The lymphatic system is made up of two main parts:

1. Lymphatic tissues and organs: These include the bone marrow, thymus, spleen, lymph nodes, and tonsils. Their main function is to produce and store lymphocytes (a type of white blood cell) and other immune cells that help protect the body against infection and disease.

2. Lymphatic vessels: These vessels are a network of thin tubes that run throughout the body, similar to blood vessels. They help transport lymph (a clear fluid that contains immune cells, waste products, and excess fluid) back to the bloodstream. The lymphatic vessels also play a role in disease resistance by filtering out harmful substances, such as bacteria and viruses, from the lymph.

3. In addition to their immune function, the lymphatic vessels also absorb digested fat at the intestinal villi. This process, known as fat absorption or lipid absorption, is important for the proper digestion and absorption of dietary fats

4. Lymph is a thin, watery fluid that is similar in composition to interstitial fluid. It is formed when plasma diffuses into tissue spaces, and it contains water, digestive nutrients, salts, hormones, oxygen, carbon dioxide, lymphocytes, and metabolic wastes. The lymphatic system helps to return materials, such as water, nutrients, and white blood cells, back to the bloodstream, while removing waste products, bacteria, fungi, cancer cells, and viruses.

5. The lymphatic vessels are a one-way system that carries lymph towards the heart. Unlike the circulatory system, the lymphatic system has no pump, so movement of skeletal muscles is necessary to move the lymph back to the heart. Valves and smooth muscle tissue prevent fluid backflow. Lymphatic capillaries are open-ended tubes that carry lymph back to the heart and away from lymph nodes.

6. Lacteals are specialized lymphatic capillaries that pick up digested lipids in the small intestine and transport chyle to the bloodstream through the thoracic duct.

7. Chyle is lymph mixed with lipids.

8. Lymph nodes are found in the neck, armpits, abdomen, and pelvis. Their main function is to filter lymph before it returns to the blood.

9. There are two types of defensive cells in the lymph nodes: macrophages, which engulf and destroy foreign substances, and lymphocytes, which provide an immune response to antigens.

10. The lymphatic ducts are vessels that join together to form larger ducts, which eventually drain into the thoracic duct or the right lymphatic duct.

11. The thoracic duct is the largest lymphatic vessel in the body and is responsible for draining lymph from the lower half of the body and the left side of the upper body. The right lymphatic duct drains lymph from the right side of the upper body.

12. The lymphoid organs are a group of tissues that produce and store lymphocytes, which are white blood cells that help protect the body against infection and disease. They include the spleen, thymus, tonsils, and Peyer's patches.

13. The spleen is located on the left side of the stomach and is the largest lymphoid organ in the body. It produces leukocytes and antibodies, and it also plays a role in destroying old or damaged red blood cells and platelets.

14. The thymus is located in the chest, overlaying the heart. It plays an important role in the immune system during childhood by producing antibodies and lymphocytes to fight infection. As we age, the thymus atrophies and its functions are taken over by the lymph nodes. The thymus also produces hormones as adults.

15. The tonsils are a group of lymphoid tissues located in the throat. They trap and remove bacteria that enter the body through the mouth and nose. There are three types of tonsils:

16. Palatine tonsils: located on each side of the soft palate

17. Pharyngeal tonsils (adenoids): located in the upper part of the throat

18. Lingual tonsils: located at the back of the tongue

19. Peyer's patches are lymphoid tissues located in the wall of the small intestine. They function similar to tonsils by destroying bacteria that enter the body through food or water

20. Red bone marrow is responsible for the production of blood cells through a process called hematopoiesis. It is located in the spongy bone at the epiphysis of a bone and is highly vascularized with many arteries.

21. Sinusoids drain into the longitudinal vein that exits the bone. Reticular cells found in the red bone marrow allow for the formation of white blood cells, and later turn into adipose tissue, forming yellow bone marrow.

22. The body's defenses against infection and disease include physical barriers like the skin and mucous membranes, as well as inflammatory and specific defenses.

23. The skin serves as a physical barrier to prevent entry of pathogens into the body. The skin's pH is slightly acidic, which helps prevent bacterial growth, and sebum is toxic to bacteria.

24. The stomach produces hydrochloric acid, saliva and tears contain lysosomes, and the mucous membranes trap foreign particles that are inhaled.

25. The inflammatory response is a non-specific defense mechanism that occurs when tissues are damaged. It involves increased metabolic rate of damaged cells and increased capillary permeability, leading to the build-up of fluid (edema) and the migration of neutrophils and monocytes to the site of damage to remove pathogens and damaged cells.

26. The specific defense mechanisms involve the immune system and the production of antibodies that target specific pathogens. T lymphocytes (T cells) mature in the thymus and stimulate the production of B cells. Natural killer cells are large lymphocytes that destroy pathogens. B lymphocytes (B cells) develop in the bone marrow and undergo a cloning process to produce copies of themselves, which then turn into plasma cells that produce antibodies. Antigen-presenting cells, such as macrophages, dendritic cells, and reticular cells found in the thymus, present antigens to T cells and B cells to initiate an immune response.

27. Self and non self: the immune system identifies foreign materials (antigens) self antigens (glycocalyx serves as cell markers)

28. Autoimmune disorders occur when the body sees your own cells as antigens

29. Humoral immune response: B lymphocytes with specific receptors bind to a specific antigen, binding activates lymphocytes, a large umber of clones are produced

30. B cells encounter antigens and produce antibodies

31. Active immunity can be naturally or artificially acquired

32. Immunoglobins: soluble proteins secrete B cells (plasma cells) they are carried in blood plasma and are capable of binding to a specific antigen

33. Passive immunity: