UNIT 2 BIOLOGY
Organisms and Their
Environment
Area of Study 1: Adaptations of Organisms
WEEK 2: Learning Outcomes
By 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 Control
 Feedback 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 Feedback
 Negative 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 Feedback
 Positive 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)
System
 Hormones 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 System
 There 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
Hormones
 There 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.
Hormones
SPECIFICITY
 The 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 ACTION
 The 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 ACTION
 Once 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 HORMONES
 Pairs 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
FUNCTION
 It 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 Wadlow
1918 - 1940
2.7m tall
Thyroid Gland
Function: 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
Pancreas
 Function: 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.
Adrenal Gland
Functions:
 The adrenal glands release
Adrenaline in the body that
helps prepare for and deal
with stress.
 Also regulates kidney
function.
Ovaries
Functions:
 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 development
 Influences skin pigmentation
Thymus
 Produces 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
SOURCE
SITE OF
ACTION
Insulin
Pancreas – islets of
Langerhans (β cells)
Body cells
Blood sugar level
Glucagon
Pancreas – 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
Adrenal
Heart and Muscles
Heart rate and
oxygen uptake
REGULATES
Questions
 What is an endocrine gland?
 What is a hormone? How does it bring about a
response?
Words To Know
Endocrine System
Hormone
Endocrine 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
Similarity
Medium of transmission
Speed of travel
Effectors
Duration of response
Example
NERVOUS SYSTEM
ENDOCRINE SYSTEM
Involves electrical
transmission
Involves chemical
transmission
Nerves
Hormones in
circulatory system
Fast
Slow
Specific location –
muscles and glands
Tissues and glands
Short
Long
Water Balance
 Water 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?
Osmoregulation
 The 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
Osmoregulation
 Increased 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.
Links
 McGraw-Hill animation
 Mr Anderson explains
 Detailed animation
How does vasopressin (ADH)
work when we are dehydrated?
1. Osmoreceptors in the hypothalamus detect high
2.
3.
4.
5.
6.
7.
8.
concentrations of solutes in the blood (low water).
A thirst sensation is generated by the osmoreceptors.
ADH is released from the hypothalamus.
ADH travels to the posterior pituitary gland where it
is released into the blood.
ADH travels to the kidneys where it increases the
permeability of the tubules to water.
The kidneys reabsorb more water; the solute
concentration decreases.
Water concentration in the blood increases.
Negative feedback leads to a decreased secretion of
ADH from the hypothalamus.
How does renin work when we
are dehydrated?
1.
2.
3.
4.
5.
6.
7.
8.
Blood volume decreases and blood pressure falls.
This reduces filtration taking place in the
glomerulus in the kidneys.
Pressure-sensitive receptors in the kidneys
detect this.
Renin is released into the blood by the kidneys.
Renin initiates chemical reactions in the adrenal
glands which releases the hormone aldosterone.
Aldosterone increases sodium ion reabsorption by
the kidneys back into the blood.
Due to osmosis, water travels in the same
direction as the sodium ions.
The blood pressure rises.
To sum it up
 Draw a negative feedback diagram showing the
stimulus, receptor, control centre,
transmission of message, effectors and
response.
Do you
remember
this
term?
Osmoregulation in Water
 Some marine organisms body fluids are isotonic
to there external environment
 As long as they remain in their external
environment their internal environmental will
stay stable
Can you
 These organisms are called Osmoconformers
remember
these
terms?
 What happens then when the external
environments are hypotonic or hypertonic to
the internal environment of an organism?
Lets have a look
Osmoregulation in Fish
Murray Cod
Fresh Water Fish
Snapper
Salt 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 Fish
Murray Cod
WHY?
Fresh Water Fish
 Would take in too much water.
 Would lose too much salt.
WHY?
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.
What types of
 Rarely drinking water.
adaptations are
these?
 Excreting large amounts of dilute urine.
 Actively absorbing salts by specialised cells in the
gills.
Osmoregulation in Fish
WHY?
Snapper
Salt Water Fish
 Would lose too much water
 Would take in to much salt
WHY?
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.
What types of
adaptations are
 Producing small amounts of urine.
these?
 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
Behavioural
Physiological
Structural
 Reabsorb water  Spend most time
 Waterproof
in burrows
from
faeces
layer
 Drinking water
 Produce highly
 Hairs or valves
from environment
concentrated
guarding openings urine
 Cocoons
 Rely on metabolic
 Store it
water
 Osmoconformers
 Osmoregulators
Words To Know
 Osmoregulation
 Osmoregulator
 Osmoconformer