objective 7 pt 2 Flashcards
basically blood plasma except the proteins
filtrate
what are the 3 processes that are involved in urine formation and adjustment of blood composition?
glomerular filtration
tubular reabsorption
tubular secretion
passive process, no metabolic energy required
hydrostatic pressure forces fluid and solutes through filtration membrane into glomerular capsule
no reabsorption into capillaries of glomerulus occurs
glomerular filtration
porous membrane between blood and interior of glomerular capsule
allows water and solutes smaller than plasma proteins to pass
filtration membrane
what are the 3 layers of the filtration membrane
fenestrated endothelium
basement membrane
foot processes of podocytes
allows all blood components except blood cells to pass through
fenestrated endothelium
physical barrier that blocks all but smallest proteins while still allowing other solutes to pass
basement membrane
contain filtration slits which repel macromolecules
foot processes of podocytes
blood enters the glomerulus
filterable blood components, such as water and nitrogenous waste, will move towards the inside of the glomerulus
non-filterable conponents, such as RBCs and plasma proteins, will exit via the efferent arteriole
the filterable components accumulate in the glomerulus to form the glomerular filtrate
filtration
forces that promote filtrate formation
outward pressure
essentially glomerular blood pressure
chief force pushing water, solutes out of blood
hydrostatic pressure in glomerular capillaries
forces inhibiting filtrate formation
inward pressure
filtrate pressure in capsule; 15 mm Hg
hydrostatic pressure in capsular space
“pull” of proteins in blood; 30 mm Hg
colloid osmotic pressure in capillaries
sum of forces
pressure responsible for filtrate formation
net filtration pressure
volume of filtrate formed per min by both kidneys
glomerular filtration rate
what is GFR directly proportional to?
net filtration pressure
total surface area
filtration membrane permeability
primarily pressure is glomerular hydrostatic pressure
net filtration pressure
available for filtration
total surface area
much more permeable than capillaries
filtration membrane permeability
renal autoregulation
enables kidneys to maintain constant blood flow and GFR
intrinsic controls and GFR
what are the two types of renal autoregulation?
myogenic mechanism
tubuloglomerular feedback mechanism
local smooth muscle
increased BP causes muscle to stretch, leading to constriction of afferent arterioles
restricts blood flow into glomerulus
protects glomeruli from damaging high BP
decreased systemic BP causes dilation of afferent arterioles and raises glomerular hydrostatic pressure
myogenic mechanism
with an increased concentration of NaCl in filtrate in the distal tubules, it causes a release of adenosine from the macula densa
cells
initiates a cascade of events that brings GFR to an appropriate level
tubuloglomerular feedback mechanism
neural and hormonal mechanisms
regulate GFR to maintain systemic blood pressure
override renal intrinsic controls if blood volume needs to be increased
extrinsic controls
renal blood vessels dilated
renal autoregulation mechanisms prevail
sympathetic nervous system under normal conditions at rest
- Norepinephrine released by sympathetic nervous system and
epinephrine is released by adrenal medulla, causing: - Systemic vasoconstriction, which increases blood pressure
- Constriction of afferent arterioles, which decreases GFR
- Blood volume and pressure increases
sympathetic nervous system under abnormal conditions
main mechanism for increasing BP. low BP causes the release of renin from granular cells of the juxtaglomerular complex
renin-angiotensin-aldosterone mechanism
what are the 3 pathways that stimulate granular cells?
sympathetic nervous system
activated macula dens cells
reduced stretch
part of baroreceptor reflex, renal sympathetic nerves activate receptors that cause granular cells to release renin
sympathetic nervous system
occurs when filtrate NaCl concentration is low. signal grandular cells to release renin
activated macula dens cells
grandular cells ac as mechanoreceptors. reduced MAP reduced tension in grandular cells plasma membranes stimulates them to release more renin
reduced stretch
quickly reclaims most of contents from filtrate and returns them to blood via a selective transepithelial process
process that moves solutes and water out of the filtrate and back into your bloodstream
tubular reabsorption
- Na+ is most abundant cation in filtrate
- Transport of Na+ out of the tubule cell via primary
active transport by a Na+-K+ ATPase pump in the
basolateral membrane - Na+ into the interstitial space
- Na+ is then swept by bulk flow of water and
solutes into peritubular capillaries. - Organic nutrients reabsorbed by secondary active
transport are cotransported with Na+
sodium transport
- Movement of Na+ and other solutes creates osmotic
gradient for water - Water is reabsorbed by osmosis into the peritubular
capillaries, aided by transmembrane proteins called
aquaporins (act as water channels)
reabsorption of water
- Aquaporins are always present in PCT
- Forces body to reabsorb water regardless if over or
under hydrated
obligatory water reabsorption
- Aquaporins are inserted in collecting ducts only if
ADH is present
facultative water reabsorption
- Solute concentration in filtrate increases as water is
reabsorbed - Creates a concentration gradient for solutes, which
drive their entry into the tubule cell and peritubular
capillaries - Fat-soluble substances, some ions, and urea will follow
water into peritubular capillaries down their
concentration gradients - For this reason, lipid-soluble drugs and environmental
pollutants are reabsorbed even though it is not
desirable
passive tubular reabsorption of solutes
Site of most reabsorption
* All nutrients, such as glucose and amino acids,
are reabsorbed
* 65% of Na+ and water reabsorbed
* Many ions/electrolytes
* Almost all uric acid
* About half of urea (later secreted back into
filtrate)
proximal convoluted tubule
H2O can leave, solutes cannot (permeable to water)
descending limb
H2O cannot leave, solutes can (impermeable to water)
ascending limb
reabsorption is hormonally regulated in these areas
distal convoluted tubule and collecting duct
- Released by posterior pituitary gland
- Causes formation of aquaporins in collecting ducts,
increasing water reabsorption - Increased ADH levels cause an increase in water
reabsorption
antidiuretic hormone
- Released by adrenal cortex in response to
decreased blood volume/BP or hyperkalemia - Targets collecting ducts and DCT
- Promotes Na+ reabsorption (water follows)
- As a result, little Na+ leaves body
- Without aldosterone, daily loss of filtered Na+
would be 2%, which is incompatible with life
aldosterone
what are the functions of aldosterone?
increase blood pressure and
decrease
K+ levels
- Reduces blood Na+, resulting in decreased blood
volume and blood pressure - Released by cardiac atrial cells if blood volume or
pressure elevated
atrial natriuretic peptide
- Acts on DCT to increase Ca2+ reabsorption
parathyroid hormone
is the opposite of reabsorption
* Occurs almost completely in DCT
* Selected substances are moved from peritubular
capillaries through tubule cells out into filtrate
* K+, H+, NH4+, creatinine, organic acids and bases
* Substances synthesized in tubule cells also are
secreted
* Helps control blood pH and acid base balance of
body by selectively secreting electrolytes
tubular secretion
what is tubular secretion important for?
- Disposing of substances, such as drugs or metabolites,
that are bound to plasma proteins - Eliminating undesirable substances that were passively
reabsorbed (example: urea and uric acid) - Ridding body of excess K+ (aldosterone effect)
- Controlling blood pH by altering amounts of H+ or HCO3–
in urine
substance not reabsorbed,
so water remains in urine; for example, in
diabetic patient, high glucose concentration pulls
water from body
osmotic diuretics
inhibit medullary gradient formation
loop diuretics
urine is examined for signs of disease
can also be used to test for illegal substances
urinalysis
volume of plasma the kidneys can clear of a particular substance in a given time
used to determine GFR
renal clearance
what is the chemical composition of urine
95% water 5% solutes
largest solute component
urea
from nucleic acid metabolism
uric acid
metabolite of creatine phosphate found in skeletal muscle
creatinine
what are they physical characteristics of urine?
color and transparency
odor
pH
specific gravity
Clear
* Cloudy may indicate urinary tract infection
* Pale to deep yellow from urochrome
* Pigment from hemoglobin breakdown
* Yellow color deepens with increased concentration
* Abnormal color (pink, brown, smoky)
* Can be caused by certain foods, bile pigments,
blood, drugs
color and transparency of urine
- Slightly aromatic when fresh
- Develops ammonia odor upon standing as
bacteria metabolize urea - May be altered by some drugs or vegetables
- Disease may alter smell
- Patients with diabetes may have acetone
smell to urine
odor of urine
- Urine is slightly acidic (~pH 6, with range of 4.5 to
8.0) - Acidic diet (protein, whole wheat) can cause drop in
pH - Alkaline diet (vegetarian), prolonged vomiting, or
urinary tract infections can cause an increase in pH
pH of urine
- Ratio of mass of substance to mass of equal volume
of water (specific gravity of water = 1) - Ranges from 1.001 to 1.035 because urine is made
up of water and solutes - Normally excrete approx. 450 ml in 24 hours (30
ml/hr)
specific gravity of urine
slender tubes that convey urine from kidneys to bladder
retroperitoneal
enter base of bladder through posterior wall
ureters
what are the 3 layers of the ureters?
mucosa
muscularis
adventitia
consists of transitional epithelium
mucosa
smooth muscle sheets contract in response to stretch
muscularis
gravity alone is not enough; must also be pushed by peristaltic wave action of smooth muscle
propels urine into bladder
outer fibrous connective tissue
adventitia
- Smooth, collapsible, Muscular sac for temporary
storage of urine - Retroperitoneal, on pelvic floor posterior to pubic
symphysis
urinary bladder
prostate inferior to bladder neck
males urinary bladder
anterior to vagina and uterus
females urinary bladder
- Smooth triangular area outlined by openings
for
ureters and urethra - Infections tend to persist in this region
trigone
what are the layers of the bladder wall?
mucosa
muscular layer
fibrous adventitia
transitional epithelial mucosa
mucosa
thick detrusor muscle that contains 3 layers of smooth muscle
muscular layer
except on superior surface where it is covered by peritoneum
fibrous adventitia
- Collapses when empty
- Mucosa folds (Rugae)
- Expands and rises superiorly during filling
without significant rise in internal pressure - Moderately full bladder is ~12 cm long (5 in.) and
can hold ~ 500 ml (1 pint) - Can hold twice that amount if necessary but
can burst if over distended
urine storage capacity
- Muscular tube that drains urinary bladder
- Mucosal lining consists mostly of pseudostratified
columnar epithelium, except: - Transitional epithelium near bladder
- Stratified squamous epithelium near
external urethral orifice
urethra
- Involuntary (smooth muscle) at bladder-urethra
junction - Controlled by autonomic nervous system to keep
closed when urine not being passed. - Contracts to open
internal urethral sphincter
- Voluntary (skeletal) muscle surrounding urethra as it
passes through pelvic floor
external urethral sphincter
tightly bound to anterior vaginal wall
female urethra
anterior to vaginal opening; posterior to clitoris
external opening
carries semen and urine
male urethra
what are the 3 named regions of the male urethra?
prostatic urethra
intermediate part of the urethra
spongy urethra
within prostate
prostatic urethra
passes through urogenital diaphragm from prostate to beginning of penis
intermediate part of the urethra
passes through penis; opens via external urethral orifice
spongy urethra
act of emptying the bladder
micturition also called urination or voiding
what are the 3 simultaneous events that must occur for micturition?
- Contraction of detrusor muscle by ANS
- Opening of internal urethral sphincter ANS
- Opening of external urethral sphincter by
somatic nervous system
- Distension of bladder activates stretch receptors
- Causes excitation of parasympathetic neurons in
reflex center in sacral region of spinal cord - Leads to contraction of detrusor and opening
(contraction) of internal sphincter - Inhibition of somatic pathways to external
sphincter allow its relaxation and opening
reflexive urination
