Chapter 5Coordination and regulation: Endocrine systems
Environments Extracellular environment Extracellular fluids: Tissue fluid, Plasma, Cerebro-spinal fluid & Lymph Intracellular environment Intracellular fluid: Cytosol Exchange of substances between all, therefore, blood tests can provide info about the state of cells in other parts of the body.
Homeostasis Maintenance of a relatively (narrow limits) stable internal environment.
What stops / prevents homeostasis occuringeffectively? Cant restore values to a normal state‘ if.... infection, trauma, toxic substances, auto- immune diseases, inherited disorders, extreme conditionsWhat variable are subject to homeostasis?Nutrients Blood volumeTemperature Blood pressureWater OxygenIons, such as Na+, Cl- Carbon dioxidepH (H+ concentration) Red blood cells
NEGATIVE FEEDBACK Step1: Detect change from a stable state. Step 2: Counteracting change=> NEGATIVE FEEDBACK
Controlling Blood Glucose (negative feedback involving hormones)Organ: Pancreas (Islets of Langerhans)Hormones: Insulin GlucagonCells: Beta cells Alpha cellsTriggered Response: Helps cells absorb Glycogen -- > Glucose glucose Decrease blood sugar Increasing blood sugar levels Draw the summary of events that occur to maintain a relatively constant level of blood glucose in a normal person. (fig 5.9 p141) Label the sensors and effectors.
POSITIVE FEEDBACK Most hormones are regulated via negative feedback but positive feedback exists as well. Hormone produced by a gland acts on same gland and stimulates it to produce more of the hormone Example: Oxytocin produced by pituitary gland
Signalling Molecules eg: hormonesA chemical produced in one part of an organism that can be transported in the blood stream to another part where it exerts its effectOR act on the of hormone OR diffuse through tissue fluid & act on Types same cell Properties nearby cells Amino acid derivates stored in vesicles until required, short life span water soluble & travel in blood stream (cant pass cell membrane) Eg. tyrosine (thyroid gland hormones) Peptide and protein made in advance & stored hormones in vesicles water soluble & travel in bloodstream Eg: TSH & Insulin Steroid hormones synthesised on demand, long life span Eg: testosterone &
Cells only respond to signalling molecules if it has a specific receptor for that molecule (hormone receptors are specific) Receptors can be located on the membrane OR in the cytosol eg: aa & protein/peptide steroid1) Hormone binds to receptor (membrane / cytosol)2) Signal detected within cell3) Signal Transduction: passing of the message from the receptor to the nucleus (which will elicit a response) - series of events from cytosol receptor to nucleus (eg steroids) OR - series of events involving a 2nd messenger or G protein (eg aas & pps)4) Response - activation of genetic material
Pheromones Pheromones are chemical signalling molecules secreted by animals (particularly insects) They influence the behaviour of members of the same species, often as sex attractants. Examples: Moths -> large feathery antennae with smell receptors. Male follows sent of female. Can detect odours from miles away
can pass through second messengercell membrane change cell LipophobicHydrophobic function affecting target membrane boundreceptors are in the cells receptorcytosol specific receptor longer life-span shorter life-spanSmall signal transduction protein carriers for travel freely in blood blood transport possible amplification aas, proteins Steroids LIPID WATER SOLUBLE SOLUBLE
Hormones as plant regulators Auxins Cytokines Gibberellins Abscisic acid Ethylene
Auxins Auxins control enlargement and elongation of plant cells They stimulate growth from the apex down the stem Auxin can also inhibit the growthof roots if the concentrationis too high They are produced bythe growing tips of plantsand are water soluble
Indoleacetic acid (IAA) Responsible for apical dominance apical dominance is the phenomenon whereby the main central stem of the plant is dominant over (i.e., grows more strongly than) other side stems
Tropism and auxins Tropism: the growth of a plant in response to a stimulus Phototropism: response to light Geotropism: response to gravity
Cytokinins Another growth promoting hormone that acts on shoots, roots and fruits Cytokinins promote cell division and are involved in cell growth and diferentiation They are often used by gardeners (for example, in ‘rooting powder’) prior to planting to help promote root development with cytokinins
Gibberellins Promote cell elongation and reproduction. Initiate seed germination and bud development. Read p. 157 & draw a flow diagram to represent the way that gibberellic acid promotes the germination of wheat.1) Water (fire / something) is needed to activate gibberellins to make gibberellic acid2) That changes the DNA which allows starch to be converted in glucose3) Respiration can start and growth can begin. Explain how / why some trees can havevery different juvenile leaves compared to theiradult leaves
Abscisic acid (ABA) Inhibits growth and influences stomatal closure. What prevents young leaves from falling off a tree? Some plants produce and accumulate abscisic acid in their leaves if they begin to wilt. It reduces water loss by causing the stomata to close.The separation of fruit or leaves from an adult plant:abscission.Before a leaf falls (for example, deciduous trees losingtheir leaves in Autumn), an ‘abscision zone’ forms. NOTcaused by abscisic acid.Draw a diagram to illustrate this (p.159)
Ethylene Ethylene is a gas produced by a range of fruits (eg: apples, bananas, tomatoes, avocados and mangoes). It assists in the ripening of the fruit by increasing the rate of respiration in the fruits cells. Petals in flowers die because of an increase in ethylene which leads to faster cellular respirationFlorigen ???A hormone produced in the leaves and transported via thephloem to the the buds of flowering plants may exert a effecton the production of flowers.Night and day length is known to be of importance butgenerally speaking, the control of flowering