APK Chapter 24

organs of the urinary system

• kidneys: upper posterior abdomen

• ureters: posterior abdominal wall

• bladder: pelvic cavity

• urethra: bladder neck to the pelvic floor

coverings of the kidneys

• fibrous (renal capsule): thin tough CT directly on the kidney surface

• perineal fat: layer of fat around the kidneys that protects and insulates the kidney

• renal fascia: dense CT anchoring the kidney

• pararenal fat: outermost layer of fat

external gross anatomy of kidneys

lateral border: convex

medial border: concave with renal hilum

renal hilum: entry/exit point for renal artery + vein, ureter, and nerves

internal gross anatomy of kidneys

renal cortex: outermost layer containing renal corpuscles and convoluted tubules of nephrons

renal medulla: deeper region composed of renal pyramids, renal columns, loops of henle, and collecting ducts

renal sinus: fat-filled cavity with major and minor calyces, renal pelvis, and ureters

parts of a nephron

• glomerulus: corpuscle

• bowman’s capsule: corpuscle

• proximal convoluted tubule: tubule

• loop of henle: tubule

• disral convoluted tube: tubule

• collecting duct

cortical vs juxtamedullary nephrons

cortical:

• located in the outer cortex

• short and shallow loop of henle

• 85% of nephrons

• functions in reabsorption and secretion

• associated with peritubular capillaries

juxtamedullary:

• located near the corticomedullary junction

• long and deep loop of henle

• 15% of nephrons

• functions in concentration of neurons

• associated with the vasa recta

location of functions of vessels of the nephron

afferent arteriole:

• enters glomerulus

• supplies high pressure blood for filtration

glomerulus:

• located inside renal corpuscle

• filters blood plasma into nephron

efferent arteriole:

• exits glomerulus

• drains glomerulus and controls outflow

peritubular capilliaries:

• surrounds cortical tubules

• functions in reabsorption and secretion in cortex

vasa recta:

• parallel to loop of henle

• maintains medullar gradient and reabsorption

histology of renal corpuscle

• glomerular endothelium: blocks blood cells, allows plasma components through

• basement membrane: blocks large proteins, repels negatively charged molecules

• podocytes with pedicels: filtration slits restrict medium proteins

• capsular space: collects filtrate

juxtaglomerular apparatus

• macula densa: senses NaCL and signals juxtaglomerular cells

• juxtaglomerular cells: releases renin in response to low BP/NaCl

• mesangial cells: support and coordinate signaling

physiological significance of the JGA:

• blood pressure regulation

• regulation of glomerular filtration rate

• electrolyte and fluid balance

location, histology, and function of the ureters

smooth muscle in the walls that move urine to the bladder via peristalsis. located in L3

location, histology, and function of the urinary bladder

collapsible, muscular sac that stores and expels urine. inferior to the peritoneal cavity, posterior to pubic symphysis.

location, histology, and function of the urethra

females:

• goes from bladder → pelvic floor → external orifice

• made of stratified squamous tissue

• functions in urination only

males:

• goes from bladder → prostate → penis → external orifice

• made of columnar and stratified squamous tissue

• functions in urination and semen transport

male vs female urethras

male:

• about 20 cm

• functions in urination and semen transport

• has prostatic, membranous, and spongy division

• internal sphincter prevents retrograde ejaculation

• external sphincter is voluntary and around membranous urethra

• lower infection risk

female:

• about 4 cm

• functions in urination only

• no named divisions

• internal sphincter is present but less distinct

• external sphincter is voluntary and encircles urethra at pelvic floor

• infection risk is higher

micturition

1. 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

2. integration in pontine micturition center initiates the micturition response. descending pathways carry impulses to motor neurons in the spinal cord

3. parasympathetic efferents stimulate contraction of the detrusor and open the internal urethral sphincter

4. sympathetic efferents to the bladder are inhibited

5. somatic motor efferents to the external urethral sphincter are inhibited. the sphincter relaxes. urine passes through the urethra, the bladder is emptied