GNM 1st Year Anatomy & Physiology: This chapter explains the heart, its chambers and valves, cardiac conduction system, cardiac cycle, blood vessels, circulation, blood pressure and pulse in a student-friendly way.
The circulatory system is one of the most important systems of the human body. It continuously transports blood throughout the body, supplying tissues with oxygen and nutrients while carrying carbon dioxide and other waste products away.
For GNM students, understanding the circulatory system is essential because the heart, blood vessels, blood pressure and circulation are closely related to many nursing assessments and clinical conditions.
This chapter covers the major topics included in GNM 1st-year Anatomy & Physiology, including the structure and functions of the heart, cardiac conduction system, cardiac cycle, blood vessels, circulation, blood pressure and pulse.
What Is the Circulatory System?
The circulatory system, also called the cardiovascular system, is the body system responsible for continuously circulating blood between the heart, lungs and tissues.
The main components are:
- Heart – acts as the muscular pump.
- Blood – transports oxygen, nutrients, hormones and waste products.
- Blood vessels – provide the pathways through which blood travels.
Main Functions of the Circulatory System
- Transports oxygen from the lungs to body tissues.
- Carries carbon dioxide from tissues toward the lungs.
- Transports nutrients absorbed from the digestive system.
- Carries hormones and other chemical messengers.
- Transports metabolic waste products.
- Helps regulate body temperature.
- Helps maintain fluid and chemical balance.
- Supports immune and protective functions.
The Heart
The heart is a muscular, hollow organ that pumps blood throughout the body.
It is located in the thoracic cavity, between the lungs, in a region called the mediastinum. Most of the heart lies slightly to the left of the body's midline.
GNM Exam Point: The heart is a muscular pump that maintains continuous circulation of blood through the pulmonary and systemic circulations.
Coverings of the Heart
The heart is enclosed in a protective sac called the pericardium.
The pericardium helps to:
- Protect the heart.
- Reduce friction during heart movement.
- Help maintain the position of the heart.
Structure of the Heart
The heart has four chambers:
- Right atrium
- Right ventricle
- Left atrium
- Left ventricle
The right and left sides of the heart are separated by muscular partitions called septa.
Right Atrium
The right atrium receives deoxygenated blood returning from most of the body through the:
- Superior vena cava
- Inferior vena cava
It also receives venous blood from the heart through the coronary sinus.
Right Ventricle
The right ventricle receives blood from the right atrium and pumps it toward the lungs through the pulmonary trunk, which divides into the pulmonary arteries.
Left Atrium
The left atrium receives oxygenated blood returning from the lungs through the pulmonary veins.
Left Ventricle
The left ventricle pumps oxygenated blood into the aorta, which distributes blood to the systemic circulation.
The wall of the left ventricle is thicker than that of the right ventricle because it generates the pressure needed to pump blood throughout the body.
Heart Valves
Heart valves help maintain one-way movement of blood through the heart.
| Valve | Location |
|---|---|
| Tricuspid valve | Right atrium → Right ventricle |
| Pulmonary valve | Right ventricle → Pulmonary trunk |
| Mitral/Bicuspid valve | Left atrium → Left ventricle |
| Aortic valve | Left ventricle → Aorta |
Easy memory aid: Right side → Tricuspid → Pulmonary. Left side → Mitral → Aortic.
Layers of the Heart Wall
The heart wall has three major layers:
1. Endocardium
The endocardium is the innermost layer that lines the chambers of the heart.
2. Myocardium
The myocardium is the thick muscular middle layer responsible for contraction of the heart.
3. Epicardium
The epicardium is the outer layer of the heart wall and forms the visceral layer of the serous pericardium.
Remember: Myocardium is the main muscular layer responsible for contraction.
Functions of the Heart
- Pumps deoxygenated blood toward the lungs.
- Pumps oxygenated blood to the body.
- Maintains blood flow to body organs and tissues.
- Helps maintain adequate blood pressure and tissue perfusion.
Conduction System of the Heart
The heart has a specialized electrical conduction system that coordinates its contractions.
The major components include:
- Sinoatrial (SA) node
- Atrioventricular (AV) node
- Atrioventricular bundle (Bundle of His)
- Right and left bundle branches
- Purkinje fibres
SA Node
The sinoatrial (SA) node is located in the right atrium and normally initiates the electrical impulse that starts each heartbeat. It is commonly known as the natural pacemaker of the heart.
AV Node
The electrical impulse reaches the AV node, where conduction is briefly delayed before the impulse continues toward the ventricles.
Bundle of His and Purkinje System
The electrical impulse travels through the atrioventricular bundle, bundle branches and Purkinje fibres, resulting in coordinated ventricular contraction.
Cardiac Cycle
The cardiac cycle refers to the sequence of electrical and mechanical events that occur during one complete heartbeat.
It includes contraction and relaxation of the atria and ventricles.
Systole
Systole is the contraction phase of the heart. During ventricular systole, the ventricles contract and eject blood into the pulmonary and systemic circulations.
Diastole
Diastole is the relaxation phase. During ventricular diastole, the ventricles relax and fill with blood.
Exam shortcut: Systole = contraction | Diastole = relaxation
Blood Vessels
Blood vessels are tubular structures through which blood circulates.
The three major types are:
- Arteries
- Veins
- Capillaries
Arteries
Arteries generally carry blood away from the heart.
Most arteries carry oxygenated blood. An important exception is the pulmonary arteries, which carry deoxygenated blood from the right ventricle toward the lungs.
Features of Arteries
- Relatively thick and muscular walls.
- Relatively narrow lumen compared with veins.
- Carry blood under relatively higher pressure.
- Usually have a palpable pulse.
- Generally do not contain valves along their length.
Veins
Veins generally carry blood toward the heart.
Most veins carry deoxygenated blood. An important exception is the pulmonary veins, which carry oxygenated blood from the lungs to the left atrium.
Features of Veins
- Thinner walls than arteries.
- Relatively wider lumen.
- Carry blood under relatively lower pressure.
- Many peripheral veins contain valves.
- Serve as an important blood reservoir.
Capillaries
Capillaries are microscopic blood vessels that connect the arterial and venous sides of the circulation.
Their thin walls allow exchange of oxygen, carbon dioxide, nutrients, water and metabolic waste products between blood and surrounding tissues.
Difference Between Arteries and Veins
| Feature | Arteries | Veins |
|---|---|---|
| Direction | Away from the heart | Toward the heart |
| Wall | Thicker and more muscular | Thinner |
| Pressure | Relatively higher | Relatively lower |
| Lumen | Relatively narrower | Relatively wider |
| Valves | Generally absent | Common in peripheral veins |
| Pulse | Usually palpable | Usually not palpable |
Important: Arteries and veins are classified according to the direction of blood flow, not simply according to whether blood is oxygenated or deoxygenated.
Circulation of Blood
Blood moves through several interconnected circulatory pathways.
Pulmonary Circulation
Pulmonary circulation carries blood between the heart and lungs.
Right ventricle → Pulmonary arteries → Lungs → Pulmonary veins → Left atrium
Its major purpose is to allow blood to exchange gases in the lungs.
Systemic Circulation
Systemic circulation carries oxygenated blood from the left side of the heart to the body and returns deoxygenated blood to the right side of the heart.
Left ventricle → Aorta → Body tissues → Veins → Venae cavae → Right atrium
Coronary Circulation
The heart muscle requires its own blood supply. The coronary arteries supply oxygenated blood to the myocardium.
Venous blood from the heart muscle returns through the cardiac veins and coronary sinus to the right atrium.
Hepatic Portal Circulation
The hepatic portal circulation carries blood from the gastrointestinal organs to the liver through the hepatic portal vein before that blood enters the general systemic circulation.
This allows the liver to process and regulate substances absorbed from the digestive tract.
Blood Pressure
Blood pressure is the pressure exerted by circulating blood against the walls of blood vessels, particularly arteries.
It is commonly expressed using two values:
Systolic Blood Pressure
Systolic blood pressure is the pressure associated with ventricular contraction.
Diastolic Blood Pressure
Diastolic blood pressure is the pressure associated with ventricular relaxation.
Blood pressure is recorded in millimetres of mercury (mmHg).
For example, in a reading of 120/80 mmHg:
- 120 represents systolic pressure.
- 80 represents diastolic pressure.
Important: Blood pressure can vary with activity, stress, body position, medications, age and health conditions. A single reading should not automatically be treated as a diagnosis.
Pulse
The pulse is the rhythmic expansion of an artery produced by the pressure wave associated with ventricular contraction.
Common Pulse Sites
- Radial artery: wrist
- Carotid artery: neck
- Brachial artery: upper arm
- Femoral artery: groin
- Popliteal artery: behind the knee
- Posterior tibial artery: ankle
- Dorsalis pedis artery: foot
Important Pulse Characteristics
When assessing a pulse, nurses commonly consider:
- Rate
- Rhythm
- Volume or strength
- Equality between corresponding sites
Pulse assessment is an important part of routine nursing observation.
Clinical and Nursing Relevance
Understanding the circulatory system provides an important foundation for nursing assessment and clinical learning.
A GNM student should understand the relationship between:
This knowledge is useful when studying conditions such as:
- Hypertension
- Hypotension
- Shock
- Heart failure
- Arrhythmias
- Peripheral vascular disorders
- Coronary artery disease
In clinical practice, nurses may monitor vital signs, assess peripheral circulation, observe changes in pulse and blood pressure, and recognize findings that require further clinical assessment.
Quick Revision Points
- The heart has four chambers.
- The right side mainly handles deoxygenated blood.
- The left side mainly handles oxygenated blood.
- The SA node normally initiates the heartbeat.
- The AV node delays conduction before ventricular activation.
- Systole means contraction.
- Diastole means relaxation.
- Arteries generally carry blood away from the heart.
- Veins generally carry blood toward the heart.
- Capillaries are major sites of exchange between blood and tissues.
- Pulmonary circulation connects the heart and lungs.
- Systemic circulation connects the heart and body tissues.
- Coronary circulation supplies the myocardium.
- Blood pressure is expressed in mmHg.
- Pulse is produced by the arterial pressure wave associated with ventricular contraction.
Ready to test your preparation? Try these important Circulatory System questions for GNM 1st Year.
Frequently Asked Questions
What are the main components of the circulatory system?
The main components are the heart, blood and blood vessels.
How many chambers does the heart have?
The heart has four chambers: two atria and two ventricles.
What is the natural pacemaker of the heart?
The sinoatrial (SA) node normally acts as the natural pacemaker of the heart.
What is the difference between systole and diastole?
Systole is the contraction phase, while diastole is the relaxation phase of the cardiac cycle.
What are the three main types of blood vessels?
The three main types are arteries, veins and capillaries.
What is pulmonary circulation?
Pulmonary circulation is the circulation of blood between the heart and lungs for gas exchange.
What is systemic circulation?
Systemic circulation is the circulation of blood between the heart and the rest of the body.
What is blood pressure?
Blood pressure is the pressure exerted by circulating blood against the walls of blood vessels.
Conclusion
The circulatory system is fundamental to maintaining life because it continuously moves blood between the heart, lungs and body tissues.
For GNM students, understanding the heart, cardiac conduction system, cardiac cycle, blood vessels, circulation, blood pressure and pulse provides an important foundation for studying cardiovascular physiology, disease processes and nursing care.