Excretory system

• Histology


  The study of the microscopic structure of tissues
• Functions of the excretory system

  • Filtration of cellular waste from blood
  • Regulation of salt and water balance
  • Excretion of the waste and excess water as urine
  • Endocrine function – Erythropoietin and Renin
  • In Male, the urethra also serves the reproductive system
• Kidney


  • Renal medulla
  • Renal cortex
• Parts of the renal cortex

  • Pars Convoluta
  • Pars Recta
• Pars Convoluta


  • Renal corpuscles or Malphigian corpuscles
  • Glomerulus and Bowman's capsule
  • Proximal convoluted tubule
  • Distal Convoluted tubule
  • Arch Collecting tubule
• Pars Recta


  • Straight tubules
  • Descending loop of Henle
  • Ascending loop of Henle
  • Straight Collecting tubules
• Nephrons


  • 1-1.4Millions
  • Renal or Malphigian corpuscle
  • Bowman's capsule
  • Glomerulus
  • PCT
  • Descending and Ascending loop of Henle
  • DCT
  • Collecting tubule
• Glomerulus


  A tuft of capillaries enclosed in the Bowman's capsule
• Bowman's capsule


  • Outer parietal layer lined by single layer of squamous cells
  • Inner visceral layer formed of modified epithelial cells called PODOCYTES
• Filtration barrier


  • Filtration slits
  • Basal lamina
  • Endothelium of a glomerular capillary
• Mesangial cells


  • Stellate-shaped
  • Phagocytic
• Mesangial cells


  Provide structural support and contraction, Phagocytosis, Secretion
• Urinary or capsular space

  Between 2 capsular layers, Receives the fluid filtered through the capillary wall and the visceral layer
• Renal corpuscle


  • Vascular pole
  • Tubular pole
• Proximal convoluted tubule


  • Longest and the most convoluted part
  • Lined by Simple cuboidal epithelium with brush border – reabsorption
  • Cells have granular cytoplasm, acidophilic
  • Reabsorb 60-65% water, All glucose, 85% Sodium, Chloride
• Loop of Henle


  • Descending limb: Thick lined by Simple cuboidal epithelium, Thin lined by Simple squamous epithelium
  • Ascending limb: lined by Simple cuboidal epithelium without brush border, Wider lumen
• Juxtamedullary nephrons


  • Located near the corticomedullary junction
  • It allows the kidney to produce concentrated hypertonic urine
  • With short thick descending limb, long thin descending and ascending limbs and long thick ascending limbs
• Distal convoluted tubule


  • Lined by Simple cuboidal cells without brush border
  • Wider lumen
  • Pale staining cytoplasm
  • Sodium reabsorption and Potassium secretion by Sodium pump – regulated by Aldosterone
  • Secrete H+ and NH4 – maintain acid-base
• Juxtaglomerular apparatus


  • Juxtaglomerular cells/ jg cells: Rounded nuclei, basophilic cytoplasm, Secretes RENIN
  • Lacis cells: Aka Extraglomerular Mesangial cells, Produce Erythropoietin
• Collecting tubules


  • Last part of each nephron
  • Join each other to form straight COLLECTING DUCTS
  • Runs to the tips of the medullary pyramids
  • Empty into the minor calyces
  • Tubules: Simple cuboidal epithelium
• Antidiuretic hormone (ADH)


  Arginine vasopressin, Makes the collecting duct more permeable to water
• Excretory passages


  • Renal pelvis
  • Ureter
• Ureter


  • 3 walls: Inner mucous layer, Middle muscular layer, Outer circular layer muscle layer
  • Inner longitudinal muscle layer
  • Outer adventitia layer – loose collagenous t.
• Urothelium


  • Single layer of small basal cells
  • Intermediate region containing 1-several layers of columnar cells
  • Superficial layer of very large polyhedral or bulbous cells called UMBRELLA CELLS
• Renal pelvis


  Flattened funnel-shaped end of the ureter in the hilum of the kidney, that branches into major and minor calyces
• Ureter


  • Mucosa: lined by Transitional epithelium
  • Lamina propia: dense superficial part, Loose superficial part, NO glands, Diffuse lymphatic tissue
  • Muscular: Upper 2/3 – thinner, 2 layers of muscle, Lower 1/3 – thicker, 3 layers
  • Terminal portion: NO circular muscle, Inner longitudinal, Outer longitudinal
  • Tunica adventitia: loose collagenous t.
• Urinary bladder


  • Mucosa: lined by Transitional epithelium
  • Lamina propia: highly vascularized
  • Submucosa
  • Muscularis: 3 layers: Detrusor muscle
  • Tunica adventitia: fibroelastic connective tissue
  • Peritoneum – covers the upper part of the urinary bladder
  • The ureter pass through the wall of the bladder obliquely forming a sphincter of the bladder
• Male urethra


  • Prostatic urethra: 3-4cm long, extends through the prostate gland, Lined by urothelium, Opening of the prostate utricle, Openings of the ejaculatory ducts
  • Membranous urethra: Short segment 1-1.5cm, Lined by Stratified Columnar or Pseudostratified epithelium
  • Spongy urethra: Longest part 15cm, Traversing the whole length of the corpus spongiosum, Lined by Pseudostratified or Stratified Columnar epithelium, Terminal portion: Fossa Navicularis lined Simple Squamous non-cornified epithelium
• Urethra mucosa


  • Recesses or deep irregular out-pocketings into the tunica propia which are called Lacunae of Morgagni
  • Lamina propia: loose collagenous tissue with abundant elastic fibers and smooth muscle, Few diffuse lymphocytes, Several small mucus secreting glands called
  • Muscular: inner longitudinal, Outer circular
  • Tunica adventitia: Areolar connective tissue, Bigger blood vessels, Nerve plexuses
• Female urethra


  • Shorter 4-5cm
  • Mucosa: First part - Transitional epithelium, Middle part – Pseudostratified epithelium, Terminal part – SSNCE
  • Lamina propia: loose c.t, Elastic fibers & lymphocytes, Litter's gland, Lacunae of Morgagni
  • Muscular: Inner longitudinal, Outer circular, Skeletal muscle – urethral sphincter
  • Tunica adventitia: Areolar tissue, Blood vessels, nerves