The Lymphatic System

Biology 2122Chapter 20

Functions of the Lymphatic System1. Drain Excess ‘interstitial’ fluid◦ 2-3 L of fluid lost from the blood stream/day

2. Transport dietary lipids◦ From GI tract to the blood (lipids and lipid-soluble vitamins)

3. Immune Response ◦ A. Cell-mediated response

T-cell response (cytotoxic cells destroy antigens)

◦ B. Humoral – response Antibody-mediated (B-Cells)

Basic Structure 1. Lymph Fluid◦ Interstitial fluid ------ lymph

capillaries

2. Lymph Vessels◦ Capillaries, ducts, etc.

3. Lymph Tissue and Organs ◦ Specialized reticular tissue◦ Large numbers of lymphocytes ◦ Organs: Thymus gland;

Tonsils; Spleen

Tissues to the Heart

Lost lymph fluid - returned to the heart. 1. Capillaries ◦ Endothelial Cells and mini-valves

Supported by collagen One way pressure from the capillaries

move lymph towards the capillaries

◦ Very permeable

2. Capillaries form vessels ◦ Skin follow veins; viscera follow path of

arteries ◦ Lymph flows into the nodes ◦ No lymph vessels (cartilage, epidermis,

cornea- all avacular); CNS and red bone marrow

Chyle and Lacteals Lipids absorption take place in the small intestine

Lacteals◦ Small capillaries in the absorptive cells◦ Lipids transported from lacteals into the blood

Specialized lipid absorption

Chyle ◦ In small intestine lymph is white or creamy due to lipid presence

(lymph is normally clear)

Flow and Structure

Capillaries ----- Collecting vessels ---- Nodes --- Trunks ------ Lymph ducts (thoracic and right lymphatic) ----- Internal jugular and Subclavian vein ---- Heart

On the way to the heart 1. Trunks – lumbar, intestinal, bronchomediastinal, subclavian, jugular ◦ A. lumbar ◦ B. intestinal◦ C. bronchomediastinal ◦ D. subclavian ◦ E. Jugular

2. Thoracic (left lymphatic) duct ◦ Cisterna chyli ◦ Main duct for return of lymph to blood from left side of body◦ Drains into the L.internal jugular and L.subclavian vein

On the way to the heart 3. Right lymphatic duct – Receives lymph from

right side of the body– Drains blood into

venous blood at junction of R. internal jugular and R. subclavian veins

Flow of Lymph against Gravity Same problems as encountered by venous return

Pumps ◦ 1. Skeletal system pump ◦ 2. Respiratory pump

Organs and Tissues

Organs and Tissues 1. Primary Organs – stem cell division produces mature cells – immunocompetent ◦ Red bone marrow

B – cells; pre-T cells ◦ Thymus

Pre-T cells migrate to thymus to become immunocompetent

2. Secondary Organs◦ Site of immune system response◦ Nodes, spleen, nodules

Thymus Bi-lobed- surrounded by CT and separated by capsule

Trabeculae -separates tissue into lobes

Lobe ◦ Cortex -(T-cells and Dendritic

cells, Epithelial cells and Macrophages)

◦ Medulla – mature T-cells, dendritic cells and macrophoges

◦ Thymic (Hassal’s corpusles)

Lymph Nodes Lymphatic Nodules ◦ B-cells (primary lymphatic nodule)◦ Plasma and memory B cells in outer

cortex (secondary lymphatic nodule)

B-cell in primary nodule recognizes antigen and transforms into a secondary nodule ◦ Germinal center ◦ B-cells, follicular dendritic cells,

macrophages

Antigen presented by APC (B-cell; dendritic , etc.) B- cells develop into plasma and memory cells

Inner cortex and medulla Covered by Dense CT capsule

Spleen

Covered by Dense CT capsule Visceral peritoneum – serous membrane

Stroma ◦ Trabeculae, reticular fibers and fibroblasts

Parenchyma ◦ 1. White pulp – lymphocytes and macrophages around central

arteries (splenic artery branches)

◦ 2. Red pulp – venous sinuses, cords of splenic tissue or splenic cords (RBCs, macrophages, lymphocytes, plasma cells, granulocytes

Nodules No capsuleFound in mucous membranes (near lamina propria) in GI

tract, urinary, reproductive, respiratory airways◦ “Mucosa-associated lymphatic tissue (MALT)

Can be small or larger tissue◦ Tonsils (5)-Pharyngeal area

Pharyngeal (adenoid- posterior nasopharynx) Palatine (2)-posterior region of oral cavity (tonsillectomy) Lingual (2)-base of tongue