Human Health and Disease

Antibody

A substance produced in response to a specific antigen; combines with the antigen to neutralise or destroy it

Antigen

Any substance capable of causing the formation of antibodies when introduced into the tissues (substances recognised as foreign by the immune system)

B-Cell

A type of lymphocyte that develops into either a plasma cell that produces antibodies or a memory cell

Disease

A malfunctioning of the body or part of the body that can be diagnosed on the basis of recognisable signs and symptoms

Infectious disease

Caused by pathogen micro or macro organisms, can be transmitted directly or indirectly from one host to another, pathogens can live both inside and outside of the body

infectious disease transmission - direct contact

person-to-person tranmission through physical contact (touching, kissing), or droplet sprays (from a cough/sneeze)

infectious disease transmission - indirect contact

involves fomites: inanimate objects that become contaminated by pathogens, transmission to a new host by touch

Aerosols: some pathogens (measles) remain viable in the air for a while

infectious disease transmission - vectors

mechanical vector: animals that carry the pathogen from one host to another without being infected themselves (fly)

biological vector: pathogen reproduces within a biological vector that transmits the pathogen from one host to another (mosquito)

Contagious disease

Diseases spread through direct/close contact between hosts/by direct contact with a contaminated object

non-infectious disease

diseases that are not spread from one host to another and not caused by a pathogen. likely to be caused by lifestyle factors, environmental toxins, gene mutation. have a known origin

examples: cystic fibrosis, sickle cell disease, scurvy, parkinson’s

zoonotic disease

transmission of pathogens from vertebrate animals to humans

disorder

a physical or mental condition that disturbs the regular or normal functions of day-to-day life, not caused by pathogens, not transmissible but can be inherited, may not have a known cause or treatment

Examples: Schizophrenia, OCD, Autism, Epilepsy

Endemic

The constant presence and/or prevalence of a disease/pathogen in a population within a geographic area

Epidemic

An increase, often sudden, in the occurrence of a specific disease above the baseline level for a particular population

why epidemics occur?

a recent increase in the virulence of the pathogen, recent introduction of a pathogen to a setting where it’s not been before, enhanced mode of transmission, change in susceptibility of hosts

Immunisation

Programming the immune system so that the body can respond rapidly to infecting micro-organisms

Immunity

Resistance to infection from invading micro-organisms

Infection

The invasion of a host by a pathogen, where it establishes itself and replicates

Infectious (communicable)

Caused by an invading pathogen and able to be transmitted from one organism to another

Macrophage

A phagocytic cell derived from a monocyte (a type of white blood cell)

Micro-organism

A microscopic organism too small for the eye to see

4 types of micro-organism

Bacteria, virus, fungi, protists

Bacteria

majority are non-pathogenic, essential to life on earth (Decomposition of organic material)

prokaryotic - no membrane bound organelles or nucleus

DNA - single circular molecule, can contain plasmids

Made of a capsule, cell wall (comprised of peptidoglycan, important for protecting the bacteria)

plasmid

small circular double stranded DNA separate from chromosomal DNA

types of bacteria

spherical = coccus

rod shaped = bacillus

curved spiral = spirilla

comma = vibrio

cholera

vibrio bacteria living in salt water and human hots, highly motile (moves using flagella)

causes acute diarrhoeal infection when ingested through contaminated food or water

virus

sub-microscopic, non-cellular, can’t make proteins or replicate on its own so depends on a host cell to synthesise proteins and replicate, can contain either DNA or RNA

virus life cycle - attachment to host cell

virus binds to host cell receptors. a portion of a molecule on the viral surface resembles the chemical shape of the body’s molecule and can bind to the host cell

virus life cycle - entry into host cell

Enveloped Viruses: Envelope fusion - viral envelope fuses with host cell membrane and nucleocapsid is released into cytoplasm

Naked Viruses: passing from capsid into cell via membrane

Endocytosis: Host cell membrane encapsulates viral particle and pinches off to form an endocytic vesicle

virus life cycle - biosynthesis

viral genome enters cell nucleus where it is replicated and transcribed into RNA (if required). the transcribed RNA enters ribosomes and translated into viral structural components and enzymes needed for replication and assembly of the virus

virus life cycle - maturation

capsid assembled around viral genome

virus life cycle - releas

naked virus are released by lysis - cell membrane ruptures, cell death

enveloped viruses released by: budding - virus gets envelope from host cell membrae. exocytosis - virus obtains envelope from membranes of nucleus, endoplasmic reticulum or Golgi apparatus and are released by exocytosis via transport vesicles

what do viruses consist of? (cellular structure)

Nucleic acid core (DNA OR RNA) surrounded by a protective protein coat (capsid)

Sometimes they have a lipid envelope covering the capsid - enveloped virus

DNA virus

•DNA can be linear or circular

•Usually double‐stranded DNA

•Rarely single‐stranded DNA

•Can encode up to hundreds of viral proteins

RNA virus

•RNA can be linear or circular

•Usually contain single-stranded RNA

•Sometimes contain double-stranded RNA

•Have smaller genomes that usually encode only a few proteins

virus mutation

usually occurs during replication: synthesis error - polymerase adds incorrect nucleotides, errors aren’t corrected by proofreading

Fungi

Most are multicellular heterotrophs, cell walls made of chitin, cell membrane has phospholipid bilayer, eukaryotic, microscopic to macroscopic

fungal disease - pneumocystis pneumonia

Mostly affect immunocompromised people

Symptoms: fever, cough, difficulty breathing, chest pain, chills, fatigue

protists

large group of eukaryotes that are’t animals, plants or fungi, microscopic to macroscopic, unicellular, multicellular or colonial

most protists are aquatic

animal-like protists = protozoa

single-celled eukaryotes, can move, are heterotrophs

plant-like protists

algae, autotrophs, no stems roots or leaves, most live in water bodies, can be unicellular or multicellular

fungi like protists

heterotrophs, reproduce by forming spores, cell walls made from cellulose, two major types - slime molds, water molds

slime molds - grow as slimy masses on decaying matter

water molds - live in moist soil

flagellates

move using large flagella (Tails) that rotate like a propeller, example is Trypanosoma causing African sleeping sickness

pseudopodia amoebae

Extends projections of cytoplasm out to form feet-like structures that propel the cell forward, example is naegleria fowleri (the brain eating amoeba)

ciliates

move using tiny tail-like projections that beat back and forth, example is paramecium

apicomplexa

don’t move but use enzymes to penetrate the host’s tissues, example is plasmodium spread by mosquitoes as malaria

Outbreak

A sudden, unexpected increase in the prevalence of a particular disease above the baseline level for that population

Pandemic

A disease that has spread rapidly throughout the world; an epidemic that has crossed international borders

Phagocyte

Cells that are able to engulf micro-organisms and cell debris

pathogen

infectious agents that spread between hosts and cause disease

T-Cell

A lymphocyte that can differentiate into a number of cells that are involved in cell-mediated response

Vaccination

The introduction of antigens to a person so they acquire immunity without suffering from the illness

Vaccine

An antigen preparation used in artificial immunisation

Vector

An agent that transmits pathogens from one host to another

Virulence

The measure of the ability of a pathogen to cause disease within its host

types of resistance

innate/non-specific: protects the body against a broad range of pathogens (provided by external and internal defences)

specific/adaptive: protects body against a specific pathogen

external non-specific defence: skin

provides a physical barrier to prevent pathogens from entering the body

has a low pH making it difficult for pathogens to grow

Chemical secretions (sebum) and antimicrobial peptides hamper growth of bacteria and fungi

external non-specific defence: mucous membranes

mucous membranes lines cavities of the respiratory, urinary, reproductive and digestive tracts

mucus protects underlying cell layers, traps particles including pathogens, and contains antimicrobial peptides

external non-specific defence: hairs and cilia

hairs line the nose cavity and ars

cilia are tiny hair-like projections, in the mucous membranes, and the beating motion moves the mucus with the trapped particles towards throat to be swallowed or coughed up

external non-specific defence: acids

stomach acids - kill ingested bacteria and many pathogens in swalloed mucus

vagina acidic - reduces growth of microorganisms

sweat and earwax are slightly acidic and contains lysozyme (bacteria killing enzyme)

internal non-specific defence: phagocytosis

phagocytosis: process where a cell binds to the item it wants to engulf on the cell surface and draws the item inward while engulfing around it

phagocytes: phagocytes are attracted by an inflammatory response of dead cells and engulf microorganisms

internal non-specific defence: inflammation

response to any tissue damage, its purpose is to destroy pathogens, prevent entry of additional pathogens, removed damage tissue and cell debris and begin repair of damaged tissue

steps in inflammatory response

injury to tissue: mast cells release histamine

histamine increases blood flow through the damaged area, which causes heat, which can kill temperature-sensitive pathogens

histamine causes capillaries to become more permeable causing fluids to collect around an injury, causing swelling

the chemicals released by mast cells attract phagocytes - dead phagocytes are pus

internal non-specific defence: fever

fever - elevation of body temp as a result of infection

purpose - inhibit growth of bacteria and viruses, speeds up rate of chemical reactions helping faster cell repair

4 protective reflexes

A reflex is an involuntary response to a stimulus. The 4 protective reflexes protect the body against infection

Sneezing, coughing, vomiting, diarrhoea

protective reflex: sneezing

Stimulus: walls of nasal cavity irritated by noxious fumes or dust

Result of Stimulus: forceful expulsion of air from the lungs out the nose and mouth. the air expelled may carry mucus, foreign particles, irritating gases

protective reflex: coughing

Stimulus: irritation in lower respiratory tract

result of stimulus: expulsion of air from lungs. the expelled air drives mucus and foreign matter up the trachea towards throat and mouth

protective reflex: vomiting

induced by psychological stimuli (pain, sight, smell), excessive stretching of stomach (gasses), bacteria toxins

protective reflex: diarrhoea

results due to irritation of small and large intestines by either bacteria, viruses, protozoa. the irritation causes increased contractions of muscles leading to rapid removal of the irritant. the faeces are watery as the material doesn’t remain in the large intestine long enough for water absorption