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The
endocrine system
Joanna
George-Johnson, Contributor
In
the last lesson, we compared the nervous system to the endocrine system since
they are the two main communication systems we have in our bodies. This week,
we will look at the endocrine system in more detail. There
is one problem that students often encounter. They often confuse the endocrine
glands with the exocrine glands. Therefore,
before we look at the endocrines, let's take some time and compare the two types
of glands.
Endocrine vs Exocrine | Endocrine
Glands | Exocrine
Glands | | Secretes
hormones | Secretes
'juices' or fluid | | Substances
are secreted into the blood stream | Substances
are secreted to the target organs via ducts |
You
would have come across some exocrine glands during your study of other topics.
They might not have been so named, but from the table above you should be able
to determine some exocrine glands and their secretions. Here is a list of some
you may know about but have not studied as yet, and others you might not know.
Some
Exocrine Glands and their Secretions and Importance | Glands
| Secretions | Purpose | | mammary
gland | milk | Nourishment
for new born | | sweat
glands | perspiration | Part
of body's cooling mechanism | | sebaceous
glands | sebum | Protect
skin from cracking | | Pancreas* | pancreatic
juice | Aids
in digestion |
You
will notice that there is an asterisk beside 'pancreas'. This
is because the pancreas is a gland that has dual purposes.
It is both an endocrine and an exocrine gland. The
pancreas produces pancreatic juice that is directed to the small intestine for
the purpose of digestion. But, it also produces insulin - a hormone that helps
in the regulation of the body's glucose level. Although
there are many harmones with varied functions, you do not need to study all of
them. For your exams you are required to do the following" - List
the location of selected endocrine glands.
- Describe
the roles of the hormones produced by the selected glands.
Selected
Endocrine Glands and their Hormones | Endocrine
Glands | Location | Hormones
and their Function | | Thyroid | neck | Calcitonin:
regulates the calcium levels in the body Thyroxine:
increase metabolic rates | | Pancreas | Behind
the stomach below the liver | Insulin:
reduces glucose levels in the blood Glucagon:
increase glucose levels in the blood | | Gonads | Males:
Found in the genital area hanging on the outside of the body. Females:
inside just below the abdominal area. | Ovaries: Oestrogen:
secondary sexual characteristics in girls, such as breast etc. prepare body
for possible pregnancy each month. Progesterone:
inhabits the development of new follicle. Therefore prevents further ovulation. Testis: Testosterone:
secondary sexual characteristics in boys, for the production of sperms. | | Pituitary** | beneath
the hypothalamus | Thyroid-stimulating
Hormone: stimulates the making of thyroxine Growth
Hormone: stimulates growth Anti
Diuretic Hormone: regulation of water levels in the body Follicle-stimulating
hormone luteinizing hormone and prolactin: work in association with the gonads. | | Adrenals | On
the upper portion of the kidneys | Adrenaline:
prepares the body for stress. (fight or flight) |
Pituitary:
Often referred to as the 'master gland', the hypothalamus controls much of
the functioning of the pituitary gland either directly through nerve stimulation
or through hormonal activation. It produces many more hormones, but these are
not a part of your syllabus. The
endocrine system broadcasts its hormonal messages to essentially all cells by
secretion into blood and extracellular fluid. As a radio broadcast does, it requires
a receiver to get the message. In the case of endocrine messages, cells must bear
a receptor for the hormone being broadcast in order to respond. Most
hormones circulate in the blood, coming into contact with essentially all cells.
However, a given hormone usually affects only a limited number of cells, which
are called target cells. A target cell responds to a hormone because it bears
receptors for the hormone. 
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