BIOL121 - Module 2

Microbiology

The study of microorganisms or microbes

Microorganism

A small living plant or animal seen only with a microscope; a microbe

Types of pathogens

Bacteria, viruses, protozoa, fungi, helminths

Pathogen

An organism that causes disease

Virus

A tiny, non-living particle that invades and then reproduces inside a living cell. Has no cellular structure

Bacteria

A single-celled organism that lacks a nucleus; prokaryotes, mostly unicellular

Protozoa

Microscopic, unicellular animals often found in decayed materials and contaminated water. Eukaryotic.

Fungi

An organism that absorbs nutrients from the environment. Eukaryotic, can be unicellular or multicellular

Helminths

Multicellular parasitic organisms commonly called worms or flukes. Don’t typically reproduce in the host

Bacteria growth requirements

Temperature, acidity, nutrients, H20, oxygen, metabolism

Thermophiles

Archaea that thrive in very hot environments, such as volcanic springs

Mesophiles

Organisms that grow best between 20 and 40 degrees Celsius; the human pathogens are in this group

Psychrophiles

Cold-loving bacteria

Optimum bacteria temperature

37 degrees Celsius

Obligate aerobic bacteria

Bacteria that require oxygen for cellular respiration

Obligate anaerobes

Organisms that cannot live where molecular oxygen is present

Normal flora

Microorganisms that reside in or on the body without causing disease

Infectious agent

The pathogen (germ) that causes diseases

Reservoir

The place in the environment where the pathogen lives

e.g. Humans, animals, equipment, soil and water

Portal of exit

The way the infectious agent leaves the reservoir

e.g. Through open wounds, aerosols and body fluids (coughing, sneezing and saliva)

Mode of transmission

A way that the causative agent can be transmitted and passed onto another reservoir or host where it can live

e.g. Direct or indirect contact, ingestion or inhalation

Portal of entry

Any body opening on an uninfected person that allows pathogens to enter

e.g. Broken skin, respiratory tract, mucous membranes, catheters and tubes

Susceptible host

Any person, most vulnerable are those receiving healthcare, immunocompromised or have invasive medical devices

Chain of infection

Infectious agent, reservoir, portal of exit, mode of transmission, portal of entry, susceptible host

Sterilisation

The process that completely destroys al microbial life, including spores

Methods of sterilisation

Gas, dry heat, chemical and steam

Disinfection

A process the eliminates many or all microorganisms, with the exception of bacteria spores, from inanimate objects

Methods of disinfection

Physical, biological and chemical

Sanitation

Maintaining a clean condition in order to promote hygiene and prevent disease

Components of skin

Epidermis, dermis and hypodermis

Epidermis

The outermost layer of skin, provides a waterproof barrier and creates out skin tone. Keratinised, stratified squamous epithelium. Avascular

Cells of the epidermis

Keratinocytes, melanocytes, langerhan’s cells, merkel cells

Keratinocytes

Produces fibrous protein keratin. Most cells of the epidermis. Tightly connected by desmosomes

Melanocytes

10-25% of the cells in the deepest epidermis. Produces pigment melanin, packaged into melanosomes. Protects apical surface of keratinocyte nucleus from UV damage

Langerhan’s cells

Located in the stratum spinosum. Is macrophages that help activate the immune system. Originates from the bone marrow

Merkel cells

Functions as touch receptors in associated with sensory nerve endings

Layers of epidermis

Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum

Stratum basale

The deepest layer of the epidermis consisting of stem cells capable of undergoing cell division to form new cells

Stratum spinosum

A layer of the epidermis that provides strength and flexibility to the skin

Stratum granulosum

A layer of the epidermis that marks the transition between the deeper, metabolically active strata and the dead cells of more superficial strata

Stratum lucidum

A layer of the epidermis found only in the thick skin of the fingers, palms and soles

Dermis

The middle layer of the skin, which contains most of the skin’s structures

Dermis cell types

Fibroblasts, macrophages and occasionally mast cells and white blood cells

Fibroblasts

In connective tissue, cells that secrete the proteins of the fibres

Macrophages

Found within the lymph nodes, they are phagocytes that destroy bacteria, cancer cells and other foreign matter in the lymphatic stream

Mast cells

Found in the connective tissue of the dermis; respond to injury, infection or allergy by producing and releasing substances, including heparin and histamine

Layers of the dermis

Papillary layer and reticular layer

Papillary layer

Outermost layer of the dermis, directly underneath the epidermis. Helps supply the epidermis

Reticular layer

Deeper layer of the dermis that supplied the skin with oxygen and nutrients

Hypodermis (subcutaneous layer)

Third layer of the skin; consists of connective tissue which binds the skin to the underlying muscle

Functions of the skin

Protection, prevents penetration, perception, temperature regulation, identification, communication, would repair, absorption and excretion, production of vitamin D

Function of the skin: protection

Skin covers the body and acts as a physical barrier that protects underlying tissue from physical cuts, bacterial invasions, dehydration and sunburn

Function of the skin: temperature regulation

Skin allows heat dissipation through sweat glands and heat storage through subcutaneous insulation

Function of the skin: cutaneous sensation

Sensory receptors on the skin allow us to feel touch, pressure, vibration, tickling, pain and etc.

Function of the skin: metabolic function

Produces vitamin D (when exposed to UV)

Function of the skin: excretion

Skin can secrete limited amounts of nitrogenous wastes, such as ammonia, urea and uric acid. Sweating can cause salt and water loss. Absorbs vitamins and oxygen

Skin colour

Three pigments contribute: melanin, carotene and hemoglobin

Melatin

A pigment that gives skin its colour, the darker the skin the more (---). Found in stratum corneum

Carotene

Yellow to orange pigment. Most obvious in the palms and soles of the feel. Accumulates in stratum corneum

globinHaem

Red pigment of the skin that carries oxygen

Jaudice

A yellow discolouration of the skin, mucous membranes and the eyes

Features of the Integumentary system

Nails, hair and glands

Nails

Horny plates made from flattened epithelial cells; found on the dorsal surface of the ends of the fingers and toes. Densely packed epithelial cells containing fibres of hard keratin. Provides protection to underlying nerves

Glands

Organs or tissues in the body that create chemicals that control many of out bodily functions. Clusters of specialised epithelia cells that secrete a substance

Sweat glands

The glands that secreate sweat, located in the dermal layer of the skin. Regulates body temperature

Hair

Compresses, keratinised cells that arise from hair follicles, the sacs that enclose the hair fibres. Provides protection and warmth

Roles of the Lymphatic system

Maintain blood pressure and fluid levels, circulation of important molecules/cells for maintaining overall body function and for defence against disease, absorption of fats from the intestine

Lymphatic system parts

Lymph nodes, lymphatic vessels, thymus, spleen, tonsils

Lymphocytes

The two types of white blood cells that are part of the body’s immune system: B lymphocytes form in the bone marrow and release antibodies that fight bacterial infections; T lymphocytes form in the thymus and other lymphatic tissue and attack cancer cells, viruses and foreign substances

Lymph

The watery fluid in the lymph vessels collected from the tissue spaces

Lymph flow through nodes

From subcapsular space (contains macrophages and dendritic cells), through outer cortex (contains B cells within germinal centers), through paracortex (dominated by T cells), through the core (medulla), organised into medullary cords, contains B cells and macrophages, then into efferent lymphatics at hilum

Red bone marrow

Contains haemopoietic stem cells (makes all red, white and platelet blood cells). Produces and matures B lymphocytes and makes T cells

Thymus gland

Located in the mediastinal cavity anterior to and above the heart; secretes thymosin for the maturation of T cells

Lymph nodes

Bean-shaped filters that cluster along the lymphatic vessels of the body. They function as a cleanser of lymph as well as a site of T an b cell activation

Spleen

An organ that is part of the lymphatic system; it produces lymphocytes, filters the blood, stores blood cells and destroys old blood cells

Diffuse lymphatic tissue

Scattered lymphocytes, macrophages and other cells found deep to mucous membranes

Oedema

Fluid-filled swelling (of an organ or structure)

Antigen

A toxin or other foreign substance that induces an immune response in the body, especially the production of antibodies

Antibody

A substance produced by the body that destroys or inactivates an antigen that has entered the body

Non-specific immunity

Defenses that stop the invasion of pathogens; requires no previous encounter with a pathogen

Acquired immunity

Immunity that the body develops after overcoming a disease, through inoculation (such as flu vaccinations), or through exposure to natural allergens, such as pollen, cat dander and ragweed

First line of defense

Intact skin, mucous membranes and their secretions, normal microbiota

Second line of defense (innate immunity)

Phagocytes (such as neutrophils, eosinophils, dendric cells and macrophages), inflammation, fever, antimicrobial substances

Phagocytosis

A process in which extensions of cytoplasm surround and engulf large particles and take them into the cell

Antimicrobial chemicals

Solids, liquids, gaseous. For convenience, solid or gaseous antimicrobial chemicals are dissolved in water, alcohol or a mixture of the two

Inflammation

A localised physical condition in which part of the body becomes reddened, swollen, hot and often painful, especially as a reaction to injury or infection

Signs of inflammation

Redness, heat, swelling, pain and loss of function

Fever

A rise in the temperature of the body in an attempt to kill the enzymatic properties

Third line of defence

Immune response in which antibodies take action against foreign cells

B cells

Cells manufactured in the bone marrow that create antibodies for isolating and destroying invading bacterial and viruses

T cells (T lymphocytes)

Lymphocytes that develop in the thymus and are responsible for cell-mediated immunity. Their cell-surface antigen receptor is called the T-cell receptor

Types of T cells

Cytotoxic T cells, helper T cells, suppressor T cells, memory T cells

B cells defense against bacteria

Bacteria live between epithelial cells, attacked mostly by antibodies from B cells

Cytotoxic T cells

T cells, often called killer cells because of their inability to kill invading organisms

Helper T cells

T cells that help the immune system by increasing the activity of killer cells and stimulating the suppressor T cells

Suppressor T cells

Decrease B-cell response after infection is gone and antibodies aren’t needed

Memory T cells

Circulate the body, proliferate and respond to eliminate subsequent invasion by same antigen. Secondary response, takes less time, \~5 days