Chapter 6: Transport in Humans - Study Notes

6.1 What Are the Main Components of Blood?

  • Learning Outcome: State the components of blood and their roles in transport and defence:

    • Plasma: transport of blood cells, ions, soluble food substances, hormones, carbon dioxide, urea, vitamins, plasma proteins

    • Red blood cells (RBCs): haemoglobin for oxygen transport

    • White blood cells (WBCs): phagocytosis, antibody formation and tissue rejection

    • Platelets: fibrinogen to fibrin, causing clotting

  • Blood components overview:

    • Yellowish liquid in blood is plasma

    • Plasma composition: mainly water, blood cells, excretory products (e.g. urea, amino acid), substances (e.g. glucose, proteins, fats, salts, hormones, vitamins)

    • Plasma role in transport: carries nutrients from the small intestine to other parts of the body, hormones from endocrine glands to target organs, and transports waste to excretory organs

  • Red Blood Cells (RBCs):

    • Primary function: transport oxygen from lungs to other parts of the body

    • Hemoglobin: binds oxygen reversibly

    • RBC features: biconcave shape increases surface area-to-volume ratio for faster diffusion; no nucleus to make more space for haemoglobin; flexible and can become bell-shaped to pass through narrow capillaries

  • White Blood Cells (WBCs):

    • Two main types: phagocytes and lymphocytes

    • Phagocytes perform phagocytosis to engulf and destroy pathogens

    • Lymphocytes produce antibodies; antibodies help recognise/destroy pathogens, clump pathogens for ingestion by phagocytes, and neutralise bacterial toxins

  • Platelets (Thrombocytes):

    • Cytoplasm fragments that aid in blood clotting

    • They contain enzymes that convert fibrinogen to fibrin, forming fibrin threads that entangle with red blood cells to form a clot and seal wounds

  • High-altitude training (context):

    • Increases the number of red blood cells and the amount of haemoglobin in RBCs

    • Effect: higher haemoglobin improves oxygen transport capacity, benefiting athletic performance

  • Challenge prompts (from the session):

    • Why would a patient require a plasma transfusion?

    • Some proteins are found in plasma. (a) Why are they not from dietary proteins? (b) Where do they originate from?

  • Very little oxygen in plasma:

    • Oxygen is largely carried by haemoglobin in RBCs; plasma contains mainly water and dissolved substances, with very little dissolved oxygen

  • High-altitude training equation reference:

    • Equation for Respiration mentioned in Textbook Page 100, not provided in transcript

6.2 What Are Blood Groups?

  • Four main ABO blood groups: A, B, AB, O

  • Blood group antigens and plasma antibodies:

    • Antigens: special proteins on the surface of red blood cells; same antigens on all RBCs of an individual

    • Antibodies: produced by white blood cells and found in plasma; react with incompatible antigens

  • Antigen–Antibody relationships by blood group:

    • Blood group A: antigen A on RBCs; anti-B antibodies in plasma

    • Blood group B: antigen B on RBCs; anti-A antibodies in plasma

    • Blood group AB: antigens A and B on RBCs; no antibodies to A or B in plasma

    • Blood group O: no A or B antigens on RBCs; both anti-A and anti-B antibodies in plasma

  • Antibody–antigen reactions:

    • Antigens provoke an immune response; certain antibodies react with specific antigens, causing agglutination (clumping), which can be fatal if transfused

  • What happens when different blood groups are mixed?

    • Agglutination occurs if incompatible; can block blood vessels and be dangerous

  • Importance of tissue matching:

    • In organ transplants and blood transfusions, donor tissue must be matched to reduce tissue rejection

  • Practical activities:

    • Blood typing game and online resources for learning blood typing

  • Enrichment prompts:

    • The medical term for reddish birthmarks (port-wine stains) and how they relate to capillary malformations

  • Special case: SCID and the Bubble Boy (David Vetter):

    • Severe Combined Immunodeficiency (SCID) led to life in a sterile bubble; ethically interesting case for tissue/immune compatibility and risk management

6.3 How Are Blood Vessels Adapted to Their Functions?

  • Context: Parts of the circulatory system include heart, arteries, arterioles, capillaries, venules, veins

  • Adaptations by vessel type:

    • Arteries: thick, muscular, and elastic walls to withstand high blood pressure; walls stretch and recoil

    • Elasticity helps recoil to maintain blood pressure; contraction/relaxation can divert blood to organs (e.g., dilation of skin arterioles during thermoregulation)

    • Veins: transport blood back to the heart; lower pressure and slower flow; thinner walls; valves prevent backflow

    • Capillaries: walls are one cell thick, very small diameter, numerous and highly branched

    • Large total surface area and short diffusion distance facilitate exchange of substances

    • Continuous blood flow through capillaries ensures sustained exchange

  • Diffusion and exchange in capillaries:

    • Role of diffusion: exchange of substances between blood and tissue fluid occurs mainly by diffusion

    • Diffusion factors: Temperature, Surface area, Diffusion distance, Steep concentration gradient

    • In the human body, temperature is effectively constant, so temperature is not a variable for diffusion in capillaries

  • Capillary network effects on blood flow:

    • The aggregate cross-sectional area of capillaries is greater than that of arteries, causing a drop in speed and pressure, which enhances exchange time

  • Tissue fluid and exchange:

    • Tissue fluid is the colourless fluid in spaces between cells; it transports dissolved substances between capillaries and tissue cells

  • Transfer between capillaries and tissue fluid:

    • Substances moved from blood to tissue fluid and from tissue fluid back to blood; specific substances depend on metabolic needs and gradients

6.4 How Does Blood Circulate in the Human Body?

  • Double circulation:

    • Movement of blood in a double circuit: heart → lungs → heart → rest of body → heart

    • Blood must pass through the heart twice in one complete circuit

  • Main blood vessels involved in circulation through the heart:

    • Through and from the heart: upper vena cava, lower vena cava, pulmonary vein, pulmonary artery, aorta

    • Through and from the lungs: pulmonary vein, pulmonary artery

    • Through and from the liver: hepatic artery, hepatic portal vein, hepatic vein

    • Through and from the kidneys: renal artery, renal vein

  • The heart as a pump:

    • Four chambers: two atria (right/left) and two ventricles (right/left)

    • Median septum; valves: tricuspid, bicuspid (mitral), aortic (semi-lunar), pulmonary (semi-lunar)

  • How valves work (one-way door analogy):

    • Blood should move from atria to ventricles; when ventricle pressure exceeds atrial pressure, AV valves close to prevent backflow into atria

  • Cardiac cycle:

    • Systole: contraction phase

    • Atrial systole: atria contract

    • Ventricular systole: ventricles contract

    • Diastole: relaxation phase

    • Atrial diastole: atria relax

    • Ventricular diastole: ventricles relax

    • One complete cardiac cycle includes one ventricular systole and one ventricular diastole

  • Pathways through the heart and major vessels:

    • During circulation, lungs, liver, kidneys are connected via specific vessels (e.g., hepatic and renal circulations)

  • Key learning tools:

    • Cardiac cycle graphs (as in Textbook Page 116) and anatomy labeling (12 vessels labeled 1–12 in Review activity)

  • Practical considerations:

    • The “hole in the heart” (atrial or ventricular septal defect) leads to mixing of oxygenated and deoxygenated blood, reducing gas exchange efficiency and potentially causing fatigue and heart failure

6.5 What Is Coronary Heart Disease?

  • CHD overview:

    • Occlusion or narrowing of coronary arteries reduces blood flow to the heart muscle (myocardial ischemia)

  • Common causes and risk factors:

    • Unhealthy diet, sedentary lifestyle, smoking (risk factors for atherosclerosis and CHD)

  • Consequences:

    • Chest pain (angina), heart attack (myocardial infarction), fatigue, shortness of breath; long-term consequences include heart failure if not managed

  • Prevention and management:

    • Lifestyle changes: healthier diet, regular exercise, quitting smoking

    • Medical interventions may include medications, lifestyle counseling, and, in some cases, surgical procedures

  • The heart attack video and discussion prompts:

    • What happens during a heart attack? Why does coronary occlusion cause damage? What are the signaling and treatment implications?