The Endocrine System
The endocrine system uses chemical messengers called hormones to transfer
information around your body. Hormones are made in special organs called endocrine
glands.
The major glands that make up the
human endocrine system are the:
hypothalamus, pituitary gland, thyroid,
parathyroids, adrenals, pineal body,
reproductive glands (ovaries and testes),
and the pancreas.
The pituitary gland is the master gland
as it makes hormones but also tells
many other endocrine glands to release
their hormones as well. The pituitary
gland receives messages from the
hypothalamus in the brain so it provides
the link between the nervous system and
the endocrine system.
Hormones travel all around your body in
the blood but only act on target cells
that have the right receptor.
The
hormone binds to the receptor like a key
fits in a lock then it triggers changes in
the cells behaviour.
Several hormones come into play as you
exercise. Glucogon and insulin are
produced by the pancreas and regulate glucose levels and therefore the amount of energy
available for muscle contractions. Antidiuretic hormone (ADH) is produced by the
posterior lobe of the pituitary gland and helps control body water balance through its effect
on the kidneys and urine output. Aldeosterone is produced by the adrenals and also
helps regulate salt and water balance. The adrenals also produce adrenaline which
increases blood pressure and heart rate. If you have been exercising for an extended
period of time, you will appreciate the effects endorphins which are secreted by the
pituitary gland and act on the nervous system to reduce sensitivity to pain (think runner’s
high!).
Some hormones including testosterone, epitestosterone, human growth hormone and
erythropoietin have been identified as performance-enhancing drugs and may be used by
athletes in an attempt to improve performance in their chosen field.
The Endocrine System
Label the organs of the endocrine system on the diagram below.
The Endocrine System
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Chemical messengers that transfer information around your body.
Organs where hormones are made.
This gland is referred to as the master gland.
This part of the brain sends messages to the master gland.
Hormones only act on these.
These secrete the female sex hormones.
This gland secretes hormones that regulate glucose levels.
These secrete the male sex hormones.
These glands are found on the top of the kidneys.
This lobe of the pituitary gland is responsible for the production of ADH.
Along with ADH this hormone helps regulate salt and water balance.
This hormone increases blood pressure and heart rate.
Responsible for runner's high.
A hormone binds to this.
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The Nervous System
Your nervous system controls and co-ordinates all parts of your body. It can be
divided into two parts: the central nervous system (CNS) and the peripheral
nervous system (PNS).
The central nervous system (CNS)
is made up of the brain and spinal
cord. It acts as the control centre,
receiving messages from all parts of
the body then sending messages to
tell different parts of the body how to
respond. The brain and spinal cord
are surrounded by three layers of
connective
tissue
called
the
meninges. The brain is protected by
the cranium and the spinal cord is
protected by the bony spinal column.
The peripheral nervous system
(PNS) connects the CNS to the rest of
the body. The nerves in the CNS fall
into two categories, sensory neurons
and motor neurons.
Sensory or
afferent nerves carry information to
the CNS, while motor or efferent
nerves carry information away from
the CNS. Interneurons are found
only in the central nervous system
where they connect sensory neurons
to other neurons. They are also
called connecting neurons.
The motor nerves can be further divided into autonomic and somatic nerves.
Autonomic (involuntary) nerves control things that you don’t think about – like your
heart beating or your small intestine working. Somatic (voluntary) nerves control
movements that you are aware of – like your skeletal muscles, bones and sensory
organs. We can further divide the autonomic nerves into two types (sympathetic
and parasympathetic).
Sympathetic nerves generally excite or speed up an
organ in response to stimuli (e.g. heart beating faster after a fright) while
parasympathetic nerves general retard or slow down an organ after it has
responded (e.g. slow heart beat back to normal).
The Nervous System
The CNS and PNS are made of neurons or nerve cells. They are special cells that
transmit and receive messages in the form of electrical impulses. Neurons come in
different shapes and sizes, but they all have 3 distinct parts:
1. Cell body or soma – contains the
nucleus and all the things needed for
the neuron to keep functioning (the
nucleus is the ‘brain’ of the cell).
2. Dendrites – these small branches stick
out from the cell body. Their job is to
carry information to the cell body.
3. Axon – also called the nerve fibre, this
part of the neuron carries information
away from the cell body. The end of
the nerve fibre is called the terminal
end. Most axons are wrapped in a
sheath called the myelin sheath. The
myelin sheath is made up of glial cells
referred to as Schwann’s cells. Gaps
in the myelin sheath are called Nodes
of Ranvier.
Neurons communicate with other cells by
means
of
chemicals,
known
as
neurotransmitters.
In the nervous
system, the passage of a nerve impulse
along one neuron involves electrical
changes (an action potential), while the
transmission from cell to cell involves diffusion
of neurotransmitters across the synapse or
gap between the axon terminals of the
transmitting neuron and the dendrites of the
receiving neuron. As nerve impulse travels, it
changes from an electrical message (within
the neuron) to a chemical message across the
synapses, then back to an electrical message
again in the next neuron. Painkilling drugs
work
by
blocking
the
release
of
neurotransmitters into the synapses.
The Nervous System
Label the neuron below using the words in the box below.
soma
nucleus
dendrites
axon
myelin sheath
terminal end
Nodes of Ranvier
The Nervous System
Down
1. these small branches stick out from the cell body of a neuron.
3. the gap between the axon terminals of a transmitting neuron and the dendrites of the receiving
neuron.
4. the autonomic nervous system is called autonomic because the organs it activates or retards
function ________________ of our control.
5. neurons use these chemicals to communicate with other cells.
9. electrical changes within an axon are referred to as an ________________ potential.
11. gaps in the myelin sheath are referred to as Nodes of ______________.
12. the somatic nervous system controls _______________ muscles.
13. breathing and salivation are functions controlled by this branch of the PNS.
15. motor neurons are also called ________________ neurons.
16. three layers of connective tissue surrounding the brain and spinal cord.
17. _____________ neurons carry information away from the CNS towards your muscles, skin,
internal organs and glands.
18. _______________________ nerves carry information from the internal organs or outside
environment to the CNS.
Across
2. PNS stands for this.
6. the myelin sheath is composed of this type of cell.
7. These work by blocking the release of neurotransmitters into the synapses.
8. Another name for the cell body of a neuron.
9. sensory neurons are also called ________________ neurons.
10. also known as the nerve fibre.
14. This type of neuron is only found in the CNS.
19. your nervous system controls and ________________ all parts of your body.
20. CNS stands for this.