Cardiovascular System: Blood, Heart, and Vessels – Study Guide

Cardiovascular System Overview

The cardiovascular system is responsible for the transport of blood, nutrients, gases, and wastes throughout the body. It consists of the heart, blood vessels, and blood. This study guide covers key concepts related to blood composition, heart anatomy and function, and the structure and function of blood vessels.

Blood

Components of Blood

Blood is a specialized connective tissue composed of plasma and formed elements.

• Plasma: The liquid matrix of blood, making up about 55% of its volume. Contains water, proteins (albumin, globulins, fibrinogen), electrolytes, nutrients, hormones, and waste products.

• Formed Elements: The cellular components of blood, including:

  • Red blood cells (erythrocytes): Transport oxygen and carbon dioxide.

  • White blood cells (leukocytes): Defend against infection. Subdivided into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes).

  • Platelets (thrombocytes): Involved in blood clotting.

Blood Types

Blood types are determined by the presence or absence of specific antigens on the surface of red blood cells.

• ABO System: Based on the presence of A and/or B antigens.

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

• Antibodies: Naturally occurring proteins in plasma that react against foreign antigens.

• Blood Type Example: Type A+ has A antigens and the Rh antigen; plasma contains anti-B antibodies.

Additional info: Blood typing is crucial for safe blood transfusions and organ transplants.

Heart

Blood Flow Pathway Through the Heart

The heart pumps blood through two main circuits: the pulmonary circuit (to the lungs) and the systemic circuit (to the body).

1. Deoxygenated blood enters the right atrium via the superior and inferior vena cava.

2. Passes through the tricuspid valve into the right ventricle.

3. Pumped through the pulmonary valve into the pulmonary arteries to the lungs.

4. Oxygenated blood returns via pulmonary veins to the left atrium.

5. Passes through the bicuspid (mitral) valve into the left ventricle.

6. Pumped through the aortic valve into the aorta and systemic circulation.

Cardiac Muscle Histology

Cardiac muscle tissue is specialized for continuous, rhythmic contraction.

• Intercalated discs: Specialized junctions between cardiac muscle cells that allow rapid transmission of electrical impulses.

• Striations: Alternating light and dark bands due to organized actin and myosin filaments.

• Single central nucleus: Most cardiac muscle cells have one nucleus.

Electrical Conduction System

The heart's electrical system coordinates contraction.

• Sinoatrial (SA) node: The pacemaker; initiates the heartbeat.

• Atrioventricular (AV) node: Delays the impulse before it passes to the ventricles.

• Bundle of His, bundle branches, Purkinje fibers: Conduct impulses through the ventricles.

Additional info: Electrical signals can be visualized using an electrocardiogram (ECG).

Sheep Heart Dissection

Dissection of a sheep heart helps students identify anatomical structures and understand the flow of blood through the heart.

• Identify chambers, valves, and major vessels.

• Observe the thickness of ventricular walls (left thicker than right).

Vessels

Blood Vessel Structure

Blood vessels are classified by structure and function.

• Arteries: Carry blood away from the heart; thick, elastic walls.

• Veins: Carry blood toward the heart; thinner walls, larger lumen, often have valves.

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

• Arterioles and Venules: Small branches of arteries and veins, respectively.

Layers of Blood Vessels

• Tunica intima: Innermost layer; endothelium and subendothelial connective tissue.

• Tunica media: Middle layer; smooth muscle and elastic fibers.

• Tunica externa (adventitia): Outermost layer; connective tissue.

Elastic vs. Muscular Arteries

• Elastic arteries: Large arteries (e.g., aorta) with abundant elastic fibers to withstand high pressure.

• Muscular arteries: Medium-sized arteries with more smooth muscle for vasoconstriction and vasodilation.

Artery vs. Vein Histology

Feature	Artery	Vein
Wall thickness	Thick	Thin
Lumen size	Small, round	Large, irregular
Valves	Absent	Present (especially in limbs)
Elastic tissue	More	Less

Blood Pressure

Blood pressure is the force exerted by circulating blood on the walls of blood vessels.

• Systolic pressure: Pressure during ventricular contraction.

• Diastolic pressure: Pressure during ventricular relaxation.

Formula:

$\text{Blood Pressure} = \frac{\text{Cardiac Output} \times \text{Total Peripheral Resistance}}{\text{Area}}$

Additional info: Normal adult blood pressure is approximately 120/80 mmHg.

Major Arteries and Veins of the Body

Understanding the major arteries and veins is essential for clinical practice and anatomical study. The following are key vessels to identify:

• Upper limb: Radial artery, ulnar artery, deep palmar arch

• Lower limb: Femoral artery and vein, popliteal artery and vein, anterior tibial artery, posterior tibial artery, common iliac artery and vein, internal and external iliac arteries and veins

• Trunk and head: Common carotid artery, jugular vein, subclavian vein, axillary vein, cephalic vein, brachial vein, hepatic portal vein, splenic vein, renal artery, inferior and superior vena cava, aorta, celiac trunk, superior and inferior mesenteric arteries

Additional info: Images provided in the study materials illustrate the anatomical locations of these vessels in the limbs and trunk.

Summary Table: Differences Between Vessel Types

Vessel Type	Function	Wall Structure	Key Features
Artery	Carry blood away from heart	Thick, elastic, muscular	High pressure, no valves
Vein	Carry blood toward heart	Thin, less elastic	Low pressure, valves present
Capillary	Exchange of substances	Single layer endothelium	Microscopic, permeable