Animal Form & Function III - Endocrine
System
Endocrine System
Endocrine glands perform a wide variety of functions. They are grouped into
a common system because of a similarity in their mode of secretion, which entails
secretion into the blood stream rather than through a system of ducts. Some
of the endocrine glands are highly specialized for endocrine function and do
little else of note: others, such as the pancreas
and gonads, perform
an endocrine function in addition to other functions performed within the primary
system of which they are a part. Because of this dual function of some organs,
you will have previously seen much of the material to be considered in this
section. One major endocrine gland, the pituitary,
is closely associated with the ventral surface of the brain and hence is best
studied, after the brain has been removed from the braincase which will be done
in the next laboratory.
- Thyroid
Gland:
- In the rat this gland is on the ventral surface of the trachea
at its anterior end where it joins the
larynx. The thyroid gland is in two main lobes lying on either
side of the midline and joined by a narrow isthmus.
- Parathyroid Glands:
- These glands are small and usually difficult to locate. The rat has
only one pair and they are embedded in the dorsal surface of the thyroid gland.
Adrenal
Glands:
In the rat, the adrenal glands are separate structures, lying just anterior
to the kidneys. They have their own blood supply.
Pancreas:
- In Mammals, the pancreas consists of two functionally and anatomically
separate parts. The main body of the gland that secretes digestive enzymes
into the duodenum by way of one or more pancreatic ducts and the endocrine
portion of the gland which secretes hormones into the blood stream. The
latter portion consists of many small Islets of Langerhans,
scattered throughout the gland.
Gonads:
- In the rat, the gonads produce sex hormones. In the male the testes contain
glandular
interstitial tissue in addition to the sperm producing seminiferous
tubules. The interstitial cells function in the synthesis of the
male sex hormone, testosterone. In the female, the ovarian
follicles produce estrogens. These follicles, which also
contain the eggs, rupture when an egg becomes ripe (this is controlled by
pituitary hormones). The old follicle then develops rapidly into a new structure,
the corpus luteum,
which also secretes hormones.
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-
Examine the following gonad images:
- Rat
Ovaries
- Rat
Testes
