The endocrine system is one of two systems that coordinate the functions of the body. The other system is the nervous system. Read 11 Facts About the Nervous System Every Nursing Student Should Know.
The endocrine system consists of a series of organs and glands throughout the body that produce, store, and secrete special chemical messengers. These chemical messengers are hormones. Hormones travel through the blood to specific target cells throughout the body.
The endocrine system is responsible for (1) the reproductive system, (2) growth and development, (3) homeostasis, (4) and metabolism. Hormones can also influence behavior. This article contains 10 Facts About the Endocrine System Every Nursing Student Should Know.
1. Hormones are the Chemical Messengers.
Hormones are chemical messengers. They are released into the bloodstream and travel to a distant target tissue and bind to receptor sites. Consequently, an alteration of the cellular environment or the regulation of the level of a hormone causes the release of hormones.
The release of hormones can be constant or only when needed. The amount of hormone secreted can change as needed. Therefore, the effects of hormones can be immediate or it can take time. The effect of hormones can be short or long-lasting. Also, hormones can affect only certain cells or the whole system.
2. A Feedback System Regulates the Hormones of the Endocrine System.
The regulation of endocrine activity is under the control of mechanisms that stimulate or inhibit hormone synthesis and secretion. In this case, these mechanisms are feedback systems. They include positive and negative feedback systems.
A feedback system is a highly specialized mechanism that regulates hormone levels. Hence, the feedback is dependent upon the blood level of a particular substance. The substance can be a hormone or another chemical compound which is regulated by, or responsive to, a hormone.
Negative feedback is the most common type of feedback system. Accordingly, with negative feedback, the gland responds to the stimulus by increasing or decreasing the secretion of a hormone based on feedback from different factors.
A common example of a negative feedback system is a thermostat. A thermostat keeps a room regulated at a set temperature. When cold air enters a room it activates the thermostat and causes the system to release heat. When the room reaches the preset temperature, the thermostat turns off preventing more warm air entering the room.
An additional example would be with blood glucose levels. Elevated blood glucose levels stimulate the pancreas to secrete insulin. When blood glucose levels decrease the secretion of insulin also decreases.
Positive feedback is an additional system that regulates hormone secretion. Unlike the negative feedback mechanism which reduces the original effect of the stimulus, the positive feedback system enhances the original target action greater than normal.
An example of this would be the action of oxytocin during childbirth. An increase in uterine contractions due to pressure receptors in the vagina stimulates the release of oxytocin. Increase pressure on the vagina during childbirth signals the brain to release more oxytocin. This causes stronger uterine contractions. After birth and the pressure ends, oxytocin secretion decrease.
3. The Organs of the Endocrine System are Called Glands.
The endocrine gland includes the hypothalamus, pituitary gland, thyroid gland, parathyroid gland, adrenals, pancreas, ovaries, testes, and pineal. Consequently, these glands are where hormones are produced and secreted into the bloodstream. When hormones enter the bloodstream, they eventually affect a specific tissue called the target tissue.
The target tissue is the body tissue or organ that the hormone affects. So, the hormone recognizes a target tissue by the receptors. Accordingly, the receptors are sites on or within cells of the target tissue in which the hormones interact.
4. The Hypothalamus and the Pituitary Gland are two of the Major Organs of the Endocrine System.
The hypothalamus is located in the diencephalon. This gland controls much of the body’s physiological functions including hunger, thirst, fluid balance, and body temperature. Therefore, the hypothalamus is an important part of the endocrine system. It also controls the pituitary gland and most of the other glands in the endocrine system. The relationship between the hypothalamus and the pituitary gland is an important part of the endocrine system.
The hypothalamus secretes many different hormones. Firstly, an important group of hormones that are secreted from the hypothalamus is the releasing hormones. And, secondly, another important group of hormones that are secreted by the hypothalamus is the inhibiting hormones. These hormones function to either stimulate release or inhibit secretions of hormones from the anterior pituitary gland.
The pituitary gland is a small gland about the size of a grape. It is part of the diencephalon and located at the base of the brain. Another name for the pituitary gland is the hypophysis. It is very important in the control of other endocrine glands. The pituitary acts only under the control of the hypothalamus.
There are two portions or segments of the pituitary gland. These segments are the posterior pituitary and the anterior pituitary.
Another name for the anterior pituitary is the adenohypophysis. The anterior pituitary is under the control of the hypothalamus. It makes and secretes a number of different hormones called tropic hormones. These hormones affect the function of specific target organs.
Hormones of the Anterior Pituitary
|Growth hormone (GH)||Essential to normal tissue growth and maturation. It also has an impact on aging, sleep.|
|Thyroid stimulating hormone (TSH)||Regulates the activity of the thyroid.|
|Adrenocorticotropic hormone (ACTH)||Regulates the release of cortisol from the adrenal cortex.|
|Melanocytes stimulating hormone (MSH)||Promotes pituitary secretion of melanin which darkens the skin.|
|Follicle-stimulating hormone (FSH)||Stimulates estrogen secretion and sperm production.|
|Luteinizing hormone (LH)||Stimulates ovaries for ovulation and the testes for sperm production.|
|Prolactin||Increase milk production in lactating women.|
The posterior pituitary is an extension of the hypothalamus. Another name for the posterior pituitary is the neurohypophysis. The hormones secreted by the posterior pituitary are the antidiuretic hormone (ADH) and oxytocin. The antidiuretic hormone is also known as vasopressin which is a potent vasoconstrictor.
These hormones are actually produced by the hypothalamus and stored by the posterior pituitary gland. So, the release of these hormones is under the control of the appropriate stimuli.
The major role of the antidiuretic hormone is the regulation of fluid volume in the body. The purpose of an antidiuretic is to decrease urination. Therefore, when there is a decrease in urination there is an increase in fluid volume in the body.
There is the secretion of the antidiuretic hormone by the hypothalamus when there is a decrease in blood volume in the body and an increase in osmolarity of the blood. An increase in osmolarity in the blood means that there are more solid particles in the blood. So, the release of the antidiuretic hormone causes the kidneys to absorb more water thereby increasing circulating fluid volume.
Oxytocin causes an increase in uterine contractions. It also stimulates the ejection of milk from the mammary ducts. Oxytocin release is stimulated by receptors in the nipple of lactating women and by vaginal pressure.
5. The Thyroid Gland is Responsible for Many Metabolic Processes in the Endocrine System.
The thyroid gland is located in front of the trachea. It is a highly vascular organ and controls metabolic processes throughout the body. The release of the thyroid-stimulating hormone (TSH) from the anterior pituitary gland regulates the thyroid gland.
When circulating levels of thyroid hormone are low, the hypothalamus releases the thyrotropin-releasing hormone (TRH). Thereby, the release of TRH causes the release of the thyroid-stimulating hormone (TSH) by the anterior pituitary gland. There are three hormones produced and secreted by the thyroid gland. These include thyroxine(T4), triiodothyronine(T3), and calcitonin.
Thyroxine and Triiodothyronine
Thyroxine (T4) is the most abundant thyroid hormone. Triiodothyronine is more potent and has a greater metabolic effect. Thyroxine (T4) and Triiodothyronine (T3) affect metabolic rate, caloric requirements, oxygen consumption, carbohydrate and lipid metabolism, growth and development, brain functions, and other nervous system activities.
The cells of the thyroid gland produce calcitonin in response to high circulating calcium levels. When released calcitonin inhibits calcium reabsorption. It also increases renal secretion of calcium and phosphorus. Another role is the increased storage of calcium in the bone. These effects lower calcium levels.
6. The Parathyroid Gland Regulates Blood Levels of Calcium.
The parathyroid glands are small and oval-shaped. They are located behind each of the thyroid lobes. Thus, the parathyroid glands secrete the parathyroid hormone. The major role of the parathyroid gland is to regulate the blood level of calcium.
The actions of the parathyroid hormone are on the bone and the kidneys. It also acts indirectly on the gastrointestinal tract. When the parathyroid hormone is secreted it increases serum calcium concentration and decreases serum phosphate levels. So, when the serum calcium level is low, parathyroid hormone secretion increases. When the serum calcium level is high, parathyroid hormone secretion decreases.
The adrenal glands are small glands located on the upper portion of each kidney. Each gland consists of a medulla and a cortex.
The adrenal medulla is the inner part of the gland. Thus, the medulla secretes the catecholamines, epinephrine, norepinephrine, and dopamine.
Catecholamines are usually considered neurotransmitters but are considered hormones when secreted by the adrenal medulla. Catecholamines are an essential part of the body’s response to stress.
The adrenal cortex is the outer part of the adrenal gland. It is responsible for the secretion of steroid hormones. These hormones are classified as glucocorticoids, mineralocorticoids, and androgens. Also, any hormone synthesized by the adrenal cortex is called a corticosteroid.
Glucocorticoids regulate blood sugar. Cortisol is the most abundant and potent glucocorticoid. One major function of cortisol is the regulation of blood glucose concentration. It also has anti-inflammatory action. Also, cortisol helps maintain vascular integrity and fluid volume.
Mineralocorticoids are essential for the regulation of fluid and electrolyte balance. Aldosterone is a potent mineralocorticoid. It maintains extracellular fluid volume. Also, It acts at the renal tubule to promote renal reabsorption of sodium and excretion of potassium.
Adrenal Androgen stimulates sex drive, and also, pubic and axillary hair growth in females. Androgens are converted to estrogen in the peripheral tissue of females. However, there is a negligible effect of adrenal androgen in males.
7. The Pancreas has Both Exocrine and Endocrine Functions.
The pancreas is a lobular, soft gland. It is located behind the stomach. The pancreas has both exocrine and endocrine functions. The Islets of Langerhan is the hormone-secreting portion of the pancreas.
The pancreas is an accessory organ of the digestive system. Therefore, this part of the gland is the exocrine gland. It produces and secretes digestive enzymes that help to break down starches, fats, and proteins. In contrast, the part of the pancreas that acts as an endocrine organ produces hormones that regulate blood sugar.
There are four types of cells in the pancreas that secrete hormones. These include alpha, beta, delta, and F cells. However, only alpha and beta cells are discussed below.
Alpha cells synthesize and release the hormone glucagon. Consequently, glucagon is released in response to low blood glucose levels, the ingestion of protein, and exercise.
Beta cells produce and secrete insulin. Insulin is the principal regulator of metabolism. Moreover, Insulin facilitates the transport of glucose across cell membranes. The major stimulus for insulin synthesis and secretion is an increase in blood glucose levels.
8. Melatonin is Released by the Pineal Gland.
The pineal gland is located near the center of the brain. It is composed of cells that secrete melatonin. Consequently, exposure to darkness causes the release of melatonin. Therefore, melatonin regulates the timing of the circadian rhythm and also has effects on the reproductive system. It also has an effect on immune regulation and the aging process.
9. Ovaries are the Reproductive Organ in Females.
The chief function of the ovaries in females is to produce and store eggs. In females, the ovaries produce estrogen. Therefore, it is responsible for the development of the reproductive organ and secondary sex characteristics in females. The ovaries also produce progesterone. This helps regulate the menstrual cycle in females.
10. Testes are the Reproductive Organ in Males.
The chief function of the testes in males is to produce and store sperm. The testes also produce testosterone. Therefore, the secretion of testosterone is responsible for the development of the reproductive organs and secondary sex characteristics and males.
The endocrine system consists of a series of organs and glands throughout the body that produce, store, and secrete special chemical messengers. Moreover, the endocrine system is one of two systems that coordinate the functions of the body. The other system is the nervous system. so, don’t forget the check out 11 Facts About the Nervous System Every Nursing Student Should Know. Also, read Spinal and Cranial Nerves. As a result, these three articles will help with your understanding of the control systems of the human body.
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Mosby’s Medical Dictionary (2017). 10th ed. St Louis, MO. Elsevier Inc.
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