Chapter 18: The Cardiovascular System – Blood (Anatomy & Physiology Study Notes)

Blood: Structure and Function

Overview of Blood Cells

Blood is a specialized bodily fluid that transports nutrients, gases, hormones, and waste products throughout the body. It consists of several types of cells suspended in plasma.

• Red Blood Cells (Erythrocytes): Carry oxygen from the lungs to tissues and remove carbon dioxide.

• White Blood Cells (Leukocytes): Defend the body against infection and foreign substances.

• Platelets (Thrombocytes): Play a crucial role in blood clotting and wound repair.

• Example: A single drop of blood contains millions of erythrocytes, leukocytes, and platelets, each with distinct morphology and function.

Blood Composition and Hematocrit

Plasma and Formed Elements

Blood is composed of plasma (the liquid matrix) and formed elements (cells and cell fragments). The relative proportion of these components can be measured as hematocrit.

• Plasma: Contains water, proteins, nutrients, hormones, and waste products.

• Formed Elements: Includes erythrocytes, leukocytes, and platelets.

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

• Normal Hematocrit: 37%–47% for females, 42%–52% for males.

• Anemia: Depressed hematocrit, indicating fewer erythrocytes.

• Polycythemia: Elevated hematocrit, indicating excess erythrocytes.

Major Blood Components

Plasma Proteins and Cellular Elements

Blood contains various proteins and cells, each with specific functions and sites of production.

Subcomponent	Type/Name	Site of Production	Major Function
Water	Plasma	Produced by body metabolism	Transport medium
Plasma Proteins	Albumin	Liver	Maintains osmotic pressure
Plasma Proteins	Globulins	Liver, lymphatic tissue	Transport, immunity
Plasma Proteins	Fibrinogen	Liver	Blood clotting
Formed Elements	Erythrocytes	Red bone marrow	Oxygen transport
Formed Elements	Leukocytes	Red bone marrow, lymphatic tissue	Immunity
Formed Elements	Platelets	Red bone marrow	Hemostasis

Hematopoiesis: Formation of Blood Cells

Hematopoietic System of Bone Marrow

Hematopoiesis is the process by which all formed elements of blood are produced from stem cells in the bone marrow.

• Multipotent Stem Cells: Give rise to all blood cell types.

• Myeloid Lineage: Produces erythrocytes, platelets, neutrophils, eosinophils, basophils, and monocytes.

• Lymphoid Lineage: Produces lymphocytes (T cells, B cells, and natural killer cells).

• Example: Megakaryocytes in the bone marrow fragment to form platelets.

Summary of Formed Elements

Characteristics of Blood Cells and Platelets

Each formed element in blood has unique structural and functional properties.

Element	Appearance	Size	Function	Comments
Erythrocyte	Biconcave disc	~7-8 μm	Oxygen and carbon dioxide transport	No nucleus; contains hemoglobin
Neutrophil	Multi-lobed nucleus	~12-15 μm	Phagocytosis of bacteria	Most abundant leukocyte
Eosinophil	Bilobed nucleus, red granules	~12-15 μm	Combat parasites, modulate allergic responses	Increased in parasitic infections
Basophil	Bilobed nucleus, blue granules	~12-15 μm	Release histamine, mediate inflammation	Least abundant leukocyte
Lymphocyte	Large nucleus, small cytoplasm	~7-10 μm	Adaptive immunity (T cells, B cells)	Second most abundant leukocyte
Monocyte	Kidney-shaped nucleus	~15-20 μm	Phagocytosis, differentiate into macrophages	Largest leukocyte
Platelet	Small cell fragments	~2-4 μm	Blood clotting (hemostasis)	Derived from megakaryocytes

Additional info: The biconcave shape of erythrocytes increases surface area for gas exchange and allows flexibility in capillaries. Hematopoiesis is regulated by growth factors such as erythropoietin and thrombopoietin.