Module 2 The Endocrine System

1.2.1 page 6

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Endocrine Glands

In the previous module you learned about the basic unit of the nervous system—the neuron and how communication occurs through neural pathways. Now, you will learn about the major glands of the endocrine system and how communication through the use of special chemical messengers called hormones occurs.

 

 Endocrine glands are ductless glands; they do not release their secretions into a duct as exocrine glands do. Instead, endocrine glands secrete their hormones directly into the blood which acts as their transport medium. As the hormones pass cells, only those cells with special receptors will react to their presence. These cells are called target cells. Lipid-soluble hormones and water-soluble hormones activate their target cells very differently. Hormones interact together and in many instances, one hormone counteracts the action of a second hormone. Hormones such as these are called antagonistic hormones. This type of action is illustrated in the figure on the left.

 

Some hormones, called tropic hormones, influence other endocrine glands. These hormones are very important in the control and regulation of the endocrine system. They are secreted by the hypothalamus/pituitary complex. You can view the regulatory pathway of tropic hormones in Figure 13.10 on page 441 of your textbook. You may want to copy this pathway and store it in your course folder for later reference.

 

 

Read

To help you identify the main endocrine glands read pp. 436 – 441 in your textbook. Summarize your readings about the endocrine glands in a chart with the following headings: “endocrine gland”, “hormone produced by gland” and “primary effect of the hormone”. Place this chart in your course folder for future reference.

Watch and Listen

To further explore and review these concepts visually, watch the following video

Hormones

 

Try This

Instructions

TR 4

Practice labeling the endocrine glands, identifying the hormones they produce and describing the main functions of the hormones in the exercise that follows. After you have completed the exercise and have auto-checked it, file it in your course folder for access when you are studying.

 

Download the diagram of the endocrine system.

1. Label the major endocrine glands numbered 1 - 5 on the diagram.
2. List the hormones (the number of hormones to be identified is indicated in brackets) that each gland produces. The ovary and testis will be studied in Unit B. Although the thymus and pineal gland are part of the endocrine system, you are not responsible for studying them for this course.
3. Construct and complete a table with the following headings:
   
   

   Endocrine Gland

   Hormone

   Target Cells

   Primary Function

   
   

 

Self-Check Answers

TR 4b.

Labeling of the glands on the diagram and the hormones that the glands produce is as follows:

 

Structure #1: hypothalamus; secretes releasing and inhibiting factors/hormones

 

Structure #2a: anterior pituitary gland; secretes human growth hormone, thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), and follicle stimulating hormone (FSH), luteinizing hormone (LH), and prolactin, the last three hormones to be studied in detail in Unit B.

 

Structure #2b: posterior pituitary: releases oxytocin (to be studied in detail in Unit B) and antidiuretic hormone (ADH);

 

Structure #3: Parathyroid glands; secrete parathormone (PTH)

 

Structure #4: Thyroid gland; secretes thyroxine and calcitonin

Structure #6: Adrenal glands; adrenal cortex secretes cortisol, aldosterone, and gonadotropins (which are studied in Unit B); adrenal medulla secretes epinephrine and norepinephrine

 

Structure #7: Islet cells of pancreas; insulin and glucagon

 

Structure #8: Ovary secretes estrogen and progesterone; to be studied in Unit B

 

Structure #9: Testis secretes testosterone and inhibin; to be studied in Unit B

 

The completed table should incorporate the following:

Endocrine Glands, Their Hormones, Target Cells and Main Functions

EndocrineGland	Hormone	Target Cells	Primary Functions
Hypothalamus	Releasing/Inhibiting hormones	Pituitary Gland	Regulates secretion by anterior pituitary
Posterior Pituitary	Antidiuretic Hormone (ADH)     Oxytocin	Kidney     Uterus/Breasts	Increases water reabsorption   Stimulates contraction of uterus and release of milk by breast glands
Anterior Pituitary	Thyroid Stimulating Hormone (TSH)   Adrenocorticotropic Hormone (ACTH)   Growth Hormone (hGH)       Follicle Stimulating Hormone (FSH)   Luteinizing Hormone (LH)       Prolactin	Thyroid Gland     Adrenal Cortex     Most Cells       Ovary/Testis     Ovary/Testis       Breast cells	Stimulates thyroid gland to secrete thyroxine   Stimulates adrenal cortex to secrete cortisol   Stimulates cell division, growth of bones, and metabolism   Stimulates production of egg and sperm cells   Stimulates production of male and female sex hormones   Stimulates milk production
Adrenal Medulla	Epinephrine/Norepinephrine	Most cells	Fight or flight hormones
Adrenal Cortex	Cortisol     Aldosterone	Most cells     Kidney	Raises blood glucose and breaks down protein   Increases sodium retention and increases water reabsorption
Parathyroid Glands	Parathormone (PTH)	Bone cells	Stimulates calcium release from bones
Thyroid Gland	Thyroxine       Calcitonin	Most cells       Bone cells	Increases metabolic rate and regulates growth and development   Stimulates bones to absorb calcium
Pancreas	Insulin         Glucagon	Most cells         Liver cells	Increases permeability of glucose in cells; stimulates liver cells to convert glucose to glycogen   Stimulates release of glucose by converting glycogen to glucose
Ovary	Estrogen           Progesterone	Uterus/Other cells         Uterus	Stimulates growth of uterine lining; stimulates development of female secondary sex characteristics   Promotes growth of uterine lining; inhibits uterine contractions during pregnancy
Testes	Testosterone           Inhibin	Testis/Other cells         Testis	Promotes sperm production; stimulates development of male secondary sex characteristics   Inhibits sperm production