lymphatic system

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What does the lymphatic system include?

lymph, lymphatic vessels, lymphatic tissue, lymphatic nodules, lymph nodes, tonsils, the spleen, and the thymus

Functions of Lymphatic System

1. part of the body's defense system against microorganisms and other harmful substances.
2. Fluid balance (fluid that doesn't transfer from interstitial space back to blood capillaries goes into lymphatic capillaries where fluid is called lymph)
3. Fat absorption (absorbs fats and other substances through lacteals in the digestive tract)
4. Defense (microorganims and other foreign substances are filtered from lymph by lymph nodes and from blood by the spleen)

How does fluid move in the lymphatic system?

Unlike circulatory system, the lymphatic system carries fluid in one direction, from tissues to circulatory system (not to and from tissues). Fluid moves from blood capillaries into interstitial spaces and what doesn't return to blood goes to the lymphatic capillaries to become lymph.

description of lymphatic capillaries

tiny, closed-ended vessels consisting of simple squamous epithelium. Because they lack a basement membrane and are loosely attached, lymphatic capillaries are much more permeable than blood capillaries and no interstitial fluid is excluded. The overlapping epithelium also acts as one way valves that allow fluid to enter capillary but prevent it from passing back into interstitial space.

What tissues of the body are lymphatic capillaries NOT in?

central nervous system, bone marrow, and tissues without blood vessels (such as epidermis and cartilage)

lymphatic vessels

-formed by joined lymphatic capillaries
-beaded appearance b/c of one-way valves.
-compression causes lymph to move through them and valves prevent back-flow

3 factors that cause compression of lymphatic vessels

1. the periodic contraction of smooth muscle in the lymphatic vessel wall
2. the contraction of surrounding skeletal muscle during activity
3. pressure changes in the thorax during respiration

How does fluid leave lymphatic vessels?

Vessels converge and eventually empty into blood at either right lymphatic duct (from upper right limb, and the right half of head, neck, and chest) or thoracic duct (rest of body). Right lymphatic duct empties into right subclavian vein and thoracic duct empties into left subclavian vein.

What is the largest lymphatic vein?

thoracic duct

What are the lymphatic organs and what do they contain?

Organs include tonsils, lymph nodes, spleen, and thymus.
Lymphatic organs contain lymphatic tissue (consists primarily of lymphocytes) but also macrophages, dendritic cells, reticular cells, and other cell types.

What are the 2 types of lymphocytes and what is their role?

B cells and T cells. Originate from red bone marrow and are carried by blood to lymphatic organs and other tissues. When body is exposed to microorganisms, lymphocytes divide, increase in number and are part of immune response to destroy microorganisms.

What kind of fibers does lymphatic tissue have and what is their role?

Reticular fibers (produced by reticular cells) that act as an attachment sites for lymphocytes and other cells. Also, when lymph or blood filters through lymphatic organs, the fiber network traps microorganisms and other particles in the fluid.

encapsulated vs. nonencapsulated

-lymphatic tissue surrounded by a connective tissue capsule is said to be ENCAPSULATED (lymph nodes, the spleen, and the thymus)
-lymphatic tissue without a capsule is called NONENCAPSULATED (lymphatic tissue, lymphatic nodules, and the tonsils)

diffuse lymphatic tissue

tissue with no clear boundary that blends with surrounding tissues and contains lymphocytes and other cells. Located deep to mucous membranes, around lymphatic nodules, and within the lymph nodes and spleen.

lymphatic nodules

denser lymphatic tissue organized into compact, somewhat spherical structures and are numerous in the loose connective tissue of the digestive, respiratory, urinary, and reproductive systems.

Peyer's patches

aggregations of lymphatic nodules found in distal half of small intestine and appendix.

tonsils

large groups of lymphatic nodules and diffuse lymphatic tissue located deep to the mucous membranes within the pharynx (throat).

3 types of tonsils

1. palatine (each side of posterior opening)... usually referred to as "the tonsils"
2. pharyngeal (internal opening of nasal cavity)
3. lingual (posterior surface of the tongue)

adenoids

enlarged pharyngeal tonsil

lymph nodes

small, round, or bean-shaped structures distributed along the course of the lymphatic vessels. They filter the lymph (removing bacteria) and congregate, function and proliferate with lymphocytes

superficial lymph nodes

in the subcutaneous tissue. There are 3 superficial groups of lymph nodes on each side of body: 1. inguinal nodes 2. axillary nodes 3. cervical nodes

trabeculae

extensions (IN node) of capsule surrounding each lymph node. They subdivide lymph nodes into compartments.

lymphatic sinuses

spaces between lymphatic tissue containing macrophages on a network of reticular fibers

cortex

consists of lymphatic nodules separated by diffuse lymphatic tissue and lymphatic sinuses

inner medulla

organized into branching, irregular strands of diffuse lymphatic tissue separated by lymphatic sinuses.

What are the only structures to filter lymph?

lymph nodes

afferent vs. efferent lymphatic vessels

afferent- carry lymph to the lymph nodes
efferent- carry lymph away from the nodes

What 2 functions are perfromed as lymph moves through the lymph nodes?

1. activation of immune system
2. removal of microorganisms and foreign substances from the lymph by macrophages.

spleen

-has an outer capsule
-trabeculae from capsule divide spleen into small, interconnected compartments containing two specialized types of lymphatic tissue called white pulp (1/4 volume of spleen) and red pulp (3/4 volume).

organization of spleen and white/red pulp

Splenic artery enter spleen and their branches follow trabeculae into spleen to supply white pulp w/in compartments. Blood flows from white to red pulp. Veins from red pulp converge, forming the splenic vein, which exits the spleen.

what is red pulp?

associated with the VEINS and consists of the splenic cords and the venous sinuses

what is white pulp?

diffuse lymphatic tissue and lymphatic nodules surrounding the ARTERIES within the spleen

splenic cords

a network of reticular cells that produce reticular fibers

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