Circulatory System Overview

Circulatory System Overview

• The circulatory system, also known as the transport system or cardiovascular system, is an organ system responsible for blood and nutrient circulation in the body.
• Circulation is the continuous, one-way movement of blood throughout the body.
• The process involves blood, the heart, and blood vessels.

Functions of the Circulatory System

• The circulatory system plays a vital role in homeostasis.
• Function A: It controls the chemical makeup of the environment surrounding cells by exchanging molecules.
• Function B: It continuously transports blood through organs, regulating chemical composition (e.g., liver, kidneys).

Types of Circulatory Systems

• Open Type: Blood is pumped through open-ended vessels and diffuses into the body cavity. Found in invertebrates like crustaceans, spiders, and grasshoppers.
• Closed Type (Cardiovascular System): Blood circulates within a network of vessels. This system is suited for organisms with high metabolic rates. The closed system consists of a heart and a network of vessels.

Parts of the Circulatory System

• Heart: A muscular organ about the size of a clenched fist located between the lungs, slightly pointed to the left. It contracts approximately 72 times per minute, or over 100,000 times a day.
  • Structure of the Heart:
    • Endocardium: The membrane lining the heart's interior.
    • Myocardium: The thickest layer, cardiac muscle responsible for pumping blood.
    • Epicardium: The thin, outermost layer of the heart wall.
    • Pericardium: The covering that protects the heart and connects it to the diaphragm and sternum.
    • Septum: The wall separating the heart's two sides.
    • Atria: The two upper chambers that receive blood and pump it to the ventricles.
    • Ventricles: The two lower chambers that pump blood out of the heart.
    • Valves: One-way valves regulate and direct blood flow in the heart, preventing backflow.
      • Atrioventricular valves: Include the tricuspid and bicuspid (mitral) valves – situated between the atria and ventricles.
      • Semilunar valves: Found at the exit of the ventricles, regulate flow into arteries (pulmonary and aortic).
• Blood Vessels:
  • Arteries: Carry oxygenated blood away from the heart to capillaries, except for Pulmonary arteries. The largest artery is the aorta; smaller branches are arterioles.
  • Veins: Carry deoxygenated blood back to the heart, except for Pulmonary veins. Most veins have one-way valves. Smallest veins are venules.
  • Capillaries: The smallest blood vessels that facilitate the exchange of materials between the blood and body cells.

Heartbeat

• The heart's pumping action creates a heartbeat sound, "lub-dub."
• "Lub" is produced when valves between the atria and ventricles close.
• "Dub" occurs after valves between the ventricles and arteries close.

Blood Circulation

• Pulmonary Circuit: Oxygen-poor blood is pumped from the right side of the heart to the lungs for oxygenation. Blood is returned to the left side of the heart.
• Systemic Circuit: Oxygen-rich blood is pumped from the left side of the heart to the rest of the body's tissues, delivering oxygen and nutrients. Deoxygenated blood returns to the right side of the heart.

Blood Pressure

• Blood pressure is the pressure exerted by blood on the artery walls during heart contractions.
• Systolic Pressure: Blood pressure during contraction of the heart
• Diastolic Pressure: Blood pressure during relaxation of the heart.
• Normal blood pressure for a healthy adult is generally below 120 systolic and 80 diastolic (in mmHg).
  • Specific blood pressure ranges and classifications are presented in other sections.

Blood Composition

• Blood Plasma (55%): The liquid portion of blood, mostly water (90%), containing proteins, nutrients, wastes, electrolytes, hormones, etc.
• Formed Elements (45%): The cellular components.
  • Red Blood Cells (Erythrocytes): Tiny, concave discs that carry oxygen using hemoglobin. They lack a nucleus, have short lives, and are made in bone marrow.
  • White Blood Cells (Leukocytes): Round cells with nuclei (varying sizes and shapes) involved in protecting the body against infections.
    • Granular Leukocytes: Neutrophils (fight bacteria), Eosinophils (kill parasites and cancer cells, allergic responses) and Basophils (allergic responses).
    • Agranular Leukocytes: Lymphocytes (immunity), Natural Killer Cells (infection defense) and Monocytes (phagocyte).
  • Platelets (Thrombocytes): Cell fragments essential for blood clotting.

Circulatory System Disorders

• Atherosclerosis: Cholesterol buildup in arteries forming plaques, narrowing the arteries, and hindering blood flow.
• Stroke: A disorder arising from blockage in brain or neck arteries, reducing blood flow.
• Coronary Heart Disease: Blood flow to the coronary arteries (in the heart) is blocked.
• Hypertensive Heart Disease: The smallest arteries tighten/constrict impacting blood flow.
• Hemophilia: Blood does not clot properly.
• Anemia: Consistently low red blood cell count, impacting oxygen delivery.
• Leukemia: Characterized by an abnormal increase in white blood cells.
• Thrombocytopenia: Low platelet count causing bleeding issues.
• Thrombocythemia: Excess platelet count potentially causing blood clots leading to stroke or heart attack.