotensive effects
  • all help to correct the original stimulus that brought about release of ANP
47
Q

Reabsorption of Other Solutes

A
  • reabsorption of glucose and amino acids: by soda-dependent, secondary active transport
  • other reabsorbed electrolytes Ca, Mg (Cl- follows passively)
  • generally, unwanted waste products are not reabsorbed
48
Q

Water Reabsoportion

A
  • water is passively reabsorbed throughout the tubule as it follows reabsorbed Na+
  • 80% of the water reabsorbed is uncontrolled:
  • 65% is reabsorbed in proximal tubule
  • 15% is reabsorbed from the loop of Henle
  • 20% of water reabsorbed is controlled: under hormonal control of vasopressin (ADH)
  • water follows Na+
49
Q

Water Reabsorption in Proximal Tubule

A
  • in proximal tubule and loop of Henle NOT subject to regulation (same as Na+)
  • 65% PT + 15% LoH = 80% of filtrate
  • via aquaporins (water channels)
  • bulk flow enhanced by increased plasma colloid osmotic pressure of peritubular capillaries
  • in distal portion of nephron: water reabsorption is regulated by vasopressin (ADH)
50
Q

Tubular Secretion

A
  • transfer of substances from peritubular capillaries into the tubular lumen
  • involves transepithelial transport (steps are reversed)
  • kidney tubules can selectively add some substances to the substances already filtered
51
Q

Most Important Secretory Systems Are For…

A

H+
- important in regulating acid-base balance
- secreted in proximal, distal, and collecting tubules
K+
- keeps plasma K+ concentration at app. levels to maintain normal membrane excitability in muscles and nerves
- all filtered K+ is reabsorbed
- secreted only in the distal and collecting tubules under control of aldosterone
Organic Ions
- accomplish more efficient elimination of foreign organs compounds from the body
- secreted only in the proximal tubule

52
Q

Potassium Ion Secretion

A
  • movement of K+ from capillaries to interstitial fluid
  • into tubular cell via the pump and out via ion channels into tubular fluid
  • location of K+ channels is key
  • if on basolatereral membrane, K+ is recycled (proximal tubule and loop of Henle)
  • if on luminal membrane, K+ secretion (distal portions)
53
Q

Dual Control of Aldosterone Secretion of K+ and NA+

A
  • if aldosterone pathway activated by decreased Na+ etc could cause deficiency in K+
54
Q

Kidneys and Urine of Varying Concentrations

A
  • depending on the body’s state of hydration, the kidneys secrete urine of varying concentrations
  • too much water in the ECF establishes a hypotonic ECF
  • a water deficit established a hypertonic ECF
55
Q

Osmolarity

A
  • measured in mosmol/L
  • cells is about 300 most/L
  • plasma is about 300 most/L:
    = isotonic
  • if cells plasma = ECF Hypotonic
56
Q

Urine Excretion

A
  • large, vertical osmotic gradient is established in the interstitial fluid of the medulla ( 300-1200 most/L)
  • follows the hairpin loop of Henle deeper and deeper into the medulla
  • this osmotic gradient exists between the tubular lumen and the surrounding interstitial fluid
57
Q

Countercurrent Multiplication

A
  • medullary vertical osmotic gradient is established by countercurrent multiplication
  • fluid in one tube flows the opposite way in the adjoining tube
58
Q

Countercurrent Multiplication (descending and ascending)

A
  • descending limb is highly permeable to water, but not sodium
  • ascending limb actively transports NaCl out of the tubular lumen into the surrounding interstitial fluid
  • impermeable to water, therefore, water does not follow the salt by osmosis
59
Q

Water Reabsorption (how much)

A
  • 20% of filtered water in distal tubule and collecting ducts
  • 36 L/day for regulated reabsorption
  • collecting ducts pass through the osmotic gradient in medulla
  • hypoosmotic solution in distal tubule (100 mosm/L) can concentrated up to 1200 most/l
  • water movement out of collecting duct controlled by vasopressin (=ADH)
60
Q

Water Reabsorption: Vasopressin

A

vasopressin- controlled, variable water reabsorption occurs in the final tubular segments

  • 65% of water reabsorption is obligatory in the proximal tubule
  • the distal tubule and collecting duct it is variable, based on the secretion of vasopressin (ADH)
61
Q

Role of Vasopressin

A
  • secretion of vasopressin increases the permeability of the tubule cells to water
  • an osmotic gradient exists outside the tubules for the transport of water by osmosis
  • produced in the hypothalamus and stored in the posterior pituitary: release of this substance signals the distal tubule and collecting duct, facilitating the reabsorption of water
  • vasopressin works on tubule cells through a cyclic AMP mechanism
62
Q

During Water Changes Vasopressin…

A
  • deficit: secretion increases (increases water reabsorption)
  • excess of water: secretion of vasopressin decreases (less water is reabsorbed and more is eliminated)
63
Q

Water Excess

A
  • no vasopressin released (DT and CD impairment to water)
  • fluid remains at 100 most/L after distal tubule and collecting ducts
  • 20% of glomerular filtrate can be excreted giving dilute urine (25 ml/min compared to normal 1ml/min)
64
Q

Vasa Recta

A
  • supplies metabolic needs to JMN
  • removes reabsorbed Na and water
  • maintains osmotic gradients
65
Q

Osmotic Diuresis

A
  • Diuresis: increased urine production
  • increased excretion of water and solute:
  • increased unreabsorbed solute in fluid
  • holds water in tubule
  • glucose in diabetes mellitus (“sweet urine”)
  • diuretic drugs
66
Q

Water Diuresis

A
  • increased urine with no or little increased solute
  • excess water intake
  • diabetes insipidus
67
Q

Urine

A
  • final urine may contain virtually no NaCl the excreted solute being urea, creatinine, urate, K+, etc.
  • excretion of large quantities of Na+ is always accompanied by the excretion of large amounts of water
  • however, the excretion of large amounts of water does not necessitate the excretion of Na+
68
Q

Micturition

A
  • bladder can accommodate large fluctuations in urine volume: SM stretches
  • sphincters control urine release:
  • internal urethral sphincter- smooth muscle (relaxed bladder causes closure)
  • external urethral sphincter- skeletal muscle (under voluntary control)
  • eliminated of urine by micturition
69
Q

Micturition (Muscles and Innervation)

A
  • detrusor (smooth muscle): PS causes contraction

- external urethral sphincter (skeletal muscle): Somatic motor causes contraction

70
Q

Eliminated by Micturition

A
  • urine in bladder stimulates stretch receptors
  • stimulated stretch receptors signal smooth muscle in bladder wall by parasympathetic neutrons
  • contraction of bladder pushes urine out of the body
71
Q

Micturition (summary)

A
  • urine in bladder stimulates stretch receptors
  • stimulated stretch receptors signal smooth muscle in bladder wall by PS neutrons: contraction of bladder pushes urine out of the body
  • micturition reflex:
  • relation of external urethral sphincter muscle allowing urine to pass through urethra and out of the body
  • urinary incontinence: inability to prevent discharge of urine

Human Physiology 2 (10 decks)

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