16: Lymphatic System & Immunity

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The organs of the lymphatic system also

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defend the body against infx by disease causing agents

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Lymphatic capillaries

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are microscopic, closed end tubes that extend into interstitial space, The walls of lymphatic capillaries are similar to blood capillaries, The thin walls of capillaries make it possible for tissue fluid from interstitial space to enter the lymphatic capillaries

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Lymph is fluid

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inside a lymphatic capillary

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The lymphatic system

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is a vast collection of cells that travel in lymphatic vessels & the organs & glands that produce them.

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The lymphatic system includes a network of

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vessels that assist in circulating body fluids

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Lymphatic vessels transport

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excess fluid away from interstitial spaces & return it to the bloodstream

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The organs of the lymphatic system also

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defend the body against infx by disease causing agents

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Lymphatic capillaries

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are microscopic, closed end tubes that extend into interstitial space, The walls of lymphatic capillaries are similar to blood capillaries, The thin walls of capillaries make it possible for tissue fluid from interstitial space to enter the lymphatic capillaries

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Lymph is fluid

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inside a lymphatic capillary

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Lacteals are

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lymphatic capillaries in the lining of the small intestine

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lacteals

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fx to transport fats to the venous system.

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Lymphatic Vessel walls

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similar to those of veins, Lymphatic vessels have valves that prevent backflow of lymph

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Larger lymphatic vessels

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lead to lymph nodes

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After leaving nodes, lymphatic vessels merge

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in larger lymphatic trunks

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Lymphatic trunks drain

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lymph from lymphtic vessels & are named for the regions they serve Examples of lymphatic trunks are lumbar, intestinal, intercostal, bronchomediastinal, subclavian, & jugular trunks

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Lymphatic trunks join

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one of two collecting ducts

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The two collecting ducts are

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the thoracic duct & right lymphatic duct

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The thoracic duct is located

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along side the aorta in the abdominal & thoracic cavity & empties into the left subclavian vein

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The thoracic duct drains

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lymph from the intestinal, lumbar, & intercostal trunks, as well as from the left subclavian, left jugular, & left bronchomediastinal trunks

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The right lymphatic duct is located

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on the right side of the thorax & empties into the right subclavian vein

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The R lymphatic duct drains

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right jugular, right subclavian, & R bronchomediastinal trunks

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After leaving the 2 collecting ducts, lymph enters

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venous sys & becomes part of the plasma

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Lymph is

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tissue fluid that has entered a lymphatic capillary, Lymph formation depends on tissue fluid formation

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Tissue Fluid Formation

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Capillary blood pressure filters water & small molecules from plasma & the resulting fluid consists of water, nutrients, gases, & hormones (a similar composition to plasma)Water is drawn back into capillaries because of plasma colloid osmotic pressure

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Lymph Formation

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Filtration from plasma normally exceeds reabsorption, leading to the formation of tissue fluid. Tissue fluid moves into lymphatic capillaries because of interstitial fluid hydrostatic pressure. 3. Lymph formation prevents edema.

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Lymph fx

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1. Lymphatic vessels in the small intestine play a major role in the absorption of dietary fats.
2. Lymph returns small proteins that most of the blood capillaries filtered to the bloodstream.
3. Lymph transports foreign particles to lymph nodes.

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Lymphatic capillaries

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can receive proteins & foreign particles that blood capillaries cannot because the epithelial cells that form the walls of lymphatic vessels overlap each other but are not attached.

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The lumen of a lymphatic capillary remains

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open because their epithelial cells are attached to surrounding connective tissue cells by protein filaments.

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The hydrostatic pressure of tissue fluid

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drives lymph into lymphatic capillaries

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Muscular activity

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largely influences movement of lymph through lymphatic vessels.

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Lymph is under relatively

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low hydrostatic pressure

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Contracting skeletal muscles

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compress lymphatic vessels.

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Lymph does not flow back because

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of valves

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Breathing aids lymph circulation by

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creating a relatively low pressure in the thorax & a relatively high pressure in the abdomen during inhalation

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Conditions that interfere w/lymph mvmnt causes fluid to

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accumulate within interstitial spaces

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The continuous movement of lymph from interstitial spaces into blood capillaries & lymphatic capillaries

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stabilizes the volume of fluid in interstitial spaces.

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Lymph nodes are located

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along lymphatic pathways

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Lymph nodes contain

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lymphocytes & macrophages which fight invading microorganisms

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The hilum of a lymph node is

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the indented region

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Afferent lymphatic vessels

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are those that carry lymph to a node

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Efferent lymphatic vessels

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are those that carry lymph away from a node

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Lymph nodules

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are divisions of a lymph node

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Germinal centers

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contain dense masses of actively dividing lymphocytes & macrophages

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Tonsils

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composed of partially encapsulated lymph nodules

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Peyer’s patches

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are located in the mucosal lining of the distal portion of the small intestine & are composed of M cells, macrophages, & lymphocytes

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Lymph sinuses

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are a network of chambers & channels through which lymph circulates.

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Locations of Lymph Nodes

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Lymph nodes generally occur in groups or chains along the paths of larger lymphatic vessels but are absent in the central nervous systems.
Major locations of lymph nodes are cervical region, axillary region, supratrochlear region, inguinal region, pelvic cavity, abdominal cavity, & thoracic cavity.


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Lymph nodes of the cervical region are associated with

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lymphatic vessels that drain the skin of the scalp & fact, as well as tissues of the nasal cavity & pharynx.


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Lymph nodes of the axillary region are associated with

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lymphatic vessels that drain the upper limbs, wall of the thorax, mammary glands, & upper abdominal wall.


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Lymph nodes of the supratrochlear region are associated with

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lymphatic vessels that drain the elbow region.


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Lymph nodes of the inguinal region are associated with

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lymphatic vessels that receive lymph from the lower limbs, external genitalia, & lower abdominal wall.


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Lymph nodes of the abdominal cavity are associated with

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lymphatic vessels that drain the abdominal viscera.


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Lymph nodes of the thoracic cavity are associated with

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lymphatic vessels that drain thoracic viscera & the internal wall of the thorax

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The two primary fxs of lymph nodes are

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to filter potentially harmful particles from lymph & to monitor body fluids.

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Along with the red bone marrow, lymph nodes are centers for

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lymphocyte production

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Lymphocytes attack

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viruses, bacteria, & other parasitic cells.
The fxs of macrophages are to engulf & destroy foreign substances, damaged cells, & cellular debris

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Thymus

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is composed of lymphocytes & connective tissues & is located in the mediastinum

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After puberty, the thymus

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begins to shrink

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Most cells of the thymus gland are

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thymocytes

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The hormones secreted by the thymus gland are called

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thymosins

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Thymosins fx

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to stimulate maturation of T lymphocytes

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Spleen

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The largest lymphatic organ

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The spleen is located

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in the upper left portion of the abdominal cavity

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The spleen resembles

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a large lymph node

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White pulp contains

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many lymphocytes

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Red pulp contains

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red blood cells, lymphocytes, & macrophages

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The fxs of the spleen

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to remove foreign particles, damaged red blood cells, & cellular debris from the blood.

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An infection

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is the presence of pathogens

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Examples of pathogens are

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bacteria, protozoa, fungi & viruses

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Innate defenses

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are general defenses & protect against many types of pathogens & include species resistance, mechanical barriers, chemical barriers, enzyme actions, interferon, complement, natural killer cells, inflammation, phagocytosis, & fever

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Adaptive defenses are

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very precise defense mechanisms targeting specific pathogens & are carried out by lymphocytes

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Species resistance

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refers to the fact that a given kind of organism or species develops diseases that are unique to it

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A species may be resistant to diseases that affect others because

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its tissues somehow fail to provide the temperature of chemical environment that a particular pathogen requires

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Mechanical barriers

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prevent the entrance of some infectious agents

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Examples of mechanical barriers are

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skin, mucous membranes, & hair.

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The first line of defense is

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a mechanical barrier

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The second line of defense is

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a collection of the other nonspecific defenses.

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Chemical barriers

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are body fluids containing enzymes or antimicrobial substances

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Examples of chemical barriers are

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gastric juice, interferons, defensins, & collectins

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Interferon

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is produced by lymphocytes & fibroblasts & its fxs include stimulation of phagocytosis, & to prevent viral infections

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Defensins

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are produced by white blood cells, & certain epithelial cells.

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The fxs of defensins are

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to make holes in bacterial cells walls & to destroy certain pathogens

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Collectins

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are proteins

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Collectins fxs include

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protect the body against viruses, bacteria, & yeasts.

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Complement

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is a group of proteins in plasma & other body fluids that interact in a series of reactions

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Activation of complement

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stimulates inflammation, attracts phagocytes, & enhances phagocytosis.

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Natural killer cells

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are a small population of lymphocytes

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fxs of natural killer cells

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are to protect the body against cancer & viruses

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Perforins are cytolytic substances are secreted by

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natural killer cells.

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Inflammation produces

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redness, swelling, heat & pain

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Redness of inflammation is the result of

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dilated blood vessels

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Swelling of inflammation is the result of

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increases capillary permeability

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Heat of inflammation is the result of

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the entry of blood from deeper body parts

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Pain of inflammation is the result of

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stimulation of pain receptors

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Cells that commonly migrate to areas of inflammation are

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neutrophils & monocytes

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Pus

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is the result of an accumulation of white blood cells, bacterial cells, & cellular debris

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The fxs of inflammation

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are to prevent the spread of infection, to clear infection, & to promote healing of damaged tissues

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Phagocytosis

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removes foreign particles

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Examples of phagocytic cells are

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neutrophils, monocytes, & macrophages.

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Mononuclear phagocytic system is

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monocytes, macrophages, & neutrophils that are spread throughout the body

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A fever begins when a viral or bacterial infection

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stimulates lymphocytes to produce interleukin

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The fxs of fever

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to increase phagocytosis & to prevent bacteria & other pathogens from obtaining iron

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Immunity

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resistance to particular pathogens or to their toxins or metabolic by products

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An immune response is based on

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the ability to distinguish molecules that are part of the body from those that are foreign

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Antigens

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are molecules that can elicit an immune response.

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Cells that carry out immune responses

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Lymphocytes & macrophages

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Receptors on lymphocyte surfaces

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enable cells to recognize foreign antigens

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Antigens may be

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proteins, polysaccharides, glycoproteins, or glycolipids

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The antigens most effective in eliciting an immune response is

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large & complex, with few repeating parts

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Hapten

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a small molecule that must bind to a larger molecule to elicit an immune response

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Examples of haptens

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are chemicals found in drugs, household cleaners, dust, & skins of certain animals.

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T cells are derived from

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red bone marrow & the thymus gland

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B cells are derived from

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red bone marrow

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The blood distributes

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B cells

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B cells & T cells

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are abundant in lymph nodes, the spleen, bone marrow, & the intestinal lining

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Lymphocyte fxs

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1. The cellular immune response is cell to cell contact between a T cell & antigen cell.
2. Cytokines are produces by T cells

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Examples of cytokines

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are interleukins, colony stimulating factors, interferons, & tumor necrosis factors

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fxs of cytokines

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are to stimulate the production of lymphocytes, block viral replication, stimulate phagocytosis, stimulate production of antibodies, & to stop growth of tumor cells

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T cells may also secrete

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toxins that kill antigen bearing cells, growth inhibiting factors that prevent target cell growth, or interferon that prevent viral & tumor cell proliferation

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B cells differentiate into

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plasma cells

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Plasma cells produce

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antibodies

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The humoral immune response

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is the immune response that is mediated by antibodies

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A clone is

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a cell that is identical to the cell from which it was derived

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Different varieties of T cells & B cells have

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a particular type of antigen receptor on their cell membranes that can respond only to a specific antigen

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A lymphocyte must be activated before

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it can respond to an antigen

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T cell activation requires

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the presence of processed fragments of antigen attached to the surface of another kind of cell

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Antigen presenting cells

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are macrophages, B cells, & other cell types.

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T cell activation begins

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when a macrophage phagocytizes a bacterium & moves the antigens of the bacterium to its membrane

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The major histocompatibility complex

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is a complex of proteins found on the surface of antigen presenting cells

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MHC antigens help

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T cells recognize an antigen as foreign

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Class I MHC antigens are located

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on cell membranes of all cells except red blood cells

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Class II MHC antigens are located

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on cell membranes of antigen presenting cells, thymus cells, & activated T cells

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The fxs of helper T cells are

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to stimulate B cells to produce antigens & to secrete cytokines

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The fxs of cytotoxic T cells are

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to eliminate viral infected cells & tumor cells

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The fxs of memory T cells are

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to respond to an antigen during a future exposure & to differentiate immediately into cytotoxic T cells

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B cells may become activated when

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an antigen binds to its membrane bound receptor

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Upon activation, B cells

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divide repeatedly

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T cells help B cells by

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releasing cytokines that stimulate B cell proliferation & antibody production

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The fxs of memory B cells

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are to respond rapidly to subsequent exposures to a specific antigen

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The fxs of plasma cells are

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to secrete antibodies

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An immune response may include several types of antibodies manufactured against a single microbe because

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pathogens often have different antigens on their surfaces

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A polyclonal response

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is the production of several different antibodies against one pathogen

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Antibodies are

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soluble, globular proteins

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Each antibody composed of

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four chains of amino acids that are linked together

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The light chains are

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identical & contain about half the number of amino acids as the heavy chains

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The heavy chains are

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identical & contain twice as many amino acids as the light chains

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The five major types of antibodies are distinguished by

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a particular kind of heavy chain

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The variable region is

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the part of the antibody that contains variable sequences of amino acids

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Variable regions

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are specialized to react to the shape of a specific antigen molecule

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Antigen binding

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sites are specialized ends of antibodies that bind to antigens

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Idiotypes

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are the particular parts of antigen binding sites that actually bind to antigens.

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Constant regions

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are the parts of an antibody other than their variable regions

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The five major types of immunoglobulins are

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IgG, IgA, IgM, IgD, & IgE

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The three types of immunoglobulins that make up the bulk of circulating antibodies are

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IgG, IgA, & IgM

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IgG

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is found in tissue fluid & plasma

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The fxs of IgG

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to defend against bacterial, viruses, & toxins; it also activates complement

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IgA is found

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in exocrine gland secretions

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The fxs of IgA

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are to defend against bacteria & viruses

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IgM is found

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in plasma

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The fxs of IgM

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to react with antigens occurring on red blood cells & to activate complement

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IgD is found

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in the cell membranes of B cells

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The fxs of IgD

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to act as receptors for B cells

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IgE is located

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in exocrine gland secretions

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The fxs of IgE

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to promote inflammation & allergic reactions

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The three ways antibodies react to antigens

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directly attack antigens, activates complement, or stimulate localized changes (inflammation) that help prevent the spread of the pathogen

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In a direct attack, antibodies combine with

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antigens & cause them to clump

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Phagocytic cells

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can engulf antigen bearing pathogens more readily when they have clumped together

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Antibodies can also

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cover the toxic portions of antigens & neutralize their effects

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Complement is activated by

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the binding of certain antibodies to antigens

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fxs of complement

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opsonization, chemotaxis, cell lysis, & inflammation.

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IgE antibodies are usually attached

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to membranes of mast cells

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Mast cells release their biochemicals when

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antigens combine to antibodies on their surfaces

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The primary immune response

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occurs when a person is first exposed to an antigen

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Following a primary immune response, some B cells produce

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memory cells

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The secondary immune response occurs when

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a person is later exposed to an antigen & memory cells are activated

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Naturally acquired active immunity

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develops when a person is naturally exposed to an antigen

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Artificially acquired active immunity

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develops when a person is given a vaccine

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A vaccine

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a preparation that includes a antigen that stimulate a primary immune response

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Artificially acquired passive immunity

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occurs when a person is injected with antibodies or anti toxins

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Naturally acquired passive immunity

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occurs when antibodies are passed across the placenta or through mother’s milk

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Allergic reaction

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is an immune response against a nonharmful substance

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Allergens are

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substances that trigger allergic reactions

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An immediate reaction allergy

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occurs when an allergens bind to IgE antibodies & allergy mediators are released from mast cells & basophils

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Anaphylactic shock

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is a severe form of immediate reaction allergy that may lead to death

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Antibody dependent cytotoxic reactions

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occur when an antigen binds a specific cell, simulating phagocytosis & complement mediated lysis of the antigen

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Immune complex reactions

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occur when antigen antibody complexes cannot be cleared from the body

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Autoimmunity

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refers to the loss of the ability to tolerate self antigens

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A delayed reaction allergy

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occurs when a person is repeatedly exposed to an allergen & the allergic reaction occurs about 48 hours after exposure to the antigen

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Transplanted tissues & organs include

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corneas, kidneys, lungs, pancreases, bone marrow, skin, livers, & hearts

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A tissue rejection reaction

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is the destruction of transplanted tissue by the recipient’s immune system

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Tissues are rejected because

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the cell surface molecules (MHC antigens) of the donor tissue are recognized as foreign by the recipient

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Isografts

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are grafts from an identical twin

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Autografts

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are grafts from one’s self

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Allografts

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are grafts from another person

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Xenografts

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are grafts from a different species

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Immunosuppressive drugs

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are used to reduce rejection of transplanted tissues

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Autoantibodies are

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antibodies that cannot distinguish self from nonself

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Reasons people develop autoimmunities are

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viruses may incorporate some self proteins into its coating & the body then recognizes the self proteins as foreign in all cells, T cells may never learn to differentiate between self & nonself cells, or some antigens may resemble self antigens

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Scleroderma

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is a condition caused by autoimmunity that produces fatigue, swollen joints, stiff fingers, hardened blood vessels, & a mask like face

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The immune system begins to decline

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early in life

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By age 70, the thymus

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is one tenth of its original size

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Elderly people have a higher risk of developing cancer & infections because

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the strength of their immune systems has declined

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AIDS is more difficult to diagnose in older people because

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physicians do not initially suspect the condition

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Elderly people may not be candidates for certain medical treatments because

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of their declining immune systems.