Ch 21 Learning Objectives

Lymphatic System

21.1.1 Describe lymph and its contents.

lymph: interstitial fluid entering lymph capillaries

• composed of water, dissolved solutes, protein, & immune cells

  • can also contain debris, microorganisms, & cancer cells

21.1.2 Discuss the location and anatomic structure of lymphatic capillaries and the process of fluid entry.

lymphatic capillaries: smallest lymph vessels

• microscopic, closed ended vessels that absorb interstitial fluid

lacteals: lymphatic capillaries located within GI tract

larger in diameter than blood capillaries

anchoring filaments help hold endothelial cells to nearby structures

driving force to move fluid into lymphatic cap. is to increase hydrostatic pressure in interstitial space

21.1.3 Explain the mechanisms that move lymph through lymphatic vessels, trunks, and ducts.

lymph moves through vessels to trunks to ducts

• skeletal muscle contractions: squeeze lymphatic vessels & push lymph forward

• respiratory movements: pressure changes during breathing pull lymph towards thoracic cavity

• smooth muscle contractions in larger lymphatic vessels: contracts to propel lymph

• one way valves: prevent lymph from flowing backward

• pressure from nearby organs & arteries: compresses lymphatic vessels & move lymph forward

• lymphatic ducts: deliver lymph into venous blood stream

Muscles + breathing + smooth muscle = move lymph

Valves = keep it moving one direction

Vessels → trunks → ducts → veins

21.1.4 Describe the flow of lymph from lymphatic capillaries through the various types of lymph vessels until it is returned to the cardiovascular system.

1. lymphatic capillaries: collect excess interstitial fluid from tissues

2. collecting lymphatic vessels: carries lymph away from capillaries (contains one way valves to prevent backflow)

3. lymphatic trunks: larger vessels that receive lymph from multiple collecting vessels

4. lymphatic ducts: largest lymph vessels:

   1. right lymphatic duct: drains right upper portion of body

   2. throracic duct: drains rest of body

5. subclavian veins: lymphatic ducts empty lymph into subclavian veins & returns to blood stream

6. cardiovascular system: lymph becomes part of plasma

Capillaries → Vessels → Trunks → Ducts → Veins → Blood

21.2.5 Name the two categories of lymphoid structures, and identify components of the body that belong to each category.

primary lymphoid structures: involved in formation & maturation of lymphocytes

• red bone marrow & thymus

secondary lymphoid structures: not involved in lymphocyte formation

• house both lymphocytes & other immune cells following their formation

• site where immune response is initiated

• lymph nodes, spleen, tonsils, lymphoid nodules, MALT

21.3.6 Describe the location and general function of red bone marrow.

located within trabeculae in portions of spongy bone within skeleton

• in adults: flat bones of skull, vertebrae, ribs, sternum, hip bones, proximal epiphyses of humerus & femur

red bone marrow is responsible for hematopoiesis

21.3.7 Identify the unique step required by T-lymphocytes in their maturation.

T-lymphocytes are not mature when released from red bone marrow

• thymocytes: immature t-lymphocytes

• migrate to the thymus to complete maturation

• mature t-lymphocytes exit the thymus & enter blood

main result of thymic maturation of t cells is the production of the cells that are immunocompetent & self tolerant

21.3.8 Describe the structure and general function of the thymus.

bilobed organ that is located in superior mediastinum

• each lobule is arranged into an outer cortex & inner medulla

functions in t-lymphocyte maturation

• immature t-lymphocytes reside in cortex of thymus & are protected in the blood by a blood-thymus barrier

• after initial steps in maturation they migrate to medulla of thymus; they then complete their maturation here

• mature t-lymphocytes enter blood & migrate to secondary lymphoid structures

21.4.9 Describe both the structure and function of lymph nodes.

• small, round/oval encapsulated structures located along the pathways of lymphatic vessels

• lymphoid organs that function in the filtering of lymph & are sites for initiating an immune response if harmful substances are found in the lymph

• located throughout body both superficially & deep

  • cervical lymph nodes: receive lymph from head & neck

  • axillary: receive from breast, axilla, & upper limb

  • inguinal: in groin that receive from lower limb & pelvis

have multiple afferent vessels, typically only one efferent vessel: (promotes filtration time & slows down movement)

• afferent lymphatic vessels: transports lymph into lymph node

  • enter at the convex surface

• efferent lymphatic vessel: lymph is drained

  • exits at the hilum

cortex contains lymphoid follicles

macrophages kill pathogens in lymph

21.4.10 Describe the location, structure, and function of the spleen.

largest lymphoid organ

located in the left upper quadrant of abdomen

• lateral to left kidney & posterolateral to stomach

splenic artery delivers blood to spleen & is drained by splenic vein

lacks cortex & medulla

• trabeculae subdivide spleen into regions of white & red pulp

spleen filters blood

• as blood oves through sinosoids, macrophages kill bacteria & debris from blood

functions:

• initiates immune response

• kills bacteria & foreign materials

• kills old erythrocytes & platelets

• serves as blood reservoir for platelets & erythrocytes

21.4.11 Distinguish between white pulp and red pulp.

white pulp: consists of t-lymphocytes, b-lymphocytes, & macrophages which surround a central artery

• initiates immune response

red pulp: consists of erythrocytes, platelets, macrophages & b-lymphocytes

• housed in reticular CT & form structures called splenic cords

• serves as a blood reservoir for erythrocytes & platelets (30% of all platelets are stored in spleen)

21.4.12 Identify the main groups of tonsils and their location and function.

secondary lymphoid structures that are not completely surrounded by a connective tissue capsule

21.4.13 Describe the composition of individual lymphoid nodules.

21.4.14 Compare the locations of MALT and Peyer patches.