W11 - Urinary System

Urinary System Organs

• 2 Kidneys

• 2 Ureters

• Urinary Bladder

• Urethra

Functions of the Kidneys

• regulates electrolyte levels in blood, pH of blood, blood volume

• regulates BP thru secreting renin

• secretes erythropoietin for RBC synthesis

• excretion of waste products

• activates Vitamin D for Ca2+ homeostasis

Functions of the Ureters, Bladder and Urethra

transportation, storage and excretion of wastes in the urine

Kidneys Location

• within retroperitoneal space

• located T12-L3

Additional Supporting Connective Tissue for Kidneys

1. renal fascia = superficial layer that anchors kidneys to ABD wall

2. adipose capsule = provides protection 

3. renal capsule = covers kidney surface to maintain shape

Renal Hilum Composition  

• renal artery

• renal vein

• ureter 

• renal nerves

Kidney Composition

• Parenchyma = contains nephrons, which produce urine

• Renal Cortex → Renal Medulla/Renal Column → Renal Papilla → Renal Sinus/Minor Calyx → Major Calyx → Renal Pelvis → Renal Hilum

Nephron

• basic functional unit of the kidney

• comprised of 

  • renal corpuscle = filters blood

  • renal tubule = transports filtered fluid

Classification of Nephrons

• cortical nephrons 80-85%

  • renal corpuscle in outer cortex

  • performs most reabsorption and secretion

  • no thin ascending limb

• juxtamedullary nephrons 15-20%

  • renal corpuscle in inner cortex

  • performs urine concentration 

Blood Flow to Nephrons

renal artery → segmental arteries → interlobar arteries → arcuate arteries → cortical radiate (interlobular) arteries → afferent arterioles

→ nephrons → glomerulus (capillary where filtration occurs) → efferent arteriole → peritubular capillaries/ vasa recta (both function to return fluid/solutes reabsorbed back to bloodstream)

→ cortical radiate (interlobular) veins → arcuate veins → interlobar veins → segmental veins → renal vein

Ureters

• transport urine from renal pelvis to bladder via peristalsis, hydrostatic pressure and gravity  

• descends retroperitoneally, then cross over the bifurcation of the common iliac arteries to enter pelvic cavity → pass thru posterior bladder wall 

Histology of Ureters

1. Adventitia

2. Smooth Muscle

3. Lamina Propria, transitional epithelium

4. Lumen 

Urinary Bladder

hollow, distensible muscular organ located in pelvic cavity

Average Bladder Capacity

700-800ml, may be less for female due to uterus

Histology of Bladder

1. Adventitia: Serosa, Areolar Connective tissue

2. Muscularis = smooth muscle

3. Mucosa: transitional epithelium, lamina propria, presence of rugae 

Ureter to Urethra 

ureters enter bladder posteriorly → bladder → trigone (smooth inner surface comprised of rugae)→ urethra exits bladder inferiorly via internal urethral orifice → external urethral sphincter

Male vs. Female Urethrae

• female: 4cm passageway from internal urethral orifice to exterior of body

• male:

1. PREPROSTATIC 

2. PROSTATIC

3. MEMBRANOUS 

4. SPONGY

Micturition

= discharge of urine from bladder

• occurs through involuntary + voluntary innervation to smooth and skeletal muscle

• triggered when urine volume exceeds 200-400ml → stretch receptors send nerve impulses to micturition center (S2-3) → trigger micturition reflex (parasympathetic response, inhibits somatic motor neurons)