The Cardiovascular System, Study notes of Medicine

Download The Cardiovascular System and more Study notes Medicine in PDF only on Docsity!

TABLE OF CONTENTS

• Unit 1.1 Unit outline Page
• Unit 1.2 Unit objectives Page
• Unit 1.3 Introduction to the Cardiovascular System Page
• Unit 1.4 Structure of the Heart Page
• Unit 1.4.1 The Heart Chambers Page
• Unit 1.4.2 The Heart Valves Page
• Unit 1.4.3 Pathway of blood flow through the heart Page 5 -
• Unit 1.4.4 The Heart Wall Layers Page 6 -
• Unit 1.4.5 Blood vessels of the Heart Page
• Unit 1.4.6 The Pericardium Page 7 -
• Unit 1.4.7 The Heart Muscles Page
• Unit 1.5 Cardiovascular Diseases Page 10 –
• Unit 1.6 Heartbeat and electrical conduction system Page 12 –
• Unit 1.7 Blood Pressure and Regulation Page 15 –
  • Cardiovascular system Page 18 – Unit 1.8 Diagnostic Tools & Investigations for the

1.4.1 The Heart Chambers

The heart is divided into four chambers: two atria (upper chambers) and two ventricles (lower chambers).These chambers are separated by septa (walls) to prevent the mixing of oxygenated and deoxygenated blood. The Heart Chambers are:

a. Right Atrium: Located in the upper right side of the heart. It receives deoxygenated blood from the body via the superior vena cava (from the upper body) and the inferior vena cava (from the lower body). It pumps this blood into the right ventricle.

b. Left Atrium: Located in the upper left side of the heart. It receives oxygenated blood from the lungs via the pulmonary veins. It also pumps this oxygen-rich blood into the left ventricle.

c. Right Ventricle: Located in the lower right side of the heart. It pumps deoxygenated blood to the lungs through the pulmonary artery for oxygenation.

d. Left Ventricle: Located in the lower left side of the heart. It is the strongest chamber of the heart, pumping oxygenated blood to the entire body via the aorta. It has a thicker muscular wall compared to the right ventricle, as it needs to generate more pressure to pump blood through the systemic circulation.

1.4.2 The Heart Valves

The heart contains four main valves that control the flow of blood and prevent it from flowing backward. These valves open and close in response to the heart's pumping action, ensuring one-way blood flow. The Heart Valves are:

a. Tricuspid Valve: Located between the right atrium and the right ventricle. It prevents backflow of blood from the right ventricle into the right atrium. b. Pulmonary Valve: Located between the right ventricle and the pulmonary artery. The pulmonary valve prevents backflow of blood into the right ventricle after it has been pumped to the lungs.

c. Mitral (Bicuspid) Valve: Located between the left atrium and the left ventricle. This prevents backflow of blood from the left ventricle into the left atrium.

d. Aortic Valve: Located between the left ventricle and the aorta. It prevents backflow of blood into the left ventricle after it is pumped into the aorta.

Fig. 2 The Heart Valves

1.4.3 Pathway of blood flow through the heart

The pathway of blood through the heart is a well-organized loop that ensures deoxygenated blood goes to the lungs to pick up oxygen, and oxygen-rich blood is sent to nourish the body. This constant flow keeps every organ alive and working. To do this, the heart must pump deoxygenated blood to the lungs to receive oxygen, and then send the oxygenated blood to the rest of the body.

Types of Circulation

1. Pulmonary circulation – between the heart and lungs Pulmonary circulation is the part of the circulatory system that moves blood between the heart and the lungs. It carries deoxygenated blood from the right ventricle to the lungs to be oxygenated, and then returns the oxygenated blood to the left atrium. This process is necessary for gaseous exchange, where carbon dioxide is removed from the blood and oxygen is added.
2. Systemic circulation – between the heart and the rest of the body. Systemic circulation is the type of circulation that carries oxygenated blood from the heart to the rest of the body and returns deoxygenated blood back to the heart. It is essentially the circuit that nourishes all the tissues in the bodywith oxygen and nutrients, while removing waste products.

Overview of the Blood Flow Pathway

The blood follows a specific step-by-step route through the heart, passing through chambers, valves, and blood vessels. The flow must happen in the correct order for oxygen and nutrients to reach all parts of the body efficiently.

***** Step-by-Step Pathway of Blood Flow

1. Deoxygenated Blood from the Body Enters the Heart: Blood low in oxygen returns from the body to

the right atrium of the heart through two large veins:

Superior vena cava – brings blood from the upper body

Inferior vena cava – brings blood from the lower body

Fig. 3 Pathway of blood flow through the heart

a. Endocardium - The inner lining of the heart chambers and valves. allow blood to flow easily and to prevent clotting. b. Myocardium - The middle layer, which is composed of cardiac muscle tissue. layer and is responsible for the contraction of the heart, c. Epicardium - The outer layer of the heart. that surrounds and cushions the heart. of the heart.

1.4.5 Blood Vessels of the Heart

Arteries carry blood away from the heart under high pressure. The largest artery is the aorta. return blood to the heart under lower pressure and have valves to prevent backflow. tiny, thin-walled vessels where exchange of gases, nutrients, and wastes occurs between blood and tissues. These blood vessels are directly connected to the heart to help transport blood to and from different parts of the body:

a. Aorta - The largest artery in the body. body. b. Pulmonary Arteries: Carry deoxygenated blood from the right ventricle to the lungs for oxygenation. c. Pulmonary Veins: Carry oxygenated blood from the lungs to th d. Superior and Inferior Vena Cava: to the right atrium.

1.4.6 The Pericardium

The Pericardium is the outer layer around the heart, acting like the protective sac. The perica keeps the heart in place and provides protection contains pericardial fluid to lubricate the heart and prevent it from rubbing against other organs. inner part of the pericardium is called The pericardium, a double-walled sac

Fig. 4,

The inner lining of the heart chambers and valves. It is made up of smooth tissue to flow easily and to prevent clotting. The middle layer, which is composed of cardiac muscle tissue. layer and is responsible for the contraction of the heart, enabling it to pump blood. of the heart. This layer is part of the pericardium, a protective sac that surrounds and cushions the heart. It is also called the visceral layer. It directly

the Heart

carry blood away from the heart under high pressure. The largest artery is the aorta. return blood to the heart under lower pressure and have valves to prevent backflow. walled vessels where exchange of gases, nutrients, and wastes occurs between blood and blood vessels are directly connected to the heart to help transport blood to and from

artery in the body. This carries oxygenated blood from the left ventricle to the

Carry deoxygenated blood from the right ventricle to the lungs for

Carry oxygenated blood from the lungs to the left atrium. These large veins return deoxygenated blood from the body back

The Pericardium is the outer layer around the heart, acting like the protective sac. The perica keeps the heart in place and provides protection from infections and frictions during heartbeats. It also to lubricate the heart and prevent it from rubbing against other organs. inner part of the pericardium is called serous pericardium. walled sac which enclose the heart has two main parts:

4,5,6 The Heart Layers

ade up of smooth tissue to

The middle layer, which is composed of cardiac muscle tissue. This is the thickest enabling it to pump blood. This layer is part of the pericardium, a protective sac directly covers the surface

carry blood away from the heart under high pressure. The largest artery is the aorta. Veins return blood to the heart under lower pressure and have valves to prevent backflow. Capillaries are walled vessels where exchange of gases, nutrients, and wastes occurs between blood and blood vessels are directly connected to the heart to help transport blood to and from

arries oxygenated blood from the left ventricle to the

Carry deoxygenated blood from the right ventricle to the lungs for

e left atrium. These large veins return deoxygenated blood from the body back

The Pericardium is the outer layer around the heart, acting like the protective sac. The pericardium from infections and frictions during heartbeats. It also to lubricate the heart and prevent it from rubbing against other organs. The

has two main parts:

Fibrous pericardium : The outer layer that helps protect and anchor the heart. It is tough and protective. Serous pericardium : The inner layer that produces fluid to reduce friction as the heart beats. It contains the parietal layer and visceral layer.

*** Pericardial fluid** The Pericardial fluid is a clear, watery fluid found between the two layers (the parietal and visceral layers) of the pericardium. It is secreted by the serous pericardium. Function:
Acts as a lubricant to reduce friction as the heart beats and moves.
Allows the heart to contract and relax smoothly within the chest.
Helps to protect the heart from physical shock or injury. *** Serous Pericardium** The serous pericardium is the inner part of the pericardium. It is a thin, double-layered membrane that produces pericardial fluid to reduce friction as the heart beats. Functions:
Lubrication – Produces pericardial fluid which serves as a lubricant.
Protection – Forms part of the protective covering of the heart.
Smooth movement – Allows the heart to expand and contract without rubbing against other tissues in the chest. The serous pericardium has two layers: Parietal layer and Visceral layer. *** Parietal layer** The parietal layer is the outer layer of the serous pericardium. It provides structure and protection and helps hold the pericardial fluid in place around the heart. *** Visceral layer** The visceral layer is the inner layer of the serous pericardium. It directly covers the surface of the heart. Since it sits right on the heart wall, it is also known as the epicardium, which is the outermost layer of the heart wall. It protects the heart surface, produces part of the pericardial fluid, and plays a role is supporting and protecting blood vessels and nerves that supply (feed or control) heart muscles.

Fig. 7 Pericardium

`1.5 CARDIOVASCULAR DISEASES

Cardiovascular diseases (CVDs) are a group of disorders that affect that affect the heart and blood vessels. { Cardio – heart ; Vascular – blood vessels }. They are some of the leading causes of death worldwide and can affect people of all ages. Most CVDs are linked to problems in blood circulation, such as blocked or narrowed blood vessels, which can lead to heart attacks, strokes, or organ damage. Diseases associated with the cardivascular system include;

1. Heart Failure : This is a situation in which the heart muscle can’t pump (systolic) or fill (diastolic) adequately. It is usually caused by CAD (Coronary Artery Disease), but it can happen also when one has thyroid disease, high blood pressure, heart muscle disease (cardiomyopathy), or other conditions. Symptoms include shortness of breath, fatigue, swollen legs, and rapid heartbeat. Treatments can include eating less salt, limiting fluid intake and taking prescription medication. In some cases, a defibrillator or pacemaker can be implanted.
2. Cardiomyopathy : This is an acquired or hereditary disease of the heart which makes the heart stiff, thereby making it difficult for the heart to pump blood to the rest of the body. Symptoms of cardiomyopathy includes, fatique, heart palpitations, chest pain, shortness of breath (dyspnea), arrhythmia, swelling of the legs and ankles, syncope (fainting). Treatments include drugs, implanted devices, surgery and in service cases, transplant.
3. Coronary Artery disease (CAD) : Coronary Artery Disease is a common heart condition that affects the major blood vessels that supply the heart muscle. When fats, cholesterol, and other substance build up in and on the artery walls, it leads to CAD. This buildup is called plaque. The buildup of plaque is called atherosclerosis (ath-ur-o-skluh-ROE-sis). Atherosclerosis reduces blood flow to the heart and other parts of the body. It can lead to stroke, heart attack, or chest pain (angina). Symptoms of coronary artery disease are;
   Shortness of breath
   Chest pain, chest tightness, chest pressure and chest discomfort called angina
   Pain in the neck, jaw, throat, upper belly or back
   Pain, numbness, weakness or coldness in the legs or arms if the blood vessels in those areas are narrowed

Fig. 9 Heart Failure

Fig. 10 Cardiomyopathy

3. Rheumatic heart disease : Rheumatic heart disease (RHD) is a condition where the heart valves are damaged due to rheumatic fever, an autoimmune reaction to a streptococcal infection. This damage can lead to heart failure and other complications, particularly in low- and middle-income countries. Rheumatic fever is an inflammatory disease that can develop after an untreated or inadequately treated strep throat or scarlet fever infection caused by group A streptococcus bacteria. The body's immune response to the infection can mistakenly attack heart tissues, leading to rheumatic fever. When rheumatic fever affects the heart, it can cause inflammation and damage to the heart valves. This damage can result in: ~ Stenosis: Narrowing of the valve opening, restricting blood flow. ~ Regurgitation: Leaky valves, allowing blood to flow backward. ~ Scarring: Permanent damage to the valve structure.
4. Pericarditis : Pericarditis is the inflammation of the pericardium, causing sharp chest pain. The chest pain occurs when the irritated layers of the pericardium rub against each other. It may go away without treatment but in severe cases, medicines, and rarely, surgery is needed. The most common symptom of pericarditis is chest pain. Other symptoms are cough, fatigue, swelling of legs or feet, fever, rapid heartbeat, swelling of the belly, and shortness of breath.
5. Hypertension (High Blood Pressure): This is a condition where the force of the blood against the artery walls is too high. It is a condition where the blood vessels have persistently raised pressure. Overtime, it puts strain on the heart blood vessels, increasing the risk of heart failure. Symptoms of high blood pressure include headaches, dizziness, nosebleeds, blurred vision, and fatigue. It can be prevented by reducing salt intake, exercising regularly, maintaining a healthy weight, avoiding alcohol and smoking, and stress management.
6. Myocardial Infarction (Heart Attack): This is the blockage of blood flow to the heart muscle causing tissue death. It occurs when a coronary artery is completely blocked, and part of the heart muscle doesn’t get enough oxygen. That part of the heart can die if blood flow is not restored quickly. The symptoms include chest pain, shortness of breath, nausea or vomiting, cold sweat, feeling faint or lightheaded. It can be prevented through the following ways; Control cholesterol and blood pressure, avoid smoking, eat healthy fats, fruits, and vegetables.
7. Stroke : This is the interruption of blood flow to the brain either from a blockage (ischemic) or bleeding (hemorrhagic).
   Ischemic stroke: caused by a blocked blood vessel.
   Haemorrhagic stroke: caused by a burst blood vessel. This can cause permanent brain damage or even death. Symptoms are; sudden weakness/numbness (especially on one side of the body), trouble speaking or understanding speech, loss of balance or

The right atrium contracts first → sends blood to the right ventricle. The right ventricle then contracts → pumps deoxygenated blood to the lungs through the pulmonary artery to get oxygen. ***** Left side: The left atrium contracts → sends blood to the left ventricle. The left ventricle then contracts → pumps oxygen-rich blood to the body through the aorta. The left ventricle is especially strong and muscular because it needs to pump blood to the entire body. THE HEART'S ELECTRICAL CONDUCTION SYSTEM The heart’s electrical system is made up of specialized cells that generate and carry electrical signals. The main parts of this system include: a. Sinoatrial Node (SA Node) – Located in the right atrium. It starts the electrical signal that triggers each heartbeat. The SA node sets the pace for the heart — that's why it's called the natural pacemaker. b. Atrioventricular Node (AV Node) – Located between the atria and ventricles. It receives the signal from the SA node and slows it down slightly, giving the atria time to contract fully before the ventricles contract. c. Bundle of His: This is the pathway that carries the signal from the AV node to the ventricles. d. Right and Left Bundle Branches: These branches carry the electrical impulse down through the right and left ventricles. e. Purkinje Fibers: These spread the impulse throughout the ventricles, causing them to contract strongly and push blood out of the heart. How Electrical Activity Creates a Heartbeat The heartbeat is controlled by electrical signals that move through the heart in a specific pattern. These signals make the different parts of the heart contract (squeeze) in the right order so that blood is pumped properly throughout the body. Here is how the electrical activity creates each heartbeat: Step 1: The SA Node Sends the Signal The process begins in the sinoatrial (SA) node, which is located in the right atrium of the heart. This SA node is called the natural pacemaker because it starts the electrical impulse that begins each heartbeat. When the SA node fires, it sends an electrical signal through the walls of the atria, causing the atria (upper chambers of the heart) to contract. This contraction pushes blood from the atria into the ventricles (lower chambers). Step 2: The Signal Reaches the AV Node After the atria contract, the electrical impulse travels to the atrioventricular (AV) node. This node is located between the atria and the ventricles. The AV node slows down the electrical signal just a little. This delay gives the ventricles time to fill with blood from the atria before they contract. Step 3: The Signal Travels Down the Bundle of His

From the AV node, the signal moves into a group of specialized fibers called the Bundle of His. This bundle is like a highway that carries the signal down toward the ventricles. Step 4: The Signal Moves Through the Bundle Branches The Bundle of His splits into two pathways: the right bundle branch and the left bundle branch. These branches carry the signal to the right and left ventricles, guiding the impulse toward the bottom of the heart. Step 5: The Signal Spreads Through the Purkinje Fibers Finally, the signal travels into the Purkinje fibers, which are tiny fibers that spread throughout the walls of the ventricles. This causes the ventricles to contract strongly, pumping blood out of the heart: The right ventricle pumps blood to the lungs for oxygen. The left ventricle pumps oxygen-rich blood to the rest of the body.

Measuring Electrical Activity – The ECG (Electrocardiogram) An ECG or EKG is a test that that shows how the electrical signals move through the heart and records the electrical signals in the heart. It helps doctors see if the heart is beating normally. The ECG has different waves:

1. P Wave – Atrial Depolarization The P wave represents the electrical activity that causes the atria to contract. This is called atrial depolarization. It occurs just before the atria contract, pushing blood into the ventricles. Key point: P wave = atria get the signal to contract.
2. QRS Complex – Ventricular Depolarization The QRS complex represents the electrical activity that causes the ventricles to contract. This is known as ventricular depolarization. It is a large and sharp wave on the ECG because the ventricles are larger and need more force to pump blood. Key point: QRS complex = ventricles get the signal to contract. Note: During the QRS complex, the atria also relax (atrial repolarization), but this is hidden by the bigger QRS wave.
3. T Wave – Ventricular Repolarization The T wave shows the recovery phase of the ventricles after they contract. This process is called ventricular repolarization. It prepares the heart for the next heartbeat. Key point: T wave = ventricles recover and get ready for the next beat.

Disorders Related to Electrical Activity If something goes wrong with the heart’s electrical system, it can lead to irregular heart rhythms, called arrhythmias. Some examples include: Bradycardia : heart beats too slowly

NORMAL AND ABNORMAL BLOOD PRESSURE RANGES

Category Systolic (mmHg) Diastolic (mmHg) Normal Less than 120 Less than 80 Elevated 120 – 129 Less than 80 High Blood Pressure (Stage 1)

High Blood Pressure (Stage 2)

140 or higher 90 or higher

Low Blood Pressure (Hypotension)

Less than 90 Less than 60

FACTORS THAT AFFECT BLOOD PRESSURE

Several factors influence blood pressure, such as:

Heart rate and strength of contraction
Amount of blood being pumped (cardiac output)
Resistance in the arteries (narrower vessels increase pressure)
Volume of blood in the body
Elasticity of the artery walls
Hormones and nervous system activity

Regulation of Blood Pressure

The body has smart mechanisms to regulate blood pressure automatically to maintain balance (homeostasis).

1. Nervous System Regulation a. Baroreceptors: These are special pressure sensors located in the walls of major arteries (like the aorta and carotid arteries). They detect changes in blood pressure and send signals to the brain (medulla oblongata). The brain responds by:
Increasing or decreasing heart rate
Widening or narrowing blood vessels b. Autonomic Nervous System

Sympathetic nerves: Increase heart rate and constrict blood vessels → raises blood pressure Parasympathetic nerves: Slow heart rate and relax blood vessels → lowers blood pressure

2. Hormonal Regulation Certain hormones play key roles in blood pressure control: a. Adrenaline (Epinephrine): This is released in response to stress. It increases heart rate and constricts blood vessels → raises blood pressure b. Renin-Angiotensin-Aldosterone System (RAAS): This is triggered when blood pressure drops It causes blood vessels to constrict and the kidneys to retain sodium and water. It also leads to increased blood volume → raises blood pressure c. Antidiuretic Hormone (ADH): This also helps the kidneys retain water. It increases blood volume and pressure
3. Kidney Function in Regulation The kidneys help regulate blood pressure by controlling fluid balance. If blood pressure is high, kidneys remove more water and salt in urine. If blood pressure is low, kidneys conserve fluid. EFFECTS OF ABNORMAL BLOOD PRESSURE  High Blood Pressure (Hypertension):
   Damages arteries and organs (especially the heart, brain, kidneys, and eyes)
   Increases risk of stroke, heart attack, and kidney failure  Low Blood Pressure (Hypotension):
   May lead to dizziness, fainting, and organ failure in severe cases due to poor blood flow

TIPS FOR MAINTAINING HEALTHY BLOOD PRESSURE

Eat a balanced diet (low salt, low fat)
Stay physically active
Avoid smoking and reduce alcohol intake
Maintain a healthy weight
Manage stress
Check blood pressure regularly, especially if there's family history

5. Blood Tests Common Blood Markers:
Troponin – released during a heart attack
Cholesterol levels – to assess risk for heart disease
BNP (B-type natriuretic peptide) – used to detect heart failure Purpose:
Help confirm heart attacks or risk factors like high cholesterol 6. Chest X-ray What it Does:
Creates an image of the heart, lungs, and chest bones Purpose:
Check for enlarged heart, fluid in the lungs, or lung disease that may affect the heart 7. Cardiac Catheterization (Angiography) In this process, a thin tube (catheter) is inserted into a blood vessel and guided to the heart. Then a dye is injected and X-rays are taken to view blood flow in the coronary arteries Purpose:
Detect blockages or narrowing in the coronary arteries
Used before performing surgeries like angioplasty 8. MRI (Magnetic Resonance Imaging) of the Heart This uses magnetic fields and radio waves to create detailed images of the heart Purpose:
Show heart structure and function
Detect damaged tissue, tumors, or congenital defects 9. CT Scan (Cardiac CT or CT Angiography)

This uses X-rays and computer technology to create 3D images of the heart and vessels Purpose:
Check for plaque build-up in arteries (atherosclerosis)
Detect aneurysms or structural defects

10. Doppler Ultrasound (Vascular Ultrasound) It measures blood flow through the blood vessels using sound waves Purpose:
Detect blood clots, blockages, or narrowed arteries
Commonly used for leg veins, neck arteries (carotids), etc. 11. Holter Monitor (24-hour ECG) This is a portable ECG device worn for 24–48 hours which records heart activity continuously

Purpose:
Detect irregular heart rhythms that don’t appear during a regular ECG
Monitor symptoms like palpitations or fainting

SUMMARY TABLE

Test/Tool What it checks Purpose Physical Exam Heart Sounds, Pulse, BP Detect visible/physical signs of heart problems ECG/EKG Electrical activity Detect rhythm problems, heart attacks Echocardiogram Heart structure and motion

Check heart valves and pumping function Stress Test Heart function under stress

Reveal hidden heart issues Blood Tests Heart enzymes, cholesterol, BNP

Confirm heart attack, assess risk factors Chest X-ray Heart size, lungs Show enlarged heart or fluid Cardiac Catheterization Artery blockages Guide treatment for coronary artery disease MRI Detailed structure and tissue health

Detect damage or defects

CT Scan Arteries and plaques Detect blockages and aneurysms Doppler Ultrasound Blood flow in vessels Find clots or narrowed arteries Holter Monitor Long-term ECG monitoring

Track irregular heartbeats over time