Organisms and Their Environment

Area of Study 1: Adaptations of Organisms

UNIT 2 BIOLOGY

WEEK 2: Learning OutcomesBy the end of the week, you should be

able to: Describe the structure of the endocrine

system. Explain hormonal control in complex

multicellular organisms. Explain how organisms regulate water

balance (osmoregulation).

Feedback Systems: Hormonal ControlFeedback systems are the general mechanism

of nervous or hormonal regulation in animals. Feedback occurs when the response to a

stimulus has an effect of some kind on the original stimulus. The nature of the response determines how the feedback is 'labelled'.

Negative feedback: is when the response reduces the effect of the original stimulus. It works in the opposite direction.

Positive feedback: is when the response enhances the original stimulus. It works in the same direction.

Negative FeedbackNegative feedback is most

common in biological systems. Examples of this are:Blood glucose concentrations

rise after a sugary meal (the stimulus), the hormone insulin is released and it speeds up the transport of glucose out of the blood and into selected tissues (the response), so blood glucose concentrations decrease (thus decreasing the original stimulus).

Draw a flowchart to illustrate this

Another example of negative feedback

Exercise creates metabolic heat which raises the body temperature (the stimulus), cooling mechanisms such as vasodilation (flushed skin) and sweating begin (the response), body temperature falls (thus decreasing the original stimulus).

Draw a flowchart to illustrate this

Positive FeedbackPositive feedback is less common, which is

understandable, as most changes to steady state pose a threat, and to enhance them would be most unhelpful. However, there are a few examples:A baby begins to suckle her mother's nipple and

a few drops of milk are released (the stimulus). This encourages the baby and releases a hormone in the mother which further stimulates the release of milk (the response). The hungry baby continues to suckle, stimulating more milk release until she stops. (Positive feedback, it would not have helped the baby if suckling decreased milk flow, as in negative feedback!)

Another example...A ripening apple releases the volatile plant

hormone ethylene (the stimulus). Ethylene accelerates the ripening of unripe fruit in its vicinity so nearby fruit also ripens, releasing more ethylene (the response). All the fruit quickly becomes ripe together. ("One 'bad' apple has ruined the whole lot." The biological explanation - positive feedback - for an old saying!)

Draw a flowchart!

Yet another...Fever is an example of a positive feedback

mechanism.

Explain to the person next to you how you

think it works...

The Endocrine (Hormonal) SystemHormones act by altering biochemical

reactions in target cells.Exocrine glands secrete their products

straight onto the target tissue via a duct.Endocrine glands secrete their products

into the circulatory system via the capillary network. These hormones are carried by the

bloodstream, to target tissues elsewhere in the bodies, which then interpret the messages and act on them.

The Endocrine SystemThere are many different glands in the body that

release hormones.Hypothalamus – midbrain.Pituitary gland – base of the brain; beneath the

hypothalamus.Thyroid gland – in the throat.Parathyroid gland – rear surface of the thyroid

gland.Thymus – just behind the sternum, over the

heart.Adrenal glands – above the kidneys.Pancreas – organ attached to the small intestine.Ovaries – in females.Testes – in males.

Label me! Hypothalamus

ENDOCRINE EXOCRINE

Hypothalamus Sweat glands

Pituitary gland Mammary glands

Thyroid and Parathyroid glands Salivary glands

Pancreas Digestive glands

Adrenal Glands

Testes and Ovaries

HormonesThere are 2 types of hormones which differ

slightly in their mode of action.Amino acid hormones - these are

proteins, which act by binding directly to receptors on the cell membrane. E.g. insulin and glucagon.

Steroid hormones - these are lipid based, they act by crossing the plasma membrane. E.g. testosterone and oestrogen.

HormonesSPECIFICITYThe stimuli will only affect a particular group of

hormone secreting cells. The hormone released will then only affect

those cells with the appropriate receptor.E.g. growth stimulating hormone produced in

the pituitary gland only affects bone and muscle and promotes protein synthesis.

SPEED OF ACTIONThe hormonal system is slower than the

nervous system because the molecules have to be passed through blood or tissue to reach the target cells.

MODE OF ACTIONOnce hormones have entered the cell they

can bind to internal receptors.They then cause the release of second

messengers or they can enter the nucleus and regulate the production of other proteins by switching genes on or off.

ANTAGONISTIC HORMONESPairs of hormones with opposite effects.

ANTAGONISTIC HORMONES

E.g. insulin converts glucose to glycogen and glucagon converts glycogen back into glucose when needed.

Interaction of Glands - Hypothalamus

The hypothalamus is:

located in the brain and controls the release of hormones from the pituitary gland.

an important link between the endocrine and nervous systems.

Pituitary Gland

FUNCTIONIt secretes nine hormones that directly regulate

many body functions and controls functions of other glands.

Two distinct portions:Anterior (front)Posterior (back)

HOW IT IS CONTROLLED Hypothalamic releasing hormones stimulate cells

of anterior pituitary to release hormones. Nerve impulses from hypothalamus stimulate

nerve endings in the posterior pituitary gland to release hormones.

Pituitary Gland

Pituitary Gland

Disorders: Too much growth

hormone (GH) in early childhood can result in a condition called gigantism from a hyperactive anterior pituitary gland.

Too little GH can result in Pituitary Dwarfism.

Robert Wadlow1918 - 19402.7m tall

Thyroid GlandFunction: plays a major role in regulation the body’s metabolism.

Thyroid Gland

Thyroid Gland

Disorders: If the thyroid gland produces too

much thyroxin, it can cause a condition known as Hyperthyroidism - fast heart beat resulting in palpitations, a fast nervous system with tremor and anxiety symptoms, a fast digestive system resulting in weight loss and diarrhoea. – Graves’ disease

If too little thyroxin is produced it is called hypothyroidism – weight gain, fatigue and constipation – Hashimoto’s Thyroiditis

PancreasFunction: Glycogen in the Pancreas help to

keep the level of glucose in the blood stable.

Disorders: When the Pancreas fails to produce or properly use Insulin, it can cause a condition known as Diabetes Mellitus.

Functions: The adrenal glands

release Adrenaline in the body that helps prepare for and deal with stress.

Also regulates kidney function.

Adrenal Gland

OvariesFunctions: Pair of reproductive organs found in women that

produce eggs.Also secrete oestrogen and progesterone, which

control ovulation and menstruation.

Testes

Functions: Pair of reproductive glands that produces sperm. Also secrete testosterone to give the body its

masculine characteristics.

Pineal Gland

Functions:Secretes Melatonin

Regulates circadian rhythms (helps with sleeping)Promotes sexual developmentInfluences skin pigmentation

ThymusProduces the hormone thymosin, which

promotes the development of T lymphocytes (white blood cells) that are involved in immunity.

The thymus helps establish the immune system in the first few years of life, but stops working after puberty. It will then gradually reduce in size as we get older.

HORMONE SOURCESITE OF ACTION

REGULATES

InsulinPancreas – islets of

Langerhans (β cells)

Body cells Blood sugar level

GlucagonPancreas – islets of

Langerhans (α cells)

Liver Blood sugar level

Antidiuretic hormone (ADH)

Pituitary gland Kidney Water absorption

Thyroid stimulating

hormone (TSH)Anterior pituitary Thyroid gland

Thyroid hormone production

Thyroxine Thyroid Body cells Metabolic rate

Adrenaline AdrenalHeart and Muscles

Heart rate and oxygen uptake

QuestionsWhat is an endocrine gland?What is a hormone? How does it bring

about a response?

Words To KnowEndocrine SystemHormoneEndocrine gland

Comparison of Nervous System and Endocrine System

Neurons release neurotransmitters into a synapse, affecting postsynaptic cells.

Glands release hormones into the bloodstream.

Only target cells of hormone respond.

Comparison of Nervous System and Endocrine System

Complete this Table

FEATURE NERVOUS SYSTEM ENDOCRINE SYSTEM

Similarity

Medium of transmission

Speed of travel

Effectors

Duration of response

Example

Involves electrical transmission

Involves chemical transmission

Hormones in circulatory system

Nerves

Slow Fast

Tissues and glands

Specific location – muscles and

glands

Long Short

Water BalanceWater is the fluid medium in which

everything happens at the cellular level in organisms.

There must be a balance between loss and gain.

How can water be lost?

How can water be gained?

OsmoregulationThe regulation of water is described as

osmoregulation, a feedback mechanism that is under the control of hormones.

Effectively controlling the amount of water available for the cells to absorb.

Osmoregulation in Mammals

Water balance in mammals is directly link to blood pressure

It is also link to maintaining the salt levels in the body

Involves the kidney

OsmoregulationIncreased water raises the blood pressure

and decreased water lowers the blood pressure.

Two chemical compounds play a part:The hormone vasopressin is an ADH (Anti-

Diuretic Hormone) that aids reabsorption of water.

Renin is an enzyme that helps regulate sodium levels, and thus water levels in the blood.

LinksMcGraw-Hill animationMr Anderson explainsDetailed animation

How does vasopressin (ADH) work when we are dehydrated?

1. Osmoreceptors in the hypothalamus detect high concentrations of solutes in the blood (low water).

2. A thirst sensation is generated by the osmoreceptors.3. ADH is released from the hypothalamus.4. ADH travels to the posterior pituitary gland where

it is released into the blood.5. ADH travels to the kidneys where it increases the

permeability of the tubules to water.6. The kidneys reabsorb more water; the solute

concentration decreases.7. Water concentration in the blood increases.8. Negative feedback leads to a decreased secretion of

ADH from the hypothalamus.

How does renin work when we are dehydrated?1. Blood volume decreases and blood pressure falls.2. This reduces filtration taking place in the

glomerulus in the kidneys.3. Pressure-sensitive receptors in the kidneys detect

this.4. Renin is released into the blood by the kidneys.5. Renin initiates chemical reactions in the adrenal

glands which releases the hormone aldosterone.6. Aldosterone increases sodium ion reabsorption by

the kidneys back into the blood.7. Due to osmosis, water travels in the same

direction as the sodium ions.8. The blood pressure rises.

To sum it upDraw a negative feedback diagram showing

the stimulus, receptor, control centre, transmission of message, effectors and response.

Osmoregulation in WaterSome marine organisms body fluids are

isotonic to there external environmentAs long as they remain in their external

environment their internal environmental will stay stable

These organisms are called Osmoconformers

What happens then when the external environments are hypotonic or hypertonic to the internal environment of an organism?

Lets have a look

Do you remember this term?

Can you remember

these terms?

Osmoregulation in Fish

Murray CodFresh Water Fish

SnapperSalt Water Fish

With your knowledge of osmosis describe what would happen to each of these animals in terms of their salt and water levels if they did not have

ways to control it?

Osmoregulation in FishMurray CodFresh Water FishWould take in too much water. Would lose too much salt.

WHY?

WHY?

What types of adaptations are

these?

How does it maintain its salt water balance?Gills that are highly permeable to water and

salt. Scales that are impermeable to water and

salt.Rarely drinking water.Excreting large amounts of dilute urine.Actively absorbing salts by specialised cells in

the gills.

Osmoregulation in Fish

SnapperSalt Water FishWould lose too much waterWould take in to much salt

WHY?

WHY?

What types of adaptations are

these?

How does it maintain its salt water balance?Scales that are impermeable to water and

salt. Gills that are highly permeable to water and

salt.Drinking almost continuously.Producing small amounts of urine.Actively excreting salts from specialise cells in

the gills.

Adaptations to Regulate Water Balance

TO DO:Come up with a list of

Structural, Physiological and Behavioural

Adaptations that could help an organism regulate water

balance.

Adaptations to Regulate Water Balance

StructuralWaterproof

layerHairs or valves

guarding openings

CocoonsStore it

PhysiologicalReabsorb water

from faecesProduce highly

concentrated urine

Rely on metabolic water

Osmoconformers

Osmoregulators

BehaviouralSpend most time

in burrowsDrinking water

from environment

Words To KnowOsmoregulationOsmoregulatorOsmoconformer