Human Bio Ch 7 Flashcards
What is a pathogen?
Are a disease causing organism, often referred to a pathogenic organism.
What is a virus?
Is an infectious agent, too small to be seen with a light microscope, consisting of a protein sheath surrounding a core of nucleic acid, viruses are totally dependent on cells for reproduction. Viruses all contain either RNA or DNA but not both.
What is the process of viral replication?
Viruses are not living therefore cannot reproduce by themselves so instead infect a living cell and its RNA or DNA to manufacture more virus particles. They do this by:
- HIV binds to the receptor site of a T-lymphocyte
- Uncoated RNA from the virus enter the lymphocyte
- The virus contains an enzyme that enable it to make a DNA copy of its RNA
- Host cell DNA is in the nucleus and the DNA copy of the HIV RNA integrates with the host cell DNA.
- New viral DNA is produced
- Budding of new virus particle from the lymphocyte means new HIV able to infect other cells.
What is a bacteriophage?
A virus that infects bacteria
What is a vector in terms of transmission of pathogens?
An agent such as an insect capable of transferring a disease causing organism from one person to another.
What are the main ways pathogens are transmitted?
- Transmission by contact - direct (skin to skin) or indirect (touching an object an infected person has touched)
- Ingestion of food or drink that has been contaminated with the pathogen
- Transfer of body fluid from one person to another (blood)
- Infection by droplets - tiny droplets of moisture from an infected person and infect someone who breathes is in
- Airborne transmission through an infected person exhaling or sneezing and then inhaled by others.
- Vectors - transmission of pathogens from an animal to to a person. Direct (insect to person) indirect (animal to food to person.)
What is the difference between nonspecific defenses and specific defenses?
Nonspecific - defense of the body that acts against all pathogens
Specific - defence of the body that is directed against a specific pathogen
What are the external defences of the body?
The body has many external defences to stop any pathogens or foreign particles from entering the body.
- Skin - stops microorganisms from entering the body as long as it is not cut. The skin contains many bacteria that occupies the skin meaning there is not enough room for pathogens. The skin has an oily secretion called sebum that contains a substance that kills some pathogens. Sweat also contain salt and fatty acids that prevents the growth of many microorganisms.
- Mucus - mucous membranes line body cavities that open to the exterior. They secrete mucous that trap the particles and inhibit the entry of the microorganisms to the organs of the body. The digestive, urinary and reproductive tracts are all protected in this way.
- Hairs - hairs are found in the nasal cavity in the nose and in the ears. In the nose the hair and mucus trap up to 90% of particles inhaled.
- Cilia - tiny hair like projections from cells that are capable of a beating motion. The mucous membranes lining the nose, trachea and other air passages have cilia. The cilia traps the particles and microorganisms and beats them towards the throat where they are couched up or swallowed.
- Acids - stomach juices are strongly acidic, this acid kills many of the bacteria taken in with food or those contained in mucous and swallowed. Urine and sweat on the skin are also slightly acidic.
- Lysozyme - an enzyme that kills bacteria. They eyes are protected by the flushing action of tears which contain this enzyme. Also found in saliva, sweat, secretions of the nose and tissue fluid.
- Cerumen - also known as earwax, protects the outer ear against infection by some bacteria. It is slightly acidic and contains lysozyme.
- Movement of fluid - flushing action of body fluids helps to keep some areas relatively free of pathogens. urine flowing through the urethra has a cleansing action. Prevents bacterial growth and helps to stop bacteria entering the body. Tears, sweat and saliva are also involved in flushing movements.
What are the protective reflexes?
Sneezing - stimulated by the irritation of the walls of the nose cavity. Forceful expulsion of the air from the lungs carries mucus, foreign particles and irritating gases out through the nose and mouth.
Coughing - stimulated by irritation of the lower respiratory tract. Air is forced out of the lungs to try and remove the irritant. The air drives mucus and foreign matter up the trachea towards the throat and mouth.
Vomiting - psychological stimulus, excessive stretching of the stomach and bacterial toxins that can all induce vomiting.
Diarrhoea - irritation of the intestines by bacteria or viruses can cause diarrhoea. Causes increased contractions of the muscles of the walls of the intestines, so that the irritant is removed as quickly as possible.
What are the 3 examples of internal non-specific defences?
- Phagocytosis
- Inflammatory response
- Fever
What are the different types of phagocytic cells?
Phagocytosis - engulf and digest microorganisms and cell debris. Different cells that are phagocytic are:
- Monocytes and Macrophages - when a tissue becomes infected or inflamed, monocytes leave the bloodstream and enter the tissue. Here they differentiate into macrophages which are large phagocytic cells. Some macrophages move through the tissue looking to destroy the pathogen whilst others are fixed in one place and only deal with the pathogen when it comes to them. Important in removing microbes and dying cells through phagocytosis.
- Neutrophils - are described as a granulated leucocyte. During an infection neutrophils are the first cells to move into the tissue and destroy the pathogen by phagocytosis. They are particularly important in killing pathogens inside a cell. They have a short life span and die within a few days.
- Dendritic cells - characterised by projections from the cytoplasm. They are slightly different from macrophages and neutrophils in that their function goes beyond just phagocytosis. These cells have the ability to detect, engulf, and process foreign particles.
What is the process of phagocytosis?
- Phagocyte moves to the invading bacterium
- Phagocyte changes shape os it completely encloses bacterium
- Lysosomes contain destructive enzymes
- Enzymes are released and destroy the bacterium
- Harmless particles are released from the phagocyte.
What are the steps of the inflammatory response?
- Mechanical damage or local chemical changes cause specialised leucocytes called mast cells to be activated by complement proteins. This results in the release of histamine, heparin and other chemicals into the tissue fluid.
- Histamine increases blood flow due to vasodilation making the walls of the blood capillaries more permeable. The increased blood flow caused heat and redness and the escape of fluid from the blood causes swelling.
- Heparin prevents clotting, the release or heparin from the mast cells prevents clotting in the immediate are of the injury. A clot of the fluid around the area forms which slows the spread of the pathogen into healthy tissue.
- Complement system proteins and some chemicals released by mast cells attract phagocytes, particularly neutrophils which actively consume microorganisms and debris by phagocytosis.
- The abnormal conditions in the tissue stimulate pain receptors, and so the person feels pain in the inflamed area.
- The phagocytes filled with bacteria, debris and dead cells begin to die and form a yellow liquid called pus.
- New cells are produced by mitosis and repair of the damaged tissue takes place.
What is a fever and how does it act as an internal defence?
A fever is an elevation of the body temperature often caused by an infection such as a common cold or flu.
A fever is thought to be caused by pyrogens that are released by white blood cells during the inflammatory response and act of the hypothalamus which causes the body to reset its internal thermostat to a higher level than normal.
When a person has a fever the body temperature is still regulated in response to heat or cold but the set point is higher.
The persons thermoreceptors will detect that the body temp is lower than the new, higher set point and causes the body to vasoconstrict and become shiver. This drives the fever up rapidly and eventually causes it to break.
When it breaks the bodies thermostat has been reset to normal and sweating and vasodilation will occur to bring body temp down.
What is the lymphatic system?
A system of vessels that drains excess fluid from the tissues. Consists of:
- network of lymph capillaries joined to larger lymph vessels
- lymph nodes, which are located along the length of some lymph vessels.
Each lymph node contains masses of lymphoid tissue, the cells of which are criss crossed by a network of fibres. Lymph entering the nodes contain cell debris, foreign particles and microorganisms that have penetrated the bodies external defence.
