Chapter 8 - Transport in Humans Summary

Importance of Transport Systems

  • Multicellular organisms require transport systems due to the limitations of diffusion over long distances.

  • Transport systems deliver nutrients and oxygen to cells and remove waste products.

Substances Transported

  • Digested food: From the ileum of the small intestine to body cells for respiration and storage.

  • Nitrogenous waste (urea): From liver cells to kidneys for excretion.

  • Oxygen: From lungs to body cells for respiration.

  • Carbon dioxide: From body cells to lungs for excretion.

  • Hormones: From endocrine glands to target organs.

The Circulatory System

The human circulatory system consists of:

  • Blood: Carries materials.

  • Blood vessels: Interconnecting tubes for blood flow.

  • Heart: Muscular pump.

The Structure of the Heart

  • Located behind the sternum, between the lungs, composed of cardiac muscle, and covered by the pericardium.

  • Coronary arteries supply glucose and oxygen to the cardiac muscles.

  • The heart is divided into right and left sides by the septum.

  • ‘ Each side has an atrium (upper chamber) and a ventricle (lower chamber).

  • Vena cava: Connected to the right atrium, brings blood back from the body; superior vena cava brings blood back from the upper tissues, while inferior brings blood back from the lower tissues.

  • Pulmonary artery: Connected to the right ventricle, carries blood to the lungs.

  • Pulmonary vein: Connected to the left atrium, brings blood back from the lungs.

  • Aorta: Connected to the left ventricle, carries blood to the body (except lungs).

Valves of the Heart

  • Atrioventricular valves (bicuspid and tricuspid) prevent backflow of blood into the atria.

  • Semi-lunar valves in the pulmonary artery and aorta prevent backflow into the ventricles.

Blood Flow in the Heart

  • Deoxygenated blood enters the right atrium, flows to the right ventricle, and is pumped to the lungs via the pulmonary artery.

  • Oxygenated blood returns to the left atrium from the lungs via the pulmonary vein, flows to the left ventricle, and is pumped to the body via the aorta.

The Cardiac Cycle

  • Diastole: Atria and ventricles are relaxed, blood flows into atria.

  • Atrial systole: Atria contract, forcing blood into ventricles.

  • Ventricular systole: Ventricles contract, closing atrioventricular valves and opening semi-lunar valves to pump blood into the aorta and pulmonary arteries.

Heart Sounds

  • "Lub" sound: Atrioventricular valves close.

  • "Dub" sound: Semi-lunar valves close.

Double Circulation

  • Pulmonary circulation: Deoxygenated blood to the lungs.

  • Systemic circulation: Oxygenated blood to the body.

Blood Vessels

  • Arteries: Carry blood away from the heart (usually oxygenated, except for the pulmonary artery).

  • Veins: Carry blood to the heart (usually deoxygenated, except for the pulmonary vein).

  • Capillaries: Link arteries and veins; facilitate the exchange of materials.

Artery Structure

  • Thick walls with elastic fibers to withstand high pressure.

  • No valves (except in the aorta and pulmonary artery).

Vein Structure

  • Thinner walls with less muscle and elastic fibers.

  • Semi-lunar valves to prevent backflow.

Capillary Structure

  • One-cell-thick walls for rapid diffusion.

  • Narrow diameter to bring blood close to cells.

Blood Composition

  • Plasma (55%): Transports heat and dissolved substances.

  • Blood cells (45%): Red blood cells, white blood cells, and platelets.

Red Blood Cells (Erythrocytes)

  • Contain hemoglobin to transport oxygen.

  • Biconcave disc shape to increase surface area.

  • Lack a nucleus.

White Blood Cells (Leucocytes)

  • Protect against infection.

  • Phagocytes: Engulf foreign particles.

  • Lymphocytes: Produce antibodies.

Platelets

  • Cell fragments involved in blood clotting.

  • Release clotting factors.

Blood Clotting

  • Platelets adhere to damaged vessels, releasing chemicals.

  • Thromboplastin converts prothrombin to thrombin (requires calcium ions).

  • Thrombin converts fibrinogen to fibrin, forming a mesh that traps blood cells.

Blood Groups

  • A, B, AB, O based on antigens and antibodies.

  • Mixing incompatible blood can cause agglutination (clumping).

  • Type O is the universal donor; type AB is the universal recipient.

Hypertension

  • High blood pressure (e.g., 160/95 mmHg).

  • Risk factors: smoking, stress, lack of exercise, obesity, alcohol, high salt/cholesterol diet, genetics.

Diastole is the stage in the cardiac cycle when the atria and ventricles are relaxed, allowing blood to flow into the atria.

Atrial systole is the phase of the cardiac cycle in which the atria contract, forcing blood into the ventricles.

Ventricular systole is the phase of the cardiac cycle in which the ventricles contract, closing atrioventricular valves and opening semi-lunar valves to pump blood into the aorta and pulmonary arteries.

Pulmonary circulation involves the flow of deoxygenated blood to the lungs, where it gets oxygenated before returning to the heart.