urinary system Flashcards
functions of the liver
breaks down exogenous toxins
functions of kidneys
excrete toxins
nephron
smallest funtional unit of the kidney
fluid movement through the nephron
- Renal corpuscle (glomerulus + Bowman’s capsule)
- Proximal tubule
- Descending loop of Henle
- Ascending loop of Henle
- Distal tubule
- Collecting ducts
the loop of henle sepertes
the proximal from distal tubules
nephron functions (fluid movement)
- Nephron functions (fluid movement):
1. Filtration: from blood into Bowman’s capsule
2. Reabsorption: from tubule back to bloodstream
3. Secretion: from bloodstream (capillaries around
tubules) into the tubules except for Bowman’s capsule
excretion:
expelling urine from the bladder through urethra
amount excreted equatuation
Amount excreted = amount filtered – amount resorbed
+ amount secreted
what substances are totally reabsorbed after filtration
glucose and amino acids
what substances are partially reabsorbed
sodium
what substances are totally excreted
medications and toxins
what are the hormones affecting the distal tubule and collecting duct
- Parathyroid hormone (PTH) increases Ca++ reabsorption
- Antidiuretic hormone (ADH) increases water reabsorption
- Aldosterone increases Na+ reabsorption the nephron (and thus increases water reabsorption) but also increases K+ secretion
how much of water is reabsorbed
alomst 100% only 1% goes to urine
how much urine do we make a day
1-2 L a day
molecules passing into or out of nephron tubules must move through
the cuboidal epithelial cells lining the tubule
The side facing the tubule lumen (inside) is called the
apical or luminal membrane
the side NOT facing the tubule lumen is the
basolateral membrane
Tight junctions between epithelial cells prevent
most molecules from moving between the cells, so they must go through the epithelial cells
This means the cells can regulate which molecules move back to the bloodstream by using membrane proteins (channels and transporters)
(the rest of the water molecules become urine)
Like in intestines, water can be reabsorbed by:
- Osmosis
- Through aquaporins (upregulated by ADH),
- Paracellular transport (tight junctions can’t completely stop water)
As more ions are reabsorbed, more water is reabsorbed (same as small intestine)
Transport mechanisms vary depending on the molecule:
simple diffusion, osmosis (water), facilitated diffusion, coupled transport and active transport
Glucose and amino acids are completely reabsorbed by the
proximal tubule – co-transport with Na+ (apical membrane), then GLUT (basolateral) in healthy people.
The Na+ from glucose/amino acid co-transport needs to be
emoved from the cell, so the Na+/K+ pump on the basolateral side pumps it back into the circulation
Angiotensin II effects (all increase BP):
- Stimulates adrenal cortex to produce aldosterone
- Vasoconstriction
- Posterior pituitary to release antidiuretic hormone
- Sympathetic nervous system increase blood pressure
- Reabsorption of Na+ and Cl- (and so water)
- Causes thirst and salt craving
(renin-antogensin system) Decreased blood pressure causes
decreased stretch of baroreceptors in the afferent arterioles (entering glomerulus)
RAS signal
juxtaglomerluar cells to secrete renin into the bloodstream
renin cleaves angiotensinogen into
angiotensin I
angiotensin I is cleaved into
angiotensin II (by ACE
low blood sodium decreases
the glomerular filtration rate (GFR) as well as causing renin production and release
what is GFR
the amount of blood filtered by the glomeruli each minute.
Macula densa cells signal smooth muscle cells in the
afferent arteriole to constrict, thus decreasing pressure and reducing filtration and so urinary output
They also signal juxtaglomerular cells which store renin and secrete it when blood pressure is low
low blood sodium or water causes blood pressure to
decrease
low sodium is detected by
the macula densa cells in the upper ascedning loop of henle
