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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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It also cracks down on pre-pregnancy's natural contractions of the
smooth muscle of the uterus, allowing your baby to grow in the expanding womb
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Lax muscles in the lower intestine, for example, allow gases to distend the bowel, bringing
about a bloated belly
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5
Oxytocin:
Produced by hypothalamus and secreted by pituitary
Released during sex, childbirth and lactation
Crucial role in the childbirth process
Increases the production of prostaglandins stimulating the onset of labour
Increases uterine motility causing contractions
Initiates lactation, moving milk to breast and stimulating release in response to suckling by baby
Impacts emotional, cognitive and social behaviours – may decrease stress responses
Prolactin:
Secreted during pregnancy to prepare breasts for lactation, even in early pregnancy
Produced in the puerperium to initiate and prepare for lactation
Production of prolactin is controlled by two main hormones = oestrogen and dopamine:
- The hormones send a message to the pituitary gland primarily indicating whether to begin or
cease the production of prolactin
- Dopamine restrains the production whereas oestrogen increases it
- Too much prolactin in the blood causes hyperprolactinaemia, a condition that can lead to
menstrual disturbances, oestrogen deficiency and unwanted lactating in non-pregnant women
(can be linked to pituitary tumours)
Suckling stimulates nerves
in the nipple and the areola

Oxytocin stimulates let down reflexes
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whattoexpect
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36 weeks
Frees fatty acids to provide a source of energy for maternal and fetal nutrition
Inhibits glycogenesis (the synthesis of glucose into glycogen for storage in the body) through an anti-insulin
effect
Promotes growth of the fetus due to increased supply of fatty acids, glucose and amino acids
Affects maturation of the breast tissue
Relaxin:
Released by corpus luteum and later by placenta
Relaxin levels in circulation rise after ovulation in the second half of the menstrual cycle
Works with progesterone to prevent uterine contractions in early pregnancy
Levels are at their highest in first trimester
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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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g
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7% of pregnant women in Europe and north America are treated with synthetic GSs to promote
lung maturation in fetuses at risk of preterm delivery
Somatomammotropin:
Secreted about 5th week of pregnancy
Stimulates corpus luteum to secrete oestrogen and progesterone
Stimulates breast development
Stimulates cellular growth
Inhibits glucose transport (by inhibiting insulin effect) – similar to growth hormone

Target Cells:
Hormones only work on certain cells = target cells
Have special receptors that recognise the hormones and allow them to influence that cell
These receptors recognise the hormones and allow them to influence that cell
They fit like ‘lock and key’

If a hormone and receptor site do not match, there is no binding
Glands:
There are 8 glands
Pituitary gland – ‘master gland’, releases growth hormone and regulates all other glands
Thyroid gland – metabolism, body heat, bone growth
Parathyroids – use of calcium and phosphorus
Hypothalamus – links nervous system to endocrine system, regulates homeostasis
Adrenal Gland – response to emergency and stressful situations, metabolism, blood pressure, salt balance
Pancreas – blood sugar, production of insulin
Ovaries – production of eggs; female characteristics
Testes – production of sperm; male characteristics
Thymus – parts of the immune system
Peter The Parrot Had A Pretty Orange To Taste
Glands release hormones
Hypothalamus:
Located in brain beneath two lobes of thalamus
Link brain and endocrine function
Receives information for brain, organs and structures
Alters functions by nerve impulses
Responses to release hormones
Hormones with act or travel to pituitary gland
Increase/decreases hormonal secretion of pituitary
Produce own hormones in specialised nerves
Pituitary Gland:
Located in the base of the brain
Has anterior and posterior lobes
Role is to maintain homeostasis
Anterior pituitary (front) =
- Stimulate or inhibit hormone release from endocrine cells and body cells
- Directly effects body’s tissues
- Responds to signals from hypothalamus
Posterior pituitary (back) =
- Specialised pituitary glands
- Releases oxytocin and antidiuretic hormone (ADH): for suppression of urine formation
Thyroid Gland:
Largest gland located in the neck
Anterior to the trachea and posterior to the larynx (voice box)
Produces thyroxine and calcitonin
Peaks at 10-15 weeks gestation
Increased thyroxine production in pregnancy = increased maternal and Fetal oxygen consumption
Hypothalamus releases thyroid releasing hormone (TRH) -> pituitary gland releases thyroid stimulating
hormone (TSH) -> thyroid gland releases triiodothyronine hormone (T3), thyroxine hormone (T4) and
calcitonin

Parathyroid:
Four tiny glands around the thyroid gland (4 corners)
Secretes parathyroxine
Promotes kidney function
Maintains calcium/phosphate and calcitonin
Adrenal Glands:
Triangular shaped
Situated on top on kidneys
Regulates response to stress by synthesising corticosteroids (from cortex of gland) and catecholamines
(from medulla of gland)
Fight or flight response
Pineal Gland:
Located in brain and nerve pathways terminate here
Releases melatonin
Thymus gland:
Activates lymphocytes released to immune system
Gonads:
Responsible for production of the sex steroids
A name for ovaries and testes
Trophoblast Cells:
The trophoblast is the outer sphere of cells of the blastocyst (hollow cavity, and an inner mass of cells
which develop into the embryo and the placenta
Enables implantation to occur
Trophoblast cells release hCG maintaining the corpus luteum (remnants of follicle that contains the now
fertilised ovum)
Corpus Luteum:
Transient endocrine structure formed from the ovarian follicle after ovulation
Secretes oestrogen and progesterone during the first trimester (12 weeks) until placenta takes over
function
Corpus luteum maintained by hormone hCG
Oestrogen stimulates growth of the uterine muscle while progesterone inhibits uterine contractions
Placenta:
Develops in early pregnancy and fully functional at approx
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