LYMPHATIC AND

IMMUNE SYSTEMS

Chapter 33

THE LYMPHATIC SYSTEM

The lymphatic system has three main functions• Take up excess tissue fluid and return it to the

bloodstream

• Receive fats called lipoproteins and return them to the

blood stream

• Work with the immune system for defense against disease

The lymphatic system is a one-way system. Lymphatic

capillaries absorb fluid in the blood that has not been

reabsorbed by the blood capillaries.• At this point, the fluid is called lymph

THE LYMPHATIC SYSTEM

The lymphatic capillaries join to lymphatic vessels

that enter either the thoracic duct or the lymphatic

duct.• The thoracic duct serves the lower extremities, abdomen,

and left side of the head, neck and torso

• The lymphatic duct serves the right side of the head, neck,

and torso

Both ducts remove harmful substances from blood

and carry them to lymph nodes where they are isolated

from the rest of the body

LYMPHOID ORGANSLymph nodes

• Lymph nodes are found along the lymphatic

vessels.

• A lymph node contains a cortex and a medulla• Cortex: where lymphocytes congregate when fighting off

a pathogen (hence, the swelling of the lymph nodes if a

patient is sick or fighting a disease)

• Medulla: where macrophages cleanse the lymph as it

passes through

• Lymph nodes are found in the groin, armpits, and

neck and tend to swell when isolating and

containing pathogens

LYMPHOID ORGANS

Tonsils

• Tonsils are located just above the pharynx

• Tonsils behave like lymph nodes for pathogens and

antigens that enter the body through the mouth and

nose

• The function of tonsils was only recently discovered in

the past century, making the 3,000 year old surgery of

tonsillectomy much more rare

LYMPHOID ORGANSSpleen

• The spleen is the primary blood filtering organ

• Located in the upper left abdominal region,

just beneath the diaphragm

• Spleens contain two tissues called white pulp

and red pulp.• The white pulp filters out bacteria and debris from

blood

• The red pulp filters out old red blood cells

LYMPHOID ORGANS

Thymus gland• Located along the trachea behind the sternum

• T lymphocytes mature in the thymus

• Immunity hormones, such as thymosin, are produced

here

Bone Marrow• Contains the stem cells for all types of blood cells

• The bone marrow is connected to sinuses, where

matured and differentiated blood cells enter the

blood stream

IMMUNE SYSTEM:

INNATE DEFENSE

Immunity is the body’s ability to defend itself against

infectious agents, foreign cells, and even abnormal body

cells such as cancer.

Innate defense systems recognize most common

microbe invaders automatically whether or not the

immune system has encountered this particular microbe

before.

They lack any “memory” system. Even if they

encounter the same microbe 1000’s of times the response

doesn’t change.

INNATE IMMUNITY:P HYSICAL & CHEM ICAL BARRIERS

Skin and mucus membranes limit where pathogens can

enter the body to only a few locations (mouth, nose, ears,

genitals)

Oil secretions contain additional chemicals that weaken

or kill some bacteria that make contact with the skin

Respiratory tracts are lined with cilia. Mucus surrounds

and collects pathogens, then cilia sweep the pathogen to the

throat where it can be swallowed or expectorated (coughed

out)

Symbiotic bacteria in our bodies also fight off invaders

INNATE IMMUNITY:

INFLAMMATORY RESPONSEDamaged tissues initiate an inflammatory response which

makes both the organism and the immune system aware of a

problem.

Inflamed areas show redness, heat, swelling and pain.

Histamines trigger the capillaries of the tissues to dilate and

allow a higher volume of blood cells to enter.

White blood cells enter the area to cleanse any foreign

microbes

Clotting occurs to prevent any bacteria from entering while

the tissue is repaired and allow the internal homeostatic

environment to continue.

PHAGOCYTES AND NKC’SNatural Killer Cells

• NK cells kill virus-infected cells and tumor cells. They

are triggered only by chance cell-to-cell encounters

• They know if a cell is foreign because the cell doesn’t

know how to build the specific antigens for that cell

Neutrophils

• These immune cells can leave bloodstreams and enter

tissues to fight infections

Eosinophils

• These cells are designed to attack larger parasitic

infections like roundworm or tapeworm that are too

big for individual phagocytizing cells.

INNATE IMMUNITY:

PROTECTIVE PROTEINS Protective Proteins are produced in a domino effect called the complement system. One protein activation triggers production of all othersThese proteins are only activated by pathogens and work in one of three ways:

• 1: They increase the inflammation response if large microbes are involved

• 2: They increase phagocytosis by binding to pathogens and giving neutrophils and macrophages something to latch on to.

• 3: They poke holes in pathogens to force water and salts to enter until the molecule bursts.

Interferon is a protective protein produced by virus-infected cells. Interferon binds to non-infected cells causing them to go into hibernation mode and limiting the number of cells the virus could spread to.

IMMUNE SYSTEM: ADAPTIVE

DEFENSE

Adaptive defenses are designed to respond to specific diseases

with higher frequency after each encounter

Adaptive defense relies on B cells (which are made in marrow)

and T cells (which are made in the thymus)• Both B and T cells recognize your personal antigens and distinguish

them from other microbial antigens

• B and T cells have millions of different antigen receptors on their

plasma membranes for recognizing foreign invaders.

The simplest difference between B cells and T cells is that B

cells attack pathogens from the outside and T cells attack from

the inside.

https://goo.gl/Hq6YGg

B CELLS & ANTIBODY-MEDIATED

(HUMORAL) IMMUNITY

Antibodies help to prevent an infection BEFORE it

occurs• Antibodies match with antigens and act as beacons for the

immune system to respond to.

• They also cover the invading microbes to the point that it

has difficulty binding to a new victim cell

Microbes are delivered to the spleen and lymph

nodes thanks to the lymphatic system, where B cells are

waiting for them.

B CELLS & ANTIBODY-MEDIATED

(HUMORAL) IMMUNITY

When the B cell finds the antigen on a microbe it

divides over and over again creating…• Plasma Cells: Cells filled with Rough ER for producing antibodies

that match with this specific antigen

• Memory B Cells: Seek out this specific antigen for increased

immune response.

The most common antibody is IgG, a Y-shaped

protein.• The Y-shape is altered in the presence of specific antigens

• Leukocytes recognize the shape of this antigen and begin

phagocytosis.

T CELLS & CELL-MEDIATED

IMMUNITYT cells come in two categories: helper and cytotoxic.

Helper T cells cannot recognize foreign antigens on their own.

• Antigen presenting cells seek out and respond to foreign antigens.

• When they find an antigen, they “cap” it with an MHC protein.

• The MHC protein then attracts a helper T cell which binds to the microbe.

Helper T cells attract B cells to the microbe

Helper T cells also clone themselves upon binding to a microbe to

create memory T cells, which look for the same microbe in the future

to attract T cells.

At this point, B cells would normally have completed their task. But

T cells go one step further.

T CELLS & CELL-MEDIATED

IMMUNITY

Cytotoxic T cells contain vacuoles filled with a chemical

called perforins and granzymes

The cytotoxic T cell is incredibly deadly, so it can only be

activated with the presence of specific MHC proteins and

helper T cells

When the cell locates its target, perforins create a pore in

the plasma membrane of the microbe or cancerous cell

Granzymes then enter the cell through the pore and force

apoptosis

ACTIVE INDUCED IMMUNITYActive immunity is your body’s direct response to a specific threat.

We can artificially preempt an active immune response thanks to

immunizations

• A vaccine is a substance that contains the antigen to which the

immune system responds (not the whole cell, just the antigen)

and produces antibodies

• Antibodies are destroyed every time they fight off an infection.

Unless your body makes new antibodies, you’ll eventually run

out.

• Over the course of the year or lifetime the titer will eventually

dwindle as the antibodies are used up or broken down while

fighting off disease

• Some vaccines are good for life; other’s require periodic “booster”

shot

PASSIVE INDUCED IMMUNITY

Passive immunity is when an individual is given

prepared antibodies through natural means to

combat a disease.

• Infants are given antibodies from their mother

through blood that passes the placenta or

through transfer within breast milk

IMMUNITY DISORDERS

Allergies are hypersensitivities to substances that ordinarily would do no harm to the body.The response to these antigens, called allergens, is either: Immediate Allergic Response

• An IAR can occur within seconds. Coldlike symptoms are common, but the worst-case scenario is anaphylactic shock, a sudden drop in blood pressure.

• IgE Antibodies attached to the plasma membrane of tissue and blood release histamines as if a dangerous pathogen just invaded them, triggering these cold or anaphylactic symptoms

Delayed Allergic Response• Memory T cells are initiated at the site of the allergen.• These trigger cytokines, which trigger the immune response.

IMMUNITY DISORDERS

Autoimmune disease is when cytotoxic T cells or

antibodies accidentally attack the body’s own cells.

These are sometimes the result of overactive T cells

still functioning after a foreign-pathogen-initiated

infection has occurred.

Lupus, rheumatoid arthritis, and muscular disorders

are believed to be triggered by an autoimmune disease.