Unit 2.docx

Homeostasis Homeostasis refers to the ability to maintain a constant internal environment, despite changes in the external environment. Why is homeostasis important? - Enzymes function best in specific conditions - When the temperature is too hot the enzymes start to denature - When it's...

Homeostasis Homeostasis refers to the ability to maintain a constant internal environment, despite changes in the external environment. Why is homeostasis important? - Enzymes function best in specific conditions - When the temperature is too hot the enzymes start to denature - When it's too cold, the enzymes work very slowly - There is an optimal (limited) tolerance range Homeostasis occurs in two stages: 1. The body detects a change from the optimum state, either in the internal or external environment 2. Next there is a response to the changes in order to restore the optimum state. Known as the **stimulus-response model.** Regulation of temperature is known as thermoregulation. There are many other things that needs to be regulated such as: - pH - water levels - salt concentration - glucose levels - oxygen levels - carbon dioxide levels - urea concentration - blood pressure Messages are either carried around the body by the nervous system, or by chemicals called hormones, which are produced by glands of the endocrine system. **Receptor** **Type of stimulus** -------------- ---------------------- Chemo Chemicals Thermo Temperature Mechano Pressure Photo light Noci Pain The effector is the part of the body which brings about the necessary change needed to achieve homeostasis. Stimulus response model and negative feedback: - Negative feedback reduces the initial stimuli. E.g. - If your body is too hot, a negative feedback pathway will cool it down - Negative feedback keeps the internal environment as stable as possible -- like an air conditioner Positive feedback: - Push internal environment to escalate a response - Amplifies the initial response to keep it going Hormonal Homeostatic Control Pathways Three ways hormones produce a change: - Autocrine -- bind to receptors in the same cell that produced them - Paracrine -- bind to receptors on neighbouring cells - Endocrine -- travel long distances through the blood to reach target cells Hormones as chemical messengers: - Hormones are chemical messengers produced by an organism to regulate the activity of cells and organs - Each hormone targets and activates particular cells and causes a specific response Endocrine system: - Includes tissues or glands that secret hormones - Cells communicate with one another to coordinate processes within tissues and to maintain homeostasis - Coordination of activities associated with the endocrine system is often connected to the pituitary gland (the master gland) because it produces many hormones that affect hormone production by other endocrine glands "Lock and Key" approach describes the interaction between the hormone and its specific receptor on target cell - Only the cells in the body that express receptors for a particular hormone will respond to it Receptor binding & signal transduction: - When a hormone binds to its receptor protein, the receptor changes shape and becomes activated - The triggers a chain of events inside the cell which leads to effector proteins producing a response **(Signal transduction)** - Occurs through the use of second messengers, which are activated when the initial hormone binds to the receptor Upregulation and Downregulation of cellular processes: - Upregulation, receptors increase in response to rising hormone levels, making the cell more sensitive to the hormone and allowing for more cellular activity - Downregulation, receptors decrease in response to rising hormone levels, cellular activity is reduced - A hormone activates two pathways when it binds to a receptor: - Triggers production of its receptor - The pathway it signals for Immunity Types Lesson goals: **Analyse the differences and similarities between passive immunity (antibodies gained via the placenta and via antibody serum injection) and active immunity (acquired via natural expose to a pathogen or through the use of vaccines) for both naturally and artificially acquired immunity.** **Natural active immunity:** - When the body is infected by a pathogen, memory T and B cells are produced. They lie and wait in the lymph nodes, ready to be rapidly activated if that antigen is encountered again. Once activated, they will destroy the pathogen before symptoms of the disease arise - This type of immunity, stimulated by natural exposure to a pathogen, is an example of active immunity and generally lasts many years **Natural passive immunity:** - Is obtained when a mother is exposed to the living pathogen (natural) and then passes her antibodies to the foetus through the placenta. - As the baby does not produce memory cells, the immunity is termed passive - The antibodies are also present in the first 'milk' secreted after birth - This immunity lasts for only a short time after birth, but further antibodies are contained in the mother's milk. **Artificial passive immunity:** - Serums that contain antibodies to specific antigens have been developed. In the case of serious infections, such as diphtheria and tetanus, the reaction to the bacterial toxin may be too fast for the individual to develop antibodies - Specific antibody serums are administered to counteract the infection and produce immediate resistance. - In the case of most snake or spider bites, serums containing the antibodies to the specific toxins found in the venom are produced. - This is termed **artificial passive immunity,** this type of immunity invariably lass for a year or so **Artificial active immunity:** - Immunity can also be acquired artificially - Injection of an individual with parts of or deactivated antigens can 'trick' the immune system to react and ultimately produce memory cells. - This vaccination or immunisation is called **artificial active immunity** - Three general types of antigens used in vaccines are: - **Sterile bacterial exotoxins** - **Sterile, dead microorganisms** - **Living infectious microorganisms whose ability to cause serious infection has been altered** Modes of Disease Transmission **Lesson goals:** **Identify from given data and describe the following modes of diseases transmission** - **Direct contact** - **Contact with body fluids** - **Contaminated food and water, and Disease-specific vector** Transmission - Infectious diseases can spread rapidly within and between regions given the right conditions - **Transmission and the spread of a pathogen depends on:** 1. Growth rate of pathogen 2. Density of the host population 3. Mobility of the host population 4. Mode of transmission - The transmission of infectious diseases can be virtually eliminated by observing hygienic practices +-------------+-------------+-------------+-------------+-------------+ | **Mode** | **Summarise | **Pathogen | **Example | **Strategie | | | mode** | types that | of disease | s | | | | use this | using this | to limit | | | | mode** | strategy** | transmissio | | | | | | n | | | | | | via this | | | | | | mode** | +=============+=============+=============+=============+=============+ | **Direct | Type of | Fungus | Tinea | Avoid | | contact** | transmissio | | | contact | | | n | Virus | Ringworm | | | | involves | | | | | | the spread | Bacteria | Cold sore | | | | of microbes | | | | | | person-pers | | | | | | on | | | | | | or | | | | | | animal-pers | | | | | | on | | | | +-------------+-------------+-------------+-------------+-------------+ | **Bodily | Transmissio | Virus | Common Cold | Avoid | | fluids** | n | | | transmittin | | | of body | | AIDS | g | | | fluids | | | bodily | | | including | | | fluids | | | sweat, | | | | | | tears, | | | | | | vomit, | | | | | | nasal | | | | | | secretions, | | | | | | blood and | | | | | | saliva | | | | +-------------+-------------+-------------+-------------+-------------+ | **Food and | Transmissio | Bacteria | Hepatitis A | Ensure food | | water | n | | | is cooked | | borne** | through | Virus | | and water | | | regions | | | is clean. | | | with poor | | | | | | sanitation | | | | | | or when | | | | | | food is | | | | | | insufficien | | | | | | tly | | | | | | cooked, | | | | | | poorly | | | | | | store or | | | | | | prepared in | | | | | | an | | | | | | unsanitary | | | | | | environment | | | | +-------------+-------------+-------------+-------------+-------------+ | **Disease | Transmissio | Virus | Malaria | Use bug | | specific | n | | | repellent. | | vector** | by insect | | | | | | or animal | | | | | | vectors | | | | | | | | | | | | -Intermedia | | | | | | ry | | | | | | organisms | | | | | | that are | | | | | | capable of | | | | | | transferrin | | | | | | g | | | | | | infective | | | | | | pathogens | | | | | | such as | | | | | | viruses, | | | | | | bacteria, | | | | | | and protoza | | | | +-------------+-------------+-------------+-------------+-------------+ Pathogens Lesson goals: **Identify the following pathogens: prions, viruses, fungi, protists and parasites.** Infectious Diseases and pathogens (recap) - Pathogens vary greatly in size, type and mode of transmission - The terms 'infection' and 'disease' are not synonymous. An infection results when a pathogen invades and begins growing within a host. A disease results only if and when, the pathogen causes impairment of tissue function Viruses: - Non-living pathogens - They lack a cellular structure and their own ribosomes - Due to an inability to carry out life processes on their own, they rely on their host cell. - They must invade a host cell and use the hosts ribosomes to construct new viruses. They have the ability to 'switch off' the hosts DNA and, using their own nucleic acid, instruct the cell to make copies of themselves Parasites: - A parasite is an organism that lives in or on a n organism of another species and benefits by deriving nutrients at the others expense - As viruses and prions are not classified as living organisms, parasites include bacteria, fungi and protists Prions: - Prions are non-living pathogens - They are an abnormal form of a normally harmless protein found in the brain that is responsible for a variety of fatal neurodegenerative diseases of animals, including humans Fungi: - Eukaryotes that reproduce by spores and have cell walls made of chitin rather than cellulose - Not all fungi are pathogenic, nut those that are can cause disease in a wide range of organisms, including plants and animals - Fungi secret enzymes into their host, digest their food externally and absorb nutrients directly through their cell walls Protists - Protists are living organisms - Protists are unicellular, eukaryotic organisms - 24 species cause diseases in humans - Most protists require warm climates to thrive +-----------+-----------+-----------+-----------+-----------+-----------+ | **Pathoge | **Relativ | **Descrip | **Mode of | **Reprodu | **Real | | n** | e | tion** | transmiss | ctive | world | | | size** | | ion** | strategy* | examples* | | | | | | * | * | +===========+===========+===========+===========+===========+===========+ | **Prion** |  30-35 |  Non |  Oral |   |  Mad cow | | | kDa | living | intake | recruitin | dieases | | | | pathogens | | g | | | | | | | the | | | | | | | normal, | | | | | | | cellular | | | | | | | isoform | | | | | | | of the | | | | | | | prion | | | | | | | protein | | | | | | | (PrPC) | | | | | | | and | | | | | | | stimulati | | | | | | | ng | | | | | | | its | | | | | | | conversio | | | | | | | n | | | | | | | into the | | | | | | | disease-c | | | | | | | ausing | | | | | | | isoform | | | | | | | (PrPSc). | | +-----------+-----------+-----------+-----------+-----------+-----------+ | **Virus** |  20 -450 |  Non |   From |   the |  Covid 19 | | | nm | living | other | lytic | | | | | pathogens | people | cycle and | | | | | which | (through | lysogenic | | | | | lack | coughing, | cycle | | | | | cellular | sneezing | | | | | | structure | or close | | | | | | and | contact). | | | | | | ribosomes | From | | | | | | , | surfaces | | | | | | have | or | | | | | | string of | objects | | | | | | DNA which | that | | | | | | is used | someone | | | | | | to take | with a | | | | | | over | virus has | | | | | | other | touched | | | | | | cells | (like | | | | | | | counterto | | | | | | | ps, | | | | | | | doorknobs | | | | | | | or | | | | | | | phones). | | | +-----------+-----------+-----------+-----------+-----------+-----------+ | **Bacteri |  2 μm |  Bacteria |   |   binary |  Tinea | | a** | | are | contact, | fission | (Athletes | | | | ubiquitou | airborne, | | foot) | | | | s, | droplet, | | | | | | mostly | vectors, | | | | | | free-livi | and | | | | | | ng | vehicular | | | | | | organisms | | | | | | | often | | | | | | | consistin | | | | | | | g | | | | | | | of one | | | | | | | biologica | | | | | | | l | | | | | | | cell. | | | | +-----------+-----------+-----------+-----------+-----------+-----------+ | **Fungi** |  2- 10 μm |   |   direct |   |  Penicill | | | | Eukaryote | skin | asexually | um | | | | s | contact | by | | | | | that | (with | fragmenta | | | | | reproduce | humans or | tion, | | | | | by spores | animals), | budding, | | | | | and have | or | or | | | | | cell | indirectl | producing | | | | | walls | y | spores, | | | | | made of | from | or | | | | | chitin | contamina | sexually | | | | | rather | ted | with | | | | | than | articles | homothall | | | | | cellulose | on floors | ic | | | | | | or in the | or | | | | | | soil | heterotha | | | | | | | llic | | | | | | | mycelia | | +-----------+-----------+-----------+-----------+-----------+-----------+ | **Protist |  3μm \* |  Living |   direct |   binary |  Algae | | s** | | organisms | contact | fission | | | | | which are | with the | | | | | | unicellul | pathogen | | | | | | ar | via | | | | | | and | fomites | | | | | | eukaryoti | like | | | | | | c | water or | | | | | | | faeces; | | | | | | | or | | | | | | | through | | | | | | | contact | | | | | | | with | | | | | | | another | | | | | | | sick | | | | | | | infected | | | | | | | organism. | | | +-----------+-----------+-----------+-----------+-----------+-----------+ Thermoregulation **Lesson goals: Identify and explain the varying thermoregulatory mechanisms of endotherms and how they control heat exchange and metabolic activity.** Endotherm -- an animal which can maintain a constant body temperature independent of the environment. Thermoregulation -- maintenance of a constant internal temperature of an organisms independent of the temperature of the environment **Organisms can gain in two main ways:** 1. Metabolism of food 2. Absorption of solar energy either directly of indirectly from: - Heat radiated from objects - Heat convection from the warming of the ground - Heat conducted from the ground. **Organisms can lose heat from the body through:** - Evaporation of water (e.g. through the stomata of plant leaves or sweating) - Conduction from the body to the environment - Convection from the body to the air or water - Radiation from the body to the environment 4 categories of strategy 1. Structural features (Brown adipose tissue, increased number of mitochondria per cell, insulation) **[The physical structure of an organism]** 2. Behavioural responses (kleptpothermy, hibernation, aestivation and torpor) **[Behaviours that reduce energy consumption]** 3. Physiological mechanisms (vasomotor control, evaporative heat loss, counter -- current heat exchange, thermogenesis / metabolic activity from organs and tissues) **[Internal mechanisms, often accompany a structural feature]** 4. Homeostatic mechanisms (thyroid hormones, insulin) **[Hormones that maintain negative feedback]** Vertebrate Defences The body has many defences against disease that constitute the immune system. There are two parts of the immune system, each of which plays a role in defending the body: The innate immune system: - The innate immune system is present in all organisms and is always working - It does not require any special preparation to prevent infection - It includes both physical and chemical barriers and components of the blood The acquired immune system: - This system needs to be primed before it can be fully effective - It uses specialised white blood cells called B and T lymphocytes - These cells can distinguish two groups of foreign substances First line of Defence: - Non-specific defence (innate) - Effective surface barriers that reduce the chance of pathogens gaining entry - Includes physical and chemical barriers Non-specific (innate) defences - If a pathogen breaches the first line of defence, is it dealt with by the host's second line of defence (Inflammation) Skin as a physical barrier - Like all the inner and outer linings of vertebrates the skin is made from epithelial cells - Structured proteins such as keratin are depositied which causes Virulence Factors Lesson goals: - **[Identify] the following pathogen: bacteria.** - **[Describe] the following virulence factors that aid in pathogenesis: adherence factors, invasion factors, capsules, toxins and lifestyle changes.** - **[Understand] how pathogens (bacterial and viral) can cause both physical and chemical changes in host cells that stimulate the host immune responses (introduction of foreign chemicals via the surface of the pathogen, production of toxins, recognition of self and non-self)** Bacteria: - Bacteria are some of the smallest living organisms - There is no specialisation of the cells for a particular function Causing Disease: - For an organism to cause disease, it must: 1. Enter the host 2. Multiply in host tissues 3. Resist, or not stimulate, the host defence mechanisms; and 4. Damage the host The **virulence** of a pathogen refers to its ability to cause disease. It can be measured by how many individuals the microorganisms infects, how quickly it spreads through the body and how many hosts die to the infection. Virulence Factors: - Virulence depends on the number of infecting microorganisms, their route of entry into the body and the response of the host immune system. - Virulence factors are molecules that can contribute to the survival of the pathogen -- typically proteins -- and include: adhesions, colonisation factors, invasion factors, toxins and immune response blockers. **They are features the pathogen has that help it infect the host** **Pathogenesis** is the biological mechanism that leads to the development of disease. Adherence factors: - **Adherence** is the ability to adhere to host cells and resist physical removal - Bacteria resist physical removal by producing **pili** and Biofilm-producing cell coating - **If the pathogen can adhere to the host, this ultimately helps the pathogen infect the host** - **Invasion** is the ability of microorganisms to enter hosts tissues, multiply there and spread to other tissues - Invasion factors facilitate pathogen invasion - Often enzymes which destroy the host cell's extra cellular matrix Capsules: - The ability to resist host immune defence - Bacteria resist host immune defence by: 1. Capsules -- thick outer layer of a bacterial cell which block or switch off the host's immune system 2. **Coagulase enzymes** -- accelerates the formation of a clot. This clot can protect the bacteria from phagocytosis **If the pathogen can resist the host's immune defence, this helps the pathogen infect the host.** Toxins: - Proteins that poison host cells and cause tissue damage -- mostly produced by bacteria and fungi - **Endotoxins** A toxin present inside a bacterial cell that is released when it disintegrates. - **Exotoxins** More toxic that endotoxins, they are proteins that are produced and released by the pathogen Exotoxins: - Can damage cell membranes by altering the movement of ions into or out of the cell, eventually causing cell death - Interfere with cell signalling pathways - Affect the immune response, causing it to release a high volume of inflammatory chemicals = toxic shock syndrome Lifestyle changes: - Some pathogens will have a life cycle with different stages, each with different surface molecules, to help them colonise their host - The host's immune system has difficulty in recognising there, enabling the survival of the pathogens Distinguishing "Self vs Non self" - Organisms are able to distinguish 'self' from 'non-self' -- that is, in most situations, they can recognise their own cells as being distinct from the cells of other species or indivudals.\