Download Lab 01 - Endocrine Anatomy

Week 01 Lab
Endocrine Anatomy
LEARNING OUTCOMES:
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Identify each endocrine gland on laboratory models.
Describe the histological appearance of each endocrine gland.
Identify each endocrine gland when viewed microscopically.
Relate the major endocrine organs to the hormones they secrete.
ACTIVITY 1: Laboratory Safety
In Lab:
1. Watch the safety video at the beginning of lab. You can find a link to it in the Course Policies area in
Canvas.
2. Complete the bottom portion of the Laboratory Safety Sheet and pass it in with your Lab Report.
3. Before leaving the lab today, find the safety equipment listed below:
❍ first aid kit
❍ eye wash station
❍ glass disposal box
❍ dissecting gloves and eye guards
❍ fire extinguisher
❍ fire blanket
❍ hand soap and paper towels at sinks
ACTIVITY 2: The Pituitary Gland
Anatomy
The pituitary gland, or hypophysis, is located in the sella turcica of the sphenoid of the skull, immediately
inferior to the hypothalamus of the brain. A stalk called the infundibulum attaches the pituitary to the brain
at the hypothalamus. The pituitary gland is organized into two lobes, an anterior lobe, also called the
adenohypophysis, and a posterior lobe, also called either the neurohypophysis or the pars nervosa.
The two pituitary lobes are easily distinguished from each other by how they accept stain. The posterior lobe
consists mostly of lightly stained unmyelinated axons from hypothalamic neurons. Darker-stained cells
called pituicytes are scattered in the lobe and are similar to glial cells in function.
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The darker-staining anterior lobe is populated by a variety of cell
types that are classified into two main groups determined by their
histological staining qualities. Chromophobes are light-colored
cells that do not react to most stains. Chromophils react to
histological stains and are darker than chromophobes.
Hormones
The pituitary gland is commonly called the master endocrine gland
because it has a critical role in regulating endocrine function and
produces hormones that control the activity of many other
endocrine glands. Regulatory hormones from the hypothalamus
travel down a plexus of blood vessels in the infundibulum and
signal the anterior lobe to secrete tropic hormones that target
other endocrine glands, inducing them to produce and secrete
their own hormones.
The posterior lobe does not produce hormones. Instead, its
function is to store and release antidiuretic hormone (ADH) and
oxytocin (OT), which are both produced in the hypothalamus and
then passed down the infundibulum to the pituitary gland. ADH acts on the kidney where it promotes the
reabsorption of water from urine back into the blood, while OT acts on smooth muscle in both the male and
female reproductive tracts. It is usually associated with uterine contractions during childbirth.
In Lab:
1. Locate the pituitary gland on the brain models in the lab. (Sometimes they break off, so if you can’t find
them on the regular brain models, check out the torso model’s brain.)
On the lab models, you need to:
❍ identify the pituitary gland and the infundibulum; and
❍ identify the hypothalamus.
2. Use the dissecting microscope to survey the pituitary gland slide at low magnification.
On the slide, you need to be able to:
❍ identify the anterior and posterior lobes; and
❍ identify (microscopically) the locations of the glandular tissue and neural tissue.
ACTIVITY 3: The Thyroid Gland
Anatomy
The thyroid gland is located in the anterior aspect of the neck, directly inferior to the thyroid cartilage
(Adam's apple) of the larynx and just superior to the trachea. This gland consists of two lateral lobes
connected by a central mass, the isthmus. The thyroid produces two groups of hormones associated with the
regulation of cellular metabolism and calcium homeostasis.
Under the microscope, the thyroid gland is very distinctive. It is composed of spherical follicles embedded
in connective tissue. Each follicle is composed of a single layer of simple cuboidal epithelial cells called
follicular cells. The lumen of each follicle is filled with a glycoprotein called thyroglobulin that is used in the
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production of thyroid hormones. On the superficial margins of the follicles are parafollicular cells, also
called C cells, which are larger and less abundant than the follicle
cells. On most slides, the parafollicular cells have a lightstained
nucleus.
Hormones
Follicle cells produce the hormones thyroxine (T4) and
triiodothyronine (T3), both of which regulate metabolic rate and both
of which are called thyroid hormone. They are synthesized in the form
of the glycoprotein thyroglobulin. It is secreted into the lumen of the
follicles and stored there until needed by the body, at which time it is
reabsorbed by the follicle cells and released into the blood.
Parafollicular cells produce the hormone calcitonin (CT), which decreases blood calcium levels. Calcitonin
stimulates osteoblasts in bone tissue to store calcium in bone matrix and lower fluid calcium levels. It also
inhibits osteoclasts in bone from dissolving bone matrix and releasing calcium. Calcitonin has a minor role
in calcium regulation in humans but is more active in lowering blood calcium in other animals.
In Lab:
1. Locate the thyroid gland on the torso model and endocrine chart.
2. Use the compound microscope to view the thyroid slide at low and medium powers.
On the slide, you need to be able to:
❍ find thyroid follicles and colloid; and
❍ distinguish between follicular and parafollicular cells.
ACTIVITY 4: The Parathyroid Glands
Anatomy
The parathyroid glands are two pairs of oval masses on the posterior surface of the thyroid gland. Each
parathyroid gland is isolated from the underlying thyroid tissue by the parathyroid capsule. The parathyroid
glands are composed mostly of chief cells, also called principal cells. These cells have a round nucleus, and
their cytosol is basophilic and stains pale with basic (high pH) histological stains. The oxyphil cells of the
parathyroid are larger than the chief cells, and their acidophilic cytosol reacts to acidic stains and turns
colorless.
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Hormone
The parathyroid glands produce parathyroid
hormone (PTH), which is antagonistic to
calcitonin from the thyroid gland. Although
calcitonin is relatively ineffective in humans,
PTH is important in maintaining blood calcium
level by stimulating osteoclasts in bone to
dissolve small areas of bone matrix and release
calcium ions into the blood. PTH also
stimulates calcium uptake in the digestive
system and reabsorption of calcium from the
filtrate in the kidneys.
In Lab:
1. Locate the parathyroid glands on the torso
model. Their position has been somewhat
exaggerated to make them visible; in reality,
they are on the posterior side of the thyroid
and would not be visible.
2. Examine the parathyroid slide with the
dissecting microscope. Scan the gland for
thyroid follicles that may be on the slide
near the parathyroid tissue.
3. Observe a parathyroid slide at low and medium powers with the compound microscope.
On the slide, you need to be able to:
❍ identify the chief cells; and
❍ identify the oxyphil cells.
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ACTIVITY 5: The Adrenal Glands
Anatomy
Superior to the kidneys are adrenal glands. A protective adrenal capsule encompasses the gland and
attaches it to the kidney. The gland is organized into two major regions: the outer adrenal cortex and the
inner adrenal medulla.
The adrenal cortex is glandular and is differentiated into three distinct regions, each producing specific
hormones. The zona glomerulosa is the outermost cortical region. Cells in this area are stained dark and
arranged in oval clusters. The next layer, the zona fasciculata, is made up of larger cells organized in tight
columns. These cells contain large amounts of lipid, making them appear lighter than the surrounding
cortical layers. The deepest layer of the cortex, next to the medulla, is the zona reticularis. Cells in this area
are small and loosely linked together in chainlike structures. The many blood vessels in the adrenal medulla
give this tissue a dark red color.
Hormones
The adrenal cortex secretes hormones collectively called adrenocortical steroids, or simply corticosteroids,
which are lipid-based steroids. The zona glomerulosa secretes a group of hormones called
mineralocorticoids that regulate, as their name implies, mineral or electrolyte concentrations of body fluids.
A good example is aldosterone, which stimulates the kidneys to reabsorb sodium from the liquid being
processed into urine. The zona fasciculata produces a group of hormones called glucocorticoids that are
involved in fighting stress, increasing glucose metabolism, and preventing inflammation. Two of the
glucocorticoids, cortisol and corticosterone, are commonly found in creams used to treat rashes and allergic
responses of the skin. The zona reticularis produces androgens, which are male sex hormones. Both males
and females produce small quantities of androgens in the zona reticularis.
The adrenal medulla is regulated by sympathetic neurons from the hypothalamus. In times of stress, exercise,
or emotion, the hypothalamus stimulates the adrenal medulla to release its hormones, the neurotransmitters
epinephrine (E) and norepinephrine (NE), into the blood, resulting in a bodywide sympathetic fight-or-flight
response.
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In Lab:
1. Locate the adrenal glands on the torso model and kidney models.
2. Examine the slide of the adrenal gland on low magnification on a compound microscope.
On the slide, you need to be able to identify:
❍ the capsule;
❍ the adrenal cortex; and
❍ the adrenal medulla.
(Most of our slides aren’t good enough to see the three adrenal cortex layers.)
ACTIVITY 6: The Pancreas
Anatomy
The pancreas, a glandular organ that lies posterior to the stomach, performs important exocrine and
endocrine functions. The exocrine cells secrete digestive enzymes, buffers, and other molecules into a
pancreatic duct that empties into the small intestine. The endocrine cells produce hormones that regulate
blood sugar metabolism.
The pancreas is densely populated by dark-stained cells called the pancreatic acini. These cells make up the
exocrine part of the pancreas, and they secrete pancreatic juice, which contains digestive enzymes (see
areas circled with solid lines in figure above). Connective tissues and pancreatic ducts are dispersed in the
tissue. The endocrine cells of the pancreas occur in isolated clusters of pancreatic islets, or islets of
Langerhans, that are scattered throughout the gland (see area with dark dashed line above). Each islet houses
four types of endocrine cells: alpha cells, beta cells, delta cells, and F cells. These cells are difficult to
distinguish with routine staining techniques and will not be individually examined.
Hormones
Pancreatic hormones affect carbohydrate metabolism. Alpha cells secrete the hormone glucagon, which
raises blood sugar concentration by catabolizing glycogen to glucose for cellular respiration. This process is
called glycogenolysis. Beta cells secrete insulin, which accelerates glucose uptake by cells and also
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accelerates the rate of glycogenesis, the formation of glycogen. Insulin lowers blood sugar concentration by
promoting the removal of sugar from the blood. Normal blood plasma glucose concentration is generally
considered to range between 70 and 110 mg/dL. The interaction of pancreatic and other hormones plays a
key role in regulating blood sugar.
In Lab:
1. Locate the pancreas on the torso models.
2. Examine the slide of the pancreas on low and medium magnification on a compound microscope.
On the slide, you need to be able to identify:
❍ the darkly-staining pancreatic acini; and
❍ the pancreatic islets.
(Our slides are not stained to distinguish between the different cell types in the islets.)
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