Cardiovascular and Blood System: Anatomy & Physiology Study Guide

Cardiovascular System

Anatomy of the Heart

The heart is a muscular organ responsible for pumping blood throughout the body. Its structure and vascular supply are essential for its function.

• Major Structures: Includes the pericardium (protective sac), chambers (right/left atria and ventricles), and major blood vessels (aorta, vena cava, pulmonary arteries and veins).

• Vascular Supply: The coronary arteries supply oxygenated blood to the heart muscle itself.

• Blood Flow Pathway: Blood enters the right atrium, passes to the right ventricle, is pumped to the lungs, returns to the left atrium, and is then pumped by the left ventricle to the systemic circulation.

• Pericardium: A double-walled sac that surrounds and protects the heart, consisting of fibrous and serous layers.

Electrical Activity and Action Potentials in Cardiac Muscle

Cardiac muscle contraction is initiated and regulated by electrical impulses known as action potentials.

• Action Potential: A rapid change in membrane potential that triggers muscle contraction. In cardiac muscle, this involves the influx of calcium ions ($Ca^{2+}$) which is crucial for contraction.

• Conduction System: Includes the SA node (pacemaker), AV node, bundle of His, bundle branches, and Purkinje fibers.

• Electrocardiogram (ECG): Records the electrical events of the heart, including P wave (atrial depolarization), QRS complex (ventricular depolarization), and T wave (ventricular repolarization).

• Importance of Calcium: Calcium ions are essential for the plateau phase of the cardiac action potential and for muscle contraction.

Cardiac Cycle Events

The cardiac cycle describes the sequence of events in one heartbeat, including contraction (systole) and relaxation (diastole) of the heart chambers.

• Systole: Period of ventricular contraction and blood ejection.

• Diastole: Period of ventricular relaxation and filling.

• Heart Sounds: Produced by the closing of heart valves ("lub-dub").

• Phases: Atrial systole, ventricular systole, and complete cardiac diastole.

Cardiac Output and Regulation

Cardiac output is the volume of blood the heart pumps per minute. It is influenced by several physiological factors.

• Formula: $\text{Cardiac Output (CO)} = \text{Heart Rate (HR)} \times \text{Stroke Volume (SV)}$

• Heart Rate: Number of beats per minute.

• Stroke Volume: Amount of blood ejected per beat.

• Regulation: Adjusted by autonomic nervous system, hormones, and physical activity.

• Physical Activity: Increases both heart rate and stroke volume, thus increasing cardiac output.

Types of Blood Vessels

Blood vessels are classified based on their structure and function.

• Arteries: Thick-walled vessels that carry blood away from the heart under high pressure.

• Veins: Thinner-walled vessels that return blood to the heart; often contain valves.

• Capillaries: Microscopic vessels where exchange of gases, nutrients, and wastes occurs.

Blood Flow, Pressure, and Resistance

Blood flow through vessels is determined by pressure gradients and resistance.

• Blood Pressure: The force exerted by blood on vessel walls.

• Vascular Resistance: Influenced by vessel diameter, blood viscosity, and vessel length.

• Perfusion: The process of delivering blood to capillary beds in tissues.

Local and Systemic Control of Blood Flow

Blood flow is regulated by local and systemic mechanisms to ensure adequate tissue perfusion.

• Local Control: Autoregulation by tissues in response to metabolic needs.

• Systemic Control: Involves the cardiac, vasomotor, and respiratory centers in the brainstem.

• Homeostatic Response: Adjustments during exercise or hemorrhage to maintain blood pressure and flow.

Special Circulations

Certain organs have specialized circulatory requirements.

• Brain: Requires constant blood flow; protected by the blood-brain barrier.

• Heart: Receives blood via coronary circulation.

• Lungs: Pulmonary circulation is responsible for gas exchange.

Blood: Composition and Function

Components and Functions of Blood

Blood is a connective tissue with multiple components, each serving specific functions.

• Major Components: Plasma (liquid matrix), red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

• Collection Sites: Commonly collected from veins (venipuncture), capillaries (fingerstick), or arteries (arterial puncture).

• Physical Characteristics: Blood is viscous, slightly alkaline (pH ~7.4), and constitutes about 8% of body weight.

Plasma: Composition and Functions

Plasma is the liquid portion of blood, making up about 55% of its volume.

• Composition: 90% water, 7% proteins (albumin, globulins, fibrinogen), 2% other solutes (electrolytes, nutrients, gases, hormones, waste products).

• Functions: Transports nutrients, hormones, and waste; maintains osmotic balance; aids in clotting and immune responses.

Red Blood Cells and Hemoglobin

Red blood cells (RBCs) are specialized for oxygen transport.

• Hemoglobin: Protein that binds oxygen and carbon dioxide; gives blood its red color.

• RBC Lifecycle: Produced in bone marrow (erythropoiesis), circulate for ~120 days, then recycled in the spleen and liver.

• Gas Transport: RBCs carry oxygen from lungs to tissues and return carbon dioxide for exhalation.

Blood Typing and Compatibility

Blood types are determined by the presence of specific antigens on RBC surfaces.

• ABO System: Four main types: A, B, AB, O, based on presence/absence of A and B antigens.

• Rh Factor: Presence (+) or absence (−) of Rh antigen (D antigen).

• Compatibility: Important for safe blood transfusions; mismatches can cause serious reactions.

White Blood Cells: Types and Functions

White blood cells (WBCs) are key players in the immune system.

• Types: Neutrophils, lymphocytes, monocytes, eosinophils, basophils.

• Functions: Defend against pathogens, remove debris, and mediate immune responses.

• Production: Regulated by cytokines and growth factors in response to infection or inflammation.

Platelets: Structure, Function, and Production

Platelets are cell fragments essential for blood clotting.

• Structure: Small, disc-shaped fragments derived from megakaryocytes in bone marrow.

• Function: Initiate clot formation to prevent blood loss after injury.

• Production: Stimulated by thrombopoietin.

Hemostasis and Blood Clotting

Hemostasis is the process that stops bleeding after vascular injury.

• Mechanisms: Vascular spasm, platelet plug formation, and coagulation cascade.

• Clotting Sequence: Involves activation of clotting factors, conversion of fibrinogen to fibrin, and stabilization of the clot.

Table: Comparison of Blood Vessel Types

Vessel Type	Structure	Function
Artery	Thick, muscular, elastic walls	Carry blood away from heart under high pressure
Vein	Thinner walls, larger lumen, valves present	Return blood to heart under low pressure
Capillary	Single layer of endothelium	Exchange of gases, nutrients, and wastes