Cardiovascular System: Structure, Function, and Blood Composition

Cardiovascular System Overview

Introduction

The cardiovascular system is essential for transporting blood, nutrients, hormones, wastes, and heat throughout the body. It also plays a critical role in disease protection and fluid loss prevention through clotting.

• Main components: heart, blood vessels, blood

• Functions: transport, protection, homeostasis

Heart

Location and Structure

The heart is located in the mediastinum, the space between the lungs within the thoracic cavity. It is surrounded by a double-walled sac called the pericardium.

Coverings: Pericardium

• Fibrous pericardium: Dense irregular connective tissue, protects and anchors the heart.

• Serous pericardium:

  • Parietal pericardium: Lines the fibrous pericardium.

  • Visceral pericardium (epicardium): Covers the heart surface.

  • Between layers is pericardial cavity with fluid for lubrication.

Heart Wall

• Epicardium: Outer layer, simple squamous epithelium and connective tissue.

• Myocardium: Middle layer, cardiac muscle arranged in spiral/circular patterns.

• Endocardium: Inner layer, simple squamous epithelium and connective tissue.

Chambers and Associated Blood Vessels

• Right Atrium: Receives deoxygenated blood from the body via three major veins.

• Left Atrium: Receives oxygenated blood from the lungs via pulmonary veins.

• Right Ventricle: Pumps deoxygenated blood to the lungs via pulmonary arteries.

• Left Ventricle: Pumps oxygenated blood to the body via the aorta.

Septa

• Interatrial septum: Separates atria.

• Interventricular septum: Separates ventricles.

Cardiac (Fibrous) Skeleton

• Fibrous connective tissue separates atria and ventricles.

• Provides attachment for cardiac muscles and valves.

• Prevents simultaneous contraction of atria and ventricles.

Valves

• Atrioventricular (AV) valves:

  • Bicuspid (mitral) valve: Between left atrium and ventricle (2 cusps).

  • Tricuspid valve: Between right atrium and ventricle (3 cusps).

• Semilunar valves:

  • Aortic valve: Separates left ventricle and aorta.

  • Pulmonary valve: Separates right ventricle and pulmonary trunk.

Cardiac Muscle Cells

• Contractile cells: Majority of myocardium, single nucleus, intercalated discs, gap junctions.

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

Conduction System Parts

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

• Atrioventricular (AV) node: Delays impulse, base of right atrium.

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

• AV Bundle Branches: Carry impulse to apex of heart.

• Purkinje fibers: Terminal fibers in ventricles, spread impulse for contraction.

Anatomy of Blood Vessels

General Structure

• Tunica externa: Connective tissue

• Tunica media: Smooth muscle, elastic fibers

• Tunica intima/interna: Simple squamous epithelium (endothelium)

• Lumen: Contains blood

Blood Vessel Types

• Arteries: Carry blood away from heart

• Arterioles: Regulate blood flow and pressure

• Capillaries: Exchange of gases and nutrients, single cell layer

• Venules: Collect blood from capillaries

• Veins: Carry blood to heart, have valves to prevent backflow

Circulatory Routes

Overview

• Closed, double circulation: Blood confined to heart and vessels, two routes: pulmonary and systemic

Pulmonary Circulation

• Right ventricle to lungs via pulmonary arteries (deoxygenated blood)

• Oxygenated blood returns to left atrium via pulmonary veins

Systemic Circulation

• Left ventricle to body via aorta (oxygenated blood)

• Deoxygenated blood returns to right atrium via vena cavae

• Includes subdivisions for individual organs (e.g., cerebral, coronary, bronchial)

Coronary Circulation

• Supplies blood to heart muscle via coronary arteries and veins

Fetal Circulation

• Umbilical vein carries oxygenated blood from placenta

• Three shunts bypass nonfunctional organs:

  • Ductus venosus: Bypasses liver

  • Foramen ovale: Bypasses lungs (right atrium to left atrium)

  • Ductus arteriosus: Bypasses lungs (pulmonary trunk to aorta)

• Umbilical arteries return mixed blood to placenta

Blood Composition

Overview

• Plasma: ~55-60% of blood volume, mostly water with solutes

• Formed elements: ~40-45% of blood volume, cellular portion

Plasma Details

• Water: 90%

• Proteins: 8%

  • Albumin: Maintains water balance, transports substances

  • Fibrinogen: Clot formation

  • Globulin: Immunity, transport

• Other solutes: Nutrients, wastes, electrolytes, gases

Formed Elements

• Red Blood Cells (Erythrocytes): Most abundant, transport oxygen, contain hemoglobin

• White Blood Cells (Leukocytes): Defend against disease

  • Granulocytes: Neutrophils, eosinophils, basophils

  • Agranulocytes: Lymphocytes (T and B cells), monocytes

• Platelets: Fragments of megakaryocytes, involved in clotting

Hemopoiesis/Hematopoiesis

Formation of Blood Cells

• Occurs in red bone marrow from hematocytoblast stem cells

• Adult red marrow found in axial skeleton and pelvic/pectoral girdles

Common Cardiovascular Disorders

Overview

• Congenital heart defects: Most commonly due to incomplete closure of foramen ovale

• Atherosclerosis: Fat deposits in tunica intima cause narrowing/blockage of arteries

Key Tables

Blood Vessel Types and Functions

Type	Main Function	Structural Features
Arteries	Carry blood away from heart	Thick tunica media, elastic fibers
Arterioles	Regulate blood flow/pressure	Smaller diameter, smooth muscle
Capillaries	Exchange gases/nutrients	Single cell layer (endothelium)
Venules	Collect blood from capillaries	Thin walls, some smooth muscle
Veins	Carry blood to heart	Valves, thinner tunica media

Major Plasma Proteins and Functions

Protein	Function
Albumin	Maintains osmotic pressure, transports substances
Fibrinogen	Blood clotting
Globulin	Immunity, transport

Key Equations

• Blood pH: $7.35 - 7.45$

• Hemoglobin Oxygen Transport: $Hb + O_2 \rightarrow HbO_2$

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