Kidneys Urinary System 06

Kidneys and Urinary System • Kidneys • Ureters • Urinary Bladder • Urethra

Kidneys • Move as much as 1 inch during respiration • The kidneys lie in a retroperitoneal position on the posterior abdominal wall in the superior lumbar region T11-T2 • The right kidney is lower than the left • The lateral surface is convex; the medial surface is concave - hilum • Renal vein, 2 branches of the renal artery, the ureter, another branch of renal artery (VAUA) • Lymph vessels and sympathetic fibres also pass through hilum

Location and Relations – Right Kidney • Anteriorly – Adrenal gland, the liver, 2nd duodenum, right colic flexure

• Posteriorly – Diaphragm (and costodiaphragmatic recess), 12th rib, psoas, – subcostal (T12) iliohypogastric and ilioinguinal nerves (L1) run downwards and laterally

Location and Relations – Left Kidney • Anteriorly – Adrenal, spleen, stomach, pancreas, left colic flexure

• Posteriorly – Diaphragm (and costodiaphragmatic recess), 11th and 12th rib, psoas, – subcostal (T12) iliohypogastric and ilioinguinal nerves (L1) run downwards and laterally

Coverings of the Kidneys • Renal / fibrous capsule - that prevents kidney infection • Perirenal fat – fatty mass that cushions the kidney and helps attach it to the body wall • Renal fascia – outer layer of dense fibrous connective tissue that anchors the kidney • Pararenal fat – external to the renal fascia

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Renal capsule Perirenal fat

Renal fascia Pararenal fat

• Major calyces – large branches of the renal pelvis

Renal Structure • Cortex – the light colored, granular superficial region • Medulla – exhibits dozen cone-shaped medullary (renal) pyramids separated by columns • Each apex of renal pyramid projects into minor calyces • 2-3 minor calyces – major calyx

– Collect urine draining from papillae – Empty urine into the renal pelvis

• Renal pelvis – flat funnel shaped tube expanded upper end of the ureter • The renal sinus – space within the hilum which contains the renal pelvis and vessels • Urine flows through the pelvis and ureters to the bladder

columns cortex

medullary pyramid

Minor calyx

Major calyx

pelvis Renal papilla ureter

Figure 25.71

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Blood Supply

The Kidneys and Adrenal Glands

• Approximately 1/4 (1200 ml) of systemic cardiac output flows through the kidneys each minute • Arterial flow into and venous flow out of the kidneys follow similar paths • Renal artery – segmental arteries (2-4 ant, 1 post) – lobar arteries (1 per pyramid) • Renal vein emerges at hilum anterior to arteries • Lymph drainage to lateral aortic lymph nodes

Nerve Supply • The nerve supply is via the renal plexus – Sympathetic, Parasympathetic, Visceral afferent – From thoracic and lumbar splanchnics and vagus nerve

• The afferent fibres that travel through the renal plexus enter T10-12 Referred pain to small of back, flank (lumbar quadrant, and genitals (calculi)

Ureters • Retroperitoneal, muscular tubes • Pass over the pelvic brim at bifurcation of common iliac arteries • Run on lateral walls of pelvis • Opposite ischial spine, curve anteromedially • Oblique entrance into bladder – one way flap valve • posterosuperior angles of the bladder

Ureters • Ureters have a trilayered wall – Transitional epithelial mucosa – Smooth muscle muscularis – Fibrous connective tissue adventitia

• Ureters actively propel urine to the bladder via response to smooth muscle stretch

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Urinary Bladder • Smooth, collapsible, muscular sac that stores urine • It lies retroperitoneally on the pelvic floor posterior to the pubic symphysis • It is connected anteriorly to the umbilicus – median umbilical ligament (urachus) • The bladder is distensible and collapses when empty • As urine accumulates, the bladder expands without significant rise in internal pressure

Male Bladder • 2 vas deferentia lie posterior surface of bladder between seminal vesicles • Peritoneum – rectovesical pouch • prostate gland surrounds the neck inferiorly

Ureteric orifices

Urinary Bladder – Internal Anatomy

peritoneum

• The bladder wall has three layers – Transitional epithelial mucosa – A thick muscular layer – A fibrous adventitia

• Trigone – triangular area outlined by the openings for the ureters and the urethra – Clinically important because infections tend to persist in this region

Detrusor muscle prostate

trigone

Internal Urethral Orifice

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Urethra

Urethra

• Muscular tube that: – Drains urine from the bladder – Conveys it out of the body

• Sphincters keep the urethra closed when urine is not being passed – Internal urethral sphincter – involuntary sphincter at the bladder-urethra junction – External urethral sphincter – voluntary sphincter surrounding the urethra as it passes through the urogenital diaphragm – Levator ani muscle – voluntary urethral sphincter

• The female urethra is tightly bound to the anterior vaginal wall • Its external opening lies anterior to the vaginal opening and posterior to the clitoris

peritoneum peritoneum

Paravesical fascia Detrusor muscle

Levator ani

ureter

Paravesicular fascia

Obturator internus

Levator ani prostate

trigone Crus of clitoris Internal urethral orifice Bulb of vestibule + bulbospongiosus

Pubic ramus Crus of penis

Levator ani Bulbospongiosus / corpus cavernosum

Rectovesical pouch Ureteric orifice

Seminal vesicle

trigone

trigone

Internal Urethral spincter

Prostatic urethra

Spongey urethra

Internal urethral orifice

prostate

Prostatic Membranous Spongey urethra

Sphincter Urethrae and Perineal membrane Ejaculatory duct

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Micturition (Voiding or Urination) • The act of emptying the bladder • Distension of bladder walls initiates spinal reflexes that: – Stimulate contraction of the external urethral sphincter – Inhibit the detrusor muscle and internal sphincter (temporarily)

• Voiding reflexes: – Stimulate the detrusor muscle to contract – Inhibit the internal and external sphincters

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