L1A Heart and blood vessels anatomy

Anatomy and Function of the Cardiovascular System

I. Overview of the Heart

A. Anatomy and Function

  • The cardiovascular system

    • Comprises heart and blood vessels

    • Crucial for blood circulation

    • Network facilitates nutrient delivery and waste removal

      • Pulmonary: blood transport to the lungs.

      • Systemic: blood transport to the rest of the body

Positioning

  • Located in the mediastinum

    • a cavity between the lungs

  • Resting on diaphragm between the 2nd rib and 5th intercostal space

    • slightly rotated to the left

Orientation of the Heart

  • Base: Broad superior portion, attaching to major vessels (aorta, vena cavae).

  • Apex: Inferior portion, points anteriorly and leftward; located near the 5th intercostal space.

  • Left side (high pressure side)

    • Pumps blood into the systemic arteries efficiently at a specific pressure that transports blood to tissues.

    • known as pressure pump.

  • Right side (low pressure side)

    • Pumps blood into the pulmonary arteries at a low pressure to efficiently transport blood to the lungs.

  • Borders of the Heart

    • Right Border:

      • formed by right atrium

    • Left Border:

      • formed by left ventricle

    • Inferior Border:

      • mostly right ventricle, extends to diaphragm

    • Superior Border:

      • formed by both atria; greater vessels arise here

    • Anterior Surface:

      • primarily composed of the right ventricle.

    • Posterior Surface:

      • mainly formed by the left atrium.

Structure of the Heart Wall and muscle tissue

  • Pericardium

    • double layer sac that the heart is contained in.

    • outer layer is fibrous pericardium.

    • inner layer is serous pericardium.

      • consist of two layers: parietal and visceral.

  • Three layers:

    • Epicardium (Epi = outer layer): A protective layer of connective tissue, and fat.

      • contains blood vessels and nerves

      • also called visceral percardium

    • Myocardium (Myo= muscle, middle layer): The thickest layer composed of cardiac muscle.

      • responsible for the heart's contractions (pumping action)

    • Endocardium (inner layer) : Lines the heart's chambers and covers the heart valves.

      • helps in smooth blood flow

  • Heart muscle:

    • consist of cardiomyocytes; heart muscle cells

      • contain one nucleus and multiple mitochondria.

      • contains intercalated Discs

        • Structures in heart muscle cells that allow ions to pass between cells.

        • Help heart muscle cells contract at the same time (synchronized contraction).

    • striated (straight)

    • works as a single functional syncytium

      • cardiomyocytes work together as a unit.

Chambers of the Heart

  • Septum

    • muscular wall that separates the left and right sides of the heart, preventing the mixing of oxygenated and deoxygenated blood

      • crucial for efficient circulation.

    • interventicular septum

      • separates the left and right ventricles

    • interatrial septum

      • separates the left and right atria.

  • Four chambers:

    • Right Atrium

      • Upper right chamber

      • receives poorly oxygenated blood from the body through the superior and inferior vena cavae and pumps it into the right ventricle.

    • Right Ventricle

      • Lower right chamber

      • pumps poorly oxygenated blood to the lungs through the pulmonary arteries, facilitating the exchange of carbon dioxide for oxygen in the pulmonary capillaries.

      • forms the inferior border.

      • dominates a large part of the anterior surface

    • Left Atrium

      • Upper left chamber

      • receives oxygenated blood from the lungs via the pulmonary veins then pumps it into the left ventricle through the atrioventicular valve.

      • dominates the superior surface; the base

    • Left Ventricle

      • Lower left chamber

      • pumps oxygenated blood to the body through the aorta

      • responsible for maintaining systemic circulation, ensuring that all organs and tissues receive the necessary oxygen and nutrients.

      • largest and strongest champer

      • forms the apex

Major Veins of the Heart

  • carry poorly oxygenated blood back to the heart, ensuring proper circulation and maintaining the body's overall function.

    • Superior Vena Cava: Venous trunk for the head, neck, upper limb, and thorax to the heart.

    • Inferior Vena Cava: Venous trunk for the lower limb, pelvis, and abdominal viscera.

    • Coronary Sinus: Short trunk receiving most cardiac veins.

    • Anterior Cardiac Veins: Drain blood from the anterior wall of the right ventricle.

    • Venae Cordis Minimi: Numerous small, valve-less venous channels that open directly into the chambers of the heart.

Heart Valves and Heart Sounds

  • Control the one-way flow of blood and prevent backflow.

  • Types of Valves:

    • Atrioventricular (AV) Valves: Located between the atria and ventricles

      • ensure proper blood flow during the cardiac cycle.

    • Semilunar Valves: Located at the base of the pulmonary artery and aorta

  • Atrioventricular Valves:

    • Tricuspid Valve: Controls blood flow from right atrium to right ventricle (3 cusps).

    • Mitral Valve: Controls blood flow from left atrium to left ventricle (2 cusps).

    • Attached to ventricles with chord-like tendons called Chordae Tendineae.

    • Chordae Tendineae: Connect to Papillary Muscles to prevent valve inversion during contraction (systole).

    • Heart Sound S1 (Lub): Caused by the closure of the AV valves when ventricles contract.

  • Semilunar Valves:

    • Aortic Valve: Between left ventricle and aorta.

    • Pulmonary Valve: Between right ventricle and pulmonary artery (both have 3 cusps).

    • Open when ventricular pressure exceeds arterial pressure (systole).

    • Close to prevent backflow from arteries to ventricles.

    • Heart Sound S2 (Dub): Caused by the closure of the semilunar valves

Function of the Cardiovascular System

  1. Transport Blood

    • Facilitates blood movement throughout the body, delivering oxygen and nutrients to tissues and organs

  2. Pulmonary Circulation

    • Carries deoxygenated blood to the lungs for oxygenation and returns oxygen-rich blood to the heart

  3. Systemic Circulation

    • Delivers oxygenated blood to the body, ensuring cells receive essential oxygen and nutrients

Blood Vessels

  • Structure of blood vessels

    • Majority consist of three layers surrounding the vessel lumen.

      • Tunica Interna (Intima):

        • Inner layer.

        • Mainly made of endothelial cells.

      • Tunica Media:

        • Middle layer.

        • Mainly made of smooth muscle cells.

      • Tunica Externa:

        • Outer layer.

        • Mainly made of collagen fibers and fibroblasts.

Arteries

  • Function: Carry oxygenated blood from the heart to body tissues and poorly oxygenated blood from the heart to the lungs.

  • Types:

    • Elastic Arteries

      • Large arteries capable of stretching.

      • Contain more elastic fibers than any other vessel type.

      • Size

        • Large with thick walls and close to the heart (average lumen diameter = 1.5 cm, wall thickness = 1.10 mm).

        • Large diameter lumen allows low resistance to blood pumped from the heart.

        • Fibers allow vessels to expand when blood is ejected and recoil to push blood forward (also known as conducting arteries).

      • examples:

        • aorta

        • carotid

        • subclavian

        • vertebral

    • Muscular Arteries

      • Smooth Muscle

        • Larger amount in the media layer allows for significant vasoconstriction and vasodilation, crucial for blood pressure control.

      • Size

        • Medium-sized with an average lumen diameter of 6 mm and wall thickness of 1 mm.

      • Role

        • Also known as distributing arteries as they direct blood to different body parts (e.g., splenic, brachial, radial arteries).

      • examples:

        • Femoral artery

        • Renal artery

        • Coronary arteries

    • Arterioles

      • Connection

        • Link arteries to capillaries.

      • Blood Flow Regulation

        • Their constriction and dilation impact blood pressure and flow.

      • Wall Structure:

        • Closest to arteries: 3-layered wall, more smooth muscle than elastic fibers.

        • Closest to capillaries: Smallest diameter, one layer of endothelial lining with few muscle fibers.

      • Size

        • Lumen diameter = 37 µm, wall thickness = 6 µm.

      • examples:

        • Afferent arterioles

        • Subcutaneous arterioles

        • Pulmonary arterioles

Veins

  • Function: Carry oxygenated blood from the lungs to the heart and poorly oxygenated blood from body tissues to the heart.

  • Types:

    • Veins: Major blood vessels that return blood to the heart.

    • Venules: Small vessels connecting capillaries to veins.

    • Venous Sinus: Thin-walled veins without smooth muscles or elastic fibers.

  • Structure of Veins

    • Composed of three layers:

      • Intima: Thinner than in arteries.

      • Media: Thinner with fewer smooth muscle cells, less ability to constrict/dilate.

      • Adventitia: Thickest layer, made of collagen and elastic fibers.

    • Key Characteristics

      • Average diameter: 5 mm, wall thickness: 0.5 mm.

      • Majority have valves to prevent backflow.

  • Structure of Venules

    • Small blood vessels connecting capillary beds to veins.

    • Average lumen diameter: 20 µm, wall thickness: 1 µm.

    • Wall consists of a single layer of epithelium and a few smooth muscle fibers.

  • Structure of Venous Sinus

    • Very thin walls, consist only of endothelium.

    • Form channels in a branching sinus network, mainly in the brain.

    • Collect oxygen-depleted blood from cerebral veins to direct it to the internal jugular vein.

    • Examples:

      • Dural venous sinuses (e.g., superior sagittal, inferior sagittal, transverse sinuses).

Capillaries

  • Microscopic vessels involved in nutrient and waste exchange between blood and tissues

  • Common in tissues with high oxygen demand because of metabolic activity.

  • Types:

    • Continuous

      • uninterrupted endothelial lining, allowing for selective exchange

    • Fenestrated

      • contain pores, allowing for increased permeability (found in kidneys, intestines)

    • Sinusoid

      • larger openings, facilitating movement of larger molecules and cells (found in liver, spleen)