Urine Formation, Storage, and Elimination Flashcards
does total fluid volume in ones body fluctuate or remain stable?
despite daily fluctuations in fluid intake, total fluid volume in ones body remains stable
the osmolarity of the glomerular filtrate
is similar to that of the blood
the osmolarity of the tubular fluid
increases as it flows down the descending limb of the nephron loop, then decreases as it flows up the ascending limb of the nephron loop, and decreases even more as it flows through the DCT and the collecting duct
water
gets reabsorbed by osmosis as tubular fluid flows through descending limb
sodium, potassium, and chloride ions
actively reabsorbed from the ascending limb; water doesn’t follow because ascending limb impermeable
additional solutes, but no more water, get
reabsorbed from the DCT
principal cells in collecting ducts
are impermeable to water when ADH levels are low
urine can be as much as _______ _______ more dilute than blood plasma or glomerular filtrate
four times
when water intake is low or when water loss is high
the kidneys produce small volumes of highly concentrated urine because ADH has a strong influence on the collecting ducts
osmolarity of the interstitial fluid
increases four-fold from renal cortex to renal medulla because of presence of sodium ions, chloride ions, and urea
medullary portion of the collecting duct
is more permeable to water than to NaCl
concentrated urine is formed why
because the nephron loop creates a countercurrent multiplier to maintain an osmotic gradient in the interstitial fluid of the renal medulla
descending limb permeability
permeable to water but not permeable to sodium or chloride
water leaves the descending limb
which increases concentration of tubular fluid
ascending limb permeability
impermeable to water;
sodium ions, potassium ions, and chloride ions are transported out of tubular fluid
concentration of the tubular fluid
decreases but osmolarity of renal medulla stays high
collecting duct
somewhat permeable to urea; urea continually recycles between collecting ducts and medulla to increase osmolarity in medulla
countercurrent exchange system
develops from the arrangement of juxtamedullary nephrons and the vasa recta
as blood flows into the medulla
water diffuses out of the vasa racta and sodium ions and chloride ions diffuse into vasa recta
as blood flows out of the medulla
sodium ions and chloride ions diffuse out of the vasa recta and water diffuses into vasa recta
net result of the countercurrent exchange system
reabsorption of water from tubular fluid; volume of blood at end of vasa recta is greater than at beginning of vasa recta
overall effect of forming concentrated urine
ADH makes the collecting ducts more permeable to water by inserting aquaporins into the membranes of the principal cells, and the osmotic gradient in the renal medulla “pulls” water out of the collecting ducts to form concentrated urine
how much water in the filtrate can be reabsorbed
up to 99%
urinalysis
examines the physical, chemical, and microscopic properties of urine
the color of urine
urine varies from nearly colorless to yellow to amber depending on diet and concentration
yellow color of urine
is due to urochrome pigment produced during break down of hemoglobin
what other factors may affect the color of urine
foods, vitamins, and drugs
urine is typically clear
but it will turn cloudy as a consequence of bacterial growth or from pus formation caused by a urinary tract infection
the odor of urine
becomes ammonia-like upon standing, because bacteria change urea to ammonia
some people inherit a tendency to form
methylmercaptan after eating asaparagus; their urine has a very pungent odor
diabetics odor of urine
produce ketone bodies; their urine has a sweet and fruity odor
people with phenylketonuria
produce urine that smells like a mouse cage
people with urinary tract infections
can produce urine with a rotten odor
the pH of urine ranges from
4.5 to 8.2; but is usually slightly acidic
high protein diets
increase acidity of urine
vegetarian diets
decrease acidity of urine
urine has a higher specific gravity than water, depending on
solute concentration
composition of urine
95% water and 5% solutes; urea is most abundant solute, but NaCl, KCl, creatinine, uric acid, and other mineral salts may also be present
normal urine volume
1-2 liters per day
polyuria
excessive production of urine
oligouria
scanty output of urine
anuria
an output of less than 100mL per day
diabetes
one of several metabolic disorders characterized by polyuria
excess glucose in the tubular fluid
blocks reabsorption of water and leads to dehydration
diabetes mellitus and gestational diabetes
result from hyperglycemia and can be diagnosed from glycosuria
hyposecretion of ADH
prevents the collecting ducts from reabsorbing water, causing diabetes insipidus to develop
diuretics
substances that increase urine volume by increasing glomerular filtration and/or reducing tubular reabsorption
caffeine
a diuretic; dilates afferent arterioles, which increases GFR
alcohol
a diuretic; inhibits ADH secretion, which reduces tubular reabsorption of water
Lasix
a diuretic; inhibits sodium reabsorption from nephron loop, which reduces reabsorption of water from collecting duct
renal clearance
measures the volume of blood that is cleared of a particular substance and it is expressed in mL/min
solute clearance
depends on glomerular filtration, tubular reabsorption, secretion
blood sample and urine sample
are collected and concentration of urea in each is measured and compared to rate of urine output
importance of renal clearance
important during drug therapy because it allows drug dosage to be set to maintain therapeutic levels of that drug
glomerular filtration rate can be assessed by
measuring the rate of urine output and the concentration of a solute that completely remains in the tubular fluid and gets cleared in the urine
inulin
completely filtered by glomerulus and added to urine; found in artichokes and garlic; renal clearance is equal to GFR
clearance value less than that of inulin
means substance has been reabsorbed
clearance value greater than that of inulin
means substance has been secreted into tubular fluid
ureter
is 25 cm long and transports urine from the renal pelvis to the urinary bladder
arrangement of ureters
at back of bladder prevents backflow of urine as bladder fills
the wall of the ureter is composed of
three layers
adventitia of ureter
connective tissue that anchors ureters to surrounding tissues
muscularis of ureter
composed of two layers of smooth muscle
contractions of muscularis
initiate peristalsis to move urine through ureter toward urinary bladder
mucosa of ureter
has transitional epithelium and underlying lamina propria that contains collagen and elastic fibers
mucus of mucosa layer of ureter
is secreted to protect ureter from acidity of urine
the urinary bladder
a hollow muscular organ on the floor of the pelvic cavity
trigone of urinary bladder
a small triangular area in the floor of the bladder; bounded by openings of ureters and urethra
the wall of the urinary bladder consists of
three layers
fibrous adventitia of urinary bladder
continues with adventitia of ureters
detrusor muscle of urinary bladder
consists of three layers of smooth muscle that form internal urethral sphincter at base of bladder
mucosa layer of urinary bladder
has transitional epithelium
when the bladder is relaxed
mucosa exhibits conspicuous rugae
the bladder is highly distensible and typically holds
500 mL of urine, but it can hold up to 800 mL
the urethra
a small tube leading from the floor of the bladder to the outside of the body
female urethra
3-4 cm long
male urethra
15-20 cm long
prostatic urethra
passes through prostate gland
membranous urethra
passes through urogenital diaphragm
penile urethra
passes through length of penis
the urethral mucosa
contains transitional epithelium near the bladder, pseudostratified epithelium along most of its length, and stratified squamous epithelium near the external urethral orifice
male urethra contains
urethral glands that secrete mucus
the muscularis of the urethra
contains skeletal muscle fibers where it passes through the urogenital diaphragm to form the external urethral sphincter
micturition
(urination; voiding) empties urinary bladder and is controlled by a spinal micturition reflex
for micturition to occur
detrusor muscle must contract, internal urethral sphincter must relax, external urethral sphincter must open
when urine volume reaches 200 mL to 400 mL
stretch receptors in the wall of the urinary bladder send nerve impulses to the sacral portion of the spinal cord
when urine volume reaches 200 mL to 400 mL- signals are also sent to
micturition center in pons that integrates information about filling urinary badder with information from other brain centers
urination can be triggered by
fear or inhibited by behavioral standards
parasympathetic motor impulses from the spinal cord stimulate
the detrusor muscle to contract and the internal urethral sphincter to relax
parasympathetic motor impulses- also send signals to
cerebral cortex; allows voluntary relaxation of external urethral sphincter to control emptying of bladder
if a person chooses not to urinate
these reflexes cease within one minute and bladder continues to fill with urine
a lack of voluntary control over micturition is referred to as
incontinence
incontinence is common in
infants and young children who have not yet mastered voluntary control over external urethral sphincter
stress incontinence
in adults results from physical stressors (coughing, laughing, exercise, pregnancy, walking) that increase abdominal pressure
other causes of incontinence
include neurological disorders from spinal cord injuries, smoking, aging
urinary retention prevents the urinary bladder from
emptying its contents
urinary retention is a consequence of
general anesthesia
an enlarged prostate gland can cause
urinary retention in older males
