Download Option H Further Human Physiology

Option H
Further Human Physiology
Section
Hormonal Control
Digestion
Absorption of Digested Foods
Functions of the Liver
The Transport System
Gas Exchange
Self-test Quiz
Answers
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IB Biology Option H 2012
Hormonal
Control
™
Hormonal Control
A genetically conditioned target cell means
that it has the specific hormone receptor
either on its surface or in the cytoplasm.
Hormones are chemical messengers secreted into
the blood by endocrine glands and transported by
the blood to genetically conditioned target cells.
Hormones can be –
ƒ steroids, eg. progesterone;
ƒ peptides, eg. oxytocin;
ƒ tyrosine derivatives, eg. thyroxin.
Mode of Action of Hormones
1. Steroid hormones
1
1
Steroid hormone in blood passes
through plasma membrane into
cytoplasm of target cell and binds
to specific receptor protein.
2
Receptor-hormone complex enters
nucleus through nuclear pore and
binds to DNA.
3
Transcription results in mRNA
which leaves nucleus and binds to
ribosome.
4
Translation results in a protein such
as an enzyme that alters the
metabolism of the target cell.
2
3
4
blood plasma
target cell
2. Peptide hormones
1
2
Peptide hormone in blood binds to
specific receptor glycoprotein
on plasma membrane of
target cell.
1
2
This triggers the release of a second
messenger system
within the cell.
3
A
3
This in turn modifies the activity of
the cell, usually by activating or
inhibiting an enzyme controlling a
specific reaction.
enzyme
B
blood plasma
target cell
IB Biology Option H 2012
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Hormonal
Control
The Hypothalamus and Pituitary Gland
Key features
¾ The pituitary gland has two parts.
¾ The posterior pituitary is part of the brain and connected to it directly. It simply
stores hormones that have been produced by neurosecretory cells in the
hypothalamus. Examples are ADH and oxytocin.
¾ The anterior pituitary is a separate glandular structure producing its own
hormones. The release of these hormones is still controlled by the brain by
another set of hormones, called releasing hormones, produced by the
hypothalamus. An example is thyroid stimulating hormone (TSH) controlled by
thyrotropin releasing hormone (TRH).
neurosecretory
cells
hypothalamus
Neurosecretory cells are
modified nerve cells that
secrete chemicals that act
as hormones. They are
sometimes called
neurohormones. These
(neuro)hormones travel
down the axon and are
stored at the ends. Their
release is controlled by
nerve impulses from the
cell body.
neurosecretory
cells
From carotid
artery
The portal vessel carries the
releasing hormones from the
capillaries in the hypothalamus
to the capillaries in the anterior
pituitary.
posterior pituitary
portal vessel
anterior pituitary
To vena cava
A vertical section through the
hypothalamus and pituitary gland.
Control of ADH Secretion
Key sequence
Osmoreceptors
in hypothalamus
+
Neurosecretory cells in
hypothalamus secrete ADH
Blood concentration too
low - negative feedback
to decrease plasma ADH
Blood concentration too
high - negative feedback
to increase plasma ADH
Water potential of blood
monitored by osmoreceptors
in hypothalamus. The
osmoreceptors control the
activity of the neurosecretory
cells.
Relate this
sequence to the
structures in the
diagram above.
Transported by axons,
stored in and released
from posterior pituitary
If the posterior pituitary does not
release any ADH it quickly
disappears from the blood as it
only lasts for a few minutes.
transported by blood
Kidney absorbs more water
(ADH present) or less water
(ADH absent)
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IB Biology Option H 2012