White Blood Cells Overview

Overview

This lecture covers the five main types of white blood cells, their structure, lifespan, and specific roles in the immune system.

General Features of White Blood Cells

• White blood cells (leukocytes) protect the body against diseases and foreign invaders.
• They are the largest cell type in blood but make up less than 1% of blood volume.
• White blood cells contain nuclei, unlike red blood cells.
• Their lifespan ranges from 18 hours to several years.
• White blood cells are found in blood and lymphatic tissue.

Basophils

• Basophils trigger allergic reactions by releasing heparin (blood thinner) and histamine (vasodilator).
• They defend against parasites and bacteria non-specifically.

Neutrophils

• Neutrophils are the most abundant white blood cell in most mammals.
• They rapidly target and destroy bacteria and fungi.
• Formed from stem cells in bone marrow, they respond quickly to infection.

Eosinophils

• Eosinophils target larger parasites such as worms.
• They help modulate allergic inflammatory responses.
• Eosinophils comprise about 1–6% of all white blood cells.

Monocytes

• Monocytes are the largest white blood cell type.
• Produced in bone marrow, they circulate in the blood 1–3 days before moving into tissues.
• They differentiate into macrophages, dendritic cells, and foam cells.
• Monocytes make up about 3–8% of white blood cells.

Lymphocytes

• Lymphocytes identify and help destroy foreign invaders.
• Main cell type in lymph; three subtypes: B cells, T cells, and natural killer cells.
• B cells (10% of lymphocytes) help identify foreign invaders.
• T cells (75% of lymphocytes) mature in the thymus and directly attack invaders.
• Natural killer cells defend mainly against tumors and viruses.

Key Terms & Definitions

• Leukocytes — white blood cells involved in immune defense.
• Basophils — leukocytes involved in allergies and parasite defense via chemical release.
• Neutrophils — most common leukocyte, targets bacteria and fungi.
• Eosinophils — white cells that fight parasites and regulate allergies.
• Monocytes — largest leukocytes, differentiate into other immune cells in tissues.
• Lymphocytes — immune cells (B, T, NK cells) key to producing targeted immune responses.
• Histamine — chemical that widens blood vessels during inflammation.
• Heparin — chemical that prevents blood clotting.

Action Items / Next Steps

• Review the functions and characteristics of each white blood cell type.
• Prepare to identify white blood cells by role and percentage in blood for exams.