Human Heart Anatomy Quiz

Heart:

• Cardiac muscle comprises the heart.
• Four chambers:
  • Left ventricle: Propels blood to the systemic circulation.
  • Right ventricle: Propels blood to the pulmonary circulation (lungs).
  • Left atrium: Receives blood from pulmonary veins.
  • Right atrium: Receives blood from the body.
• Endocardium inner layer of the heart wall
  • Simple squamous epithelium
  • Loose connective tissue
  • Myoelastic layer: smooth muscle fibers and connective tissue
  • Subendocardial layer: contains Purkinje fibers that contribute to the heart's impulse-conducting system.
• Myocardium:
  • Thickest layer due to the strong force of blood pumping, especially in the left ventricle.
  • Cardiac muscle is arranged in a spiral pattern.
  • Contains a fibrous skeleton of collagen and elastic fibers for structural support and electrical insulation.
  • Numerous blood vessels for nourishment.
• Pericardium: Double-walled sac surrounding the heart, containing pericardial fluid.
  • Parietal pericardium (outer layer): Tough outer fibrous layer, thin serous lining of epithelial tissue, anchors the heart to the aorta and vena cava.
  • Visceral pericardium (inner layer): Epithelial tissue (Simple Squamous Epithelial), Connective tissue (Loose Connective Tissue), directly in contact with the heart surface.

Cardiac Conduction System

• Generates and propagates electrical impulses for heartbeats.
• Key components:
  • Sinoatrial (SA) node: Initiates impulses in the right atrial wall, near the superior vena cava. Also known as the natural pacemaker.
  • Atrioventricular (AV) node: Delays impulses received from the SA node to allow complete atrial contraction before ventricular contraction, located on the floor of the right atrium near the AV valve.
  • AV bundle (Bundle of His): Conducts impulses from the AV node to the ventricles, extending from the AV node into the interventricular septum.
  • Subendocardial conducting network: Rapidly transmits electrical impulses throughout the ventricles via Purkinje fibers, ensuring coordinated contraction for effective blood pumping.

Heart wall structures:

• Purkinje fibers:
  • Larger than cardiac fibers, with more glycogen and lighter staining.
  • Located beneath the endocardium, on either side of the interventricular septum.
  • Branch throughout the myocardium to deliver stimuli via gap junctions to the rest of the heart.

Systemic circuit (Blood vessels):

• Distributes blood throughout the body.
• Components:
  • Arteries: Transport blood away from the heart.
  • Capillaries: Site of exchange between blood and tissues.
  • Veins: Carry blood back to the heart.

Vessel tunics (layers of blood vessel walls):

• Tunica intima: Innermost layer, appears flat.
  • Endothelium: Simple squamous epithelium lining the lumen of the vessel.
  • Subendothelial layer: Loose connective tissue lining beneath endothelial cells.
  • Internal elastic lamina: Well-developed in muscular arteries, composed of elastin, separating the tunica intima from the tunica media.
• Tunica media: Thickest layer, composed of concentric layers of smooth muscle cells arranged helically. Contains elastic fibers, collagen fibers, and proteoglycans.
  • External elastic lamina: More delicate than the internal elastic lamina, only seen in larger muscular arteries.
• Tunica adventitia: Outermost layer, composed of dense irregular connective tissue, blending with surrounding connective tissue. Contains fibroblasts, collagen, and elastic fibers.

Vasa Vasorum:

• "Vessels of the vessels" - small vessels that provide nourishment to thicker vessel walls where diffusion is insufficient, more prevalent in veins than arteries.

Types of Artery:

• Elastic artery:
  • Largest arteries (e.g., aorta, common carotid artery, subclavian artery, common iliac artery, pulmonary trunk).
  • Yellow in fresh state due to elastin.
  • Tunica intima: Contains endothelium, connective tissue with few fibroblasts, smooth muscle, collagen, internal elastic lamina, and Weibel-Palade bodies.
  • Tunica media: Composed of 40-70 fenestrated membranes, smooth muscle cells (less abundant), ECM (chondroitin, sulfate, collagen, reticular, and elastin fiber).
  • Tunica adventitia: Thin layer of fibroelastic connective tissue, vasa vasorum, lymphatic vessels, nerve fibers.
• Muscular artery:
  • Most vessels arising from the aorta (e.g., brachial artery, ulnar artery, femoral artery, renal artery).
  • Tunica intima: Thinner than elastic arteries, prominent internal elastic lamina.
  • Tunica media: Predominant smooth muscle cells arranged in layers (3-4 in smaller arteries, 40 in larger arteries).
  • Tunica adventitia: ECM composed of elastic fibers, collagen fibers, and ground substance.
• Arterioles:
  • Smallest arteries.

Capillaries:

• Smallest blood vessels, 50 µm in length and 8-10 µm in width.
• Structure: Single layer of squamous endothelial cells.
• Three types:
  • Continuous capillaries: Tight gap junctions, found in muscle, nervous, and connective tissues.
  • Fenestrated capillaries: Have pores that allow for diffusion, found in the kidneys, intestines, and endocrine glands.
  • Sinusoidal capillaries: Wider and more irregular, found in the liver, bone marrow, and spleen.