Understanding the Lymphatic System: Functions, Lymphocytes, and Composition

1. Know the functions of the lymphatic system

· Produce, maintain, and distribute lymphocytes and other lymphoid cells that provide defense against infections and foreign substances PRIMARY FUNCTION. Return of excess fluid to bloodstream. Transport of lipids absorbed in digestive tract

2. Know the three subtypes of lymphocytes and what type of immunity each is responsible for

· T cells à Cell-mediated immunity (4+ subtypes)

• Cytotoxic T Cells (T_c) - direct cellular attack
• Helper T Cells (T_H) and Suppressor T Cells (T_S) - regulatory roles
• Memory T Cells.

B Cells à Antibody-mediated immunity

• Antibodies (immunoglobulins)
• Antigen - usually proteins (specific chemical targets)

· NK Cells à Immunological surveillance

3. Know where the three types of lymphocytes are produced

· T Cells à thymus

· NK cells à Red bone marrow

· B cells à Red bone marrow

4. Describe the composition of lymph and describe the network of lymphatic vessels

Lymph is interstitial fluid that has entered lymphatic vessels, which vary in size. Lymph first enters lymphatic capillaries and then drains into larger major lymph-collecting vessels, known as trunks and ducts.

Lymphatic capillaries:

• Smallest lymphatic vessels
• Beginning of lymph circulation

Lymphatic vessels:

• Comparable to veins: Have valves
• Vessels converge to form lymphatic trunks
• Trunks empty into 2 large collecting vessels:

• Thoracic Duct
• Right Lymphatic Duct

a) How do lymph capillaries differ from blood capillaries?

Lymphatic capillaries:

• Originate as pockets (not continuous tubes)
• Have larger diameters
• Have thinner walls (permit one-way transport)
• Have flattened/irregular outline in cross-section

b) Describe the flow of lymph through the body – where is originates and what its ultimate destination is

Peripheral tissues à Lymphatic Capillaries à Afferent vessels à Lymph nodes à Efferent Vessels à Lymphatic Ducts à Venous System (Subclavian Veins)

c) Differentiate between the thoracic duct and the right lymphatic duct

Thoracic Duct à Left Subclavian Vein

Right Subclavian Duct à Right Subclavian Vein