1. The document discusses how hormones work and their mechanisms of action. It describes how steroid hormones bind to receptors and act as transcription factors, while peptide hormones bind to membrane receptors and trigger secondary messenger systems. 2. The hypothalamus controls hormone secretion from the pituitary gland via releasing factors. The pituitary gland secretes hormones that control processes like growth, reproduction, and homeostasis. 3. Iodine deficiency can cause goiter and harm fetal development. Scientists collaborate internationally to eliminate iodine deficiency disorders.

1. D.5. Hormones and metabolism
Miltiadis-Spyridon Kitsos
Platon IB Diploma
http://thumbs.dreamstime.com/z/mechanisms-hormone-action-hormones-bind-to-
receptors-plasma-membrane-itself-first-messenger-binding-to-40174339.jpg

2. The official IB Diploma Biology guide
Essential idea: Hormones are not secreted at a uniform rate and exert their effect at low concentrations.
https://ibpublishing.ibo.org/server2/rest/app/tsm.xql?doc=d_4
_biolo_gui_1402_1_e&part=3&chapter=6

3. Endocrine glands
Endocrine glands secrete hormones directly into the bloodstream
Endocrine glands are structures that secrete
chemical messages, called hormones, directly into
the blood. These messages are transported to
specific target cells
Types of hormones
• Steroids
• Proteins
• Glycoproteins
• Polypeptides
• Amines
• Tyrosine derivatives
http://www.myfirstbrain.com/thaidata/image.aspx?id=1045616
https://upload.wikimedia.org/wikipedia/commons/e/ea/1802
_Examples_of_Amine_Peptide_Protein_and_Steroid_Hormon
e_Structure.jpg
https://upload.wikimedia.org/wikipedia/commons/e/ea/1802_Exam
ples_of_Amine_Peptide_Protein_and_Steroid_Hormone_Structure.j
pg
http://www.austincc.edu/rfofi/NursingRvw/NursingPics/EndocrinePics/hormonesneurotrans
mitters.jpg

4. The mechanism of action of steroid hormones
Steroid hormones bind to receptor proteins in the cytoplasm o•the target cell to •orm a receptor-
hormone complex.
Steroid hormones can cross directly through the plasma membrane and the nuclear membrane and
bind to receptors
An example is estrogen. The receptor-hormone complex then serves as a transcription factor,
promoting or inhibiting the transcription of a certain gene.
http://physiologyonline.physiology.org/content/nips/16/6/251/F1.large.jpg?download=true

5. The receptor-hormone complex
The receptor-hormone complex promotes the transcription of specific genes
Transferred to specific target cells
Calciferol (steroid)-> binds to specific receptor in nucleus->promotes expression of calbindin (calcium
transport protein) -> absorption of calcium from the intestine.
http://www.thenutritiondr.com/files/CarbsProFat-Gluconeogenesis.jpg
Some steroids, such as cortisol, bind to receptors in the
cytoplasm and the receptor-hormone complex then
passes through the nuclear membrane into the nucleus
to effect transcription.

6. Cortisol may have different effects in different kinds of cells.
The receptor-hormone complex promotes the transcription of specific genes
The hormone may have different efects in different
cells and it may even have an inhibitory effect.
For example, when the steroid hormone cortisol
binds to its receptor in the cytoplasm of a liver cell
and enters the nucleus it activates many of the
genes needed for gluconeogenesis; i.e., the
conversion of fat and protein into glucose raising
blood glucose.
At the same time, it decreases the expression of the
insulin receptor gene, preventing glucose from
being stored in the cells and also raising blood
glucose.
In the pancreas, the cortisol receptor complex
inhibits the transcription of insulin genes.

7. Mechanism of action of peptide hormones
Peptide hormones bind to receptors in the plasma membrane of the target cell.
Protein hormones are hydrophilic so they
cannot pass through the membrane directly.
Instead they bind to surface receptors that
can trigger a cascade reaction mediated by
chemicals called second messengers.
http://lh5.ggpht.com/-
dqtzvTxoQxY/UL1RakaZIQI/AAAAAAAABhc/hgYZcTHFtJE/peptide%252520hormonal%252520a
ction_thumb%25255B6%25255D.png?imgmax=800

8. The role of secondary messengers
Binding of hormones to membrane receptors activates a cascade mediated by a second messenger
inside the cell
Second messengers: small water soluble molecules
spread throughout the cells
Relay messages
Calcium ions and cyclic AMP (cAMP) are the two
most common second messengers.
See how epinephrine (“fight or flight” hormones)
works
http://lh5.ggpht.com/-
dqtzvTxoQxY/UL1RakaZIQI/AAAAAAAABhc/hgYZcTHFtJE/peptide%252520hormonal%252520a
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http://highered.mheducation.com/sites/0072507470/student_view0/chapter17/animation__
second_messenger__camp.html

9. The role of secondary messengers
Binding of hormones to membrane receptors activates a cascade mediated by a second messenger
inside the cell
+GTP
(energy)

10. The pituitary hormones
Hormones secreted by the pituitary control growth, developmental changes, reproduction and
homeostasis.
http://www.zyropathy.com/wp-
content/uploads/2016/10/Pituitary-gland-anatomy.jpg
The anterior pituitary synthesizes and secretes a number
of hormones that control growth, reproduction and
homeostasis.
Examples include FSH and LH.
The posterior pituitary gland secretes oxytocin and ADH,
but these hormones are not produced there. Instead, they
are synthesized in unusual cells called neurosecretory
cells found in the hypothalamus.
The hormones travel down the axons
of the neurosecretory cells and are
stored at the ends of the axons, until
impulses pass down the axons from
the hypothalamus, stimulating
secretion.
http://highered.mheducation.com/sites/0072943696/student_v
iew0/chapter10/animation__hormonal_communication.html

11. The role of the hypothalamus
The hypothalamus controls hormone secretion by the anterior and posterior lobes of the pituitary gland
1. The hypothalamus links the nervous
system to the endocrine system via
the pituitary gland.
1. Both the nervous system and
the endocrine system play a role
in homeostasis and in the control
of other processes including
reproduction.
3. The role of the hypothalamus
is to secrete releasing factors,
which stimulate the secretion of
the anterior pituitary gland
hormones. The releasing factors
are carried from the
hypothalamus to the anterior
pituitary gland by a portal vein.
4. Negative feedback
mechanisms (e.g., ADH)
http://image.slidesharecdn.com/ch19lecturepresentation-140913124201-phpapp01/95/dr-b-
ch-19lecturepresentation-11-638.jpg?cb=1410612186

12. Regulation of milk secretion
Control of milk secretion by oxytocin and prolactin
Prolactin is a hormone produced by the anterior
pituitary found
During pregnancy, high levels of estrogen increase
prolactin production but inhibit the effects of prolactin on
mammary glands.
The abrupt decline in estrogen and progesterone
following delivery removes this inhibition and the
production of milk begins.
However, the release of the milk after it is produced
depends on the hormone oxytocin.
Nursing by an infant stimulates the continued creation
of prolactin. It also stimulates oxytocin release.
Oxytocin stimulates the contraction of cells that
surround the structures holding the milk leading to the
ejection of the milk.
Positive feedback loops
http://archive.cnx.org/resources/75a2ecfbb8e17ade7cfcff7595c410a62
49ba2a0/2922_Let_Down_Reflex-new.jpg

13. Injection of growth hormone by athletes
Some athletes take growth hormones to build muscles
Growth hormone is another polypeptide hormone
produced in the anterior pituitary.
The binding of growth hormone to liver cells stimulates
the release of insulin-like growth factor which circulates
in the blood and stimulates bone and cartilage growth.
Additional effects, one of which is increase in muscle
mass.
While it is clear that it leads to greater muscle mass, the
data is not clear that it leads to greater strength.
Another claim is that it allows tired muscles to recover
more quickly allowing an individual to train harder and
more often
The scientific research on the topic suggests that the
benefits provided in terms of enhanced performance
are small or non-existent compared to the risks of
injecting the hormone. For this reason, use of the drug
is banned by most international sporting federations.
https://upload.wikimedia.org/wikipedia/commons/thumb/9/99/Endocri
ne_growth_regulation.svg/240px-Endocrine_growth_regulation.svg.png

14. The negative effects of the use of the human growth hormone
Some athletes take growth hormones to build muscles
https://lehman-cuny.digication.com/files/M0045c1f4ed6a253aeaf19acc1c695f61.jpg

15. Eradicating iodine deficiency
Cooperation and collaboration between groups of scientists: the International Council for the Control of
Iodine Deficiency Disorders includes a number of scientists who work to eliminate the harm done by
iodine deficiency.
http://wisemensvitamins.com/wp-content/uploads/2010/12/iodine-deficiency-symptoms.jpg
Thyroid hormone refers to two similar
hormones derived from tyrosine.
Triiodothyronine (T3 ) contains three iodine
atoms and tetraiodothyronine (T 4 ) contains
four iodine atoms.
Correct functioning of the thyroid requires
iodine in the diet. If there is dietary
insufficiency, then there are a number of
consequences including a condition known
as goiter.
https://highered.mheducation.com/sites/9834092339/student
_view0/chapter46/mechanism_of_thyroxine_action.html
The inability to produce the thyroid hormones because
of the absence of iodine means that the hypothalamus
and the anterior pituitary continuously stimulate the
thyroid and enlargement of the thyroid results.
Iodine defciency during pregnancy can affect fetal
nervous development and can lead to mental
retardation in children.

16. Eradicating iodine deficiency
Cooperation and collaboration between groups of scientists: the International Council for the Control of
Iodine Deficiency Disorders includes a number of scientists who work to eliminate the harm done by
iodine deficiency.