Chapter 22 - The Lymphatic System and Immunity

Question 1

22.1

Question 2

Lymph

Answer 2

Fluid similar to blood plasma, but contains a much lower concentration of suspended proteins than blood plasma

Question 3

More fluid is carried by arterioles TO capillary network, then is carried AWAY by venules.
This is because of that some of the fluids filtered via arterioles go into lymphatic capillaries, whilst the rest goes into venules.

Question 4

Primary lymphoid tissues

Answer 4

Places where lymphocytes are formed and mature; red bone marrow and thymus

Question 5

Secondary lymphoid tissues

Answer 5

Places where lymphocytes are activated upon exposure to antigens; tonsils, spleen, MALT, lymph nodes…

Question 6

Important:

Answer 6

Capillaries deliver more blood than they carry away. The excess blood is carried away (exits capillaries into surrounding tissue, becoming interstitial fluid. it then goes into lymphatic capillaries) and returns to the bloodstream by lymphatic vessels.

This continuous circulation of extracellular fluid helps transport lymphocytes and white blood cells from one organ to another. In the process, it maintains normal blood volume. It also eliminates local variations in the composition of the interstitial fluid by distributing hormones, nutrients, and wastes from their tissues of origin to the general circulation.

Question 7

Lymphatic capillaries

Answer 7

Are closed at one end, large diameter, irregular cross section

**Lined by endothelial cells, usually have incomplete basement membrane
- The overlapping endothelial cells (lining basement membrane) act as a one way valve letting in fluids, solutes, proteins, viruses, bacterias… but doesn’t let them out, they travel with the lymph fluid

Question 8

Large lymphatic vessels

Answer 8

From the lymphatic capillaries (one layer, endothelial incomplete membrane), lymph flows into larger lymphatic vessels that lead toward the body’s trunk. The walls of these vessels contain three layers comparable to those of veins.

Also, many small and medium sized lymphatic vessels (especially in the limbs) have valves just like veins do. Pressures within the lymphatic system are minimal, and so these valves permit one-way flow of lymph in these vessels towards the thoracic cavity. The contractions of surrounding skeletal muscles also aid in the movement of lymph through the lymphatic vessels.

Question 9

Superficial and deep lymphatics

Answer 9

Two sets of lymphatic vessels collect lymph from the lymphatic capillaries: superficial lymphatics and deep lymphatics. Superficial lymphatics are located in the subcutaneous layer deep to the skin; in the areolar tissues of the mucous membranes lining the digestive, respiratory, urinary, and reproductive tracts; and in the areolar tissues of the serous membranes lining the pleural, pericardial, and peritoneal cavities. Deep lymphatics are larger lymphatic vessels that accompany deep arteries and veins supplying skeletal muscles and other organs of the neck, limbs, and trunk, and the walls of visceral organs.

Question 10

Lymphatic trunks (the convergence of deep and superficial lymphatics)

Trunks empty into ducts!!

Answer 10

Superficial and deep lymphatics converge to form even larger vessels called lymphatic trunks. The trunks in turn empty into two large collecting vessels: the thoracic duct and the right lymphatic duct. The thoracic duct collects lymph from the body inferior to the diaphragm and from the left side of the body superior to the diaphragm. The smaller right lymphatic duct collects lymph from the right side of the body superior to the diaphragm.

The thoracic duct (beginning at vertebra L2 and extending towards the clavicle) empties into the left subclavian vein. The right lymphatic duct empties into the right subclavian vein.

Question 11

Cisterna chyli

Answer 11

The base of the thoracic duct (where it starts, at vertebra L2)

The cisterna chyli receives lymph from the inferior part of the abdomen, the pelvis, and the lower limbs by way of the right and left lumbar trunks and the intestinal trunk

Question 12

Thoracic duct pathway -
collects lymph from the left bronchomediastinal trunk, the left jugular trunk, and the left subclavian trunk

Answer 12

The inferior segment of the thoracic duct lies anterior to the vertebral column. From the second lumbar vertebra, it passes posterior to the diaphragm alongside the aorta. It then ascends along the left side of the vertebral column to the level of the left clavicle. It collects lymph from the left bronchomediastinal trunk, the left subclavian trunk, and the left jugular trunk, and then empties into the left subclavian vein near the left internal jugular vein (see Figure 22–4b). In this way, lymph reenters the venous circulation from the left side of the head, neck, and thorax, as well as from the entire body inferior to the diaphragm.

Question 13

Right lymphatic duct

Answer 13

Collects lymph from the right bronchomediastinal trunk, the right jugular trunk, and the right subclavian trunk. In this way, the right lymphatic duct collects lymph from the entire right side of the body superior to the diaphragm, emptying it into the right subclavian vein.

Question 14

Lymphedema

Answer 14

Obstruction of lymphatic vessels.

As large amounts of lymph accumulate in the affected region, this causes swelling, especially in subcutaneous tissues. If the condition persists, the connective tissues lose their elasticity and the swelling becomes permanent. Lymphedema by itself does not pose a major threat to life. The danger comes from the constant risk that an uncontrolled infection will develop in the affected area. Because the interstitial fluids are essentially stagnant, toxins and pathogens can accumulate and overwhelm local defenses without fully activating the immune system.

Question 15

Lymphoid cells

Answer 15

Include immune system cells found in lymphoid tissues as well as the cells that support those tissues.
Immune system cells that function in defense include phagocytes (macrophages and microphages) and lymphocytes.
Phagocytes function as a general first line of defense against invading pathogens, where lymphocytes are more specific and respond to specific invading pathogens, abnormal body cells, and harmful proteins.

Question 16

(general, from Google search)

Answer 16

The main difference between monocytes and lymphocytes is that monocytes are in charge of phagocytosing pathogens, whilst lymphocytes are in charge of inducing a specific immune response. Monocytes can also enter organs and change into macrophages or dendritic cells, whereas lymphocytes circulate.

Lymphocytes account for 20-40% of circulating leukocytes (WBC’s).

Question 17

3 Classes of Lymphocytes circulate in the blood:

Answer 17

1) T (thymus-dependent) cells
2) B (bone marrow-derived) cells
3) NK (natural killer) cells

**However, circulating lymphocytes are only a small fraction of the total lymphocyte population. The body contains some 10^12 lymphocytes, with a combined weight of more than a kilogram (2.2 lb).

Question 18

Lymphoid tissues - Lymphatic /lymphoid nodules

Answer 18

Lymphoid tissues are connective tissues dominated by lymphocytes.

In a lymphoid nodule, or lymphatic nodule, the lymphocytes are densely packed in an area of areolar tissue. In many areas, lymphoid nodules form large clusters. Lymphoid nodules occur in the connective tissue deep to the epithelia lining the respiratory tract, where they are known as tonsils, and along the digestive, respiratory, urinary, and reproductive tracts (Figure 22–5). They are also found within more complex lymphoid organs, such as lymph nodes or the spleen.

Its boundaries are not distinct, because no fibrous capsule surrounds it. Each nodule often has a central zone called a germinal center, which contains dividing lymphocytes (see Figure 22–5). - usually T cells!

Question 19

Tonsils (secondary lymphatic organ)

Answer 19

• large lymphoid nodules in the walls of the pharynx; most people have five.

A single pharyngeal tonsil, often called the adenoid, lies in the posterior superior wall of the nasopharynx. Left and right palatine tonsils are located at the posterior, inferior margin of the oral cavity, along the boundary of the pharynx. A pair of lingual tonsils lies deep to the mucous epithelium covering the base (pharyngeal portion) of the tongue. Because of their location, the lingual tonsils are usually not visible unless they become infected and swollen. Tonsillitis is an inflammation of the tonsils (especially the palatine tonsils) although the other tonsils may also be affected. Tonsils reach their largest size by puberty and then begin to atrophy.

Question 20

Lymphoid Organs (not tissues) - Lymph Nodes, Thymus, Spleen

Question 21

MALT

Answer 21

The collection of lymphoid tissues that protect the epithelia of the digestive, respiratory, urinary, and reproductive systems is called the mucosa-associated lymphoid tissue (MALT). Clusters of lymphoid nodules deep to the epithelial lining of the intestine are known as aggregated lymphoid nodules, or Peyer’s patches (Figure 22–5b). Other examples of MALT include the appendix and the tonsils.
The appendix, or vermiform (“worm-shaped”) appendix, is a tube-shaped sac opening into the junction between the small and large intestines. Its walls contain a mass of fused lymphoid nodules.

Question 22

Lymph Nodes

Answer 22

• small typhoid organs, mostly found in neck, axillae, and groin where they defend us against pathogens
  -Unlike lymphatic nodules, lymph nodes are surrounded by a dense connective tissue capsule
• bundles of collagen fibers extend from the surrounding capsule into the lymph node interior - these fibrous partitions are known as trabeculae

***The typical lymph node is shaped like a kidney bean (see Figure 22–6). Blood vessels and nerves reach the lymph node at a shallow indentation called the hilum. Two sets of lymphatic vessels, afferent lymphatics and efferent lymphatics, are connected to each lymph node. Afferent (afferens, to bring to) lymphatics bring lymph to the lymph node from peripheral tissues. The afferent lymphatics penetrate the capsule of the lymph node on the side opposite the hilum. Efferent (efferens, to bring out) lymphatics leave the lymph node at the hilum. These vessels carry lymph away from the lymph node and toward the venous circulation.

• Macrophages are fixed in lymphatic sinuses of lymph nodes and assist in phagocytosis of pathogens. Nearby infections release antigens into the interstitial fluid, which are then brought as lymph to lymph nodes stimulating lymphocytes (which enter lymph node via exiting bloodstream) and macrophages. Additionally, dendritic cells can bring antigens to lymph nodes.

***LOOK AT FLOW!

Question 23

Hilium

Answer 23

Indentation where blood vessels and nerve reach the lymph node

Question 24

Lymphadenitis

Answer 24

Inflammation of lymph nodes

Question 25

Thymus

Answer 25

Primary lymphoid organ, place where T cells mature
- superior to the heart posterior to the sternum; important for immunity in childhood, but atrophies later on in life

**The capsule that covers the thymus divides it into two thymic lobes (Figure 22–7b). Fibrous partitions called septa (singular, septum) originate at the capsule and divide the lobes into lobules averaging 2 mm in diameter (Figure 22–7b,c). Each lobule consists of an outer cortex densely packed with lymphocytes and a paler, central medulla.

-Lymphocytes in the cortex are arranged in clusters that are completely surrounded by epithelial reticular cells. The epithelial reticular cells in the medulla cluster together in concentric layers, forming distinctive structures known as thymic (Hassall’s) corpuscles (Figure 22–7d). Epithelial reticular cells also encircle the blood vessels of the cortex.

-Cortex contains actively dividing T cell lymphocytes. Epithelial reticular cells maintain the blood thymus barrier around the blood vessels of the cortex, which separates developing T cells from the general circulation. (Both developing T cells and blood vessels are found in cortex, and the epithelial reticular cells prevent the two from mixing). These epithelial cells also regulate T cell development and function. Maturing T cells leave the cortex and enter the medulla of the thymus. The medulla has no blood thymus barrier. After about 3 weeks, these T cells leave the thymus by entering one of the medullary blood vessels. T cells in the medulla can enter or leave the bloodstream across the walls of blood vessels in this region or within one of the efferent lymphatics that collect lymph from the thymus.

*Blood thymus barrier only in cortex (outer of thymus), not medula (inner of thymus)

• The thymus produces several hormones that are important to the development and maintenance of T cells for normal immunological defenses. Thymosin (THĪ-mō-sin) is the name originally given to an extract from the thymus that promotes the development and maturation of T cells. This extract actually contains several complementary hormones. They include thymosin-a, thymosin-b, thymosin V, thymopoietin, and thymulin. The plural term thymosins is sometimes used to refer to all thymic hormones.

Question 26

Spleen

Answer 26

• The adult spleen contains the largest collection of lymphoid tissue in the body
• In essence, the spleen performs the same functions for blood that lymph nodes perform for lymph. Functions of the spleen can be summarized as (1) removing abnormal blood cells and other blood components by phagocytosis, (2) storing iron recycled from red blood cells, and (3) initiating immune responses by B cells and T cells in response to antigens in circulating blood.
• On left side; it is attached to the lateral border of the stomach by the gastrosplenic ligament, a broad band of mesentery

-The spleen has a soft texture, so its shape reflects the shapes of the structures around it. The spleen is in contact with the muscular diaphragm, the stomach, and the left kidney. The diaphragmatic surface is smooth and convex, conforming to the shape of the diaphragm and body wall. The visceral surface contains indentations that conform to the shape of the stomach (the gastric area) and the kidney (the renal area) (Figure 22–8b). Splenic blood vessels (the splenic artery and splenic vein) and lymphatic vessels communicate with the spleen on the visceral surface at the hilum, a groove marking the border between the gastric and renal areas.

-The spleen is surrounded by a capsule containing collagen and elastic fibers. The cellular components within make up the pulp of the spleen (Figure 22–8c). Red pulp contains large quantities of red blood cells, and white pulp resembles lymphoid nodules. Interestingly, the spleens of dogs, cats, and other mammals have extensive smooth muscle layers that contract to eject blood into the bloodstream. The human spleen lacks these muscles and therefore cannot contract.
The splenic artery enters at the hilum and branches to produce a number of arteries that radiate outward toward the capsule. These trabecular arteries in turn branch extensively, and their finer branches are surrounded by areas of white pulp. Capillaries then discharge the blood into the red pulp.
The cell population of the red pulp includes all the normal components of circulating blood, plus fixed and free macrophages. The structural framework of the red pulp consists of a network of reticular fibers. The blood passes through this meshwork and enters large sinusoids, also lined by fixed macrophages. The sinusoids empty into small veins, which ultimately collect into trabecular veins that continue toward the hilum.
This circulatory arrangement gives the phagocytes in the spleen an opportunity to identify and engulf damaged or infected cells in circulating blood. Macrophages are scattered throughout the red pulp, and the area surrounding the white pulp has a high concentration of lymphocytes and dendritic cells. For this reason, any microorganism or other antigen in the blood quickly triggers an immune response.

Rupture of the Spleen
The spleen tears so easily that a seemingly minor hit to the left side of the abdomen can rupture the capsule. The result is serious internal bleeding and eventual circulatory shock. Such an injury is a known risk of contact sports (such as football, hockey, and rugby) and of more individual athletic activities, such as skiing and sledding.
Because the spleen is so fragile, it is very difficult to repair surgically. (Sutures typically tear out before they have been tensed enough to stop the bleeding.) A severely ruptured spleen is removed, a process called a splenectomy (splē-NEK-tō-mē). A person can survive without a spleen but lives with an increased risk of bacterial infection.

Question 27

3. How would blockage of the thoracic duct affect lymph circulation?

Answer 27

Answer: A blockage of the thoracic duct would impair the drainage of lymph from inferior to the diaphragm and from the left side of the head and thorax, slowing the return of lymph to the venous blood and promoting the accumulation of fluid in the limbs (lymphedema) - lymph would remain in interstitial fluid with no where to go

Question 28

4. If the thymus failed to produce thymic hormones, development of which population of lymphocytes would be affected?

Answer 28

Answer: A lack of thymic hormones would drastically reduce the population of T lymphocytes.

Question 29

22.2

Question 30

Immunity

Answer 30

Ability of the body to resist and defend against pathogens

Question 31

Immune response

Answer 31

Body’s reaction to these infections organisms/pathogens

Question 32

Resistance

Answer 32

Ability of body to maintain immunity

Question 33

Two types of immunity: innate and adaptive

Answer 33

Innate (nonspecific) immunity is a type of body defense that you are born with and does not distinguish among different threats. Adaptive (specific) immunity is acquired after birth and after exposure to a particular antigen.

Question 34

Innate Immunity (nonspecific)

Answer 34

The body has several physical barriers and internal defense processes that either prevent or slow the entry of infectious organisms, or attack them if they do enter. For example, the skin serves as a physical barrier, and phagocytes attack invading bacteria. This type of immunity is called innate because you are born with it, and nonspecific because it does not distinguish one potential threat from another. Therefore, this category of immunity is called innate (nonspecific) immunity and it depends on a class of lymphocytes called NK cells.

Question 35

Adaptive Immunity (specific)

Answer 35

In contrast, two classes of lymphocytes, T cells and B cells, respond to specific antigens. If a bacterial pathogen invades peripheral tissues, these lymphocytes organize a defense against that particular type of bacterium, but not other bacteria and viruses. More importantly, this type of immunity also protects us against further attacks by the same type of pathogen. For this reason, we say that T cells and B cells provide an adaptive defense. Many specific defenses develop after birth as a result of accidental or deliberate exposure to antigens. Adaptive (specific) immunity depends on the activities of specific lymphocytes—B cells and T cells

Question 36

B cells

Answer 36

Lymphocytes capable of differentiating into plasma cells, which produce antibodies.

***Antibody-mediated immunity: When stimulated, B cells can differentiate into plasma cells which produce and secrete antibodies. These antibodies bind onto pathogens, resulting in a chain reaction leading to the destruction of those pathogens.

Question 37

T cells

Answer 37

Lymphocytes responsible for cell-mediated immunity (does not depend on antibodies for its adaptive immune functions and is primarily driven by mature T cells, macrophages and the release of cytokines in response to an antigen) and for the coordination and regulation of the immune response; includes cytotoxic T cells, helper T cells, regulatory T cells, and memory T cells.

***Cell-mediated Immunity: One type of T cell, called cytotoxic T cell, plays a role in cell-mediated immunity. These cells attack and destroy foreign cells and body cells infected by viruses.

Question 38

NK cells

Answer 38

Attack foreign cells, body cells infected by viruses, and cancer cells. They secrete chemicals that lyse the plasma membrane of abnormal cells.

Question 39

Lymphocytes: General Information

Answer 39

The lymphocytes in these organs are visitors, not residents. All types of lymphocytes move throughout the body. They wander through tissues and then enter blood vessels or lymphatic vessels for transport.
T cells move quickly. For example, a wandering T cell may spend about 30 minutes in the blood, 5–6 hours in the spleen, and 15–20 hours in a lymph node. B cells move more slowly. A typical B cell spends about 30 hours in a lymph node before moving on.
Lymphocytes have relatively long life spans. About 80 percent survive 4 years, and some last 20 years or more. Throughout your life, you maintain normal lymphocyte populations by producing new lymphocytes in your red bone marrow and lymphoid tissues.

Question 40

Lymphocyte production (lymphocytopoiesis)

Answer 40

Involves the red bone marrow, thymus, and peripheral lymphoid tissues

Red bone marrow plays the primary role in maintaining normal lymphocyte populations. Hemocytoblasts divide in the red bone marrow of adults to generate the lymphoid stem cells that produce all types of lymphocytes. The red bone marrow produces two distinct populations of lymphoid stem cells.
One group of lymphoid stem cells remains in the red bone marrow and the other group migrates to the thymus (see Figure 22–9). Lymphoid stem cells in the red bone marrow divide to produce immature B cells and NK cells. B cell development involves intimate contact with large stromal cells (not shown) in the red bone marrow. Bone marrow stromal cells provide a specialized microenvironment to control hemopoiesis. The cytoplasmic extensions of stromal cells contact or even wrap around the developing B cells. Stromal cells of the red bone marrow produce a cytokine called interleukin-7, which promotes the differentiation of B cells.
As they mature, B cells and NK cells enter the bloodstream and migrate to peripheral tissues (see Figure 22–9). Most of the B cells move into lymph nodes, the spleen, or other lymphoid tissues. The NK cells patrol the body, moving through peripheral tissues in search of abnormal cells.
The second group of lymphoid stem cells migrates to the thymus (see Figure 22–9). These stem cells and their descendants develop and mature in an environment that is isolated from the general circulation by the blood thymus barrier. Under the influence of thymic hormones, the lymphoid stem cells divide repeatedly, producing the various kinds of T cells. When the development of the T cells nears completion, they reenter the bloodstream and travel to peripheral tissues, including lymphoid tissues and organs, such as the spleen (see Figure 22–9).
The T cells and B cells that migrate from their sites of origin retain the ability to divide, producing daughter cells of the same type. For example, a dividing B cell produces other B cells, not T cells or NK cells. As we will see, the ability of specific types of lymphocytes to increase in number is crucial to the success of the immune response.

Question 41

22.3

Question 42

First line of defense in immunity?

Answer 42

Pathogens

Question 43

Lymphocytes that assist in the regulation and coordination of the immune response are __________.

Answer 43

Helper and Regulatory T cells.
**B cells and NK cells are not involved in the regulation and coordination of the immune response

Lymphocytes that assist in the regulation and coordination of the immune response are helper T and regulatory T cells. These T cells produce cytokines, which help communicate with other branches of the immune system and also help eliminate the immune response after a threat has been resolved. T helper cells are the main communication network that helps coordinate activity among multiple branches of the immune system. These cells are greatly reduced in number during an HIV infection, which contributes to the eventual collapse of the immune system if left untreated

Question 44

Innate (nonspecific) defenses make up the first line of defense in innate immunity. They include physical barriers, phagocytes, immune surveillance, interferons, complement, inflammation, and fever.

Question 45

1. Physical Barriers

Question 46

2. Phagocytes

Question 47

3. Immune Surveillance

Answer 47

NK Cells:
NK cells respond much more rapidly than T cells or B cells. The activation of T cells and B cells involves a complex and time-consuming sequence of events. NK cells respond immediately on contact with an abnormal cell.

-Cancer cells have “tumor-specific antigens” that NK cells detect
-Some cancer cells don’t have this, and so are out of reach of NK cell detection

Immunological escape: the process of avoiding NK cell detection or neutralizing body defenses

Question 48

4. Interferons

Answer 48

• Not cells, but proteins that are released by activated lymphocytes and macrophages, and by cells infected by viruses

-Examples of cytokines. Cytokines (SĪ-tō-kīnz) are chemicals that tissue cells release to coordinate local activities. Cytokines include hormones and paracrine-like glycoproteins important to the immune response. Most cells produce cytokines only for paracrine communication—that is, cell-to-cell communication within one tissue p. 611. However, defense cells also release cytokines; we discuss their role in Section 22–5.

Interferon alpha attracts and stimulates NK cells as a way to enhance viral resistance to viral infection

Question 49

5. Complement

Question 50

6. Inflammation

Question 51

7. Fever

Answer 51

body temp greater than 37.2

Question 52

A rise in the level of interferon in the body suggests what kind of infection?

Answer 52

Answer: A rise in the level of interferon suggests a viral infection. Interferon does not help an infected cell, but “interferes” with replication of the virus and thus the virus’s ability to infect other cells.

Answer 53

• T cells can only recognize antigens when they are presented by “antigen resenting cells” like macrophages and phagocyte

-Helper T cells, activated upon exposure to mhc4-antigen combo, release cytokines that “translate” message from antigen presenting cells and that stimulate T cells and B cells for specific defenses

Question 54

B cell activation process:
- sensitization, activation, division and differentiation

Answer 54

B cells have class II mch proteins alongside antibodies in their plasma membrane. Once encounter upon an antigen, the antigen first binds to antibodies, then to class II mch protein. This is called sensitization.

Nearly Helper T cells can costimulate with the B cells and lead to their activation, which then leads to division of unactivated memory B cells and activated B cells