Chapter 25, Problem 1.1BGL

Summary Introduction

To label: The major endocrine glands in the given figure.

Introduction: The endocrine system is the collection of the endocrine glands. There are two types of glands found in the human body, namely endocrine or ductless glands and exocrine or duct glands. The secretions of the endocrine glands are called hormones. They are secreted directly into the bloodstream and are found to regulate the metabolisms of the body. The endocrine system is under the control of the hypothalamus.

Answer to Problem 1.1BGL

Pictorial representation:

Fig.1: Major endocrine glands

Explanation of Solution

1. 1. Hypothalamus: It is located in the brain below the thalamus and acts as a control center that connects the functions of the nervous system with the endocrine system. It regulates the secretion of the anterior pituitary gland. The hypothalamus is extended to form the posterior pituitary.
2. 2. Pituitary gland: It is situated at the base of the brain. The pituitary gland is divided into anterior (adenohypophysis) and posterior pituitary (neurohypophysis). The secretions of the anterior pituitary gland are called tropic hormones, which stimulate the secretion of other endocrine glands.
3. 3. Pineal gland: It is a small gland located in the brain. It is also called conarium or epiphysis cerebri. The secretion of the pineal gland is called melatonin, a serotonin-derived hormone, which regulates the sleep cycle.
4. 4. Thyroid gland: The thyroid gland is located at the base of the neck (below Adam’s apple). It is a butterfly-shaped organ having two lobes (left and right) connected by an isthmus. The thyroid gland secretes triiodothyronine (T₃), thyroxine (T₄), and calcitonin. Thyroid hormones regulate the metabolism of body.
5. 5. Parathyroid glands: The parathyroid glands are found in the neck region behind the thyroid gland. There are four parathyroid glands, each pair located above (superior parathyroid glands) and below (inferior parathyroid glands). The parathyroid glands secrete parathyroid hormone (PTH).
6. 6. Thymus gland: The thymus gland is located in the area between the lungs behind the sternum. It secretes thymosin, which induces the development of T lymphocytes, which plays a major role in the immune system.
7. 7. Adrenal glands: They are triangular-shaped glands and are called suprarenal glands since they are found on the top of the renal system. The adrenal gland is divided into two portions, adrenal cortex, and adrenal medulla. Hormones secreted by adrenal glands play a role in regulating metabolism, stress, immune system, and blood pressure by maintaining the salt level in blood.
8. 8. Pancreas: The pancreas is a dual or heterocrine gland, which secretes hormones (endocrine) and enzymes (exocrine). It is located behind the stomach as a long flattened gland. The main function of the pancreas is to regulate the blood glucose level.
9. 9. Ovaries: Ovaries are the part of the female reproductive system situated along the left and right side of the uterus. At puberty, ovaries secrete hormones, namely estrogen, testosterone, progesterone, and inhibin. These hormones play a vital role in menstruation and fertility.
10. 10. Testes: Testes are the male reproductive gland located within the scrotum. Testes secrete hormones like androgens. Testosterone is the primary androgen produced by the testes. The main function of testes is the production of sperm.