Cardiovascular System

CARDIOVASCULAR SYSTEM

Introduction

The cardiovascular system is the main transport system of the human body. It is responsible for carrying essential substances such as oxygen, nutrients, water, hormones, and other important materials to the body cells. At the same time, it removes waste products like carbon dioxide and metabolic wastes from the tissues.

This system also plays an important role in:

• Maintaining body temperature
• Regulating pH of body fluids
• Maintaining homeostasis, which means keeping the internal environment of the body stable

The cardiovascular system mainly consists of:

• Heart
• Blood
• Blood vessels

Together, these components ensure continuous circulation of blood throughout the body.

THE HEART

The branch of science that deals with the study of the normal structure, function, and diseases of the heart is called Cardiology.
(Cardio = heart, logy = study)

The heart is the central organ of the cardiovascular system and acts as a powerful muscular pump that maintains continuous blood circulation.

ANATOMY OF HEART

The heart is a hollow, muscular organ located in the thoracic cavity.

Important anatomical features of the heart are:

• It lies between the two lungs, slightly towards the left side
• It is cone-shaped, with a broad base above and a pointed apex below
• The size of the heart is approximately equal to the closed fist of the individual
• Average dimensions:
• Length: 12 cm
• Width: 9 cm
• Thickness: 6 cm
• The apex is located about 9 cm to the left of the midline at the level of the fifth intercostal space
• The base extends up to the level of the second rib
• Average weight:
• Adult female: 250 g
• Adult male: 300 g
• It rests on the diaphragm near the midline of the thoracic cavity

The heart is situated in the mediastinum, which is the central space in the thorax extending:

• From sternum to vertebral column
• From first rib to diaphragm
• Between the two lungs

About two-thirds of the heart lies to the left of the midline.

Organs Associated with the Heart

FUNCTIONS OF THE HEART

The heart functions as a muscular pump that maintains constant blood circulation.

The sequence of blood flow is as follows:

1.     Superior vena cava and inferior vena cava bring deoxygenated (venous) blood from the body to the right atrium

2.     The right atrium contracts, pushing blood into the right ventricle

3.     The right ventricle contracts, sending blood to the lungs through the pulmonary trunk

4.     In the lungs, blood becomes oxygenated

5.     Oxygenated blood returns to the left atrium through pulmonary veins

6.     The left atrium contracts, sending blood into the left ventricle

7.     The left ventricle contracts, pumping blood into the aorta, which supplies blood to the entire body

This continuous pumping action ensures proper circulation.

STRUCTURE OF HEART WALL

The heart wall consists of three layers:

• Pericardium
• Myocardium
• Endocardium

Pericardium

The pericardium is a fibro-serous sac that surrounds the heart.

Functions of pericardium:

• Protects the heart
• Prevents overstretching
• Reduces friction during heart movements
• Keeps the heart in proper position

The pericardium has two main parts:

Fibrous Pericardium

• Outer tough layer
• Made of dense connective tissue
• Prevents excessive expansion of the heart
• Anchors the heart in the thoracic cavity

Serous Pericardium

• Thin, delicate membrane
• Forms a double layer around the heart

It has:

• Parietal layer (lines the fibrous pericardium)
• Visceral layer (Epicardium) (covers the heart)

Between these layers is the pericardial cavity, which contains pericardial fluid that lubricates the heart.

Layers of the Heart Wall

Epicardium

• Outermost layer
• Also called the visceral layer of pericardium
• Protects and lubricates the heart surface

Myocardium

• Thick muscular middle layer
• Composed of cardiac muscle fibers
• Responsible for pumping action of the heart
• Thickest in the left ventricle

Endocardium

• Innermost layer
• Made of simple squamous epithelium
• Lines heart chambers and valves
• Continuous with the lining of blood vessels

CHAMBER OF THE HEART

The heart is divided into right and left sides by a septum and consists of four chambers.

Chambers of the Heart:

• Atria are receiving chambers with thinner walls
• Ventricles are pumping chambers with thicker muscular walls
• Right side pumps blood to lungs (pulmonary circulation)
• Left side pumps blood to the whole body (systemic circulation)

VALVE OF THE HEART

Heart valves ensure that blood flows in one direction only.

There are four heart valves, divided into two groups:

1. Atrioventricular Valves

Located between atria and ventricles.

• These valves close during ventricular contraction
• Closure produces the first heart sound (Lub)

2. Semilunar Valves

Located between ventricles and arteries.

• Each has three cusps
• Close during ventricular relaxation
• Closure produces the second heart sound (Dub)

FLOW OF BLOOD THROUGH THE HEART

Right Side of Heart

The heart functions as a powerful muscular pump that maintains continuous circulation of blood throughout the body. Blood flow through the heart follows a fixed and well-organized pathway to ensure proper oxygenation and nutrient supply.

The two largest veins of the body, the superior vena cava and inferior vena cava, bring deoxygenated blood from different parts of the body and empty it into the right atrium of the heart.

From the right atrium, blood passes through the right atrioventricular valve (tricuspid valve) into the right ventricle. This valve allows blood to move forward and prevents backward flow into the atrium during ventricular contraction.

When the right ventricle contracts, blood is pumped into the pulmonary artery (pulmonary trunk). This artery is unique because it is the only artery in the body that carries deoxygenated blood.

The opening of the pulmonary artery is guarded by the pulmonary valve, which is made up of three semilunar cusps. This valve prevents the blood from flowing back into the right ventricle when the ventricle relaxes.

The pulmonary artery divides into left and right pulmonary arteries, which carry venous (deoxygenated) blood to the lungs. In the lungs, gaseous exchange takes place, where:

• Carbon dioxide is removed from the blood
• Oxygen is absorbed into the blood

This process is essential for maintaining normal respiration and cellular function.

After oxygenation in the lungs, blood is returned to the heart by two pulmonary veins from each lung. These veins carry oxygenated blood back to the left atrium.

Summary of Blood Flow (Right Side of Heart):

Left Side of Heart

Blood collected in the left atrium then passes through the left atrioventricular valve (bicuspid or mitral valve) into the left ventricle. This valve ensures that blood flows only in one direction and prevents regurgitation into the atrium.

The left ventricle has thicker muscular walls compared to the right ventricle because it has to pump blood to the entire body. When the left ventricle contracts, blood is pumped into the aorta, the largest artery of the body, which supplies oxygenated blood to all organs and tissues.

The opening of the aorta is guarded by the aortic valve, which is also composed of three semilunar cusps. This valve prevents the backflow of blood into the left ventricle when it relaxes.

From this sequence of events, it is clear that blood flows from the right side of the heart to the lungs, and then to the left side of the heart, a process known as pulmonary circulation. Blood pumped from the left ventricle to the body is called systemic circulation.

It is important to note that both atria contract at the same time, followed by the simultaneous contraction of both ventricles. This coordinated activity ensures efficient pumping and continuous blood flow.

Summary of Blood Flow (Left Side of Heart):

BLOOD SUPPLIED TO THE HEART (THE CORONARY CIRCULATION)

The heart muscle itself requires a continuous supply of oxygen and nutrients to function efficiently. This supply is provided by a special circulation known as coronary circulation.

Arterial Supply

The arterial blood supply to the heart is provided by two coronary arteries:

• Right coronary artery
• Left coronary artery

These arteries arise from the ascending aorta, just above the aortic valve.

Although the heart is relatively small in size, it receives about 5% of the total cardiac output. This rich blood supply is essential because the heart works continuously without rest. The coronary arteries branch extensively and form a dense network of capillaries within the myocardium.

Venous Drainage

Most of the venous blood from the heart muscle is collected by cardiac veins, which unite to form the coronary sinus. The coronary sinus opens into the right atrium.

A small amount of venous blood drains directly into the heart chambers through small veins.

CONDUCTING SYSTEM TO THE HEART

The conducting system of the heart is a specialized system of cardiac muscle fibers that generates and transmits electrical impulses. These impulses control the rhythmic contraction of the heart.

Components of the Conducting System:

Sinoatrial Node (SA Node)

• Located in the wall of the right atrium near the opening of the superior vena cava
• Known as the pacemaker of the heart
• Generates impulses at a rate of 60–80 beats per minute
• Initiates atrial contraction

SA node cells are electrically unstable and automatically generate impulses, which determine the normal heart rate.

Atrioventricular Node (AV Node)

• Located in the atrial septum near the atrioventricular valves
• Transmits impulses from atria to ventricles
• Introduces a delay of about 0.1 second, allowing atria to complete contraction before ventricles begin
• Can act as a secondary pacemaker with a rate of 40–60 bpm

AV Bundle, Bundle Branches and Purkinje Fibers

• The bundle of His arises from the AV node
• It divides into right and left bundle branches in the ventricular septum
• These branches break into fine fibers called Purkinje fibers

These fibers spread impulses rapidly throughout the ventricular myocardium, causing coordinated ventricular contraction from the apex upward.

Nerve Supply to the Heart

The heart is regulated by the autonomic nervous system.

FACTORS AFFECTING THE HEART

Heart Rate

Heart rate determines cardiac output.

Factors affecting heart rate include:

• Autonomic nervous system
• Hormones (adrenaline, noradrenaline)
• Body position
• Exercise
• Emotional states
• Age and gender
• Body temperature
• Baroreceptor reflex

An increase in heart rate increases cardiac output and vice versa.

CARDIAC CYCLE

The cardiac cycle is the sequence of events that occurs from the beginning of one heartbeat to the beginning of the next.

It consists of two phases:

• Systole – contraction of ventricles
• Diastole – relaxation of ventricles

A normal heartbeat lasts about 0.8 seconds, with a rate of 60–80 beats per minute.

Duration of Cardiac Cycle:

Heart Sounds

Contraction and relaxation of the heart produce sounds.

Electrical Changes in the Heart (ECG)

Electrical activity of the heart is recorded using an electrocardiograph, producing an electrocardiogram (ECG).

ECG Waves

Cardiac Output

Cardiac output is the volume of blood pumped by each ventricle per minute.

Formula:

Cardiac Output = Stroke Volume × Heart Rate

In a normal adult:

• Stroke volume ≈ 70 ml
• Heart rate ≈ 72 bpm
• Cardiac output ≈ 5 litres/minute

Stroke Volume

Stroke volume is the amount of blood pumped by the left ventricle in one beat.

Formula:

Stroke Volume = End Diastolic Volume − End Systolic Volume

Factors affecting stroke volume:

• Preload
• Contractility
• Afterload

BLOOD CIRCULATION

Blood circulation refers to the continuous movement of blood through the heart, blood vessels, and organs of the body. It ensures the supply of oxygen and nutrients to tissues and removes waste products such as carbon dioxide. Depending on the course followed by blood, circulation is classified into the following types:

1.     Systemic circulation (Greater circulation)

2.     Pulmonary circulation (Lesser circulation)

3.     Portal circulation

1. Systemic Circulation

Systemic circulation is the part of the cardiovascular system that carries oxygenated blood from the heart to all parts of the body and returns deoxygenated blood back to the heart.

The oxygenated blood is pumped out from the left ventricle into the aorta, the largest artery of the body. The aorta gives rise to many branches that carry blood to different organs and tissues.

From the aorta, blood divides into smaller systemic arteries, which further branch into arterioles. These arterioles lead to an extensive network of systemic capillaries present in all tissues of the body, except the air sacs (alveoli) of the lungs, which are supplied by pulmonary circulation.

Across the thin walls of capillaries, exchange of substances occurs. Oxygen and nutrients are delivered to the tissues, while carbon dioxide and metabolic wastes are collected from the cells.

During this exchange:

• Blood unloads oxygen (O₂)
• Blood picks up carbon dioxide (CO₂)

In most tissues, blood flows through one capillary bed and then enters a systemic venule. Venules merge to form larger systemic veins, which carry deoxygenated blood away from the tissues.

Finally, the deoxygenated blood returns to the right atrium of the heart through the superior vena cava (from upper body) and inferior vena cava (from lower body).

Thus, the circulation of blood from the left ventricle to the right atrium is called systemic circulation.

Flow Sequence of Systemic Circulation:

2. Pulmonary Circulation

Pulmonary circulation is concerned with the movement of blood between the heart and the lungs. The right side of the heart acts as the pump for pulmonary circulation.

Deoxygenated blood from the right ventricle is pumped into the pulmonary trunk, which divides into right and left pulmonary arteries. These arteries carry blood to the respective lungs.

Inside the lungs, the pulmonary arteries divide and subdivide into smaller vessels, finally forming capillaries around the alveoli (air sacs). Here, gaseous exchange takes place:

• Carbon dioxide (CO₂) moves from blood into the alveoli and is exhaled
• Oxygen (O₂) moves from the alveoli into the blood

The oxygenated blood from pulmonary capillaries then collects into venules and forms pulmonary veins. These veins leave the lungs and carry oxygenated blood to the left atrium of the heart.

There are two pulmonary veins from each lung, and pulmonary veins are unique because they are the only veins that carry oxygenated blood.

The contraction of the left ventricle then pumps this oxygenated blood into the systemic circulation.

Thus, the circulation of blood from the right ventricle to the left atrium is called pulmonary circulation.

Flow Sequence of Pulmonary Circulation:

3. Portal Circulation

Portal circulation is a special type of circulation in which venous blood passes from one capillary bed to another before returning to the heart.

In portal circulation, blood from the digestive organs, spleen, and pancreas is collected and transported to the liver through the portal vein.

A vein that carries blood from one capillary network to another is called a portal vein.

The hepatic portal vein is formed by the joining of several veins, including:

• Splenic vein (from spleen)
• Superior mesenteric vein (from small intestine)
• Inferior mesenteric vein (from rectum and colon)
• Gastric veins (from stomach)
• Cystic vein (from gall bladder)

Blood reaching the liver through portal circulation is rich in nutrients absorbed from the stomach and intestines. This allows the liver to:

• Store glucose as glycogen
• Detoxify harmful substances
• Regulate nutrient levels

The liver receives oxygenated blood separately through the hepatic artery. After processing, blood leaves the liver through hepatic veins, which drain into the inferior vena cava and return blood to the heart.

Key Features of Portal Circulation:

BLOOD VESSELS

Blood vessels are the important components of the circulatory system that transport blood throughout the human body. They form a closed network through which blood continuously circulates between the heart and body tissues.

Blood is carried through the body only via blood vessels, which vary in size, structure, and function depending on their role in circulation.

An artery is a blood vessel that carries blood away from the heart. As arteries move farther from the heart, they divide repeatedly into smaller vessels.

The smallest branches of arteries are called arterioles. Arterioles further branch into extremely thin vessels known as capillaries, where the exchange of nutrients, gases, and waste materials takes place.

After exchange occurs in the capillaries, blood enters small vessels called venules. Venules unite to form veins, which are larger blood vessels that return blood back to the heart.

The walls of blood vessels contain varying amounts of fibrous tissue, elastic tissue, and smooth muscle, depending on the type of vessel and the pressure of blood flowing through it.

Although arteries and veins differ in structure and function, both possess three basic layers of tissue.

Layers of Blood Vessel Wall

1.     Tunica interna (Intima)

o    The innermost layer

o    Made of a smooth epithelial lining

o    Provides a frictionless surface for blood flow

2.     Tunica media

o    The middle layer

o    Composed of smooth muscle and elastic connective tissue

o    Responsible for regulating blood vessel diameter

3.     Tunica externa (Adventitia)

o    The outermost layer

o    Made of connective tissue

o    Provides strength and support to the vessel

Types of Blood Vessels

Structure of an Artery and a Vein

Blood vessels differ in structure, size, and function, and are classified into arteries, arterioles, capillaries, venules, and veins.

Both arteries and veins consist of three layers of tissue, but their thickness and composition vary based on blood pressure and function.

Arteries have thicker walls to withstand high pressure, whereas veins have thinner walls because blood flows through them at lower pressure.

Relationship Between the Heart and the Different Types of Blood Vessels

Arteries and their smaller branches, arterioles, carry blood away from the heart.

Arterioles divide into a vast network of thin-walled capillaries. These capillaries allow oxygen, nutrients, and water to diffuse into tissues, while carbon dioxide and waste products diffuse into the bloodstream.

Capillaries merge to form small venules, which further unite to form large veins. These veins carry blood back to the heart, completing the circulatory loop.

Arteries

Arteries are the main blood vessels that carry oxygenated (oxygen-rich) blood from the heart to various parts of the body (except pulmonary arteries).

They are the strongest blood vessels with thick, muscular, and elastic walls designed to withstand high blood pressure.

Arteries consist of three distinct layers and are generally located deep within the body. They appear red in colour due to oxygen-rich blood.

Blood flows through arteries under high pressure, moving in a downward direction from the heart to body tissues.

Arterioles

Large arteries divide into medium-sized muscular arteries, which further divide into smaller arteries known as arterioles.

Approximately 400 million arterioles are present in the body, with diameters ranging from 15 µm to 300 µm.

Arterioles play a vital role in:

• Delivering blood to capillaries
• Regulating blood flow
• Controlling blood pressure

The terminal part of an arteriole, called the metarteriole, tapers toward the capillary junction.

Arterioles regulate blood flow by controlling vascular resistance, which is the opposition to blood flow caused by friction between blood and vessel walls.

Capillaries

Capillaries are the smallest blood vessels in the body, with diameters of approximately 5–10 µm.

They form U-shaped networks that connect arterial outflow to venous return.

Capillaries are the primary sites of exchange, where:

• Oxygen and nutrients move into tissues
• Carbon dioxide and waste products move into blood

They connect the arterial system to the venous system and play a crucial role in maintaining tissue health.

Venules

Venules drain blood from capillaries and initiate the return of blood toward the heart.

They are the smallest veins, measuring about 10 µm to 50 µm in diameter.

Venules collect deoxygenated blood from capillaries and deliver it to larger veins.

Veins

Veins are blood vessels that return blood to the heart at low pressure.

The walls of veins are thinner than those of arteries, but they still consist of the same three tissue layers.

Veins vary in size from 0.5 mm in small veins to about 3 cm in large veins such as the superior and inferior vena cava.

They are thinner because they contain less smooth muscle and elastic tissue in the tunica media, as veins carry blood at lower pressure than arteries.

Comparison of Arteries and Veins

BLOOD PRESSURE

Blood pressure is the force exerted by circulating blood on the walls of blood vessels, especially arteries. It plays a vital role in ensuring continuous blood flow to all tissues and organs.

If blood pressure becomes too high, blood vessels may get damaged, leading to:

• Formation of blood clots
• Rupture of blood vessels
• Internal bleeding

If blood pressure becomes too low, blood flow through tissue beds may be insufficient. This is particularly dangerous for vital organs such as the heart, brain, and kidneys, which require a constant supply of oxygenated blood.

The systemic arterial blood pressure, commonly called arterial blood pressure, is mainly produced due to the discharge of blood from the left ventricle into the already filled aorta.

Blood pressure varies depending on:

• Time of the day
• Body posture
• Age and gender
• Physical activity and rest

Blood pressure usually falls during rest and sleep. It generally increases with age and is often slightly higher in women than in men.

Types of Blood Pressure

Blood pressure is of two main types:

1.     Systolic Blood Pressure

2.     Diastolic Blood Pressure

Systolic Blood Pressure

Systolic blood pressure is the maximum pressure exerted on arterial walls. It occurs during systole, when the heart contracts and ejects blood into the arteries.

The normal range of systolic pressure is approximately 100–120 mm Hg.

Diastolic Blood Pressure

Diastolic blood pressure is the minimum pressure present in the arteries. It occurs during diastole, when the heart relaxes between two contractions.

The normal range of diastolic pressure is approximately 60–80 mm Hg.

Normal Blood Pressure Values:

PULSE PRESSURE

Pulse pressure is the difference between systolic and diastolic blood pressure.

Formula:

Pulse pressure = Systolic pressure − Diastolic pressure

Using average values:
Pulse pressure = 120 mm Hg − 80 mm Hg = 40 mm Hg

Pulse pressure gives an indication of the force generated by the heart during contraction.

FACTORS DETERMINING BLOOD PRESSURE

Blood pressure mainly depends on cardiac output and peripheral resistance.

Blood Pressure = Cardiac Output × Peripheral Resistance

Any change in these factors can alter blood pressure, although the body usually activates compensatory mechanisms to maintain normal levels.

Cardiac Output (CO)

Cardiac output is determined by:

• Heart rate
• Stroke volume

Factors that increase or decrease heart rate or stroke volume will directly affect cardiac output and blood pressure.

An increase in cardiac output raises both systolic and diastolic pressure.
An increase in stroke volume raises systolic pressure more than diastolic pressure.

Peripheral or Arteriolar Resistance

Arterioles are the smallest arteries and have a tunica media rich in smooth muscle, which responds to nerve and chemical stimulation.

Constriction and dilation of arterioles are the main determinants of peripheral resistance.

• Vasoconstriction → increases blood pressure
• Vasodilation → decreases blood pressure

With aging, elastic tissue in the tunica media is replaced by inelastic fibrous tissue, leading to a rise in blood pressure.

Autoregulation

Systemic blood pressure continuously rises and falls depending on activity level and body position.

However, organs can independently regulate their local blood flow and pressure, irrespective of systemic blood pressure.

This ability is known as autoregulation, and it protects tissues from sudden fluctuations in blood pressure.

CONTROL OF BLOOD PRESSURE (BP)

Blood pressure is regulated by two main mechanisms:

1.     Short-term control

2.     Long-term control

Short-term Control

Short-term regulation works on a moment-to-moment basis and involves:

• Baroreceptor reflex
• Chemoreceptors
• Circulating hormones

Long-term Control

Long-term regulation involves control of blood volume, mainly by:

• Kidneys
• Renin–angiotensin–aldosterone system

Baroreceptors

Baroreceptors are stretch-sensitive receptors that provide important input to the vasomotor center.

They are located in:

• Arch of the aorta
• Carotid sinuses

As the aorta leaves the left ventricle, it forms an arch and then descends through the thoracic and abdominal cavities.

Baroreceptors respond to stretch or distension of blood vessel walls and are therefore also called stretch receptors.

A change in blood pressure activates the baroreceptor reflex, which produces negative feedback responses to restore blood pressure to normal.

Chemoreceptors

Chemoreceptors are nerve endings located in:

• Carotid bodies
• Aortic bodies

They are primarily involved in the control of respiration.

Chemoreceptors are sensitive to changes in:

• Carbon dioxide levels
• Oxygen levels
• Blood pH

Central chemoreceptors are present on the brain surface in the medulla oblongata and measure the chemical composition of the surrounding cerebrospinal fluid.

Chemoreceptor input strongly influences the cardiovascular center only when:

• Severe respiratory disturbance occurs
• Arterial blood pressure falls below 80 mm Hg

Higher Centres in the Brain

Input to the cardiovascular centre (CVC) from higher brain centres is influenced by emotional states such as:

• Fear
• Anxiety
• Pain
• Anger

These emotions can stimulate changes in blood pressure.

The hypothalamus controls body temperature and influences the CVC by adjusting the diameter of blood vessels in the skin.

This mechanism plays an important role in heat loss and heat retention.

PULSE

The pulse is a wave of distension and elongation felt in the wall of an artery each time the left ventricle ejects blood into the circulation.

It represents the rhythmic expansion of arteries and provides valuable information about heart function and blood flow.

Clinical Significance of Pulse:

DISORDERS OF BLOOD PRESSURE

Abnormal regulation of blood pressure can lead to serious health problems. Among these, hypertension is the most common and clinically significant disorder.

HYPERTENSION

Hypertension is defined as a persistent and consistent elevation of blood pressure, in which systolic and/or diastolic pressures remain above normal limits for a prolonged period.

Hypertension is broadly classified into:

1.     Essential hypertension

2.     Secondary hypertension

Essential Hypertension

Essential hypertension is also known as primary or idiopathic hypertension, as no single identifiable cause can be determined. It accounts for the majority of hypertension cases.

Essential hypertension is further divided into:
a. Benign (chronic) hypertension
b. Malignant (accelerated) hypertension

Benign (Chronic) Hypertension

In benign hypertension, the rise in blood pressure is usually mild to moderate and develops slowly over many years.

In many individuals, the condition remains asymptomatic for a long time. Often, complications such as:

• Heart failure
• Cerebrovascular accident (stroke)
• Myocardial infarction

may be the first clinical signs of hypertension.

Risk factors for benign hypertension include:

• Obesity
• Diabetes mellitus
• Family history
• Cigarette smoking
• Sedentary lifestyle
• High intake of salt or alcohol
• Psychological stress

Stress is known to increase sympathetic activity and may contribute to raised blood pressure.

Malignant (Accelerated) Hypertension

Malignant hypertension is a rapid and severe form of hypertension with a sudden rise in blood pressure.

• Diastolic pressure often exceeds 120 mm Hg
• The condition progresses quickly
• Effects are serious and immediately apparent

Common complications include:

• Retinal haemorrhages
• Papilloedema (swelling around the optic disc)
• Encephalopathy (cerebral oedema)
• Progressive renal disease
• Cardiac failure

Malignant hypertension is a medical emergency requiring urgent treatment.

Secondary Hypertension

Secondary hypertension develops as a result of other underlying diseases and accounts for about 5% of all hypertension cases.

Kidney Disease

Raised blood pressure is a common complication of many kidney disorders.

In kidney disease:

• Salt and water retention occurs
• Excessive renin activity may be present
• Blood volume increases, leading to hypertension

Endocrine Disorders

a)    Adrenal Cortex

Excess secretion of hormones such as aldosterone and cortisol causes:

• Increased sodium and water retention
• Increased blood volume
• Elevated blood pressure

Conditions include:

• Conn’s syndrome (aldosterone-secreting tumour)
• Excess cortisol secretion due to pituitary stimulation or adrenal tumours

b)    Adrenal Medulla

Excess secretion of:

• Adrenaline (epinephrine)
• Noradrenaline (norepinephrine)

leads to marked elevation of blood pressure, as seen in phaeochromocytoma.

Structure of the Aorta

Hypertension may develop in branching arteries proximal to a narrowing or stricture, such as in congenital coarctation of the aorta.

Drug Treatment

Some drugs may cause hypertension as a side effect, including:

• Corticosteroids
• Oral contraceptives

Effects and Complications of Hypertension

Long-standing and progressively rising blood pressure produces serious effects on blood vessels and organs.

The higher the blood pressure and the longer it remains uncontrolled, the greater the damage.

Hypertension promotes atherosclerosis and affects specific organs.

i) Heart

To overcome sustained high arterial pressure:

• The heart increases the rate and force of contraction
• Cardiac workload increases

This leads to:

• Cardiac hypertrophy
• Increased risk of aneurysm formation
• Ischaemic heart disease

ii) Brain

Hypertension commonly causes stroke, often due to cerebral haemorrhage.

Effects depend on:

• Size of the ruptured vessel
• Location of bleeding

Repeated rupture of small vessels (microaneurysms) causes progressive neurological disability.

iii) Kidneys

Essential hypertension causes kidney damage.

• Early damage may be reversible
• Prolonged hypertension leads to progressive loss of kidney function
• Activation of the renin–angiotensin–aldosterone system worsens hypertension
• Ultimately leads to renal failure

iv) Blood Vessels

High blood pressure damages blood vessels by:

• Hardening small arteries
• Accelerating atheroma formation in large arteries

Damage is more severe in individuals with:

• Diabetes mellitus
• Smoking habits

DISORDERS OF CARDIOVASCULAR SYSTEM

1. Heart (Cardiac) Failure

Heart failure occurs when the heart is unable to pump sufficient blood to meet the metabolic needs of the body.

Heart failure may affect:

• Left side of the heart
• Right side of the heart

Because both sides are part of a single circuit, failure of one side often leads to failure of the other.

Left ventricular failure is more common due to the higher workload of the left ventricle.

2. Ischaemic Heart Disease

Ischaemic heart disease (IHD) is also called:

• Coronary artery disease (CAD)
• Coronary heart disease (CHD)

It occurs when blood supply to the heart muscle is reduced or obstructed, usually due to atherosclerosis of coronary arteries.

Reduced oxygen supply leads to:

• Angina pectoris
• Myocardial infarction

a) Angina Pectoris

Angina is often called angina of effort.

It occurs when increased cardiac output during:

• Physical exertion
• Cold exposure
• Emotional stress

causes severe chest pain that may radiate to:

• Arms
• Neck
• Jaw

b) Myocardial Infarction (MI)

Myocardial infarction, commonly known as a heart attack, occurs when blood flow to part of the heart muscle is blocked.

• Usually caused by a blood clot in a coronary artery
• Leads to tissue damage or death

iii) Rheumatic Heart Disease

Rheumatic fever is an inflammatory disease that may follow streptococcal throat infection, especially in children and young adults.

It is an autoimmune disorder, where antibodies damage:

• Heart
• Joints
• Skin

Although death is rare in the acute phase, permanent damage to heart valves may develop later, leading to disability and cardiac failure.

iv) Infective Endocarditis

Infective endocarditis is inflammation of the endocardium and heart valves.

• Common causative agents: bacteria (most common), fungi
• Predisposing factors include:
• Bacteraemia
• Depressed immunity
• Pre-existing heart abnormalities

v) Cardiac Arrhythmias

Cardiac arrhythmias are disorders of heart rate or rhythm caused by abnormal impulse generation or conduction.

Normal sinus rhythm:

• Rate: 60–100 beats per minute

Disruption of electrical activity leads to arrhythmias.

• Atrial fibrillation: rapid, uncoordinated atrial contraction
• Ventricular fibrillation: life-threatening emergency

In ventricular fibrillation:

• Effective pumping stops
• Pulse is absent
• Consciousness is lost
• Death occurs if untreated

vi) Congenital Abnormalities

Congenital abnormalities are structural defects present at birth.

• About 3% of newborns have major malformations
• Cause 20–25% of perinatal deaths
• Major causes of childhood illness and disability

Common congenital disorders include:

• Heart defects
• Neural tube defects
• Down syndrome

Summary Table: Major Cardiovascular Disorders