CIRCULATORY SYSTEM

Chapter Overview

  • The circulatory system plays a crucial role in maintaining homeostasis by transporting various substances throughout the body.

  • It is organized into three primary circuits:

    • Coronary Circuit: Supplies blood to the heart muscle itself via the coronary arteries.

    • Pulmonary Circuit: Transports deoxygenated blood from the heart to the lungs for oxygenation and returns it to the heart.

    • Systemic Circuit: Distributes oxygenated blood to the rest of the body (e.g., providing oxygen to the brain, kidneys, and skeletal muscles).

Circulation: "The Double Pump"

  • Blood circulates through the heart twice for each complete circuit.

  1. The right side of the heart receives deoxygenated blood from body tissues and pumps it to the lungs for oxygenation.

  2. The left side of the heart receives oxygenated blood from the lungs and pumps it to all body tissues.

Human Circulatory System

  • The circulatory system is a closed system, which means blood is always contained within blood vessels.

  • Blood does not come into direct contact with body tissues; it requires blood vessels to facilitate exchange to support body cells.

  • It consists of:

    • Blood vessels

    • Blood

    • The heart

Blood Vessel Types

1. Arteries

  • Definition: Thick-walled tubes made of elastic muscle tissue.

  • Functions:

    • Carries blood away from the heart.

    • Can expand in response to pressure changes from the heart's pumping action.

    • Branches into smaller vessels known as arterioles.

    • Example: The Aorta is the primary artery protruding from the heart that feeds the systemic circuit.

  • Anatomy includes:

    • Connective tissue

    • Smooth muscle tissue

    • Endothelial tissue

2. Veins

  • Definition: Thin-walled tubes with valves to prevent backflow of blood (one-way doors due to low pressure).

  • Functions:

    • Carries blood back to the heart from body tissues.

    • Smaller veins are known as venules.

    • Example: The Vena Cava (Superior and Inferior) are the primary veins channeling blood back into the right atrium.

3. Capillaries

  • Definition: A fine network of tiny blood vessels surrounding body tissues.

  • Structure:

    • Composed of one cell layer thick walls for efficient diffusion.

  • Functions:

    • Oxygen and nutrients diffuse from capillaries into body cells.

    • Carbon Dioxide and waste products move from body cells into capillaries.

Blood Vessel Disorders

  1. Aneurysm:

    • Definition: A bulging blood vessel that risks rupturing.

    • Complications: Can lead to stroke, internal bleeding, or death.

  2. Varicose Veins:

    • Definition: Valve failure causing backflow of blood, leading to the enlargement of superficial veins.

    • Examples: Commonly seen in the legs or as hemorrhoids in the rectum.

Arteriosclerosis

  • Definition: The narrowing of arteries due to a build-up of fatty substances (plaque), leading to decreased blood flow.

Blood Composition

  • An average 70 kg person contains approximately 5L of blood.

  • Blood is classified as a "fluid tissue" comprising individual cells functioning collectively.

Blood: The Transport Medium
Importance of Blood

  • Functions include:

    • Transporting gases: Oxygen (O{2}) and Carbon Dioxide (CO{2}).

    • Transporting waste products: For example, urea and lactic acid.

    • Transporting nutrients: For example, glucose, amino acids, and vitamins.

    • Transporting hormones: For example, insulin or adrenaline.

    • Fighting disease/infection.

    • Initiating blood clotting.

Red Blood Cells (Erythrocytes)

  • Contains hemoglobin, an iron-containing protein crucial for oxygen transport.

  • Produced in the bone marrow and has a life span of approx. 120 days.

  • Adaptation Example: The body can stimulate red blood cell production in response to decreased oxygen levels, such as when a person moves to a high-altitude environment like the Andes Mountains.

  • Red blood cells lack a nucleus and are the most abundant cells in the blood.

White Blood Cells (Leukocytes)

  • Function: Fight germs and harmful foreign cells (e.g., bacteria, viruses).

  • Life span: Ranges from a few days to weeks.

  • Contains a nucleus.

Platelets

  • Definition: Small particles that facilitate the blood clotting process when there is a skin injury (e.g., stopping the bleeding from a minor cut).

  • The fluid component of blood is known as plasma, which contains dissolved substances essential for bodily functions.

Blood Disorders (Additional Information)

  1. Anemia:

    • Characterized by insufficient hemoglobin in red blood cells, leading to reduced oxygen-carrying capacity.

    • Symptoms: Tiredness, low energy, and shortness of breath.

    • Treatment: Often includes iron supplements.

  2. Leukemia:

    • Definition: A form of cancer affecting the blood-forming tissues.

    • Symptoms: Increased quantities of immature white blood cells which are ineffective in fighting disease.

The Heart

  • Composed of cardiac muscle, contracting involuntarily.

  • Beats approximately 72 times per minute.

  • Two sides of the heart are separated by a muscular wall known as the septum.

  • Systole: Phase of muscular contraction (heart pumps blood out).

  • Diastole: Phase of muscular relaxation (heart fills with blood).

Heart Pumps

  • Each pump consists of two chambers: an atrium and a ventricle (total of four chambers).

  • Blood flow sequence:

    • Blood moves from the atrium to the ventricle.

    • Chambers: Right atrium, Right ventricle, Left atrium, Left ventricle.

Heart Chambers

  • Atrium: Thin-walled chamber that receives blood from veins.

  • Ventricle: Muscular, thick-walled chamber that pumps blood to arteries.

Diseases and Disorders of the Circulatory System

1. Coronary Artery Disease

  • The coronary arteries supply blood to the heart muscle.

  • Conditions may arise when arteries become partially obstructed by plaque (fat, cholesterol, calcium).

  • Symptoms: Tiredness, dizziness, and angina (chest pain).

  • Diagnostic Tools: Angiograms are used to visualize blockages.

2. Heart Attack

  • Occurs when arteries are fully blocked by plaque or blood clots, restricting oxygen and nutrients to heart muscles.

  • Symptoms: Severe chest pain, shortness of breath, anxiety, and dizziness.

  • Diagnosis: Can be diagnosed through blood tests (looking for specific enzymes) and electrocardiograms (ECG).

Summary of Heart Structure

  • Anatomical Components:

    • Superior Vena Cava

    • Right Atrium

    • Right Ventricle

    • Inferior Vena Cava

    • Aorta

    • Left Atrium

    • Left Ventricle

    • Septum

    • Pulmonary Artery

    • Pulmonary Vein