Learning Outcomes
By the end of this section, you should be able to:
- 26.1.1 Describe the function of the hypothalamus, pituitary gland, and adrenal cortex.
- 26.1.2 Discuss hormones associated with the hypothalamus, pituitary gland, and adrenal cortex.
Introduction to the Hypothalamus
The hypothalamus is critical to coordinating both nervous and endocrine responses to internal and external stimuli, making it a crucial component of the neuroendocrine system, which is central to regulatory function, as can be seen in Figure 26.2. This section will delve into the intricacies of the hypothalamus by exploring its functions and the hormones it produces.
Hypothalamus Function
The hypothalamus gland is located at the base of the forebrain—above the pituitary gland—and serves as a critical regulatory center in the body, responsible for coordinating both nervous and endocrine functions. The hypothalamus controls a range of essential physiological processes, including body temperature, hunger and thirst, water and electrolyte balance, blood pressure, heart rate, sleep and wake cycles, and reproductive behaviors. Additionally, the hypothalamus plays a crucial role in regulating the release of hormones from the pituitary gland, which controls many endocrine functions throughout the body.
Hypothalamus Hormones
The hypothalamus produces and releases several hormones, which play important roles in regulating various physiological processes in the body (Shahid et al., 2022). Some of the major hypothalamus hormones are included in Table 26.1. These hormones are released into the bloodstream and travel to their target organs or glands, where they stimulate or inhibit the release of other hormones or regulate various physiological processes.
| Releasing Hormone | Associated Hormones | Effect |
|---|---|---|
| Stimulating Hormones | ||
| Gonadotropin-releasing hormone (GnRH) | Luteinizing hormone (LH) Follicle-stimulating hormone (FSH) |
Stimulates gamete production and androgen production, which regulates reproductive functions |
| Thyrotropin-releasing hormone (TRH) | Thyroid-stimulating hormone (TSH) | Stimulates the thyroid gland to produce hormones and helps to regulate metabolism |
| Corticotropin-releasing hormone (CRH) | Adrenocorticotropic hormone (ACTH) | Stimulates the adrenal glands to produce cortisol, a stress hormone |
| Growth hormone–releasing hormone (GHRH) | Growth hormone | Promotes growth and development |
| Prolactin-releasing hormone (PRH) | Prolactin (PRL) | Promotes lactation from the mammary glands |
| Inhibitory Hormones | ||
| Prolactin-inhibiting hormone (PIH) | PRL | Inhibits the release of PRL from the pituitary gland |
| Somatostatin | Growth hormone TSH |
Inhibits the release of growth hormone and TSH from the anterior pituitary gland |
Introduction to the Pituitary Gland
The pituitary gland (see Figure 26.3), or pituitary, is a small, pea-sized gland that is a vital part of the endocrine system, regulating various physiological functions in the body. The pituitary, also known as the hypophysis, is located at the base of the brain and is often referred to as the “master gland” because it controls the secretion of hormones by many other glands. The pituitary is divided into two parts, the anterior pituitary and the posterior pituitary, each with unique functions and hormone secretions (Alatzoglou et al., 2020).
The anterior pituitary, also known as the adenohypophysis, is the front part of the pituitary. The adenohypophysis is composed of different types of cells that secrete various hormones (see the following section). The anterior pituitary hormones play essential roles in regulating growth and development, metabolism, reproduction, and stress response (Alatzoglou et al., 2020).
The posterior pituitary, also known as the neurohypophysis, is the back part of the pituitary. Unlike the anterior pituitary, it does not synthesize its own hormones, but stores and releases two hormones produced by the hypothalamus: oxytocin and antidiuretic hormone (ADH), also known as human vasopressin. Oxytocin is involved in the contraction of the uterus during childbirth and breast milk ejection during breastfeeding. ADH regulates water balance in the body by controlling the amount of water reabsorbed in the kidneys (Alatzoglou et al., 2020).
Pituitary Function
The pituitary’s primary function is to produce and secrete hormones that act on various organs and tissues throughout the body. Overall, the pituitary assists in regulating various bodily processes and maintaining homeostasis in the body.
Pituitary Hormones
Some of the major hormones produced by the pituitary include:
- Growth hormone (GH): Promotes the growth and development of bones, muscles, and organs
- Prolactin (PRL): Stimulates breast milk production
- Thyroid-stimulating hormone (TSH): Regulates the function of the thyroid gland
- Adrenocorticotropic hormone (ACTH): Stimulates the adrenal cortex to produce cortisol, which helps the body respond to stress
- Follicle-stimulating hormone (FSH): Stimulates the development of eggs in females and sperm in males
- Luteinizing hormone (LH): Regulates the production of sex hormones, including estrogen and testosterone
Introduction to the Adrenal Cortex
The adrenal glands, which are located on top of each kidney, consist of two layers: the adrenal medulla and the adrenal cortex. The adrenal medulla is the inner layer of the adrenal glands and is important for producing epinephrine and norepinephrine in response to stress. This chapter, however, will focus on the adrenal cortex as it relates to endocrine function. The adrenal cortex, as is seen in Figure 26.4, is the outer layer of the adrenal glands. The adrenal cortex produces several important hormones that are essential for proper functioning of the body. Each of the three layers of the adrenal cortex produces a different hormones. The outermost layer is called the zona glomerulosa; the middle layer is called the zona fasciculate; and the innermost layer is called the zona reticularis.
Adrenal Cortex Function
The hormones produced by the adrenal cortex regulate various bodily functions. These hormones maintain the body’s internal environment by regulating electrolyte, pH, and water balance; glucose metabolism; and immune function. Additionally, the adrenal cortex is involved in responding to stressors because its hormones help the body adapt to physical and emotional stress (Huecker et al., 2023; National Institutes of Health [NIH], 2017).
The adrenal cortex’s importance cannot be overstated—it is crucial for maintaining overall health and well-being. Without the hormones from the adrenal cortex, the body would struggle to maintain a stable internal environment, making it vulnerable to various health issues. Therefore, it is essential to maintain the adrenal cortex’s health and function to ensure optimal health and wellness (Huecker et al., 2023; NIH, 2017).
Link to Learning
The Hypothalamic-Pituitary-Adrenal Axis
The Foundation of Neuroscience Open Educational Resources presents information on the stress response. This educational video discusses the hypothalamic-pituitary-adrenal axis (HPA).
The HPA axis is a neuroendocrine system involved in the body’s stress response. The hypothalamus releases CRH, which stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH). ACTH then triggers the adrenal glands to produce cortisol, also known as the stress hormone, which regulates various physiological processes and helps the body cope with stress.
Adrenal Cortex Hormones
Some of the hormones produced by the adrenal cortex include:
- Mineralocorticoids: produced in the zona glomerulosa, these help regulate the balance of electrolytes, particularly sodium and potassium, in the body as well as water balance.
- Glucocorticoids: produced in the the zona fasciculate, these help regulate metabolism, immune function, and the body’s response to stress.
- Androgens: produced in the zona reticularis, these contribute to sexual development and fertility in males.