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
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
3
Q
Consists of
A
- urine forming organs (kidneys)
- structures that carry urine from kidneys: ureter, urinary bladder, and urethra
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
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
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
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)
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
9
Q
Juxtaglomerular Apparatus
A
- afferent and efferent arterioles
- distal convoluted tubule (DCT)
- nephron’s DCT passes between its own afferent and efferent arterioles
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
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
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
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
14
Q
3 Basic Renal Processes
A
- Glomerular filtration
- 20% of plasma
- protein-free
- 125ml/min
- 180L/day - Tubular reabsorption
- 178.5 L/day - Tubular secretion
- further route for excretion
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
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
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
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
19
Q
Forces Involved in Glomerular Filtration
A
- Glomerular capillary blood pressure (55mmHg)
- afferent VS efferent resistance
- filtration along entire capillary length - Plasma-colloid osmotic pressure (30mmHg)
- high because of more water filtered - Bowman’s capsule hydrostatic pressure (15mmHg)
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
21
Q
Plasma-colloid Osmotic Pressure
A
- cause by unequal distribution of plasma proteins across glomerular membrane
- opposes filtration
- 30mmHg
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
23
Q
Net Flitration Pressure
A
- Net filtration pressure= glomerular capillary blood pressure- (plasma-colloid osmotic pressure + Bowman’s capsule hydrostatic pressure)
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
25
Unregulated influences on the GFR
- 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
26
Controlled Adjustments in GFR
- glomerular capillary blood pressure can be controlled to adjust GFR to suit the body's needs
27
2 Major Control Mechanisms in GFR
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
28
Mechanisms Responsible for Auto regulation of the GFR
- 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
29
2 Intrarenal Mechanisms Contribute to Autoregulation
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
Glomerular Filtration: Tubuloglomerular feedback
- 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
Auto regulation of Glomerular Filtration Rate
- 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
Extrinsic Control of GFR
- 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
GFR influence by changes in filtration Coefficient K
- 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
Tubular Reabsorption
- 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
Tubular Reabsorption
- 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
Why is Na+ reabsorption so important?
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
Na+ Reabsorption
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
Control body Na (and Cl)
- control body water--> control blood volume--> important in BP control
39
Sodium Reabsportion
- 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
Na+ Reabsorption Fine-tuning
- 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
Na+ Reabsorportion and RAAS
- 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
Functions of the RAAS
- 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
Aldosterone
- acts on last portion of distal convoluted tubules and collecting ducts
- increase apical membrane Na channels
- more basolateral Na+/K+ ATPase pumps
44
Low ECF volume/decrease BP effect
--> renin released--> more aldosterone--> more Na reabsorption--> less body volume lost in urine
45
High ECF volume effect
--> less renin released--> less aldosterone--> less Na reabsorption--> more body volume lost in urine
46
Atrial Natiuretic Peptide (ANP)
- 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
Reabsorption of Other Solutes
- 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
Water Reabsoportion
- 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
Water Reabsorption in Proximal Tubule
- 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
Tubular Secretion
- 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
Most Important Secretory Systems Are For...
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
Potassium Ion Secretion
- 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
Dual Control of Aldosterone Secretion of K+ and NA+
- if aldosterone pathway activated by decreased Na+ etc could cause deficiency in K+
54
Kidneys and Urine of Varying Concentrations
- 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
Osmolarity
- measured in mosmol/L
- cells is about 300 most/L
- plasma is about 300 most/L:
= isotonic
- if cells plasma = ECF Hypotonic
56
Urine Excretion
- 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
Countercurrent Multiplication
- medullary vertical osmotic gradient is established by countercurrent multiplication
- fluid in one tube flows the opposite way in the adjoining tube
58
Countercurrent Multiplication (descending and ascending)
- 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
Water Reabsorption (how much)
- 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
Water Reabsorption: Vasopressin
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
Role of Vasopressin
- 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
During Water Changes Vasopressin...
- deficit: secretion increases (increases water reabsorption)
- excess of water: secretion of vasopressin decreases (less water is reabsorbed and more is eliminated)
63
Water Excess
- 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
Vasa Recta
- supplies metabolic needs to JMN
- removes reabsorbed Na and water
- maintains osmotic gradients
65
Osmotic Diuresis
- 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
Water Diuresis
- increased urine with no or little increased solute
- excess water intake
- diabetes insipidus
67
Urine
- 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
Micturition
- 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
Micturition (Muscles and Innervation)
- detrusor (smooth muscle): PS causes contraction
| - external urethral sphincter (skeletal muscle): Somatic motor causes contraction
70
Eliminated by Micturition
- 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
Micturition (summary)
- 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
