White Blood Cells: Lymphocytes and Phagocytes

White Blood Cells

• There are two main types of white blood cells: 25% lymphocytes and 75% phagocytes
• Lymphocytes:
  • Have a large, round nucleus that controls the production of antibodies
  • Have only a small amount of cytoplasm
• Phagocytes:
  • Have a variable shape
  • Can move out of capillaries through their walls and engulf pathogens
  • Have a lobed nucleus

Formation of White Blood Cells

• Develop from cells in the red bone marrow and mature in other organs (e.g. lymph nodes, spleen, thymus gland)
• Formed in the red bone marrow

Functions of White Blood Cells

• Produce antibodies to destroy disease-causing bacteria and viruses (pathogens)
• Produce antitoxins to neutralize toxins produced by pathogens
• Engulf and destroy pathogens
• Engulf pathogens destroyed by antibodies

Other Types of White Blood Cells

• Neutrophils:
  • Protect against infections
  • Make up approximately 40-60% of white blood cells
  • First cells to arrive on the scene when experiencing a bacterial infection
• Eosinophils:
  • Disease-fighting white blood cells
  • Increase with allergies and parasite infestations
• Basophils:
  • Part of the immune system
  • Play a role in its proper function
• Monocytes:
  • Destroy pathogens by phagocytosis
  • First line of defense in the inflammatory process

Platelets (Thrombocytes)

• Structure:
  • Cell fragments
  • Have no nucleus and only live for about 10 days
• Formation:
  • Formed from cells in the red bone marrow
• Functions:
  • Help the body form clots to stop bleeding
  • Respond to damaged blood vessels and form a plug (clot) to fix the damage

The Vascular System

• Also called the circulatory system
• Made up of vessels that carry blood and lymph through the body
• Delivers oxygen and nutrients to body tissues and takes away tissue waste matter
• Composed of:
  • Arteries
  • Veins
  • Capillaries

Arteries

• Transport blood away from the heart to body tissues and organs
• Blood flows through under high pressure
• Blood moves in pulses created as the ventricles contract
• Blood flows rapidly
• Blood is oxygenated, except in the pulmonary artery
• Most lie deep within the body, protected by layers of tissue
• Do not possess valves, except the aorta and pulmonary artery as they leave the ventricles of the heart
• Have walls composed of three layers, thick and elastic to withstand high pressure

Capillaries

• Transport blood throughout all body tissues and organs, linking arteries to veins
• Blood flows through under low pressure
• Blood flows smoothly
• Blood flows very slowly
• Blood becomes deoxygenated as it travels through capillaries
• Run throughout all tissues and organs
• Do not possess valves
• The walls composed of a single layer of endothelial cells, so substances pass easily between the blood and body cells
• Extremely narrow and branch repeatedly, so that all body cells are close to capillaries

Veins

• Transport blood back towards the heart from body tissues and organs
• Blood flows through under low pressure
• Blood flows smoothly
• Blood flows slowly
• Blood is deoxygenated, except in the pulmonary vein
• Many lie close to the body surface
• Possess valves to prevent low pressure, slow flowing blood from flowing backwards
• Have walls composed of three layers, thin because they do not have to withstand high pressure
• The lumen is wide, so it does not resist the flow of low pressure blood

Venipuncture

• The puncture of a vein as part of a medical procedure, typically to withdraw a blood sample or for an intravenous injection
• There are three veins primarily used by the phlebotomist to obtain venous blood specimens: the median cubital, the cephalic, and the basilic veins
• Alternate sites available for venipuncture, including the veins on the back of the hand and wrist

Blood Composition

• Blood is a mixture of fluid and cells
• The fluid portion of the blood is called plasma; the cellular portion is referred to as the formed elements
• Cellular portion: red blood cells, white blood cells, platelets
• Coagulation: the clotting of blood, which takes place within 30-60 minutes after blood is removed from the body
• Serum: the remaining fluid part of the sample, separated from the clot by spinning the sample in a centrifuge
• Plasma: the liquid part of the blood, composed of about 90% water and 10% dissolved substances, including products of digestion, waste products, hormones, and plasma proteins