Final Flashcards
four organs that make up the urinary system
Kidneys (filtration)
2) Ureters (transport urine to bladder)
3) Urinary bladder (store urine)
4) Urethra (release urine from body, “micturition”)
what are the major functions of the kidney in the body
1) Eliminate waste materials
2) Control volume and composition of body fluids (blood and urine)
3) Produce renin (blood pressure regulator)
4) Produce erythropoietin (stimulates RBC formation)
5) Metabolize vitamin D to active form (Ca++ uptake)
where is urine derived from
when blood comes through the glomularis and the podocytes filter out the filtrate the filtrate that is not reabsorbed that then becomes the urine.
what are the layers of the kidney
1) Fibrous capsule, 2) cortex (gloremuli are only found here),3) the medulla
nephron
responsible for urine formation. Because urine is derived from filtrate, which was taken from fluid in the blood, nephrons have a big role in blood volume.
urine
People produce around ~1-2 L of urine / day (around 1% of the volume of the total filtrate).
99% of filtrate is returned to blood
steps of urine filtration
- Glomerular filtration→ creates the plasma-like filtrate of blood
- Tubular reabsorption→ removes useful solutes from filtrate & returns them to blood
- Tubular secretion→ removes additional wastes from blood & adds to filtrate
renal corpuscle
consists of the glomerulus and the glomerular capsule.
Glomerular (or Bowman’s) Capsule
is the widened and expanded proximal end of tubule that encapsulates glomerulus
layers of the glomerular capsule
the parietal layer (outer) is made of simple squamous epithelium.
The visceral layer is the podocytes that cover the glomerular capillaries. These are thin cells that cover capillaries, with filtration slits between the podocytes.
proximal convoluted tubule
a coiled tubule near the renal corpuscle, which is made of simple cuboidal epithelium that has microvilli to increase the surface area. The majority (80%) of tubular reabsorption (step 2 of urinary production) occurs in the PCT.
loop of henle
a long, thin hairpin loop in the renal tubule. It contains Descending and ascending limbs.
descending tubule of the loop of henle
The descending limb contains a thin segment that is permeable only to water
ascending limb of the loop of henle
a thick segment, made of simple cuboidal epithelium, and a thin segment, made of simple squamous epithelium. The thin segment of the ascending limb is permeable to solutes and not water.
what solutes does the ascending limb pump out
Na+, K+, Cl-
distal convoluted tubule
The DCT is made of simple cuboidal epithelium without microvilli.
The DCT plays a role in acid/base balance (helps keep pH of the filtrate and the body in balance).
The DCT is targeted by the antidiuretic hormones ADH and Aldosterone.
collecting ducts
The collecting duct is made of simple cuboidal epithelium without microvilli.
It collects filtrate that is nearly urine. By the time the filtrate moves through the collecting duct, it is urine.
The collecting duct is also targeted by ADH and aldosterone.
glomerular filtration rate
is defined as the volume of filtrate formed each minute by the combined activity of all ~2 million nephrons.
net filtration pressure
The glomeruli and associated podocytes are very porous, have a large surface area, and thus large volumes of filtrate can be produced with a relatively modest NFP.
Only moderate pressure at the glomeruli is needed to produce a large amount of filtrate.
However, a drop in NFP of only 15% will stop filtration from occurring at all!
tubular reabsorption
is the act of returning fluid (H2O) & substances (glucose, amino acids, sodium, etc.) from the filtrate in renal tubules back to blood.
80% of tubular absorption occurs in the PCT (remember, the microvilli increase surface area to allow absorption to occur).
tubular secretion
During tubular secretion, substances that are not already in filtrate are eliminated (e.g. antibiotics)
Substances that were reabsorbed in step 2 are eliminated from the body (e.g. urea, sometimes Na+)
Substances are secreted in order to balancing pH (occurs at the proximal/distal convoluted tubules)
Renin-Angiotensin mechanism
Renin is an enzyme that activates the release of angiotensin II
Angiotensin II acts to vasoconstrict arterioles throughout body
Efferent arterioles constrict more than afferent arterioles, this increases the glomerular hydrostatic pressure
In addition to its role in vasoconstriction, angiotensin II also stimulates release of:
Aldosterone: increases Na+ reabsorption by kidney
ADH: increases water reabsorption by kidney – “water follows salt”
medullary osmotic gradient
allows the kidneys to vary the urine concentration dramatically.
how does the nephron concentrate filtrate and then dilute it.
In the descending loop, water leaves the renal tubule into the interstitial fluid (this water will then be picked up by the vasa recta).
In the ascending loop, water cannot enter or leave, but solutes are actively pumped out of the renal tubule into the interstitial fluid.
Solutes are actively transported from the renal tubule to the interstitial space. The saltier the filtrate, the more salt is removed.