Cardiovascular System Overview

General Functions

The cardiovascular system is essential for transporting substances throughout the body and maintaining homeostasis.

• Transport: Moves blood, gases, nutrients, hormones, wastes, and heat.

• Protection: Defends against disease and fluid loss (clotting).

Heart

Location and Structure

The heart is located in the mediastinum, the space between the lungs within the thoracic cavity.

• Coverings - Pericardium: Double-walled sac surrounding the heart.

  • Fibrous pericardium: Outermost layer, dense irregular connective tissue, anchors heart to surrounding structures.

  • Serous pericardium: Composed of two layers:

    • Parietal pericardium: Connected to fibrous pericardium.

    • Visceral pericardium (epicardium): Directly covers the heart.

  • Between layers: pericardial cavity with serous fluid (reduces friction).

• Heart Wall: Three layers:

  1. Epicardium: Outer layer, same as visceral pericardium.

  2. Myocardium: Middle layer, cardiac muscle.

  3. Endocardium: Inner layer, simple squamous epithelium, lines heart chambers and valves.

• Chambers: Four chambers (right/left atria, right/left ventricles).

• Major Blood Vessels: Veins and arteries connected to each chamber.

Cardiac Skeleton

The cardiac skeleton is a fibrous connective tissue structure that supports the heart valves and provides electrical insulation.

• Prevents simultaneous contraction of atria and ventricles.

Valves of the Heart

Valves ensure unidirectional blood flow through the heart.

• Atrioventricular (AV) valves:

  • Bicuspid (mitral) valve: Between left atrium and ventricle.

  • Tricuspid valve: Between right atrium and ventricle.

  • Chordae tendineae: Tendinous cords that anchor valves to papillary muscles.

• Semilunar valves:

  • Aortic valve: Separates left ventricle and aorta.

  • Pulmonary valve: Separates right ventricle and pulmonary trunk.

Cardiac Muscle Cells

Cardiac muscle cells are specialized for contraction and electrical conduction.

• Contractile cells: Form the majority of myocardium, responsible for heart contractions.

• Conduction system cells: Modified to produce and conduct electrical impulses; do not contract.

• Cells are connected by intercalated discs (contain anchoring and gap junctions).

Conduction System

The heart's conduction system coordinates the heartbeat.

• Sinoatrial (SA) node: Pacemaker, initiates heartbeat.

• Atrioventricular (AV) node: Delays impulse, allows atria to contract before ventricles.

• AV bundle (Bundle of His): Conducts impulse to ventricles.

• Purkinje fibers: Spread impulse through ventricles.

Anatomy of Blood Vessels

General Structure

Blood vessels are composed of three main layers (except capillaries):

• Tunica externa: Connective tissue.

• Tunica media: Smooth muscle, elastic fibers.

• Tunica intima/interna: Simple squamous epithelium (endothelium), continuous with endocardium.

• Lumen: Central cavity through which blood flows.

Types of Blood Vessels

• Arteries: Carry blood away from the heart; regulate blood flow and pressure.

• Capillaries: Site of exchange of gases, nutrients, and wastes between blood and tissues; only endothelium and basement membrane.

• Venules: Collect blood from capillaries.

• Veins: Carry blood toward the heart; have valves to prevent backflow; larger lumen than arteries.

Blood Vessel Classification Table

Circulatory Routes

Adult Circulation

The adult circulatory system is a closed, double system with pulmonary and systemic routes.

• Pulmonary circulation: Carries deoxygenated blood from right ventricle to lungs, returns oxygenated blood to left atrium.

• Systemic circulation: Delivers oxygenated blood from left ventricle to body, returns deoxygenated blood to right atrium.

• Coronary circulation: Supplies blood to the heart muscle itself.

Fetal Circulation

Fetal circulation includes special shunts to bypass nonfunctional organs (lungs, liver).

• Ductus venosus: Bypasses liver.

• Foramen ovale: Bypasses lungs by connecting right and left atria.

• Ductus arteriosus: Bypasses lungs by connecting pulmonary trunk and aorta.

• Umbilical vein: Carries oxygenated blood from placenta to fetus.

• Umbilical arteries: Return mixed blood to placenta.

Blood (Connective Tissue)

Characteristics

• Higher viscosity than water.

• pH: 7.35 - 7.45.

• Volume: 4-6 L in adult.

Composition Overview

• Plasma: Matrix, ~55-60% of blood volume, contains water, proteins, solutes.

• Formed elements: ~40-45% of blood volume, includes cells and cell fragments.

Plasma Composition Table

Formed Elements

• Red Blood Cells (Erythrocytes):

  • Most abundant cell type; transport oxygen via hemoglobin.

  • Biconcave disc shape; anucleate; lifespan ~120 days.

  • Hemoglobin contains four globin chains, each with a heme group (binds O2).

  • Hematocrit: Percentage of blood volume made up of RBCs (usually ~45%).

• White Blood Cells (Leukocytes):

  • Nucleated; defend against disease.

  • Granulocytes: Visible granules; include neutrophils, eosinophils, basophils.

  • Agranulocytes: No visible granules; include lymphocytes (T and B cells), monocytes.

• Platelets: Cell fragments from megakaryocytes; involved in clotting; lifespan ~10 days.

Hemopoiesis/Hematopoiesis

Formation of Blood Cells

All blood cells arise from hemocytoblast cells (stem cells) in red bone marrow.

• Red marrow in adults is found in axial skeleton, pelvic and pectoral girdles, and proximal ends of humerus and femur.

Related Medical Conditions

• Atrial septal defect: Hole in the interatrial septum, often due to incomplete closure of the foramen ovale.

• Atherosclerosis: Build-up of fat deposits in the tunica intima, leading to narrowing or blockage of arteries.

Key Equations

• Hematocrit calculation:

Additional info: Academic context and expanded explanations have been added to ensure completeness and clarity for college-level Anatomy & Physiology students.