In case you weren’t already sure the human endocrine system is the collection of glands that produce hormones that regulate a number of factors within the body including metabolism, growth, reproduction, sleep and mood among others!
There are six major endocrine glands in the human system: 1) Pituitary gland 2) Adrenal glands 3) Thyroid gland 4) Pancreas 5) Ovaries 6) Testes.
Endocrine glands secrete hormones directly into the bloodstream, which are carried around the body in the blood plasma. They can therefore have an effect on whichever organs the blood passes through, so their effects are widespread and long-lasting in comparison to the effects of the nervous system.
In this section you basically need to know quite a few different hormones and how they impact the human body, so let’s get stuck in:
The antidiuretic hormone (ADH) is secreted into the bloodstream by the pituitary gland and increases reabsorption of water in the collecting ducts of nephrons in the kidneys.
Adrenaline is secreted by, you’ve guessed it, the adrenal gland. Adrenaline stimulates the fight or flight response. Adrenaline causes your heart rate to increase, heart stroke volume to increase, pupils to dilate, hairs to stand on end, the brain to become more alert, blood to be redirected from organs to muscles and the liver to convert glycogen into glucose. All these responses prepare the body to either fight, or run away from a perceived threat.
Depending on how much revision you do, it’s likely you’ll have an adrenaline rush before you sit your exam – but it’s probably best not to go down the flight response route!
Insulin is secreted from the pancreas gland. High blood glucose (e.g. after a meal) stimulates the pancreas to secrete insulin into the blood, which causes the liver to convert glucose into a storage molecule called glycogen. This lowers blood glucose levels, which stimulates the pancreas to stop or decrease insulin production. This is an example of negative feedback, which is found in many biological systems involved in homeostasis.
The testes secrete testosterone and they help regulate male puberty (pubic, underarm and facial hair growth, increased aggression, muscle growth and penis growth).
Alternatively women secrete progesterone and oestrogen from the ovaries, both of which are involved in the menstrual cycle.
Oestrogen helps rebuild the uterus lining just after menstruation and also brings about ovulation on day 14 of the cycle, while progesterone is only released after ovulation (from day 14 onwards) and acts to maintain the lining of the uterus in case fertilisation occurs.
Once progesterone levels drop off near the end of the cycle, the uterus lining degrades and menstruation begins anew. Both hormones are also involved in female puberty and development of secondary sexual characteristics such as the widening of hips, growth of pubic and underarm hair and the development of a sex drive.