Physiological Systems Week 6

pathogen

foreign agent that causes diseases

immune system

animal body’s system of defenses against agents that cause disease

innate immunity

form of defense in all animals that’s active immediately upon exposure to pathogens and is the same whether or not the pathogen has been previously encountered, includes barrier and internal defenses, provides a generic response from a small set of receptors

adaptive immunity

vertebrate-specific defense that develops following exposure to pathogens, mediated by B & T lymphocytes, includes humoral & cell-mediated responses, provides a specific response

phagocytosis

ingestion and breakdown of foreign substances

exoskeleton

physical barrier against infection

lysozyme

enzyme that destroys bacterial cell walls in the digestive tract; found in sweat, tears, and saliva

hemocytes

immune cells of insects that produce proteins that bind to molecules specific to a broad class of pathogens, carry out phagocytosis and release antimicrobial proteins

characteristics of innate immunity of all animals

barrier defenses, phagocytosis, antimicrobial proteins

characteristics of innate immunity unique to vertebrates

natural killer cells, interferons, inflammatory response

Where can a mucous membrane be found?

urinary, respiratory, reproductive, and digestive systems

mucus

viscous fluid produced by the mucous membrane that traps pathogens and other particles

components of the body hostile to many pathogens

saliva, mucus, tears because of lysozymes and skin and digestive system because of low pH

What do phagocytic cells recognize and how?

recognize viral, fungal, and bacterial components by Toll-like receptors (TLRS)

Toll-like receptor (TLR)

membrane receptor on a phagocytic WBC that recognizes fragments of molecules common to a set of pathogens

main types of phagocytic cells

neutrophils and macrophages

neutrophil

phagocytic WBC that circulates in blood and are attracted by signals from infected tissues; tends to self-destruct as they destroy foreign invaders, limiting life span to a few days

macrophage

large, phagocytic WBC found in body tissues that destroys microorganisms in innate immunity and functions as an antigen presenting cell in adaptive immunity

leukocytes

white blood cells of the vertebrate immune system

dendritic cell

WBC that populates tissues that contact the environment, stimulates adaptive immunity against pathogens it encounters and engulfs

mast cell

WBC found in connective tissue that releases histamine to sites of damage, initiating inflammatory response

natural killer cell

WBC that circulates in the blood and detects abnormal cells, releases chemicals that causes cell death

main types of antimicrobial proteins

interferons and complement proteins

process of antimicrobial proteins

pathogen recognition —> release of proteins —> attack pathogen or impede production

interferons

antimicrobial protein that interferes with viruses and activate macrophages

complement proteins

proteins that circulate in an inactive state and are activated by substances on pathogen surfaces; can amplify inflammatory response, enhance phagocytosis, or lyse extracellular pathogens

inflammatory response

innate immune defense triggered by injury or infection of tissue involving the release of substances to promote swelling, enhance filtration of WBCs, & aid in tissue repair/destruction of invading pathogens

cytokines

small peptides that act as signaling molecules, regulate the function of other cells

role of macrophages in the inflammatory response

discharge specific cytokines that recruit neutrophils to site of damage

role of mast cells in the inflammatory response

release histamine to site of damage

What allows for increased influx of immune cells and dilution of toxins in the inflammatory response?

blood vessel dilation and increased permeability

What do activated complement proteins do in the inflammatory response?

promote more histamine release to attract more phagocytic cells to the site of damage

What does increased blood flow do in the inflammatory response?

produces redness, increased skin temp, & helps deliver antimicrobial proteins

What happens in the inflammatory response as a result of increased blood supply and more histamine release by activated complement proteins?

accumulation of pus

pus

fluid rich in WBCs, dead pathogens, and debris from damaged tissue

main complications of the inflammatory response

fever and sepsis/septic shock

fever

systemic inflammatory response that is hypothesized to enhance phagocytosis and speed up tissue repair

sepsis

overwhelming inflammatory response that causes organ damage; increased leakiness of blood vessels, causing swelling and low blood pressure

barrier defenses of innate immunity

skin, mucous membranes, secretions

internal defenses of innate immunity

phagocytic cells, natural killer cells, antimicrobial proteins, inflammatory response

lymphocytes

type of WBC that mediates immune responses, two main types important to adaptive immunity are B and T cells

characteristics of the adaptive immune system

large diversity of lymphocytes & receptors, self-tolerance, B and T cell proliferation, immunological memory

antigen

substance that elicits an immune response by binding to receptors of B cells, antibodies, or T cells

antigen receptor

surface proteins on B and T cells that bind to antigens and initiate an adaptive immune response

When/how does recognition of foreign particles occur in the adaptive immune response?

B or T cell binds to an antigen via an antigen receptor

epitope

small, accessible region of an antigen to which an antigen receptor or antibody binds

clonal selection

process where an antigen selectively binds to and activates only those lymphocytes bearing receptors specific for the antigen, the selected lymphocytes proliferate and differentiate into a clone of effector cells and a clone of memory cells specific for the stimulating antigen

effector cells

short-lived cells that take effect immediately against an antigen and any pathogens producing that antigen

What is the B cell effector cell?

plasma cells

memory cells

long-lived cells that can give rise to effector cells if the same antigen is encountered later in the animal’s life, result of clonal selection

plasma cells

effector cells in B cells that secrete antibodies in adaptive immunity, arise from antigen-stimulated B cells, result of clonal selection

structure of T cell receptors

alpha and beta polypeptide chains, each with a constant (C) region and the tips form a variable (V) region that together form an antigen-binding site

What condition has to be met for antigen receptors of T cells to bind?

they bind only to antigen fragments that are displayed on the surface of host cells

major histocompatibility complex (MHC)

host protein that displays the antigen fragment on the cell surface for T cell antigen receptors

antigen presentation

display of an antigen fragment in an exposed groove of an MHC protein

main types of T cells

cytotoxic and helper

cytotoxic T cells

type of lymphocyte that, when activated, secretes toxic proteins to kill cells infected by viruses or other pathogens

helper T cells

type of T cell that, when activated, secretes cytokines that promote the response of B cells in the humoral response and cytotoxic T cells in the cell-mediated response

structure of B cell receptors

Y-shaped molecule with two identical heavy chains and two identical light chains, each chain has a constant (C) region and a variable (V) regions, the V regions of the heavy and light chains form the antigen-binding sites

How are B cells activated and what do the activated cells do?

activated by binding to an antigen, secrete soluble antibodies

antibodies

secreted form of B cell receptors, not membrane bound, provides direct defense against pathogens

types of adaptive immunity

cell-mediated or antibody-mediated

antibody-mediated (humoral) immune response

branch of adaptive immunity; involves activation of B cells and leads to production of antibodies, which help neutralize or eliminate toxins and pathogens in blood and lymph

cell-mediated immune response

branch of adaptive immunity; involves activation of cytotoxic T cells, which destroy infected host cells

steps of the cell-mediated response

1. cytotoxic T cells secrete perforin

2. cytotoxic T cells secrete granzymes

3. granzymes cause apoptosis

perforin

protein that perforates the cell membrane

What do granzymes do in the cell-mediated immune response?

secreted by cytotoxic T cells, enter the cell through the pores created by perforin

steps of the antibody-mediated immune response

1. B cells are activated by helper T cells or by binding to an antigen

2. B cells produce memory B cells and plasma cells (clonal selection)

What do plasma cells produce?

thousands of antibodies

methods that antibodies use to fight infection

neutralization, agglutination, precipitation, activation of complement proteins

Where are memory B cells found?

lymph nodes

primary immune response

initial adaptive immune response to an antigen, appears after 10-17 days, B and T cells produce effector cells

secondary immune response

adaptive immune response elicited on subsequent exposures to an antigen; faster, stronger, and longer responses; facilitated by memory B cells

active adaptive immunity

resistance built up following exposure to an antigen, can be natural (ex: caught pox) or artificial (ex: vaccination)

passive adaptive immunity

antibodies in the recipient are produced by another individual (ex: antibodies in breastmilk)

immunization

use of antigens artificially introduced into the body to generate an adaptive immune response and memory cell formation