Ch 23- Urinary System Flashcards
Urinary system consists of
2 kidneys- filter plasma, produce urine
2 ureters- transport urine to bladder
1 urinary bladder- temporarily stores urine
-1 urethra- urine to exterior
functions of kidneys
-waste and blood filtration
-regulate blood vol, pressure, and osmolarity
-regulate electrolytes and acid base balance
-regulate calcium levels
Wastes removed by the kidneys from body fluids
urea- products of amino acid breakdown
-urobilinogen- product of hemoglobin break down
- Creatinine – products of the
breakdown of creatine phosphate in muscle fibers.
-Uric acid – products of nucleic acid breakdown.
-Foreign chemicals – e.g., drugs and environmental toxins.
kidney and water balance
The kidneys work to
maintain the water
balance in the body
Structure of the nephron
-Nephrons are the functional units of the kidneys
-Two Parts
-Renal corpuscle – site of blood filtration. composed of two parts: Glomerulus – capillary network and Glomerular capsule
– cup that surrounds the glomerulus.
-capsular capsule between glomerulus and capsule wall
Renal tubule – passageway where filtered fluid
(called tubular fluid) passes from the glomerular
capsule. It is composed of various parts:
o Proximal convoluted tubule (PCT).
o Loop of Henle (nephron loop):
Descending limb.
Ascending limb.
o Distal convoluted tubule (DCT)
The tubular fluid from the distal convoluted tubules of
several nephrons is then collected in collecting
ducts. The fluid that drains from the collecting ducts
is called urine
To produce urine, the nephrons and collecting ducts
perform three basic functions
Filtration – blood pressure forces water and most
small solutes in blood plasma to move across the
wall of the glomerulus into the capsular space and
then into the renal tubule.
- Reabsorption – in the renal tubule and collecting
duct, water/ solutes reabsorbed back into the peritubular
capillaries. - Secretion – cells in the renal tubule and collecting
duct secrete wastes, drugs and excess ions into the
tubular fluid.
-water conservation
filtration membrane (glomerulus) - layers
fenestrations- inside
lamina densa- middle
podocytes- outside
passed through: water, electrolytes, glucose, amino and fatty acids, urea, creatine etc
Filtration- why kidneys can filter large volumes of blood
-large surface area
-thin
-high blood pressure
Filtration- Pressures involved in filtration
-Blood hydrostatic pressure
-Hydrostatic pressure in capsular space
-Colloid osmotic pressure
Regulation of Glomerular filtration rate
can be modified by altering blood pressure in the arterioles by vasodilation or vasoconstriction
induced by:
-Autoregulation
-Autonomic regulation
-Hormonal regulation
-Angiotensin II
Regulation of Glomerular filtration rate- Auto regulation
Muscle walls can constrict and relax, depending on high or low blood pressure to increase or decrease the GFR
filtration-Tubuloglomerular feedback
glomerulus receives feedback on the status of
downstream tubular fluid and adjusts filtration rate accordingly.
Regulation of Glomerular filtration rate- Autonomic regulation
-sympathetic activation can cause vasoconstriction of
afferent arterioles, and reduce GFR and urine output
-This type of activation would override autoregulation in the event of an
acute drop in blood pressure or heart attack.
Regulation of Glomerular filtration rate- Hormonal Regulation
-renin can increase blood pressure, and increase GFR
-The renin–angiotensin–aldosterone mechanism is hormones that helps control blood pressure and GFR
-renin converts into angiotensin I. from angiotensinogen
-angiotensinogen in lungs and kidneys produces I and II
Regulation of Glomerular filtration rate- Angiotensin II
-active hormone that increases BP
-Potent vasoconstrictor raising BP throughout body.
-Constricts efferent arteriole raising GFR
-stimulates adrenal cortex to secrete aldosterone, Na+ and H2O reabsorption in PCT, posterior pituitary to secrete ADH which promotes water
reabsorption, thirst
Filtration- Juxtaglomerular Apparatus
-Macula densa—patch of slender, closely spaced sensory cells in
nephron loop
-When GFR is high, filtrate
contains more NaCl.
- When macula densa absorbs
more NaCl, it secretes ATP
ATP is metabolized by nearby
mesangial cells into
adenosine.
* Adenosine stimulates nearby
granular cells.
* Granular cells respond to
adenosine by constricting
afferent arterioles; constriction
reduces blood flow which
corrects GFR.
The renin-angiotensin system
a hormonal system that regulates blood pressure and fluid balance, involving key components like renin, angiotensin II, and aldosterone
Reabsorption
-Proximal convoluted tubule -the filtrate produced is reabsorbed
-Cells in this portion of the tubule have microvilli that greatly increase surface area and enhance reabsorption.
Reabsorption- substances reabsorbed from kidney
-reabsorbed from the filtrate in the proximal convoluted tubule (PCT), mainly including water, electrolytes like sodium, glucose, and amino acids
-ons (e.g., K+, Ca2+, Cl–, HCO3–, glucose, amino acids, vitamins, proteins)
Reabsorption- Transport Maximum
-Transport of substances is
limited by the amount of
transporters (transporter
saturation). With high blood
glucose, not all glucose can
be reabsorbed and some is
excreted in urine
(glucosuria).
Reabsorption- Distal Convoluted tube
-Distal convoluted tubule – only about 15-20% of the initial filtrate reaches the DCT
-major site where the parathyroid hormone
(PTH) stimulates reabsorption of calcium
Reabsorption- Nephron Loop
-about 15-20% of fluid
is reabsorbed in the loop of Henle
-The two parallel segments with different permeability characteristics:
-The descending limb is
permeable to water, but
impermeable to solutes.
o The ascending limb is
permeable to sodium and
chloride, but impermeable to
water.
Secretion- What substances are secreted into kidney tubules
Kidneys secrete substances like (H+), (K+), creatinine, ammonia, and certain drugs
- into the nephron tubules, primarily in the distal and proximal convoluted tubules, and collecting ducts
Multiplier of nephron loop
-continuous salt added by PCT
-higher osmolarity will have more water leave descending limb by osmosis
-more water that leaves, the saltier the fluid
-saltier the fluid in ascending limb, the more salt pumps into ECF
-the more salt pumped out, the saltier the ECF is in the renal medulla
