Excretory System

• Excrete

  To eliminate, remove unwanted products from the body or waste from metabolic processes
• Structures of the excretory system

  • Kidney
  • Ureter
  • Urinary bladder
• Kidney

  • 2; left and right
  • Bean-shaped
  • Approx. the size of a tightly clenched fist (a bit smaller than the heart)
  • Main job is excretion
  • Eliminates waste from the body in the form of urine
• Urine formation and transport

  1. Urine is formed in the kidney

  2. Urine is transported posteriorly through the ureter

  3. Urine is stored in the urinary bladder
• Ureter

  • 2; left and right
  • Narrow tubes connecting each kidney to the urinary bladder
  • Transport urine from the kidneys to the bladder
  • Lined with smooth muscle that propels urine through peristaltic contractions
  • Utilize gravity and peristalsis to move urine, aided by the ureterovesical junction valve preventing urine reflux
  • Can be susceptible to blockages, causing kidney issues or urinary tract infections
• Urinary bladder

  • Hollow, muscular organ located in the pelvis
  • Stores urine produced by the kidneys until it's expelled from the body
  • Contains stretch receptors that signal when it's full, triggering the urge to urinate
  • Composed of smooth muscle tissue called detrusor muscle
  • Controlled by the autonomic nervous system for involuntary contractions during urination
  • A full bladder is approx. 300 ml
• Urethra

  Tube connecting the bladder to the outside of the body
• Urethra

  • Functions to transport urine from the bladder out of the body
  • Contains internal and external sphincters to control urine flow
  • In males, also functions as the passageway for semen during ejaculation
  • Vulnerable to infections such as urinary tract infections (UTIs) due to its proximity to the anus in both males and females
• Functions of the urinary system

  • Excretion
  • Regulation of blood volume and pressure
  • Regulation of the concentration of solutes in the body
  • Regulation of extracellular fluid pH
  • Regulation of red blood cell synthesis
  • Regulation of Vitamin D synthesis
• Excretion

  • Kidneys – major excretory organ of the body; removing waste products that are toxic
  • Waste products – metabolic by-products of cells and substances absorbed from the intestine
• Regulation of blood volume and pressure


  • Kidneys- control the extracellular fluid volume in the body
  • When drinking large amounts of liquids the body produces large volume of dilute urine
  • When skipping a few glasses per day the body will produce a small volume of concentrated urine
• Regulation of the concentration of solutes in the body


  Kidney help regulate the concentration of major molecules or ions such as glucose, sodium, chlorine, potassium, calcium, bicarbonate, hydrogen phosphate
• Regulation of extracellular fluid pH


  Kidneys excrete variable amounts of H to help regulate extracellular fluid pH
• Regulation of red blood cell synthesis


  Kidneys not only excretes waste but also secrete a hormone called erythropoietin, which regulates the synthesis of RBC in the bone marrow (hematopoiesis)
• Regulation of Vitamin D synthesis


  Kidneys play important role in controlling blood levels of calcium by regulating the synthesis of vitamin D
• Location of the kidney

  • In the abdominal cavity along with the digestive structures
  • Right kidney is right below the liver
  • Left kidney is right below the spleen (beside the pancreas)
  • Above each kidney is an adrenal gland
  • Behind the parietal peritoneum - a thin membrane surrounding the abdominal cavity
  • Described as retroperitoneal organs (retro means "behind")
  • Surrounded by adipose tissues
• Renal Artery


  Supplies the kidney with oxygenated blood; the oxygenated blood is supplied by the abdominal aorta
• Renal Vein


  Removes deoxygenated blood from the kidney
• Parts of the kidney

  • Renal Capsule
  • Cortex
  • Medulla
• Renal Capsule


  • A thin, dark brown outer covering surrounding the kidney
  • Tough fibrous covering surrounding each kidney
  • Provides structural support and protection to the kidney
  • Consists of two layers: outer parietal layer and inner visceral layer
  • Inner visceral layer directly adheres to the kidney surface
  • Helps maintain the shape and integrity of the kidney
• Cortex

  • Outer region of the kidney
  • Contains nephrons, the functional units responsible for filtering blood and producing urine
  • Site of filtration, reabsorption, and secretion processes in urine formation
  • Rich in blood vessels, including glomeruli and peritubular capillaries
  • Responsible for producing about 80-85% of the urine formed in the kidneys
• Inner Medulla


  Innermost region of the kidney
• Inner Medulla


  • Consists of renal pyramids, renal columns, and renal papillae
  • Contains structures involved in urine concentration and transportation, such as the loops of Henle and collecting ducts
  • Receives filtrate from the cortex and helps in the concentration of urine by reabsorbing water
  • Rich in tubules and blood vessels, forming the renal medullary pyramid structure
• Hilum

  Indented part of the kidney where the blood vessels and the ureter emerge from
• Hilum

  • Indentation on the concave side of the kidney
  • Point of entry and exit for structures such as blood vessels, nerves, and the ureter
  • Allows passage of the renal artery, renal vein, nerves, lymphatics, and ureter into and out of the kidney
  • Site where these structures connect to the renal pelvis and then extend into the renal sinus within the kidney
  • Plays a crucial role in maintaining the kidney's vascular and neural connections
• Renal sinus


  • Hollow cavity within the kidney
  • Located in the renal hilum area
  • Contains the renal pelvis, blood vessels, nerves, and lymphatics
  • Provides a space for structures to enter and exit the kidney at the hilum
  • Helps maintain the structural integrity and organization of the kidney's internal components
• Renal sinus


  • cavity
  • where the hilum opens into
  • contains blood vessels
  • part of the system for collecting urine and adipose tissue
• Renal Pyramids


  • Triangular structures in the renal medulla
  • Consist of nephrons and collecting ducts
  • Responsible for the concentration and excretion of urine
  • Each pyramid has a base facing the cortex and a papilla pointing towards the renal pelvis
  • Function in the process of urine formation and transport within the kidney
• Renal Pyramids


  • cone-shaped
  • locates at the boundary between cortex and medulla
• Calyx

  Cup-like structures in the kidney that collect urine from the renal pyramids
• Calyx

  • Attached to each renal pyramids
  • Funnel-shaped
  • Serve as the initial collecting structures in the urinary system
  • Merge to form the renal pelvis
  • Play a role in transporting urine from the kidney to the ureter
• Renal Pelvis


  Passage way for the collected urine that joins with the ureter
• Renal Pelvis


  • Collects urine from the calyces
  • Funnel urine into the ureter for transport to the urinary bladder
  • Located in the renal sinus area of the kidney
  • Contains smooth muscle to aid in urine transport through peristaltic contractions
• Nephron

  Functional unit of a kidney
• There are about 1-1.3 million nephrons in each kidney
• Parts of a nephron


  • Renal Corpuscle
  • Proximal Tubule/Proximal Convoluted Tubule
  • Loop of Henle/Henle's Loop
  • Distal Tubule/Distal Convoluted Tubule
• Renal Corpuscle


  Main part of the nephron, rounded part consisting of Bowman Capsule and Glomerulus
• Proximal Tubule/Proximal Convoluted Tubule


  Attached next to the renal corpuscle
• Loop of Henle/Henle's Loop


  Attached next to the proximal tubule, consisting of ascending and descending loop
• Distal Tubule/Distal Convoluted Tubule


  Located away from the renal corpuscle