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Introduction to Blood and Circulation

Overview of the Internal Environment of the Body

• The lesson begins with a focus on blood and circulation, emphasizing that the human body is an open system where cells are formed from blood through plasma filtration via capillary walls.

• Nutrient exchange and waste removal occur through tissue fluid, which comprises about 90% of the interstitial fluid returning to the bloodstream; excess accumulation can lead to swelling.

Lymphatic System Functions

• Lymph, a clear fluid derived from tissue fluid, plays crucial roles in transporting water, proteins back to blood, absorbing fats and fat-soluble vitamins from intestines, and combating microorganisms.

• Movement of lymph occurs upward towards the thoracic duct due to muscle contractions and valves preventing backflow; lymph nodes along vessels serve immune functions.

Composition and Functions of Blood

Blood as Connective Tissue

• Blood consists of liquid connective tissue containing intercellular substances and formed elements (cells), performing vital functions such as nutrient distribution and waste removal.

• Oxygen delivery occurs via blood circulation through capillaries in lungs where carbon dioxide is released; hormones secreted by endocrine glands travel through blood affecting organ function.

Temperature Regulation

• Blood helps maintain body temperature by transporting heat generated by muscles and liver; total blood volume constitutes 7-8% of body mass, varying between children and adults.

Components of Blood

Plasma Composition

• When allowed to settle or centrifuged, blood separates into layers: plasma (about 50%), white blood cells (4%), red blood cells (approximately 41%).

• Key organs for blood cell formation include red bone marrow, spleen, thymus gland, tonsils, appendix, and lymph nodes.

Plasma Proteins

• Plasma contains approximately 92% water; major proteins include albumins (transporting hormones/medications), globulins (carrying glucose/iron), antibodies for defense (gamma globulin), and fibrinogen for clotting.

Osmotic Pressure in Plasma

Importance of Osmotic Balance

• Inorganic salts constitute about 0.99%, essential for osmotic pressure regulation critical for cellular function; normal pH level is around 7.36.

Effects on Red Blood Cells

• Erythrocytes placed in isotonic solutions remain unchanged; exposure to hypertonic solutions causes dehydration while hypotonic solutions lead to swelling or hemolysis due to water influx.

Characteristics of Erythrocytes

Structure and Functionality

• Erythrocytes have a biconcave shape with up to 5 million per milliliter; they mature in red bone marrow losing their nuclei as they fill with hemoglobin—essential for oxygen transport.

Hemoglobin Dynamics

• Hemoglobin binds oxygen forming oxyhemoglobin—a bright red compound easily releasing oxygen. Low nutrient levels can reduce hemoglobin leading to anemia.

Understanding Carbon Monoxide and Hemoglobin

The Dangers of Carboxyhemoglobin

• Carboxyhemoglobin is a stable compound formed when carbon monoxide binds to hemoglobin, contrasting with the more transient oxyhemoglobin.

• High levels of carbon monoxide can be life-threatening due to its poor dissociation from hemoglobin, especially in oxygen-rich environments.

Erythrocytes and Their Lifespan

• Erythrocytes (red blood cells) have an average lifespan of 120 days, after which they are destroyed in the liver and spleen.

• The sedimentation rate of erythrocytes (ESR), typically between 1 to 10 mm, can increase significantly during infections or inflammation.

Leukocytes: The Body's Defense Mechanism

Types and Functions of Leukocytes

• Leukocytes (white blood cells), numbering between 6,000 to 8,000 per millimeter of blood, exhibit amoeboid movement allowing them to traverse capillary walls.

• They are categorized into granulocytes (with granules in their cytoplasm) and agranulocytes (without granules). Neutrophils make up the majority at 50-70% and are crucial for pathogen defense.

Neutrophils and Inflammation Response

• Neutrophils circulate for about 8-12 hours before migrating to sites of infection where they release enzymes that contribute to inflammation.

Other Granulocyte Types

• Eosinophils account for 2-4% of leukocytes; they play roles in allergic reactions and combat helminths.

• Basophils are large leukocytes involved in rapid allergic responses like anaphylactic shock; they contain heparin which reduces blood clotting.

Monocytes and Lymphocytes: Key Players in Immunity

Monocyte Functionality

• Monocytes are the largest type of leukocyte, active phagocytic cells that transform into macrophages after circulating for four days. They help clear debris from inflammation sites.

Lymphocyte Roles

• Lymphocytes are essential for both humoral immunity (antibody production) and cellular immunity by interacting with infected host cells. They constitute about 40% of all leukocytes in adults.

Thrombocytes: Blood Clotting Agents

Characteristics of Thrombocytes

• Thrombocytes (platelets), the smallest blood cells, play a critical role in coagulation. Their count ranges from 250,000 to 400,000 per millimeter.

• Formed from megakaryocyte cytoplasmic fragments, thrombocytes lack nuclei and survive approximately 10–12 days. Proper clotting requires various proteins, vitamins, and minerals.