Introduction to the Cardiovascular System

Functions of the Cardiovascular System

Transport Functions:
- The system carries vital nutrients and oxygen ( $O_{2}$ ) to all cells in the body.
- It transports hormones to their target tissues.
- It removes metabolic wastes, specifically carbon dioxide ( $CO_{2}$ ) and nitrogenous wastes, from cells for excretion.
Protection Functions:
- The system transports white blood cells and antibodies designed to combat foreign microbes and toxins.
- It incorporates clotting mechanisms to prevent excessive blood loss following injuries.
Regulation Functions:
- The system facilitates the regulation of body temperature.
- It maintains fluid pH levels.
- It regulates the water content within cells.

Main Components of the Cardiovascular System

Blood: Composed of red blood cells, white blood cells, plasma, and platelets.
Blood Vessels: Include arteries, veins, and capillaries.
The Heart: Acts as the central pump for the entire system.

Blood Composition and Characteristics

Blood Plasma ( $55\%$ by volume): A complex liquid medium that carries various substances:
- Inorganic ions: Examples include $Ca$ , $Mg$ , $Cl$ , and $HCO_{3}$ ions.
- Nutrients: Examples include glucose and amino acids.
- Waste products: Examples include $CO_{2}$ and urea.
- Hormones: Examples include insulin and adrenalin.
- Proteins: Includes antibodies and other essential proteins.
Blood Cells (Corpuscles) ( $45\%$ by volume):
- Red Blood Cells (Erythrocytes): Specialized for carrying oxygen throughout the body.
  - Anatomy: Biconcave shape provides a large surface area for oxygen transport.
  - Components: Contain the protein haemoglobin, which requires iron to function.
  - Life Cycle: No nucleus is present, meaning they live only $3-4\text{ months}$ . They are produced in the bone marrow, while worn-out cells are destroyed in the liver.
  - Chemical Reaction: $\text{haemoglobin} + \text{oxygen} \rightarrow \text{oxyhaemoglobin}$ . Blood turns from dull red to bright red during this process.
- White Blood Cells (Leucocytes): Responsible for destroying pathogens. There are five main types:
  - Monocyte.
  - Eosinophil.
  - Lymphocyte.
  - Neutrophil.
  - Basophil.
- Platelets: Assist in blood clotting processes and the repair of broken blood vessels.

Anatomy and Function of Blood Vessels

Arteries:
- Function: Carry blood away from the heart.
- Structure: Feature thick, elastic muscular walls to withstand high blood pressure.
- Arterioles: Small arteries that connect to capillaries.
Capillaries:
- Function: Connect arterioles to venules.
- Structure: Walls are only one cell thick to facilitate the transfer of gases, nutrients, and wastes between the blood and bodily tissues.
Veins:
- Function: Carry blood back toward the heart.
- Structure: Thinner walls than arteries and lower pressure. They contain valves to ensure one-way blood flow.
- Venules: Small veins that receive blood from capillaries.

Vascular Health and Pathologies

Healthy Veins: Valves open to allow normal blood flow toward the heart and close to prevent backflow.
Varicose Veins: Occur when valves are damaged or do not close properly. This results in abnormal blood flow, where blood can move in both directions.
Atherosclerosis: A condition where the buildup of cholesterol and other substances forms plaque, narrowing the arteries. Any reduced flow to the heart muscle significantly impairs the heart\'s ability to pump blood.

Detailed Heart Structure and Chambers

The Four Chambers:
- Right Atrium: Receives deoxygenated blood from the body.
- Right Ventricle: Pumps deoxygenated blood toward the lungs.
- Left Atrium: Receives oxygenated blood from the lungs.
- Left Ventricle: Pumps oxygenated blood to the rest of the body. Note that the atria are significantly smaller than the ventricles.
The Four Valves:
- Tricuspid Valve (Right Atrioventricular Valve): Located between the right atrium and right ventricle.
- Pulmonary Valve (Right Semilunar Valve): Located between the right ventricle and pulmonary artery.
- Mitral Valve (Biscuspid Valve / Left Atrioventricular Valve): Located between the left atrium and left ventricle.
- Aortic Valve (Left Semilunar Valve): Located between the left ventricle and the aorta.
The Four Main Blood Vessels:
- Vena Cava (Inferior and Superior): Carry deoxygenated blood from the body into the right side of the heart.
- Pulmonary Artery: Carries deoxygenated blood from the heart to the lungs.
- Pulmonary Vein: Carries oxygenated blood from the lungs back to the left side of the heart.
- Aorta: Carries oxygenated blood from the heart to the entire body.
Additional Internal Structures:
- Chordae Tendineae: Known as \"heart strings.\" These hold the atrioventricular valves in place to prevent the backflow of blood into the atria when the ventricles contract.
- Coronary Arteries: Located on the exterior of the heart to supply the heart muscle itself with the oxygen and nutrients required for its continuous function.

The Pathway of Blood Flow

Deoxygenated blood enters the Superior/Inferior Vena Cava.
Blood flows into the Right Atrium.
Blood passes through the Tricuspid Valve into the Right Ventricle.
Blood is pumped through the Pulmonary Valve into the Pulmonary Artery to reach the lungs.
Oxygenated blood returns from the lungs via the Pulmonary Vein.
Blood enters the Left Atrium.
Blood passes through the Mitral (Bicuspid) Valve into the Left Ventricle.
Blood is pumped through the Aortic Valve into the Aorta to be distributed to the body.

The Heart\'s Pacemaker and Electrical System

Autonomous Beating: The heart possesses a built-in system to generate and conduct electrical messages independently of the brain.
Sinoatrial Node (SA Node): The primary pacemaker of the heart. It sends nerve impulses over the atria to trigger contraction, pushing blood into the ventricles. It sets the basic heart rhythm.
Atrioventricular Node (AV Node): A second clump of specialized tissue that conducts the impulse to the ventricles. There is a slight delay at the AV node to allow the atria time to finish contracting before the ventricles begin their contraction.
Central Nervous System Modification:
- The Cardiac Center located in the Medulla Oblongata of the brain can alter the basic rhythm.
- It modifies heart rate and contraction strength based on the body\'s needs.
- It monitors sensor information regarding blood pressure, oxygen levels, and carbon dioxide levels.

Blood Pressure Mechanics

Definition: Blood pressure is the amount of pressure exerted by blood on the walls of blood vessels.
Measurement:
- Measured using a sphygmomanometer and a stethoscope.
- A cuff is inflated to cut off circulation and then slowly deflated.
- Systolic Pressure: The first sound of rushing blood heard as the cuff deflates (heart contracting).
- Diastolic Pressure: The pressure measured once the sound fades (heart at rest).
- Units: Millimeters of mercury ( $mm\,Hg$ ).
Standard Values:
- Normal high (Systole): $120\,mm\,Hg$ .
- Normal low (Diastole): $80\,mm\,Hg$ .
Pathological Thresholds:
- Hypertension (High Blood Pressure): Consistent readings of > 140\,mm\,Hg Systole or > 90\,mm\,Hg Diastole.
- Hypotension (Low Blood Pressure): Consistent readings of < 120\,mm\,Hg Systole or < 80\,mm\,Hg Diastole. Lower blood pressure is generally associated with lower cardiovascular risk compared to high pressure.