ENDOCRINE SYSTEM: Very Detailed Notes for a Grade 9 student
Endocrine system is made of endocrine glands which release hormones that affect the
internal environment of the body. Hormones are chemical messengers that move
through the blood to their target organs. They are slow but have a long-lasting effect.
Also, they are produced for a general response.
Homeostasis means maintaining the constant internal environment of the body. -
controls water content, temperature levels in the body and blood glucose
concentration.
The endocrine glands are:
1. Pituitary gland- master gland that releases hormones that trigger the other endocrine
glands to release specific hormones.
This is located below the hypothalamus.
The hormones released from this gland are luteinising hormone, follicle stimulating
hormone, anti-diuretic hormone and thyroid stimulating hormone.
2. Thyroid gland- controls metabolic processes and the digestion of food. This gland
releases thyroxine.
When there is a low thyroxine blood level, the hypothalamus releases thyrotropin
releasing hormone, which signals the Pituitary gland to release thyroid stimulating
hormone, this triggers the thyroid gland to release more thyroxine.
This leads to negative feedback as the normal concentration of thyroxine is now in the
body.
This process also happens when there is too much thyroxine blood concentration but
vice versa, as the production of TRH, TSH and thyroxine is reduced so that negative
feedback can occur.
3. Adrenal gland- releases adrenaline for fight or flight response.
The adrenaline breaks down the stored glycogen in the liver cells into glucose so that
more is released into the blood and so that more energy is available for the action that
will occur (increased respiration).
The heart muscles contract because the adrenaline binds onto the heart receptors
which increases blood flow and pressure- more rapidly and strongly. More blood is
, pumped by the heart and the heart rate increases.
Also, more oxygen is breathed in as the breathing rate increases.
4. Ovaries- produces oestrogen and progesterone. These hormones are used in the
menstrual cycle of 28 days.
When FSH is high, oestrogen is also high. When LH is high, progesterone is also high.
Menstrual cycle
1-5 days: the levels of hormones are low, and the uterus wall breaks down so bleeding
happens with the unfertilised egg cell being moved out of the body.
6-13 days: the rebuilding of the uterus wall. The Pituitary gland releases FSH which
moves through the blood and stimulates the production of oestrogen in the ovaries. The
oestrogen thickens the uterus wall and matures an egg
14th day: ovulation happens as the matured egg follicle moves from the ovary to the
oviduct
15-21 days: the FSH is inhibited so the oestrogen decreases. The Pituitary gland
releases LH which moves through the blood and stimulates the production of
progesterone in the ovaries. The progesterone further thickens the uterus wall and
maintains it.
22-28 days: the progesterone is still being produced but after the 28th day, it stops
being produced if fertilisation hasn't occurred.
The menstrual cycle happens again.
Hormonal and barrier contraceptives:
Oestrogen as a pill could be used to prevent the release of an egg follicle because when
oestrogen is taken continually, it inhibits the release of FSH which eventually stops the
production and development of an egg follicle.
Progesterone as a pill reduces fertility as when a lot is taken in, the progesterone
Endocrine system is made of endocrine glands which release hormones that affect the
internal environment of the body. Hormones are chemical messengers that move
through the blood to their target organs. They are slow but have a long-lasting effect.
Also, they are produced for a general response.
Homeostasis means maintaining the constant internal environment of the body. -
controls water content, temperature levels in the body and blood glucose
concentration.
The endocrine glands are:
1. Pituitary gland- master gland that releases hormones that trigger the other endocrine
glands to release specific hormones.
This is located below the hypothalamus.
The hormones released from this gland are luteinising hormone, follicle stimulating
hormone, anti-diuretic hormone and thyroid stimulating hormone.
2. Thyroid gland- controls metabolic processes and the digestion of food. This gland
releases thyroxine.
When there is a low thyroxine blood level, the hypothalamus releases thyrotropin
releasing hormone, which signals the Pituitary gland to release thyroid stimulating
hormone, this triggers the thyroid gland to release more thyroxine.
This leads to negative feedback as the normal concentration of thyroxine is now in the
body.
This process also happens when there is too much thyroxine blood concentration but
vice versa, as the production of TRH, TSH and thyroxine is reduced so that negative
feedback can occur.
3. Adrenal gland- releases adrenaline for fight or flight response.
The adrenaline breaks down the stored glycogen in the liver cells into glucose so that
more is released into the blood and so that more energy is available for the action that
will occur (increased respiration).
The heart muscles contract because the adrenaline binds onto the heart receptors
which increases blood flow and pressure- more rapidly and strongly. More blood is
, pumped by the heart and the heart rate increases.
Also, more oxygen is breathed in as the breathing rate increases.
4. Ovaries- produces oestrogen and progesterone. These hormones are used in the
menstrual cycle of 28 days.
When FSH is high, oestrogen is also high. When LH is high, progesterone is also high.
Menstrual cycle
1-5 days: the levels of hormones are low, and the uterus wall breaks down so bleeding
happens with the unfertilised egg cell being moved out of the body.
6-13 days: the rebuilding of the uterus wall. The Pituitary gland releases FSH which
moves through the blood and stimulates the production of oestrogen in the ovaries. The
oestrogen thickens the uterus wall and matures an egg
14th day: ovulation happens as the matured egg follicle moves from the ovary to the
oviduct
15-21 days: the FSH is inhibited so the oestrogen decreases. The Pituitary gland
releases LH which moves through the blood and stimulates the production of
progesterone in the ovaries. The progesterone further thickens the uterus wall and
maintains it.
22-28 days: the progesterone is still being produced but after the 28th day, it stops
being produced if fertilisation hasn't occurred.
The menstrual cycle happens again.
Hormonal and barrier contraceptives:
Oestrogen as a pill could be used to prevent the release of an egg follicle because when
oestrogen is taken continually, it inhibits the release of FSH which eventually stops the
production and development of an egg follicle.
Progesterone as a pill reduces fertility as when a lot is taken in, the progesterone
