Ch. 22: The Immune System

The lymphatic system consists of: (8 things)

1. Lymph
2. Lymphatic vessels
3. Lymphatic tissue
4. Lymphatic nodules
5. Lymph nodes
6. Tonsils
7. Spleen
8. Thymus

T or F: The only function of the lymph system is immunity.

False

DO: Describe the functions of the lymphatic system.

3 functions of the lymphatic system

1. Fluid balance
2. Lipid absorption
3. Defense

What volume of lymph is drained by lymph vessels (out of all the fluid that passes from capillaries into the interstitial fluid on a daily basis?

3 liters out of 30 total liters

What are lymphatic vessels in the small intestine called?

lacteals

Chyle

Lymph passing through the lymphatic vessels and on to venous circulation

How does the lymphatic system function in defense?

Filters microorganisms/foreign substances out of lymph in lymph nodes and out of blood in spleen

What 3 things does lymph consist of?

1. Water
2. Solutes from plasma (ions, nutrients, gases, some proteins)
3. Cells (hormones, enzymes, waste products)

How does lymph return to circulation?

via veins

DO:

* List the parts of the lymphatic system.
* Describe the structure of lymphatic vessels.
* Explain how lymph is formed and transported through lymphatic vessels.
* Distinguish between lymphatic tissue and a lymphatic organ.
* Describe the structure and function of tonsils, lymph nodes, the spleen, and the thymus.

What are lymphatic vessels formed from?

joined capillaries

What are lymphatic essential for?

fluid balance

What do lymphatic vessels carry lymph away from?

tissues

What is unique about lymphatic capillaries? (2 things)

they are dead end tubes, and they only accept fluid in, not out (“one-way valves”)

Lymphatic capillaries are more permeable than what?

blood capillaries (anything can enter lymphatic capillaries)

Lymphatic capillaries drain all parts of the body, except: (3 things)

1. CNS
2. Bone marrow
3. Tissues without blood vessels (cartilage, epidermis, cornea)

Lymph nodes

structures along lymphatic vessels that filter lymph

Lymphatic trunks

structures that drain a major portion of the body are connect to large veins directly or lymphatic ducts

Lymphatic ducts

structures that drain tissues and move lymph into major veins

3 examples of lymphatic trunks and what do they all collectively drain?

1. Jugular trunk
2. Subclavian trunk
3. Bronchomediastinal trunk

They typically join a right thoracic vein separately and drain lymph from the right side of the head, right-upper limb, and right thorax.

In what percentage of people do the three trunks (the jugular, subclavian, & bronchomediastinal trunks) join to form the right lymphatic duct, which then joins a right thoracic vein?

about 20%

What does the thoracic duct drain?

the remainder of the body (that the jugular, subclavian, and bronchomediastinal trunks don’t)

Lymph Drainage Into Veins (figure)

3 mechanisms of lymph movement

1. Contraction of lymphatic vessels (where primitive heart pumps with pacemaker cells)
2. Contraction of skeletal muscles (where the surrounding muscle cells contract, compressing lymph vessels)
3. Thoracic pressure changes (where vessels expand and fill upon inhalation and vessels compress and push lymph upon exhalation)

Lymphedema

Lymphatic organs contain: (4 things)

1. lymphatic tissue (lymphocytes primarily)
2. macrophages
3. dendritic cells
4. reticular cells

Where do lymphocytes come from?

bone marrow, but they may mature elsewhere

What do reticular fibers do?

filter & trap microorganisms

Which structures of the lymphatic system are encapsulated? (3 things)

1. lymph node
2. spleen
3. thymus

Which structures of the lymphatic system are unencapsulated? (4 things)

1. digestive, respiratory, urinary, and reproductive tracts
2. lymphatic tissue
3. lymphatic nodules
4. tonsils

What specific tissue makes up unencapsulated lymphatic system structures?

MALT - mucosa associated lymphoid tissue that is in and beneath the mucous membranes of the structures we covered

What 2 cells mainly make up diffuse lymphatic tissue?

1. lymphocytes
2. macrophages

Where is diffuse lymphatic tissue located? (3 things)

1. deep to mucous membranes
2. around lymphatic nodules
3. in lymph nodes & spleen

Lymphatic nodules

denser arrangements of lymphatic tissue

Lymphatic nodules are numerous in:

the loose connective tissue of the digestive, respiratory, urinary, & reproductive systems

Peyer’s patches

aggregations of lymphatic nodules in small intestine & appendix

Lymphatic follicles

Lymphatic nodules found in the lymph nodes and spleen

How many lymph nodes are there dispersed primarily on or near blood vessels?

Approximately 450 superficial & deep

Parts of a lymph node

capsule, cortex, and medulla (trabeculae extend from the cortex to within)

What fibers form the supporting network of lymph nodes?

reticular fibers

Macrophages line lymphatic sinuses and do what?

remove things like bacteria

Lymphocytes proliferate in ____ when stimulated by bacteria, then end up in ____, ____, and ____.

germinal centers & blood, lymph, and lymph tissue

How do cancer cells often spread to circulation?

by migrating to lymph nodes

p. 777 activity:

* Why does removing axillary lymph nodes result in lymphedema?
* Explain why exercise can help reduce lymphedema.
* Explain why a compression bandage or garment can help reduce lymphedema.

Tonsils

Large groups of lymphatic nodules & dense lymphatic tissue located in the mucous membranes in the pharynx

What is the function of the tonsils?

protection from bacteria and other harmful substances entering the pharynx from the nasal or oral cavity

3 tonsil groups

1. Pharyngeal (the “adenoids”)
2. Palatine (the “tonsils”)
3. Lingual

Tonsillitis (picture)

The tonsils that are referred to as "the tonsils" are the

A. lingual tonsils.

B. palatine tonsils.

C. pharyngeal tonsils.

D. splenic tonsils.

B. palatine tonsils.

Where is the spleen located? What does it do?

Left superior abdomen, filters blood

What does rupture of the spleen result in?

bleeding, shock, death

What is 1/4 of the volume of the spleen?

white pulp surrounding arteries

What does white pulp consist of?

the periarterial lymphatic sheath that extends into lymphatic nodules (lymphocytes)

What is 3/4 of the volume of the spleen?

red pulp associated with veins (the venous sinus and splenic cord)

What are venous sinuses?

enlarged capillaries between splenic cords that join with trabecular veins to form the splenic vein

What do splenic cords (reticular cells) produce?

reticular fibers with splenic macrophages in between the spaces

Spleen micrograph, labelled

T or F: Most blood flows through the spleen rapidly.

true

When does slower blood flow through the spleen occur?

when blood percolates through splenic cords

3 functions of the spleen

1. Destroys defective RBCs
2. Detects & responds to foreign substances
3. Limited reservoir for blood

What is the thymus?

a bi-lobed gland in the superior mediastinum made up of cortex and medulla that grows in size during the first year then decreases after 60 years old

Which has more lymphocytes, the cortex of the thymus or the medulla?

the cortex

Where are thymic corpuscles found?

the medulla of the thymus

What is the function of thymic corpuscles?

to develop regulatory T cells that suppress the immune response and protect against autoimmune diseases

The thymus is the _____ site of T cells.

maturation

Thymosin plays an important role in _____.

T cell maturation.

How does thymosin play an important role in T cell maturation?

Large numbers of lymphocytes are produced in the thymus, but most degenerate. The lymphocytes that survive the maturation process live to react to foreign substances

The thymus

A. decreases in size in older adults.

B. produces neutrophils that move to other tissues.

C. produces a hormone called lymphopathin.

D. all of these

A. decreases in size in older adults.

Overview of the Lymphatic System (diagram)

How is the small intestine important to the lymphatic system?

Lacteals absorb lipids, forming chyle (lymph + lipids), which then passes through the thoracic duct or right lymphatic trunks before entering the blood.

How is the spleen important to the lymphatic system?

It filters blood and is a site where lymphocytes respond to infections.

How is red bone marrow important to the lymphatic system?

Pre-B cells mature into B cells and are released with Pre-T cells into the blood.

How is the thymus important to the lymphatic system?

Pre-T cells mature into T cells in the thymus and are released into the blood.

What happens to B and T cells once they enter the blood?

They populate all lymphatic tissues and either remain there or pass through back into the bloodstream to respond to infections

T cells

A. are processed in the thymus.

B. are responsible for antibody-mediated immunity.

C. originate in the spleen.

D. produce antibodies when activated.

A. are processed in the thymus.

DO:

* Define the concepts of specificity and memory as they apply to immunity
* Distinguish between the general characteristics of innate immunity and adaptive immunity

Adaptive immunity (specific)

can recognize a particular substance and remember previous encounters with it to respond stronger and more rapidly with each encounter

Innate immunity (nonspecific)

can recognize and destroy certain foreign substances, but the response to them is the same each time the body is exposed

3 classes of innate immunity with functions

1. Physical barriers: prevent entry & remove microbes
2. Chemical mediators: kill bacteria, promote phagocytosis and inflammation
3. Cells: phagocytosis and production of chemicals

7 examples of physical barriers

1. Skin
2. Mucous membranes
3. Tears
4. Saliva
5. Urine
6. Cilia (in respiratory tract)
7. Coughing & sneezing

6 examples of chemical mediators

1. Lysozymes
2. Sebum
3. Mucus
4. Histamines
5. Complement proteins
6. Interferons

What is complement?

a group of 20 inactive plasma proteins in the blood that form a cascade when activated

2 complement pathways

1. Alternative pathway: C3 binds with foreign substance
2. Classical pathway: C1 binds to an antigen-antibody complex, which then activates C4

Which immunity is the alternate pathway a part of?

innate immunity

Which immunity is the classical pathway a part of?

adaptive

Activated complement proteins can: (3 things)

1. C3–C7 promote phagocytosis, inflammation, & chemotaxis at the site of infection
2. C5–C9 combine to form a membrane attack complex (MAC) which forms a channel through a cell’s plasma membrane, resulting in the lysis of that cell
3. Opsonization

What is opsonization?

when complement proteins attach to the surface of bacteria to stimulate macrophages and phagocytize the bacteria

What are interferons?

proteins that protect the body against viral infection and perhaps some forms of cancer

How do interferons work in the immune system?

Interferons are produced by the infected cell, paracrinely causing neighboring cells to produce antiviral proteins, which prevents viral replication in neighboring cells.

Is interferon viral resistance innate or adaptive?

innate

Which of the following is a protein that disrupts virus production, and is produced by most cells in response to a viral infection?

A. complement

B. interferon

C. lysozyme

D. mucus

B. interferon

DO:

* Describe the three components of innate immunity
* Describe the chemical mediators and cells involved with innate immunity
* List the events of the inflammatory response and explain their significance

6 examples of cells used in innate immunity

1. White blood cells
2. Neutrophils
3. Macrophages
4. Basophils and mast cells
5. Eosinophils
6. Natural killer (NK) cells

Where are white blood cells produced?

red bone marrow and lymphatic tissue

What is the function of white blood cells?

travel in blood to infected tissues to destroy infections via phagocytosis (chemotaxis)

Where are neutrophils produced?

red bone marrow

What is the function of neutrophils?

one of the most important phagocytic cells that is the first responder to foreign substances

How many neutrophils leave the blood and pass through the wall of the digestive tract to provide phagocytic protection to the GI tract?

approximately 126 billion per day

Where do macrophages come from?

they are derived from monocytes and enter tissues