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Circulatory system cont.

The following headings are discussed.

1. Cardiac cycle 

2. Cardiac output

3. Stroke volume 

4. Heart rate 

5. Blood pressure 

6. Blood and it's components 

7. Classification of blood (ABO and Rhesus)

8. Diseases of circulatory system 


1. Cardiac Cycle

The cardiac cycle refers to the sequence of events that occur during one complete heartbeat. It involves the coordinated contraction (systole) and relaxation (diastole) of the atria and ventricles, resulting in the pumping of blood throughout the body.

Phases are:

  •    Diastole (Relaxation and Filling): The heart chambers are relaxed, and blood flows from the atria into the ventricles. This is the longer phase, allowing the ventricles to fill adequately.
  •    Systole (Contraction and Ejection): The ventricles contract, forcing blood into the pulmonary artery (from the right ventricle) and the aorta (from the left ventricle).


2. Cardiac Output (CO)

Cardiac output is how many liters of blood your heart pumps in one minute(usually measured from the left ventricle) per minute. It is a crucial indicator of the heart's efficiency in meeting the body's metabolic demands.

 * Formula: CO = HR × SV

   * Where:

     * CO = Cardiac Output (L/min)

     * HR = Heart Rate (beats/min)

     * SV = Stroke Volume (mL/beat)

Typical Resting Value: Approximately 5-6 litres per minute in a healthy adult. This can increase significantly during exercise.

3. Stroke Volume (SV)

Stroke volume is the volume of blood pumped out by one ventricle with each beat. It represents the efficiency of each heart contraction.

4. Heart Rate (HR)

Heart rate is simply the number of heartbeats per minute. It's a readily measurable indicator of cardiovascular function. Normal Resting heart rate Range is  60-100 beats per minute for adult.

Factors Influencing Heart rate include

  1. Autonomic nervous system (sympathetic increases, parasympathetic decreases), hormones (e.g., adrenaline),
  2. age, 
  3. fitness level,
  4. body temperature,
  5. stress.

5. Blood Pressure (BP)

Blood pressure is the force exerted by circulating blood against the walls of blood vessels. It's typically measured in the brachial artery and expressed as two values: systolic over diastolic pressure.

Systolic Pressure: The maximum pressure in the arteries during ventricular contraction (systole).

 Diastolic Pressure: The minimum pressure in the arteries during ventricular relaxation (diastole).

 The Units is Millimetres of mercury (mmHg).

 Normal Resting Range is Approximately 120/80 mmHg.

 Factors Influencing BP include:

  1. Cardiac output, 
  2. peripheral resistance, 
  3. blood volume, 
  4. elasticity of blood vessels.
  5. Exercise 

6. Blood and Its Components

Blood is a vital connective tissue that circulates throughout the body, delivering oxygen and nutrients and removing waste products.

 Components:

  1. Plasma (Approx. 55%): The liquid matrix of blood, primarily water, containing dissolved proteins (albumins, globulins, fibrinogen), electrolytes, hormones, nutrients, and waste products.
  2. Red Blood Cells (Erythrocytes): Biconcave discs, anucleated, responsible for oxygen transport via haemoglobin.
  3. White Blood Cells (Leukocytes): Part of the immune system, defending against pathogens. (e.g., neutrophils, lymphocytes, monocytes, eosinophils, basophils).
  4. Platelets (Thrombocytes): Cell fragments crucial for blood clotting (haemostasis).

7. Classification of Blood (ABO and Rhesus Systems)

Blood types are determined by the presence or absence of specific antigens (protein markers) on the surface of red blood cells. These classifications are critical for safe blood transfusions.

 ABO Blood Group System: Based on the presence or absence of A and B antigens.

  1.    Type A: Has A antigens.
  2.    Type B: Has B antigens.
  3.    Type AB: Has both A and B antigens (universal recipient).
  4.    Type O: Has neither A nor B antigens (universal donor).

 Rhesus (Rh) System: Based on the presence or absence of the Rh antigen (D antigen).

  1.   Rh-positive (Rh+): Has the Rh antigen.
  2.   Rh-negative (Rh-): Lacks the Rh antigen.

  Clinical Significance: Important in pregnancy to prevent haemolytic disease of the newborn if an Rh- mother carries an Rh+ fetus.

8. Diseases of the Circulatory System

The circulatory system is susceptible to various diseases that can significantly impact health.

  1.  Hypertension (High Blood Pressure): Persistently elevated blood pressure, increasing the risk of heart attack, stroke, and kidney disease.
  2.  Atherosclerosis: Hardening and narrowing of arteries due to plaque buildup (fats, cholesterol, etc.), leading to reduced blood flow.
  3.  Coronary Artery Disease (CAD): Narrowing or blockage of the coronary arteries (supplying the heart muscle), often due to atherosclerosis, leading to angina or heart attack.
  4.  Stroke: Occurs when blood flow to a part of the brain is interrupted, either by a clot (ischemic stroke) or a ruptured blood vessel (haemorrhagic stroke).
  5.  Heart Failure: The heart's inability to pump enough blood to meet the body's needs.
  6.  Anemia: A condition where the blood lacks healthy red blood cells, leading to reduced oxygen transport.
  7.  Arrhythmias: Irregular heartbeats, which can be too fast, too slow, or irregular.

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