chapter 24 - urinary system Flashcards
homeostatic regulatory systems involving kidneys
- regulates blood volume and pressure by adjusting volume of water lost in urine + releasing erythropoietin and renin
- regulates plasma ion concentrations of Na+ K+ Cl- (controlling qualities lost in urine) and Ca2+ levels (through synthesis of calcitriol)
- helps stabilize blood pH by controlling loss of H+ ions and bicarbonate ions in urine and excretion of nonvolatile acids
cortical nephrons
85% of all nephrons
Located mostly within superficial cortex
Nephron (henele) loop is short, descends little into medulla
Efferent arteriole delivers blood to a network of peritubular capillaries
juxtamedullary nephrons
15% of nephrons
Contribute to kidney’s ability to concentrate urine
Nephron loops extend deep into medulla
Peritubular capillaries connect to vasa recta
how many nephrons are in each kidney?
~1,000,000 per kidney
layers of filtration membrane
Fenestrated endothelium of the capillary (~60-100 nm) Basement membrane (~20 nm) Slit diaphragm between foot processes (or pedicels) of the podocytes (~6-9 nm)->This and basement membrane hold back MOST proteins (ex albumin) but allow passage of water, ions, glucose, amino acids, urea, etc
juxtaglomerular complex function
regulates blood pressure
cells in juxtaglomerular complex
granular cells –> secrete renin in response to failing blood pressure in aferent arteriole
macula densa -> monitor solute concentrate in filtrate by signaling granular cells to secrete renin
mesangial cells –> contractile cels that regulate intraglomerular capillary blood flow
extraglomerular mesangial cells –> interact w/ macula densa +granular cels to help regulate glomerular filtration rate (GFR)
peritubular capillaries
reclaims filtrate and helps concentrate urine
vasa recta
helps concentrate urine
what are the parts of the urine transport system?
ureter, urinary bladder, urethra
ureter
Pair of muscular tubes that connect renal pelvis to urinary bladder
Contractions occur every ~30 seconds to force urine toward bladder
Ureteral openings are slit-like rather than rounded to help prevent backflow when urinary bladder contracts
urinary bladder
Hollow, muscular organ
Wall folded into rugae (wrinkles) when empty
Function: temporary reservoir for urine storage (up to ~1L)
urinary bladder wall layers
Mucosa - transitional epithelium
Muscularis - 3 layers of smooth muscle = detrusor muscle (longitudinal-circular-longitudinal)
Causes expulsion of urine from bladder
Thickened around urethral opening to create internal urethral sphincter (controls involuntary urine release)
Adventitia - fibrous, anchors bladder to pelvic floor
urethra
From neck of urinary bladder to exterior
Lined with stratified squamous epithelium
Passes through band of skeletal muscle that forms external urethral sphincter
Relaxation results in micturition
urethral sphincters
internal and external urethral sphincters
differences in external urethral sphincter by gender
Females -> ~3-4 cm
Males -> 20 cm in length
Prostatic urethra → passes through the prostate gland
Intermediate part of urethra → through the urogenital diaphragm
Spongy (penile) urethra → passes through the length of the penis
steps of micturition reflex
Visceral afferent impulses from stretch receptors in the bladder wall are carried to the spinal cord and then, via ascending tracts, to the pontine micturition center
Integration in the pontine micturition center initiates the micturition response. Descending pathways carry impulses to motor neurons in the spinal cord
Parasympathetic efferents stimulate the contraction of the detrusor and open the internal urethral sphincter
Sympathetic efferents to the bladder are inhibited
Somatic motor efferents to the external urethral sphincter are inhibited; the sphincter relaxes. Urine passes through the urethra; the bladder is emptied
steps of urination
see diagram
external urethral sphincter
voluntary striated muscles that RELAXES during urination, which relaxes internal urethral sphincter and opening –> causes nicturition
Urinary Tract Infections
more common in females; burning sensation during micturition
renal calculi
kidney stones
bladder cancer
3% of cancers; more common in men
kidney cancer
typically in epithelial cels of kidney tubules
effects of aging
declined kidney and bladder function
Nephrons decrease in size and number
Tubules are less efficient at secretion and reabsorption
Filtration declines
Recognition of desire to urinate is delayed; can lead to incontinence
Loss of muscle tone in the bladder; can lead to incontinence
