Chp 7- Infections Human Bio

Define Pathogens

A disease-causing organism;

often referred to as a pathogenic organism

What is Bacteria?

Unicellular, prokaryotic organisms

with a cell wall but lacking membrane-bound organelles and an organised nucleus;

singular: bacterium

What are the structures of a typical bacterial cell?

1. slime layer

2. Cell membranes

3. Flagella

4. Cytoplasm

5. Cell wall

6. DNA

7. Capsule

What is the purpose of the slime layer?

• around outside of some bacteria

• Protect?

What is the purpose of the cell membrane?

• Provide structural support & stability to maintain cell shape

• Regulate transport of nutrients in and waste out

• Enabling cellular communication

What is the purpose of the Flagella

• movement

• One or many

• Not found in all bacteria

What is the purpose of the Cell wall?

• often made up of peptodoglycan

• → combination of carbohydrate-protein

What is the purpose of the Cytoplasm?

• lots of ribosome

• → cytoplasm appears granular

• Do not have membrane-bound organelles

• E.g: mitochondria, Golgi apparatus

How is DNA stored in bacterial cells?

• no nuclear membrane

• → DNA forms tangle inside cell

• Some in form of loops called plasmids that can e exchanged during reproduction

What is the purpose of the Capsule?

• formed of complex carbohydrates by some bacteria

• For protection

Are all bacteria harmful?

Majority non-pathogenic

But can, infect host in order to exploit goof potential of host’s body tissue

→ exploitation cause disease, bacteria don’t care

What are cocci?

• spherical cells

• Occur singly (coccus)

• pairs (diplococci)

• Clusters (staphylococci)

• Chains (steptococci)

What are bacilli

• type of bacteria with flagella (for movement) & have rod-shaped cells

• Singular (bacillus)

What are spirilla?

• twisted cells

• Singular (spirillum)

• 

What are vibrio?

• Curved rods, often shaped like comma

• 

Define a virus

An infectious agent, viruses are totally dependent on living cells for reproduction

What are the structures of a virus?

a protein sheath surrounding a core of nucleic acid (DNA OR RNA)

• some have external lipid envelope

Why are viruses dependent on living cells for reproduction?

• viruses are not living things

• → cannot reproduce by themselves

• Must infection living cell,

• → its DNA/RNA induces cell to manufacture more virus particles

• New virus particles able to leave host cell to infect others

What happens to the cells during the infection of a virus?

• become damaged, changed or die

What are viruses that multiply in bacterial cells, and cause the death of bacterium?

Bacteriophages

How can communicable disease be spread?

Transmission of pathogenic organisms from one person to another.

Some are said to be contagious: directly passed

Or passed through vectors: intermediate hosts

How can communicable diseases be spread through transmission by contact?

• spread of pathogens by physical contact

• → direct (touching infected person)

• → indirect (touching object that infected individual touched)

• E.g: skin infections, STI’s

How can communicable diseases be spread through Ingestion?

• ingest good or drink contaminated w pathogens

How can communicable diseases/infections be spread through Transfer of body fluids?

• when blood/body fluids from infected person comes into contact w mucous membranes of uninfected person

• → nose, mouth, throat, genitals, bloodstream

• Pathogens may enter body of that person

How can communicable diseases/ infections be spread through droplets?

• tiny droplets of moisture containing pathogenic organisms emitted when talking, sneezing, or coughing

• → droplets may be breathed by others, or settle on food, utensils, or later ingested w food

How can communicable diseases/infections be spread through Airborne transmission?

• when moisture in exhaled droplets evaporates, many bacteria killed

• → but virsuses & some bacteria viable 7 can cause infection when inhaled

• Particles lighter, remain viable for greater distance than those transmitted by droplets

How can communicable diseases be spread through Transmission by vectors?

• vectors = transfer of pathogens by other animals

• Some vectors transfer pathogen directly, some spread pathogen to food or water

• Many vector-borne diseases spread by specific vector

What are non-specific vs specific defences?

Non-specific: work against all pathogens

→ body’s first line of defence

Specific: directed at particular pathogen

How does skin act as an external defence to pathogens?

• covers whole outside of body

• Stop entry of micro-organisms→ provided not broken by curs & abrasions

• Skin have normal bacteria, so potential pathogen difficult to become established

• Sebum, oily secretion produced by oil glands in skin, contains substances that kill some pathogenic bacteria

• Sweat secreted onto skin contains salts & fatty acids that prevent growth of micro-organisms

How does Mucus act as an external defence to pathogens?

• mucous membranes line body cavities that open to exterior

• → secrete mucus

• Traps particles, therefore inhibits entry of micro-organisms to organs

• → digestive, urinary & reproductive tract

How do hairs act as an external defence to pathogens?

• found in nasal cavity

• Hairs & layer of mucus trap 90% of particles inhaled when breathing

How does cilia act as an external defence to pathogens?

Cilia: tiny hair-like projections from cells, capable of beating motion

• mucous membranes lining nasal cavity, trachea & other air passages have cilia

• → beating of cilia moves mucus, containing trapped particles & micro-organisms

• → towards throat, where coughed or swallowed

How do ancids act as an external defence to pathogens?

• stomach juice, strongly acidic : hydrochloric

• → kills many bacteria taken in w food or those contained in mucus swallowed from nose & windpipes

• Vagina also has acid secretions, reduce growth of microorganisms-organisms

• Urine & sweat slightly acidic

What is a reflex?

• automatic, involuntary response to stimuli

• Help protect body form injury

How does sneezing act as a protective reflex against pathogens?

• stimulus: Irritation of walls of nasal cavity

• → may be caused by noxious fumes or dust particles, likely carrying micro-organisms

• Forceful expulsion of air from lungs carries mucus, foreign particles & irritating gases out through nose & mouth

How does coughing act as a protective reflex against pathogens?

Stimulus: irritation in lower respiratory tract (bronchi & bronchioles)

• air forced from lungs to remove irritant

• Air drives mucus & foreign matter up trachea, towards throat & mouth

How does vomiting act as a protective reflex against pathogens?

• psychological stimuli

• Excessive stretching of stomach & bacterial toxins can induce vomiting

• Contraction of muscles of abdomen & diaphragm, not contractions of stomach expels stomach contents

How does diarrhoea act as a protective reflex against pathogens?

• irritation of small & large intestine by bacteria, viruses, or protozoans can cause

• Irritation causes increased contractions of muscles of wall of intestines, so irritant removed asap

• Material does not stay in large intestine long enough for water to be absorbed, so faeces watery

What happens to organisms that penetrate the external defences?

• attacked by phagocytes

What are phagocytes?

• specialised white blood cells, or leukocytes

• → engulf & digest micro-organisms & cell debris

• Eliminates pathogens before infection has chance to take hold.

What are the different types of cells that are phagocytic?

• monocytes & macrophages

• Neutrophils

• Dendritic cells

What do monocytes & macrophages do?

• When tissue becomes infected or inflamed

• → monocytes leave bloodstream & enter tissue

• → differentiate to macrophages

• Large phagocytic cells,

• move through tissue looking for & destroying pathogens or fixed in one place & deal w pathogens that come to them

• → particularly important in removing microbes & dying cells through phagocytosis

What do neutrophils do?

• granulated leucocyte

• Characterised lobulated nucleus

• Most abundant leucocyte

• During infection, neutrophils first cells to move into tissue to destroy pathogen

• → by phagocytosis

• Important in killing pathogen inside cells

• Die after few days → makes up pus after infection

What do dendritic cells do?

• characterised by projections from cytoplasm

• Function beyond just phagocytosis

• Cells have ability to detect, engulf, & process foreign particles

• Use info abt ingested particles to assist w specific immunity

What is inflammation & its 4 signs?

• response to any damage to the tissues

Signs: redness, swelling, heat & pain

What is the purpose of inflammation?

• reduce spread of any pathogens

• → destroy & prevent entry of additional pathogens

• Remove damaged tissue & cell debris

• Begin repair of damaged tissue

How does the complement system work?

• some steps in inflammatory response assisted by proteins in complement system

• → Produced by liver cells & macrophages

• Series of more than 20 proteins

• Normally inactive, when initiated one protein activates the next

What is the 1st step in the inflammatory response? (Stimulus)

1. Mechanical damage or local chemical changes cause specialised leucocyte, mast cells, to be activated by complement proteins

→ results in release of histamine, heparin & other chemicals into tissue fluid

What is the 2nd step in the inflammatory response? (Histamine)

2. histamine increases blood flow through area due to vasodilation, = redness & heat

→ making walls of blood capillaries more permeable, loss of fluid from blood = swelling

→ more fluid moves through capillary walls into tissue

What is the 3rd step in the inflammatory response? (Heparin

3. prevents clotting in immediate area of injury

• → release from mass cells

• Clot of fluid forms around damaged area

• → slows spread of pathogen into healthy tissues

What is the 4th step in the inflammatory response? (Neutrophils)

4. Complement system proteins & some chemicals released by mast cells, attract phagocytes

→ particulary neutrophils

→ actively consume micro-organisms & debris by phagocytosis

What is the 5th step in the inflammatory response? (Pain)

5. Abnormal conditions in tissue, stimulate pain receptors, so person feels pain in inflamed area

What is the 6th step in the inflammatory response? (Dead phagocytes)

6. Phagocytes filled with bacteria, debris, & dead cells being to due

→ dead phagocytes & tissue fluid form pus

What is the 7th step in the inflammatory response? (Mitosis & repair)

7. New cells are produced by mitosis, & repair of damaged tissue takes place

Define a fever

An elevation of internal body temperature above the normal level of 37*C

What stimulates the hypothalamus to raise the body’s thermostat?

Chemicals called pyrogens

→ Released by white blood cells during inflammatory response

What is an example of a pyrogen?

Interleukin-1

→ produced by activated macrophages, also by dendritic & epithelial cells

What causes a fever?

1. Infection by pathogen or toxin

2. Phagocytic White blood cells ingests bacterium, destroying it, and releasing small proteins called pyrogens

3. thermostat reset

→ pyrogens act directly on hypothalamus & rest body’s thermostat to higher temp, producing fever

What are the benefits of a fever?

1. Inhibits growth of some bacteria & viruses

2. Speeds up metabolic reactions, which helps increase rate of tissue repair

3. Increases heart rate, so WBC delivered to sites of infection more rapidly

4. May inhibit viral replication by allowing interferons to operate more quickly

What does the lymphatic system consist of?

• network of lymph capillaries joined to larger lymph vessels

• Lymph nodes, located along length of some lymph vessels

What is the main function of he lymphatic system?

• collect some of fluid tat escapes from blood capillaries & returns it to circulatory system

• → important part of body’s internal defect against pathogenic organisms

Where are lymph nodes situated in the body?

• occur at intervals along lymphatic vessels

• Each node contains masses of lymphoid tissue

• → cells of which are Criss-crossed by network of fibres

What does lymph contain when it enters lymph nodes?

• cell debris, foreign particles, & micro-organisms that have penetrated body;S external defences

What could happen if some of the micro-organisms in the lymph are not destroyed?

If pathogenic

→ cause disease

How does the body destroy larger particles that enter the lymphatic system?

• larger particles (bacteria) trapped in meshwork of fibres as lymph flows through spaces in noes.

• Macrophages ingest & destroy particles by phagocytosis

What happens during an infection to the lymphatic system?

• formation of lymphocytes increases

• → lymph nodes become swollen & swore

• Lymphocytes important in specific immune response to particular pathogen

What is the immune system composed of?

• cells & proteins that protect against foreign organisms, a range of alien chemicals, and well as cancerous and other abnormal cells

What are phagocytes and what do they do?

• non-specific cell

• Able to engulf & digest micro-organisms & cell debris

What is an immune response?

• reaction and protection against a specific micro-organisms or disease-causing substance by B-cells & T-cells

Why os an immune response a homeostatic mechanism?

• when micro-organisms or foreign substances enter body, immune response helps deal w invasion & restore interval environment to its normal conditions

What are the key cells involved in the immune response?

B-cells & T-cells

→ white blood cells called lymphocytes

Where are B-cells & T-cells produced & matured?

• produced in bone marrow

• T-cells matureL Thymus

• B-cells mature: Bone marrow

• → both end up in lymphoid tissue

Where are lymphoid tissues located?

• most in lymph node

• → also in spleen, thymus, tonsil

What are the two parts to the immune response?

1. Humoral response/ antibody-mediated immunity

2. Cell-mediated reponse

→ both triggered by antigens

What is humoral response/ antibody-mediated immunity?

• production of special proteins called antibodies by B-cells

• → which circulate body & attack invading agents

What is cell-mediated response?

• T-cells

• Involved formation of special lymphocytes that destroy invading agents

What are antigens?

• any substance capable of causing a specific immune response

• Large molecules such as proteins, carbohydrates, lipids or nucleic acids

What are some examples of antigens?

• virus particle

• Whole micro-organisms (bacterial cell)

• Part of bacterium (flagella, cell wall, capsule)

• Toxins

• Molecules on cells

• Pollen grains

• Egg whites

What are self-antigens and non-self antigens?

Self-antigens: large molecules produced in person’s own body

→ does not cause immune response

Non-self antigen: foreign compounds that do trigger immune response

How does your body distinguish between self, and non-self antigens?

• immune system becomes programmed before birth to distinguish between self-antigens & non-self antigens

What is an antibody?

• Y-shaped specialised protein produced by plasma cells in response to non-self antigen

• Belong to grp of proteins: immunoglobulins

What is an antigen-antibody complex?

• antibody produced in response to antigen can combine w that antigen to form: antigen-antibody complex

• → antigen molecules have specific active site w particular shape

• → antibody has complementary shape, Allowing 2 molecules to fit tgt

• *each antibody can combine w only one particular antigen

What are antigen-presenting cells?

• Specific cells that recognise & respond appropriately when non-self antigen enters body

What are some examples of antigen-presenting cells?

• dendritic cells

• Macrophages

• Undifferentiated b-cells

What do antigen-presenting cells do?

1. Detect presence of non-self antigen

2. Engulf pathogen

3. Digest pathogen, producing small fragments that move to surface of cell (wear it)

4. Present antigen to lymphocytes

What are the 6 steps of the humoral response/ anti-body edited immunity?

1. Antigen presenting cells present the antigen, activating a particular b-cell

2. B-cell enlarges & divides into a group of cells called a clone

3. Most clones become plasma cells

4. Plasma cells secrete the specific antibody capable of attaching to active site of antigen

5. Some B-cells differentiate into long lived memory cells

6. Memory cells spread to all body tissues & will rapidly produce antibodies if same pathogen enters body again

What is the primary immune response?

• first exposure to particular antigen

• →Slow bcs takes time:

1. For B-cells to multiply & differentiate into plasma cells

2. For plasma cells to secrete antibodies

3. To. Build up large amounts of antibodies

What is the secondary immune response?

• second or subsequent exposure to same antigen

• → fast because:

1. Memory cells recognise antigen

2. Produce antibodies at much faster rate in higher concentrations

How may antibodies work?

1. Inactivate foreign enzymes or toxins by combining w them or inhibiting their reaction w other cells/ compounds

2. Bond to surface of viruses & prevent them entering cells

3. Coat bacteria so more easily consumed by phagocytes

4. Cause particles (bacteria, viruses, foreign blood cells) to clump tgt

→ agglutination

5. Dissolve organisms

6. React w soluble substances to make insoluble & thus more easily consumed by phagocytes

How would antibodies interact with antigen sot inactivate the antigens? (Diagram)

What does cell-mediated immunity provide resistance to?

• intracellular phase of bacterial & viral infections

• Fungi & parasites (round worm)

• Transplants of foreign tissue

• Cancer cells

What are the 6 steps to cell-m educated immunity?

1. Antigen-presenting cells presents foreign antigen to T-cells in nearest lymph node

2. Specific T-cell gets activated or sensitised

3. T-cell enlarges & divides into group of cells called clone

4. Most clones become plasma cells produce different type of T-cell cells

5. Some T-cells differentiate into one-lived memory cells

6. Memory cells spread to all body tissues & will initiate much faster response

If T-cells don’t become memory cells, what do the develop further into?

1. Killer T-cells (aka cytotoxic T-cells)

2. Helper T-cells

3. Suppressor T-cells

What are killer/Cytotoxic T-cells?

• migrate to site of infection & deal w invading antigen

• Attach to invading cells & secrete chemical that destroy antigen

• → then go in search of more antigens

What are Helper T-cells?

• play important role in humoral & cellular immunity

• Bind to antigen on antigen-presenting cells,

• → stimulating secretion of cytokines

What do cytokines do?

1. Attract lymphocytes to infection site

→ which become sensitised & activated, thus intensifying response

2. Attract macrophages to place of infection so macrophages can destroy antigen by phagocytosis

3. Intensify phagocytic activity of macrophages

4. Promote action of killer T-cells

What do Suppressor T-cells do?

• act when immune activity becomes excessive or infection has been dealt with successfully

• Release substances that inhibit T- & B-cell activity, slowing down immune response

Define immunity

Resistance to infection by inaving microorganisms

Natural vs Artificial immunity

Natural: occurs without human interventions

Artificial: results from administering

to people an antibody or antigen

Passive vs Active immunity

Passive: acquired when antibodies are transferred from one person to another

Active: develops after exposure to microorganisms or foreign substances