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Regulatory
Mechanisms
in Animals
Regulatory Pathways
In animals the two regulatory pathways are the endocrine system
and the nervous system. The overall aim of these two pathways is to
maintain a stable internal environment in the face of changing
conditions: to maintain homeostasis.
Both the nervous system and the endocrine system exert their effects
by highly specific interactions with a receptor on, or within, the
responding or target cell. This means that both systems use chemical
communication.
Negative Feedback System
-
The negative feedback system
involves the nervous or hormonal
systems, or both acting together
to promote stability of the internal
environment. They are stimulusresponse mechanisms in which Response
which restores
the response produced
original state
reduced the effect of the
original stimulus.
The response provides
feedback that has a
negative effect on the
stimulus.
Stimulus
Receptor
Control Centre
Effector
Hormones:
‘Hormone’ does not refer to a particular type of chemical
compound but to a diverse group of compounds that act as
intercellular messengers and regulate cell function.
• In animals hormones are produced by cells in one o[part
of the body and is transported throughout the organism
via internal transport systems
• They transmit their signal to target cells which have
receptors that are specific for certain hormones.
• Hormones exert their effects either directly by passing
straight through the plasma membrane into the cell or by
interactging with the receptor on the outside of the cell.
Hormone Specificity and Speed:
Hormonal communication is specific for two reasons:
Firstly:
• A particular stimulus will only affect a specific group of
hormone secreting cells.
Secondly:
• Although hormones pass throughout the organism only those
cells which posses specific receptors are capable of
responding to the hormone.
Hormonal effects are generally slower than nervous responses,
longer in duration and affect cells which are widely distributed
around the body.
Types of Hormones
The are two main groups of hormone: hormones produced from
fatty acids and hormones produced from amino acids.
Hormones produced from fatty acids:
• Are small and lipid soluble
• Can easily pass through plasma membranes
• Usually interact eith genes in the nuleus to cause a change or
response
• Include hormones such as oestrogen and testosterone
Hormones produced from amino acids:
• Are water soluble
• Cannot pass through the plasma membrane
• Binds to receptors on the outside of the cell which cause a
response inside the cell
• Include hormones such as adrenaline and growth hormone
Endocrine Glands:
In animals cells that produce hormones are usually clustered
together in discrete organs known as endocrine glands.
Examples of hormones in animals:
Gland
Hormone
Tangent
Function
Adrenal
cortex
Glucocorticoids
Many cell types
Promotes synthesis of glucose
Mineralocorticoids
Kidney tubes
Regulates reabsorption of salts
Adrenal
medulla
Adrenaline
Heart, blood
vessels, liver, fat
Increases cardiac output,
mobilises glucose, prepares body
for action
Anterior
pituitary
Adrenocorticotrophic Hormone
(ACTH)
Adrenal cortex
Promotes release of adrenal
cortex hormone
Growth Stimulating Hormone
(GSH)
Bone, muscle
Promotes protein synthesis and
growth
Follicle Stimulating Hormone
(FSH)
Ovary
Promotes development of follicle
and secretion of oestrogen
Luteinising Hormone (LH)
Ovary
Promotes ovulation and the
secretion of progesterone
Prolactin
Mammary glands
Stimulates milk secretion
Thyroid Stimulating Hormone
(TSH)
Thyroid
Promotes production and release
of thyroxine
Gland
Hormone
Tangent
Function
Hypothalamus
Several releasing
hormones
Anterior pituitary
Controls release of anterior
pituitary hormones
Ovary
Oestrogen
Reproductive tract,
body generally
Promotes menstruation cycle,
development of female
features and behaviours
Progesterone
Uterus
Prepares uterus for and
maintains pregnancy
Insulin
Muscle, liver, fat
Lowers blood glucose
Glucagon
Liver, fat
Raises blood glucose
Parathyroid
Parathyroid
Hormone
Bone, kidney
Raises blood calcium
Posterior
Pituitary
Oxytocin
Mammary gland
Causes release of milk
Antidiuretic
hormone
Kidney
Promotes reabsorption of
eater from collecting tubules
Pineal
Melatonin
Brain
Daily and seasonal cycles
Pancreas
Gland
Hormone
Tangent
Function
Testis
Testosterone
Reproductive tract, the
body generally
Development of masculine
features and behaviour
Thyroid
Thyroxine
Most cells
Regulates cellular metabolic
rate
The Pituitary Gland:
The pituitary gland plays a central role in overall endocrine regulation. More
than half of the hormones in mammals are either released from the pituitary
gland or are used to release hormones from the pituitary gland.
The pituitary gland secretes hormones involved in:
• The regulation of growth
• Lactation
• Reproductive state
• Skin pigmentation
• Fat tissue
• Kidney function
• The activity of the thyroid gland
• The activity of the adrenal glands
The pituitary gland lies immediately below the hypothalamus. The
hypothalamus receives information from the body regarding its overall
state of well being, such as the level of hunger or thirst, smell, pain and
emotions. This information is used to regulate hormone release from the
pituitary gland.
The Nervous System:
• The nervous system is usually a more direct mode of communication
between parts of the body than hormones.
• Control by nerves is generally rapid, short in duration and precisely located.
• Nervous responses require more energy than hormonal responses
Reflex Responses:
The ability to detect and quickly respond to changes in the internal and
external environments in fundamental to the survival of all animals. Many reflex
response protect the body from further injury.
A common example of a reflex response
occurs when you prick your finger. You will
find that your finger has already been removed
form the stimulus before you feel the pain. This
occurs because the scnsory receptor on your
finger has sent a message via the sensory
neuron to the CNS where interneurons connect
this neuron to motor neruron to send a message
back to an effector mucle to contract and
escape the stimulus causing the pain.
The Human Nervous System:
Mammals have a central nervous system and a peripheral nervous system.
Central Nervous System:
• Is made up of the brain and the spinal cord.
• Different regions of the brain are associated with different functions:
- The cerebral cortex has areas associated with motor activity ,
sensory input, speech, sight and hearing
- The hypothalamus recieves information relating to the wellbeing of the body and functions in maintaining homeostasis
- The cerebellum is involved in the coordination of muscular
activity, including posture, balance and movement
- The brainstem has centres associated with the control of the
heart, blood vessels and lung ventilation
The Peripheral Nervous System:
•
•
Includes sensory nerves which carry information towards the CNS and motor nerves
which carry information away from the CNS to effector organs such as muscles and
glands
The peripheral nervous system can also being split into two different divisions:
The somatic nervous system:
• which is voluntary movement such as movement by skeletal muscles
The autonomic nervous system:
• it conveys signals to smooth muscle, heart muscle and gladnular tissues, and
regulates the activities of the digestive, cardiovascular, respiritory andf endocrine
systems
System/Role
Function
Cardiovascular system
Controls the rate and strength od the heartbeat and the distribution of blood to
different organs by change in the diameter of the arteries
Digestive system
Controls mixing and movement of food through gut and secretion of various enzymes
Respiratory system
Controls the diameter of major airways of lungs and the secretion of mucus over surface
Excretory system
Promotes emptying of the bladder and the rate urine production by kidneys
Reproductive system
Controls contraction of reproductive tract and thus passage of eggs, sperm and embryo
Metabolic regulation
Control the formation and release of hormones affecting overall metabolism
Temperature regulation
Controls cutaneous blood flow and sweating
Eye function
Controls the diameter of the pupil to regulate incoming light and focusing of lens
The Senses:
Sense
Receptor/ Response
Structure
Vision:
Photoreceptor cells
which contain light
sensitive pigments
interact with the light
to produce an
electrical signal in a
sensory nerve.
Simple eyes:
• Are single
chambered eyes
which rely on a lens,
cornea or both to
form an image on the
photoreceptors of the
retina.
• This type of creates a
higher resolution than
compound eyes.
• Humans have a
simple eye.
There are two types
of eyes:
Compound eyes:
• Are found in insects.
• They have several
lens systems which
are all used to form
the one image.
Picture
Hearing:
Sound travels as vibrations through the air, water and solids.
Animals can detect sound using mechanoreceptors, which are
sensory neurons that can detect minute vibrations
Taste and Smell
Chemoreceptors are cells sensitive to different chemicals.
Many animals have receptors for specific chemicals which can
signal sexual readiness, or the proximity of predators or prey.
Mechanoreception:
Cutaneous mechanoreceptors detect external stimuli such as
pressure and touch. Whilst a range of receptors detect
internal mechanical stimuli such as joint position, muscle
tensions and tension in the walls of the lungs and stomach
Pain:
All animals with a nervous system avoid encounters with
harmful external stimuli.
Neurons
Neurons, the functional unit of the nervous system, consist of:
• A cell body which performs normal cell functions (such as making proteins)
• Dendrites which carry impulses towards the cell body
• Axons which carry impulses away from the cell body to the next neuron
There is only one axon leaving the cell body but many dendrites bringing
impulses into the cell body.
Synapses are found at the axon terminals. Synapses are specialised regions
where information is communicated from a nerve cell to another nerve cell of
effect muscle.
Myelin sheath is a fatty tissue which
insulates the axon.
Neurons are grouped together into
bundles called nerves. A single nerve
may have several hundred axons
running side by side
Neurons are excitable cells:
In excitable cells movement of ions across
the membrane causes changes in the level
of polarisation causes a physiological
response by the cell.
There are 3 basic steps involved in the function of nerve cells and the way
they conduct signals in the nervous system:
1. Generation of a nerve impulse (action potential) by sensory neurons
2. Conduction (propagation) of an impulse along axons
3. Chemical transmission of a signal to another cell across a synapse
Sensory nerves respond to stimuli by depolarising the nerve cell. It does this
by making the inside of the cell less negative. If depolarisation is large
enough an action potenial will be generated.
The action potential will then be conducted along the axon to the axon
terminal
At the terminals neurotransmitters are released and they diffuse across the
synapse and bind to specific receptors on the postsynaptic plasma
membrane
The Action Potential:
• A nerve impulse or action potential is a wave of electrical change
which passes rapidly along the axon membrane.
• The action potential does not vary in size. It is either sufficient to
generate the action potential (pass the threshold potential) or it is not.
This is often referred to an the ‘all or none’ law.
• The intensity of a stimulus is conveyed by the number of action
potentials generated.
• A region that has just generated an action potential cannot produce
another one for a brief period known as a refractory period.
Glossary:
Homeostasis
Negative feedback
Target cells
Endocrine glands
Pituitary gland
Neuron
Effector cells
Reflex
Interneurons
Flexion
Extension
Action potential
Conduction
Transmission
Synapse
Depolarisation
Threshold potential
Refractory period
Complete the following:
Key Questions:
1, 2, 3, 4, 5, 6, 7, 9, 11, 12, 13, 14
Chapter Review Questions:
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12