Transport in Humans (Circulatory System)

The Transport (Circulatory) System

• Substances that need to be transported in humans: Oxygen, Glucose, water, carbon dioxide, wastes, nutrients, hormones, etc. (From starter: Oxygen and Glucose specifically listed; other substances implied throughout the notes.)
• Primary transport systems in humans:
  • Heart
  • Blood (composed of platelets, white blood cells, red blood cells, plasma)
  • Blood vessels (veins, arteries, capillaries)
• The circulatory system is described as a system of blood vessels with a pump (the heart) and valves to ensure one-way flow of blood.

Double Circulation: Pulmonary and Systemic

• Substances circulate through two separate circuits:
  • Pulmonary circulation: low-pressure circulation to the lungs; blood passes through the heart twice per complete circuit.
  • Systemic circulation: high-pressure circulation to the body tissues; blood passes through the heart twice per complete circuit.
• Direction of blood flow:
  • From the body → enters heart → pumped to lungs (pulmonary circuit) and/or to the rest of the body (systemic circuit)
• Key vessels involved in the circuits include pulmonary veins/arteries, vena cavae, aorta, and capillaries in the lungs and body tissues.
• The pulmonary circuit is characterized by low pressure because the distance is short. The systemic circuit is high pressure to reach distant tissues.

The Heart: Structure and Function

• The heart is a muscular organ about the size of a clenched fist, located between the lungs.
• It is made up of cardiac muscle tissue and pumps blood to all parts of the body.
• Major external vessels attached to the heart:
  • Vena cava (superior and inferior)
  • Aorta
  • Pulmonary artery
  • Pulmonary veins
• The heart contains 4 chambers: Right atrium, Left atrium, Right ventricle, Left ventricle.
• Cardiac tissue and coronary arteries supply the heart muscle itself.
• Visuals commonly show the heart with external features such as the right/left atria and ventricles, and the major vessels.

Chambers of the Heart and Their Roles

• Right atrium: receives deoxygenated blood from the rest of the body via the vena cavae.
• Right ventricle: pumps deoxygenated blood to the lungs via the pulmonary artery.
• Left atrium: receives oxygenated blood from the lungs via the pulmonary veins.
• Left ventricle: pumps oxygenated blood to the rest of the body via the aorta.
• In diagrams and videos, channels show blood flow from: body → right atrium → right ventricle → lungs → left atrium → left ventricle → body.
• The valves ensure one-way blood flow between chambers and into major arteries.

Major Blood Vessels Attached to the Heart

• Vena cava: carries blood from the body into the heart (to the right atrium).
• Pulmonary artery: carries blood from the right ventricle to the lungs.
• Pulmonary veins: carry blood from the lungs to the left atrium.
• Aorta: carries blood from the left ventricle to the rest of the body.
• Blood flow directions corresponding to these vessels:
  • From the lungs to the heart: Pulmonary veins (oxygenated blood into the heart).
  • From the heart to the rest of the body: Aorta.
  • From the rest of the body to the heart: Vena cava.
  • From the heart to the lungs: Pulmonary artery.

Oxygenated vs Deoxygenated Blood

• Oxygenated blood is typically represented in red in diagrams and travels through parts of the heart that handle oxygen-rich blood.
• Deoxygenated blood is typically represented in blue in diagrams and travels through parts of the heart that handle oxygen-poor blood.
• In the heart, the left side handles oxygenated blood; the right side handles deoxygenated blood.

Wall Thickness of the Heart Chambers

• The left ventricle has a thicker wall than the right ventricle.
• Why? The left ventricle pumps blood to the rest of the body (high pressure, long distance).
• The right ventricle pumps blood to the lungs (short distance, lower pressure).
• This difference explains the left ventricle’s higher muscle mass and thicker wall.

Labeling the Heart: Vessels, Valves, and Chambers

• Important vessels and valves include: Vena cava, Pulmonary artery, Pulmonary vein, Aorta, Right atrium, Left atrium, Right ventricle, Left ventricle, Tricuspid valve, Bicuspid (Mitral) valve, Aortic valve, Pulmonary valve, Papillary muscles, Chordae tendineae (tendons).
• Valves are held in place by cord-like tendons connected to the walls of the ventricles.
• Valves ensure one-way flow and prevent backflow; they are opened and closed during the cardiac cycle.

The Cardiac Cycle and Heart Sounds

• The cardiac cycle is the rhythmic contraction and relaxation of the heart that produces one heartbeat (often described as the sounds “lub-dub”).
• Systole: cardiac muscle contraction.
• Diastole: cardiac muscle relaxation.
• A single heartbeat lasts about 0.8 ext{ s}, with a short pause between two heartbeats.
• The atria and ventricles work in sequence: atrial systole followed by ventricular systole, then both chambers relax (diastole).
• The cycle involves three main stages:
  1) Contraction of the atria (atrial systole)
  2) Contraction of the ventricles (ventricular systole)
  3) Relaxation of both atria and ventricles (diastole)
• Phases of valve operation during the cycle: AV valves open during atrial systole to allow ventricular filling; AV valves close at the start of ventricular systole; semilunar valves open when the ventricles contract and eject blood; semilunar valves close to prevent backflow during diastole.
• The “lub-dub” sounds correspond to valve closures:
  • Lubb: closure of the atrioventricular (AV) valves at the start of systole.
  • Dubb: closure of the semilunar valves at the end of systole.

Pressure Changes During the Heartbeat

• The heartbeat involves distinct changes in pressure across the heart chambers and major vessels.
• Phases include: atrial systole, ventricular systole, and diastole (relaxation).
• A typical visualization shows pressures in different chambers and the aorta during the phases, with references to peak pressures and valve openings/closures.
• Key relationships:
  • During ventricular systole, ventricular pressure rises and exceeds aorta pressure, causing the aortic valve to open.
  • AV valves close as the pressure in the ventricles rises, preventing backflow to the atria.
  • During diastole, the ventricles relax, pressure falls, and the aortic valve closes, preventing backflow into the ventricles.
• A common summary of the sequence: Atria contract (Systole) → Ventricles contract (Systole) → All chambers relax (Diastole).

Monitoring the Heart

• Electrocardiograms (ECG): monitors electrical activity related to heartbeat and can indicate rhythm and conduction.
• Pulse rate: determined by feelable heartbeats; linked to heart rate and blood pressure.
• Blood pressure: measured as the force of blood against vessel walls, resulting from heart contraction and relaxation; commonly measured with a sphygmomanometer.
• Heart sounds can be heard with a stethoscope, reflecting valve closures:
  • First sound (lub): closure of AV valves between atria and ventricles.
  • Second sound (dub): closure of the semilunar valves at the exits of the heart.

Coronary Heart Disease (CHD)

• CHD occurs when the coronary arteries supplying the heart muscle become blocked by fat deposits or blood clots, reducing oxygen and nutrient supply to heart tissue.
• Consequences: heart muscle cannot function properly, potentially causing a heart attack (myocardial infarction).
• Possible causes (risk factors):
  • Smoking: chemicals damage arterial walls and promote clot formation.
  • High-fat diet: increases blood cholesterol, elevating CHD risk.
  • Being overweight: excess fat deposits contribute to plaque formation.
  • Lack of exercise: slower blood flow can promote fat deposition in vessels.
  • Stress: hormone adrenaline raises blood pressure, increasing CHD risk.
• Preventive measures include lifestyle changes to reduce these risk factors (e.g., quitting smoking, improving diet, increasing physical activity, stress management).
• By-pass surgery discussion: options include artificial blood vessels or using a vein from elsewhere in the body to replace a blocked coronary artery; consider advantages and disadvantages of each approach.

Blood Vessels: Structure, Types, and Function

• Three main types of blood vessels: arteries, veins, and capillaries.
• Function overview:
  • Arteries: carry blood away from the heart; typically thick-walled with small lumens and high pressure.
  • Veins: carry blood toward the heart; typically have larger lumens, thinner walls, and valves to prevent backflow; operate under lower pressure.
  • Capillaries: connect arteries and veins; very thin walls (often one cell layer) to facilitate exchange.
• Tissue fluid exchange and lymphatic system:
  • Capillaries exchange oxygen, nutrients, carbon dioxide, and wastes with body tissues.
  • Plasma filtered into tissue fluid; tissue fluid bathes cells and then drains back into capillaries or via the lymphatic system.
• Important example vessels:
  • Hepatic artery and hepatic vein (liver circulation)
  • Renal artery and renal vein (kidney circulation)
• General pathway examples: arteries branch into arterioles, which lead to capillary networks, which drain into venules and then veins.
• Blood vessel structure: all three types have three layers (tunics): smooth lining (endothelium), elastic/muscle tissue, and connective tissue. Capillaries consist of a single endothelial cell layer.

Blood Components and Their Roles

• Blood is the fluid that transports substances throughout the body and consists of:
  • Red blood cells (RBCs, erythrocytes): transport oxygen; disc-shaped, biconcave, nucleus-free; contain hemoglobin.
  • White blood cells (WBCs): immune cells; larger than RBCs, fewer in number; types include phagocytes (engulf bacteria) and lymphocytes (antibody production).
  • Platelets: cell fragments without a nucleus; essential for blood clotting by converting fibrinogen to fibrin to prevent bleeding and aid healing.
  • Plasma: the liquid component; mostly water; transports nutrients, hormones, proteins, antibodies, wastes like carbon dioxide and urea, and other solutes.
• Practical activity (modeling blood): using foods and dyes to represent RBCs, WBCs, platelets, and plasma to visualize quantities and sizes.

Exchange in Capillaries and Tissue Fluid

• In capillaries, oxygen and nutrients move out of blood into body tissues; carbon dioxide and wastes move from tissues into the blood.
• The exchange is driven by hydrostatic and osmotic pressures, leading to net movement of fluids and solutes across capillary walls.
• Some plasma becomes tissue fluid that surrounds cells; excess tissue fluid is drained into the lymphatic system.

Structure and Function of Blood Vessels (Recap)

• Arteries
  • Thick walls, narrow lumen, no valves, carry high-pressure blood away from the heart.
• Veins
  • Thinner walls, larger lumen, valves present to prevent backflow, carry blood back toward the heart.
• Capillaries
  • Very small lumen, one-cell-thick walls, enable exchange between blood and tissues.
• Overall differences summary (Artery vs Vein vs Capillary):
  • Artery: thick walls, small lumen, no valves, oxygenated blood (except pulmonary artery).
  • Vein: thin walls, large lumen, valves, deoxygenated blood (except pulmonary veins).
  • Capillary: one-cell-thick, very small lumen, no valves.

Quick Reference: Vessels Within the Heart and Major Circulation

• Main arteries and veins of the heart:
  • Arteries: pulmonary artery, aorta
  • Veins: pulmonary vein, vena cava (systemic return to heart)
• Flow direction examples:
  • From the lungs to the heart: pulmonary veins
  • From the heart to the body: aorta
  • From the body to the heart: vena cavae
  • From the heart to the lungs: pulmonary artery

Practice and Application Notes

• Cardiovascular monitoring:
  • ECG traces electrical activity of the heartbeat.
  • Pulse rate measures heart rate; blood pressure measures force of blood against artery walls.
  • Heart sounds (stethoscope): S1 and S2 correspond to AV valve closure (lub) and semilunar valve closure (dub).
• Coronary artery health:
  • CHD risk factors and prevention are critical for maintaining heart health.
• By-pass scenarios:
  • Vein grafts vs artificial vessels present different advantages and limitations in coronary bypass surgery.

Key Formulas and Numerical References

• Cardiac cycle duration: one heartbeat lasts approximately 0.8 ext{ s}.
• Pressure-related concepts (from capillary and heart diagrams): pressures are often expressed in ext{mmHg}; common references include systolic and diastolic values in the arteries during the cardiac cycle, and the pressure changes across the ventricles and valves during systole and diastole.
• Time markers on cardiac diagrams may include intervals such as 0 ms, 100 ms, 200 ms, 300 ms, 400 ms, 500 ms, 600 ms, representing the progress of the heartbeat cycle.
• Layered structure of blood vessels uses units and scales appropriate to histology and physiology (no explicit formulae beyond descriptive thickness and lumen distinctions).

Connections to Foundational Principles and Real-World Relevance

• The circulatory system embodies a pump-and-pipes model with valves to maintain one-way flow, illustrating principles of pressure gradients, resistance, and flow.
• The concept of double circulation explains why the heart must manage two separate high- and low-pressure circuits, reflecting specialized pathways for gas exchange and tissue perfusion.
• Understanding CHD risk factors highlights the intersection of physiology with public health, lifestyle, and preventive medicine.
• Knowledge of blood vessel structure explains how anatomy supports function: thick-walled arteries sustain high-pressure flow; veins adapt to low pressure with valves; capillaries enable effective exchange due to thin walls.

Quick Practice Questions (Derived from Transcript Prompts)

• Name the four chambers of the heart.
• Identify the valves that are open or closed during atrial systole and ventricular systole.
• Describe the sequence of events in one cardiac cycle and the corresponding heart sounds.
• Explain why the left ventricle has a thicker wall than the right ventricle.
• List the three types of blood vessels and summarize their primary functions.
• What changes occur in capillary blood flow and tissue fluid during exchange?
• Describe how ECG, pulse, and listening to heart sounds help monitor heart activity.
• Outline risk factors for coronary heart disease and two strategies to reduce risk.
• Compare and contrast arteries, veins, and capillaries in terms of structure (thickness, lumen, valves) and the type of blood they carry.
• Explain how a blocked coronary artery might be bypassed using either an artificial vessel or a vein graft, and discuss advantages and disadvantages of using a vein.