Biology 242 – Lab LAB #1 ( 1 st /19 Labs for Winter Quarter, 2009)
TOPICS TO BE COVERED:
»Overview of the Major Endocrine Glands
»Discussion of the Anatomy, Histology, and Hormones of six of the major endocrine glands
( Pituitary ( both Anterior and Posterior ), Thyroid Gland, Pancreas, Adrenal ( Cortex and Medulla ), Ovary, & Testis )
»Histological observation, drawing and labeling of Endocrine organs and structures
DESIRED OUTCOMES:
After completing the activities described for this lab session, students should:
»Be able to identify each major endocrine gland on models, preserved specimens, or diagram
»Be able to name the main hormones secreted by each major endocrine gland
»Be able to identify and describe the histological appearance of selected endocrine gland
MATERIALS NEEDED:
»Human torso »Dissectible Human Brain model »Lens Paper »Lens Cleaning Solution
»Blue Boxes: Endocrine Series -prepared microscope slides »Photographic Atlas, Ch. 10 , Ch.17
»Anatomical Charts of Endocrine Structures »Dissection Tools
Activity #1: Overview of the major Endocrine Glands
The Endocrine System is composed mainly of a diverse group of ductless glands that secrete hormones into the bloodstream. These hormone chemicals are transported throughout the body via the blood and bind to target cells that have specific cell membrane receptors for a specific hormone. Hormones cause changes in activity in these target cells and direct a variety of cellular activities to keep the body in homeostasis. Thus, the Endocrine System is one of the major homeostatic systems in the body – the other major system acting to maintain homeostasis, is the Nervous System. The method by which these two systems maintain homeostasis is quite different, though. The Nervous System works via nerve impulses to produce effects that are nearly immediate, but temporary. The Endocrine System works via secretion of hormones whose actions typically are not immediate, but the effects are longer-lasting.
There are ten major endocrine glands, although any one individual only has nine of them (due to having only one gender.) Starting superiorly from the head and proceeding inferiorly, these ten are:
1. Pineal Gland
2. Hypothalamus
3. Pituitary Gland aka, the Hypophysis (both Anterior Pituitary = Adenohypophysis
and Posterior Pituitary = Neurohypophysis )
4. Thyroid Gland
5. Parathyroid Glands (usually there are 4 of these; variable, up to 8)
6. Thymus
7. Adrenal Glands (2) (Having two distinct endocrine compartments: the outer Cortex, and the inner Medulla)
8. Pancreas
9. Ovaries (2)
10. Testes (2)

BIOLOGY 242 – LAB #1 – continued Page Two
Activity #2: Discussion of the Anatomy, Histology, and Hormones of Six selected Endocrine Glands
In this part of today’s Lab, we will examine the anatomy, histology, and hormones of the following six endocrine organs: the Pituitary gland aka Hypophysis ) - both its Anterior and its Posterior lobes; the Thyroid
Gland; the Pancreas; the Adrenal Gland – both its outer cortex and its inner medulla regions; the Ovaries; and the Testes.
The Pituitary Gland
The Pituitary gland , aka Hypophysis , produces hormones, many of which serve to control the activity of other endocrine glands. It is a small gland located in the sella turcica of the sphenoid bone of the skull, immediately inferior to the hypothalamus of the brain. (Note how this landmark of the sphenoid bone serves as a protective cradle around this gland.) A stalk, the infundibulum , attaches the pituitary gland to the hypothalamus. Hormones and regulatory molecules from the hypothalamus travel down a plexus of blood vessels in the infundibulum to reach the hypophysis.
The two division of the Pituitary gland are composed of two different types of tissue. The Anterior
Pituitary (aka Adenohypophysis consisting of a pars distalis and a pars tuberalis ) is glandular epithelium, while the Posterior Pituitary (aka Neurohypophysis aka pars nervosa ) is neural tissue. ( This is why knowing the more
“technical” names is helpful; since adeno = of or pertaining to glandular tissue and neuro = of or pertaining to nervous tissue .) There is a smaller part of the adenohypophysis, the pars intermedia , which separates the anterior and posterior pituitary; and this part produces a single hormone, melanocyte-stimulating hormone (MSH).
The Posterior Pituitary is composed of unmyelinated axons from hypothalamic neurons, which appear fine and granular; and scattered neuroglial cells called pituicytes. In general, the neurohypophysis contains fewer cells and looks far less dense than the adenohypophysis. The neurohypophysis does not actually produce hormones; rather the neurosecretory cells of the hypothalamus produce antidiuretic hormone (ADH) and oxytocin (OT) which then pass down the infundibulum to enter the neurohypophysis for storage and release.
The Anterior Pituitary contains five types of cells that are difficult to distinguish based upon their staining properties alone: (1) somatotrophs secrete Human growth hormone ( hGH ); (2) thyrotrophs secrete Thyroidstimulating hormone ( TSH ); (3) gonadotrophs secrete Folicle-stimulating hormone ( FSH ) and Luteinizing hormone ( LH ); (4) lactotrophs secrete Prolactin ( PRL ); and (5) corticotrophs secrete Adrenocorticotropic ( ACTH ) and Melanocyte-stimulating hormone ( MSH ). Somatotrophs and lactotrophs tend to stain more reddish-brown
( acidophiles ) and the others more bluish-purple ( basophils ). (The additional population of cells, which do not take up any stain, therefore are called chromophobes , have an unknown function.
It is suggested that you begin your examination of the Pituitary gland on low power ( TM = 40X) so that you may first concentrate on the basic “texture” differences between the Anterior and Posterior lobes. Then, move up to higher powers to differentiate the three types of cells in the Anterior Pituitary and the axons in the
Posterior. (Refer to Figs 10.1
, 10.2
, 10.3
, and 10.4
in the Photographic Atlas.)
The Thyroid Gland
The thyroid gland is located in the anterior aspect of the neck, directly inferior to the thyroid cartilage of the larynx and just superior to the trachea. This gland consists of two lateral lobes connected by a central mass, the isthmus. You should be able to locate it easily on the torso mannequin. This gland produces two groups of hormones associated with the regulation of cellular metabolism and calcium hoemostasis.
Microscopically, the Thyroid gland is composed of structural units called thyroid follicles . Follicles are oval-to-spherical, hollow structures composed of simple cuboidal epithelium. These epithelial cells are called follicular cells and are the ones that produce the thyroid hormones, T
3
(aka triiodothyronine) and T
4
(aka tetraiodothyro-nine or thyroxin). Inside the follicles is the reddish-brown, iodine-containing substance called colloid , composed chiefly of a sticky, glycoprotein substance called thyroglobulin ( TGB ) .
As the follicle cells make the TGB, this enters the lumen of the follicle where oxidized iodine residues are added to it ( it becomes iodinated ). Droplets of this colloid re-enter follicle cells where digestive enzymes in lysosomes break down
TGB cleaving off the attached T
3
and T
4
molecules…whose fate is to diffuse through the follicle cells’ basal plasmalemma ( being lipid soluble, these hormones can do that!
) into a capillary to bind with transport proteins
(mainly thyroxine-binding globulin ( TBG ) to be carried in the blood.

BIOLOGY 242 – LAB #1 – continued Page Three
In between the follicles are clusters of cells called parafollicular cells (aka C cells ). These cells produce the hormone calcitonin , which works with parathyroid hormone to maintain calcium balance in the blood.
(Remember, from last quarter, calcitonin’s nickname is the “pro-bone hormone” because it stimulates osteoblasts in bone connective tissue to store calcium in bone matrix. To do this, Ca ++ is taken out of the blood ( thus decreasing blood calcium levels ) and stored in osseous connective tissue. This results in new deposits of this mineral in bones. Thus, the “pro-bone” label. Calcitonin also inhibits osteoclasts from dissolving bone matrix.)
The features of thyroid follicles are best viewed on high power. TM = 400X. ( Fig. 10.6
in Ph. Atlas.)
The Pancreas
The pancreas lies between the stomach and the duodenum of the small intestine, and is retroperitoneal in this position. The gland is a “double gland”, performing both exocrine and endocrine functions. Exocrine glands have ducts or tubules that transport secretions to the body surface or to an exposed internal surface. Exocrine cells of the pancreas secrete digestive enzymes, buffers, and other molecules into pancreatic ducts for transport to the duodenum. Endocrine portions of the pancreas produce hormones that regulate blood sugar metabolism. ( In the Photographic Atlas refer to Fig. 10.1
for anatomical location and Fig. 10.12
for histologic detail .)
So, the pancreas is a gland that has both endocrine and exocrine functions. When we study the Digestive
System in just a few weeks, we will study the specific roles the exocrine part of this gland has in that system. In fact, 99% of the Pancreas is composed of the exocrine glandular pancreatic cells called acinar cells . However, the remaining 1% of pancreatic glandular cells are aggregated into isolated cluster-like structures, or “islands” of tissue, called Islets of Langerhans – or simply pancreatic islets . It is only these pancreatic islets which constitute the endocrine component of this gland. Typically, the islets are lighter in color than the surrounding acinar cells . You will need to ovserve the specimen on scanning power (40X) at first to discern these islets ; but then go to high power, and the differences between the islet cells and the acinar cells is quite distinct: acinar cells are cuboidal in shape and are always arranged around a duct; whereas the islet cells have no such regularity of arrangement, and there are often larger, stain-free spaces between the islet cells. Each Islet of Langerhans contains four different types of cells: alpha (or A ) cells, beta (or B ) cells, delta cells, and F cells. Alpha cells constitute about 17% of pancreatic islet cells and secrete glucagon ; beta cells constitute about 70% of pancreatic islet cells and secrete insulin ; delta cells constitute about 7% of pancreatic islet cells and secrete somatostatin ; and F cells constitute the remaining 6% of pancreatic islet cells and secrete pancreatic polypeptide ( which acts to inhibit gallbladder contraction and secretion of digestive enzymes by the exocrine pancreas .) Since these four cell types are difficult to distinguish with routine staining techniques, we will not be individually examining them.
The Adrenal Gland
Above each kidney is an adrenal gland (aka suprarenal gland, because of its location superior to the kidney.) An adrenal capsule protects and attaches the adrenal gland. (See Figures 10.1
, 10.8
, and 10.9
)
The Adrenal gland is composed of two main regions: the outer, adrenal cortex, which secretes steroid hormones, and the inner, adrenal medulla, which secretes catecholamines ( epinephrine/ norepinephrine ) in response to sympathetic nervous stimulation. The adrenal cortex may be further subdivided into three zones:
(1) The outer zona glomerulosa , a thin layer where the cells are stained dark and arranged in oval clusters. Cells in this zone secrete a group of hormones called mineralocorticoids which regulate, as their name implies, mineral or electrolyte concentrations of body fluids. A good example is aldosterone , which stimulates the kidney to reabsorb more sodium from the fluid being processed into urine.
(2) The middle zona fasciculata , where the cells are larger and are stacked on top of one another in an arrangement resembling columns. These cells contain large amounts of lipd, making them appear lighter than the surrounding cortical layers. The zona fasciculta produces a group of hormones called glucocorticoids which are involved in fighting stress, increasing glucose metabolism, and preventing inflammation. Cortisol and cortisone are commonly used in creams to control irritating rashes and allergic responses of the skin.
(3) The deepest layer of the cortex, adjacent to the medulla, is the zona reticularis . Cells in this area are small, more darkly stained, tightly packed and linked together in chainlike structures. Interestingly, the zona reticu-

BIOLOGY 242 – LAB #1 – continued Page Four laris produces androgens , male sex hormones, with the main one being DHEA (dehydroepiandrosterone). Both males and females produce small quantities of androgens in this zone. ( Note: Some of the peripheral target tissues of DHEA convert this hormone to a more powerful hormone, testosterone; while other peripheral target tissues convert
DHEA into estrogen .)
The adrenal medulla is the innermost part of the gland, and it is easily distinguished from the zones of the cortex because of the many blood vessels it contains and its loosely arranged cells. It is the presence of all the blood vessels in the medulla that give this tissue its dark-red coloration. The cells of the medulla are modified sympathetic neurons that secrete epinephrine and norepinephrine, hormones involved in the sympathetic fight-or-flight response. (See Fig. 10.10
in the Photographic Atlas.)
The regions of the adrenal gland are best viewed on scanning (40X) or low power (100X). To get more detail of the individual cells, switch to high power. (Refer to Fig. 10.11
)
The Ovary
Gonads are the male and female reproductive organs that produce gametes, the spermatozoa and oocytes that give new life. The ovaries and testes secrete hormones to regulate development of the reproductive system and maintenance of the sexually mature adult. Ovaries are the female gonads, located in the pelvic cavity.
Within the ovaries, you will see developing oocytes encased in structures called ovarian follicles .
These follicles are present in various stages, ranging from the immature primordial follicles to the mature
Graafian (aka vesicular ) follicles .
Each ovarian cycle, a small group of immature primary oocytes begin to develop an outer capsule of follicular cells . Eventually, one follicle becomes a Graafian follicle , a fluid-filled structure containing a secondary oocyte for release at ovulation. The Graafian follicle is a temporary endocrine structure and secretes the hormone estrogen to prepare the uterus for implantation of a fertilized egg. After ovulation, the ruptured Graafian follicle becomes the corpus luteum , another temporary endocrine structure which secretes progesterone that promotes further thickening of the uterine wall. ( See Figs. 10.1, 17.1, 17.29
, 17.30
, 17.31
of the Photographic Atlas.)
The Testis
Testes are the male gonads, located outside the body in the pouchlike scrotum. A testis , or testicle , is made up of coiled seminiferous tubules which produce spermatozoa. The spermatogonia cells are on the peripheral-most lying basement membrane of these tubules, and the spermatozoa, in various stages of development occupy the lumen, or transport canal, of these tubules.
Between the seminiferous tubules of the testes are triangular-shaped spaces called interstitial spaces that contain Leydig cells or interstitial endocrinocytes . These interstitial cells, located between the seminiferous tubules, are endocrine cells, that when stimulated by lutenizing hormone from the anterior pituitary, produce and secrete the male sex hormone testosterone. Testosterone is the hormone that produces and maintains secondary male sex characteristics such as facial hair and broadened shoulders. ( See Fig. 10.1
, 17.1
, 17.6
, 17.8
, 17.9
, 17.10
)
Activity #3: Histological observation, drawing and labeling of Endocrine organs and structures
You will need to make sketches, to scale, of each of the six endocrine organs discussed above. Be sure to note the TM at which your drawing is made; label the endocrine gland, structural/functional unit, all pertinent cell-types; if an epithelial layer is evident, be sure to label the basement membrane and the “free edge” (and lumen ); connective tissue capsule structures, and other important structures. Also, list the hormone(s) produced by each cell-type, structure, or gland; as well as describing what stimulates each secretion.
Your labeled drawings and lists will be turned in and graded for accurate representation, appropriate size, completeness of labels, overall neatness, and correct hormonal information.