8. structure and function of urinary system

fluid balance

• achieved by ensuring water consumed in food and drink (+gen by metabolism) = water excreted

• regulated by fluid intake + output and hormonal controls

fluid intake

• reg by behavioural mechanisms incl. thirst and salt cravings

• RDI

  • 3.7 L/day for adult m

  • 2.7 for f

• too much water = dilute blood (electrolytes/ sodium)

fluid output

• homeostatic control mechanisms

• 1l/d lost thru skin, lungs and feces

• urinary system = major site of regulated excretion of water (1-2l/d)

hormonal controls - ADH

• ADH → water reabsorption by kidneys

  • <vol of urine output

  • lowering osmolarity (adding water alone without electrolyte)

hormonal controls.- Renin-Angiotensin II-Aldosterone

• renal tubes reabsorb > Na and water from urine

• conserve vol while maintaining osmolarity

kidneys and peritoneum

kidneys lie retro-peritoneally (behind peritoneum) on posterior abdominal wall

outside peritoneum (membrane)

R and L kidney

• R inferior to L (1cm)

  • bc downward displacement by bulk of liver

• change in size → kidney failure

• measurements?

at concave medial margin of each kidney

lies hilum, contains

• sympathetic nerves and lymphatics

• renal vein and artery

• pelvis of ureter

ureter vs urethra

• ureter: urine from kidney → bladder

• urethra: bladder → outside

where is hilum and kidneys wrt ribs

• near transpyloric plane at vertebral level L1

• posteriorly

  • superior pole/ end of L kidney lies deep within 11th rib

  • R lies deep to 11th intercostal space

posterior relations of kidney

anterior relations of kidney R

anterior relations of kidney L

kidneys

• pelvis of ureter divides into 2/ 3 major calyces

  • each divided into minor calyces

    • each indented by renal papilla

      • receives urine from apex of pyramid

      • corresponding to collecting tubules microscopically (what pyramid made of)

renal corpuscle

glomerular (bowman’s) capsule + glomerulus

layers surrounding the kidney

1. renal capsule (fibrous) of kidney

2. perinephric fat

3. renal fascia

4. external to renal fascia = pararenal fat

• fat + fascia hold kidneys in relatively fixed position but can move about (3cm) during respiration

renal capsule

blood vessels in kidneys

• renal arteries derive from descending aorta

• renal veins drain into IVC

• L renal vein longer

  • L artery shorter

  • passes in front of aorta immediately below origin of superior mesenteric artery

• R renal artery passes behind IVC

lymphatic system

lymphatics drain to paraaortic lymph nodes (1 way/ drain upward)

which drain into cistern chill and then thoracic duct

nerve supply

by renal plexus (both sympathetic and para fibres)

ureter

made up of:

pelvis of ureter

abdominal portion

pelvic portion

intravesical portion

abdominal ureter

• lies on transverse process of lumbar vertebrae separated by muscle psoas major

• crossed anteriorly by testicular arteries in m

  • suspensory ligament in f (water under bridge)

• cross into pelvis lateral to bifurcation of common iliac artery in front of sacroiliac joint

pelvic ureter

• runs on lateral wall of pelvis in front of internal iliac artery

  • then turns forward and medially to enter bladder

• crossed by uterine artery anteriorly/ superiorly in f

  • (water under bridge)

ureter in m

ureter in f

intravesical ureter

• passes obliquely (diagonally thru wall of bladder for ~2cm

• sphincteric arrangement (ring of muscles that squeeze tubes)

  • termination of ureter surrounded by vesicle muscle

  • to avoid reflux of urine into ureter during micturition (urination)

ureter receives segmental blood supplies from

ureter has nerve supplies form

urinary bladder

• pelvic retroperitoneal structure in adults

  • in pelvis, outside peritoneal sac

• when urinary retention, adult bladder can distend into abdomen, stripping peritoneum upwards

  • (ave opacity = 300ml)

• 3yo bc pelvis small, urinary bladder = abdominal organ

parts of urinary bladder

bladder - trigone, bladder wall, urethral sphincter

trigone

• triangle formed by 2 ureteric orifices and internal urethral orifice

bladder wall

• made up of detrusor muscle

circular component of it condenses as involuntary internal urethral sphincter around internal urethral orifice

• external = skeletal muscle (voluntary)

• internal = smooth (involuntary)

bladder anterior

bladder inferior and lateral

bladder superior

covered by peritoneum

bladder posterior m

bladder posterior f

bladder blood supply

lymphatic drainage in bladder

urinary bladder has nerve supplies from