The pancreas, located partially behind the stomach in the abdomen, functions as both an endocrine and exocrine gland. It produces digestive enzymes as well as insulin and glucagon, important hormones concerned with the regulation of blood sugar levels.

Figure 9.13

Insulin
Elevated blood glucose levels stimulate release of insulin, which decreases blood sugar levels, primarily by accelerating the transport of glucose into the body cells, where it is oxidized for energy or converted to glycogen or fat for storage.

Glucagon
acts antagonistically to insulin. Its release is stimulated by low blood glucose levels, and its action is basically hyperglycemic. It stimulates the liver, its primary target organ, to break down its glycogen stores to glucose and subsequently to release the glucose to the blood.

Observe pancreas tissue in Figure 9.14 and 9.15 and identify the roughly circular pancreatic islets (islets of Langerhans), the endocrine portions of the pancreas. The islets are scattered amid the more numerous acinar cells and stain differently (usually lighter), which makes their identification possible.

Focus on an islet and examine its cells. Notice that the islet cells are densely packed and have no definite arrangement. In contrast, the cuboidal acinar cells are arranged around secretory ducts. Unless special stains are used, it will not be possible to distinguish the alpha cells, which tend to cluster at the periphery of the islets and produce glucagons, from the beta cells, which synthesize insulin. With these specific stains, the beta cells are larger and stain gray-blues, and the alpha cells are smaller and appear bright pink.

Sketch and Label the Pancreas (Microscopic)

Beta cells, Alpha cells

Figure 9.14	Figure 9.15

The female gonads, or ovaries, are paired, almond-sized organs located in the pelvic cavity. In addition to producing the female sex cells (ova), the ovaries produce two steroid hormone groups, the estrogens and progesterone. The endocrine and exocrine functions of the ovaries do not begin until the onset of puberty, when the anterior pituitary gonadotropic hormones prod the ovary into action that produces rhythmic ovarian cycles in which ova develop and hormonal levels rise and fall.

Estrogen
Are responsible for the development of the secondary sex characteristics of the female at puberty and act with progesterone to bring about cyclic changes of the uterine lining that occur during the menstrual cycle. The estrogens also help prepare the mammary glands for lactation.

Progesterone
Acts with estrogen to bring about the menstrual cycle. During pregnancy it maintains the uterine musculature in a quiescent state and helps to prepare the breast tissue for lactation.

Because you will consider the ovary in greater histologic detail when you study the reproductive system, the objective in this laboratory exercise is just to identify the endocrine-producing parts of the ovary. Scan the ovary section (Figure 9.16) and look for a (Graafian) follicle, a circular arrangement of cells enclosing a central cavity. Examine the Graafian follicle an identify the follicular cells that produce estrogens. The ovum will be the largest cell in the follicle. Scan the image to find a corpus luteum a large amorphous-looking area that produces progesterone (and some estrogens).

Sketch and Label the Ovaries (Microscopic)

Graafian follicle, Corpus luteum, ovum

Figure 9.16

The paired oval testes of the male are suspended in a pouch-like sac, the scrotum, outside the pelvic cavity. In addition to the male sex cells, sperm, the testes produce the male sex hormone.

Testosterone
Promotes the maturation of the reproductive system accessory structures, brings about the development of the secondary sex characteristics. Both the endocrine and exocrine functions of the testes begin at puberty under the influence of the anterior pituitary gonadotropins.

Examine the image (Figure 9.17) of a section of testis. Identify the seminiferous tubules, which produce sperm, and the interstitial cells, which produce testosterone. The interstitial cells are scattered between the seminiferous tubules in the connective tissue matrix.

Sketch and Label the Testes (Microscopic)

Interstitial cells, Sperm cells

Figure 9.17

The thymus is a bilobed gland situated in the superior thorax, posterior to the sternum and anterior to the heart and lungs. Conspicuous in the infant, it begins to atrophy at puberty, and by old age is relatively inconspicuous.

Thymosin
Helps direct the maturation and specialization of a unique population of white blood cells called T lymphocytes or T cells. T lymphocytes are responsible for the cellular immunity aspect of body defense; that is, rejection of foreign grafts, tumors, or virus infected cells.

Figure 9.18

The pineal body is a small cone-shaped gland located in the brain.

Melatonin
The endocrine role of the pineal body in humans is still controversial, but it is known to play a role in the biological rhythms (particularly mating and migratory behavior) of other animals. In humans, melatonin appears to exert some inhibitory effects on the reproductive system that prevents precocious sexual maturation.

2) Table of Endocrine Gland Function

Construct a table listing all of the endocrine glands, their hormones and functions. Construct a table or use the table you can print off from the link below

TABLE OF ENDOCRINE GLAND FUNCTION