EXCRETORY

• Excretory System

  System that removes waste products from the body
• Figure 18.1
• Functions of the Urinary System


  • Excretion
  • Regulation of blood volume and pressure
  • Regulation of the concentration of solutes in the blood
  • Regulation of extracellular fluid pH
  • Regulation of RBC synthesis
  • Vit D synthesis

  
• Excretion


  Kidneys remove waste products, mostly toxic, which are metabolic by-products of cells & substances absorbed from the intestine

  
• Regulation of blood volume and pressure


  Kidneys control the extracellular fluid volume in the body by producing either a large volume of dilute urine or a small volume of concentrated urine

  
• Regulation of the concentration of solutes in the body


  Kidneys help regulate the concentration of the major molecules and 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 secrete a hormone, erythropoietin, which regulates the synthesis of RBC in bone marrow
• Regulation of vitamin D synthesis


  Kidneys play an important role in controlling blood levels of calcium by regulating the synthesis of vitamin D
• Figure 18.2a
• Figure 18.2b
• Kidneys


  • Bean-shaped organs, each about the size of a tightly-clenched fist
  • Located behind the peritoneum, thus are retroperitoneal
  • Renal capsule - connective tissue surrounding each kidney
  • Hilum - medial side where renal artery & nerves enter & where renal vein, ureter, lymphatic vessels exit
  • Renal sinus -cavity where hilum opens into & contains blood vessels, part of the system for collecting urine & adipose tissue
  • Outer Cortex & Inner Medulla - surround the renal sinus
  • Renal Pyramids - cone-shaped & located at boundary between cortex & medulla
  • Calyx - funnel-shaped that surrounds the tip of each renal pyramid
  • Renal pelvis - large funnel formed from calyces
  • Ureter - a small tube formed from the narrowing of renal pelvis that exits the kidney & connects to urinary bladder

  
• Figure 18.3a
• Figure 18.3b
• Figure 18.4
• Nephron


  Functional unit of a kidney, composed of Renal Corpuscle (Bowman's capsule & glomerulus), Proximal Convoluted Tubule, Loop of Henle, Distal Convoluted Tubule

  
• Figure 18.5a
• Figure 18.6a
• Figure 18.7a
• Urine Production


  1. Filtration - the movement of water, ions, and small molecules through the filtration membrane into Bowman's capsule

  2. Tubular reabsorption - the movement of substances from the filtrate across the wall of the nephron back into the blood of the peritubular capillaries

  3. Tubular secretion - the transport of substances, usually waste products, from the intestinal fluid across the wall of the nephron into the filtrate

  
• Urine - consist of substances (95% water, urea, uric acid, electrolytes) that are filtered and secreted from the peritubular capillaries into the nephron, minus those substances that are reabsorbed
• Antidiuretic hormone (ADH)


  Secreted by posterior pituitary gland, regulates the amount of water reabsorbed by the distal tubules and collecting ducts
• Micturition reflex


  Activated by stretch of the urinary bladder wall, made possible by the external urinary sphincter

  
• Bladder capacity - 1000ml urine