The Lymphatic System LAB # 5 1- List the functions of Lymphatic System. 2- Describe the exchange of blood plasma, extracellular fluid, and lymph. 3- Describe the structure of a lymph node. 4- Explain how the lymphatic system drains into the vascular system 5- Describe the gross anatomy and basic histology of the spleen.

Functions of the Lymphatic System 1- Lymphocyte Production, Maintenance, and Distribution 2- Collection and Returning of Interstitial Fluid from Tissues to the Circulatory System 3- Distribution of Nutrients, Waste, and Hormones from Tissues to the Circulatory System

1- Lymphocyte Production, Maintenance, and Distribution. After maturation, most of the lymphocytes move into lymph nodes, the spleen and other lymphoid tissues. Immature lymphocytes are produced in the bone marrow. B lymphocytes mature in the bone marrow and T lymphocytes mature in the thymus. Lymphoid organs and tissues

One function of the lymphatic system is to reabsorb this excess and to return it to the blood. Fluid continually filters from the blood capillaries into the tissue spaces. But the blood capillaries reabsorb only 85%. 15% (2 – 4 L/day) of the water and about half of the plasma proteins are not absorbed by capillaries. 13 mm Hg 7 mm Hg 2- Collection and Returning of Interstitial Fluid from Tissues to the Circulatory System. 85 % 15 % 85%

The Lymphatic System - Lymphatic capillaries - Lymphatic collecting vessels - Lymphatic trunks Aggregates of lymphocytes in the connective tissue of mucous membrane and various organs. Mucosa-associated lymphatic tissue (MALT) 1- Peyer patches in the distal portion of the small intestine. They have well – defined anatomical sites and at least partial connective tissue capsules. 2- Thymus 1- Lymph nodes 3- Spleen It is the recovered fluid. Lymph is usually a clear colorless fluid, similar to blood plasma but low in protein. Lymphatic Vessels Diffuse Lymphoid Tissues Encapsulated Lymphoid Organs Lymph - Collecting duct 3- Tonsils (palatine tonsils and pharyngeal tonsils or adenoids). 2- Vermiform appendix

Lymphoid Organs Lymphatic Vessels Lymphoid Tissues

1- Lymphatic Vessels

Pulmonary circuit Superior vena cava Blood flow Systemic circuit Lymphatic system Cardiovascular system The lymphatic capillaries converge to form collecting vessels. Lymphatic capillaries Collecting vessels Lymphatic trunks Collecting ducts (2) The collecting vessels converge to form lymphatic trunks. The lymphatic trunks converge to form collecting ducts. The collecting vessels travel alongside veins and arteries, and at irregular intervals they empty into lymph nodes. In the lymph nodes, bacteria are phagocytized and immune cells monitor the fluid for foreign antigens. The names indicates their locations and part of the body they drain 1- Jugular trunks, 2- Subclavian trunks, 3- Bronchomediastinal trunks, 4- Intestinal trunk, and 5- Lumbar trunks 1- Right lymphatic duct 2- Thoracic duct Subclavian veins

Inferior Trunks Inferior vena cava 3- Lymphatic Trunks and Lymphatic Ducts Lymph Capillaries Collecting Vessels Lymphatic Trunks Lymphatic Ducts Right Lumbar Trunk Left Lumbar Trunk Intestinal Lumbar Trunk Cisterna Chyli Thoracic Duct Right lumbar trunk Left lumbar trunk Intestinal trunk Cisterna Chyli Thoracic duct

Superior vena cava Superior Trunks Right Jugular Trunk Right Bronchomediastinal Trunk Right Subclavian Trunk Right Lymphatic Duct Right Jugular Trunk Right Subclavian Trunk Right Bronchome- diastinal Trunk Thoracic Duct Right Lymphatic Duct RIGHTLEFT Left Jugular Trunk Left Subclavian Trunk Left Bronchome- diastinal Trunk Right subclavian vein Left Subclavian veint

Inferior Trunks

Right Lymphatic Duct Thoracic Duct Right side of the tissues superior to the diaphragm Right Lymphatic Duct Thoracic Duct Tissues inferior to the diaphragm and from left side of the upper body

2- Lymphoid Tissues and Lymph Nodes

Lymphoid Tissues Lymphoid tissues are areolar connective tissues with concentrations of lymphocytes. The lymphatic nodules or follicles have no fibrous capsule surrounding them. When lymphocytes are densely packed they form lymphoid or lymphatic nodules or follicles. Germinal center It contains dividing lymphocytes.

It is the collection of lymphoid tissues that protect the epithelia of the respiratory, digestive, urinary, and reproductive systems. Clusters of lymphoid nodules deep to the epithelial lining of the intestine are known as Peyer’s patches. MALT (Mucosa-Associated Lymphatic Tissue) The appendix vermiform is other example of MALT. It walls contain a mass of fused lymphoid nodules.

Tonsils Functions They are large concentration of lymphoid nodules in the walls of the pharynx. Pharyngeal tonsil or adenoid (single) Palatine tonsils (two) Lingual tonsils (two) They guard against ingested or inhaled pathogens.

Lymphatic organs have well-defined anatomical sites and have connective tissue capsule that separates the lymphatic tissue from neighboring tissues. Lymphoid Organs - Thymus - Lymph nodes - Spleen Lymph nodes They are the smallest and most numerous lymphatic organs (about 450 in typical young adult). Thymus Spleen Lymph nodes They range in diameter from 1 mm to 25 mm (about 1 inch)

Cervical lymph nodes Axillary lymph nodes Lumbar lymph nodes Pelvic lymph nodes Inguinal lymph nodes Lymph nodes are wide- spread but specially concentrated in some locations.

Lymph nodes Lymph vessel Lymph nodes Hilum Medullary sinus Outer cortex (B cells) Afferent vessel Medullary cord (B cells and plasma cells) Capsule Dense connective tissue Deep cortex (T cells) Subcapsular space Medulla Trabeculae Efferent vessel Lymph node artery and vein Lymph nodes are shaped like kidney beans. Cortex

Lymph Node Functions: 1- They filter and purify the lymph before return to venous circulation (they remove 99% of cell debris, bacteria, viruses, fungi). 2- They provide an early warning system against infection in peripheral tissue, responding before infections reach vital organs of trunk. 3- The first step in immune response takes place in the lymph nodes (extracted antigens are “presented” to lymphocytes).

The Thymus The thymus is located in the mediastinum. It atrophies after puberty. The thymus is divided into two thymic lobes. Right lobe Left lobe Septa Lobule Septa divide lobes into smaller lobules. Thymus

Lobule The thymus gland LM  50 Cortex Septa Medulla

Lymphocytes Cortex Septa Medulla Lobule The thymus gland LM  50 A thymic corpuscle LM  550 Reticular cells Thymic corpuscle Mature T cells leave thymus by medullary blood vessels. T lymphocytes divide in the cortex and mature while they migrate to the medulla. The thymus secretes thymic hormones that stimulate T cell differentiation.

Spleen Rib Pancreas Aorta Parietal peritoneum Visceral peritoneum Stomach Diaphragm Gastric area Diaphragmatic surface Renal area Kidneys Liver Gastrosplenic ligament SPLEEN Hilum The Spleen It is the body’s largest lymphatic organ.

The spleen LM  50 White pulp of splenic nodule Capsule Red pulp Trabecular artery Central artery in splenic nodule White pulp is dominated by lymphocytes. Red pulp contains a large number of red blood cells. Functions: 1- Removal of abnormal and worn out blood cells. 2- Storage of iron recycled from red blood cells. 3- Initiation of immune responses by B cells and T cells. Histology of the Spleen