0-1 Chapter 23 Urinary System Flashcards
urinary system
principal means of waste removal
kidney functions
regulate blood volume and pressure, erythrocyte count, blood gases, blood pH, and electrolyte and acid base balance, eliminates wastes
urologists
treat both urinary and reproductive disorders
urinary system consists of 6 organs
2 kidneys, 2 ureters, urinary bladder, and urethra
Kidney
Secrete
secretes enzyme, renin, which activates hormonal mechanisms that control blood pressure and electrolyte balance
•secretes the hormone, erythropoietin, which stimulates the production of red blood cells
•final step in synthesizing hormone, calcitriol, which contributes to calcium homeostasis
waste
any substance that is useless to the body or present in excess of the body‟s needs
metabolic waste
waste substance produced by the body
urea formation
- proteins
- amino acids
- NH2 removed
- forms ammonia
- liver converts to urea
uric acid
product of nucleic acid catabolism
blood urea nitrogen (BUN)
expression of the level of nitrogenous waste in the blood
azotemia
elevated BUN
•indicates renal insufficiency
uremia
syndrome of diarrhea, vomiting, dyspnea, and cardiac arrhythmia stemming from the toxicity of nitrogenous waste
excretion
separation of wastes from body fluids and eliminating them
four body systems carry out excretion
respiratory system
integumentary system
digestive system
urinary system
respiratory system
CO2, small amounts of other gases, and water
integumentary system
water, inorganic salts, lactic acid, urea in sweat
digestive system
water, salts, CO2, lipids, bile pigments, cholesterol, other metabolic waste, and food residue
urinary system
many metabolic wastes, toxins, drugs, hormones, salts, H+ and water
Kidney
location
retroperitoneal along with ureters, urinary bladder, renal artery and vein, and adrenal glands
three protective connective tissue coverings
renal fascia
perirenal fat capsule
fibrous capsule
renal parenchyma
glandular tissue that forms urine
–appears C-shaped in frontal section
–encircles the renal sinus
renal sinus
contains blood and lymphatic vessels, nerves, and urine-collecting structures
•adipose fills the remaining cavity and holds structures into place
two zones of renal parenchyma
outer renal cortex
inner renal medulla
inner renal medulla
- renal columns –extensions of the cortex that project inward toward sinus
- renal pyramids –6 to 10 with broad base facing cortex and renal papilla facing sinus
lobe of the kidney
one pyramid and its overlying cortex
minor calyx
cup that nestles the papilla of each pyramid
•collects its urine
major calyces
formed by convergence of two or three minor calyces
renal pelvis
formed by convergence of two or three major calyces
ureter begins at
renal pelvis
ureter
a tubular continuation of the pelvis and drains the urine down to the urinary bladder
Blood Supply Diagram
Aorta, Renal a., Segmental a., Interlobar a., Arcuate a., Interlobular a.,Afferent arteriole —
Glomerulus, Efferent arteriole, Peritubular capillaries—–Vasa recta
Interlobular v., Arcuate v., Interlobar v., Renal v., Inferior vena cava
renal fraction
kidneys account for only 0.4% of body weight, they receive about 21% of the cardiac output
renal artery divides into segmental arteries that give rise to
- interlobar arteries -up renal columns, between pyramids
- arcuate arteries -over pyramids
- interlobular arteries -up into cortex
- branch into afferent arterioles -each supplying one nephron
- leads to a ball of capillaries -glomerulus
- blood is drained from the glomerulus by efferent arterioles
- lead to either peritubular capillaries or vasa recta around portion of the renal tubule
- interlobular veins or directly into arcuate veins -interlobar veins
renal vein empties into
inferior vena cava
peritubular capillaries
in the cortex, peritubular capillaries branch off of the efferent arterioles supplying the tissue near the glomerulus, the proximal and distal convoluted tubules
vasa recta
in medulla, the efferent arterioles give rise to the vasa recta, supplying the nephron loop portion of the nephron
filtration unit of the kidney is the
nephron
Nephron
each composed of two principal parts:
–renal corpuscle –filters the blood plasma
–renal tubule –long coiled tube that converts the filtrate into urine
renal corpuscle consists of
the glomerulus and a two-layered glomerular (Bowman) capsule that encloses glomerulus
glomerular (Bowman) capsule
–parietal (outer) layer of Bowman capsule is simple squamous epithelium
–visceral (inner) layer of Bowman capsule consists of elaborate cells called podocytes that wrap around the capillaries of the glomerulus
–capsular space separates the two layers of Bowman capsule-collects filtrate
vascular pole
the side of the corpuscle where the afferent arteriole enters the corpuscle and the efferent arteriole leaves
urinary pole
the opposite side of the corpuscle where the renal tubule begins
renal (uriniferous) tubule
a duct that leads away from the glomerular capsule and ends at the tip of the medullary pyramid
divided into four regions –
proximal convoluted tubule, nephron loop, distal convoluted tubule –parts of one nephron
–collecting duct receives fluid from many nephrons
proximal convoluted tubule(PCT)
arises from glomerular capsule
–longest and most coiled region
–simple cuboidal epithelium with prominent microvilli for majority of absorption - increase surface area for absorption
nephron loop (loop of Henle)
long U-shaped portion of renal tubule
–descending limb and ascending limb
thick segments
have simple cuboidal epithelium
-water impermeable
•initial part of descending limb and part or all of the ascending limb
•heavily engaged in the active transport of salts and have many mitochondria
thin segment
has simple squamous epithelium
•forms lower part of descending limb
•cells very permeable to water
distal convoluted tubule (DCT)
begins shortly after the ascending limb reenters the cortex
–shorter and less coiled that PCT
–cuboidal epithelium without microvilli
–DCT is the end of the nephron
collecting duct
receives fluid from the DCTs of several nephrons as it passes back into the medulla
–numerous collecting ducts converge toward the tip of the medullary pyramid
papillary duct
formed by merger of several collecting ducts
•30 papillary ducts end in the tip of each papilla
•collecting and papillary ducts lined with simple cuboidal epithelium
becomes urine when it enters the
collecting duct
flow of fluid from the point where the glomerular filtrate is formed to the point where urine leaves the body:
glomerular capsule → proximal convoluted tubule → nephron loop → distal convoluted tubule → collecting duct → papillary duct → minor calyx → major calyx → renal pelvis → ureter → urinary bladder → urethra
cortical nephrons
–85% of all nephrons
–short nephron loops
–efferent arterioles branch into peritubular capillaries around PCT and DCT
juxtamedullary nephrons
–15% of all nephrons
–very long nephron loops, maintain salinity gradient in the medulla and helps conserve water
–efferent arterioles branch into vasa recta around long nephron loop
cortical nephrons have
peritubular capillaries
juxtamedullary nephrons have
vasa recta
renal plexus
nerves and ganglia wrapped around each renal artery
–follows branches of the renal artery into the parenchyma of the kidney
–issues nerve fibers to the blood vessels and convoluted tubules of the nephron
carries sympathetic innervation from the abdominal aortic plexus
- stimulation reduces glomerular blood flow and rate of urine production
- respond to falling blood pressure by stimulating the kidneys to secrete renin, an enzyme that activates hormonal mechanisms to restore blood pressure
carries parasympathetic innervation from the vagus nerve
increases rate of urine production
kidneys convert blood plasma to urine in three stages
glomerular filtration
–tubular reabsorption and secretion
–water conservation
glomerular filtrate
–fluid in capsular space
–blood plasma without protein
tubular fluid
–fluid in renal tubule
–similar to above except tubular cells have removed and added substances
urine
–once it enters the collecting duct
–only remaining change is water content
glomerular filtration
a special case of the capillary fluid exchange process in which water and some solutes in the blood plasma pass from the capillaries of the glomerulus into the capsular space of the nephron
NO REABSORPTION
filtration membrane
barriers
three barriers through which fluid passes
fenestrated endothelium of glomerular capillaries
•highly permeable
basement membrane
- proteoglycan gel, negative charge, excludes molecules greater than 8nm
- albumin repelled by negative charge
- blood plasma is 7% protein, the filtrate is only 0.03% protein
filtration slits
podocyte cell extensions (pedicels) wrap around the capillaries to form a barrier layer with 30 nm filtration slits
•negatively charged which is an additional obstacle for large anions
Filtration Membrane passes
•almost any molecule smaller than 3 nm can pass freely through the filtration membrane
–water, electrolytes, glucose, fatty acids, amino acids, nitrogenous wastes, and vitamins
•some substances of low molecular weight are bound to the plasma proteins and cannot get through the membrane
–most calcium, iron, and thyroid hormone
•unbound fraction passes freely into the filtrate
kidney infections and trauma
can damage the filtration membrane and allow albumin or blood cells to filter.
proteinuria (albuminuria
presence of protein in the urine
hematuria
presence of blood in the urine
blood hydrostatic pressure (BHP)
–much higher in glomerular capillaries (60 mm Hg compared to 10 to 15 in most other capillaries)
–because afferent arteriole is larger than efferent arteriole
–larger inlet and smaller outlet
hydrostatic pressure in capsular space
–18 mm Hg due to high filtration rate and continual accumulation of fluid in the capsule
colloid osmotic pressure (COP) of blood
about the same here as elsewhere -32 mm Hg
–glomerular filtrate is almost protein-free and has no significant COP
higher outward pressure of 60 mm Hg
opposed by two inward pressures of 18 mm Hg and 32 mm Hg
net filtration pressure
60out–18in–32in= 10 mm Hgout
glomerular filtration rate (GFR)
the amount of filtrate formed per minute by the 2 kidneys combined
–GFR = NFP x Kf125 mL / min or 180 L / day, male
–GFR = NFP x Kf105 mL / min or 150 L / day, female
total amount of filtrate produced equals
50 to 60 times the amount of blood in the body
–99% of filtrate is reabsorbed since only 1 to 2 liters urine excreted / day
GFR too high
–fluid flows through the renal tubules too rapidly for them to reabsorb the usual amount of water and solutes
–urine output rises
–chance of dehydration and electrolyte depletion
GFR too low
–wastes reabsorbed
–azotemia may occur
GFR controlled
by adjusting glomerular blood pressure from moment to moment
GFR control is achieved by three homeostatic mechanisms
–renal autoregulation
–sympathetic control
–hormonal control
renal autoregulation
the ability of the nephrons to adjust their own blood flow and GFR without external (nervous or hormonal) control
•enables them to maintain a relatively stable GFR in spite of changes in systemic arterial blood pressure
two methods of autoregulation
myogenic mechanism and tubuloglomerular feedback
myogenic mechanism
based on the tendency of smooth muscle to contract when stretched
–increased arterial blood pressure stretches the afferent arteriole
–arteriole constricts and prevents blood flow into the glomerulus from changing much
–when blood pressure falls
–the afferent arteriole relaxes
–allows blood flow more easily into glomerulus
–filtration remains stable
tubuloglomerular feedback
mechanism by which glomerulus receives feedback on the status of the downstream tubular fluid and adjust filtration to regulate the composition of the fluid, stabilize its own performance, and compensate for fluctuation in systemic blood pressure
juxtaglomerular apparatus
complex structure found at the very end of the nephron loop where it has just reentered the renal cortex
–loop comes into contact with the afferent and efferent arterioles at the vascular pole of the renal corpuscle
three special kind of cells occur in the juxtaglomerular apparatus
macula densa
juxtaglomerular (JG) cells
mesangial cells
macula densa
patch of slender, closely spaced epithelial cells at end of the nephron loop on the side of the tubules facing the arterioles
–senses variations in flow or fluid composition and secretes a paracrine that stimulates JG cells
juxtaglomerular (JG) cells
enlarged smooth muscle cells in the afferent arteriole directly across from macula densa
–when stimulated by the macula
–they dilate or constrict the arterioles
–they also contain granules of renin, which they secrete in response to drop in blood pressure
mesangial cells
in the cleft between the afferent and efferent arterioles and among the capillaries of the glomerulus
–connected to macula densa and JG cells by gap junctions and communicate by means of paracrines
–build supportive matrix for glomerulus, constrict or relax capillaries to regulate flow
if GFR rises
–the flow of tubular fluid increases and more NaCl is reabsorbed
–macula densa stimulates JG cells with a paracrine
–JG cells contract which constricts afferent arteriole, reducing GFR to normal OR
–mesangial cells may contract, constricting the capillaries and reducing filtration
if GFR falls
–macula relaxes afferent arterioles and mesangial cells
–blood flow increases and GFR rises back to normal
Effectiveness of Autoregulation
•maintains a dynamic equilibrium -GFR fluctuates within narrow limits only
•renal autoregulation can not compensate for extreme blood pressure variation
–over a MAP range of 90 –180 mm Hg, the GFR remains quite stable
Sympathetic Control of GFR
- sympathetic nerve fibers richly innervate the renal blood vessels
- sympathetic nervous system and adrenal epinephrine constrict the afferent arterioles in strenuous exercise or acute conditions like circulatory shock
Renin-Angiotensin-Aldosterone Mechanism
- renin secreted by juxtaglomerular cells if BP drops dramatically
- renin converts angiotensinogen, a blood protein, into angiotensin I
- in the lungs and kidneys, angiotensin-converting enzyme (ACE) converts angiotensin I to angiotensin II, the active hormone
Angiotensin II
- potent vasoconstrictor raising BP throughout body
- constricts efferent arteriole raising GFR despite low BP
- lowers BP in peritubular capillaries enhancing reabsorption of NaCl & H2O
- angiotensin II stimulates adrenal cortex to secrete aldosterone promoting Na+and H2O reabsorption in DCT and collecting duct
- stimulates posterior pituitary to secrete ADH which promotes water reabsorption by collecting duct
- stimulates thirst & H2O intake
Tubular Reabsorption and Secretion
•conversion of glomerular filtrate to urine involves the removal and addition of chemicals by tubular reabsorption and secretion
–occurs through PCT to DCT
–tubular fluid is modified
Tubular Reabsorption and Secretion
steps involved include:
–tubular reabsorption
–tubular secretion
–water conservation
Proximal Convoluted Tubule
PCT reabsorbs about 65% of glomerular filtrate, removes some substances from the blood, and secretes them into the tubular fluid for disposal in urine
–prominent microvilli and great length
–abundant mitochondria provide ATP for active transport
–PCTs alone account for about 6% of one‟s resting ATP and calorie consumption
tubular reabsorption
process of reclaiming water and solutes from the tubular fluid and returning them to the blood
two routes of reabsorption
transcellular route
transcellular route
•substances pass through the cytoplasm of the PCT epithelial cells and out their base
paracellular route
- substances pass between PCT cells
* junctions between epithelial cells are quite leaky and allow significant amounts of water to pass through
solvent drag
water carries with it a variety of dissolved solutes
sodium reabsorption is the key to everything else
–creates an osmotic and electrical gradient that drives the reabsorption of water and other solutes
–most abundant cation in filtrate
–creates steep concentration gradient that favors its diffusion into the epithelial cells
two types of transport proteins in the apical cell surface are responsible for sodium uptake
–symports that simultaneously bind Na+ and another solute such as glucose, amino acids or lactate
–a Na+-H+ antiport that pulls Na+ into the cell while pumping out H+ into tubular fluid
sodium is prevented from accumulating in the epithelial cells by Na+-K+pumps in the basal surface of the epithelium
–pumps Na+out into the extracellular fluid
–picked up by peritubular capillaries and returned to the blood stream
–ATP consuming active transport pumps
secondary active transport
Na+transporting symports in apical cell membrane do not consume ATP, are considered an example of secondary active transport for their dependence on the Na+-K+pumps at the base of the cell
negative chloride ions follow the positive sodium ions by electrical attraction
–various antiports in the apical cell membrane that absorb Cl-in exchange for other anions they eject into the tubular fluid –K+-Cl-symport
potassium, magnesium, and phosphate ions
diffuse through the paracellular route with water
phosphate
phosphate Is also cotransported into the epithelial cells with Na+
some calcium is reabsorbed
through the paracellular route in the PCT, but most Ca2+reabsorption occurs later in the nephron
glucose
is cotransported with Na+by sodium-glucose transport (SGLT) proteins.
urea
diffuses through the tubule epithelium with water –reabsorbs 40 –60% in tubular fluid
–kidneys remove about half of the urea from the blood -creatinine is not reabsorbed at all
Water Reabsorption
- kidneys reduce 180 L of glomerular filtrate to 1 or 2 liters of urine each day
- two-thirds of water in filtrate is reabsorbed by the PCT
Reabsorption of all the salt and organic solutes makes the tubule cells and tissue fluid
hypertonic
aquaporins
water follows solutes by osmosis through both paracellular and transcellular routes through water channels called aquaporins
obligatory water reabsorption
in PCT, water is reabsorbed at constant rate called obligatory water reabsorption
Uptake by the Peritubular Capillaries
•after water and solutes leave the basal surface of the tubular epithelium, they are reabsorbed by the peritubular capillaries
–reabsorbed by osmosis and solvent drag
three factors promote osmosis into the capillaries
–accumulation of reabsorbed fluid around the basolateral sides of epithelial cell creates high interstitial fluid pressure that drives water into the capillaries
–narrowness of efferent arterioles lowers blood hydrostatic pressure in peritubular capillaries so there is less resistance to absorption
–proteins remain in blood after filtration, which elevates colloid osmotic pressure
Transport Maximum of Glucose
there is a limit to the amount of solute that the renal tubules can reabsorb
•limited by the number of transport proteins in the plasma membrane
•if all transporters are occupied as solute molecules pass
–excess solutes appear in urine
transport maximum is reached when
transporters are saturated
•each solute has its own transport maximum
glycosuria
any blood glucose level above 220 mg/dL results in
tubular secretion
process in which the renal tubule extracts chemicals from the capillary blood and secretes them into tubular fluid
two purposes in proximal convoluted tubule and nephron loop
waste removal
acid-base balance
waste removal
•urea, uric acid, bile acids, ammonia, catecholamines, prostaglandins and a little creatinine are secreted into the tubule
•secretion of uric acid compensates for its reabsorption earlier in PCT
•clears blood of pollutants, morphine, penicillin, aspirin, and other drugs
–explains need to take prescriptions 3 to 4 times/day to keep pace with the rate of clearance
acid-base balance
•secretion of hydrogen and bicarbonate ions help regulate the pH of the body fluids
primary function of nephron loop
is to generate salinity gradient that enables collecting duct to concentrate the urine and conserve water
electrolyte reabsorption from filtrate
–thick segment reabsorbs 25% of Na+, K+, and Cl-
•ions leave cells by active transport and diffusion
–NaCl remains in the tissue fluid of renal medulla
–water can not follow since thick segment is impermeable to water
–tubular fluid very dilute as it enters distal convoluted tubule
DCT and Collecting Duct
•fluid arriving in the DCT still contains about 20% of the water and 7% of the salts from glomerular filtrate
–if this were all passed as urine, it would amount to 36 L/day
DCT and collecting duct reabsorb variable amounts of water salt and are regulated by several hormones
–aldosterone, atrial natriuretic peptide, ADH, and parathyroid hormone
two kinds of cells in the DCT and collecting duct
principal cells
intercalated cells
principal cells
- most numerous
- have receptors for hormones
- involved in salt and water balance
intercalated cells
•involved in acid/base balance by secreting H+ into tubule lumen and reabsorbing K+
aldosterone
the “salt-retaining” hormone –steroid secreted by the adrenal cortex •when blood Na+concentration falls or •when K+concentration rises •or drop in blood pressure renin release angiotensin II formation stimulates adrenal cortex to secrete aldosterone
functions of aldosterone
–acts on thick segment of nephron loop, DCT, and cortical portion of collecting duct
•stimulates the reabsorption of more Na+and secretion of K+
•water and Cl-follow the Na+
•net effect is that the body retains NaCl and water
–helps maintain blood volume and pressure
•the urine volume is reduced
•the urine has an elevated K+concentration
atrial natriuretic peptide (ANP)
secreted by atrial myocardium of the heart in response to high blood pressure
•has four actions that result in the excretion of more salt and water in the urine, thus reducing blood volume and pressure
has four actions
–dilates afferent arteriole, constricts efferent arteriole -INCREASE GFR
–inhibits renin and aldosterone secretion
–inhibits secretion of ADH
–inhibits NaCl reabsorption by collecting duct
antidiuretic hormone (ADH)
secreted by posterior lobe of pituitary
•in response to dehydration and rising blood osmolarity
–stimulates hypothalamus
–hypothalamus stimulates posterior pituitary
•action -make collecting duct more permeable to water
–water in the tubular fluid reenters the tissue fluid and bloodstream rather than being lost in urine
parathyroid hormone
(PTH) secreted from parathyroid glands in response to calcium deficiency (hypocalcemia)
–acts on PCT to increase phosphate excretion
–acts on the thick segment of the ascending limb of the nephron loop, and on the DCT to increase calcium reabsorption
–increases phosphate content and lowers calcium content in urine
–because phosphate is not retained, the calcium ions stay in circulation rather than precipitating into the bone tissue as calcium phosphate
–PTH stimulates calcitriol synthesis by the epithelial cells of the PCT
Summary of Tubular Reabsorption and Secretion
PCT reabsorbs
65% of glomerular filtrate and returns it to peritubular capillaries
–much reabsorption by osmosis & cotransport mechanisms linked to active transport of sodium
nephron loop reabsorbs
another 25% of filtrate
DCT reabsorbs
Na+, Cl-and water under hormonal control, especially aldosterone and ANP
•the tubules also extract drugs, wastes, and some solutes from the blood and secretethem into the tubular fluid
DCT completes the process of
determining the chemical composition of urine
collecting duct
conserves water
Water Conservation
- the kidney eliminates metabolic wastes from the body, but also prevents excessive water loss as well
- as the kidney returns water to the tissue fluid and bloodstream, the fluid remaining in the renal tubules passes as urine, and becomes more concentrated
Collecting Duct Concentrates Urine
- collecting duct (CD) begins in the cortex where it receives tubular fluid from several nephrons
- as CD passes through the medulla, it reabsorbs water and concentrates urine up to four times
- medullary portion of CD is more permeable to water than to NaCl
- as urine passes through the increasingly salty medulla, water leaves by osmosis concentrating urine
water diuresis
drinking large volumes of water will produce a large volume of hypotonic urine
–cortical portion of CD reabsorbs NaCl, but it is impermeable to water
–salt removed from the urine stays in the CD
–urine concentration may be as low as 50 mOsm/L
producing hypertonic urine
–dehydration causes the urine to become scanty and more concentrated
–high blood osmolarity stimulates posterior pituitary to release ADH and then an increase in synthesis of aquaporin channels by renal tubule cells
–more water is reabsorbed by collecting duct
–urine is more concentrated
If BP is low in a dehydrated person
GFR will be low.
–filtrate moves more slowly and more time for reabsorption –
–more salt removed, more water reabsorbed and less urine produced
vasa recta
capillary branching off efferent arteriole in medulla
–provides blood supply to medulla and does not remove NaCl and urea from medullary ECF
urinalysis
the examination of the physical and chemical properties of urine
appearance
clear, almost colorless to deep amber -yellow color due to urochrome pigment from breakdown of hemoglobin (RBCs) –other colors from foods, drugs or diseases
–cloudiness or blood could suggest urinary tract infection, trauma or stones
pyuria
pus in the urine
hematuria
blood in urine due to urinary tract infection, trauma, or kidney stones
odor
bacteria degrade urea to ammonia, some foods impart aroma
specific gravity
compared to distilled water
•density of urine ranges from 1.001 -1.028
osmolarity-
blood = 300 mOsm/L)
•ranges from 50 mOsm/L to 1,200 mOsm/L in dehydrated person
pH
range: 4.5 to 8.2, usually 6.0 (mildly acidic)
chemical composition:
95% water, 5% solutes
normal to find
urea, NaCl, KCl, creatinine, uric acid, phosphates, sulfates, traces of calcium, magnesium, and sometimes bicarbonate, urochrome and a trace of bilirubin
abnormal to find
glucose, free hemoglobin, albumin, ketones, bile pigments
Urine Volume - normal
normal volume for average adult -1 to 2 L/day
polyuria
output in excess of 2 L/day
oliguria
output of less than 500 mL/day
anuria
0 to 100 mL/day
diabetes
any metabolic disorder resulting in chronic polyuria
at least four forms of diabetes
–diabetes mellitus type 1, type 2, and gestational diabetes
–diabetes insipidus
diabetes mellitus type 1, type 2, and gestational diabetes
- high concentration of glucose in renal tubule
- glucose opposes the osmotic reabsorption of water
- more water passes in urine (osmotic diuresis)
- glycosuria –glucose in the urine
–diabetes insipidus
- ADH hyposecretion causing not enough water to be reabsorbed in the collecting duct
- more water passes in urine
diuretics
any chemical that increases urine volume
•commonly used to treat hypertension and congestive heart failure by reducing the body‟s fluid volume and blood pressure
some increase GFR
caffeine dilates the afferent arteriole
reduce tubular reabsorption of water
alcohol inhibits ADH secretion
act on nephron loop (loop diuretic)
inhibit Na+ -K+-Cl-symport
•impairs countercurrent multiplier reducing the osmotic gradient in the renal medulla
•collecting duct unable to reabsorb as much water as usual
Renal Function Tests
- tests for diagnosing kidney disease
- evaluating their severity
- monitoring their progress
- determine renal clearance
- determine glomerular filtration rate
renal clearance
the volume of blood plasma from which a particular waste is completely removed in 1 minute
represents the net effect of three processes:
+ glomerular filtration of the waste
+ amount added by tubular secretion
–amount removed by tubular reabsorption
renal clearance
kidney disease often results in
lowering of GFR –need to measure patient‟s GFR
–can not use clearance rate of urea
•some urea filtered by glomerulus is reabsorbed in the tubule
•some urea is secreted into the tubule
inulin
use inulin, a plant polysaccharide to determine GFR
–neither reabsorbed or secreted by the renal tubule
–inulin GFR = renal clearance on inulin
Urine Storage and Elimination
- urine is produced continually
- does not drain continually from the body
- urination is episodic –occurring when we allow it
- made possible by storage apparatus
- and neural controls of this timely release
ureters
retroperitoneal, muscular tube that extends from the kidney to the urinary bladder
–about 25 cm long
–passes posterior to bladder and enters it from below
–flap of mucosa acts as a valve into bladder
•keeps urine from backing up in the ureter when bladder contracts
3 layers of ureter
adventitia
muscularis
mucosa
adventitia
connective tissue layer that connects ureter to surrounding structures
muscularis
2 layers of smooth muscle with 3rdlayer in lower ureter
–urine enters, it stretches and contracts in peristaltic wave
mucosa
transitional epithelium
–begins at minor calyces and extends through the bladder
urinary bladder
muscular sac located on floor of pelvic cavity
–inferior to peritoneum and posterior to pubic symphysis
3 layers
parietal peritoneum,
muscularis
mucosa
parietal peritoneum,
superiorly, fibrous adventitia other areas
muscularis
detrusor muscle -3 layers of smooth muscle
mucosa
transitional epithelium
rugae
conspicuous wrinkles in relaxed bladder
trigone
smooth-surfaced triangular area marked with openings of ureters and urethra
capacity
moderately full is 500 ml, max. is 700 -800 ml
–highly distensible
–as it fills, it expands superiorly
–rugae flatten
–epithelium thins from five or six layers to two or three
renal calculus (kidney stone)
hard granule of calcium phosphate, calcium oxalate, uric acid, or a magnesium salt called struvite
•form in the renal pelvis
•usually small enough to pass unnoticed in the urine flow
causes
include hypercalcemia, dehydration, pH imbalances, frequent urinary tract infections, or enlarged prostate gland causing urine retention
treatment
includes stone dissolving drugs, often surgery, or lithotripsy–nonsurgical technique that pulverizes stones with ultrasound
lithotripsy
nonsurgical technique that pulverizes stones with ultrasound
Female Urethra
- 3 to 4 cm long
* bound to anterior wall of vagina
external urethral orifice
–between vaginal orifice and clitoris
internal urethral sphincter
–detrusor muscle thickening
–smooth muscle under involuntary control
external urethral sphincter
–where the urethra passes through the pelvic floor
–skeletal muscle under voluntary control
Male Urethra
18 cm long •3 regions of male urethra –prostatic urethra (2.5 cm) •passes through prostate gland –membranous urethra (.5 cm) •passes through muscular floor of pelvic cavity –spongy (penile) urethra (15 cm) •passes through penis in corpus spongiosum
internal urethral sphincter
detrusor muscle thickening
external urethral sphincter
part of skeletal muscle of pelvic floor
Urinary Tract Infection (UTI)
cystitis
pyelitis
pyelonephritis
cystitis
infection of the urinary bladder
–especially common in females due to short urethra
–frequently triggered by sexual intercourse
–can spread up the ureter causing pyelitis
pyelitis
infection of the renal pelvis
pyelonephritis
infection that reaches the cortex and the nephrons
–can result from blood-borne bacteria
Voiding Urine
•between acts of urination, the bladder is filling
–detrusor muscle relaxes
–urethral sphincters are tightly closed
•accomplished by sympathetic pathway from upper lumbar spinal cord
•postganglionic fibers travel through the hypogastric nerve to the detrusor muscle (relax) and internal urethral sphincter (excite)
–somatic motor fibers from upper sacral spinal cord through pudendal nerve to supply the external sphincter give us voluntary control
voluntary control
somatic motor fibers from upper sacral spinal cord through pudendal nerve to supply the external sphincter give us voluntary control
micturition
the act of urinating
micturition reflex
spinal reflex that partly controls urination
involuntary control
–filling of the bladder to about 200 mL excites stretch receptors in the bladder wall
–send sensory signals through fibers in pelvic nerve to sacral spinal cord (S2or S3)
–motor signals travel back from the spinal cord to the bladder by way of motor fibers in pelvic nerve and parasympathetic ganglion in bladder wall
–excites detrusor muscle and relaxes internal urethral sphincter
–results in emptying bladder
–if there was no voluntary control over urination, this reflex would be the only means of control
voluntary control
–nucleus integrates information about bladder tension with information from other brain centers
•urination can be prompted by fear
•inhibited by knowledge that the circumstances are inappropriate for urination
–fibers from micturition center descend the spinal cord
•through reticulospinal tracts
–some fibers inhibit sympathetic fibers than normally keep internal urethral sphincter contracted
–others descend farther to sacral spinal cord
•excite parasympathetic neurons that stimulate the detrusor to contract and relax the internal urethral sphincter
–initial detrusor contraction raises pressure in bladder, stimulate stretch receptors, bringing about more forceful contraction
–external urethral sphincter receives nerve fibers from cerebral cortex by way of corticospinal tract
•inhibit somatic motor neurons that normally keep that sphincter constricted
micturition center
nucleus in the pons that receives some input from bladder stretch receptors that ascends the spinal cord
Micturition Reflex
•urge to urinate usually arises at an inconvenient time
–one must suppress it
–stretch receptors fatigue and stop firing
•as bladder tension increases
–signals return with increasing frequency and persistence
•there are times when the bladder is not full enough to trigger the micturition reflex but one wishes to „go‟ anyway
–Valsalva maneuver used to compress bladder
–excites stretch receptors early getting the reflex started
renal insufficiency
a state in which the kidneys cannot maintain homeostasis due to extensive destruction of their nephrons
causes of nephron destruction
–hypertension, chronic kidney infections, trauma, prolonged ischemia and hypoxia, poisoning by heavy metals or solvents, blockage of renal tubules in transfusion reaction, atherosclerosis, diabetes, or glomerulonephritis
nephrons can
regenerate and restore kidney function after short-term injuries
–others nephrons hypertrophy to compensate for lost kidney function
•can survive with one-third of one kidney
•when 75% of nephrons are lost and urine output of 30 mL/hr is insufficient (normal 50 -60 mL/hr) to maintain homeostasis
hemodialysis
procedure for artificially clearing wastes from the blood
–wastes leave bloodstream and enter the dialysis fluid as blood flows through a semipermeable cellophane tube; also removes excess body water
