Chapter 14 - Urinary System Flashcards
Kidney Functions
-maintaining stable ECF volume
-electrolyte composition
-osmolarity
-waste elimination
-H₂O balance
-plasma volume
-acid-base balance
-erythropoietin and renin production
-converting vitamin D to active form
Osmolarity Maintenance
-solute concentration
-through regulating H₂O balance
-prevents osmotic fluxes that could cause shrinking or swelling of cells
Plasma Volume Maintenance
-long-term regulation of arterial blood pressure
-through NaCl and H₂O balance
Erythropoietin
-hormone that stimulates red blood cell production
Renin
-enzymatic hormone
-triggers a chain reaction important in salt conservation
Renal Pelvis
-where formed urine drains
-in the medial inner core of each kidney
Ureters
-smooth muscle walls
-exits kidney at medial border
-carry urine to the bladder
Urethra in Females is _____ and _______.
straight; short
Urethra in Males
-longer and curving
-2 functions a) urine elimination b) semen passageway
Nephron
-functional unit of the kidney
~1 million nephrons/kidney
-regulate water and solute
-2 components: a) vascular b) tubular
Renal Cortex
-located in the outer region of the nephron
-granular appearance
Renal Medulla
-inner region of the nephron
-made of renal pyramids (striated triangles)
Juxtaglomerular Apparatus
-intersection of the afferent and efferent arterioles and the distal convoluted tubule
-the DCT passes between the arterioles
Vascular Component
-glomerulus is the dominant part
Glomerulus
-a tuft of capillaries
-filters protein-free plasma into the tubular component
Path of Blood
-renal artery, afferent arterioles, glomerulus, efferent arteriole, peritubular capillaries, venules, renal vein
Peritubular Capillaries
-surround the tubular part
-supply the renal tissue
-exchange fluid with tubular lumen
_____ arterioles are the only in the body to drain from capillaries?
efferent
Tubular Component
-hollow, fluid-filled tube
-single layer of epithelial cells
-begins at the glomerulus and ends at the renal pelvis
Bowman’s Capsule
-part of the tubular component
-collect the glomerular filtrate
-double walled
Proximal Tubule
-part of the tubular component
-lies entirely in the cortex
-coiled
-uncontrolled reabsorption and secretion
Loop of Henle
-part of the tubular component
-U-shaped that dips into the medulla
-ascending (NaCl) and descending (H2O) limbs
-establishes and osmotic gradient
-controls urine concentration
Juxtaglomerular Apparatus
-vascular AND tubular component
-produces substances in controlling kidney function
Distal Tubule
-lies in cortex
-controlled reabsorption (Na+ and H₂O) and secretion (K+ and H+)
Collecting Duct
-where distal tubule empties
-brings urine to renal pelvis
Cortical Nephrons
-glomeruli lie in the outer cortex layer
-80% of nephrons
Juxtamedullary Nephrons
-glomeruli lie in the inner cortex layer
-long looped nephron
-establishes osmotic gradient
-most of urine concentration
Vasa Recta
-part of juxtamedullary nephrons
-long vascular loops
Glomerular Filtration
-180L/day
-1st step in urine formation
-protein-free fluid passes through 3 layers of the glomerular membrane
The 3 Glomerular Layers
- Glomerular capillary wall: more permeable to water and solutes than anywhere in the body
- Basement membrane
- Inner Bowman’s Capsule layer
The glomerular capillary wall is made of __________ capillary
fenestrated
The inner Bowman’s capsule layers consists of ______ that encircle the glomerulus
podocytes
Podocytes
-role in glomerular filtration
-terminate in foot processes
-surround basement membrane
Filtration Slits
-clefts between the foot processes
-where filtrate enters the Bowman’s capsule
Glomerular filtration is a ________ process where ________ ________ force fluids and solute through a membrane.
passive; hydrostatic pressures
Filtration Membrane
-has a large surface area
-is very permeable to water and solutes
Glomerular pressures is ______ vs other capillaries.
-higher
-180L/day vs 20L/day (all other capillary beds combined)
Glomerular Filtration: Forces
-recall bulk flow
-3 physical forces involved
Glomerular Capillary Blood Pressure
-outward direction
-55 mmHg
-afferent vs efferent resistance
-filtration along entire capillary length
-favours filtration
Plasma-colloid Osmotic Pressure
-inward direction
-30 mmHg
-high due to more water being filtered
-opposes filtration
-caused by unequal distribution of plasma proteins across the membrane
Bowman’s Capsule Hydrostatic Pressure
-into the outside
-15 mmHg
-opposes filtration
-pressure exerted by fluid in initial part of tubule
-pushes fluid out of Bowman’s capsule
Net Filtration Pressure Equation
-glomerular capillary bp - (plasma-colloid osmotic + Bowman’s capsule hydrostatic) = net pressure
-favours filtration
-55-(30+15)=10mmHg
Glomerular Capillary Blood Pressure
-the fluid pressure exerted by blood in glomerular capillaries
-depends on: resistance to flow by afferent and efferent arterioles
Glomerular Filtration Rate (GFR)
-depends on net filtration pressure, surface area, permeability
Unregulated GFR Influences
-pathological changes in plasma-colloid osmotic pressure and Bowman’s capsule hydrostatic pressure
Changes in Plasma-colloid Osmotic Pressure
-affect GFR
-due to: a) severely burned patient (↑GFR) b) diarrhea (↓GFR)
Changes in Bowman’s Capsule Hydrostatic Pressure
-affect GFR
-due to obstruction (ie. kidney stone)
Controlled GFR Influences
-glomerular capillary bp adjusted to suit body needs
Autoregulation
-prevent spontaneous GFR changes
-kidneys maintain a constant blood flow despite driving changes in BP
-done by adjusting resistance to flow
-a myogenic mechanism
-TGF
Myogenic Mechanism
-used in autoregulation
-property of vascular smooth muscle
-contraction in response to stretch (increased pressure)
Tubuloglomerular Feedback
-used in autoregulation
-involves the Juxtaglomeruluar apparatus
-granular cells and macula densa which release ATP to induce vasoconstriciton (vv.)
Macula Dense
-detects changes in salt levels of fluid flowing past and stimulates release of ATP
-ATP degrades to adenosine and constricts the afferent arteriole
-this will decrease blood flow and hence GFR
Extrinsic Sympathetic Control
-long term BP regulation
-sympathetic input to afferent arterioles
-override autoregulation
Baroreceptor Reflex
-responds to a fall or rise in BP to sympathetically vasoconstrict or vasodilate
-affects heart and blood vessels (renal too!)
Vasoconstriction______ blood flow to the glomerulus and ______ GFR
decreases, reduces
Vasodilation______ blood flow to the glomerulus and ______ GFR
increases, increases
Will natural BP increases/decreases affect GFR?
-No
-ie. exercise
-this prevents the needless loss of water and solutes
Kidneys receive ___-___% of cardiac output
20 to 25
Blood flows through the kidneys at about _L/min
1
___% of plasma leaves the glomerulus not filtered
80
Tubular Reabsorption
-178.5L/day
-the transfer of substances from tubular lumen into peritubular capillaries
-a highly selective and variable process
-must cross 5 barriers
____% of water is reabsorbed and ____% is excreted
99; 1
____% of sodium is reabsorbed and ____% is excreted
99.5; 0.5
____% of glucose is reabsorbed and ____% is excreted
100; 0
____% of urea is reabsorbed and ____% is excreted
50; 50
____% of phenol is reabsorbed and ____% is excreted
0; 100
Path in Transepithelial Transport
luminal cell membrane, cytosol, basolateral cell membrane, interstitial fluid, capillary wall
Passive Reabsorption
-no energy is required
-substances move down the electrochemical/osmotic gradient
Active Reabsorption
-occurs if any of the substances being transported requires energy
-movement against the electrochemical gradient
What % of Na+ is absorbed at the proximal tubule?
67%
What is the role of Na+ reabsorption at the proximal tubule?
-reabsorbing glucose, amino acids, H2O, Cl-, urea
What % of Na+ is absorbed at the ascending limb of the loop of henle?
25%
What is the role of Na+ reabsorption at the ascending loop of henle?
-kidney’s ability to produce urine of varying concentrations
What % of Na+ is absorbed at the distal and collecting tubules?
8%
What is the role of Na+ reabsorption at the distal and collecting tubules?
-variable
-subject to hormonal control
-regulating ECF volume
Na+ K+ ATPase Pump
-located on basolateral membrane
-essential for Na+ reabsorption
What % of total energy is spent by kidneys for Na+ transport?
80%
Water + Sodium = BFFs
-water follows reabsorbed sodium
-follows by osmosis
-main effects: a) ECF water volume b) blood volume c) blood pressure
Na+ reabsorption is almost always _____ transport
active
Co-Transporters
-move glucose, amino acids, Cl-
-generated by the electrochemical gradient
-coupled passive entrance as a result of active Na+ pumping
Fine-tuning of Na+ reabsorption is carried out in the _______ ________.
distal tubule
Too much body Na+, _____ is reabsorbed and hence ______ is excreted in urine.
less; more
Too little body Na+, _____ is reabsorbed and hence ______ is excreted in urine.
more; less
Renin-angiotensin-aldosterone System (RAAS)
-important for fine-tuning of Na+ regulation
Granular Cells and Na+ Reabsorption
-detect sodium load, change in pressure, volume
-lead to release of the Renin hormone
Renin coverts angiontensinogen (inactive) into ________________.
angiotension I
Angiotension I is converted to angiotension II (active) by _________-__________ enzyme.
angiotensin-converting
Angiotension II stimulates the secretion of ___________.
aldosterone (released by adrenal cortex)
Aldosterone Action
-acts of kidneys, DCT and collecting ducts
-this will increase Na+ reabsorption (Cl- follows)
-H2O is conserved
-ECF volume and arterial BP decrease
Increased Na+ reabsorption promotes _______ retention.
-water
The RAAS acts as a +/- feedback system.
negative feedback loop
Functions of the RAAS
-water retention
-constricting systemic arterioles
-stimulates thirst
-vasopressin secretion
Where does aldosterone act?
-on the last portion of the distal convoluted tubules and collecting ducts
What does aldosterone do?
-increase apical Na channels
-increases Na+/K+ ATPase pumps
Aldosterone Negative Feedback Loop
low ECF volume or low BP, more renin, more aldosterone, more Na reabsorption, increased ECF volume
Atrial Natriuretic Peptide (ANP)
-inhibits Na+ reabsorption
-opposes aldosterone
-decreases Na+ reabsorption
-decreases RAAS action
ANP Secretion
-secreted by atria in response to: a) being stretched (Na+ retention increased blood volume) b) expansion of ECF volume c) increased arterial pressure
Glucose and Amino Acid Reabsorption
-done by sodium dependent secondary active transport
Water Reabsorption
-80% is uncontrolled: 65% by proximal tubule 15% by loop of henle
-20% is controlled by vasopressin
ADH/Vasopressin
-Anti Diuretic Hormone
-regulates water reabsorption
-produced in the hypothalamus and released from the posterior pituitary
-acts on distal tubule and collecting duct
Aquaporine
-water channels
How is bulk flow enhanced?
increased plasma colloid osmotic pressure of peritubular capillaries
Regulated Water Reabsorption
-in distal portion of the nephron
Waste Products
-increase in concentration as water is reabsorbed
-cannot permeate tubular wall are are excreted in urine
Tubular Secretion
-the transfer of substances from peritubular capillaries into the tubular lumen
-tubules can selectively add some substances to filtrate
H+ Secretory Systen
-regulates acid-base balance
Where is H+ secreted?
-proximal, distal, collecting tubules
K+ Secretory System
-maintain normal membrane excitability in muscles and nerves
-K+ moves from capillaries to interstitial fluid
All filtered __ is reabsorbed
K+
Where is K+ secreted?
-only in distal and collecting tubules
-under control of aldosterone
Organic Ion Secretory System
-more efficient elimination of foreign organic compunds
Where are organic ions secreted?
-only in the proximal tubule
If on the basolatereral membrane, K+ is__________.
-recycled
-proximal tubule and loop of henle
If on the luminal membrane, K+ is ________.
-secreted
-distal portions
K+ Deficiency
-may be caused by aldosterone pathway activated by Na+
Isotonic
-the inside and outside are equal
If the concentration in the ECF is greater than in the cells: ECF __________
hypertonic
-water deficit
If the concentration in the ECF is less than in the cells: ECF __________
Hypotonic
-too much water in the ECF
Vertical Osmotic Gradient
-established in the interstitial fluid of the medulla
-the gradient exists between the tubular lumen and the surrounding interstitial fluid
-the gradient starts in the cortex (300) and increases as it moves into the medulla (1200)
Countercurrent Multiplication
-established the vertical osmotic gradient
-fluid in one tube flows the opposite way in the adjoining tube
Which limb of the loop of henle is permeable to H2O?
-the descending limb
Which limb of the loop of henle is used for NaCl reabsorption?
-the ascending limb (it is impermeable to water)
Water reabsorption is ________ in the distal tubule and collecting duct
variable, based on the secretion of ADH
Action of Vasopressin
- ADH binds with receptor sites on basolateral membrane
- cAMP second messenger system activated
- cAMP increases membrane permeability to H2O, water channels are inserted into the membrane
- water enters through the water channel
Dehydration
-small volume of concentrated urine excreted
-reabsorbed H2O picked up by peritubular capillaries and conserved for the body
-vasopressin secretion increases
Water Excess
-large volume of dilute urine
-no H2O reabsorbed
-excess H2O eliminated
-vasopressin secretion decreases
Diuresis
-increased urine production
Diabetes Mellitus
-sweet pee
-glucose in urine
-the filtered load exceeds reabsorption capacity
Diabetes Insipidus
-ADH deficiency
-produce 25-30L of urine per day
-always drinking water
Internal Urethral Sphincter
-smooth muscle (parasympathetic)
-relaxed bladder causes closure
External Urethral Sphincter
-skeletal muscle
-under voluntary control
