Biology 2404 A&P Basics

Biology 2404 A&P Basics Lab Exercise 15 Lymphatic System Dr. Weis

Objectives

Background

Medical Terms

Objectives:

Students should be able to

* define lymph

* describe the circulation of lymph through lymphatics

* Give the location, function, and anatomy of the lymphoid organs:

lymph node, spleen, tonsils, thymus, and peyers patches

* Define related terms

A&P Background

Read related material in textbook

The lymphatic system is similarly composed as the cardiovascular system. There is a fluid called lymph, a system of vessels called lymphatics, and related organs such as lymph nodes, spleen, tonsils, peyers patches, and the thymus.

Lymph is the remaining 30% of tissue (interstitial) fluid that was collected by lymphatic vessels (lymphatics) after the blood capillary exchange. The lymph fluid resembles plasma in composition as it will contain water, ions, nutrients, and gases. However, lymph has a higher protein and cellular content than plasma. Lymph enters lymphatic vessels called lymphatic capillaries. These vessels resemble the venous structure in relation to valves and vessel walls and follow the venules and veins as they return to the heart. The lymphatic vessels drain into regional trunks that end in two major ducts: the right lymphatic duct and the thoracic duct. These ducts connect to the right and left brachiocephalic veins and allow the lymph to be returned back to the cardiovascular system. The process of returning lymph back to the cardiovascular system takes about 24 hours. If the excess interstitial fluid is not returned, pressures around the tissue increase causing swelling known as edema.

The lymphatic capillary lining consists of valve like flaps that open and close based on fluid pressure gradients. These vessels are passive in their collection of substances so that large proteins and even damaged or cancerous cells can enter lymphatic circulation. In order to clear and clean the lymphatic fluid before it is returned to the heart, the lymph vessels pass through lymph glands or nodes. These oval to bean shaped structures differ in respect to size and location. Their size can range from 1-25 mm and major locations are found in the inguinal, axillary, cervical, and intestinal regions.

Lymph Nodes

The structure of a lymph node consists of a capsule, cortex, and medulla.

General Lymph Node Model Exterior

General Lymh Node Model Interior Transverse Section

The connective tissue capsule forms a subcapsular space or sinus that allows for lymph collection from the afferent lymphatics. The lymph node cortex is arranged into lymph nodules with a germinal center that produces daughter lymphocytes. The lymph node medulla is reticular connective tissue with associated macrophages and lymphocytes forming the medullary cords.

Lymph Node Model: Cortex and Medulla

As lymph fluid flows through the cortex and medulla it is cleaned and filtered as it encounters the various WBCs that form the two major divisions of the immune system.

Specialized lymphatic vessels that occur in the small intestine of the gastrointestinal tract are called lacteals and function in fat absorption. Because of the milky appearance, the lymphatic fluid is called chyle. Chyle follows the normal flow of lymph and will be returned to the heart the same way as lymph is returned. Fats are then made available to the body organs for energy use or storage. Lymphatics return lymph back to the heart. Those from the lower legs combine to form the Cysterna Chyli. More lymph from the left trunk, left arm and head together with the cysterna chyli form the Thoracic Duct which empties cleansed lymph into the left brachiocephalic vein.

Lymph returning from the right side of the head, arm and trunk enters the right lymphatic duct to be emptied into the right brachiocephalic vein.

Torso model

Lymph man model: General

Lymph Node Model (above) Labeled

Lymph node drawing

Lymph node histology

Lymph vessel histology

Cat Specimen : LN

Regional Lymph Nodes: Cervical, Inguinal, Intestinal

Thoracic Duct

Cysterna Chyli

Other lymphatic organs / tissues

Spleen located in the left upper abdominal quadrant

Histologically has a capsule and red and white pulp

Red pulp is composed of RBCs

White pulp is composed of WBCs around arterioles

Function to recycle red blood cells and immune defense

Tonsils located in a circular ring in the pharyngeal regions

Names reflect location: Tubular, Pharyngeal, Palantine, Lingual

Histologically are lymphatic nodules embedded in the throat lining

Function in immune defenses related to respiratory and digestive

Peyer’s Patches located in the last portion of the small intestine called the ileum

Lymphatic nodules embedded under the lining of the digestive tract

Function to provide immune defense and alert for the digestive tract

Thymus located in young mammals in the mediastinum, above the heart

Histologically is composed of a capsule, cortex, and medulla

Bilobed in humans, elongated triangle shape

Functions to program lymphocytes to become various T-cells for

the Specific immune defenses.

Torso model: Spleen, Ileum, LN, Appendix

Sagittal head model: Tonsils

Cat specimen: Spleen, Thymus, Ileum

Histology

Spleen

Tonsils

Peyer’s patches

Thymus

Lymphocytes

Macrophages

Medical Terminology

Lymph/o- lymph splen/o- spleen

Tonsil/o- tonsils -asis condition, state

Lien- spleen lymphaden/o- lymph gland

Exercises/Activities

I. Palpate lymph nodes : Locate regional lymph nodes on drawings or models and see if you can palpate these organs. List the locations where you palpated a lymph node. What would a painful, enlarge lymphnode found on palpation possibly indicate?

II. ID lymphatic organs

A Drawing

B Model