Urinary System Prelab Notes

Overview

• Gross anatomy and histological structures of the urinary system.
• Functions: Filtering blood and lymphatic fluids, creating waste products.
• Main components: Ureters, Bladder, Urethra (together called the urinary tract).

Gross Anatomy

Kidneys

• Two kidneys (left and right) are located behind the abdominal pelvic cavity.
• Adrenal glands on the superior border of the kidneys.
  • Releases adrenaline (epinephrine) during sympathetic nervous system activation.

Vascular Structures

• Inferior Vena Cava, Aorta, Common Iliac Arteries.
• Renal Arteries bring blood to the kidneys, Renal Veins return blood.

Muscles

• Iliacus: muscle visible in the gross anatomy.
• Psoas major, Quadratus lumborum (QL): other notable muscles.

Microscopic Anatomy

Kidney Histology

• Cortex and Medulla regions.
• 8 to 15 Renal Pyramids within each kidney.
  • Tips (apex) pointing toward minor calyx (cup-like structures).
  • Urine flows from minor calyx to major calyx, then to renal pelvis, and finally to the ureters.
• Kidney Capsule Layers (from deep to superficial):
  • Fibrous/Renal Capsule: Dense connective tissue covering the kidney.
  • Perinephric Fat: Layer of fat around the kidney.
  • Renal Fascia: Saran wrap-like sheath anchoring the kidney to the posterior abdominal wall.
  • Paranephric Fat: Fat layer near the kidney.

Functional Aspects

Role of Kidneys

• Filter waste products from blood and lymphatic fluids.
• Store urine (up to about a liter) and regulate blood volume.
• Regulate red blood cell production via erythropoietin (EPO).
  • EPO released when blood oxygen levels are low; stimulates red blood cell production in the bone marrow.

Blood Flow Through Kidneys

1. Renal Artery -> Segmental Arteries -> Interlobar Arteries -> Arcuate Arteries -> Interlobular Arteries.
2. Blood enters the Afferent Arteriole -> filters through the Glomerulus (ball of capillaries).
3. Unfiltered blood exits via the Efferent Arteriole -> moves to the Peritubular Capillaries.
4. Blood eventually exits the kidney through veins, ultimately through the Renal Vein.
5. Glomerulus involved only in filtration, not gas exchange.

Nephron: Functional Unit of the Kidney

• 2.5 million nephrons in both kidneys.
• Types: Cortical Nephrons and Juxtamedullary Nephrons.
  • Juxtamedullary Nephrons use Vasa Recta for deep medullar interaction.

Nephron Structures

1. Renal Corpuscle: Contains Glomerulus and Bowman’s Capsule.

• Capillaries are fenestrated (have holes for filtration) supported by Podocytes (cells with foot-like extensions).

2. Proximal Convoluted Tubule: Reabsorption of useful molecules and water occurs here.
3. Loop of Henle (Nephron Loop): Further concentrates the filtrate.
4. Distal Convoluted Tubule: Secretion of H+ ions and other processes.

Collecting Ducts

• Collect urine from multiple nephrons.
• Regulated by Antidiuretic Hormone (ADH) in response to hydration status.
• Urine flows from collecting ducts -> minor calyx -> major calyx -> renal pelvis -> ureter -> bladder.

Bladder and Urination

Bladder

• Expandable muscular container, located below the peritoneum.
  • Contains Trigone area: Two ureter openings and one urethral opening.
  • Detrusor Muscle: Smooth muscle forming the bladder wall.
  • Four tunics: Mucosa, Submucosa, Muscularis, and Adventitia.

Urethra

• Conveys urine out of the body.

• Two sphincters regulate urination process:

  • Internal Urethral Sphincter (smooth muscle, involuntary).
  • External Urethral Sphincter (skeletal muscle, voluntary).

• Differences in male and female urethras:

  • Females: Short, passes straight to exterior.
  • Males: Longer, passes through the prostate (prostatic urethra), urogenital diaphragm (membranous urethra), and penile tissues (spongy urethra).

• Enlarged Prostate: Can cause urination problems by squeezing the urethra or pushing on the bladder sphincter.

Kidney Dissection

• Identify: Cortex, Medulla, Renal Pyramids, Minor/Major Calyces, Renal Pelvis, Ureter, Renal Artery/Vein, Renal Columns, Fibrous Capsule.

Summary

• The urinary system involves complex structures and physiological processes critical to waste filtration, blood volume regulation, and urine storage and excretion.