The Endocrine System: Structure and Functions

This article explains the endocrine system, its glands, hormones, and functions. It describes the roles of insulin and glucagon in controlling blood glucose levels. It also explores the effects of hormone imbalance, using underactive thyroid. The article also discusses the modes of action in the endocrine and nervous system.

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The Endocrine System: Structure and Functions
The endocrine system is composed of glands that generate and release, chemical compounds,
hormones produced in the body that control cells’ or organs functions. The primary functions
of these hormones are to control body development, metabolism, body processes, and sexual
development and function (Hoar and Randall, 2014). The hormones travel through the
bloodstream and are distributed to various body organs.
The primary glands making up the endocrine system comprise of the sexual reproductive
organs, pituitary, hypothalamus, pineal body, thyroid, adrenals, and parathyroids. The
pancreas also plays an active role in hormonal secretion and in digestion thus making up the
endocrine system.
 Hypothalamus
Situated at the brain in its inferior middle part and is essential in metabolism, satiety control,
and the control of heat in the body. It also produces hormones that function to suppress or
stimulate the hormonal secretion in the pituitary gland (Harris, 2009).
 Pituitary gland
Positioned at brain base below the hypothalamus and secretes hormones that regulate the
roles of the most of other endocrine glands. Examples of hormones secreted by the pituitary
gland include development hormones, thyroid-stimulating hormone (TSH),
adrenocorticotropin hormone (ACTH), luteinizing hormone (LH), antidiuretic hormone,
prolactin, follicle stimulating hormone (FSH) and oxytocin.
 Thyroid gland

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Found in the bottom front part of the neck and secretes thyroid hormones responsible for
regulation of body metabolism (Ranade et al., 2008).
 Parathyroid glands
These comprises of two minor glands entrenched on the thyroid gland. They secrete the
parathyroid hormone responsible for controlling calcium levels in bones and bloodstream
(Fancy et al., 2010).
 Adrenal Glands
These are triangular-shaped glands located at the superior part of both kidneys and comprises
of two parts. The adrenal cortex is the outer part, and it secretes corticosteroid hormones
responsible for balancing water and salt in the body. The inner part is the adrenal medulla in
charge of the secretion of catecholamine hormones that aid the body in acclimatizing with
emotional and physical stress.
 Penal body
This is located centrally in the brain. It produces melatonin hormone which aids in the body’s
control of the wake-sleep cycle.
 Reproductive Glands
These the primary producers of sex hormones. Testes in men are found in the scrotum and
produce androgen hormones, which influences various sexual growth and development
features in males. The ovaries in the females are located on both sides of the uterus, and
function to secrete estrogen and progesterone and ovum. These hormones are responsible for
the regulation of different female sexual development features.
 Pancrease

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This is an organ that extends to the rear part of the stomach. The digestive enzymes are
released by the pancreas, whereas glucagon and insulin are produced by the endocrine
pancreas and are responsible for the regulation of blood glucose level.
Source: (Hoar and Randall, 2014)
Control of blood glucose levels --Roles of insulin and glucagon
The islet cells found in the pancreas secrete insulin and glucagon as feedback to blood sugar
levels but in an opposite manner. Beta cells in the pancreas produce insulin which is
stimulated by high blood glucose. While the pancreas always secrets low level of insulin, the

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amount released into the blood increases with the increase in glucose levels. Likewise, the
fall in blood glucose level causes the pancreatic islets to lower the amount of insulin secretion
(Bansal and Wang, 2008).
The alpha cells of the pancreatic islets in the pancreas produce glucagon just like in the case
of insulin, but in the opposite direction (Quesada et al., 2008). High levels of glucose in the
blood cause none secretion of glucagon which prompts the release of glucose stored in the
liver into the bloodstream, with the overall effect of raising the level of glucose in the blood.
Glucagon also triggers some muscle cells in addition to the liver to produce glucose from the
building blocks sourced from other body nutrients (Taborsky, 2010).
Source: (Bansal and Wang, 2008).
Effects of hormone imbalance, using underactive thyroid

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Hormone imbalance also called hypothyroidism is a condition caused by underactive thyroid.
A decrease in the production of thyroid hormone slows down body processes and change.
Hypothyroidism affects different body systems.
Hypothyroidism causes brain fog by affecting the memory and the ability to think straight
thus causing mental fuzziness. Low levels of thyroid hormone can lead to sadness and
depression. An underactive thyroid can also cause the thinning of the eyebrow by causing
loss of eyebrow hair which commonly begins at the outer edges of the browns. The condition
can also lead to jaundice especially in infants, the yellowing of the whites of the eyes and
skin (Rastogi and LaFranchi, 2010). Goiter is another illness caused by hypothyroidism
which is also prevalent in people diagnosed with diseases such as Hashimoto thyroiditis.
An underactive thyroid also leads to high blood pressure through interactions with the blood
vessels in the circulatory system. Low production of thyroid hormone slows down the
metabolism of the body and can lead to general symptoms such as fatigue, swelling of hands
and feet, intolerance to cold, and overweight. The condition can also cause menstrual
changes. Women diagnosed with the condition may experience irregular periods and
alterations in menstrual flow. As a result, this may affect fertility presenting the challenge of
becoming pregnant (Rastogi and LaFranchi, 2010).
Modes of action in the endocrine and nervous system
The central nervous system (CNS) and the endocrine system are well adapted to respond to
the changes in the external environment and within the body through specialized cells known
as neurons and hormones respectively. The nerve impulse transmission along a neuron from
either sides takes place due to changes in electrical variations over the neuron membrane. On
the other hand, hormones contained in the endocrine system affect physiological activity and

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only respond to specific receptors sites in the body. Both the CNS and the endocrine systems
send impulses to all parts of the body in response to external stimuli (Mai and Paxinos, 2011).

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References
Hoar, W.S. and Randall, D.J., 2014. The endocrine system(Vol. 2). Academic Press.
Ranade, A.V., Rai, R., Pai, M.M., Nayak, S.R., Krisnamurthy, A. and Narayana, S., 2008.
Anatomical variations of the thyroid gland: possible surgical implications. Singapore medical
journal, 49(10), p.831.
Fancy, T., Gallagher, D. and Hornig, J.D., 2010. Surgical anatomy of the thyroid and
parathyroid glands. Otolaryngologic Clinics of North America, 43(2), pp.221-227.
Bansal, P. and Wang, Q., 2008. Insulin as a physiological modulator of glucagon
secretion. American Journal of physiology-endocrinology and metabolism, 295(4), pp.E751-
E761.
Taborsky Jr, G.J., 2010. The physiology of glucagon. Journal of Diabetes Science and
Technology, 4(6), pp.1338-1344.
Quesada, I., Tudurí, E., Ripoll, C. and Nadal, Á., 2008. Physiology of the pancreatic α-cell
and glucagon secretion: role in glucose homeostasis and diabetes. Journal of
Endocrinology, 199(1), pp.5-19.
Rastogi, M.V. and LaFranchi, S.H., 2010. Congenital hypothyroidism. Orphanet journal of
rare diseases, 5(1), p.17.
Mai, J.K. and Paxinos, G. eds., 2011. The human nervous system. Academic Press.
Harris, G.W., 2009, September. Hypothalamic control of the anterior pituitary gland.
In Hormonal Influences in Water Metabolism, Volume 4: Book 2 of Colloquia on
Endocrinology(Vol. 831, p. 106). John Wiley & Sons.

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