Biology: Integumentary Respiration

Respiration

• Integumentary respiration: occurs in organisms living in moist environments, where oxygen diffuses through the skin, which must be moist
• Examples: ¼ of oxygen in frogs is acquired via cutaneous respiration, and lungless salamanders rely solely on cutaneous respiration in the buccal-pharyngeal region

Tracheal Systems

• Present in some terrestrial environments
• Composition:
  • Trachea: contains openings with spiracles
  • Spiracle: coverings that can open and close to prevent water from entering the tracheal system
  • Tracheole: connected to the trachea

Gills (Brachia)

• Formed by evaginations/external outgrowths from the body surface
• Types:
  • External gills: found on the external side
  • Internal gills: covered by the epidermis
• Composed of gill arches: fish possess 4 gill arches, each with two layers of gill filaments
• Countercurrent gas exchange:
  • Flow of blood is opposite the direction of the flow of water
  • Allows for easier capture of oxygen: oxygen-poor blood will capture oxygen quickly with the oxygen-rich waters

Lungs

• For air respiration in terrestrial environments
• Alveoli:
  • Where the exchange of gas occurs
  • Rich in capillaries that release CO2 and capture O2
  • Composed of simple squamous epithelium to allow easy passage of gases
  • Thinner membrane increases the rate of diffusion of gases
• From the trachea → bronchi → bronchioles → alveoli
• Lung ventilation:
  • Positive pressure pumping mechanism
  • Example: how frogs respire/inspire

Hematopoeisis (Hemopoiesis)

• Formation of cells in the blood
• All cells are from multipotent stem cells
• Differentiation into:
  • Lymphoid stem cells: give rise to lymphocytes (B and T-lymphocytes)
  • Myeloid stem cells: give rise to erythrocytes (red blood cells), leucocytes (white blood cells), and platelets

Erythrocytes (Red Blood Cells)

• 3 cellular features:
  • Biconcavity increases surface area for gas exchange
  • Contain heme consisting of hemoglobin for binding oxygen
  • Anucleate (no nucleus) to increase space for oxygen
• Short lifespan: 120 days
• Recycled by the liver and spleen to be broken down into components (hemoglobin)
• Comprise 90% of cells in the blood

Life Cycle of RBC

• Macrophages break down RBC to its major components: globin and heme
• Globin broken down to amino acid components, reused for protein synthesis
• Iron in the heme has two pathways:
  • Transported to the liver via transferrin, stored in ferritin
  • Converted into biliverdin, then bilirubin, transferred to the liver, and excreted into bile

Control of Erythrocyte Level

• Anemia: low concentration of RBC, causing hypoxia (low oxygen levels)
• Imbalance of RBC detected by kidneys, triggered by low oxygen levels in the blood
• Kidneys (and sometimes liver) release erythropoietin to stimulate bone marrow to enhance erythropoiesis

Leukocytes (White Blood Cells)

• Types:
  • Granular: have granules in the cytoplasm (basophils, neutrophils, eosinophils)
  • Agranular: no granules in the cytoplasm (lymphocytes, monocytes)
• Functions: fight foreign materials/objects detected in the body (except NK cells)

Thrombocytes (Platelets)

• Function: blood clotting
• After some time, a bleeding wound will stop bleeding because of platelets

Blood Circulation

• Blood flow:
  • From the upper body, passes through the anterior vena cava, and also through the posterior vena cava for the lower body
  • Enters the right atrium, then the right ventricle, monitored by the atrioventricular valve (tricuspid valve)
  • Enters the pulmonary artery to be oxygenated in the lungs, monitored by the semilunar valve
• Oxygenated blood:
  • From the lungs, passes through the pulmonary veins
  • Enters the left atrium, then the left ventricle, monitored by the atrioventricular valve (bicuspid valve)
  • Glomerular filtration: where most of the filtration occurs