Heart Anatomy and Circulatory System Quiz

Mammalian Heart

• The heart is a complex muscle that pumps blood
• The circulatory system has three divisions
• Systemic circulation: heart to body
• Pulmonary circulation: heart to lungs
• Coronary circulation: within the heart
• The heart has three layers
  • Epicardium (outer layer)
  • Pericardium (surrounds and protects the heart)
  • Myocardium (middle layer, bulk of heart wall)
  • Endocardium (inner wall)

Structure of the Heart - Atria and Ventricles

• The heart muscle is asymmetrical
• Humans have four chambers
  • Two atria: receive blood into the heart
  • Two ventricles: pump blood out of the heart
• One atrium and one ventricle are on each side
• Right atrium receives deoxygenated blood
  • Superior vena cava (jugular vein from brain and arms)
  • Inferior vena cava (veins from lower organs and legs)
• The coronary sinus drains blood from the heart itself

Structure of the Heart - Atria and Ventricles (cont.)

• Deoxygenated blood moves to the right ventricle
• The right ventricle pumps blood through pulmonary arteries to the lungs for reoxygenation.
• Oxygen-rich blood from the lungs enters the left atrium via pulmonary veins.
• The left ventricle pumps oxygen-rich blood out through the aorta (major artery) to organs and muscles.

Structure of the Heart - Valves

• Valves are flaps that open and close to control blood flow direction.
• Atrioventricular valves (tricuspid and mitral/bicuspid).
  • Right atrium and right ventricle
  • Left atrium and left ventricle
• Pulmonic valve: right ventricle to the lungs
• Aortic semilunar valve: left ventricle to the aorta

Divisions of the Circulatory System

• Pulmonary (heart and lungs)
• Systemic (heart to other body parts)
• Coronary (vessels that serve the heart)
• The right side of the heart is less thick than the left, to support blood flow to the legs.

Blood Vessels - Arteries

• Arteries have three layers
  • Innermost: tunica intima (squamous epithelium)
  • Middle: tunica media (smooth muscle, thickest layer)
  • Outermost: tunica externa (connective tissue with elastic and collagenous fibers)
• Arteries carry blood away from the heart
  • Pulmonary arteries carry deoxygenated blood to the lungs
  • Systemic arteries carry oxygenated blood to the body tissues
• Arterioles are smaller branches of arteries which regulate blood flow to capillaries

Blood Vessels - Veins

• Veins have similar three layers as arteries.
• Veins have less smooth muscle and connective tissue, thinner walls, less pressure.
• Veins carry blood toward the heart
  • Pulmonary veins carry oxygenated blood from the lungs to the heart
  • Systemic veins carry deoxygenated blood from body tissues to the heart
• Blood flows from capillaries into venules, then progressively larger veins until reaching the heart.

Blood Vessels - Capillaries

• Capillaries are the smallest and most numerous blood vessels.
• They form connections between arteries and veins, exchanging materials between blood and tissue cells.
• Capillary distribution varies based on tissue's metabolic activity. Active tissues (muscles, liver, kidneys) have extensive capillary networks.

Differences between Veins and Arteries

Cardiac Cycle

• The heart's purpose is to pump blood throughout the body
• The cardiac cycle has a repeating sequence of filling and emptying the heart
• Electrical signals cause heart muscles to contract (systole) to pump blood
• Systole is followed by relaxation (diastole), allowing the heart to fill with blood
• Blood pressure is measured using systolic and diastolic readings (e.g., 120/80).

Electrical Signals in the Heart Muscles

• Heart muscle contraction is stimulated by depolarization (reducing negative charge)
• The heart has specialized "self-excitable" muscle cells (autorhythmic fibers)
• Sinoatrial node (SA node) in the right atrium serves as a pacemaker, generating electrical impulses
• Electrical impulses spread through atria and ventricles, causing them to contract to pump blood.
• Electrocardiogram (ECG) measures electrical activity of the heart

Blood

• Blood is a connective tissue with a fluid matrix
• Blood has cells and other elements
• It transports essential components for cellular metabolism, including oxygen (carried by red blood cells)
• Blood regulates temperature and hormones
• Blood protects against injury, microbes, and toxins via leukocytes, white blood cells

Components of Blood

• Plasma: the fluid matrix (about 55%) with proteins, ions, nutrients, wastes, gases
• Red blood cells/Erythrocytes: transport oxygen via haemoglobin
• White blood cells/Leukocytes: less than 1%, larger than red blood cells, with nuclei, essential for immune defense
• Platelets: cell fragments involved in blood clotting.

Red Blood Cells-Erythrocytes

• A microliter of blood contains millions of red blood cells.
• Hematocrit is the fraction of blood occupied by red blood cells (about 45%).
• Red blood cells lack nuclei and are doughnut shaped with central depression.
• Red blood cells contain hemoglobin which carries oxygen.

White Blood Cells-Leukocytes

• Less than 1% of blood cells are white blood cells (larger than red blood cells and have nuclei).
• White blood cells migrate across capillaries into interstitial fluid
• Granular leukocytes (neutrophils, eosinophils, basophils).
• Agranular leukocytes (lymphocytes, monocytes).
• Granules in the cytoplasm contain lysozyme, defensins, and antioxidants.

Platelets

• Platelets are cell fragments involved in blood clotting
• They are about 3 µm in diameter
• In case of injury, platelets release clotting factors into the blood
• Fibrinogen is converted to insoluble fibrin threads.
• Fibrin aggregates to form a clot.

Formation of Blood Cells

• Blood cell formation begins in bone marrow.
• Stem cells (pluripotent) give rise to the various types of blood cells.
• Erythropoietin, produced by the kidneys, stimulates erythrocyte production in response to low oxygen levels (erythropoiesis).
• Liver produces erythrocyte during embryonic development
• Lymphocyte proliferation is a result of antigen encounters and binding to cell receptors.

Role of Bone Marrow Stem Cells

• Hematopoietic stem cells (HSCs) continuously differentiate into various types of blood cells (e.g. lymphocytes).
• HSCs give rise to lymphocytes (T-cells, B-cells, natural killer cells) for immune defense.
• MSCs contribute to tissue repair at injury sites through differentiation and paracrine signaling.