5 - Detecting and responding

Coordination and regulation: Endocrine systems

Chapter 5

Our external environment often changes, but our internal environment must stay

constant, how can this be achieved?

The FluidsThe fluids in most mammals can be separated along the

following linesFluid

Intracellular

Cytosol

Extracellular

Plasma Interstitial fluid (aka

tissue fluid)

Cerebro-spinal fluid

Lymph

There is constant exchange between these fluids, so the makeup of one is often a very good indication of the makeup of the others

HomeostasisIn order to maintain function, our bodies are

required to operate within some very narrow limits

The mechanisms used to detect, react and restore homeostasis are:The Endocrine SystemThe Nervous System

Variables subject to homeostasis

NutrientsTemperature water Ions, such as Na+, Ca+,

Cl− pH (hydrogen ion

concentration)

Blood volumeBlood pressureOxygenCarbon dioxideRed blood cells.What can stop / prevent

homeostasis from being maintained?

InfectionTraumaToxic Substances

Auto-immune disease Inherited disordersExtreme conditions

Body systems involved in Homeostasis

Nervous

Endocrine (hormonal)

Respiratory

Circulatory

Digestive

Excretory

Integumentary (skin)

Hormones

Hormones maintain homeostasisStage 1: Detect

changeStage 2

Counteract change

This is most frequently accomplished via a negative feedback system

A (hopefully) useful analogy)SENSORS

detect if car speed is lesser or greater than 60kph

Going too fast

Going tooslow

Brake Accelerate

Go slowerGo faster

EFFECTORSincrease or decrease speed

Controlling Blood Glucose2 hormones produced in pancreas:GLUCAGON

Produced by alpha cellsStimulates liver to convert more glycogen to glucoseResults in more glucose being released in to bloodstream

INSULINProduced by beta cellsCauses the cells of the body to absorb glucose from the bloodResults in less glucose in the bloodstream

Blood glucose can be lowered by:

Blood glucose can be raised by:

Alpha cells decreasing production of glycogen

Alpha cells increasing production of glycogen

Beta cells increasing production of insulin

Beta cells decreasing production of insulin

DiabetesGlucose is usually reabsorbed from the filtrate

in the kidneysDiabetes can be detected through the presence

of glucose in a person’s urine.Diabetes mellitus (Type 1 diabetes) occurs as a

result of the body being unable to produce sufficient insulin.

Medication and exercise is required to control their blood glucose levels

Diabetics must keep a constant eye on their blood glucose levels

Not all feedback mechanisms are negative (but most are)

Cell CommunicationAdjacent cells can communicate through

communicating junctions (see chapter 2).How can cells that are further apart

communicate with each other?HORMONESHormones are produced by cells and can

then travel through the bloodstream, where they are picked up by the receptors of the intended cell

NOT ALL hormones go in to the bloodstream, some just go to the adjacent cell and others are excreted only in to the extracellular fluid.

Communication between adjacent cells

Cell CommunicationSome cells have receptors for only one type of

hormone, whilst others have two or moreSome hormones act only on one type of cell, whilst

some act on multiple typesSome hormones trigger different actions in different

cell types

Three types of HormonesAmino acid derivatives

Made in advanceStored in precursor form (in secretory vessicle)Leave cell via exocytosis (if a hormone) / simple

diffusion (if a precursor)Short life span

Steroid HormoneSynthesised on demand (from precursor in cell)Leave cell via simple diffusionLong life span

Protein hormones & peptide hormonesMade in advanceStored in precursor formLeave cell via exocytosisShort life span

Three types of Hormones

Cell Receptors & Transduction Pathway

Cell receptors can either be inside or outside the cell

Hydrophilic hormones will interact with receptors within the cytosol

The hormone will undergo the signal transduction process which will amplify the signal and transform it in to a chemical response

Hydrophobic hormones are unable to penetrate the membrane and must contact receptors on the surface of the cell membrane

In this case a secondary step of activating a G protein or other second messenger must take place before signal transduction can occur

The Next Steps

COMMON RESPONSES TO SIGNALSDNA is stimulated to begin the process of

protein productionor recipient cell is stimulated to release a

hormone

HORMONE ELIMINATIONWhen the hormone’s action is compled, it

does not linger in the body but is broken down and either recycled or excreted via kidneys or faeces.

Pheromones

Chemical signalling molecules excreted by animals or plants

Often used as sex attractantsAre species specific (see next point)Can only be detected and responded to if

the recipient has the appropriate receptorsCan be used to control insects

Males can be baited to insecticide trap, thereby breaking life cycle

Control movement and containment of biological control species (eg Cane Toads)

FAIL !!

Plant growth and development

Plant growth and development (formation of buds, expanding of leaves, lengthening of stems, ripening of fruits, etc) is influenced by internal and external factors.

Internal factorsHormones

External factors (egs)Light intensityDay lengthGravity

Plant HormonesSome stimulate growth & development, some

inhibit itTransported via the xylem, phloem or bothOnly small amounts required as response is

amplifiedEvident mainly in developing plantsCan act in different ways in different parts of the

plant5 distinct groups

AuxinsCytokyninsGibberellinsAbscisic AcidEthylene

AuxinsEnlargement and elongation of plant cellsEg of Auxin is in bambo – can grow up to

4cm per hour!!Produced in the growing tips of plants

IAA – Indoleacetic Acid (an Auxin)

Inhibits lateral growth and promotes apical dominance

Translaton: makes tree grow up instead of outBut wait – if you nip off the growth node

Uninhibited lateral growth takes precedence

This is a very useful technique used by gardeners

Tropisms and AuxinsExternal factors can affect hormone

productionThis is referred to as a tropism

Growing towards stimulus = positive tropismGrowing away from stimulus = negative

tropismeg Phototropism (growth towards light) is a

positive tropism

PhototropismIn even sun, auxin is evenly spreadIf sun is from one side, auxin moves to the

opposite side of the coleoptile (new shoot)Thereby making cells on the opposite side

elongate faster

GeotropismGeotropism is the movement with regard to

gravityAuxin always moves to the underside of the

plantThis promotes growth in coleoptile cells

and inhibits growth in root cellsSo coleoptile

grows against gravity (negative geotropism)

And Root grows with gravity (positive geotropism)

Gibberellins

Promote both cell elongation and reproduction

Also initiate seed germination andbud development

Initiate production of amylase

Breaks down starch in endosperm to glucose

Provides fuel for growth of embryo

Abscisic AcidInhibits growth and

closes stomata in fruit and leaves about to fall

Also used to close stomata in very hot conditions

Stomata closed by inhibition of potassium / sodium import in to guard cells

Before falling (called abscission), abscission zone is formed to form a protective layer against environment and bacterial infestation

EthyleneAirborne hormone that increases rate of respiration and

therefore quickens ripening of fruit and wilting of flowersRipening can be artificially controlled by regulating

exposure to ethyleneA few days after picking of flower / fruit, ethylene

production increases dramatically

Promote cell reproductionCytokinins

FlorigensIf they exist: control the flowering of plantsVery little is known about this mechanism

The burning of kerosene releases ethylene gas which would have made the fruit ripen more rapidly

Pair the plant hormone with its function

Auxin A) Promotes seed dormancy

Giberellins B) Promotes stem growth through cell elongation

Ethylene C) Promotes cell division

Abscisic Acid D) Stimulates seed germination

Cytokinins E) Increases rate of cellular respiration

B

D

E

A

C

C

D

Holiday Homework!!

Chapter 5 reviewQs 2-8

Biozonepp 56 - 60