Chapter 25 Urinary System Flashcards
Urinary system organs
- kidneys are major excretory organs
- urinary bladder is the temporary storage reservoir for urine
- ureters transport urine from the kidneys to the bladder
- urethra transports urine out of the body
kidney functions
- removal of toxins, metabolic wastes, and excess ions from the blood
- regulation of blood volume, chemical composition, and pH
- gluconeogenesis during prolonged fasting
- endocrine function
- activation of vitamin D
endocrine functions
- renin- regulation of blood pressure and kidney function
- erythropoietin (EPO)- regulation of RBC production
renal cortex
a granular superficial region
renal medulla
-the cone shaped pyramids separated by renal columns
renal pelvis
the funnel-shaped tube within the renal sinus, continuous with the ureter
urine flow
-urine flow from pyramid -> minor calyces -> major calyces -> renal pelvis -> ureter
nephrons
- structural and functional units that form urine
- about 1 million per kidney (correction pyramid)
- 2 main parts:
- renal corpuscle
- renal tubule
renal corpuscle
-capsule (bowman’s) and glomerulus
renal tubule
-prox and distal convoluted tubule, nephron loop and collecting duct
two types of nephrons
- cortical nephrons
- juxtamedullary nephrons
cortical nephrons
- 85% of nephrons
- almost entirely in the cortex
- has short loop of henle and glomerulus
- efferent arteriole supplies peritubular capillaries
juxtamedullary nephrons
-long loops of henle deeply invade the medulla
-outside the cortex
-important in the production of concentrated urine
efferent arteriole supplies vasa recta
nephron capillary beds: glomerulus
- afferent arteriole -> glomerulus -> Efferent arteriole (only place in body)
- specialized for filtration
- blood pressure is high because:
- arterioles are high pressure
- afferent arterioles are larger in diameter than efferent arterioles
nephron capillary beds: peritubular capillaries
- low pressure
- porous
- meandering
- associated with cortical nephron
nephron capillary beds: vasa recta
- long and straight vessel loops of Henle
- juxtamedullary nephrons
- formation of concentrated urine
renal tubule
- glomerular capsule
- proximal convoluted tubule (PCT)- functions in reabsorption and secretion
- loop of Henle- descending and ascending limbs
- distal convoluted tubule (DCT)- secretion
- collecting duct- receives filtrate from many nephrons
juxtaglomerular complex (JGC)
- one per nephron
- important in regulation of filtrate formation and blood pressure
- involved modified portion of the:
- distal portion of the ascending limb of the loop of henle
- afferent (sometimes efferent) arteriole
juxtaglomerular complex: granular cells
- wall of afferent arteriole
- mechanoreceptors (monitor BP)
- secrete enzyme renin
juxtaglomerular complex- macular dense cells
- cells in ascending limb of tubule
- chemoreceptors monitor NaCl of filtrate entering the distal convoluted tubule
filtration membrane
- porous membrane between the blood and the capsular space
- consists of:
- fenestrated endothelium (pores) of the glomerular capillaries
- visceral membrane of the glomerular capsule (podocytes with foot processes and filtration slits)
- basement membrane- negatively charged basement membrane repels large plasma proteins
which of the following is not associated with the renal corpuscle
- a podocyte
- a vasa recta**
- a fenestrated capillary
- an efferent arteriole
which of the following is true about the macula dense cells
- they are mechanoreceptors
- they are found in the wall of the arteriole
- they monitor NaCl content*
- all of the above
mechanisms of urine formation
- glomerular filtration- “clean out closet”- passive nonselective
- tubular reabsorption- returns all glucose and amino acids, 99% of water, salt, and other components to the BLOOD
- tubular secretion- reverse of reabsorption - selective addition to urine
Step 1- glomerular filtration
- passive, nonselective process (no ATP)
- filtration membrane (Efficient)
- large plasma proteins are not filtered and function to maintain colloid osmotic pressure of the blood
- net filtration pressure (NFP) = pressure responsible for filtration
- negative pressure drives filtration
- glomerular filtration rate due to 3 factors:
- net filtration pressure
- total surface area (large)
- membrane permeability
Regulation of glomerular filtration rate
- GFR is tightly regulated to serve 2 crucial needs
- kidneys need a constant GFR to make filtrate
- body as a whole needs a constant BP
- the 2 are closely related, if GFR increases, urine output increases which reduced blood volume and BP
- GFR is tightly controlled by two types of mechanisms
- INTRINSIC CONTROLS
- EXTRINSIC CONTROLS
intrinsic controls of GFR
- renal autoregulation
- act locally within the kidney
- maintains a nearly constant GFR when MAP (mean arterial pressure) is in the range of 80-100 mm Hg
- two types of renal autoregulation
- myogenic mechanism- (stretch)
- tubuloglomerular feedback mechanism, which senses changes in Na concentration of filtrate
extrinsic controls of GFR
-nervous and endocrine mechanisms that maintain blood pressure, but affect kidney function
intrinsic controls: myogenic mechanism
- increased systemic BP stretches vascular smooth muscle -> constriction of afferent arterioles
- prevents glomerulus BP from rising
- protects glomeruli from damaging high BP
- decreased systemic BP -> dilation of afferent arterioles
- helps maintain normal GFR
intrinsic controls: tubuloglomerular feedback mechanism
- macula densa cells (in walls of ascending limb, salt monitoring)- flow dependent
- if GFR increases, filtrate flow rate increases in the tubule
- NaCl concentration in filtrate will be high because of insufficient time for reabsorption
- macula dense cells respond to increased NaCl by releasing a chemical that vasoconstricts the afferent arteriole -> decreased GFR (slows down rate of flow)
- the opposite occurs if GFR decreases and causes vasodilation of afferent arterioles
tubuloglomerular mechanism of autoregulation
- GFR increases
- increased filtrate flow
- flow past macula dense increases (in JGC)
- release of vasoactive chemicals
- afferent arteriole contracts
- resistance in afferent arteriole increases
- hydrostatic pressure in glomerulus decreases
- GFR decreases
extrinsic controls: sympathetic nervous system
- under normal conditions at rest: renal blood vessels are dilated and renal autoregulation (intrinsic) mechanisms prevail
- under extreme stress (low BP shock - need to maintain BP):
- norepinephrine and epinephrine are released
- both cause constriction of afferent arterioles which inhibit filtration of afferent arterioles which inhibit filtration and renin is released
- goal: restore blood volume and pressure
summary of intrinsic control
- myogenic mechanism- if increased BP, stretches arteriole wall, causes constriction and decreases BP
- tubuloglomerular feedback- if GFR increases, will have increased flow rate, NaCl will be high, macula dense cells (ascending limb) will detect and release a chemical for constriction
which of the following factors contributes to the higher filtration rate in the glomerular capillaries compared with other capillary beds
- the glomerular capillaries are fenestrated
- the diameter of the efferent arteriole is smaller than the diameter of the afferent arteriole
- the visceral layer of the glomerular capsule is very porous
- all of the above contribute*
where does filtration occur in the nephron
- glomerular capsule*
- proximal convoluted tubule
- loop of henle
- distal convoluted tubule
extrinsic controls renin-angiotensin-aldosterone
- main mechanism for raising BP**
- low BP causes granular cells to release renin
- renin assists in changing angiotensinogen to angiotensin 2
effects of angiotensin 2
- constricts arteriolar smooth muscle, causing MAP to rise
- triggers aldosterone secretion from adrenal cortex- stimulates the reabsorption of Na+ (Na moves into blood, water follows, conserves blood volume)
- stimulates the hypothalamus to release ADH (antidiuretic hormone) and activates the thirst center
step 2. tubular reabsorption
- a selective process that begins in the proximal convoluted tubule
- all organic nutrients are reabsorbed
- water and ion reabsorption are hormonally regulated
- includes active (requires ATP) and passive transport
- different areas of the tubules have different absorptive capabilities
- if not for tubular reabsorption all our plasma would drain away as urine in 30 mins
reabsorption of nutrients, water, and ions
- Na+ reabsorption- active transport
- organic nutrients (glucose, AA, vitamins)- by secondary active transport (carriers) -> when the carriers are saturated, the excess of that substance is excreted (glucose in urine is sign of DM)
- water- reabsorbed by osmosis- aided by pores called aquaporins
resabsorptive capabilities of renal tubules and collecting ducts
- PCT- site of most reabsorption (ions, water, nutrients)
- loop of henle- descending limb- H20
- ascending limb- Na, K, Cl
- DCT and collecting duct:
- hormonally regulated
- Na- aldosterone
- water- ADH
- Ca- parathyroid hormone
which of the following general functions can be assigned to the renin-angiotensin-aldosterone system
- water conservation
- blood pressure elevation
- lowering blood sodium levels
- both a and b*
- all of the above
if systemic BP is extremely low, epinephrine is released form adrenal medulla. This type of control is called
- extrinsic*
- myogenic mechanism
- intrinsic
- tubuloglomerular feedback
step 3: tubular secretion
- eliminates undesirable substances (e.g. urea and uric acid)
- disposes of substances such as drugs
- rids the body of excess K+
- controls blood pH by altering amounts of H+ or HCO3- in urine
- these solutes move from peritubular capillaries into filtrate
regulation of urine concentration and volume
- kidneys make adjustments to keep solute concentration constant, whether dehydrated or overhydrated
- osmolality of body fluids:
- the kidneys maintain osmolarity of plasma at about 300 mOsm, using countercurrent mechanisms
- allow the kidneys to vary urine concentration
countercurrent mechanism
- occurs when fluid flows in opposite directions in two adjacent segments of the same tube
- filtrate flow in the loop of henle
- blood flow in the vasa recta
- fluid flows in the opposite direction through two adjacent parallel sections of a nephron loop
countercurrent multiplier: loop of henle
- DESCENDING LIMB: reabsorption of water
- freely permeable to H20 NOT salt
- filtrate osmolality increases to about 1200 mOsm
- ASCENDING LIMB: reabsorption of salt
- selectively permeable to solutes
- impermeable to water and pumps out salt
- filtrate osmolality decreases to 100 mOsm
- filtrate is diluted in the ascending loop
dehydrated- maximal ADH
- if ADH is present, aquaporins are inserted in collect ducts
- water is reabsorbed back into capillaries
the descending limb of the nephron loop ___
- is not permeable to water
- is freely permeable to sodium and urea
- pulls water by osmosis into the lumen of the tubule
- contains fluid that becomes more concentrated as it moves down into the medulla*
at the collecting ducts, which hormone is required for the reabsorption of Na
- antidiuretic hormone (ADH)
- parathyroid hormone
- atrial natriuretic peptide
- aldosterone
diuretics
- chemicals that enhance the urinary output
- osmotic diuretics- substances not reabsorbed (e.g. high glucose in a diabetic patients, water follows glucose)
- ADH inhibitors such as alcohol
- substances that inhibit Na reabsorption and obligatory H2O reabsorption such as caffeine and many drugs
physical characteristics of urine
- color and transparency:
- clear, pale to deep yellow
- cloudy urine may indicate a UTI
- pink urine= blood
- odor:
- slightly aromatic when fresh
- develops ammonia odor upon standing
- may be altered by some drugs and vegetables
- diabetics= fruity smelling
ureters
- convey urine from kidneys to bladder
- enter the base of the bladder through the posterior wall
- as bladder pressure increases, distal ends of the ureters close, preventing backflow of urine
urinary bladder
- muscular sac for temporary storage of urine
- collapse when empty; rugae (folded walls) appear
- trigone (inferior portion of bladder)- infections tend to persist in this region
urethra
- sphincters:
- internal urethral sphincter- involuntary (smooth muscle) at bladder- > urethra function -> internal sphincter opens
- external urethral sphincter- voluntary (skeletal) muscle surrounding the urethra as it passes through the pelvic floor
drinking too much alcohol results in a headache the next day. Why does this happen
- alcohol stimulates pain receptors in the brain
- alcohol stimulates sodium reabsorption
- alcohol stimulates aldosterone secretion
- alcohol inhibits ADH secretion* i think
urine flows from kidney to bladder via
- nephrons
- urethra
- ureter *
- loop of henle
micturition
- urination or voiding
- three simultaneous events
- contraction of detrusor muscle by ANS
- opening of internal urethral sphincter by ANS
- opening of external urethral sphincter by somatic nervous system
reflexive urination infants
- distention of bladder activates stretch receptors
- excitation of parasympathetic neurons in reflex center of spinal cord
- contraction of the detrusor muscle
- opening of internal sphincter
- inhibition of somatic pathways to external sphincter, allowing its relaxation (opening)
pontine control centers mature between ages 2-3
- pontine storage center inhibits micturition- inhibits parasympathetic pathways and excites sympathetic and somatic efferent pathways
- pontine micturition center promotes micturition- excites parasympathetic pathways and inhibits sympathetic and somatic efferent pathways
