Overview of Respiratory, Circulatory, and Immune Systems (Bio 11 Unit 3)

RESPIRATORY SYSTEM

• Two gases involved in gas exchange:
  • Oxygen (O_2): Taken into the body.
  • Carbon dioxide (CO_2): Removed from the body.
• Gas exchange in simple organisms and plants:
  • Simple animals (e.g., hydra, flatworms): Diffusion across their moist outer body surface directly with the environment.
  • Plants: Gases enter and exit through stomata (tiny openings in leaves); oxygen is released during photosynthesis, and CO_2 enters for photosynthesis.
• Gas exchange in larger organisms:
  • Larger animals use specialized respiratory structures (like lungs or gills) because simple diffusion is not efficient enough.
  • Oxygen diffuses from alveoli in lungs into capillaries.
  • CO_2 diffuses from blood into alveoli to be exhaled.
  • This occurs by passive diffusion driven by concentration gradients.
• Negative Pressure Breathing:
  • How humans (and other mammals) breathe.
  • The diaphragm contracts (moves down) and rib cage expands.
  • This increases chest cavity volume, causing pressure inside the lungs to drop below atmospheric pressure.
  • Air is sucked in (inhalation).
  • During exhalation, the diaphragm relaxes and air is pushed out as pressure increases.

CIRCULATORY SYSTEMS — General Concepts

• Circulation:
  • Movement of fluids (usually blood) throughout the body to deliver oxygen and nutrients and remove wastes and CO_2.
  • Supports cell function, homeostasis, and immunity.
• Circulation in amoeba (single-celled organisms):
  • No circulatory system.
  • Uses cytoplasmic streaming and diffusion to move materials directly between the cell and the environment.
• Three components in all animal circulatory systems:
  • Fluid (e.g., blood or hemolymph): Carries gases, nutrients, hormones, and wastes.
  • Vessels: Tubes that transport the fluid.
  • Pump (usually a heart): Moves the fluid through vessels.
• Open vs. Closed Circulatory Systems:
  • Open:
    • Blood (hemolymph) flows freely in body cavities; no separation between blood and other fluids.
    • Examples: Insects, crustaceans.
  • Closed:
    • Blood stays inside vessels and is pumped under pressure.
    • Examples: All vertebrates, earthworms, squid.
• Evolutionary trends in vertebrate circulatory systems:
  • Increase in the number of heart chambers:
    • Fish: 2 chambers → Amphibians: 3 chambers → Mammals & birds: 4 chambers
  • Separation of oxygenated and deoxygenated blood:
    • Prevents mixing, improving oxygen delivery to cells.
  • Development of double circulation:
    • Two loops: one to the lungs, one to the body.

HUMAN CIRCULATORY SYSTEM

• Diagram of the Heart & Functions:
  • Right atrium: Receives deoxygenated blood from the body.
  • Right ventricle: Pumps deoxygenated blood to the lungs.
  • Left atrium: Receives oxygenated blood from the lungs.
  • Left ventricle: Pumps oxygenated blood to the body.
  • Valves: Prevent backflow of blood.
  • Aorta: Carries blood from the heart to the body.
  • Pulmonary artery: Carries blood from the heart to the lungs.
  • Pulmonary vein: Carries blood from the lungs to the heart.
  • Vena cava: Returns blood from the body to the heart.
• Blood flow through the heart:
  • Deoxygenated Pathway: Body → Vena cava → Right atrium → Right ventricle → Pulmonary artery → Lungs
  • Oxygenated Pathway: Lungs → Pulmonary veins → Left atrium → Left ventricle → Aorta → Body
• Double vs. Single Circulation:
  • Single Circulation:
    • Blood passes through the heart once per full loop.
    • Example: Fish.
    • Less efficient.
  • Double Circulation:
    • Blood passes through the heart twice per loop (body + lungs).
    • Examples: Mammals, birds.
    • More efficient oxygen delivery.
• Systole vs. Diastole:
  • Systole: Contraction of heart muscles; pumps blood out of chambers.
  • Diastole: Relaxation of heart muscles; chambers fill with blood.
• Blood Pressure:
  • The force of blood against the walls of arteries.
  • Measured in mmHg (normal: ~120/80).
    • 120 = systolic pressure (during contraction).
    • 80 = diastolic pressure (during relaxation).
• Functions of Arteries, Capillaries, and Veins:
  • Arteries: Carry blood away from the heart; have thick muscular walls and high pressure.
  • Veins: Carry blood to the heart; have thinner walls, valves, and low pressure.
  • Capillaries: Exchange gases/nutrients/wastes with tissues; have very thin walls (1 cell thick).
• Purpose of the Lymphatic System:
  • Returns excess fluid from tissues to the bloodstream.
  • Filters lymph through lymph nodes (where immune cells fight infection).
  • Transports white blood cells and absorbs fats from intestines.

IMMUNE SYSTEM

• Importance of the Immune System:
  • Defends against pathogens, abnormal cells, and foreign substances.
  • Maintains homeostasis and prevents infections or disease.
• Composition of Blood:
  • Blood Cells:
    • Red blood cells (RBCs): Carry oxygen (via hemoglobin).
    • White blood cells (WBCs): Immune defense (Neutrophils, lymphocytes (B and T cells), monocytes, eosinophils, basophils).
    • Platelets: Clot blood.
  • Plasma Constituents:
    • 90% water.
    • Proteins (antibodies, clotting factors, albumin).
    • Nutrients, hormones, wastes, electrolytes, gases (CO2, O2).
• Human Blood Groups: ABO System:
  • Blood Type A:
    • Antigens on RBCs: A
    • Antibodies in Plasma: Anti-B
  • Blood Type B:
    • Antigens on RBCs: B
    • Antibodies in Plasma: Anti-A
  • Blood Type AB:
    • Antigens on RBCs: A and B
    • Antibodies in Plasma: None
  • Blood Type O:
    • Antigens on RBCs: None
    • Antibodies in Plasma: Anti-A and Anti-B
  • O = universal donor.
  • AB = universal recipient.
• Rh Factor:
  • If present → Rh⁺
  • If absent → Rh⁻
  • Important in pregnancy and transfusions.
• How the Immune System Defeats Pathogens:
  • Bacteria: Antibodies neutralize, phagocytes engulf.
  • Viruses: Killer T cells destroy infected cells; interferons released.
  • Parasites/Fungi: Eosinophils, macrophages respond.
  • Toxins: Neutralized by antibodies.
  • Antibodies mark invaders.
  • Memory cells make future responses faster.
• HIV Mechanism:
  • HIV attacks helper T cells → weakens immune response.
  • Person becomes vulnerable to other infections = AIDS.
  • No cure, but antiretroviral therapy (ART) controls virus.
• How Immunity is Maintained:
  • After infection, memory B and T cells stay in the body.
  • If the pathogen returns, the immune system responds faster (you might not even get sick).
  • This is called immunological memory.