Biology 212: Human Anatomy and Physiology II
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THE ENDOCRINE SYSTEM
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th
References: Saladin, KS: Anatomy and Physiology, The Unity of Form and Function 5th (2010) or 6 (2012) ed.
Be sure you have read and understand Chapter 17 before beginning this lab.
INTRODUCTION:
The endocrine system consists of a number of glands distributed in the head, neck, thorax, and
abdomen. They secrete hormones which enter the blood to be distributed throughout the body to regulate
growth, metabolism, and the function of many other cells, tissues, and organs. The functions of these
endocrine glands, in turn, are regulated by other hormones and by negative feedback mechanisms from
the organs and tissues they regulate.
Hormones are classified into three groups by their chemical structures. Peptide or protein hormones
such as insulin, glucagon, and growth hormone are chains of amino acids. Steroid hormones such as
progesterone, testosterone, and aldosterone are formed from the lipid cholesterol. Monoamine hormones
such as epinephrine and the thyroid hormones are modified amino acids.
Each hormone can only stimulate a response in cells which have receptors for it. Thus, increasing or
decreasing levels of that hormone will only affect those tissues and organs whose cells have these
receptors, and will not affect other tissues or organs. This allows each hormone to regulate specific
physiologic functions, making the endocrine system critically important for maintaining homeostasis of
those functions.
The pituitary gland (hypophysis), thyroid gland, parathyroid glands, pancreatic islets, adrenal cortex,
adrenal medulla, ovaries, and testicles are all discussed in Chapter 17 of your Saladin text. We will
examine these organs at both the histologic and gross anatomy levels. Be sure you are familiar with the
functions of each of these endocrine organs before you begin this exercise. From the reading assignment
on the endocrine system, you should understand that these organs are not the only places where
hormones are produced – dozens of others are secreted by cells in other organs of the body.
GROSS ANATOMY OF THE ENDOCRINE SYSTEM:
Exercise 1: Examine a model of the brain and a preserved human brain and identify the hypothalamus
on its inferior surface. Although not shown, identify where the pituitary gland attaches to it. Examine a
skull and identify the sella turcica of the sphenoid bone where this gland sits. Examine a torso model and
identify the pituitary gland (you may need to remove half of the brain).
The pituitary gland consists of two separate parts (Figure 17.4 in your Saladin text) which lie together in
the sella turcia: the anterior pituitary or adenohypophysis, and the posterior pituitary or
neurohypophysis. The secretions of both are regulated by the hypothalamus of the brain.
Identify the thyroid gland in the neck of the torso model, with two lobes lateral to the trachea connected
by a midline isthmus which lies anterior to the trachea. Although not shown on this torso model, attached
to its posterior surface are four parathyroid glands. From Figure 17.10 in your Saladin text you should
understand where these are located.
In the abdomen of the torso model, identify the pancreas. The vast majority of cells in this organ are not
part of the endocrine system - they secrete digestive enzymes and bicarbonate which they send through a
duct to the small intestine to assist with digestion. However, embedded among those exocrine cells are
approximately a million small groups of endocrine cells called pancreatic islets.
Identify the two adrenal glands just superior to each kidney on the torso model. Using Figure 17.11 in
your Saladin text, you should understand that each adrenal gland consists of two separate parts: the
adrenal cortex is wrapped around the adrenal medulla.
The gonads which produce the sperm and eggs for reproduction are also endocrine glands. On the
torso models which have male and female genitalia, identify the ovaries and the testicles. We will
examine these in more detail during the reproductive system lab later in the course,
HISTOLOGY OF THE ENDOCRINE SYSTEM:
Exercise 2: Examine slide #34 of the pituitary gland or hypophysis under low power. In most of our
slide collections this shows primarily the adenohypohysis (anterior pituitary) with only a small section of
the lighter-staining and less cellular neurohypophysis (posterior pituitary). Switch to higher power and
observe the many cords of cells in the former (Figure 17.5 in your Saladin text). You should also note
many blood vessels (mostly arterioles and venules), identifiable by the erythrocytes they contain. Large
numbers of capillaries are also present, but these collapse during the process of the tissue for microscopy
and are thus very difficult to identify.
Name the six major hormones secreted by the adenohypophysis and identify which chemical group
(peptide, steroid, monoamine) each of them is classified into.
1.
2.
3.
4.
5.
6.
Briefly explain the action of each of these hormones to the other members of your lab group.
Identify the two major hormones secreted by the neurohypophysis and identify which chemical group
(peptide, steroid, monoamine) into which each of them is classified .
1.
2.
Briefly explain the action of each of these hormones to the other members of your lab group.
Exercise 3: Examine slide #4, the thyroid gland, under low power. Identify the large colloid-filled
follicles and under higher power (Figure 17.9 in your Saladin text) observe how these are surrounded by
a simple squamous (if the gland in inactive) or simple cuboidal (if the gland is active) epithelium. Look
carefully between these follicles and identify the parafollicular cells. You should be able to identify
arterioles and venules within this tissue – they contain erythrocytes – and you should realize that
capillaries, although present, have collapsed during processing of the tissue for microscopy and thus can
not be easily identified.
Identify the major hormones secreted by the thyroid follicles and by the parafollicular cells , and identify
which chemical group (peptide, steroid, monoamine) into which each of them is classified.
Follicles
Parafollicular cells:
Briefly explain the action of each of these hormones to the other members of your lab group.
Exercise 4: We do not have a slide of the parathyroid glands, but you should know the hormones
they secrete and their action.
Identify the major hormone secreted by this gland and which chemical group (peptide, steroid,
monoamine) it is classified into.
Briefly explain the action of this hormone to the other members of your lab group.
Exercise 5: Examine slide #20, the pancreas under low power. As noted above, the vast majority of
this organ has an exocrine secretory function, consisting of cells which secrete digestive enzymes and
bicarbonate and send these through a duct to the small intestine. However, under low or medium power
you should be able to identify a number of lighter-staining pancreatic islets (Figure 17.12 in your Saladin
text). Examine these under higher power and identify the cells which secrete the pancreatic hormones.
Throughout the pancreas you should also be able to identify blood vessels by the erythrocytes they
contain and realize that capillaries would also be present but have collapsed during processing of the
tissue for microscopy.
Identify the two major hormones secreted by these pancreatic islets and which chemical group (peptide,
steroid, monoamine) each of them is classified into.
1.
2.
Briefly explain the action of each of these these hormones to the other members of your lab group.
Exercise 6: Examine slide #36, the adrenal gland, under low and medium powers. Using Figure
17.11 in your Saladin text, identify its cortex and its medulla. At medium and high powers, identify the
three zones of the cortex: the superficial zona glomerulosa, the zona fasciculata, and the zona
reticularis next to the medulla.
As in the tissues you have previously examined, you should be able to identify blood vessels In both the
medulla and the cortex by the erythrocytes they contain and you should understand that capillaries are
also present in the living tissues but have collapsed during processing for microscopy.
Cells of the zona glomerulosa produce a group of hormones called ____________________________
Identify the primary hormone of this group.
Into which chemical group (peptide, steroid, monoamine) are hormones in this group classified?
To other members of your lab group, briefly explain the function of these hormones.
Cells of the zona fasciculata produce a group of hormones called ____________________________
Identify one major hormone of this group.
Into which chemical group (peptide, steroid, monoamine) are hormones in this group classified?
To other members of your lab group, briefly explain the function of these hormones.
Cells of the zona reticularis produce a group of hormones called ____________________________
Identify one major hormone of this group.
Into which chemical group (peptide, steroid, monoamine) are hormones in this group classified?
To other members of your lab group, briefly explain the function of these hormones.
Cells of the adrenal medulla produce two closely related hormones
Name these two hormones.
Into which chemical group (peptide, steroid, monoamine) are these hormones classified?
To other members of your lab group, briefly explain the function of these hormones.
Exercise 7: Examine slide #12, the testis or testicle. A large majority of this organ is composed of the
seminiferous tubules within which sperm are produced (Figures 17.13 and 27.10 in your Saladin text);
under low power, look in the spaces between these tubules and identify the endocrine interstitial cells.
Examine these under medium and high power. You should also be able to identify some blood vessels
within the organ.
Identify the primary hormone secreted by the interstitial cells and identify which chemical group (peptide,
steroid, monoamine) into which this hormone is classified.
Briefly explain the action of this hormone to the other members of your lab group.
Exercise 8: Examine slide #40 showing an ovary. This was taken from an animal which gives birth to
multiple young, so unlike the human ovary it shows more than one follicle developing at the same time.
Identify one or two of these under low power, then examine them under medium and higher powers to
identify the follicular cells or granulosa cells which surround the developing egg (Figures 17.13 and
28.12 in your Saladin text).
Identify the primary hormone secreted by the follicular cells of an ovarian follicle when an egg is
developing within it.
Into which chemical group (peptide, steroid, monoamine) is this hormone classified?.
Briefly explain the action of this hormone to the other members of your lab group.
Although not shown on this slide, after ovulation the remaining follicular cells are converted to a structure
called a corpus luteum which secretes a different hormone.
Identify the primary hormone secreted by the corpus luteum of an ovary. .
Into which chemical group (peptide, steroid, monoamine) is this hormone classified?.
Briefly explain to other members of your lab group the action of this hormone.
ENDOCRINE ORGANS IN THE LIVING HUMAN:
Exercise 9: This exercise will require you to remove clothing, so you should do it at home.
On yourself or another person, use a washable pen to mark the location of the pituitary gland, thyroid and
parathyroid glands, pancreas, adrenal glands, and either ovaries or testicles.
Show off your artwork to your roommate or mother if you wish, then go take a shower to wash it off.