7.1 Endocrine Introduction

The endocrine system is considered the body’s “chemical messenger system.” It is a complex network that plays a role in maintaining homeostasis within the human body. Endocrine glands secrete hormones into the bloodstream, where they travel to target organs and tissues and initiate specific physiological responses.

Central to the endocrine system’s responsibilities are the regulation of metabolism, growth, and energy balance. Metabolism, the complex set of chemical reactions that occur within our cells, determines how our bodies use and store energy. For example, insulin, a hormone produced by the pancreas, plays a critical role in regulating glucose metabolism and ensures that blood sugar levels are maintained within an optimal range. Thyroid hormones, produced by the thyroid gland, influence the metabolic rate and affect how our bodies utilize energy and synthesize essential molecules.

Growth, a second responsibility of the endocrine system, is primarily governed by the secretion of growth hormone from the pituitary gland. This hormone stimulates the growth and development of various tissues, particularly during childhood and adolescence. It also continues to play a role in tissue maintenance and repair throughout adulthood.

Energy balance, the third responsibility of the endocrine system, refers to the equilibrium between energy intake (through food and drink) and energy expenditure (through physical activity and metabolic processes). Hormones like leptin, released by adipose (fat) tissue, help regulate appetite and satiety, while others, such as adrenaline, manage short-term energy demands, like the “fight or flight” response.

Although the endocrine system has intricate control over these vital processes of metabolism, growth, and energy balance, it is vulnerable to disruption. One of the most common endocrine disorders, diabetes mellitus, impacts millions of individuals worldwide. Diabetes mellitus disrupts the finely tuned balance of blood glucose levels when the pancreas does not produce enough insulin (type 1 diabetes) or when the body’s cells do not respond effectively to insulin (type 2 diabetes). This disruption results in chronically elevated blood sugar levels, which can cause serious complications affecting the cardiovascular system, kidneys, and nerves.

Adrenal and thyroid disorders encompass a wide spectrum of conditions that manifest in various ways. These disorders can range from minor hormonal imbalances to significant impacts on metabolism, energy levels, and overall well-being. For example, an overactive thyroid, referred to as hyperthyroidism, can cause symptoms like rapid heart rate, weight loss, and anxiety. An underactive thyroid, referred to as hypothyroidism, can cause fatigue, weight gain, and depression. The adrenal glands, situated atop the kidneys, secrete hormones like cortisol and adrenaline, which play crucial roles in stress responses and metabolic regulation. Disorders of the adrenal glands, such as Cushing’s syndrome or Addison’s disease, can disrupt these processes with a wide range of symptoms, affecting blood pressure, immune function, and more.

This chapter will review the anatomy and physiology of the endocrine system and discuss risk factors, cultural factors, socioeconomic factors, and assessments related to the general endocrine system. Three major glands of the endocrine system include the pancreas, thyroid, and adrenal glands. This chapter will also discuss common alterations affecting these three glands.