NHA MOD 2
MODULE 2: NHA CPT Exam 1
Chapter 6: The Cardiovascular System
The Circulatory System
Blood Components
Hemostasis & Complications
Career Development: Building a Professional Resume
Laboratory: Vein Identification & Mock Blood Draws
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Date: October 20-22, 2025 | Anatomy & Physiology for the Phlebotomist
Learning Outcomes
1. Describe circulation and the purpose of the vascular system.
2. Identify and describe the structures and functions of the different types of blood vessels.
3. Locate and name the veins most commonly used for phlebotomy procedures.
4. Identify the major components of blood and describe the major functions of each.
5. Define hemostasis and describe the basic coagulation process.
6. Describe how A B O and Rh blood types are determined.
Importance of Anatomy & Physiology in Phlebotomy
Understanding the circulatory system, including blood composition and clotting mechanisms, is essential for safe blood draws, error minimization, and accurate patient reaction interpretation.
Anatomy: Refers to the structure of the body.
Physiology: Refers to how those structures function.
Together, these two fields provide the scientific basis for every blood draw, test, and patient interaction.
Clinical Relevance: Knowledge of anatomy prevents injuries when drawing blood, avoiding damages to arteries, nerves, or tendons, mislabeling specimens, or misinterpreting abnormal blood behavior in patients.
Discussion Prompt: Describe how knowledge of vascular anatomy can boost confidence during venipuncture.
The Circulatory System: Overview
The circulatory system is a network that connects every organ, tissue, and cell, delivering oxygen, nutrients, hormones, and removing carbon dioxide and waste products.
It spans over 70,000 miles of vessels and operates continuously from birth to death.
Main Structures of the Circulatory System
Heart: A muscular pump ensuring unidirectional blood flow.
Blood Vessels: Comprises arteries, veins, and capillaries.
Blood: The connective tissue responsible for transportation of essential elements.
Circuits:
Pulmonary Circuit:
Pathway: Right heart → Lungs → Left heart (gas exchange).
Systemic Circuit:
Pathway: Left heart → Body → Right heart (delivery of oxygen/nutrients).
Blood Volume
An average adult contains 8–12 pints of blood, comparable to the volume of a gallon of milk.
Clinical Relevance: Phlebotomists collect systemic venous blood, which appears darker in color because it returns to the heart carrying metabolic by-products from body tissues.
Discussion Prompt: Why is venous blood typically collected instead of arterial blood? Arterial blood shows oxygenated status directly from the lungs, while venous blood reflects what tissues have utilized.
The Heart: Overview
The heart is a strong, hollow muscle approximately the size of a fist located in the center of the chest, slightly to the left of midline. It functions as a double pump, where:
The right side sends blood to the lungs for oxygen.
The left side distributes oxygen-rich blood throughout the body.
Each heartbeat pushes approximately 70 mL of blood, producing a detectable pulse.
Chambers and Valves of the Heart
Four Chambers
Right Atrium
Right Ventricle
Left Atrium
Left Ventricle
Septum
A wall separating oxygen-poor (right) from oxygen-rich (left) sides of the heart.
Valves
Tricuspid Valve: Between Right Atrium (RA) and Right Ventricle (RV).
Pulmonary Valve: Between Right Ventricle (RV) and pulmonary artery.
Mitral (Bicuspid) Valve: Between Left Atrium (LA) and Left Ventricle (LV).
Aortic Valve: Between Left Ventricle (LV) and aorta.
Function: These valves ensure a one-way blood flow and prevent backflow.
The Layers of the Heart
Introduction
To understand the pumping mechanism, it is crucial to examine the heart's structure.
Heart Wall Composition
Endocardium (Inner Layer):
Function: Provides a smooth, frictionless surface for blood flow, prevents clots.
Analogy: Similar to a non-stick coating in a pot to promote smooth blood flow.
Location: Lines all heart chambers and covers valves.
Composition: A thin layer of endothelial cells.
Clinical Relevance: Infection (endocarditis) can result in clot shedding into circulation, risking stroke or organ damage.
Myocardium (Middle Layer):
Function: Provides the pumping force; cardiac muscle; contracts 60–100 times per minute.
Analogy: Comparable to an engine block, producing the heart's power stroke.
Composition: Specialized cardiac muscle fibers (involuntary, striated).
Clinical Relevance: Myocardial infarction (MI) occurs when coronary artery blood flow is blocked, leading to oxygen deprivation and potential muscle death.
Tests for cardiac enzymes (Troponin, CK-MB) are crucial during heart attacks.
Epicardium (Outer Layer):
Function: Protects the heart; contains blood vessels, lymphatics, and nerves that nourish the myocardium.
Analogy: Acts as the heart's skin, facilitating lubrication like oil for an engine.
Location: Lies directly on the myocardium; part of the pericardium.
Clinical Relevance: Inflammation (epicarditis) can cause pain and fluid buildup, causing cardiac tamponade, diminishing blood pressure.
The Pericardium
A two-layered membrane enclosing and anchoring the heart, preventing friction and over-expansion, allowing normal movement.
Fibrous Pericardium: The tough outer layer anchoring to the diaphragm and chest wall.
Serous Pericardium: Inner layer with parietal (outer) and visceral (epicardium) layers.
Pericardial Cavity: Contains 10–20 mL of fluid for lubrication.
Clinical Relevance: Pericarditis can cause chest pain and circulation disturbances, influencing venipuncture success.
Function of the Heart
Overview
The heart operates as the body’s central pump, creating a one-way cycle to keep blood circulating to the entire system.
Pulse Creation: Contractions generate the pressure that drives blood through arteries, veins, and capillaries.
Function: It facilitates the delivery of nutrients and oxygen while removing carbon dioxide and waste.
Circulatory Pathways
Systemic Circulation:
Carries oxygen-rich blood from the left ventricle through the aorta to all tissues, returning oxygen-poor blood to the right atrium.
Pathway: Left Ventricle → Aorta → Arteries → Capillaries → Veins → Vena Cava → Right Atrium.
Clinical Relevance: Phlebotomists access this venous blood, typically darker and lower in pressure, making it ideal for sampling.
Pulmonary Circulation:
Moves oxygen-poor blood from the right ventricle to the lungs for gas exchange and returns oxygen-rich blood to the left atrium.
Pathway: Right Ventricle → Pulmonary Arteries → Lungs → Pulmonary Veins → Left Atrium.
Clinical Relevance: Blood sampled has likely just exited systemic circulation; changes in color during draws are critical indicators of respiratory health.
Coronary Circulation:
Supplies the myocardium with oxygen and nutrients necessary for heart function.
Pathway: Aorta → Coronary Arteries → Myocardium → Cardiac Veins → Coronary Sinus → Right Atrium.
Clinical Relevance: Blockages leading to ischemia can result in heart damage and emergency laboratory tests.
Blood Vessels - Structure, Function, and Clinical Relevance
Vascular Pathways of Circulation
Blood vessels form a network connecting all tissues to the heart and involve three main types:
Arteries: Carry blood away from the heart, functioning like high-speed outgoing roads.
Function: Use muscular pressure to maintain high flow.
Veins: Carry blood back to the heart, acting as slower return routes with valves to prevent backflow.
Function: Utilize skeletal muscle contractions for venous flow.
Capillaries: Smallest vessels that facilitate nutrient and gas exchange between blood and tissues.
Function: Rely on diffusion for exchange processes.