The Circulatory System: Blood

Introduction

The circulatory system is a vital organ system responsible for the transport of substances throughout the body. It consists of the heart, blood vessels, and blood. Blood serves as the internal transport system, delivering nutrients, gases, and waste products, and playing a crucial role in protection and regulation.

Functions of the Circulatory System

The circulatory system performs three primary functions:

• Transport: Moves oxygen, carbon dioxide, nutrients, hormones, and waste products.

• Protection: Defends against infection and blood loss through immune cells and clotting mechanisms.

• Regulation: Maintains pH, temperature, and fluid balance.

  • reroutes blood to skin to regulate temp

Components and General Properties of Blood

Blood is a liquid connective tissue composed of plasma and formed elements. It has unique physical and chemical properties:

• Volume: 4-6 liters in adults

• Body weight: ~8%

• Temperature: 38°C

• Viscosity: 5 times thicker than water

  • so it will not leak and is allowed to be pumped properly

• pH: 7.35-7.45 (acidosis < 7.35, alkalosis > 7.45)

Blood Composition

• Plasma: ~55% of blood volume; least dense component

• Formed Elements: ~45% (mainly erythrocytes); most dense component

• Buffy Coat: <1% (leukocytes and platelets)

Blood Plasma

Blood plasma is a straw-colored fluid consisting of:

• Water: 92%

• Proteins: 7% (albumin, globulins, fibrinogen)

• Other solutes: 1% (nutrients, wastes, hormones, gases)

Plasma Proteins

• Albumin: Smallest and most abundant; maintains osmotic pressure and viscosity, buffers pH, transports solutes.

  • major contributer to

    • blood viscocity: thickness or stickiness

    • blood osmolarity: concentration of particles that can pass through blood vessels

• Globulins: Immune defense and transport.

• Fibrinogen: Essential for blood clotting.

Production of Blood (Hematopoiesis)

Blood cells are continuously produced in the bone marrow. Hematopoiesis is the process by which formed elements are generated from hematopoietic stem cells.

• Daily production: 400 billion platelets, 200 billion RBCs, 10 billion WBCs

Erythrocytes (Red Blood Cells)

Erythrocytes are the most abundant formed element, responsible for oxygen and carbon dioxide transport.

• Structure: Bi-concave disc, no nucleus, few organelles

• Function: Oxygen transport from lungs to tissues; carbon dioxide transport from tissues to lungs

• Hematocrit: Clinical measurement of RBC percentage

• NO NUCLEUS and few organelles

• No DNA or mitosis or self repair or protein synthesis

Hemoglobin

Hemoglobin is a red, iron-containing protein in RBCs. Each iron atom binds one oxygen molecule. RBCs lack mitochondria and rely on anaerobic fermentation for ATP production.

Erythrocyte Life Cycle

• Lifespan: ~120 days

• Production: Erythropoiesis (from hematopoietic stem cells)

• Death: Membrane deteriorates, cells rupture (hemolysis), components recycled

Sickle-Cell Anemia

Sickle-cell anemia is caused by a genetic mutation in hemoglobin, resulting in crescent-shaped RBCs that can block blood flow and cause pain.

Leukocytes (White Blood Cells)

Leukocytes are immune cells that protect the body from infection. They reside mainly in connective tissues and use the bloodstream for transport.

• Granulocytes: Neutrophils, eosinophils, basophils

• Agranulocytes: Monocytes, lymphocytes

Leukocyte Life Cycle

• Leukopoiesis: Production of WBCs from hematopoietic stem cells

Leukocyte Disorders

• Leukemias: Cancerous overproduction of abnormal WBCs

• Infectious mononucleosis: Viral disease causing excess lymphocytes

Platelets and Control of Bleeding

Platelets are small fragments of megakaryocytes, essential for blood clotting and hemostasis.

• Structure: Small, non-nucleated cell fragments

• Function: Initiate clotting, prevent blood loss

Hemostasis

Hemostasis is the process of stopping bleeding, involving three stages:

1. Vascular spasm: Constriction of blood vessels

2. Platelet plug formation: Platelets adhere to injury site

3. Coagulation: Formation of a fibrin clot

Agglutination vs. Coagulation

• Coagulation: Formed elements stick together by fibrin

• Agglutination: RBCs stick together by antibodies

Blood Types and Transfusion

Blood typing is based on antigens (cell surface markers) and antibodies. Incompatible transfusions can cause agglutination and be fatal.

• ABO System: Type A (A antigens, B antibodies), Type B (B antigens, A antibodies), Type AB (A and B antigens, no antibodies), Type O (no antigens, A and B antibodies)

• Universal donor: Type O

• Universal recipient: Type AB

Rh Typing

• Rh antigen: Present (+) or absent (-)

• Rh-negative individuals produce antibodies only if exposed to Rh antigen

• Rh incompatibility can cause problems in pregnancy

Summary Table: Blood Components

Key Equations

• Blood pH:

• Osmolarity:

Conclusion

The circulatory system, through its blood components, ensures the transport, protection, and regulation necessary for human life. Understanding blood's structure, function, and disorders is essential for clinical practice and physiology.