The Lymphatic and Immune Systems

Question 1

What is the purpose of the lymphatic system?

Answer 1

it is responsible for recovering excess tissue fluid and returning it to the bloodstream in addition to housing and producing cells of the immune system, monitoring the body for pathogens, absorbing dietary lipids

Question 2

What organs are included within the lymphatic system?

Answer 2

lymphatic vessels, lymphoid tissues, red bone marrow, tonsils, thymus, spleen, lymph nodes

Question 3

What does the lymphatic system reabsorb?

Answer 3

water, electrolytes, nutrients, hormones, and other substances not reabsorbed by the capillaries - lymphatic vessels collect this excess fluid moving it to the subclavian vein of the shoulders where it is returned to the blood stream

Question 4

What is the fluid absorbed by lymphatic vessels called?

Answer 4

lymph

Question 5

What is the function of the lymph nodes?

Answer 5

filtration of lymph - macrophages within the lymph nodes phagocytize impurities and cleanse the lymph, monitoring for potential pathogens before the lymph reenters the blood stream

Question 6

What is edema?

Answer 6

A collection of fluid in the tissues resulting in swelling and potential circulatory collapse from loss of blood volume - happens when the lymphatic system fails to collect excess fluid

Question 7

What two cell types are vital to the immune system for monitoring?

Answer 7

macrophages and lymphocytes

Question 8

What are lacteals?

Answer 8

located in the small intestine - special lymphatic vessels that absorb dietary fats, cholesterol, and fat-soluble vitamins

Question 9

What are the three major components of the lymphatic system?

Answer 9

Lymphatic vessels, Lymphatic Tissues, Lymphatic Organs

Question 10

What are Lymphatic vessels?

Answer 10

lymphatic capillaries converge to form collecting vessels which lead into lymph nodes and move node to node -

collecting vessels converge into 6 lymphatic trunks which are coordinated to different regions of the body -

lymphatic trunks converge into collecting ducts that empty into true blood vessels called the subclavian veins

Question 11

What are Lymphatic tissues? Are there subtypes of these tissues?

Answer 11

these are aggregations of lymphocytes within connective tissues of various organs and in loose connective tissue lying below epithelia

subtypes: MALT (mucosa-associated lymphatic tissue), GALT (gut-associated lymphoid tissue), BALT (bronchus-associated lymphoid tissue)

Question 12

Describe the significance of MALT.

Answer 12

mucosa-associated lymphatic tissue

mucous membranes line passages open to the exterior: digestive, respiratory, reproductive, urinary - which are subject to invasion of outside pathogens

MALT guards these openings against the entrance of pathogens - sometimes becoming concentrated into dense masses of lymphocytes called lymphatic nodules

Question 13

What are Lymphatic organs?

Answer 13

A mass of lymphatic tissue that is enclosed in a fibrous capsule that separtes it from neighboring tissues/organs.

These organs hace a refined structure

e.g. red bone marrow, tonsils, thymus, lymph nodes, spleen

Question 14

What types of cells are a part of the lymphatic-immune system?

Answer 14

Natural Killer (NK) Cells, B Lymphocytes (B Cells), Antigen-presenting Cells (APCs), T Lymphocytes (T Cells) - Helper (TH Cells), Cytoxic T (TC) Cells, Regulatory T (TR) Cells, Memory T Cells

Question 15

Natural Killer (NK) Cells

Answer 15

nonspecific defenses in the body - retain no memory of a given pathogen

only attack host cells (of one’s own body) that are either cancerous or have been antigenically modified by viral infection

destroying precancerous cells - prevent growth of tumors

limit the spread of virus to new cells

~ 10 - 15% of the circulating blood lymphocytes

Question 16

B Lymphocytes (B Cells)

Answer 16

small lymphocytes originating in the bone marrow where they become immunocompetent (where they develop antigen receptors enabling response to foreign antigens)

responsible for humoral (antibody-based) immunity

when stimulated by an antigenic challenge may have enlarged rough ER = plasma cell

may also become a memory B cell which serves to “remember” an antigen, reacting to known foreign bodies rapidly

Question 17

What are T Cells? List the types of T Lymphocytes (T Cells)

Answer 17

small lymphocytes that achieve immunocompetence (antigen sensitivity) in the thymus - responsible for cell mediated immunity.

Helper, Cytotoxic, Regulatory, Memory

Question 18

What is the function of Helper T (TH) Cells

Answer 18

recognize fragments (epitopes) presented by APCs - secrete lymphokines which activate humoral, and cellular immunity and inflammation

= coordinate nonspecific defense and both kinds of specific immunity

• target of HIV - results in highly immunocompromised state

Question 19

What is the function of Cytotoxic T (CT) Cells?

Answer 19

directly attack and destroy foreign cells (bacteria and transplanted tissue) - release perforins that create a hole in the enemy membrane as well as granzymes which enter through the perforin-created hole to degrade the enzymes of the enemy cell.

Question 20

What is the function of Regulatory T (TR) Cells?

Answer 20

prevent excess TH and TC response - preventing attacks against one’s own tissues

Question 21

What is the function of Memory T Cells?

Answer 21

like Memory B Cells - preprogrammed to respond quickly in the case of reexposure to the same antigen that caused an original immune response

Question 22

What is the function of APCs? What are the three types?

Answer 22

Antigen-Presenting Cells

these are cells that phagocytize antigens, digest them and then display antigenically active fragments of them (epitopes) on the plasma mem. surface

when a TH Cell recognizes one of these antigens it secretes lymphokines that activate humoral and cellular immunity (B and TC Cells) and inflammation

types: B Cells, Macrophages, Dendritic Cells

Question 23

Where do macrophages develop?

Answer 23

typically from blood monocytes

Question 24

Describe the organization of lymphatic vessels.

Answer 24

Lymphatic CAPILLARIES = single layer of endothelial cells form a sac - overlapping one another like shingles = very thin walled and irregular - anchored to tissues by anchoring filaments which help maintain patency

when tissue swells with fluid, endothelial flaps are pushed open and fluid enters the capillary, when pressure is higher in the capillary the flaps are shut

(cell gaps are so large that bacteria and cancer cells may enter)

fluid now in the capillaries is deemed lymph

capillaries form collecting vessels through anastamoses leading to larger collecting ducts (2 in the chest) that open into the subclavian veins

Question 25

What is a lymphoid nodule?

Answer 25

Also called a lymphoid follicle - an area with considerable lymphocyte infiltration having a pale germinal center and a dark peripheral border with no capsule but rather a precise boundary

Question 26

Describe Peyer’s Patches.

Answer 26

located on the abmesenteric side of the ileum - concentrated here to intercept bacterial infection from the large intestine to prevent spread into the small intestine.

Question 27

Describe the epithelial specialization in the bronchi and intestines characterized in lymphatic tissue.

Answer 27

epithelium laying over lymphoid follicles changes from whatever is present surrounding the typical organ to a squamous epithelium of microfold (M) Cells which are APCs

Question 28

What are the three types of tonsils?

Answer 28

Lingual, Palatine, Pharyngeal

Question 29

Where are the Palatine Tonsils located? What are its characteristics?

Answer 29

Near the back of the oral cavity two structures located on the lateral walls of the mouth

having 10-12 deep crypts lined with lymphatic nodules (dense collections of lymphocytes) and trabeculae of fibrous connective tissue lined by stratified squamous epithelium

when inflamed (tonsillitis) - exhibit abundant neutrophils within their tissue

Question 30

Where are the Lingual Tonsils located? What are its characteristics?

Answer 30

embedded at the back of the tongue, behind the vallate papillae

each of these having a single crypt and surface opening - crypts are deep and wide (distinguish against palatine tonsils) - covered with stratified squamous epithelium with a flimsy underlying capsule

*lingual glands have ducts that open into the base of each crypt of the lingual tonsils

Question 31

Where are the Pharyngeal Tonsils located? What are its characteristics?

Answer 31

There is only one!

located medially behind the nasal cavity on the dorsal wall of the nasopharynx

covered by pseudostratified columnar epithelium, distinguishing it from lingual and palatine tonsils - may have scattered patches of stratified squamous epithelium, having the thinnest and most incomplete capsule among other tonsil types.

rather than having “crypts” these tonsils hace shallow folds or pleats of tissue

seromucous gland ducts open into the base of these “pleats”

inflammation among these tonsils are called adenoids

Question 32

What is the anatomical location of the thymus?

Answer 32

within the mediastinum, superior to the heart, below the thyroid gland

surrounded by a fibrous capsule with trabeculae that penetrate into the gland and divide the parenchyme into polygonal lobules

each lobule has a dark cortex and lighter medulla and is connected to other lobules by cords of medullary tissue - exhibits thymic (Hassal) corpuscles (concentric flattened cells with degenerating central cells)

Question 33

What organ does involution apply to?

Answer 33

the thymus - very large in a newborn extending across most of the diaphragm (often mistaken for lung), growing rapidly to age 1-2 and slowing until approx. age 14

then undergoing involution the thymus shrinks rapidly and is replaced with fat and fibrous tissue - shrinking so much that little remains at old age

Question 34

What cells mature in the thymus?

Answer 34

lymphocyte class T Cells which are formed in the bone marrow and mature in the thymus

Question 35

What is the process of T Cell maturation

Answer 35

residing in the cortex as immature T cells called thymocytes where they develop a surface receptor for antigens

once mature called immunocompetent T Cells - and tested through negative selection to ensure they do not attack our own antigens but still capable of recognizing antigens

only 2% of T Cells enter the medulla where they are stimulated by thymic hormones to multiply and colonize into large identical T Cells = positive selection

These cells now disperse and colonize in other organs of the body

Question 36

Where do mature T Cells colonize within the body after positive selection?

Answer 36

bone marrow, lymph nodes, tonsils, mucous membranes, etc

Question 37

What lymphatic organ is the most numerous?

Answer 37

Lymph nodes - approx. 450 in the adult body

Question 38

Where are lymph nodes concentrated throughout the body?

Answer 38

neck, armpit, breast, groin, mesenteries, bend of the elbow and knee

Question 39

How are lymph nodes organized in relation to one another as well as independently? How does lymphatic fluid enter the nodes?

Answer 39

form a series of in-line filters along the course of the lymphatic collecting vessels

lymph enters a node through afferent lymphatic vessels along the convex side of the node, moving through the nodal tissue, exiting via two-three efferent lymphatic vessels on the same convex region of the node

*nodes are the only organs that have afferent lymphatics as well as efferent

Question 40

How do lymph nodes filter passing lymph?

Answer 40

macrophages phagocytize bacteria, APCs intercept and alert the immune system, T and B Cells carry out immune attacks on foreign disease agents - also adding lymphocytes to the lymph which will eventually make it’s way back into the blood

Question 41

Describe the anatomy of a lymph node. What structure is unique to lymph nodes?

Answer 41

Trabeculae arise from the capsule, penetrating into the node to subdivide the parenchyma

• just below the capsule, lies the subcapsular sinus - the point where lymph from afferent vessels enters continually - washing away typical lymphocytes allowing the area to appear clear

Question 42

Describe the components of the splenic cortex.

Answer 42

containing primary lymphoid nodules with pale germinal centers (secondary nodules) where B memory cells and plasma cells form.

lying between nodules are the cortical (radial) sinuses which deliver lymph to the medulla - sinuses = a network of reticular cells and adherent macrophages

Question 43

Describe the components of the splenic paracortex.

Answer 43

where cortex mets medulla - containing mostly T cells - having a specialized vascular system - high endothelial venules

*activated T Cells (Helper T Cells) activated by APCs in the spleen will proliferate quickly under antigenic stimulation and be sent into the body through the efferent lymphatic system

Question 44

Describe the components of the splenic medulla.

Answer 44

consists of large, twisting sinuses ensheathed in lymphocyte clusters aka medullary cords

Question 45

What is the largest lymphatic organ?

Answer 45

The Spleen!