Human Anatomy & Physiology



Basic Anatomy & Physiology II Dr. L. Bacha

Chapter Outline (Marieb & Hoehn 6th edition)

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( the lymphatic system consists of what three parts?

( the three primary functions of the lymphatic system are:

1. returns excess interstitial fluid to the venous system

2. surveillance and defense – protects the body from foreign cells, bacteria, cancer cells, etc.

3. transports absorbed fats from the intestine to the venous system

19.1 The lymphatic system includes lymphatic vessels, lymph, and lymph nodes

Distribution and Structure of Lymphatic Vessels

During capillary exchange, more fluid leaves the blood capillary than returns to it. Some of the interstitial fluid enters blind-ended lymphatic capillaries as fluid now called lymph. The lymph is transported to and from lymph nodes by lymphatic vessels, and eventually returned to the bloodstream.

Lymphatic Capillaries (see Fig. 19.1)

( the flow of lymph from the interstitial tissue begins with microscopic lymphatic capillaries

( located in the spaces between cells in interstitial tissue; these capillaries weave between what?

( they are widespread, but absent from what parts of the body?

( although similar to blood capillaries, lymphatic capillaries are very highly permeable; they owe their permeability to what two unique structural modifications?

- the structure of lymphatic capillaries allows interstitial fluid to move into them, but not out

Larger Lymphatic Vessels (see Fig. 19.2)

( lymphatic capillaries merge to form larger lymphatic vessels, which carry lymph into and out of lymph nodes

- ultimately, lymph flows into one of two main ducts in the thoracic region and then drains into venous blood. The two main ducts are:

1. right lymphatic duct

◦ the right lymphatic duct drains lymph from what parts of the body?

◦ the right lymphatic duct drains lymph into venous blood at the base of the right subclavian vein

2. thoracic duct (left lymphatic duct)

◦ the thoracic duct drains lymph from the rest of the body (left upper limb, the left side of the head, neck and thorax, and the rest of the body inferior to the diaphragm)

◦ the thoracic duct drains lymph into venous blood at the base of the left subclavian vein

Lymph Transport

◦ read the information on lymph transport and list the mechanisms (five of them) that help promote the flow of lymph:

19.2 Lymphoid cells and tissues are found in lymphoid organs and in connective tissue of other organs

Lymphoid Cells

( the main “warriors” of the immune system are what cells?

( there are two main varieties of lymphocytes that protect the body against antigens:

(1) T cells (T lymphocytes)

- directly attack and destroy infected cells; responsible for cell-mediated immunity

(2) B cells (B lymphocytes)

- responsible for antibody-mediated immunity

- B cells differentiate into plasma cells

- what do plasma cells secrete?

Lymphoid Tissue

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( list the two main reasons why lymphoid (lymphatic) tissue is an important component of the immune system:

( lymphoid tissue is characterized by:

( lymphocytes - the most numerous type of cell; two main varieties: T cells and B cells

( also plasma cells (derived from B lymphocytes), macrophages, and dendritic cells

( a supportive framework (stroma) of reticular connective tissue, which is a type of loose connective tissue with reticular cells and reticular fibers

( huge numbers of lymphocytes squeeze through the walls of blood vessels and course through the spaces of reticular connective tissue, then circulate throughout the body again

- the cycling of lymphocytes between the circulatory vessels, lymphoid tissues, and loose connective tissues of the body ensures what?

( there are two types of lymphoid tissue

1. DIFFUSE LYMPHOID (LYMPHATIC) TISSUE

( an unorganized accumulation of numerous lymphocytes, etc.

2. NODULAR LYMPHOID (LYMPHATIC) TISSUE

( formed by lymphoid nodules (lymphoid follicles), which are spherical, dense accumulations of numerous lymphocytes

( each has a lighter staining center called a germinal center, which contains mainly B cells; germinal centers are a site of cell division of B cells

both types of lymphatic tissue are found:

1. throughout the body, in the CT below the epithelium of many organs, such as the trachea, esophagus, stomach, intestines, urinary bladder, etc.

2. as part of lymphoid organs

19.3 Lymph nodes cleanse lymph and house lymphocytes

◦ lymph nodes are the principal lymphoid organs in the body (see Fig. 19.5)

◦ what are lymph nodes clustered along?

◦ about how many are in the body!?

◦ they occur individually, but there are also large clusters of lymph nodes that occur near the body surface of what three regions (where lymphatic vessels converge)?

◦ list and briefly describe the two basic functions of lymph nodes:

Structure of a Lymph Node

◦ most lymph nodes are what shape and size?

◦ each lymph node is formed by lymphatic nodules and diffuse lymphatic tissue

◦ throughout a lymph node are lymph sinuses

- lymph sinuses are large lymphatic capillaries spanned by reticular cells and macrophages

- the macrophages “filter” the lymph by phagocytizing foreign matter in the lymph

- additionally, some of the lymph-borne antigens in the percolating lymph leak into the surrounding lymphoid tissue, where they do what?

19.4 The spleen removes bloodborne pathogens and aged red blood cells

◦ the spleen is the largest lymphatic organ in the body; where is the spleen located ?

◦ the spleen consists of red pulp and white pulp:

( white pulp is lymphatic tissue that consists of mostly lymphocytes on reticular fibers

( red pulp consist of venous sinuses (through which blood flows) and is rich in macrophages

◦ functions of the spleen:

( the spleen provides a site for what?

( the spleen cleanses the blood

- old and defective blood cells and platelets, debris, and foreign matter are removed by macrophages as the blood flows through the sinuses in the red pulp

( read about the three additional, and related, functions that the spleen also performs

19.5 MALT guards the body’s entryways against pathogens

◦ mucosa-associated lymphoid tissues (MALT) are lymphoid tissues strategically located in what?

◦ MALT includes the tonsils, Peyer’s patches, and appendix; in addition, it also occurs where?

◦ functions of MALT:

- prevents pathogens from penetrating mucous membranes

- site for lymphocyte activation and proliferation

Tonsils

◦ form a ring of lymphatic tissue (in the connective tissue below the epithelium)

around the entrance to what?

◦ tonsils provide an immune response against inhaled or ingested foreign microbes, etc.

◦ indicate the location of the different types of tonsils:

( palatine tonsils - in the lateral walls of the oropharynx

( lingual tonsils -

( pharyngeal tonsil -

- what is another name for a pharyngeal tonsil?

( tubal tonsils -

◦ the tonsils gather and remove what?

Peyer’s Patches

( Peyer’s patches are large aggregations of lymphoid nodules that are located where?

Appendix

( the appendix, a part of the large intestine (see Fig. 22.31 on page 783), contains a high concentration of lymphoid follicles

( like Peyer’s patches, the appendix is in an ideal position to do what two things?

19.6 T lymphocytes mature in the thymus

( the thymus located in the cranial mediastinum near the heart

( it is most active during the early years of life; after puberty, what happens to the thymus?

( the thymus does not directly fight antigens. Instead, it functions strictly as what?

- T lymphocytes (T cells) become immunocompetent in the thymus, meaning that they become programmed against specific antigens by developing specific receptors for antigens in the thymus

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The End!

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