LAB 5 The Lymphatic System 1 List the

LAB # 5 The Lymphatic System 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. 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 After maturation, most of the lymphocytes move into lymph nodes, the spleen and other lymphoid tissues.

2 - Collection and Returning of Interstitial Fluid from Tissues to the Circulatory System. 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. One function of the lymphatic system is to reabsorb this excess and to return it to the blood. 85% 13 mm Hg 7 mm Hg 85% 15%

The Lymphatic System Lymph 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 - Lymphatic capillaries Aggregates of lymphocytes in the connective tissue of - Lymphatic collecting mucous membrane and various organs. vessels Mucosa-associated - Lymphatic trunks lymphatic tissue (MALT) - Collecting duct 1 - Peyer patches in the distal portion of the small intestine. 2 - Vermiform appendix 3 - Tonsils (palatine tonsils and pharyngeal tonsils or adenoids). Encapsulated Lymphoid Organs They have well – defined anatomical sites and at least partial connective tissue capsules. 1 - Lymph nodes 2 - Thymus 3 - Spleen

Lymphoid Organs Lymphoid Tissues Lymphatic Vessels

1 - Lymphatic Vessels

The lymphatic capillaries converge to form collecting vessels. 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 foreign antigens. The collecting vessels converge to form lymphatic trunks. 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 Lymphatic system Subclavian veins Cardiovascular system Pulmonary circuit Collecting ducts (2) Lymphatic trunks Superior vena cava Collecting vessels Blood flow The lymphatic trunks converge to form collecting ducts. 1 - Right lymphatic duct 2 - Thoracic duct Lymphatic capillaries Systemic circuit

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

RIGHT LEFT Right Jugular Trunk Left Subclavian Trunk Right Lymphatic Duct Right subclavian vein Right Bronchomediastinal Trunk Left Jugular Trunk Thoracic Duct Left Subclavian veint Superior vena cava Left Bronchomediastinal Trunk Superior Trunks Right Jugular Trunk Right Subclavian Trunk Right Bronchomediastinal Trunk Right Lymphatic Duct

Inferior Trunks

Right Lymphatic Duct Right side of the tissues superior to the diaphragm 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 areolar connective tissues with concentrations of lymphocytes. When lymphocytes are densely packed they form lymphoid or lymphatic nodules or follicles. The lymphatic nodules or follicles have no fibrous capsule surrounding them. Germinal center It contains dividing lymphocytes. Lymphatic nodule or follicle

MALT (Mucosa-Associated Lymphatic Tissue) 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. The appendix vermiform is other example of MALT. It walls contain a mass of fused lymphoid nodules.

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

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

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

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

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. Septa divide lobes into smaller lobules. Thymus Right lobe Septa Lobule Left lobe

Septa Lobule Mature lymphocytes Dividing lymphocytes Lobule The thymus gland LM 50 Medulla Cortex

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

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

Histology of the Spleen White pulp of splenic nodule White pulp is dominated by lymphocytes. Capsule Red pulp contains a large number of red blood cells. Trabecular artery The spleen LM 50 Central artery in splenic nodule 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.