23 Lymphatic organs and lymphatic circulation

Question 1

Well developed in newborns and younger children. However, when you hit adolescence, this organ involutes (shrinks and is gradually replaced with adipose tissue)

Answer 1

Thymus

Question 2

The lymphatic tissue found in the walls of the gut

Answer 2

Mucosa associated lymphoid tissue (MALT)

Question 3

o Principal site of hematopoiesis (production of the formed elements: RBCs, leukocytes, platelets aka thrombocytes)
o Islands of stem cells that replace lost cells
o Stem cells surrounded by a branching, leaky capillary network (aka a sinusoid)
o Site of macrophage breakdown of worn-out erythrocytes and iron storage (stored as ferritin for future recycling of erythrocytes)

Answer 3

Bone marrow

Question 4

The lumen is lined by simple squamous epithelium. Sits on a basal membrane (basal lamina). There are adventitial cells in the outer layer.

Answer 4

Sinusoid

Question 5

o Gives rise to myeloblast and lymphoblast cell lineages
 Myeloblasts: Turn into
• RBCs
• Eosinophils
• Neutrophils
• Basophils
• Monocytes: turn into macrophages upon entry into tissues
• Megakaryocytes: pieces break off to form platelets
 Lymphoblasts: turn into
• B lymphocytes: mature into plasma cells in the lymph nodes
• T lymphocytes

Answer 5

Pluripotent hematopoietic stem cells

Question 6

Found only in lymph nodes and the spleen

Answer 6

Reticular fibers

Question 7

Found in lymph nodes, spleen, thymus, and all other lymphatic organs

Answer 7

Reticulocytes

Question 8

Consists of lymphatic cells and extracellular matrix. Always surrounded by a connective tissue capsule (dense irregular connective tissue)

Answer 8

Lymphatic organs

Question 9

o Consist of multiple germinal centers and have invaginated outer edges (with crypts: or crevices). Help trap material and facilitate its identification by lymphocytes
o Several groups form a protective ring around the pharynx
 Pharyngeal
 Palatine
 Lingual: posterior-most aspect of the tongue

Answer 9

Tonsils

Question 10

Clusters of calcified material that form in the tonsillar crypts (i.e. the crevices of the tonsils). Contain volatile sulfur compounds (VSCs)

Answer 10

Tonsillolith

Question 11

o Lobulated organ w/ dark cortex, light medulla
o Immature lymphocytes mature into immunocompetent T-cells: i.e. helpers & cytotoxic T cells
o Sends mature T cells to target organs
o Hormones are produced by epithelioreticulocytes, which make up much of the cellular population of this gland.

Answer 11

Thymus

Question 12

	Thymulins
	Thymosins
	THF (thymic humoral factor)
	Thymopoietins
	Interferons (INFs)
	Interleukins

Answer 12

Hormones of the Thymus

Question 13

Cells of the thymus that produce hormones

Answer 13

Epithelioreticulocytes

Question 14

aka hassal’s corpuscle. These epithelioreticulocytes have flattened nuclei, twist around each other, they are large, and they are keratinized

Answer 14

Type 6 epithelioreticulocyte

Question 15

o	Small, round, or oval structures
o	Range in length: 1 to 25 mm, typically found in clusters
o	Clusters: axillary, inguinal, cervical
o	Individually throughout the body tissues
o	Composed of
	Capsule
	Cortex
	Medulla

Answer 15

Lymph nodes

Question 16

o Contains proliferating B-lymphocytes and some macrophages in this region of the nodule (lighter in staining)

Answer 16

Germinal center

Question 17

o T-lymphocytes are located deep to the follicles. It is in the ___ of the lymph nodes that aggregates of t-lymphocytes are found (as opposed to the nodules in which B cells are found)

Answer 17

Paracortex

Question 18

The cells of the lymphatic nodules that are mainly responsible for attacking antigens

Answer 18

Follicular dendritic cells

Question 19

o Contains proliferating B-lymphocytes and some macrophages in the germinal center of the nodule (lighter in staining)
o T-lymphocytes are located deep to the follicles. It is in the paracortex of the lymph nodes that aggregates of t-lymphocytes are found (as opposed to the nodules in which B cells are found)
o Filter and attack antigen. Follicular dendritic cells are the cells mainly responsible for attacking antigens

Answer 19

Lymphatic nodules (or follices)

Question 20

o Largest lymphatic organ
o Blood reservoir (of RBCs) and filter
o White pulp: immune component
o Red pulp: filtering component (filters blood). Everything outside the orb-shaped white pulp regions is red pulp

Answer 20

Spleen

Question 21

The regions of the spleen surrounding an arteriole. They contain T-lymphocytes

Answer 21

PALS (periarteriole lymphatic sheath)

Question 22

Cells found in the connective tissue capsule of the spleen. These are present so that the spleen can contract when blood or RBCs are needed

Answer 22

Myofibroblasts

Question 23

o Initiates an immune response when antigens are found in the blood (white pulp)
o Serves as a reservoir for erythrocytes & platelets (red pulp)
o Phagocytizes defective erythrocytes & platelets (red pulp)
o Phagocytizes foreign materials

Answer 23

Functions of the spleen

Question 24

o Detects antigens and initiates an immune response
o Prominent in the mucosa (of the gut tube)
o Includes Peyer’s patches, that are prominent in the ileum

Answer 24

MALT (mucosa associated lymphatic tissue)

Question 25

o Closed-ended tubes that are found in most blood capillary networks o Similar to a blood capillary, larger in diameter o No basement membrane o Overlapping endothelial cells

Answer 25

Lymphatic capillaries

Question 26

A worm that takes residence in capillaries. Symptoms are elephantiasis (lymphedema, or accumulation of interstitial fluid in the tissues)

Answer 26

Wuchereria bancrofti

Question 27

o Special types of lymphatic capillaries o Pick up interstitial fluid, dietary lipids, and lipid-soluble vitamins o Transport chyle

Answer 27

Lacteals

Question 28

Name for lymph that is found in the lacteals. It is more viscous than normal lymph

Answer 28

Chyle

Question 29

Unfiltered lymph enters lymphatic organs through these vessels

Answer 29

Afferent vessels

Question 30

Afferent vessels deliver lymph into these structures

Answer 30

Sinuses

Question 31

create a mesh in lymphatic channels, which filter lymph

Answer 31

Reticular fibers

Question 32

Filtered lymph exits through these vessels

Answer 32

Efferent vessels

Question 33

When lymphocytes can leave circulation and become assimilated into the lymphocyte population of lymphatic organs. This only occurs in the high endothelial venules

Answer 33

Homing

Question 34

The only location at which homing can occur

Answer 34

high endothelial venules

Question 35

Interstitial fluid that has accumulated in tissue beds. The interstitial fluid leaked out of capillaries

Answer 35

Lymph