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Functions of kidneys
  • Maintain fluid and electrolyte balance (volume control)
  • Disposal of water-soluble wastes (metabolic wastes--urea, uric acid, creatinine, ammonia)
  • Renin production
  • Prostoglandin production
  • Erythropoeitin production
  • Vitamin D activation
  • Glucose production (20% of total glucose production)
Which arterioles act as entrances?
Afferent
Which arterioles act as exits?
Efferent
Normal GFR
125 mL/min
Name the 5 "checkpoints" of the tubular system and % absorption at each
  • Proximal convoluted tubule -- 60% of Na and water reabsorbed
  • Descending loop of henle -- none
  • Ascending loop of henle -- 30% of Na and water
  • Distal convoluted tubule -- 7% of Na and water
  • Collecting duct -- 3% of Na and water
Goal of GFR
Generate enough pressure for urine formation
How does systemic BP affect GFR?
  • Incr systemic BP leads to incr GFR
  • Afferent arterioles vasoconstrict to keep GFR constant, lessening pressure felt by kidneys
The driving force of filtration in the glomerulus is _____
Hydrostatic pressure in glomerular capillaries
What gets filtered during filtration?
  • Water
  • Electrolytes (H+, K+)
  • Solutes (creatinine, urea, glucose, AAs)
  • Organic acids¬†
  • Phosphates
What does not get filtered during filtration?
  • Negatively charged particles (protein)
  • Particles to large to pass (RBCs, WBCs, platelets)
How does each individual nephron regulate GFR?
  • At the justaglomerular apparatus at macula densa (distal convoluted tubule)
  • Macula densa--sense changes in NaCl delivery
  • When NaCl incr, signal is sent to slow GFR (decr NaCl incr GFR rate)
  • Incr GFR by opening afferent arterioles and constricting efferent
What happens if GFR is too high?
All filtrate would be lost to urine (good and bad particles)
What happens if GFR is too low?
Too much tubular filtrate reabsorbed (glucose and waste products would be out of balance)
JG Cells
  • Endocrine gland made of modified smooth muscle cells of afferent/efferent arterioles
  • Baroreceptors that synthesize, store, and release renin
Enzyme that causes conversion of angi I to angi II, which leads to potent vasoconstriction of efferent arterioles
Renin
What is the role of the macula densa?
Senses changes in osmolality (NaCl), w hich will also stimulate renin release from JG cells
What is the best indicator of how well the lungs are excreting metabolic waste?
Levels of PaCO2 in the blood
What is the best indicator of how well the kidneys are excreting metabolic waste?
Levels of HCO3- in the blood
How does the kidney excrete metabolic wastes?
  • H2CO3 and excess H+ secreted with ammonia
  • Through the transfer of materials from the peritubular capillaries to the renal tubular lumen
  • Tubular secretion is caused mainly by active transport
  • Usually only a few substances are secreted
Significance of NH4
NH4 is how excess H+ is secreted (used as buffer with NH3)
Significance of HPO4
H+ in the lumen of the late distal tubule/collecitn ducts combines with HPO4-2 to form H2PO4 to be excreted
What does the RAAS system do?
Regulate BP and volume
When BP drops, what happens with RAAS?
  • JG cells secrete renin
  • Substrate of renin (precursor to angi I), Angiotensinogen, released
  • Angiotensin I is made
  • ACE (in the kidneys) catalyzes angi II, which leads to potent vasoconstriction of efferent arterioles
  • Angi II also acts on the adrenal cortex, causing aldoesterone release, which causes loss of K and retention of Na in the kidneys
  • BP incr and renin secretion is stopped (negative feedback loop)
Where is aldosterone secreted?
Adrenal cortex
What is the role of aldosterone with electrolytes?
  • Incr NaCL/Na and water reabsorption
  • Causes retention of Na, thus K is excreted
On which part of tubule does aldosterone act?
  • Distal convoluted tubule
  • Collecting duct
Where is ADH secreted?
Posterior pituitary
On which part of tubule does ADH act?
Collecting duct
How does ADH work?
  • Osmoreceptors in hypothalamus detect osmolality in ECF
  • Incr H2O reabsorption when osmolality incr (concentrated)
  • When osmolality decr (H2O reabsorbed), signal then sent to inhibit ADH
Enzyme produced and released by liver
Angiotensinogen
Renin substrate
Angiotensinogen
Enzyme that converts angi I to angi II
ACE
Double-walled, cup-shaped structure around the glomerulus of each nephrom of the vertebrate kidney
Bowman's capsule
Serves as a filter to remove organic wastes, excess inorganic salts, and water
Bowman's capsule
Inward pull of particles in the vascular fluid from dissolved proteins in the blood
Capillary oncotic/osmotic pressure
A tuft of capillaries situated within a Bowman's capsule at the end of a renal tubule in the vertebrate kidney that filters waste products from the blood and thus initiates urine formation
Glomerulus
Collection of macula densa cells in the distal convoluted tubule, afferent and efferent arterioles, and the cells located around the arterioles that work together to control GFR
Juxtaglomerular apparatus
Thickening in the wall of a distal tubule of the kidney  nephron at a point where it is in contact with the afferent glomerulus and in direct opposition to the JG cells
Macula densa
Possibly part of a negative feedback system for sodium
Macula densa
2 phases of activity for lower urinary tract
  • Storage phase
  • Voiding phase
What happens at high bladder volumes?
Afferent firing incr, causing a conscious sensation of urinary urge
Contracts when urinating to squeeze out urine
Detrusor muscle
When is the detrusor muscle relaxed?
When allowing bladder to fill
Smooth triangular region of the internal urinary bladder formed by the two ureteral orifices and the internal urethral orifice
Trigone
Area very sensitive to expansion that sends a signal to the brain when emptying is needed
Trigone
Under voluntary control of the SNS
Extenral sphincter
Where is the external sphincter located on a man and woman?
  • Man - Inferior to the prostate
  • Woman - Distal inferior end
Is the external sphincter secondary in men or women?
Men
Continuation of the detrusor muscle and is under involuntary control
Internal sphincter
Where is the internal sphincter located?
Located at the bladder's inferior end and the urethra's proximal end at the junction of the urethra with the urinary bladder
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