excretory system

• Excretory System


  Organs that facilitates filtering of blood plasma and removal of nitrogenous wastes such metabolic waste, toxins, and excrete them in urine out of the body
• Functions of Excretory System

  • Eliminates waste and chemical products via Urine
  • Maintains osmotic level of blood and plasma
  • Maintain electrolyte balance in the body
  • Helps in metabolizing drugs that do not get metabolized in the liver
• Kidney


  • A pair of dark-red pea-sized bean shaped organs that sits on each side of the spine against the posterior body wall
  • Retroperitoneal (lies between the dorsal wall and peritoneum)
  • Holds 20% of total blood volume
• Structure of Kidney


  • Cortex - outer area
  • Renal Medulla - inner area which composed of seven cone shaped renal pyramids
• Parts of the Nephron

  • Glomerulus - composed of specialized mass of capillaries and is enclosed by the bowman's capsule
  • Bowman's Capsule
  • Tubules - consist of the proximal and distal tubule and Loop of Henle
• Steps of Urine formation

  1. Glomerular Filtration

  2. Tubular reabsorption and secretion

  3. Water conservation
• Filtration


  The process by which water and dissolved particles are pulled out of the blood and the resulting liquid is called Filtrate
• Substances in Filtrate


  • Water
  • Glucose
  • Amino acids
  • Salts
  • Inorganic ions
  • Medications
  • Vitamins
  • Metabolic waste (urea, creatinine)
• Ureter


  • A pair of muscular, tubular structures responsible for taking urine from the kidneys to the urinary bladder for storage, prior to excretion
  • S-shaped channels, each about 25 cm in length
  • Widest at the renal pelvis, narrow as they enter the urinary bladder
  • Lumen is lined by a mucosal layer of transitional epithelium
  • Have several in foldings caused by multiple layers of smooth muscle throughout the ureteral wall
• Parts of the Ureter

  • Abdominal Part - which lies between the Renal Pelvis and the Terminal Line of the Pelvis
  • Pelvic Part - which ends at the bladder
  • Intramural Part - when the ureter is in the wall of the urinary bladder
• Layers of the Ureter Wall

  • Tunica Mucosa
  • Tunica Muscularis
  • Tunica Adventitia
• Layers of Tunica Muscularis


  • Inner part - Longitudinal Muscle Fibers
  • Middle Part - Circular Muscle Fibers
  • Outer Part - Longitudinal Muscle fibers
• Peristalsis in the Ureters

  Urine is propelled along the ureters by peristaltic motions initiated by pacemaker cells in the proximal renal pelvis
• Path of the Right Ureter and Left Ureter

  1. Right ureter - Travels posterior to the duodenum and further down it is crossed by branches of the superior mesenteric vessels

  2. Left ureter - Travels laterally to the inferior mesenteric vessels and is subsequently crossed by its branches

  3. Pierces through the wall of the urinary bladder from lateral to medial and posterior to anterior
• Innervation of the Ureters


  • Sympathetic - Controlled by nerves from the renal plexus and ganglia
  • Parasympathetic - Provided by pelvic splanchnic nerves and the inferior hypogastric plexus
• Lymphatic Drainage of the Ureters

  • Proximal Segment - Drains into the lumbar (lateral aortic) and precaval nodes
  • Middle Segment - Drains into the common iliac and precaval nodes
  • Distal Segment - Drains into the internal and external iliac nodes
• Bladder


  • The most anterior element of the pelvic viscera
  • Entirely situated in the pelvic cavity when empty, it expands superiorly into the abdomen when full
  • The empty bladder is shaped like a three-sided pyramid
• Anatomical Parts of Urinary Bladder

  • Apex - attached to median umbilical ligament
  • Fundus (base) - contains the trigone internally
  • Body - collects the urine
  • Neck - continuous with urethra
• Trigone


  The smooth triangular area between the openings of the ureters and urethra on the inside of the bladder
• Blood Supply of the Bladder

  • Superior and inferior vesicular arteries - tributaries of the internal iliac arteries
  • Obturator artery
  • Inferior gluteal artery
• Innervation of the Bladder


  • Sympathetic - Directed to the blood vessels, urethral openings, and the trigone
  • Parasympathetic - Derived from S2,3 and 4 nerves, aimed at serving the detrusor muscle
  • Pelvic spinal nerves - Responsible for responding to the sensory response of a full bladder
• Urethra


  • The terminal part of the excretory system where urine exits through the urethral opening
  • About 1.5 inches (3 to 4 centimeters) long in females, about 8 to 9 inches long (about 20 centimeters) in males
  • Walls are thin and made up of epithelial tissue, smooth muscle cells, and connective tissue
• Parts of the Male Urethra

  • Prostatic urethra
  • Membranous urethra
  • Penile urethra (also called the spongy urethra or the cavernous urethra)
• Other Excretory Organs


  • Skin - by sweating
  • Lungs - eliminate some amount of water in the form of vapour
  • Liver - eliminates excess fats and cholesterol
• Disorders of Excretory System

  • Kidney Stones - accumulation of calcium or uric acid crystals within the kidney
  • Renal Failure - characterized by the cessation of functioning of one or both kidneys
  • Urethritis - inflammation of urethra
  • Uremia - characterized by the increased blood urea levels, treated by Dialysis
  • Anuria - condition characterized by no passage of urine
  • Polyuria - excessive or frequent passage of urine