anatomy lecture exam 4

Functions of the Oral Cavity

1. Sensory analysis of material before swallowing
2. Mechanical processing through actions of teeth, tongue, and palatal surfaces
3. Lubrication - mixing with mucus and salivary gland secretions
4. Limited digestion of carbohydrates (salivary amylase) and lipids (lingual lipase)

the tongue

Manipulates materials inside mouth

Functions of the tongue

1. Mechanical processing by compression, abrasion, and distortion
2. Manipulation to assist in chewing and to prepare material for swallowing
3. Sensory analysis by touch, temperature, and taste receptors
4. Secretion of mucins and the enzyme lingual lipase

Salivary Glands

produces saliva (1.0–1.5 liters of each day) with different properties

Submandibular salivary glands (70%)

produces buffers, glycoproteins (mucins – gives saliva its lubricating property), and salivary amylase

Parotid salivary glands (25%)

produces serous secretions with salivary amylase - breaks down starches

Sublingual salivary glands (5%)

produces mucous secretions that act as buffer and lubricant

Specific resistance (immunity)

Responds to specific antigens with coordinated action of T cells and B cells

T-cells

* Provide cell-mediated immunity
* Defend against abnormal cells and pathogens inside cells

B-cells

* Provide antibody-mediated immunity
* Defend against antigens and pathogens in body fluids

innate immunity

present at birth

adaptive immunity

gained after birth

active immunity

Antibodies develop after exposure to antigen

passive immunity

Antibodies are transferred from another source

Active: Naturally acquired

Through environmental exposure to pathogens (ex. Catching the flu)

Active: Artificially acquired

Through vaccines containing pathogens (stimulates immune system to produce antibodies) (Ex: Flu vaccine)

Passive: Naturally Acquired

Antibodies acquired from the mother (Ex: Breast milk)

Passive: Artificially Acquired

By an injection of antibodies (Ex: RhoGAM anti-D antibodies)

Four Properties of Immunity: Specificity

* Each T or B cell responds only to a specific antigen and ignores all others
* Several thousand different types of lymphocyte each with a specific antigen receptor

Four Properties of Immunity: Versatility

The body produces many types of lymphocytes

* Each fights a different type of antigen
* Active lymphocyte clones itself (cell divides and makes copies of itself) to fight their specific antigen

Four Properties of Immunity: Memory

Some active lymphocytes (memory T or B cells):

* Stay in circulation
* Provide immunity against new exposure of the same antigen (previously exposed to

Tolerance

Immune system ignores “normal” antigens (selfantigens). Failure of tolerance causes auto-immune disorders

antigen presentation

T cells only recognize antigens that are bound to glycoproteins in plasma membranes

**MHC (Major Histocompatibility Complex) Proteins** AKA **Human Leukocyte Antigens (HLA’s)**

* differs among individuals
* The membrane glycoproteins that bind to antigens
* Genetically coded in chromosome 6

Class I MHC proteins

Found in membranes of all nucleated cells (not found on red blood cells… why?)

Class II MHC proteins

* Found in membranes of antigen-presenting cells (APCs)
* Found in lymphocytes, phagocytic, and non-phagocytic cells

primary reason for organic rejection

recipient’s T cells recognize transplanted tissue as foreign tissue because of antigen on surface

Class I MHC Proteins: Process

Pick up small peptides in cell cytoplasm and carry them to the surface

* T cells ignore normal peptides
* Abnormal peptides or viral proteins activate T cells to destroy cell

Class II MHC Proteins Antigenic fragments

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* From **antigen processing** of pathogens (processing through phagocytosis and breakdown of pathogens)
* Bind to Class II proteins
* Inserted in plasma membrane to stimulate T cells

Antigen presenting cells (APCs)

* Responsible for activating T cells against foreign cells and proteins
* Note – Class II MHC proteins only appear on the plasma membrane when cell has processed the antigens

Phagoocytic APCs

* Free and fixed macrophages in connective tissues
* Kupffer cells of the liver
* Microglia in the CNS

Non-phagocytic APCs

* Langerhans (dendritic) cells in the skin
* Dendritic cells in lymph nodes and spleen

Inactive T cell receptors

* Recognize Class I or Class II MHC proteins
* Recognize a specific antigen

Binding occurs when…

MHC protein is attached to the specific antigen that the T cell is programmed to detect

Binding of T cell causes …

quick production of cytotoxic T cells and memory T cells and slow production suppressor T cells

Cytotoxic T cells (also called TC cells)

* Attack cells infected by viruses
* Responsible for cell-mediated immunity

Memory T-cells

Clone more of themselves in response to “remembered” antigen – remain in body so they can quickly respond in future encounters with the antigen

Helper T cells (also called TH cells)

Stimulate function of T cells and B cells

Suppressor T cells (also called TS cells)

Inhibit function of T cells and B cells

Cytotoxic T-cell Process

1. Release perforin to destroy antigenic plasma membrane
2. Secrete poisonous lymphotoxin to destroy target cell
3. Activate genes in target cell that cause cell to die (apoptosis)

Memory T-cells are produced with…

cytotoxic t-cells

memory t-cells stay…

in circulation

memory t-cells immediately form cytotoxic t-cells if…

same antigen appears again

Suppressor t-cells secrete…

suppression factors (inhibitory cytokines)

Suppressor t-cells inhibit …

responses of t and b cells

Suppressor t-cells act after …

initial immune response

Suppressor t-cells limit…

immune reaction to single stimulus

Activation of inactive helper T cells

occurs when APC with antigen attached to Class II MHC binds to inactive helper T cell.

Binding triggers

* Active helper (CD4) T cells (TH cells)
* Secrete cytokines
* Memory helper (TH ) cells
* Remain in reserve

For T-cells to be actived

it must be costimulated by binding to stimulating cell at second site which confirms the first signal

Four Functions of Cytokines

1. Stimulate T cell divisions


1. Produce memory TH cells
2. Accelerate cytotoxic T cell maturation
2. Attract and stimulate macrophages
3. Attract and stimulate activity of cytotoxic T cells
4. Promote activation of B cells

B-cells are responsible for…

antibody-mediated immunity

B-cells attack antigens by…

producing specific antibodies

B-cells have …

Millions of populations, each with different antibody molecules

Corresponding antigens in interstitial fluids bind to

b cell receptors

B-cells preparation for activation is called

sensitization

During sensitization, antigens are:

* Taken into the B cell
* Processed
* Reappear on surface, bound to Class II MHC protein

(Helper T-cells) Sensitized B cell is prepared for activation but …

needs helper T cell activated by the same antigen

Helper T cell binds to MHC complex containing the antigen then…

Secretes cytokines that promote B cell activation and division

Activated B-cells divide into

memory b-cells and plasma cells

Memory B-cells

Like memory T cells, remain in reserve to respond to next infection

Plasma Cells

Synthesize and secrete antibodies into interstitial fluid

Antibody structure consists of

two parallel pairs of polypeptide chains

* One pair of heavy chains
* one pair of light chains
* Each chain contains Constant and Variable

Five Heavy-Chain Constant Segments

1. IgG
2. IgE
3. IgD
4. IgM
5. IgA

Determine five types of antibodies

Variable Segments of Light and Heavy Chains

Determine specificity of antibody molecule

Binding Sites

Free tips of two variable segments form antigen binding sites of antibody molecule which bind to antigenic determinant sites of antigen molecule

Antigen–Antibody Complex

An antibody bound to an antigen

A Complete Antigen

* Has at least two antigenic determinant sites
* Binds to both antigen-binding sites of variable segments of antibody

B cell sensitization

* Exposure to a complete antigen leads to:
* B cell sensitization
* Immune response

Hapten (Partial Antigens)

Must attach to a carrier molecule to act as a complete antigen

Danger of Haptens

Antibodies produced will attack both hapten and carrier molecule

If carrier is “normal”:

* Antibody attacks normal cells
* For example, penicillin allergy

Antibodies

* Are found in body fluids
* Are determined by constant segments
* Have no effect on antibody specificity

IgG

is the largest and most diverse class of antibodies - 80 percent of all antibodies

IgG antibodies are responsible for…

resistance against many viruses, bacteria, and bacterial toxins

IgG can cross the

placenta

maternal IgG provides…

passive immunity to fetus during embryological development

Anti-Rh antibodies produced by Rh-negative mothers are also IgG antibodies and produce…

hemolytic disease of the newborn

The anti-Rh antibodies can cross the placenta…

and bind onto fetal blood cells

IgD is an individual molecule on the surfaces of B cells where it can…

bind antigens in the extracellular fluid

IgD: Binding can play a role in the sensitization of…

the B cell involved (activation involves helper T cell)

IgE attaches as an individual molecule to the…

exposed surfaces of basophils and mast cells

When an antigen is bound by IgE molecules:

The cell is stimulated to release **histamine** and other chemicals that accelerate inflammation in the immediate area

IgE is also important in the…

allergic response

IgM

is the first class of antibody secreted after an antigen is encountered

IgM concentration declines as…

IgG production accelerates

Plasma cells secrete individual IgM molecules, but…

it polymerizes and circulates as a five-antibody starburst

The anti-A and anti-B antibodies responsible for the agglutination of incompatible blood types are …

IgM antibodies

IgM cannot

cross the placenta (why is this important?)

IgM antibodies may also attack…

bacteria that are insensitive to IgG

IgA is found primarily in…

glandular secretions such as mucus, tears, saliva, and semen

IgA Attack pathogens before

they gain access to internal tissues

IgA antibodies circulate in…

blood as individual molecules or in pairs

Epithelial cells absorb them from blood and attach a secretory piece, which…

confers solubility, before secreting IgA molecules onto the epithelial surface

Seven Functions of Antigen–Antibody Complexes

1. **Neutralization** of antigen binding sites
2. **Precipitation** and **agglutination** – formation of **immune complex**
3. Activation of complement
4. Attraction of phagocytes
5. **Opsonization** (coat of antibodies and complement proteins on antigen) increasing phagocyte efficiency
6. Stimulation of **inflammation**
7. Prevention of bacterial and viral adhesion

Primary and Secondary Responses to Antigen Exposure

Occur in both cell-mediated and antibody-mediated immunity

First exposure to Antigen

Produces initial primary response

Secondary exposure to same Antigen

* Triggers secondary response
* More extensive and prolonged
* Memory cells already primed

The Primary Response

* Takes time to develop
* Peak response can take two weeks to develop
* Declines rapidly
* Antigens activate B cells
* Plasma cells differentiate
* **Antibody titer** (level) slowly rises
* IgM is produced faster than IgG
* Is less effective than IgG

Secondary Response

Activates memory B cells (these cells were produced from primary response)

* At lower antigen concentrations than original B cells
* Secrete antibodies in massive quantities
* IgG - rises very high and very quickly and can remain elevated for extended time
* IgM - production is also quicker and slightly extended