Renal blood supply
- 22% of cardiac output
- unique blood flow
- 2 capillary beds
1) glomerular
2) peritubular
Glomerular capillaries
- HIGH hydrostatic pressure (60mm)
- causes rapid fluid FILTRATION
- encased in the Bowman’s capsule
Peritubular capillaries
- LOWER hydrostatic pressure (13mm)
- allows for rapid fluid REABSORPTION
Nephron
- functional unit of the kidney
- 2 diff nephron structures/areas
1) Cortical nephron
2) Juxtamedullary nephron
-can NOT regenerate new nephrons
Juxtamedullary nephron
- significantly longer Loop of Henle
- penetrates deeper into medulla
- 20-30% of the nephrons
- surrounded by specialized peritubular capillaries (VASA RECTA)
Fluid filtered from glomerular capillaries
Bowman’s Capsule -> proximal tubule -> loop of Henle -> distal tubule -> connecting tubule -> collecting duct -> renal pelvis
Cortical nephron
- short loops of Henle
- only barely penetrate into the medulla
- 70-80% of the nephrons
- surrounded by peritubular capillaries
Anatomy of urinary bladder
Smooth muscle chamber with 2 main parts
1) Body - primary part where urine collects
2) Neck - attaches to urethra
Detrusor muscle
-responsible for CONTRACTION OF BLADDER
-smooth m of bladder
-fibers are intertwined
-low-resistance to electrical impulses btwn muscle cells
(whole bladder contracts at once)
-contraction - increases pressure by 40-60 times
-major step in emptying bladder
Trigone
- on POST wall of bladder
- ureters enter at UPPER trigone
- Surface = smooth mucosa (contrast to the folded rugae of the rest of the bladder mucosa
Ureters
- obliquely enters the bladder through the DETRUSOR MUSCLE
- penetrates 1-2 cm through detrusor and mucosa
- the tone of the muscle shuts down the ureters (prevents BACKFLOW of urine)
Bladder neck (posterior urethra)
- composed of DETRUSOR M and ELASTIC tissue
- muscle here is the INTERNAL SPHINCTER - prevents emptying of the bladder until pressure rises above the critical threshold
Urethra
Passes through UROGENITAL DIAPHRAGM
External sphincter muscle
- smooth muscle
- under voluntary control (can consciously contract to prevent urine; MEN)
Innervation of urinary bladder
1) Pudendal N
2) Sympathetic Innervation
3) Pelvic N’s
4) sensory and motor nerve fibers
Pudendal N (urinary bladder)
- SOMATIC
- Innervate the EXTERNAL bladder sphincter
Sympathetic Inn (urinary bladder)
- through HYPOGASTRIC n’s (L2)
- stimulate blood supply to the bladder
Pelvic N’s (urinary bladder)
-through SACRAL PLEXUS (s2,s3)
Sensory nerve fibers (urinary bladder)
and Motor nerve fibers
Sensory - detect STRETCH of bladder wall
Motor - PARASYMP; innervate DETRUSOR M
Urine Flow
Nephron -> Collecting ducts -> Renal calyces -> Ureters -> Bladder
-CD’s to RC’s causes peristaltic contractions (in renal pelvis and ureters)
Ureters
- Innervated by SYMP (dec contraction) and PARASYMP (inc contraction) nerves
- smooth visceral m (contraction of ureters)
Ureterorenal Reflex
- ureters contain a lot of PAIN fibers
- severe pain (ie, kidney stone) =
1) reflex constriction occurs
2) symp reflex occurs back to kidney
3) constrict renal arterioles
4) dec’s flow of fluid into the kidney with a blocked ureter
Micturition
- SENSORY STRETCH RECEPTORS initiated as bladder fills
- Self-regenerative (initial contracture of the detrusor m causes further activation of the stretch receptors)
-Urination can be facilitated or inhibited by centers in the PONS and CEREBRAL CORTEX (have final control of micturition)
As micturition reflex INCREASES…
- reflex passes through the PUDENDAL N’s to the EXTERNAL sphincter
- AUTONOMIC REFLEX
