The Circulatory System

Circulatory System

• Two Types: Open and Closed Systems

Open Circulatory System

• Blood is not always contained within vessels and directly bathes the tissues
• Examples include arthropods (insects, arachnids, crustaceans, chilopods, diplopods), mollusks (except cephalopods), and echinoderms

Closed Circulatory System

• Blood is confined to vessels throughout the body
• The human circulatory system is an example of this system

Human Circulatory System

• Heart: A muscular organ pumping blood
  • Develops early (around four weeks after fertilization)
  • Beats ~2.5 billion times in a lifetime
  • Normal adult beats ~72 times/minute
  • Pumps ~5.5 liters of blood
  • Composed of cardiac muscle
  • Covered by the pericardium
  • Divided into two sides by a septum, each with atria and ventricles

Path of Blood Flow

• Deoxygenated blood enters the Right Atrium via the Superior and Inferior Vena Cava
• Passes through the Tricuspid Valve to the Right Ventricle
• The Right Ventricle pumps blood through the Pulmonary Semilunar Valve into the Pulmonary Trunk and then the Pulmonary Arteries to the lungs (Pulmonary Circulation)
• Oxygenated blood returns from the lungs via the Pulmonary Veins to the Left Atrium
• Passes through the Bicuspid Valve to the Left Ventricle
• The Left Ventricle pumps oxygenated blood through the Aortic Semilunar Valve into the Aorta for distribution to the rest of the body (Systemic Circulation)
• Coronary Circulation supplies blood to the heart muscle itself via coronary arteries and veins

Blood

• Described as the internal circulating medium
• Carries oxygen and nutrients to body parts and transports carbon dioxide and other waste for removal
  • 55% plasma (liquid portion)
  • 45% formed elements
    • Erythrocytes (red blood cells) function in oxygen transport
    • Leucocytes (white blood cells) involved in defense and immunity
    • Blood platelets (thrombocytes) essential for blood clotting
    • Plasma composed of water, proteins, electrolytes, etc.

Blood Vessels

• Arteries: Thick-walled vessels allow passage of oxygenated blood
  • Thick walls counteract the pressure exerted by heart muscle contraction
• Veins: Thin-walled vessels; carry non-oxygenated blood.
  • Superior and inferior venae cavae: large veins
  • Veins in lower extremities contain valves
• Capillaries: Thin-walled blood vessels facilitating exchange of materials between blood and cells in interstitial fluid
• Valves: Flaps preventing backward blood flow
  • Located between atria and ventricles (bicuspid and tricuspid), at base of arteries (pulmonary and aortic semilunar), and in lower extremity veins
  • Closure creates sounds heard during auscultation

Patterns of Circulation

• Pulmonary: Blood flow between the heart and lungs

• Systemic: Blood flow between the heart and body

• Blockage leads to a heart attack or myocardial infarction

Gas Exchange in Animals

• Varies with complexity

  • Simple Animals (e.g., Poriferans): Gas exchange via diffusion through cell membranes

  • Aquatic Microorganisms: Exchange gases directly with surrounding water via cell membranes

  • Complex Animals (e.g., Humans): Relies more on the respiratory system

  • Fishes: 2-chambered heart

    • Blood pumped directly to gills for oxygen uptake and carbon dioxide release
    • Countercurrent flow maximizes gas exchange efficiency

  • Amphibians: 3-chambered heart (two atria, one ventricle)

    • Deoxygenated blood enters the right atrium
    • Oxygenated blood enters the left atrium
    • Partial mixing of deoxygenated blood occurs in single ventricle
    • "Cutaneous breathing" (gas exchange through skin) underwater and lungs on land

Respiratory System

Human Respiratory System

• Breathing: Involuntary process that occurs simultaneously with blood circulation
  • Inhalation: Chest cavity expands, diaphragm flattens, abdominal muscles relax, intercostal muscles contract, increasing thoracic cavity volume and decreasing lung pressure, causing air to rush in
  • Exhalation: Diaphragm & rib muscles relax, elastic tissues of lungs recoil, decreasing thoracic cavity size and increasing lung air pressure, forcing air out

Air Passage and Gas Exchange

• External and internal respiration
• External Respiration: Occurs in lungs, exchanging gases between air and blood
  • Air passes sequentially through:
    • Nose (Nostrils): Air filtered by coarse hairs and purified by mucus, which traps bacteria and dust
    • Pharynx (Throat): Passageway for food and air
      • Epiglottis covers airway during swallowing
    • Larynx (Voice Box): Involved in sound production
      • Pitch and volume depend on vocal cord tension and airflow
    • Trachea (Windpipe): Cartilaginous tube lined with mucous membranes and cilia
    • Bronchi: Trachea divides into two bronchi, each for one lung
      • Further branched into smaller tubes within the lungs and lined with cilia and mucus for further filtration Lungs: Large, spongy, and elastic sac-like structures comprised of bronchi that branch into bronchioles, which have thin-walled, bulb-shaped alveoli (air sacs) surrounded by capillaries Internal Respiration: Gas exchange between blood and cells of body, oxygen carried by hemoglobin in red blood cells is released to cells with lower oxygen concentrations and carbon dioxide moves from the cells into the blood
• Transport and Exchange of Gases: Hemoglobin in red blood cells significantly increases oxygen-carrying capacity of blood, transporting around 95% of the oxygen

CO2 Transportation

• Carbon dioxide is transported in 3 ways

  • Dissolved in blood plasma (around 8%).
  • Bound to hemoglobin (as carbaminohemoglobin, around 25%).
  • Converted to bicarbonate ions (HCO3-) in red blood cells (majority).

• Conversion of CO2 to bicarbonate ions and reverse reaction described with chemical equations:

  • CO2 + H2O -> H2CO3
  • H2CO3 -> HCO3- + H+
  • Lungs reverses these reactions, allowing CO2 to be exhaled
  • Carbaminohemoglobin also releases CO2 in lungs

Key Quotes re: Transport by Animals, Heart, Blood

• Transport in animals depends on size, complexity, and habitat
• The human heart: muscular organ that pumps blood to all parts of the body
• Blood: 55% plasma, 45% blood cells/formed elements (erythrocytes); leucocytes for defense and immunity, blood platelets (thrombocytes) for clotting
• Capillaries are thin-walled blood vessels that facilitate exchange between blood and cells in interstitial fluid
• Valves prevent backflow/regurgitation
• Gas exchange depends on the complexity of the animal
• Breathing: Involuntary and simultaneous with blood circulation
• External Respiration: Gas exchange between the blood and the air in the lungs
• Internal Respiration: Gas exchange between blood and the body's cells
• Hemoglobin: Transports around 95% of oxygen in the blood

Immune System

• The immune system has a series of defense mechanisms

First Line of Defense

• Innate – present from birth
• External – acts at the body's surfaces
• Without Memory – responds the same way each time.
• Prevents and acts a an initial barrier to pathogen entry
• Key elements: Integumentary system: skin and mucous membranes

Second Line of Defense

• Nonspecific immunity (innate) – responds to a wide range of threats without targeting specific pathogens

• Internal - works inside the body

• Cellular: Cellular defense plays crucial role

  • Phagocytes: Engulf and destroy foreign particles; examples: neutrophils and macrophages
  • Natural Killer Cells: Help to induce apoptosis (programmed cell death) in infected or cancerous cells

Third Line of Defense

• Specific Immunity (Adaptive); it is highly specific to pathogens and develop over time.

• Lymphocytes are the key cells of adaptive immunity

  • T lymphocytes: (CD4+ Helper T activates T cells and stimulates B cells) CD8 Cytotoxic T cells produce proteins that initiates apoptosis

  • B lymphocytes: Producing antibodies

  • Memory T cells: Provide ‘rapid response upon re-exposure to the same antigen

Two Main Types of Immunity

• Inborn immunity
  • Linked to genetic predisposition
  • Received from parents
• Acquired immunity
  • Develops during an individual's lifetime

Forms of Acquired Immunity

• Natural Active: After natural exposure to antigen

• Natural Passive: Acquired through transfers of antibodies from mother

• Artificial Active: Develops through vaccinations with weakened or inactive pathogens

• Artificial Passive: Acquired from injections of antibodies from another source

Antibodies (Immunoglobulins)

• Produced by B Lymphocytes

• React specifically with the antigen that stimulate their production

• They help protect the body by fighting harmful substances called antigens.

• Each antibody matches a specific antigen

• Neutralization: Block toxins and viruses.

• Opsonization: Coating harmful microbes, make it easy for white blood cells to eat them

• Preventing attachment - Stop microbes from attaching parts

• Recognizing "foreign" cells - Know which cells belong in the body Five Types of Immunoglobulins

• IgG: Main defender in the blood & Stays in your body long-term after an infection

• IgA: The bodyguard in a fluid. Protects nose, and digestions

• IgM: The first responder

• IgE: Fights allergens

• IgD: Helps recognize infection

Antigens

• Blood types based on antigen red blood cells
• If you have A antigen, you have type A blood
• If you have B antigen, you have type B blood
• If you have A and B antigens you have type AB

The Rh is what determines if blood os negative ot positive blood

• If you have it, then your blood is positive
• If your do not have it, then you blood is negative
• Blood typing is used to identify antigens.