AREA OF STUDY 2AREA OF STUDY 2

Detecting and Responding Detecting and Responding

Chapter 5 Chapter 5

Coordination and Coordination and Regulation: Endocrine Regulation: Endocrine

SystemsSystems

Homeostasisreading pages 136 - 137

HomeostasisHomeostasis is: is:

the maintenance of the internal environment in a relatively stable the maintenance of the internal environment in a relatively stable state despite changes in either the external or internal state despite changes in either the external or internal environment.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 EnvironmentsInternal 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 Environmentreading 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.

TaskQuick Check 1-4

Definitions to learn by heart!

Internal environment = extracellular fluidInternal environment = extracellular fluid

Extracellular fluid = interstitial (tissue) Extracellular fluid = interstitial (tissue) fluid, blood plasma and cerebrospinal fluid. fluid, blood plasma and cerebrospinal fluid.

Unicellular OrganismsUnicellular Organisms

The environment of unicellular organisms is the The environment of unicellular organisms is the external external environment environment in which they live.in which they live.

Unicellular organisms can do little to control their Unicellular organisms can do little to control their environment. environment.

They are either They are either – able to tolerate the conditions or able to tolerate the conditions or – they die.they die.

Simple OrganismsSimple OrganismsHomeostasis occurs in all living organisms.Homeostasis occurs in all living organisms.

Even unicellular organisms are able to sense and Even unicellular organisms are able to sense and respond to changing environmental conditions, respond to changing environmental conditions, generally moving away from light and heat, and generally moving away from light and heat, and towards food.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 environmentreading 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 homeostasisreading 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

Transmission to nerves

StimulusStimulus

ResponseResponseTransmission to

nerves or hormones

Receptor

Control Centre

Effector

Stimulus-Response Model copy

Transmission to nerves

StimulusIncrease in blood carbon dioxideIncrease in blood carbon dioxide

ResponseDecreased carbon dioxideIn blood

Transmission to nerves or hormones

(Negative feedback is normal, good!)

Receptor

In arteries and brain

Control CentreRespiratory centre in brain

Effector

Respiratory muscles in lungs (increased

ventilations)

Negative Feedback in the Stimulus-Response Modelreading 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.

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 55-56Quick 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

1. Principles of Homeostasis Page 55-56

Role of the Endocrine Systemreading 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

Hormonesreading page 134

Examples: Hormones – Chemical MessengersGlandGland HormoneHormone ActionAction

HypothalamusHypothalamus ManyMany Many body activitiesMany body activities

PituitaryPituitary Growth HormoneGrowth Hormone The master glandThe master gland

ThyroidThyroid ThyroxineThyroxine MetabolismMetabolism

GrowthGrowth

AdrenalsAdrenals CortisolCortisol

AdrenalineAdrenaline

MetabolismMetabolism

Responds to stressResponds to stress

PancreasPancreas InsulinInsulin

GlucagonGlucagon

Blood glucose concentrationBlood glucose concentration

GonadsGonads TestosteroneTestosterone

OestrogenOestrogen

Fertility and sex characteristicsFertility 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 hormonesreading 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 FeedbackCase 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

• if the blood glucose level falls below normal – the pancreas responds in 2 ways:

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 55-56Quick Check 9-12

Cell Communicationreading 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 Pheromonesreading 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

TasksQuick Check17-18 Pages 151Biozone 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 Hormonesreading 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

Tropismsreading 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

Auxinsreading 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

Cytokininsreading 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

Gibberellinsreading 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 acidreading 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

Ethylenereading 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)

TasksBiozone 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

TasksBiozone page 91-92

Biochallenge

Chapter Review