• Functions of heart,

Functions of the Heart:

The heart is a vital organ responsible for pumping blood throughout the body, ensuring the delivery of oxygen and nutrients and the removal of waste products. Its main functions are as follows:

1. Pumping Blood:
   • The heart pumps oxygen-rich blood from the lungs to the rest of the body through the arteries (systemic circulation).
   • It pumps oxygen-poor blood from the body to the lungs for oxygenation (pulmonary circulation).
2. Maintaining Blood Pressure:
   • By contracting and relaxing, the heart maintains adequate blood pressure to ensure proper blood flow to all tissues and organs.
3. Regulation of Blood Flow:
   • The heart ensures blood is delivered to specific organs and tissues according to their needs by altering the rate and strength of contractions.
4. Receiving Blood:
   • The atria (upper chambers of the heart) receive blood from the body (right atrium) and the lungs (left atrium).
5. Ejecting Blood:
   • The ventricles (lower chambers of the heart) eject blood into the pulmonary artery (right ventricle) and the aorta (left ventricle).
6. Oxygenation of Blood:
   • By circulating blood through the pulmonary arteries and veins, the heart facilitates oxygenation of blood in the lungs.
7. Removal of Carbon Dioxide and Waste:
   • It helps in removing carbon dioxide and metabolic waste products by transporting blood to the lungs and kidneys.
8. Generating Heart Rhythm:
   • The heart generates and maintains its own electrical impulses via the sinoatrial (SA) node, ensuring rhythmic contractions.
9. Facilitating Hormone Transport:
   • The heart enables the transport of hormones such as adrenaline, which regulates cardiac activity and other bodily functions.
10. Thermoregulation:
    • By adjusting blood flow to the skin, the heart helps regulate body temperature.

• conduction system,

Conduction System of the Heart

The heart’s conduction system is responsible for generating and transmitting electrical impulses that coordinate the heart’s rhythmic contractions. This system ensures that the atria and ventricles contract in a synchronized manner to pump blood efficiently.

---

Key Components of the Conduction System:

1. Sinoatrial (SA) Node:
   • Location: Upper wall of the right atrium near the opening of the superior vena cava.
   • Function: Acts as the natural pacemaker of the heart, initiating electrical impulses at a rate of 60–100 beats per minute.
   • Role: Sets the rhythm and rate of the heartbeat (sinus rhythm).
2. Atrioventricular (AV) Node:
   • Location: Lower part of the right atrium near the atrioventricular septum.
   • Function: Receives electrical signals from the SA node and slows them down to allow the atria to fully contract before the ventricles contract.
   • Role: Acts as a gatekeeper to control the signal flow from the atria to the ventricles.
3. Bundle of His (Atrioventricular Bundle):
   • Location: Extends from the AV node into the interventricular septum.
   • Function: Transmits electrical impulses from the AV node to the ventricles.
   • Role: Splits into two branches to direct signals to both the left and right ventricles.
4. Right and Left Bundle Branches:
   • Location: Travel along the interventricular septum.
   • Function: Carry electrical signals to the respective ventricles.
   • Role: Ensures both ventricles receive the impulse for contraction simultaneously.
5. Purkinje Fibers:
   • Location: Spread throughout the ventricular walls and papillary muscles.
   • Function: Conduct electrical impulses rapidly to the ventricular muscle fibers.
   • Role: Triggers the contraction of the ventricles, ejecting blood into the pulmonary artery and aorta.

---

Sequence of Electrical Conduction:

1. The SA node generates an impulse.
2. The impulse spreads across the atria, causing atrial contraction.
3. The impulse reaches the AV node, where it is delayed briefly.
4. The impulse travels down the Bundle of His into the right and left bundle branches.
5. The impulse is distributed through the Purkinje fibers, causing the ventricles to contract.

---

Clinical Relevance:

• Arrhythmias: Irregularities in the conduction system can lead to abnormal heart rhythms.
• Heart Block: Impaired conduction between the SA node and AV node or along the bundle branches.
• Pacemakers: Artificial devices that mimic the function of the SA node in cases of conduction failure.

• cardiac cycle,

Cardiac Cycle

The cardiac cycle refers to the sequence of events that occur in the heart during one complete heartbeat. It involves the coordinated contraction and relaxation of the atria and ventricles to pump blood effectively through the body. A single cardiac cycle lasts approximately 0.8 seconds in a person with a heart rate of 75 beats per minute.

---

Phases of the Cardiac Cycle

The cardiac cycle consists of two main phases: systole (contraction) and diastole (relaxation). These phases occur in both the atria and ventricles.

---

1. Atrial Systole

• Duration: ~0.1 seconds
• Events:
  • The atria contract, pushing blood into the ventricles through the open atrioventricular (AV) valves (tricuspid and mitral).
  • The semilunar valves (pulmonary and aortic) remain closed.
• Significance: Ensures ventricles are completely filled with blood before ventricular contraction.

---

2. Ventricular Systole

• Duration: ~0.3 seconds
• Divided into Two Phases:
  1. Isovolumetric Contraction:
     • The ventricles begin to contract, increasing pressure.
     • All valves (AV and semilunar) are closed, and no blood is ejected.
     • Purpose: Builds sufficient pressure to open the semilunar valves.
  2. Ejection Phase:
     • Once ventricular pressure exceeds that in the pulmonary artery and aorta, the semilunar valves open.
     • Blood is ejected from the right ventricle into the pulmonary artery and from the left ventricle into the aorta.

---

3. Diastole (Relaxation Phase)

• Duration: ~0.4 seconds
• Divided into Two Phases:
  1. Isovolumetric Relaxation:
     • Ventricles relax, and pressure decreases.
     • All valves are closed, preventing backflow of blood.
  2. Filling Phase:
     • As ventricular pressure falls below atrial pressure, the AV valves open.
     • Blood flows passively from the atria into the ventricles.

---

Key Events in the Cardiac Cycle

1. Heart Sounds:
   • First Heart Sound (S1): Closure of AV valves at the start of ventricular systole (“lub”).
   • Second Heart Sound (S2): Closure of semilunar valves at the start of ventricular diastole (“dub”).
2. Pressure Changes:
   • Ventricular pressure rises during systole and falls during diastole.
   • Atrial pressure remains low except during atrial systole.
3. Volume Changes:
   • End-Diastolic Volume (EDV): Volume of blood in the ventricles at the end of diastole (~120 mL).
   • End-Systolic Volume (ESV): Volume of blood remaining in the ventricles after systole (~50 mL).
   • Stroke Volume (SV): Blood ejected by each ventricle during systole (~70 mL).
     • SV = EDV – ESV
4. Electrical Activity:
   • P Wave: Atrial depolarization (atrial systole).
   • QRS Complex: Ventricular depolarization (ventricular systole).
   • T Wave: Ventricular repolarization (ventricular diastole).

---

Duration of the Cardiac Cycle

• Atrial Systole: 0.1 seconds
• Ventricular Systole: 0.3 seconds
• Complete Diastole: 0.4 seconds

---

Clinical Significance

• Arrhythmias: Abnormalities in the cardiac cycle can lead to irregular heart rhythms.
• Heart Failure: Impaired cardiac cycle phases can reduce stroke volume and cardiac output.
• Cardiac Output (CO):
  • CO = Stroke Volume (SV) × Heart Rate (HR)
  • Indicates the amount of blood the heart pumps per minute.

• Stroke volume and cardiac output

Stroke Volume (SV)

Definition:

Stroke volume is the amount of blood ejected by a ventricle during each heartbeat.

Normal Values:

• Resting SV: Approximately 70 mL per beat in an average adult.

Formula:

Stroke Volume (SV)=End-Diastolic Volume (EDV)−End-Systolic Volume (ESV)\text{Stroke Volume (SV)} = \text{End-Diastolic Volume (EDV)} – \text{End-Systolic Volume (ESV)}Stroke Volume (SV)=End-Diastolic Volume (EDV)−End-Systolic Volume (ESV)

Where:

• EDV: The volume of blood in the ventricle at the end of diastole (~120 mL).
• ESV: The volume of blood remaining in the ventricle after systole (~50 mL).

Factors Affecting Stroke Volume:

1. Preload:
   • The amount of blood in the ventricles at the end of diastole.
   • Influenced by venous return and ventricular filling.
2. Contractility:
   • The strength of the ventricular contraction.
   • Enhanced by sympathetic stimulation or medications like inotropes.
3. Afterload:
   • The resistance the ventricles must overcome to eject blood.
   • Increased afterload (e.g., hypertension) reduces stroke volume.

---

Cardiac Output (CO)

Definition:

Cardiac output is the total volume of blood pumped by the heart per minute.

Normal Values:

• Resting CO: Approximately 4–6 liters per minute in an average adult.

Formula:

Cardiac Output (CO)=Stroke Volume (SV)×Heart Rate (HR)\text{Cardiac Output (CO)} = \text{Stroke Volume (SV)} \times \text{Heart Rate (HR)}Cardiac Output (CO)=Stroke Volume (SV)×Heart Rate (HR)

Example Calculation:

• SV = 70 mL/beat
• HR = 75 beats/minute

CO=70 mL×75 beats/min=5250 mL/min=5.25 L/min\text{CO} = 70 \, \text{mL} \times 75 \, \text{beats/min} = 5250 \, \text{mL/min} = 5.25 \, \text{L/min}CO=70mL×75beats/min=5250mL/min=5.25L/min

---

Factors Affecting Cardiac Output:

1. Heart Rate:
   • Increased HR (e.g., during exercise) raises CO.
   • Excessively high HR may reduce CO by limiting ventricular filling time.
2. Stroke Volume:
   • Changes in preload, afterload, or contractility affect SV, thus altering CO.
3. Physical Activity:
   • Increases HR and SV, leading to higher CO during exercise.
4. Age:
   • CO may decrease with age due to reduced cardiac efficiency.
5. Health Conditions:
   • Conditions like heart failure, arrhythmias, or myocardial infarction can decrease CO.

---

Clinical Relevance:

1. Low CO:
   • Symptoms: Fatigue, hypotension, organ hypoperfusion.
   • Causes: Heart failure, bradycardia, myocardial infarction.
2. High CO:
   • Symptoms: Tachycardia, palpitations.
   • Causes: Fever, anemia, hyperthyroidism.
3. Cardiac Index (CI):
   • CO normalized to body surface area.
   • Formula: CI=COBody Surface Area (BSA)\text{CI} = \frac{\text{CO}}{\text{Body Surface Area (BSA)}}CI=Body Surface Area (BSA)CO​
   • Normal Value: 2.5–4.0 L/min/m².

• Blood pressure and Pulse

Blood Pressure (BP)

Definition:

Blood pressure is the force exerted by circulating blood on the walls of blood vessels. It is a vital sign that reflects the efficiency of the heart and the state of the vascular system.

---

Components:

1. Systolic Blood Pressure (SBP):
   • The pressure in the arteries during ventricular systole (contraction).
   • Normal value: 120 mmHg (varies with age, activity, and health).
2. Diastolic Blood Pressure (DBP):
   • The pressure in the arteries during ventricular diastole (relaxation).
   • Normal value: 80 mmHg (varies with age, activity, and health).

---

Measurement:

• Units: Millimeters of mercury (mmHg).
• Example: 120/80 mmHg (SBP/DBP).

---

Factors Influencing Blood Pressure:

1. Cardiac Output (CO): Higher CO increases BP.
2. Peripheral Resistance: Resistance in blood vessels affects BP.
3. Blood Volume: Greater blood volume raises BP.
4. Elasticity of Arteries: Loss of elasticity (e.g., in atherosclerosis) increases BP.
5. Health Conditions: Hypertension, hypotension, shock, etc.

---

Classification of BP (for adults):

Category	Systolic (mmHg)	Diastolic (mmHg)
Normal	< 120	< 80
Elevated	120–129	< 80
Hypertension Stage 1	130–139	80–89
Hypertension Stage 2	≥ 140	≥ 90
Hypertensive Crisis	> 180	> 120

---

Pulse

Definition:

The pulse is the rhythmic expansion and recoil of arteries due to the pumping action of the heart, felt at specific points in the body.

---

Pulse Characteristics:

1. Rate:
   • The number of beats per minute (bpm).
   • Normal resting pulse: 60–100 bpm.
2. Rhythm:
   • Regular or irregular heartbeat.
3. Volume:
   • The strength of the pulse (e.g., weak, thready, bounding).
4. Equality:
   • Symmetry between pulses on both sides of the body.

---

Pulse Sites:

1. Radial Artery (wrist) – Most common.
2. Carotid Artery (neck).
3. Brachial Artery (elbow).
4. Femoral Artery (groin).
5. Popliteal Artery (behind the knee).
6. Dorsalis Pedis Artery (foot).
7. Apical Pulse (over the heart, measured with a stethoscope).

---

Factors Influencing Pulse:

1. Age: Infants have faster pulses; rates decrease with age.
2. Activity: Exercise increases the pulse rate.
3. Emotions: Stress or anxiety raises the pulse.
4. Health Conditions: Fever, dehydration, arrhythmias, etc.
5. Medications: Beta-blockers slow the pulse; stimulants increase it.

---

Clinical Relevance:

• Tachycardia: Pulse > 100 bpm (e.g., in fever, stress).
• Bradycardia: Pulse < 60 bpm (e.g., in athletes, hypothyroidism).
• Pulse Deficit: Difference between apical and radial pulse, indicating poor cardiac output.

---

• Circulation- principles,

Circulation Principles

Circulation is the continuous movement of blood through the heart, blood vessels, and tissues to deliver oxygen and nutrients and remove waste products. It is essential for maintaining homeostasis and supporting life.

---

Principles of Circulation

1. Double Circulation

The human circulatory system is a double circulation system, meaning blood passes through the heart twice during one complete cycle:

• Pulmonary Circulation:
  • Carries deoxygenated blood from the right side of the heart to the lungs for oxygenation.
  • Oxygenated blood returns to the left side of the heart.
• Systemic Circulation:
  • Pumps oxygenated blood from the left side of the heart to all body tissues.
  • Returns deoxygenated blood to the right side of the heart.

---

2. Blood Flow

• Blood flows from areas of high pressure to areas of low pressure.
• Pressure Gradients:
  • Created by the heart’s pumping action and maintained by arterial elasticity.
  • Ensures unidirectional blood flow.

---

3. Cardiac Output

The volume of blood ejected by the heart per minute determines circulation efficiency.

• Formula: Cardiac Output (CO)=Stroke Volume (SV)×Heart Rate (HR)\text{Cardiac Output (CO)} = \text{Stroke Volume (SV)} \times \text{Heart Rate (HR)}Cardiac Output (CO)=Stroke Volume (SV)×Heart Rate (HR)
• Factors affecting cardiac output include heart rate, stroke volume, contractility, and venous return.

---

4. Blood Pressure Regulation

Blood pressure drives circulation and is influenced by:

• Cardiac Output: Higher CO increases blood pressure.
• Peripheral Resistance: Narrower blood vessels increase resistance and blood pressure.
• Blood Volume: Larger blood volume increases pressure.
• Hormonal Regulation: Hormones like adrenaline and angiotensin influence vessel tone and blood volume.

---

5. Vessel Types and Functions

• Arteries: Carry oxygenated blood away from the heart (except pulmonary arteries).
• Capillaries: Allow exchange of gases, nutrients, and waste products at the tissue level.
• Veins: Return deoxygenated blood to the heart (except pulmonary veins).
• Principle of Elasticity: Arteries are elastic to absorb pressure fluctuations; veins are distensible to store blood.

---

6. Venous Return

• The return of blood to the heart is critical for maintaining cardiac output.
• Factors influencing venous return:
  • Skeletal Muscle Pump: Contraction of muscles compresses veins.
  • Respiratory Pump: Changes in thoracic pressure during breathing facilitate blood return.
  • Venous Valves: Prevent backflow and ensure unidirectional flow.

---

7. Oxygen and Carbon Dioxide Transport

• Oxygen is transported via hemoglobin in red blood cells.
• Carbon dioxide is transported as:
  • Dissolved CO2_22​ in plasma.
  • Bicarbonate ions (HCO3−_3^-3−​).
  • Carbaminohemoglobin (bound to hemoglobin).

---

8. Exchange of Materials

• Occurs at the capillary level.
• Mechanisms:
  • Diffusion: Movement of gases and small molecules.
  • Filtration: Movement of fluid out of capillaries.
  • Osmosis: Reabsorption of fluid into capillaries.

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9. Circulatory Pathways

• Pulmonary Circuit: Right heart → Lungs → Left heart.
• Systemic Circuit: Left heart → Body → Right heart.
• Coronary Circulation: Supplies the heart muscle itself.
• Portal Circulation: Blood flow through the hepatic portal system, processing nutrients absorbed from the gastrointestinal tract.

---

Key Factors Maintaining Circulation

1. Heart Function:
   • Acts as a pump to create pressure gradients.
2. Blood Volume:
   • Adequate blood volume ensures proper filling of vessels.
3. Vascular Resistance:
   • Determined by vessel diameter and blood viscosity.
4. Valves:
   • Prevent backflow and maintain unidirectional flow in veins.
5. Autonomic Nervous System (ANS):
   • Sympathetic and parasympathetic control heart rate and vessel tone.

---

Clinical Relevance

• Shock: Circulatory failure leading to inadequate tissue perfusion.
• Hypertension: Chronic high blood pressure, stressing the cardiovascular system.
• Heart Failure: Impaired cardiac output affects circulation.
• Varicose Veins: Dysfunction of venous valves, leading to blood pooling.

• factors influencing blood pressure,

Factors Influencing Blood Pressure

Blood pressure (BP) is influenced by a combination of physiological, environmental, and lifestyle factors. It reflects the force exerted by circulating blood on the walls of blood vessels and is regulated by complex mechanisms.

---

1. Cardiac Output (CO)

• Definition: The volume of blood pumped by the heart per minute.
• Impact on BP:
  • Increased CO (e.g., during exercise or stress) raises BP.
  • Decreased CO (e.g., in heart failure) lowers BP.
• Formula: Cardiac Output (CO)=Stroke Volume (SV)×Heart Rate (HR)\text{Cardiac Output (CO)} = \text{Stroke Volume (SV)} \times \text{Heart Rate (HR)}Cardiac Output (CO)=Stroke Volume (SV)×Heart Rate (HR)

---

2. Peripheral Vascular Resistance (PVR)

• Definition: The resistance blood encounters as it flows through blood vessels.
• Impact on BP:
  • Vasoconstriction (narrowing of blood vessels) increases resistance, raising BP.
  • Vasodilation (widening of blood vessels) decreases resistance, lowering BP.
• Influenced by:
  • Blood vessel diameter.
  • Blood viscosity.
  • Total vessel length.

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3. Blood Volume

• Definition: The total amount of blood circulating in the body.
• Impact on BP:
  • Increased blood volume (e.g., fluid retention) raises BP.
  • Decreased blood volume (e.g., dehydration) lowers BP.

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4. Elasticity of Arteries

• Healthy Arteries: Elastic arteries absorb pressure fluctuations, maintaining normal BP.
• Atherosclerosis: Stiff or narrowed arteries reduce elasticity, increasing systolic BP.

---

5. Hormonal Regulation

• Renin-Angiotensin-Aldosterone System (RAAS):
  • Increases blood volume and constricts blood vessels, raising BP.
• Adrenaline and Noradrenaline:
  • Increase heart rate and vasoconstriction, elevating BP.
• Antidiuretic Hormone (ADH):
  • Promotes water retention, increasing blood volume and BP.

---

6. Neural Regulation

• Sympathetic Nervous System (SNS):
  • Activates vasoconstriction and increases heart rate, raising BP.
• Parasympathetic Nervous System (PNS):
  • Reduces heart rate and promotes vasodilation, lowering BP.

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7. Age

• BP increases with age due to reduced arterial elasticity and increased peripheral resistance.

---

8. Gender

• Before menopause: Women generally have lower BP due to protective effects of estrogen.
• After menopause: BP increases due to hormonal changes.

---

9. Lifestyle Factors

1. Physical Activity:
   • Regular exercise lowers resting BP.
   • Sedentary lifestyle increases BP.
2. Diet:
   • High salt intake raises BP.
   • Potassium, calcium, and magnesium can help lower BP.
3. Obesity:
   • Increases workload on the heart and raises BP.
4. Smoking and Alcohol:
   • Smoking causes vasoconstriction, increasing BP.
   • Excessive alcohol raises BP.

---

10. Emotional and Psychological Factors

• Stress, anxiety, and depression can increase BP by stimulating the SNS.

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11. Medical Conditions

• Hypertension: Chronic high BP damages blood vessels.
• Diabetes: Can increase BP by affecting blood vessel health.
• Kidney Disease: Alters blood volume and RAAS function, affecting BP.

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12. Medications

• Increase BP: Corticosteroids, decongestants, and certain stimulants.
• Decrease BP: Antihypertensives, diuretics, and beta-blockers.

---

13. Environmental Factors

• Temperature: Cold weather increases BP (vasoconstriction), while warm weather decreases it (vasodilation).
• Altitude: High altitudes can initially increase BP due to lower oxygen levels.

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14. Genetic Factors

• Family history of hypertension predisposes individuals to high BP.

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15. Time of Day (Circadian Rhythm)

• BP is typically lower at night and higher in the morning.

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• pulse

Pulse

Definition:

The pulse is the rhythmic expansion and recoil of arteries resulting from the contraction of the heart. It reflects the heartbeat and can be felt at various points in the body where arteries lie close to the skin.

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Characteristics of Pulse

1. Rate:
   • The number of beats per minute (bpm).
   • Normal resting rate:
     • Adults: 60–100 bpm.
     • Children: 80–120 bpm.
     • Infants: 100–160 bpm.
   • Abnormalities:
     • Tachycardia: Pulse > 100 bpm (e.g., fever, stress).
     • Bradycardia: Pulse < 60 bpm (e.g., in athletes, hypothyroidism).
2. Rhythm:
   • The regularity of the pulse.
   • Normal: Regular rhythm.
   • Abnormal: Irregular rhythm (e.g., arrhythmias, atrial fibrillation).
3. Volume/Amplitude:
   • The strength or force of the pulse.
   • Descriptions:
     • Bounding: Strong, forceful pulse (e.g., fever, hypertension).
     • Weak/Thready: Faint pulse (e.g., shock, dehydration).
4. Equality:
   • Symmetry between pulses on both sides of the body.
   • Differences may indicate vascular obstruction or circulatory issues.
5. Tension:
   • The pressure required to obliterate the pulse.
   • High tension may indicate hypertension.
6. Condition of Arterial Wall:
   • Elasticity of the artery.
   • Hardening of the arterial wall (e.g., atherosclerosis) can affect pulse feel.

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Pulse Points in the Body

1. Peripheral Pulse Points:
   • Radial Artery: At the wrist, commonly used.
   • Brachial Artery: Inside the elbow, used in children.
   • Carotid Artery: In the neck, used in emergencies.
   • Femoral Artery: In the groin, for central circulation assessment.
   • Popliteal Artery: Behind the knee.
   • Dorsalis Pedis Artery: Top of the foot.
   • Posterior Tibial Artery: Inside the ankle.
2. Central Pulse:
   • Apical Pulse: Located at the apex of the heart, assessed using a stethoscope.

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Factors Influencing Pulse

1. Physiological Factors:
   • Age: Pulse is higher in infants and decreases with age.
   • Gender: Women tend to have a slightly higher pulse rate than men.
2. Activity:
   • Exercise increases pulse rate temporarily.
   • Regular physical activity may lower resting pulse rate.
3. Emotional State:
   • Stress, anxiety, or excitement can elevate the pulse.
4. Health Conditions:
   • Fever, dehydration, and shock can increase pulse.
   • Hypothyroidism or heart block can lower pulse.
5. Medications:
   • Stimulants (e.g., caffeine) increase pulse.
   • Beta-blockers reduce pulse rate.
6. Temperature:
   • Fever raises pulse rate.
   • Hypothermia decreases pulse rate.
7. Body Position:
   • Standing may temporarily raise pulse compared to lying down.
8. Cardiac Output:
   • Low cardiac output (e.g., in heart failure) may lead to a weak, thready pulse.

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Pulse Abnormalities

1. Tachycardia:
   • Fast pulse rate > 100 bpm.
   • Causes: Fever, anemia, dehydration, stress.
2. Bradycardia:
   • Slow pulse rate < 60 bpm.
   • Causes: Athletic conditioning, hypothyroidism, heart block.
3. Irregular Pulse:
   • Causes: Arrhythmias, electrolyte imbalances.
4. Pulse Deficit:
   • Difference between apical and radial pulse.
   • Indicates poor cardiac output (e.g., in atrial fibrillation).

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Clinical Relevance

• Pulse Monitoring: Essential in assessing cardiovascular health.
• Shock: A weak or thready pulse is an early sign.
• Hypertension: May present with a bounding pulse.
• Heart Failure: Pulse abnormalities can help diagnose severity.

• Coronary circulation

Coronary Circulation

Definition:

Coronary circulation is the blood supply system of the heart itself. It delivers oxygenated blood to the heart muscle (myocardium) and removes deoxygenated blood and waste products, ensuring the heart’s continuous function.

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Components of Coronary Circulation

1. Coronary Arteries

The coronary arteries branch from the aorta and supply oxygen-rich blood to the myocardium. They are divided into:

1. Left Coronary Artery (LCA):
   • Left Anterior Descending (LAD) Artery:
     • Supplies blood to the front of the left ventricle, anterior interventricular septum, and apex.
   • Circumflex (LCx) Artery:
     • Supplies blood to the lateral and posterior walls of the left ventricle and the left atrium.
2. Right Coronary Artery (RCA):
   • Supplies blood to the right atrium, right ventricle, sinoatrial (SA) node, and atrioventricular (AV) node.
   • Posterior Descending Artery (PDA):
     • Supplies the posterior interventricular septum and inferior part of the ventricles.

2. Coronary Veins

The coronary veins drain deoxygenated blood from the myocardium into the right atrium. Key veins include:

• Great Cardiac Vein: Runs alongside the LAD artery.
• Middle Cardiac Vein: Runs alongside the PDA.
• Small Cardiac Vein: Drains blood from the right side of the heart.
• Coronary Sinus: The main venous channel that empties into the right atrium.

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Pathway of Coronary Circulation

1. Oxygenated Blood Flow:
   • Originates from the left and right coronary arteries, which branch from the aortic root.
   • Arteries deliver oxygen-rich blood to the myocardium.
2. Deoxygenated Blood Flow:
   • Deoxygenated blood from the myocardium is collected by coronary veins.
   • Blood flows into the coronary sinus and drains into the right atrium.

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Characteristics of Coronary Circulation

1. Blood Flow During Diastole:
   • Coronary arteries primarily receive blood during diastole (heart relaxation) due to reduced compression of vessels.
2. High Oxygen Demand:
   • The heart extracts approximately 70–80% of oxygen from coronary blood, compared to 25% in other tissues.
3. Regulation of Blood Flow:
   • Coronary blood flow adjusts to meet the metabolic demands of the myocardium.
   • Mediated by:
     • Nitric Oxide (vasodilation).
     • Adenosine (metabolic regulation).

---

Clinical Importance

1. Coronary Artery Disease (CAD):
   • Narrowing or blockage of coronary arteries due to atherosclerosis.
   • Leads to ischemia (reduced blood flow) and can cause angina or myocardial infarction (heart attack).
2. Myocardial Infarction (Heart Attack):
   • Occurs when blood flow through a coronary artery is completely blocked.
   • Results in the death of myocardial tissue.
3. Angina Pectoris:
   • Chest pain due to temporary reduced blood flow to the myocardium.
4. Coronary Angiography:
   • Imaging technique to visualize coronary arteries and detect blockages.
5. Bypass Surgery:
   • Coronary Artery Bypass Grafting (CABG) involves creating alternate pathways for blood flow using grafts.

---

Factors Affecting Coronary Circulation

1. Heart Rate:
   • Increased heart rate reduces diastolic time, decreasing coronary perfusion.
2. Atherosclerosis:
   • Reduces arterial diameter and impairs blood flow.
3. Vasospasm:
   • Sudden constriction of coronary arteries can lead to ischemia.
4. Hypertension:
   • Increases the workload of the heart, demanding more coronary blood flow.

---

• Pulmonary and systemic circulation

Pulmonary and Systemic Circulation

The circulatory system is divided into two main circuits: pulmonary circulation and systemic circulation, working together to ensure efficient oxygenation of blood and its distribution throughout the body.

---

1. Pulmonary Circulation

Pulmonary circulation involves the movement of blood between the heart and the lungs for oxygenation.

Pathway of Pulmonary Circulation:

1. Deoxygenated Blood:
   • Blood from the body enters the right atrium via the superior and inferior vena cava.
   • It flows into the right ventricle through the tricuspid valve.
   • The right ventricle pumps blood into the pulmonary artery through the pulmonary valve.
2. Gas Exchange in Lungs:
   • In the lungs, blood passes through pulmonary capillaries.
   • Carbon dioxide (CO₂) is released, and oxygen (O₂) is absorbed.
3. Oxygenated Blood:
   • Oxygenated blood returns to the left atrium via the pulmonary veins.
   • It is then pumped into the systemic circulation.

Key Features:

• Purpose: Oxygenate deoxygenated blood and remove CO₂.
• Pressure: Low-pressure system to protect delicate lung capillaries.
• Vessels:
  • Pulmonary artery: Carries deoxygenated blood.
  • Pulmonary veins: Carry oxygenated blood.

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2. Systemic Circulation

Systemic circulation distributes oxygen-rich blood from the heart to the rest of the body and returns deoxygenated blood to the heart.

Pathway of Systemic Circulation:

1. Oxygenated Blood:
   • Blood from the left atrium enters the left ventricle through the mitral valve.
   • The left ventricle pumps blood into the aorta through the aortic valve.
2. Distribution to Body:
   • Blood travels through arteries, arterioles, and capillaries, delivering oxygen and nutrients to tissues.
3. Deoxygenated Blood:
   • Blood collects waste products and CO₂ from tissues.
   • It returns to the heart via veins and enters the right atrium through the superior and inferior vena cava.

Key Features:

• Purpose: Deliver oxygen and nutrients to tissues and remove waste products.
• Pressure: High-pressure system to pump blood throughout the body.
• Vessels:
  • Arteries: Carry oxygenated blood (except pulmonary arteries).
  • Veins: Carry deoxygenated blood (except pulmonary veins).

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Comparison of Pulmonary and Systemic Circulation

Aspect	Pulmonary Circulation	Systemic Circulation
Purpose	Oxygenates blood in the lungs	Delivers oxygen to tissues
Blood Flow Path	Heart → Lungs → Heart	Heart → Body → Heart
Type of Blood	Pulmonary artery: Deoxygenated	Arteries: Oxygenated
	Pulmonary veins: Oxygenated	Veins: Deoxygenated
Pressure	Low pressure	High pressure
Vessels	Pulmonary artery and veins	Systemic arteries and veins
Location	Between heart and lungs	Between heart and body

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Integrated Function of Both Circulations

1. Right Heart (Pulmonary Pump):
   • Receives deoxygenated blood from the body and sends it to the lungs for oxygenation.
2. Left Heart (Systemic Pump):
   • Receives oxygenated blood from the lungs and pumps it to the body.

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Clinical Relevance

1. Pulmonary Hypertension:
   • Elevated pressure in the pulmonary arteries, leading to right heart strain.
2. Heart Failure:
   • Left-sided failure affects systemic circulation, causing pulmonary congestion.
   • Right-sided failure affects pulmonary circulation, leading to systemic edema.
3. Shock:
   • Systemic circulation inadequacy results in insufficient tissue perfusion.

• Heart rate-regulation of heart rate,

Heart Rate and Its Regulation

Heart Rate (HR):

Heart rate is the number of times the heart beats per minute (bpm). It reflects the activity of the heart and is a vital indicator of cardiovascular health.

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Normal Heart Rate Ranges:

• Adults: 60–100 bpm (resting).
• Athletes: May have resting HR < 60 bpm due to higher cardiac efficiency.
• Children and Infants: Higher HR, varying with age:
  • Newborns: 100–160 bpm.
  • Children (6–15 years): 70–100 bpm.

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Regulation of Heart Rate

Heart rate is regulated by intrinsic and extrinsic mechanisms to meet the body’s demands. These mechanisms involve the autonomic nervous system, hormones, and other factors.

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1. Intrinsic Regulation (Pacemaker Activity):

• The sinoatrial (SA) node, the natural pacemaker of the heart, generates electrical impulses at a basic rate of 60–100 bpm.
• Factors affecting the SA node’s activity:
  • Automaticity: Ability of cardiac cells to generate impulses.
  • Ion Channels: Changes in sodium, potassium, and calcium ion permeability influence depolarization.

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2. Extrinsic Regulation:

External factors modify the intrinsic heart rate based on physiological needs.

a. Nervous System Regulation:

The autonomic nervous system (ANS) plays a key role:

1. Sympathetic Nervous System (SNS):
   • Releases norepinephrine.
   • Increases heart rate (positive chronotropic effect).
   • Mechanism:
     • Stimulates β1_11​-adrenergic receptors in the SA node.
     • Enhances depolarization and conduction velocity.
2. Parasympathetic Nervous System (PNS):
   • Releases acetylcholine via the vagus nerve.
   • Decreases heart rate (negative chronotropic effect).
   • Mechanism:
     • Stimulates muscarinic receptors in the SA node.
     • Slows depolarization, reducing impulse generation.

b. Hormonal Regulation:

1. Adrenaline (Epinephrine):
   • Released from the adrenal medulla during stress or exercise.
   • Increases heart rate by stimulating β1_11​-adrenergic receptors.
2. Thyroid Hormones:
   • Increase heart rate by enhancing the sensitivity of the heart to catecholamines.

c. Baroreceptor Reflex:

• Baroreceptors in the carotid sinus and aortic arch detect changes in blood pressure.
• Low BP: Stimulates SNS → Increases HR.
• High BP: Stimulates PNS → Decreases HR.

d. Chemoreceptor Reflex:

• Chemoreceptors in the carotid and aortic bodies respond to changes in oxygen (O2_22​), carbon dioxide (CO2_22​), and pH levels.
• High CO2_22​ or Low O2_22​: Increases HR via SNS stimulation to enhance oxygen delivery.

e. Temperature:

• Increased body temperature: Increases HR (e.g., during fever).
• Decreased body temperature: Lowers HR.

f. Physical Activity:

• Exercise increases HR to meet the elevated oxygen demand of muscles.

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3. Other Factors Influencing Heart Rate:

1. Age:
   • HR decreases with age due to reduced responsiveness of the heart to stimulation.
2. Gender:
   • Women tend to have a slightly higher resting HR than men.
3. Medications:
   • Beta-blockers: Decrease HR by blocking β1_11​-adrenergic receptors.
   • Atropine: Increases HR by inhibiting PNS activity.
4. Electrolyte Levels:
   • Potassium and Calcium imbalances affect depolarization and HR.
5. Emotional State:
   • Stress, anxiety, or excitement can elevate HR.

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Abnormalities in Heart Rate

1. Tachycardia:
   • HR > 100 bpm.
   • Causes: Stress, fever, anemia, hyperthyroidism, dehydration.
2. Bradycardia:
   • HR < 60 bpm.
   • Causes: Athletic conditioning, hypothyroidism, heart block.
3. Arrhythmias:
   • Irregular heart rates due to electrical conduction issues.

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Clinical Relevance

• Monitoring HR helps assess cardiac function and response to treatment.
• Disorders like atrial fibrillation or sinus bradycardia require regulation through medications or devices (e.g., pacemakers).

• Normal value and variations

Normal Values and Variations of Heart Rate

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Normal Resting Heart Rate:

• Adults: 60–100 beats per minute (bpm).
• Athletes: May have a resting HR as low as 40–60 bpm due to high cardiac efficiency.
• Children:
  • Newborns: 100–160 bpm.
  • Infants (1–12 months): 90–140 bpm.
  • Toddlers (1–3 years): 80–130 bpm.
  • Preschoolers (3–5 years): 80–120 bpm.
  • School-age children (6–15 years): 70–100 bpm.

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Normal Values by Conditions:

1. During Exercise:
   • Increases depending on the intensity of physical activity.
   • Maximum HR: Approximately 220 – age (e.g., for a 30-year-old: 220 – 30 = 190 bpm).
2. During Sleep:
   • HR decreases to 50–70 bpm due to reduced metabolic demand.
3. Emotional Stress:
   • HR can rise above normal during anxiety, excitement, or fear.

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Variations in Heart Rate

Heart rate can vary due to physiological, pathological, and external factors.

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1. Physiological Variations:

1. Age:
   • Newborns and Infants: Higher HR due to smaller heart size and higher metabolic rate.
   • Elderly: May have a slightly lower HR due to decreased SA node efficiency.
2. Physical Fitness:
   • Well-trained athletes have lower resting HR (40–60 bpm) due to enhanced stroke volume.
3. Body Position:
   • Standing: Slight increase in HR compared to lying down due to gravitational effects.
4. Gender:
   • Women tend to have slightly higher HR than men.
5. Circadian Rhythm:
   • HR is typically lower in the morning and higher in the afternoon and evening.

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2. Pathological Variations:

1. Tachycardia:
   • HR > 100 bpm (in adults).
   • Causes: Fever, anemia, hyperthyroidism, dehydration, stress, or arrhythmias.
2. Bradycardia:
   • HR < 60 bpm (in adults).
   • Causes: Hypothyroidism, heart block, use of beta-blockers, or extreme fitness.
3. Arrhythmias:
   • Irregular HR due to conduction issues, such as atrial fibrillation.

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3. External Factors Affecting HR:

1. Exercise:
   • Temporarily increases HR to meet oxygen demand.
2. Temperature:
   • Heat: Increases HR due to vasodilation and increased metabolic demand.
   • Cold: Decreases HR due to vasoconstriction.
3. Medications:
   • Stimulants: (e.g., caffeine, nicotine) increase HR.
   • Depressants: (e.g., beta-blockers, sedatives) decrease HR.
4. Stress and Emotions:
   • Anxiety, excitement, or fear stimulate the sympathetic nervous system, raising HR.
5. Hydration Status:
   • Dehydration can increase HR to maintain cardiac output.

• Cardiovascular homeostasis in exercise and posture

Cardiovascular Homeostasis in Exercise and Posture

The cardiovascular system plays a crucial role in maintaining homeostasis by ensuring adequate blood flow, oxygen delivery, and waste removal. It adapts dynamically to changing demands, such as during exercise or posture changes.

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Cardiovascular Homeostasis During Exercise

Exercise significantly increases the body’s demand for oxygen and nutrients, requiring adjustments in the cardiovascular system.

Key Changes During Exercise:

1. Increased Heart Rate (HR):
   • Sympathetic nervous system (SNS) activation increases HR to enhance cardiac output.
2. Increased Stroke Volume (SV):
   • Venous return improves due to the skeletal muscle pump and respiratory pump.
   • Enhanced myocardial contractility leads to greater SV.
3. Increased Cardiac Output (CO):
   • CO=HR×SV\text{CO} = \text{HR} \times \text{SV}CO=HR×SV
   • Can increase 4–6 times during intense exercise.
4. Redistribution of Blood Flow:
   • Blood is diverted away from non-essential organs (e.g., digestive system) to working muscles.
   • Vasodilation in muscles increases blood supply.
5. Increased Blood Pressure:
   • Systolic BP rises due to increased CO.
   • Diastolic BP remains relatively stable or slightly decreases.

Regulation Mechanisms:

1. Autonomic Nervous System (ANS):
   • Sympathetic stimulation enhances HR, contractility, and vasodilation in active muscles.
   • Parasympathetic withdrawal also increases HR.
2. Local Metabolic Control:
   • Accumulation of CO₂, lactic acid, and adenosine in active muscles causes vasodilation.
3. Baroreceptor Adjustment:
   • Baroreceptors reset to a higher operating point during exercise to accommodate elevated BP.
4. Hormonal Response:
   • Adrenaline and noradrenaline released by the adrenal medulla enhance cardiovascular function.

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Cardiovascular Homeostasis During Posture Changes

Changing posture (e.g., lying down to standing) causes shifts in blood distribution due to gravity, requiring the cardiovascular system to adapt rapidly.

Key Changes:

1. Blood Pooling in Lower Extremities:
   • On standing, gravity causes blood to pool in veins of the legs.
   • Reduces venous return and cardiac output temporarily.
2. Drop in Blood Pressure:
   • This initial drop is called orthostatic hypotension.
3. Compensatory Mechanisms:
   • Activation of baroreceptors in the carotid sinus and aortic arch.
   • Increased SNS activity raises HR and vasoconstriction to restore BP.

Regulation Mechanisms:

1. Baroreceptor Reflex:
   • Detects changes in BP and signals the brain to adjust HR and vascular resistance.
2. Skeletal Muscle Pump:
   • Muscle contractions compress veins, aiding venous return.
3. Respiratory Pump:
   • Deep breathing creates negative thoracic pressure, improving venous return.
4. Autonomic Nervous System:
   • Sympathetic activation increases HR and vasoconstriction.
   • Parasympathetic withdrawal supports these changes.

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Comparison: Exercise vs. Posture Changes

Parameter	Exercise	Posture Changes
Heart Rate	Increases significantly	Increases slightly upon standing
Stroke Volume	Increases due to enhanced venous return	Decreases initially when standing
Cardiac Output	Increases dramatically	Restored to normal quickly by reflexes
Blood Pressure	Systolic increases; diastolic stable	Initial drop; reflex mechanisms stabilize
Vascular Changes	Vasodilation in muscles	Vasoconstriction in lower extremities

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• Aging changes

Aging-Related Changes in the Cardiovascular System

As individuals age, the cardiovascular system undergoes structural and functional changes. These changes can impact the heart, blood vessels, and overall circulatory efficiency, increasing the risk of cardiovascular diseases.

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1. Structural Changes in the Heart

1. Increased Heart Size:
   • The left ventricle may thicken (hypertrophy) due to increased workload, often caused by elevated blood pressure or vascular resistance.
2. Decreased Elasticity of Myocardium:
   • The heart muscle becomes less compliant, reducing its ability to relax and fill properly during diastole.
3. Calcification of Heart Valves:
   • Aortic and mitral valves may thicken or stiffen, leading to stenosis or regurgitation.
4. Reduced Number of Pacemaker Cells:
   • Loss of cells in the sinoatrial (SA) node slows intrinsic heart rate, increasing the likelihood of arrhythmias.
5. Fibrosis in Cardiac Tissue:
   • Increased fibrotic tissue in the myocardium reduces contractility and electrical conduction efficiency.

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2. Functional Changes in the Heart

1. Slower Heart Rate:
   • Decreased responsiveness of the SA node and reduced sympathetic activity.
2. Reduced Cardiac Output:
   • Decreased stroke volume and slower heart rate lead to lower cardiac output, especially during stress or exercise.
3. Prolonged Recovery Time:
   • The heart takes longer to return to resting state after exertion.

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3. Changes in Blood Vessels

1. Arterial Stiffness:
   • Loss of elasticity in arteries (arteriosclerosis) increases vascular resistance and systolic blood pressure.
2. Increased Blood Pressure:
   • Higher systolic BP is common, leading to isolated systolic hypertension.
3. Thickening of Vessel Walls:
   • Intimal and medial layers of blood vessels thicken, reducing lumen diameter and impairing blood flow.
4. Impaired Endothelial Function:
   • Reduced nitric oxide production limits vasodilation, affecting blood flow regulation.
5. Vein Changes:
   • Veins may dilate, and valve efficiency decreases, contributing to conditions like varicose veins.

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4. Changes in Blood Composition

1. Decreased Hematopoietic Activity:
   • Bone marrow produces fewer red blood cells, increasing the risk of anemia.
2. Increased Coagulation Tendency:
   • Platelet activity and clotting factor levels may rise, raising the risk of thrombosis.
3. Reduced Plasma Volume:
   • Leads to reduced total blood volume in some older adults.

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5. Autonomic Nervous System Changes

1. Reduced Baroreceptor Sensitivity:
   • Slower response to changes in blood pressure, increasing the risk of orthostatic hypotension.
2. Blunted Sympathetic Response:
   • Less efficient regulation of heart rate and vascular tone during stress or exercise.

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6. Impacts on Circulation

1. Decreased Exercise Tolerance:
   • Reduced ability to increase cardiac output and oxygen delivery to muscles during activity.
2. Slower Healing and Recovery:
   • Limited perfusion delays tissue repair and recovery after injury.
3. Increased Risk of Atherosclerosis:
   • Plaque buildup in arteries narrows the lumen, leading to coronary artery disease and peripheral arterial disease.

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7. Increased Risk of Cardiovascular Diseases

1. Hypertension:
   • Common due to arterial stiffness and increased vascular resistance.
2. Heart Failure:
   • More prevalent due to impaired cardiac function and increased workload.
3. Arrhythmias:
   • Higher incidence due to loss of pacemaker cells and conduction abnormalities.
4. Aortic Aneurysm and Dissection:
   • Weakened arterial walls are prone to dilation or rupture.
5. Stroke:
   • Atherosclerosis and hypertension increase the risk of ischemic or hemorrhagic stroke.

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Healthy Aging Strategies for Cardiovascular Health

1. Regular Exercise:
   • Improves cardiac efficiency and vascular function.
2. Healthy Diet:
   • Low in saturated fats, sodium, and cholesterol to prevent atherosclerosis.
3. Weight Management:
   • Reduces strain on the heart and lowers blood pressure.
4. Control of Blood Pressure and Cholesterol:
   • Through medication or lifestyle changes.
5. Smoking Cessation:
   • Prevents further damage to blood vessels.
6. Regular Check-ups:
   • Early detection of cardiovascular changes or diseases.

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Summary of Aging Changes in the Cardiovascular System

Aspect	Change	Impact
Heart Size	Left ventricular hypertrophy	Reduced filling and output
Heart Rate	Slower resting HR	Lowered cardiac output
Arterial Elasticity	Increased stiffness	Higher systolic BP
Valves	Calcification	Stenosis or regurgitation
Blood Flow	Reduced endothelial function	Impaired circulation
Baroreceptors	Decreased sensitivity	Orthostatic hypotension
Clotting Tendency	Increased coagulation factors	Higher risk of thrombosis

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