7 CirculatorySystem

Introduction to the Circulatory System

  • The heart's primary role is to pump blood throughout the body.

Characteristics of the Circulatory System

  • Blood: Transports dissolved gases, nutrients, and waste.

  • Blood Vessels: Blood flows within blood vessels.

  • Heart: The organ that pumps blood around the body.

  • Valves: Ensure blood flows in one direction.

Types of Circulatory Systems

Open Circulatory System

  • Found in invertebrates.

  • Blood is pumped at low pressure into the body cavity (haemocoel).

  • Blood baths internal organs and moves slowly.

Closed Circulatory System

  • Blood enclosed in vessels.

  • Separate tissue fluid exists between blood vessels and cells.

  • Blood travels quickly under high pressure.

Human Circulatory System

  • Humans possess a closed circulatory system typical for vertebrates.

  • Heart:

    • Pumps blood into large vessels.

    • Large arteries lead to smaller vessels and then organs.

  • Diffusion: Exchange occurs between blood and interstitial fluid.

Anatomy of the Heart

  • Cardiac Muscle Tissue: Composed of highly interconnected cells.

  • Chambers: Four chambers (right atrium, right ventricle, left atrium, left ventricle).

Double Circulatory System

Pulmonary Circulatory System

  • Deoxygenated blood flows from the heart to the lungs.

  • Oxygenated blood flows back from lungs to the heart.

Systemic Circulatory System

  • Oxygenated blood flows from the heart to the body.

  • Deoxygenated blood returns from the body to the heart.

Advantages of the Double Circulatory System

  • Blood is pumped to the lungs for gas exchange (oxygen and carbon dioxide).

  • Blood is delivered under pressure to the body, supplying oxygen and nutrients while removing waste.

Importance of Blood Pressure

  • Tissue fluid is formed when plasma is pushed out of capillaries to enhance substance movement.

  • Oxygen is transported quickly to all body cells, crucial for respiration.

Heart Structure and Location

  • Size: Similar to a closed fist.

  • Shape: Cone-shaped with a blunt apex and a flat base.

  • Location: Thoracic cavity, mediastinum.

External Anatomy of the Heart

  • Composed of:

    • Chambers: 2 atria and 2 ventricles.

    • Coronary Arteries: Supply blood to the heart muscle.

    • Pericardium: Membranes that protect the heart, allowing smooth movement.

    • Major Veins: Superior vena cava, inferior vena cava, pulmonary veins.

    • Major Arteries: Aorta, pulmonary trunk.

Heart Valves

  • Atrioventricular Valves: Prevent backflow from ventricles to atria.

  • Semilunar Valves: Prevent backflow from arteries to ventricles.

Blood Flow Through the Heart

  1. Deoxygenated blood enters the right atrium (via superior/inferior vena cava).

  2. Blood flows to the right ventricle (through tricuspid valve).

  3. Blood is pumped to the lungs (via pulmonary arteries).

  4. Oxygenated blood returns to the left atrium (via pulmonary veins).

  5. Blood flows to the left ventricle (through bicuspid/mitral valve).

  6. Blood is pumped to the body (through aorta).

Blood Vessels

Arteries and Arterioles

  • Carry blood away from the heart.

  • Contains elastic fibers and circular smooth muscles.

Capillaries

  • Site of gaseous exchange.

  • One cell thick walls allow easy diffusion.

Veins and Venules

  • Transport blood back to the heart.

  • Skeletal muscle contractions help blood return, equipped with one-way valves.

Heartbeat and Cardiac Cycle

  • Sound: Made by closing of valves; "lub-dub" represents the closing of AV valves and semilunar valves, respectively.

  • Average Heart Rate: 70 beats per minute; beats last about ±0.8 seconds.

  • Systole: Heart muscles contract and pump blood out.

  • Diastole: Heart muscles relax, allowing blood flow into the chambers.

Process of the Cardiac Cycle

  1. General Diastole (0.4 sec): Relaxation; blood flows into ventricles.

  2. Atrial Systole (0.1 sec): Atria contract, forcing blood into ventricles.

  3. Ventricular Systole (0.3 sec): Ventricles contract, pumping blood into arteries.

Control of Heartbeat

  • Myogenic: Contraction originating from the cardiac muscle itself.

  • SA Node: Located in the right atrium; acts as a pacemaker, initiating heartbeat and setting rhythm.

  • AV Node: Located in the right atrium; relays impulses to ventricles.

Nervous Control of Heart Rate

  • Parasympathetic Nerve (Vagus): Slows heart rate.

  • Sympathetic Nerve: Speeds up heart rate based on body demands.

Measuring Blood Pressure

  • Blood pressure in veins is lower than in arteries.

  • Measurements consist of two numbers (systolic/diastolic).

  • Normal ranges: Systolic (110-139 mm), Diastolic (60-89 mm).

Composition of Blood

  • Plasma: Liquid component containing proteins, nutrients.

  • Blood Cells:

    • Red Blood Cells (Erythrocytes): Transport oxygen, lack nucleus.

    • White Blood Cells (Leucocytes): Immune response, may have nuclei.

    • Platelets (Thrombocytes): Involved in clotting.

Differences in Blood Cells

  • Red Blood Cells: Small (diameter 0.008 mm), 4-5 million/mm³.

  • White Blood Cells: Larger (0.02 mm), fewer in number (about 8,000/mm³).

  • Platelets: 250,000/mm³, smallest and irregular-shaped.

Variations in Animal Hearts

  • Different types of hearts found in birds, amphibians, fish, and spiders, reflecting evolutionary adaptations.