Chapter 21 - The Lymphatic and Immune Systems

Question 1

What is the immune system?

Answer 1

Not an organ, but a population of cells that inhabit all of our organs and defend our body from agents of disease.
- the immune cells are concentrated in a true organ system known as the lymphatic system.

Question 2

Lymphatic System

Answer 2

a network of vessels that penetrate nearly every vessel in the body, and a collection of tissues and organs that produce immune cells.

Question 3

Three functions of lymphatic system

Answer 3

1. Fluid Recovery: lymphatic system reabsorbs excess fluid that does not get reabsorbs by the capillaries (about 15%) and returns it to the blood.
2. Immunity: As lymphatic system picks up tissue fluid it also picks up foreign cells and chemicals from the tissues. On way back from bloodstream, the fluid passes through the lymph nodes, where immune cells stand guard against foreign matter. When detecting anything potentially harmful they activate immune response.
3. Lipid Absorption: In small intestine, special lymphatic vessels called lacteals absorb dietary lipids that are not absorbed by the blood capillaries.

Question 4

What are the components of the lymphatic system?

Answer 4

1. Lymph: recovered fluid
2. Lymphatic vessels: transport the lymph
3. Lymphatic tissue: composed of aggregates of lymphocytes and macrophages that populate many organs of the body.
4. Lymphatic Organs: these cells are especially concentrated and are set off from surrounding organs by connective tissue capsules.

Question 5

Lymph

Answer 5

usually a clear, colorless fluid, similar to blood plasma but low in protein.

• originates as tissue fluid that has been taken up by the lymphatic vessels.
• it’s composition varies depending on where its leaving.

Question 6

Lymphatic vessels

Answer 6

the system through which lymph flows.
they are similar to blood vessels.
- Begin with microscopic lymphatic capillaries (terminal lymphatics), which penetrate almost every tissue in body but are absent from central nervous system, cartilage, cornea, bone, and bone marrow. Unlike blood capillaries, they are closed on one end. Lymphatic capillaries consist of a sac of thin endothelial cells that loosely overlap eachother like shingles of a roof. Cells are tethered to tissue by protein filaments that prevent the sac from collapsing.

Question 7

Route of tissue fluid back to bloodstream is…

Answer 7

lymphatic capillaries, collecting vessels, six lymphatic trunks, tow collecting ducts, subclavian veins.

Question 8

Collecting vessles

Answer 8

converged from lymphatic capillaries

Question 9

Lymphatic trunks

Answer 9

converged from collecting vessels. Each drains a major portion of the body.
There are 6 whose names indicate their location and parts they drain:
jugular, subclavian, bronchomediastinal, intercoastal, intestinal, lumbar trunks (drains lumbar region and lover limbs).

Question 10

Collecting ducts

Answer 10

converged from lymphatic trunks.

- largest of lymphatic vessels.

Question 11

right lymphatic duct

Answer 11

from collecting duct
- formed by convergence of right jugular, subclavian, and bronchomediastinal trunks in the right thoracic cavity. It receives lymphatic drainage from the right arm and right side of the thorax and head and empties into the right subclavian vein.

Question 12

2. Thoracic Duct

Answer 12

from collecting duct.

• on the left, is larger and longer.
• Begins just below the diaphragm anterior to the vertebral column at the level of the seconf lumbar vertebra. Here, the two lumbar trunks and the intestinal trunk join and form a prominent sac called cisterna chili, named for the large amount of fats (chyle) that it collects after a meal.
• this duct drains all the body below the diaphragm, and the left upper limb and left side of head, neck , and thorax.

Question 13

Natural Killer (NK) Cells

Answer 13

lymphatics tissues
- large lymphocytes that attack and destroy bacteria, transplanted tissues and host cells (cells of ones own Body) that have become cancerous or infected with viruses. Tesponsible for a mode of defense called immune surveillance

Question 14

T lymphocytes (T cells)

Answer 14

lymphocytes that mature in the thymus and later depend on thymic hormones. T stands for Thymus - dependent.

Question 15

B Lymphocytes (BCells)

Answer 15

lymphocytes that differentiate into plasma cells - connective tissue cells that secrete antibodies. Names for an organ in chickens (bursa of fabricius) in which they were first discovered.
Could think of B for bone marrow where these cells mature.

Question 16

Macrophages

Answer 16

very large, avidly phagocytotic cells of the connective tissue. Develop from monocytes that have been emigrated from the blood stream. They phagocytize tissue debris, dead neutrophils, bacteria and other foreign matter.
- also process foreign matter and display antigenic fragments of it to certain T-cells, thus alerting the immune system to the presence of an enemy. Macrophages and other cells that do this are called antigen-presenting cells (APCs).

Question 17

Dendritic Cells

Answer 17

branched Mobile APCs found in epidermis, mucous membranes, and lymphatic organs. (In the skin often called Langerhans cells).

• play an important role in alerting the immune system to pathogens that have breached the body surfaces.
• engulf foreign matter by receptor mediated endocytosis rather than phagocytosis, but otherwise function like macrophages. After internalizing an antigen, they migrate to a nearby lymoh node and activate an immune reaction to it.

Question 18

Reticular Cells

Answer 18

branched stationary APCs that contribute to the connective tissue framework (stroma) of the lymphatic organs. Not to be confused with reticular fibers.

Question 19

Lymphatic (lymphoid) tissues

Answer 19

aggregations of lymphocytes in the connective tissues of mucous membranes and various organs.

Question 20

Diffused lymphatic Tissue

Answer 20

simplest form of lymphatic tissues.

• lymphocytes are scattered rather than densely clustered.
• particularly prevelant in body passages that are open to the exterior(respiratory, digestive, urinary, and reproductive tracts.

Question 21

Lymphatic nodules (follicles)

Answer 21

dense masses where lymphocytes and macrophages congregate.

-come and go as pathogens invade the tissues. and immune system answers the challenge.

Question 22

Peyer Patches

Answer 22

lymphatic nodules that form clusters in the ileum.

Question 23

Lymphatic (lymphoid Organs)

Answer 23

have well defined anatomical sites and atleast partial connective tissue capsules that separate the lymphatic tissue from neighboring tissues..
- these organd include: red bone marrow, thymus, lymph nodes, tonsils and spleen.

Question 24

Red Bone Marrow

Answer 24

involved in hempoesis (blood formation) and immunity.

• In children, it occupies medullary spaces of nearly the entire skeleton.
• In adults, it is limited to the parts of the axial skeleton and the proximal heads of the humerus and femur.
• important supplier of lymphocytes to the immune system.
• its soft highly vascular material separated from osseous tissue by the endosteum of the bone.
• produces all classes of formed elements of the blood.
• Red color comes from abundance of erythrocytes.
• in long bones of the limbs, aging reticular cells accumulate fat and transform into adipose cells, eventually red bone marrow with yellow bone marrow.

Question 25

Thymus

Answer 25

Member of the endocrine, lymphatic, and immune systems.

• houses developing lymphocytes and secretes hormones that regulate their later activity.
• bilobed organ between the sternum and aortic arch in the superior mediastinum.
• thymus shows remarkable degree of degeneration with age.
• • after developing in the cortex, T-cells migrate to the medulla, where they spend another 3 weeks. Mature T-cells enter blood or lymphatic vessels here and leave the thymus.
• if thymus is removed from newborn mammal they waste away and never develop immunity.

Question 26

Reticular epithelial cells

Answer 26

seal off the cortex from the medulla and surround blood vessels and lymphocyte clusters in the cortex.

• form a blood thymus barrier that isolates developing lymphocytes from blood-borne antigens.
• produce several signaling molecules that promote the development and action of T-cells, including thymosin, thymopoietin, thymulin, interleukins and interferon.

Question 27

Lymph Nodes

Answer 27

most numerous lymphatic organs. (450 in typical adult)

• elongated or bean shaped structure, often with indentation called hilium on one side.
• enclosed in a fibrous capsule with trabeculae that partially divide the interior of the node into compartments.
• only organs that filter lymph as it flows along its course.
• it like a bottle neck that slows the slow of lymph and allows time for cleansing it of foreign matter.
• Macrophages and reticular cells of the sinuses remove about 99% of impurities before lymph leaves the node.

Question 28

Two functions of lymph nodes

Answer 28

• cleanse the lymph

- act as a site of T and B cell activation.

Question 29

Where are lymph nodes especially concentrated?

Answer 29

• Cervical Lymph nodes: deep and superficial groups in neck. monitor lymph coming from head and neck.
• Axillary Lymph nodes: concentrated in armpit (axilla) and receive lymph from upper limb and breast.
• Thoracic Lymph node: in thoracic cavity, especially in mediastinum, receive lymph from mediastinum, lungs and airway.
• Abdominal lymph node: posterior abdominopelvic wall and receive from urinary and reproductive systems.
• Intestinal an mesenteric lymph nodes: in mesentries, and adjacent to appendix and intestines. Receive
  lymph from the digestive tract.
• Inguinal lymph nodes: occur in groin and receive lymph from entire lower limb.
• Popliteal lymph nodes: occur at back of knee and receive from leg proper.

Question 30

Lymphadenitis

Answer 30

when a lymph node is under challenge by an antigen and becomes swollen and painful to the touch.

Question 31

Lymphadenopathy

Answer 31

collective term for all lymph node diseases.

- lymph nodes are common sites of metastatic cancer.

Question 32

Tonsils

Answer 32

patches of lymphatic tissue located at the entrance of the pharynx, where they guard against ingested and inhaled pathogens.
- each is covered by an epithelium and has deep pits called tonsillar crypts lined by lymphatic nodules. Crypts often contain food debris, dead leukocytes, bacteria, and antigenic chemicals.

Question 33

What are the three main sets of tonsils?

Answer 33

1. SIngle median pharyngeal tonsil (adenoids): on wall of the pharynx just behind the nasal cavity.
2. palatine tonsils: a pair, at the posterior margin of the oral cavity. Largest and most often infected.
3. lingual tonsils: numerous, each with a single crypt, concentrated in patches on each side of the root of the tongue.

Question 34

Tonsillitis

Answer 34

acute inflammation of the palatine tonsils, usually caused by a streptococcus infection. Their surgical removal called tonsillectomy used to be most common surgical procedure on children.