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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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