Blood

Functions of Blood

Blood is a vital connective tissue that performs several essential functions in the human body.

• Transport: Blood transports oxygen, nutrients, hormones, and waste products to and from cells.

• Regulation: Blood helps regulate body temperature and maintain pH and fluid balance.

• Protection: Blood contains cells and proteins that defend against infection and disease.

Whole Blood and Its Composition

Whole blood consists of two main components: plasma and formed elements (cells and cell fragments).

• Plasma: The liquid portion of blood, making up about 55% of total blood volume. Plasma is composed of approximately 91% water, 7% proteins (such as albumin, globulin, and fibrinogen), and 2% other solutes (including electrolytes, nutrients, waste products, and gases).

• Formed Elements: These include red blood cells (RBCs), white blood cells (WBCs), and platelets.

Plasma Proteins

• Albumin: The most abundant plasma protein; helps maintain osmotic pressure and transport substances.

• Globulins: Involved in immune responses (antibodies) and transport of lipids and fat-soluble vitamins.

• Fibrinogen: Essential for blood clotting.

Formed Elements of Blood

The formed elements are the cellular components of blood, each with specialized functions.

• Red Blood Cells (Erythrocytes):

  • Primary function is to transport oxygen from the lungs to tissues and carbon dioxide from tissues back to the lungs.

  • Contain the protein hemoglobin, which binds oxygen.

  • Have a lifespan of about 120 days.

  • Produced in the bone marrow by hematopoietic stem cells.

• White Blood Cells (Leukocytes):

  • Defend the body against infection and disease.

  • Classified as granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes).

  • Lymphocytes (especially B cells) produce antibodies.

• Platelets (Thrombocytes):

  • Cell fragments involved in blood clotting.

  • Produced in the bone marrow from megakaryocytes.

Blood Typing

Blood type is determined by the presence or absence of specific antigens (agglutinogens) on the surface of RBCs and corresponding antibodies in the plasma.

• ABO System: Four main blood types: A, B, AB, and O, based on the presence of A and/or B antigens.

• Rh Factor: Presence (+) or absence (−) of the Rh antigen (D antigen) on RBCs.

• Antibodies: Proteins produced by B lymphocytes that recognize and bind to specific antigens.

Example: If a person has type A blood, their RBCs have A antigens and their plasma contains anti-B antibodies.

Key Definitions

• Antigen: A molecule recognized by the immune system as foreign, often found on the surface of pathogens or cells.

• Antibody (Immunoglobulin): A Y-shaped protein produced by B cells that binds specifically to an antigen.

Heart Anatomy and Physiology

Blood Flow Through the Heart

The heart is a muscular organ that pumps blood through two main circuits: the pulmonary and systemic circuits.

1. Deoxygenated blood enters the right atrium from the body via the superior and inferior vena cava.

2. Blood flows into the right ventricle, which pumps it to the lungs via the pulmonary artery for oxygenation.

3. Oxygenated blood returns to the left atrium via the pulmonary veins.

4. Blood moves into the left ventricle, which pumps it through the aorta to the rest of the body.

Pericardium and Heart Wall

• Pericardium: A double-layered sac that surrounds and protects the heart.

• Heart Wall Layers: Consists of the epicardium (outer), myocardium (muscular middle), and endocardium (inner lining).

Heart Chambers and Valves

• The heart has four chambers: two atria (upper) and two ventricles (lower).

• Valves ensure unidirectional blood flow:

  • Atrioventricular (AV) valves: Tricuspid (right), Mitral/Bicuspid (left)

  • Semilunar valves: Pulmonary (right), Aortic (left)

Pathways of Circulation

• Pulmonary Circuit: Carries deoxygenated blood from the right ventricle to the lungs and returns oxygenated blood to the left atrium.

• Systemic Circuit: Carries oxygenated blood from the left ventricle to the body and returns deoxygenated blood to the right atrium.

Function of Heart Valves

• Valves prevent backflow of blood and ensure efficient circulation.

• AV valves close during ventricular contraction; semilunar valves close during ventricular relaxation.

Innervation of the Heart

• The heart is innervated by the autonomic nervous system:

• Parasympathetic (Vagus nerve): Releases acetylcholine (ACh), which slows heart rate.

• Sympathetic: Releases norepinephrine (NE), which increases heart rate and force of contraction.

Key Table: Comparison of Blood Cell Types

Key Equations

• Hematocrit: The percentage of blood volume occupied by RBCs.

Additional info:

• Some context and explanations have been expanded for clarity and completeness.

• Table entries and some definitions are inferred from standard Anatomy & Physiology content.