Bihar Board - Class 11 biology - Chapter 18: Body Fluids and Circulation Handwritten Notes

The circulatory system is responsible for the transport of essential substances like oxygen, nutrients, hormones, and waste products throughout the body. This chapter explain the function of body fluids and the mechanisms involved in circulation.

Key Points

1. Composition of Body Fluids

   • Blood: The main body fluid involved in circulation, composed of plasma, red blood cells (RBCs), white blood cells (WBCs), and platelets.
     • Plasma: The liquid component, containing water, proteins, hormones, and waste products.
     • Cells in Blood: RBCs transport oxygen, WBCs defend against infections, and platelets help in clotting.
   • Lymph: A colorless fluid that circulates in the lymphatic system, carrying lymphocytes and assisting in immune responses.
   • Interstitial Fluid: The fluid found between cells, facilitating nutrient and waste exchange.

2. Circulatory Pathways

   • Closed Circulatory System: Blood is confined to blood vessels and circulates in a loop, as seen in humans and other vertebrates.
   • Double Circulation: Blood passes through the heart twice—once through the lungs for oxygenation (pulmonary circulation) and again through the rest of the body to deliver oxygen (systemic circulation).
     • Pulmonary Circulation: Carries deoxygenated blood from the right ventricle to the lungs and returns oxygenated blood to the left atrium.
     • Systemic Circulation: Carries oxygenated blood from the left ventricle to the body and returns deoxygenated blood to the right atrium.

3. The Heart

   • Structure of the Heart: Composed of four chambers—two atria and two ventricles.
   • Cardiac Cycle: The sequence of events during one heartbeat, including atrial and ventricular contractions and relaxations.
   • Valves: Ensure one-way flow of blood through the heart and prevent backflow (e.g., tricuspid valve, bicuspid valve, semilunar valves).

4. Blood Vessels

   • Arteries: Thick-walled vessels that carry oxygenated blood away from the heart (except the pulmonary artery).
   • Veins: Carry deoxygenated blood back to the heart (except the pulmonary vein).
   • Capillaries: Small, thin-walled vessels where gas exchange (oxygen and carbon dioxide) and nutrient exchange between blood and tissues occur.

5. Blood Pressure and Circulatory Regulation

   • Blood Pressure: The force exerted by blood on the walls of blood vessels. It is higher in arteries and lower in veins.
   • Regulation of Blood Flow: Controlled by the heart's pumping action, constriction, and dilation of blood vessels, and neural and hormonal signals.

6. Functions of Blood

   • Transport: Carries oxygen, nutrients, hormones, and waste products.
   • Immune Defense: White blood cells in the blood defend the body against infections.
   • Clotting: Platelets and clotting factors help in wound healing and prevent excessive blood loss.
   • Regulation: Blood helps regulate body temperature, pH levels, and water balance.

7. Disorders Related to Circulation

   • Hypertension: High blood pressure, which can lead to heart disease and stroke.
   • Anemia: A condition where there is a deficiency of red blood cells or hemoglobin, leading to oxygen deficiency in tissues.
   • Atherosclerosis: Hardening and narrowing of the arteries due to plaque buildup, which can restrict blood flow.
   • Heart Attack (Myocardial Infarction): Occurs when a part of the heart muscle is deprived of oxygen due to blocked blood flow.

Conclusion

The circulatory system and body fluids are fundamental for maintaining homeostasis in the body. Blood circulation ensures the transportation of oxygen, nutrients, and waste products, while the heart, blood vessels, and lymphatic system work together to maintain efficient flow. Understanding the components of body fluids and circulation is crucial in diagnosing and treating circulatory disorders.

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