Blood Vessels

Types and Functions of Blood Vessels

Blood vessels are tubular structures that transport blood throughout the body. They are classified into three main types, each with distinct functions:

• Arteries:

  • Function: Carry oxygenated blood away from the heart to tissues (except pulmonary arteries, which carry deoxygenated blood to the lungs).

• Veins:

  • Function: Return deoxygenated blood from tissues back to the heart (except pulmonary veins, which carry oxygenated blood from the lungs to the heart).

• Capillaries:

  • Function: Facilitate exchange of gases, nutrients, and waste products between blood and tissues.

Blood

Functions of Blood

Blood is a specialized bodily fluid that performs several vital functions:

• Transport: Delivers oxygen, nutrients, and hormones to cells; removes waste products.

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

• Protection: Defends against pathogens and prevents blood loss via clotting.

• Homeostasis: Maintains stable internal conditions.

• Communication: Transports signaling molecules.

Composition of Blood

Liquid Part (Plasma)

Plasma is the liquid component of blood, making up about 55% of total blood volume.

• Percentage of blood: ~55%

• Composition:

  • Water: ~90-92%

  • Proteins: Albumin, globulins, fibrinogen

  • Solutes: Electrolytes, nutrients, hormones, waste products

• Percentage of plasma:

  • Water: ~90-92%

  • Proteins: ~7-8%

  • Other solutes: ~1-2%

Cell and Cell Fragment Part (Formed Elements)

Formed elements make up about 45% of blood volume and include:

• Erythrocytes (Red Blood Cells):

  • Function: Transport oxygen and carbon dioxide.

• Leukocytes (White Blood Cells):

  • Function: Defend against infection and disease.

• Platelets (Thrombocytes):

  • Function: Aid in blood clotting.

Additional info: Erythrocytes are the most numerous formed element.

Formation of Blood Cells (Hematopoiesis)

Stages of Hematopoiesis

Hematopoiesis is the process of blood cell formation, primarily occurring in the bone marrow.

• Stem Cell: Hematopoietic stem cell (pluripotent)

• Myeloblasts: Differentiate into granulocytes (neutrophils, eosinophils, basophils)

• Megakaryocytes: Produce platelets

• Proerythroblasts: Develop into erythrocytes

• Hormone involved: Erythropoietin stimulates erythrocyte production

Hematology

Purpose and Scope

Hematology is the study of blood, blood-forming organs, and blood diseases.

• What does it look at: Blood composition, function, and disorders

• Types of disorders: Anemia, leukemia, clotting disorders

• Complete Blood Count (CBC): Measures red cells, white cells, platelets, hemoglobin, hematocrit

• CBC with differential: Includes breakdown of white blood cell types

Erythrocytes (Red Blood Cells)

Structure and Function

Erythrocytes are biconcave, anucleate cells specialized for gas transport.

• Primary function: Carry oxygen from lungs to tissues and carbon dioxide from tissues to lungs

• Shape: Biconcave disc increases surface area for gas exchange

• Main organelle: Lack nuclei and most organelles; packed with hemoglobin

• What can't it do: Cannot divide or repair itself

Main Protein: Hemoglobin

• Function: Binds and transports oxygen and carbon dioxide

• Iron: Each hemoglobin molecule contains iron, which binds oxygen

• Oxygen capacity: Each hemoglobin can carry up to 4 oxygen molecules

• Comparison:

  • Oxyhemoglobin: Hemoglobin bound to oxygen

  • Deoxyhemoglobin: Hemoglobin not bound to oxygen

Life Cycle of Erythrocytes

• Production: Made in bone marrow

• Lifespan: ~120 days

• Destruction: Removed by spleen and liver; hemoglobin recycled

• Waste product: Bilirubin, excreted in bile

Blood Typing

ABO Blood Groups

Blood type is determined by the presence or absence of antigens on erythrocytes.

Rh Blood Typing

• Rh antigen: Presence = Rh+; absence = Rh-

• Rh incompatibility: Can cause hemolytic disease of the newborn if Rh- mother carries Rh+ fetus

• First pregnancy: Usually not affected

• Subsequent pregnancies: Risk increases if mother has developed anti-Rh antibodies

Leukocytes (White Blood Cells)

Types and Functions

Leukocytes are immune cells that protect the body from infection.

Granulocytes

• Neutrophils: Most common; phagocytize bacteria

• Eosinophils: Combat parasitic infections and mediate allergic responses

• Basophils: Release histamine; involved in allergic reactions

Agranulocytes

• Lymphocytes: B cells and T cells; adaptive immunity

• Monocytes: Phagocytize pathogens; become macrophages in tissues

Fibrinolysis

Definition and Process

Fibrinolysis is the process of breaking down fibrin in blood clots, preventing excessive clotting and maintaining blood flow.

• Summary: Plasmin enzyme digests fibrin, dissolving the clot

Additional info: Fibrinolysis is essential for wound healing and preventing thrombosis.