Chapter 19: Blood – Structure, Function, and Disorders

Cardiovascular System Overview

Main Components

The cardiovascular system is essential for transporting substances throughout the body and maintaining homeostasis.

• Blood: The fluid medium responsible for transport.

• Heart: The pump that propels blood.

• Blood Vessels: The conducting system for blood flow.

Module 19.1: Overview of Blood

Physical Characteristics of Blood

Blood is a specialized connective tissue with unique properties.

• Temperature: 38°C (100.4°F), slightly higher than body temperature.

• Color: Ranges from scarlet (oxygen-rich) to dark red (oxygen-poor).

• Viscosity: High, making blood sticky.

• Taste: Metallic.

• pH: Slightly alkaline (7.35–7.45).

• Volume: 8% of body weight; adult males 5–6 liters, females 4–5 liters.

Functions of Blood

• Exchanging gases: Transports oxygen and carbon dioxide.

• Distributing solutes: Plasma carries ions, nutrients, hormones, and wastes.

• Immune functions: Leukocytes and immune proteins defend against pathogens.

• Maintaining body temperature: Blood absorbs and redistributes heat.

• Blood clotting: Platelets and proteins seal damaged vessels.

• Acid-base homeostasis: Buffers maintain pH between 7.35 and 7.45.

• Stabilizing blood pressure: Blood volume is a key factor.

Blood Structure

• Plasma: Liquid extracellular matrix (about 55% of blood volume).

• Formed Elements: Cells and cell fragments suspended in plasma:

  • Erythrocytes (RBCs): Transport gases.

  • Leukocytes (WBCs): Immune defense.

  • Platelets: Cell fragments involved in clotting.

Plasma Composition

Plasma is a pale yellow fluid, 90% water, and contains proteins and solutes.

Plasma Component	Function
Water	Solvent for transport and temperature regulation
Albumin	Maintains osmotic pressure, transports substances
Immune proteins	Antibodies for immune defense
Transport proteins	Bind and carry hydrophobic molecules
Clotting proteins	Form blood clots
Other solutes	Glucose, amino acids, ions, dissolved gases

Body Fluids

• Intracellular fluid (ICF): Cytosol inside cells.

• Extracellular fluid (ECF): Includes interstitial fluid (IF) and plasma.

• Key differences: Levels of respiratory gases and dissolved proteins.

Cirrhosis

Cirrhosis is a liver disease that impairs plasma protein production, leading to decreased osmotic pressure, fluid loss (ascites), and clotting deficiencies.

• Causes: Cancer, alcoholism, hepatitis.

• Effects: Edema, easy bruising, delayed clotting.

Module 19.2: Erythrocytes and Oxygen Transport

Blood Layers (Centrifuged)

• Top layer: Plasma (55%)

• Middle layer: Buffy coat (leukocytes and platelets, 1%)

• Bottom layer: Erythrocytes (44%)

Hematocrit: Percentage of blood volume composed of erythrocytes.

Erythrocyte Structure

• Biconcave disc: Increases surface area for gas exchange.

• Anucleate: No nucleus or most organelles in mature RBCs.

• Hemoglobin (Hb): Protein for oxygen transport; each RBC contains ~280 million Hb molecules.

Hemoglobin Structure and Function

• Composed of four polypeptide chains (2 alpha, 2 beta).

• Each chain binds a heme group with iron.

• Iron binds oxygen to form oxyhemoglobin ($HbO_2$).

• Also binds carbon dioxide (carbaminohemoglobin) and carbon monoxide (carboxyhemoglobin).

Red Blood Cell Count and Hematocrit

Parameter	Male	Female
RBC count (million/μL)	4.5–6.3	4.2–5.5
Hematocrit (%)	45	40
Hemoglobin (g/dL)	14–18	12–16

Erythrocyte Life Span

• 100–120 days due to harsh environment and lack of repair mechanisms.

• Continuous production required.

Hematopoiesis

Formation of blood cells from hematopoietic stem cells (HSCs) in red bone marrow.

• Embryo: Yolk sac, liver, spleen.

• Adult: Bone marrow (primary site).

• Stem cell lines:

  • Myeloid: RBCs, platelets, some WBCs.

  • Lymphoid: Lymphocytes.

Erythropoiesis

Specific process for RBC production, taking 5–7 days.

• HSCs → erythrocyte CFUs → proerythroblasts (with EPO) → erythroblasts → reticulocytes → mature erythrocytes.

• Requires amino acids, iron, B6, folic acid, B12, and EPO.

Regulation: Negative feedback via EPO in response to hypoxia.

Additional info:

• Blood disorders, leukocyte function, platelets, and hemostasis are covered in subsequent modules/slides.

• Tables and diagrams referenced in the notes provide visual summaries of cell differentiation and blood composition.