Transcript Chp 15 Homeostasis in Animals

V.C.E. Biology Unit 2
Regulatory mechanisms in animals
Homeostasis
 Homeostasis is the maintenance of a
relatively stable internal environment within
an organism.
 Sensors within the animals allow it to monitor
the levels of glucose, water, oxygen, carbon
dioxide etc and respond in an appropriate
manner.
Negative Feedback Systems
 An example of negative
feedback is the control of
glucose levels in the blood.
If glucose falls to low the
pancreas releases glucagon
to cause stores of glycogen
to be converted to glucose
and released into the blood.
If glucose then rises too high
the pancreas will release
insulin which tells the bodies
cells to absorb glucose.
Hormonal Responses
 In animals each hormone
has a particular, specific
function.
 Hormones are produced in
the endocrine glands,
travel through the blood
system and have an
impact at a specific target
cell(s), and only that
cell(s).
 The effect of hormones
last for a reasonably long
time.
Hormonal Responses
 Hormones are involved in regulating glucose,
salt, heart activity, protein synthesis, hair
follicle development, adolescence, milk
secretion, pregnancy, calcium levels, water
levels, mood, metabolic rate etc.
Nervous systems
 The nervous system is
made up of the central
nervous system (brain
and spinal cord) and
the peripheral nervous
system (the sensory
and effector tissues).
 Nervous responses are
very quick, but their
effect does not last for
long.
Nervous Systems – Sensory Organs
 A number of organs
receive information from
the external
environment. These are:
 Eyes
 Ears
 Tongue
 Nose
 Mechanoreceptors in
the skin
Nervous System - Neurons
 There are many types of nerves, but they





all contain the same major components.
Dendrites – fibres which collect
information as electrical impulses.
Cell Body – contains the cells organelles,
including the nucleus.
Axon – passes the electrical impulse to
the next nerve.
Synaptic Terminal – the end of the axon
passes a chemical signal to the next
nerve.
Myelin Sheath – this layer of fat insulates
the nerve impulse, so that it isn’t lost to
the surrounding tissue and fluid.
Nervous System – action potential
 The message is passed down an axon by
electrical differences between sodium and
potassium ions.
Nervous system - Brain
 The brain is a large
organ comprised of
neurons, blood
vessels and
endocrine glands.
 It coordinates the
information received
by the sensory
organs, processes
that information and
organises an
appropriate
response. It also
stores information –
allowing memory and
learning.
Nervous Systems – Reflex Arc
 Not all responses are coordinated by the
CNS.
 In the case of a reflex reaction, the response
to the stimulus is almost instantaneous.
 It occurs so that harm does not occur to the
individual.