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The endocrine system:
Made up of glands that produce and secrete the hormones and chemical substances made in the
body that regulate the activity of cells or organs
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Hormones are chemicals released from glands in the body into the blood at certain times to regulate
specific biological processes by affecting cells in another part of the body
Endocrine glands secrete hormones into the blood
Regulate metabolic functions of other cells (called target cells)
Carried to all cells but action is specific to cells that have specific receptors for the cells
Some hormones act on receptors in specific tissues (e
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sex hormones)
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g
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(e
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Insulin and oxytocin)
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Steroid hormones are not water soluble = circulate bound to plasma proteins (e
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oestrogen,
progesterone, testosterone)
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When hormones are secreted into the blood supply most become protein bound leaving only a few
(unbound and able to access the target cells) and physiologically active
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Hormone release is often stimulated by neurological stimulation
Sometimes hormone release is stimulated by other hormones
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The negative feedback tends to slow down a process and maintain stability whereas positive
feedback tends to speed it up and generate a rapid change
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E
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oxytocin
in labour
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The strong contractions stimulate the uterus to release
prostaglandins)1 or (the pituitary gland sends a signal by way of the hormone oxytocin to the uterus
causing contractions
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This causes more contractions
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The system continues till birth occurs)
Negative feedback:
An increase in hormone levels will cause a decrease in the levels of another substance
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g insulin
and blood glucose
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Increased glucose is detected by receptors in that notify the brain
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Pancreas stops making insulin
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Blood reduces appetite
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Most hormones work by negative feedback
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In diabetes there is a problem with the negative feedback system
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The target cells have become resistant and unresponsive to insulin
2
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Glucose does not enter the muscle and liver cells like it should and builds up in the blood
causing complications
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com/what-is-the-role-of-oxytocin-in-labor/

An agonist is a substance that binds to a receptor on the cell membrane and activates a response
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A competitive antagonist blocks the action of the specific hormone that normally binds to the site
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They have similar structures, so oxytocin
can bind to the same target cell cause the same biological response
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Follicle Stimulating Hormone (FSH):
Part of the menstrual cycle
Released from pituitary gland (anterior) after puberty to stimulate ovaries
Minimal levels in pregnancy as reproductive cycle not required
Lutenising Hormone (LH):
Released from pituitary gland (anterior)
Triggers ovulation
Protects eggs in ovaries
Oestrogen:
Secreted by the ovary
A small amount is secreted by the corpus luteum until the placenta is fully functional (around 12
weeks)
The oestrogenic group of hormones comprises three hormones:
- Oestradiol = it is the most active hormone present in almost all mammals
- Oestrone = it is a circulating hormone
- Oestriol = it is found in the urine of pregnant women and in the placenta
Regulates the menstrual cycle
Initially it makes girls develop into women (during puberty) by stimulating breast growth (prepares
the glands for future milk production), thickening the vagina (helps maintain a lubricated and thick
vaginal lining) and causing it to secrete mucous
During the follicular phase of the menstrual cycle, oestrogen grows and matures the uterine lining
and later triggers ovulation, provoking further changes if conception occurs
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When
levels of oestrogen in the blood are highest the hypothalamus in the brain release hormones that
make a follicle release an egg (LH), therefore if you are not producing enough oestrogen you will not
ovulate
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In early pregnancy,
oestrogen promotes the growth of breasts; later, it helps develop their milk-making machinery
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4
Progesterone:
2

https://www
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com/hormones/estrogen/role-effects
http://www
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org
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whattoexpect
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g
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g
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The amygdala reacts to threat
2
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The adrenal cortex releases cortisol for continued alertness
Responses include:
- Dilation of pupil
- Fast breathing
- Dry mouth
- Heart pounding
- Tense muscles
- Slow digestion
- Sweating of palms
Relation to childbirth (F or F):
- Varies for each woman
- Fear, panic, anger, disgust, anxiety are emotions that can be triggered by the fear of experience or
pain, bad or mixed emotions of previous births
- Baby in distress
- Amygdala (limbic system/emotional brain) triggers released of cortisol and catecholamines
- Blood diverted to brain and skeletal muscle, away from uterus and placenta
- Catecholamines incompatible with oxytocin = decrease in number and duration of contractions
Oxytocin vs Adrenaline in labour:
Adrenaline causes fight or flight =
- Muscles tighten
- Energy sent to limbs
- Increased sensitivity to pain
Oxytocin causes collect and protect (‘love hormone’) =
- Muscles relax
- Energy sent to uterus
- Decreased sensitivity to/awareness of pain
Growth Hormone:
Produced by the pituitary gland in response to growth releasing hormone from hypothalamus
Helps control metabolism

Stimulates growth of tissues and organs, especially bones muscle, liver, kidney
Immunological function
Increase red and white cell production
Thyroid Hormones:
Two hormones produced and released by the thyroid gland, namely triiodothyronine (T3) and thyroxine
(T4)
Primarily responsible for regulation of metabolism to regulate body functions – linked with physical,
mental growth, cardiac and nervous system
When T3 and T4 levels are low in the blood, the pituitary gland releases thyroid stimulating hormone (TSH)
to tell the thyroid gland to produce more thyroid hormones
If T3 and T4 levels are high, the pituitary gland releases less TSH to the thyroid gland to slow production of
these hormones
TSH also assists in early pregnancy to maintain pregnancy until placenta is functional
Calcitonin:
Produced by the c-cells in the thyroid gland
Regulates the blood’s calcium and potassium levels
Inhibits the activity of osteoclasts, the cells that break down bone
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By preventing the breakdown of bone, calcitonin lessens the
amount of calcium in the blood
Also decreases the amount of calcium the kidneys can reabsorb, lowering levels further
Importance not well understood
Secretion of this hormone is controlled directly by the blood’s calcium levels
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When calcium levels drop, so do calcitonin
levels

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