Human Anatomy: Urinary and Male Reproductive System

Reproductive System

• The reproductive system is responsible for producing, storing, nourishing, and transporting reproductive cells (gametes).

Male Reproductive System

• Structures:
  • Prostate gland
  • Seminal vesicle
  • Penis
  • Vas deferens
  • Testes
  • Scrotum
  • Urethra

Female Reproductive System

• Structures:
  • Fallopian tube
  • Uterus
  • Ovary
  • Cervix
  • Vagina

Urinary System

• Major Functions:

  • Excretion of waste products like urea from body fluids.
  • Elimination of these wastes into the external environment.
  • Homeostatic regulation of blood volume and solute concentration.

• Organs:

  • Two kidneys
  • Two ureters
  • Urinary bladder
  • Urethra

Kidney Location

• Located on either side of the vertebral column.
• Situated behind the peritoneum (retroperitoneal).
• Right kidney sits slightly lower than the left.
• Displaced somewhat by the liver.
• Adrenal gland located on superior surface of each kidney.

Kidney Positioning

• Kidneys held in place by:
  • Overlying peritoneum
  • Contact with adjacent organs
  • Supportive connective tissue
  • Fibrous capsule that covers each kidney, surrounded by adipose tissue
  • Anchor to surrounding structures via suspensory fibers.

Kidney Anatomy

• Bean-shaped: About 10 cm long, 5.5 cm wide, and 3 cm thick.
• Hilum: Indentation on one side, the point of entry for renal artery and nerves, and the point of exit for renal veins and ureter.
• Fibrous capsule: Covers outer surface, lines renal sinus (internal cavity).
• Renal cortex (outer layer): In contact with the fibrous capsule, projects into medulla as renal columns.
• Renal medulla (inner layer): Contains 6-18 cone-shaped renal pyramids, tip of each is renal papilla.
• Kidney lobe: Contains a renal pyramid and overlying cortex and renal columns.
• Urine production: Begins in nephrons, about 1.25 million nephrons per kidney.
• Minor calyx: Collects urine from renal papillae.
• Major calyx: Merges minor calyces, forming a large funnel-shaped chamber called renal pelvis.
• Renal pelvis: Connected to the ureter.

Blood Supply to the Kidney

• Kidneys receive 20-25% of total cardiac output (about 1200 mL/minute of blood).
• Blood flow starts with renal artery, then branches into:
  • Interlobar arteries
  • Arcuate arteries
  • Cortical radiate arteries (or interlobular arteries)
  • Afferent arterioles (delivering blood to individual nephrons)
  • Glomerular capillaries
  • Efferent arterioles
  • Peritubular capillaries
  • Cortical radiate veins (or interlobular veins)
  • Arcuate veins
  • Interlobar veins
  • Renal vein (exits kidney)

Blood Flow from Peritubular Capillaries

• Blood from peritubular capillaries follows two possible paths:
  • Cortical nephrons: Directly into cortical radiate veins
  • Juxtamedullary nephrons: Connected to the vasa recta that run parallel to the nephron loop, and then into cortical radiate veins.

Nephron

• Basic functional unit of the kidney.
• Consists of:
  • Renal corpuscle
  • Renal tubule

Renal Corpuscle

• Spherical structure consisting of:
  • Cup-shaped glomerular (Bowman's) capsule containing a network of capillaries (glomerulus).
  • Blood enters the glomerulus through the afferent arteriole and leaves through the efferent arteriole.
  • Fluid and dissolved solutes forced out of glomerular capillaries into the capsular space (filtration).
  • Produces filtrate

Renal Tubule

• Filtrate flows into segments in order:
  • Proximal convoluted tubule (PCT)
  • Nephron loop (loop of Henle)
  • Distal convoluted tubule (DCT)
  • Each nephron empties into collecting duct, to eventually become urine.

The Proximal Convoluted Tubule

• Majority of reabsorption occurs here.
• Cells lining PCT reabsorb organic nutrients, plasma proteins, and ions from tubular fluid.
• Materials reenter the blood, water follows by osmosis, reducing tubular fluid volume.

The Nephron Loop (Loop of Henle)

• Composed of descending limb and ascending limb.
• Fluid in descending limb flows toward renal pelvis, epithelium permeable to water, not solutes.
• Fluid in ascending limb flows toward renal cortex, epithelium not permeable to water, actively transports sodium and chloride out. This results in a higher solute concentration in the peritubular fluid of the renal medulla, and water moves out of descending limb by osmosis.

The Distal Convoluted Tubule (DCT)

• Site for three important processes:
  • Active secretion of ions, acids, drugs, and toxins
  • Selective reabsorption of sodium
  • Selective reabsorption of water

The Juxtaglomerular Complex:

• Combination of closely associated cells in the DCT and afferent arteriole.
• Involved in regulating blood volume and blood pressure through the secretion of erythropoietin and renin.

The Collecting System

• Many DCTs empty into one collecting duct.
• Several collecting ducts merge into a papillary duct.
• Papillary duct empties into minor calyx.
• Transports tubular fluid from nephron to renal pelvis.
• Adjusts final fluid composition.
• Determines final osmotic concentration and volume of urine.

Metabolic Wastes in Urine

• Urea: Most abundant organic waste, formed during amino acid breakdown.
• Creatinine: Generated in skeletal muscle tissue from creatine phosphate breakdown.
• Uric acid: Formed from RNA breakdown and recycling.

Ureters

• Paired muscular tubes
• Carry urine from kidneys to urinary bladder.
• Have slit-like ureteral openings to prevent urine backflow.
• Three layers:
  • Inner layer: transitional epithelium
  • Middle layer: smooth muscle (peristalsis)
  • Outer layer: connective tissue

Kidney Stones (Calculi)

• Solid substances (calcium deposits, magnesium salts, uric acid crystals) forming within kidney, ureter, or bladder.
• Results in the painful condition nephrolithiasis.
• Can obstruct urine flow and reduce/prevent filtration.

Urinary Bladder

• Hollow muscular organ that stores urine.
• Size varies with distension.
• When full (up to a liter), held in place by peritoneal folds (umbilical ligaments).
• In males: base lies between rectum and pubic symphysis.
• In females: sits inferior to the uterus and anterior to the vagina.

Internal Anatomy of the Urinary Bladder

• Base has triangular area (trigone) formed by two ureteral openings and urethral entrance.
• Area surrounding urethral entrance is the neck of the bladder.

The Urethra

• Extends from bladder neck to body exterior.
• Circular band of skeletal muscle (external urethral sphincter) under voluntary control.
• In males: 18-20 cm long, exits at tip of penis.
• In females: 2.5-3.0 cm long, near anterior vagina wall.

Test your knowledge of the urinary system and male reproductive anatomy with this quiz. It covers functions of the urinary system, the urethra's role, and the epididymis in sperm maturation. Assess your understanding of these vital systems in human biology.