biol+3+homeostasis+summary+notes

This section wil be used for making a set of summary notes of relevant concepts. Each of you will be given (in class) a specific area to cover. You will then be able to read and edit each others work.
 * IMPORTANT!** If you do edit someone elses work, then write a comment in the box at the bottom of the page (while in edit mode) or post a comment in the **discussion** section on this page and explain the reasons behind the change.

You have 2 days to complete the task and then post your summary on this page in the space below.
 * Task**
 * Analyse and scrutinise the examination-style question ( **the secret question** ) you have been given.
 * Do not reveal the question to anyone else.
 * Think about which part of the course the question relates to (refer to the study design).
 * Write a concise paragraph of cohesive notes that would allow someone to be able to successfully answer the question.
 * Give your paragraph a suitable heading.
 * Your notes must not directly contain any part of the question within it. THIS IS IMPORTANT!
 * Follow up task**
 * Read the summary notes created by others.
 * You can edit other peoples’ work if you feel it is required **BUT** you must post an explanation in the “discussion” section of the page.
 * If you are unclear about what someone else has written, then ask a question in the “discussion” section of the page.

 =**FEELING THIRSTY!?! **= WATER LEVELS IN THE BODY ARE LOWERED:
 * -** Water levels drop in the body, this change is detected by the **receptor**; the hypothalamus.
 * -** The hypothalamus responds to this change in two ways:
 * 1.** A thirst centre within the hypothalamus stimulates you to drink
 * 2.** Osmoreceptors in the hypothalamus stimulates the posterior pituitary gland to release more anti-diuretic hormone, ADH.
 * Let’s look at number 2:**
 * -** ADH which has been secreted from neurosecretory cells in the hypothalamus is stored in the posterior pituitary.
 * -** Receptors in the blood detect change in water concentration.
 * -** An increased amount of ADH is release by the pituitary into the blood.
 * -** ADH, which is the **relay messenger,** travels in the circulation to the target organ, the kidney (more specifically the collecting duct within the kidneys).
 * -** The hormone reacts on the **effector**; the collecting duct in the kidney, by causing an increase of permeability of duct (lower conc. of water inside the duct), allowing greater reabsorption of water back into the medulla.
 * -** Less water is excreted, thus conserving water.
 * -** Hence, the body produces urine which is low in volume and high in concentration of salts and waste.
 * -** The **response** of this negative feedback is water reabsorption from the kidney tubules to conserve body water by reducing the loss of water in urine, thus water levels increase and the initial stimulus is reduced.

I really like the way this summary has been set out. Well done! VM

**Glands**

 * The pineal gland** is a small endocrine gland in the brain. It produces melatonin, a hormone that may weakly adjust sleep patterns. It is shaped like a tiny pine cone, and is located near the center of the brain, between the two hemispheres
 * The pituitary gland**, or hypophysis, is an endocrine gland about the size of a pea. It sits in a small, bony cavity covered by a fold at the base of the brain.
 * The thyroid** is one of the largest endocrine glands in the body. This gland is found in the neck below the thyroid cartilage a.k.a. the Adam's apple in men and at approximately the same level as the cricoid cartilage. The thyroid controls how quickly the body burns energy, makes proteins, and how sensitive the body should be to other hormones
 * The adrenal glands** are the triangle-shaped endocrine glands that sit on top of the kidneys; their name indicates that position (ad-, "near" or "at" + -renes, "kidneys"). They are chiefly responsible for regulating the stress response through the synthesis of corticosteroids and catecholamines, including cortisol and adrenaline.
 * The pancreas** is a gland organ in the digestive and endocrine system of vertebrates. It is both exocrine (secreting pancreatic juice containing digestive enzymes) and endocrine (producing several important hormones, including insulin, glucagon, and somatostatin) it is located in the direct vicinity of the kidneys.
 * An ovary** is an egg-producing reproductive organ found in female organisms. It is often found in pairs as part of the vertebrate female reproductive system. Ovaries in females are homologous to testes in males. The term gonads refer to the ovaries in females and testes in males. The ovary (for a given side) is located in the lateral wall of the pelvis in a region called the ovarian fossa. A gonad is an organ that makes gametes
 * Testes,** the male gonads, known as the testes or testicles, secrete a class of hormones called androgens, and produce spermatozoa. The predominant androgen in males is testosterone. The testes are located behind the penis


 * SIGNALLING MOLECULES**
 * __Hormonal__

Autocrine =** release hormones stored in vesicle within the cell that end up acting on themselves
 * when horemone needed is released from the cell that needs it
 * Therefore ends up acting on the same cell that produced it
 * not released into the blood, released into interstitual fluid


 * Paracrine** = released from a cell nearby to where the horemone ends up having an effect
 * horemone effects nearby cell to its initial release
 * acts locally by travelling from its source to target cells in its immediate vicinity
 * effects cell with complimentary specific receptors
 * travings in either onterstitual fluid or the blood to target cell


 * Endocrine** = Released from a gland in one part of the body and travels to another more distant region of the body
 * horemone released effects cell farther away
 * specific target call has specialised receptors that are affected
 * travels in the blood

Pheramone = chemicals released outside the body to stimulate another oragnism
 * travel outside organism through environment to target audience
 * messages transmitted have specialised functions
 * (eg)- attract opposite sex, signals for food, predator/danger
 * affect behaviour or physiology


 * TWO TYPES OF HORMONES**


 * __Amino Hormones__**
 * Made of amino acids (chains or small molecules)
 * Water soluble (hydrohpyllic/ lipophobic)
 * travel in the bloodstream
 * unable to pass through plasma membrane
 * bind with specific receptor proteins on plasma membrane
 * receptor is activated initiating a signal transduction pathway
 * a number of interaction involving relay and second messender molocules is generated
 * A cellular response is eventually initiated by an activated protein.


 * __Steroid Horemones__**
 * structuarally related to cholesterol
 * not water soluble (hydrophobic/ lipophyllic)
 * travel in the bloodstream aided by specialised carrier proteins
 * able to pass through cell membranes to specific receptors (plasma/ nuclear)
 * some can also bind to receptors on the plasma membrane.
 * Generally bind to a receptor proteins located in the cytoplasm or nucleus
 * a horemone-receptor complex is formulated that binds to a speciefied region of the DNA molecule
 * A certain gene is either activated causing a protein to be synthesised or inactivated
 * cellular responses are then carried out by synthesised proteins

so..i bet your wondering what my secret question is. SORRY. i cant tell you because it is a **//__secret__//**, but i hope these notes help you anyway:) xoxo gossip girl

__**NEGATIVE AND POSITIVE FEEDBACK IN ORGANISM**__ -There are two types of self-adjusting systems that organisms rely on. -They are known as //positive// and //negative// //feedback systems// -Below is a table that compares the two systems -Response of the organism is designed to diminsh the origianl stimulus -Its effects are positive -Is 'negative', because the receptors are recieving signals opposite to those caused by the original stimulus -Without negative feedback, homeostatic mechanisms would not work //EXAMPLE:// -If blood glucose levels increase above the normal range, insulin will be secreted from the pancreas. This hormone will then travel in the blood to muscle and liver cells whereby glucose will be converted into glycogen. This will cause the blood glucose levels to decrease to the appropriate level. ||< -Not common -Response of the organism is designed to enhance the original stimulus -its effects are negative -Is 'positive' because the reponse causes an increase in the intensity of the original stimulus not the reversal of it (as in negative feedback) -Are not mechanisms that maintain homeostasis //EXAMPLE// Can be seen in the birth process. Pressure on the cervix (from the foetal head)causes the release of the horhome, oxytocin from the pituitary gland, which in turn causes more uterine muscle contractions and greater pressure on the cervix, leading to more oxytocin production. || These are two clear examples showing the difference between positive and negative feedback. Not sure about the phrase "Is negative because the receptors are receiving siganls opposite". You may want to think about reqording this or someone else can make a suggestion. VM
 * **Negative feedback** ||< **Positive Feedback** ||
 * -Almost always used

Just want to thank you Vojtech for this amazing question you gave me...of course I kid.


 * COMMUNICATION BETWEEN NEURONS**

Signaling molecules such as neurotransmitters communicate with target cells by attaching to receptor molecules displayed on the cell membranes of the target cells. For a signal to reach other nerve cells, sensory receptors must transform incoming stimuli into electrical impulses that are transmitted along the nerve cells (neurons).

An electrical message is passed through neurons in order for the CNS to receive the information and a response to be created. Neurons do not touch on another, therefore the message translates from an electrical to a chemical one in order to cross the gap between both neurons ( the gap is known as the synaptic cleft/gap). The electrical impulse that travels through a neuron is also called an action potential because the change in electrical potential along the cell initiates action. When there is a high concentration of Na+ outside the cell and a high concentration of K+ inside – the inside of the cell has an overall negative charge (at this time the neuron is 'at rest' and no action potential is occurring).

After an action potential has been generated, it passes along the axon very quickly. The myelin sheath is responsible for speeding up the impulse, and if this is damaged messages will be transmitted much slower. The electrical message then arrives at the end of the axon, presynaptic knob, and ‘jumps’ the gap by the use of chemical messengers, to reach the postsynaptic membrane.

This message transduction occurs in a number of steps:


 * 1.** The synaptic knob contains many mitochondria and secretory vesicles that contain a chemical – neurotransmitter.
 * 2.** K+ (potassium) ions from the surrounding tissue fluid diffuse into the knob and stimulate synaptic vesicles to move toward the presynaptic membrane.
 * 3.** Vesicles merge with membrane and release contents via exocytosis into synaptic cleft.
 * 4.** Neurotransmitters diffuse across cleft and bind with specific receptors on post-synaptic membrane.
 * 5.** When bound, the sodium channels then open and the sodium ions diffuse from cleft into postsynaptic neuron and depolarization occurs (negative charge within cell is reduced).
 * 6.** If enough channels have opened, an action potential is initiated.
 * 7.** Once message has passed, remaining neurotransmitters must be deactivated by enzymes so they don’t continue to activate the postsynaptic membrane.

** A hormone may pass through many body tissues having no effect at all until it reaches its target tissue. Target tissues have receptors which are specific to the hormones which will influence its function. The receptors may be on the surface of the cell or in the cytoplasm. The bonding of signaling molecules with its specific receptor initiates a response in a cell. ** Many hormones are steroids or other simple lipids. __ (The life of a lipid soluble hormone in a specific target cell) __ § Steroids hormones are able to enter a cell through the phospholipid bilayer. § In target cells there are specific receptors which bind with the hormone, forming a hormone-receptor complex. These receptor molecules are usually found in the cytoplasm § The hormone-receptor complex enters the nucleus where it attached to a specific region on a chromosome § The hormone receptor complex activates a particular gene causing mRNA production § mRNA travels to the ribosome’s and a new protein is assembled § This new protein affects cell function. Typically steroid hormones regulate long-term development  ** Unlike lipids, peptide hormones cannot pass through the phospholipid bilayer of cell membranes. The receptors which bind with these hormones are protein molecules embedded in the cell membrane. Hormones bind with the part of the protein which is in contact with the extracellular fluid (outside of the cell) and cause their effects on the inside of the cell (intracellular). (__The life of a peptide hormone (non-lipid soluble) in a specific target cell)__ § A hormone binds with its specific receptor molecule on the cell surface § Some of these receptor molecules have a hormone binding site on the outside of the cell and an enzyme site on the inside. (Dual purpose protein) § The binding of receptor and first messenger stimulate the enzymatic end of the protein molecule § Enzyme activates the formation of many molecules which act as second messengers. § Second messengers are the molecules which cause a change in cell functioning – a response ** Neurotransmitters are another type of signaling molecule. § Just like peptide hormones, neurotransmitters cannot pass through the phospholipid bilayer, therefore they bind with specific receptors in the cell membrane. § Neurotransmitters are within the vicinity of membrane proteins and do not have to travel as far, whereas peptide hormones, infact all hormones, have further to travel to reach the specific target cell. The specific receptors which peptide hormones bind to have a binding site on the outside of the cell and an enzyme at the other end (the inside of the cell), known as dual purpose proteins. The receptor molecules in which the neurotransmitters bind to have a binding site on the outside of the cell but do not have an enzyme at the other end of the receptor
 * __SIGNAL TRANSDUCTION __**
 * Cell receptors
 * Lipid soluble hormones
 * Peptide hormones
 * Neurotransmitters

Classic reflex response Ø Stimulus ; change in the external or internal environment Ø Receptor ; cells or tissues that detect the change due to the stimulus (sensory receptors) Four types of sensory receptors: - chemoreceptor ; usually detect pheromones - Mechanoreceptors ; stimulated by the change in the mechanoreceptor shape à eg. Loud sound in ear, mechanoreceptors shape are changed due to force of sound - Photoreceptors ; detect light and colour à eg. Photoreceptor in eyes - Thermoreceptors ; detect heat levels Ø Control centre ; usually the brain where a decision is made as to the manner of the response Ø Relay/chemical messengers ; transmit signals from the control centre to the effector hormones (motor neuron ;  conducts impulses to a muscle, gland, or <span style="FONT-SIZE: 13pt; COLOR: rgb(51,51,51)">other effector. ) Ø <span style="FONT-SIZE: 13pt; COLOR: rgb(0,204,255)">Effector ; the cells or tissue, usually a gland or muscle, that causes a response to happen Ø <span style="FONT-SIZE: 13pt; COLOR: rgb(0,204,255)">Response ; an action (at the cell, tissue or whole organism level) that wouldn’t have occurred in the absence of the stimulus //__ Insulin & Blood Glucose Regulation __// Insulin is an example of a hormone that has an integral role in the negative feedback pathway that is used to lower blood glucose levels in the body if levels rise above the normal level that is associated with homeostasis. As a hormone, insulin is made up of a chain of less than 200 amino acids and is therefore water-soluble. As a result of this, insulin is unable to pass through the plasma membrane of a target cell. When glucose levels in the blood increase, generally after eating, cells in the pancreas detect this change. These cells instruct beta cells of the Islets of Langerhans (clusters of endocrine cells in the pancreas) to release insulin into the blood stream. The insulin travels to muscle and liver cells of the body and causes these cells to begin taking up glucose from the blood and converting it into the storage form referred to as glycogen. At this point, blood glucose levels will begin to decrease. But how does insulin interact with the target cell? As it cannot simply pass through the phospholipid bilayer of the cell membrane due to its lipophobic nature, the insulin binds to specific receptors on the surface of the membrane. This initiates a signal transduction pathway within the cell. **Signal Transduction** generally refers to receptors converting incoming signals into information that culminates in a coordinated response by the cell. In this case, the binding of insulin to the receptor results in a series of events within the cell that involve secondary messengers (for insulin, protein kinase) that produce the required response. That is, glucose channels in the muscle or liver cell membrane will be opened and glucose that floods into the cell will be readily converted into glycogen.

Stimulus à receptor à sensory neuron à effector à motor neuron à response

Different Types of Hormones: Endocrine: are hormones which affect receptors on specific target cells further away from the gland from which they are produced and travel in the blood stream.

Autocrine: are hormones which are released by the cell when it is needed effectively acting on the cell they are released from. They do not enter the blood stream but the interstitial fluid surrounding the cell.

Paracrine: are hormones which have short lived local affects on cells that have specific receptors in their immediate vicinity. They can travel i neither the interstitial fluid or the blood stream to reach their target cell.

Apocrine: are hormones which are relased by the cell via excocytosis. The cell buds off its secretions off the plasma memrbane producing membrane bound hormones. An example of a apocrine gland is the lactating mammary gland.