Detecting and Responding AREA OF STUDY 2 Detecting and Responding

Coordination and Regulation: Endocrine Systems Chapter 5 Coordination and Regulation: Endocrine Systems

Homeostasis reading pages 136 - 137 Homeostasis is: the maintenance of the internal environment in a relatively stable state despite changes in either the external or internal environment. is the condition of a relatively stable internal, maintained within narrow limits when changes occur in the internal environment, homeostatic mechanisms act to restore it to the ‘normal’ state if the body deviates too far from the normal steady state of a variable, death can occur.

Internal and External Environments The external environment is the medium surrounding an organism The internal environment, or extracellular fluid, is the internal fluid that surrounds cells in multicellular organisms

Defining the Internal Environment reading page 134 the body’s internal environment consists of the tissue fluid (surrounding cells) and blood plasma plasma is the liquid part of the blood. both tissue fluid and plasma are located outside of cells. Together they are called extracellular fluid the composition of the extracellular fluid is regulated so that body cells can operate at their optimum fluids located outside cells are extracellular. fluids located inside the cells are intracellular. Task Quick Check 1-4

Definitions to learn by heart! Internal environment = extracellular fluid Extracellular fluid = interstitial (tissue) fluid, blood plasma and cerebrospinal fluid.

Unicellular Organisms The environment of unicellular organisms is the external environment in which they live. Unicellular organisms can do little to control their environment. They are either able to tolerate the conditions or they die.

Simple Organisms Homeostasis occurs in all living organisms. Even unicellular organisms are able to sense and respond to changing environmental conditions, generally moving away from light and heat, and towards food. In this Petri dish, tiny green Volvox colonies have moved towards the light source, allowing increased levels of photosynthesis.

Key Variables controlled in the internal environment reading page 136 -138 core body temperature blood glucose concentration water levels in body tissues ph (hydrogen ion concentration) ions, such as sodium, calcium and chloride ions blood oxygen concentration carbon dioxide concentration blood volume blood pressure

Key Body Systems contributing to homeostasis reading page 137 nervous system endocrine system respiratory system circulatory system digestive system excretory system integumentary (skin)system

Stimulus-Response Model a change in the internal or external environment acts as a stimulus that is detected by receptors if the intensity of the stimulus is sufficient (threshold), messages are transferred to a control centre messages are then passed to effectors which produce a response

Stimulus-Response Model copy Transmission to nerves Stimulus Response Transmission to nerves or hormones Receptor Control Centre Effector

Negative Feedback in the Stimulus-Response Model reading page 139 In the stimulus-response model, negative feedback occurs when the effector brings about a response that counteracts the original stimulus, so that the variable within the internal environment is returned to its optimal level. Transmission to nerves Stimulus Increase in blood carbon dioxide Response Decreased carbon dioxide In blood Transmission to nerves or hormones (Negative feedback is normal, good!) Receptor In arteries and brain Control Centre Respiratory centre in brain Effector Respiratory muscles in lungs (increased ventilations)

Positive Feedback rare but does exist Case Study: production of oxytocin page 144 Far less common than negative feedback Involve a situation where a hormone produced by a gland acts on the same gland to stimulate it to produce even more hormone Example: production of oxytocin Produced by the pituitary gland during childbirth Once birthing process commences, oxytocin stimulates uterine contractions that help push baby out of the uterus Also acts on the pituitary to produce more oxytocin Continues until baby is born Tasks Biozone page 55-56 Quick Check 9-12

Stimulus Response Stimulus: some change in the internal or external environment. Receptors: specialised cells that detect a stimuli. A receptor transmits information about the detected change to the central nervous system. The CNS coordinates the action to be taken and transmits this to the tissue/s or organ/s which will respond (effector). Two systems that are involved in this coordination: nervous and endocrine (hormonal).

BIOZONE Principles of Homeostasis Page 55-56

Role of the Endocrine System reading page 134 acts with the nervous system to coordinate and regulate the activity of body cells and so maintain homeostasis endocrine glands are ductless glands that secrete hormones into the bloodstream hormones are signalling molecules (proteins) that: Are produced by cells within an organism act on target cells by binding to a receptor either on a plasma membrane or within a target cell can communicate signals to a cell only if the cell has receptors that recognise hormone the receptor- hormone complex brings about a change in the target cell Hormones reading page 134

Examples: Hormones – Chemical Messengers Gland Hormone Action Hypothalamus Many Many body activities Pituitary Growth Hormone The master gland Thyroid Thyroxine Metabolism Growth Adrenals Cortisol Adrenaline Responds to stress Pancreas Insulin Glucagon Blood glucose concentration Gonads Testosterone Oestrogen Fertility and sex characteristics

Different hormones there are three different kinds of hormones based on their chemical structures: - amino acid derivatives - steroid hormones - protein hormones and peptide hormones. hormones may be hydrophilic or lipophilic; this effects the way in which hormones are transported through the blood and how a signal is transmitted across the membrane.

Different hormones reading page 146 the key difference in different types of hormones can be summarised in table 5.3, page 146. position of the cell receptors are important for cell response. figure 5.15 page 147 illustrates the sequence of events in the signaling pathways.

Hormones &Negative Feedback Case Study: Controlling Blood Glucose page 139-144 the pancreas produces 2 hormones – insulin and glucagon. these hormones are involved in the control of glucose in the blood. the hormone insulin controls the uptake by cells of glucose from the blood. the hormone glucagon acts on the liver to release more glucose into the blood. if the blood glucose level falls below normal – the pancreas responds in 2 ways: some cells called ‘alpha cells’ increase their production of glucagon, which acts on the liver to convert stored glycogen to glucose. other cells called ‘beta cells’ decrease their production of insulin. less insulin in the body results in less glucose being taken from the blood by the cells of the body See Fig 5.10 pg 141 – Summary of blood glucose regulation.

Positive Feedback rare but does exist Case Study: production of oxytocin page 144 Far less common than negative feedback Involve a situation where a hormone produced by a gland acts on the same gland to stimulate it to produce even more hormone Example: production of oxytocin Produced by the pituitary gland during childbirth Once birthing process commences, oxytocin stimulates uterine contractions that help push baby out of the uterus Also acts on the pituitary to produce more oxytocin Continues until baby is born Tasks Biozone page 55-56 Quick Check 9-12

Cell Communication reading page 145-148 As we saw in chapter 2 (pages 52-56), cells have connections with other cells and in some cases, small molecules can pass from one cell to another through those connections.this provides only limited communication. In addition, communication between cells can take place by means of chemical messengers called signalling molecules of which hormones are one group (also includes pheromones, neurotransmitters, neurohormones) when a hormone is secreted by a cell, only cells with receptors specific for the hormone respond to the hormone gland. some hormones act on one kind of cell only while others act on different tissue types in the same way. Tasks Quick Check 13-16

Communication by Pheromones reading pages 150-151 Pheromones are: signalling molecules that are released by animals into their environment enabling them to communicate with members of their own species pheromones can be used for: attracting mates inducing mating activity marking territories signalling alarm marking food trails Tasks Quick Check17-18 Pages 151 Biozone page 111

Plant Hormones reading page 152 hormones are plant growth regulators environmental factors control the production and amount of a particular hormone hormones produced in plant cells can diffuse to adjacent target cells or be transported in the xylem or (particularly) phloem of vascular plants to target cells Some of these hormones stimulate growth, others inhibit it parts of a vascular plant most likely to contain hormone producing cells are: growing regions of stems and leaves young leaves growing seeds developing fruits

Plant Hormones reading page 152 similar in structure and function to animal hormones produced in relatively small amounts able to produce specific effects even in low concentrations action depends on concentration (low concentration of a hormone can do opposite effect to high concentration!) Can result in a signal transduction pathway (see Gibberellins paragraph 3 page 157) same hormone can produce more than one effect (i.e auxin) Classifications of plant hormones: auxins cytokinins gibberellins abscic acid ethylene Florigen Jasmonates brassinosteroids

Tropisms reading page 154 is a growth response towards (positive) or away from (negative) a given stimulus Examples: Positive Phototropism: is growth towards a stimulus (light) Thigmotropism: change in the direction of growth because of contact another object Geotropism: is a growth response due to gravity (positive (grows down!- with) Hydrotropism: growth response due to stimulus of water See figure 5.22, 5,24 & 5.26

Auxins reading page 152-156 are a group of hormones whose major actions is to control (stimulate or inhibit) the enlargement and elongation of cells Action of auxins include: simulate enlargement and elongation in stems but also, in large concentrations, inhibit the growth of root cells Stimulate growth of lateral and adventitious roots Promote growth of flowers and fruits Influence the differentiation of unspecialised cells in vascular tissue some promotes apical dominance (example IAA)- inhibition of lateral buds! promote photropism (auxin moves away from light side!) Promote geotropism (auxin builds up on lower side and inhibits root cell growth in lower cells (upper cells turn over and down – geotropism) auxins are produced by the growing tips of plants (coleoptile- first leaves) See figures 5.22b, 5.25

Cytokinins reading page 156 Are another group of growth promoting plant hormones Act on shoots and roots- promote cell replication high concentration in growing cells: growing fruits

Gibberellins reading page 157 promote both cell elongation and replication in stems and leaves also initiate seed germination and bud development can result in a signal transduction pathway (gibberelin becomes activated diffuses with aleurone, and acts on dna to induce synthesis of the enzyme amylase which converts starch to glucose which is in turn used as a nutrient for the initial stages of new plant growth in some plants, gibberelins promote the development of branches with juvenille leaves See figure 5.28 Example: Gibberellic acid

Abscisic acid reading page 158 Found in high concentrations in fruit about to fall (abscission!) and dormant buds Inhibits growth stimulates stomatal closure (reduces water loss by causing stomata to close, by interferring with ion concentrations in guard cells See figure 5.32

Ethylene reading page 159-161 is a hormone in gas form! produced by the metabolism in some plants interacts with other hormones to influence events such as ripening increases respiration rate of cells, encouraging ageing (ripening) Tasks Biozone 90 Quick-Check 19-22

Photoperiodism refers to the response of plants to particular periods of light and dark plants may be classified as short day (only flower when the day is short), day-neutral or long day plants Tasks Biozone page 91-92 Biochallenge Chapter Review