Lab 2: Endocrine Anatomy & Histology

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Lab 2: Endocrine Anatomy & Histology

Reading LABPAQ: Endocrine System pages 14-34

Objectives 1. To identify the major endocrine glands and tissues of the body. 2. To identify the histology of the major endocrine glands and relate their structure to their function. Identify the major endocrine glands and tissues of the body. 3. Relate each endocrine gland to the hormone(s) it produces. 4. Explain how hormones work to maintain homeostasis in the body.

Introduction The endocrine system consists of a series of glands that

are not physically interconnected. A gland makes a product and releases it. The endocrine glands create and release hormones into the blood stream which than function as chemical messengers. Endocrine glands differ from exocrine glands like sweat glands in that they do not have a duct.

Many organs such as the heart and thymus have a minor endocrine functions. We will not focus on those organs and functions at this time, we will pick them up when we get to those systems. In addition the reproductive organs have a major endocrine function but we will focus on the ovaries and testes when we cover the reproductive system. For this lab we will be focusing on the anatomy of all remaining endocrine organs and glands, and the histology of some of the glands. Why do we need to look at the tissues? The tissues produce the hormones, most problems with the endocrine system start in the tissues.

Hypothalamus: The hypothalamus is located under the thalamus in the lower part of the brain. It is part of the diencephalon of the brain. Histologically it looks a great deal like the posterior pituitary.

Pituitary (hypophysis) The pituitary is attached to the distal part of the hypothalamus. It divides into to lobes: anterior and posterior. Anterior Pituitary (adenohypophysis) creates a number of different hormones. Looking at it under a microscope and it looks `busy.' It contains a large number of cells called secretory cells. Posterior Pituitary (neurohypophysis) does not create hormones it stores hormones from the hypothalamus. When compared to the anterior pituitary it looks empty. It contains neural cells called pituicytes.

Anterior Pituitary

Posterior Pituitary

Mark any cell as a secretory slide

Mark any nuclei as a pituicyte

Thyroid The thyroid is located anterior to the larynx. It consists of 2-lobes connected by an isthmus. Thyroid tissue looks like it contains bubbles. The bubble is a follicle. Each follicle is made up of follicular cells (those are the building blocks of a follicle) and it is filled with a colloid mixture. Parafollicular cells make up all of the cells outside of the follicle.

Parathyroid The parathyroid is found on the posterior side of the thyroid. It is made up of 4 small glands although the number may vary. The tissue is densely packed with chief cells. Most of the cells present are chief cells and those are the cells that produce parathyroid hormone.

Thyroid

Parathyroid

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Adrenal Gland (also called suprarenal gland) Paired adrenal glands are located on the top of the kidneys. They are made up of a capsule, cortex (outer region) and medulla (inner region). An opening in the middle of the adrenal medulla is just the blood vessel. The cortex divides into 3 zones or zona. Each zone produces a separate steroid hormone. Adrenal Gland

To the left the adrenal cortex is broken into zones. For this lab students will not be asked to label the zones. The notation for the medulla means that it depends on how the slide was cut. Sometimes the medulla is not clear. That should not be a problem in this lab.

 Pancreas The pancreas is located under the stomach and close to the upper small intestine (duodenum). It looks like `knobby' tissue. In addition to its endocrine function the pancreas is an exocrine organ. The exocrine function involves producing digestive enzymes released into the small intestine. We make more digestive enzymes than insulin so most of the cells are acinar cells that produce digestive enzymes. The pancreatic isles, also called isles of Langerhan, produce insulin. It is very difficult to identify islets. Many students identify ducts as islets. It is easy to tell the difference. If you focus closely and there is a hole in the middle than it is a duct. If not it is an islet. You have to use a lower power to identify them. If you are using a higher power you cannot separate them from the background acinar cells.

Pancreas

Pancreas under the stomach

Pancreas at low scanning power

Duct compared to islets The duct has a very small opening and the

islets are labeled with an I.

Islet at high power, it is difficult to seprate from the rest of the tissues. That is why it is best to identify them using a

lower power.

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Pineal gland The pineal gland is part of the diencephalon. It is located behind the thalamus. The histology is primarily nervous and it looks very much like the posterior pituitary.

Reproductive Glands The ovaries and testes are very important endocrine glands, but we will focus on them in the upcoming unit.

Thymus The thymus is located anterior to the heart distal to the thyroid. It primarily functions as a lymphoid tissue although it has an important endocrine function that involves the production of thymosins. We will view the histology during the lymphatic and immunity unit.

Materials Microscope Slides LABPAQ Kit

o Slide - Adrenal Gland o Slide - Anterior Pituitary Gland o Slide - Thyroid Gland o Slide ? Pancreas Images (supplied) o Endocrine system o Posterior pituitary o Parathyroid Digital Camera Paint program or other labeling software

Procedure Although the LABPAQ kit is pretty complete it does not include some of the slides that we need nor does it include some of the images that you need to review. When that happens I will supply the images in 2 locations. The first location will be embedded in the lab assignment; the second location will be as independent files that can be added to the write-up. All images must be completely labeled with all of the structures listed in blue. Points will be lost for images that are not completely labeled.

HINT: When we examined tissue types in API, students needed to use the highest power possible to focus on the small structures. In APII we will be looking at larger structures so you will want to use 4x (40x total) or 10x (100x total) first, you may need 40x (400x) but use the best image. If you use the higher power you may not be able to identify structures. I will recommend a power for the first couple of labs but it is really up to what gives you the best image. I am just giving suggestions.

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