Endocrine Glands And Hormones: Function, Organs, Diseases

What are Endocrine Glands?

The endocrine glands in the human body are organs that produce and secrete hormones directly into the bloodstream. They control a wide array of physiological processes as those related to growth, metabolism, and homeostasis. This includes major glands such as the pituitary, thyroid, adrenals, and pancreas, which participate in the maintenance of internal balance.

Unlike exocrine glands, which release secretions through ducts to specific locations like sweat glands or salivary glands, the endocrine glands are ductless and require the circulatory system for transmission. This direct release into the circulatory system results in a diffuse action, systemic in nature, required for the coordination of activities of the body over long periods and responses to internal and external stimuli. The endocrine system plays a vital role in maintaining homeostasis, affecting growth and development, and regulating reproduction, therefore, keeping a person healthy and fit.

Pituitary Gland — The Master Gland

The pituitary gland is a pea-sized endocrine gland located at the base of the brain directly behind the socket of the eye and just below the hypothalamus. It is enclosed within a bony prominence of the sphenoid bone, the sella turcica.

Pituitary Hormones

• Growth Hormone (GH): Stimulation of growth and cell reproduction.

• Prolactin: Milk production within the mammary glands.

• Adrenocorticotropic Hormone (ACTH): Stimulation of the adrenal cortex to release cortisol.

• Thyroid-Stimulating Hormone (TSH): Stimulation of the thyroid gland to produce thyroid hormones.

• Follicle-stimulating hormone (FSH): It regulates the reproductive process. This includes activities such as maturation of ovarian follicles and spermatogenesis.

• Luteinizing Hormone (LH): Ovulation stimulation and maintenance of sex hormone secretion.

• Antidiuretic Hormone (ADH): Water amount regulation in the body, water reabsorption in kidneys.

• Oxytocin: Uterine contractions at birth, Milk letdown, lactation.

Functions

This is also known as the "master gland". Such functions, through the release of hormones, actually do different facets of the body to control other endocrine glands. It has a very vital role in growth, metabolism, stress response, and reproductive processes.

Hypothalamus — The Master Regulator

The hypothalamus lies just above the pituitary gland and communicates with it through the hypothalamic-pituitary portal circulation, a system of blood vessels that enables the direct exchange of hormones between the two.

Hypothalamic Hormones

• Thyrotropin Releasing Hormone (TRH): Stimulates TSH release from the pituitary.

• Corticotropin Releasing Hormone (CRH): Stimulates ACTH release from the pituitary.

• Gonadotropin-releasing hormone (GnRH): Controls the release of FSH and LH from the pituitary.

• Growth Hormone Releasing Hormone: stimulates growth and development.

• Somatostatin: Inhibits GH and TSH release.

• Dopamine: Inhibits prolactin release.

Role

It has control over the activities of the pituitary. The hypothalamus indirectly regulates many of the body's functions, from overall growth and development to metabolic rate, responses to stress and reproductive activities.

Thyroid Gland

It is located anterior to the trachea in the neck. The thyroid gland has two lobes joined at an isthmus

Thyroid Hormones

Thyroxine (T4) and Triiodothyronine (T3): This mediates the metabolic processes, producing energy, and growth.

Calcitonin: This reduces blood calcium through the inhibition of bone resorption and with an increased calcium deposition within the bones.

Functions

Thyroid hormones regulate the metabolic rate, which affects growth. In addition, they are also necessary for maturation of nervous tissue.

Parathyroid Glands

The parathyroid gland has four small glands on the posterior surface of the thyroid gland.

Parathyroid Hormone

Parathyroid Hormone (PTH): As a result of increased bone resorption, improved renal calcium reabsorption, and stimulation of intestinal calcium absorption, PTH brings up the level of calcium in the blood.

Functions

PTH controls the level of calcium required to keep the proper working of the muscles, transmission of nerve impulses, and correct bone health.

Adrenal Glands — Cortex & Medulla

Two adrenal glands sitting at the top of each kidney are divided into two distinct parts—the cortex and the medulla.

Hormones of Adrenal Cortex

Cortisol: Controls the metabolism, and immune response, and enables the body's response to stress.

Aldosterone: Controls the balance of sodium-potassium. The product of this event affects blood pressure.

Hormones of Adrenal Medulla

Adrenaline (Epinephrine) and Noradrenaline (Norepinephrine): These are also referred to as "fight-or-flight" hormones. During dangerous situations, they increase heart rate, blood pressure, and energy supply.

Functions

The adrenal glands are mainly concerned with the management of stress reactions and controlling a wide array of metabolic and physiological activities.

Pancreas — Endocrine + Exocrine

The pancreas acts both as an endocrine gland concerning the production of hormones and as an exocrine gland concerning the secretion of digestive enzymes.

Pancreatic Hormones

• Insulin: It reduces blood sugar by increasing the uptake of glucose by cells.

• Glucagon: It increases blood sugar by releasing glucose that is stored in the liver.

• Somatostatin: This is against the release of both insulin and glucagon.

Functions

The pancreas controls the concentration of glucose in the blood through actions of insulin and glucagon. Hence this maintains homeostasis in energy

Pineal Gland

Pineal Gland is a very small, pea-shaped gland, which rests in the epithalamus of the brain close to the middle of the brain.

Melatonin

Runs an individual's sleep-wake cycle and is also responsible for seasonal biological rhythms.

Functions

Melatonin appears to play a role in the production of the 'circadian rhythm' and sleep-wake cycles and, therefore, acts as the 'body clock.'

Gonads (Testes and Ovaries)

Testes are in the scrotum whereas ovaries are in the pelvic cavity.

Hormones

• Testosterone: It controls male reproductive functions as well as secondary sexual characteristics.

• Estrogen and Progesterone: They regulate female reproductive activity, the menstrual cycle, and the manifestation of secondary sexual characteristics.

Functions

Gonads play a crucial role in reproduction and in expressing secondary sexual traits and, therefore impact the physical characteristics and behaviours defining sexual maturation.

Endocrine Glands & Hormone NEET MCQs (With Answers & Explanations)

Important questions asked in NEET from this topic are:

• Glands and their hormones

• Functions of hormones

Practice Questions for NEET

Q1. Which of the following are the types of Chemical hormones?

1. Proteins, steroids & biogenic amines

2. Proteins only

3. Steroids only

4. Biogenic amines only

Correct answer: 1) Proteins, steroids & biogenic amines

Explanation:

Chemically, hormones are composed of proteins, steroids, and biogenic amines. Protein hormones are composed of amino acids and include examples such as insulin and growth hormone. Steroid hormones are derived from cholesterol and include examples such as testosterone and cortisol. Biogenic amine hormones are derived from amino acids and include examples such as epinephrine and serotonin.

Hence, the correct answer is option 1) Proteins, steroids & biogenic amines.

Q2. How many of the following hormones given below will interact with the membrane-bound receptor?

Thyroxin, epinephrine, progesterone, relaxin, estrogen:

1. Three

2. Two

3. Five

4. One

Correct answer: 2) Two

Explanation:

Out of the given hormones, only two hormones will interact with membrane-bound receptors. These two hormones are thyroxine and epinephrine.

Thyroxine is a thyroid hormone that interacts with membrane-bound receptors to regulate metabolism and growth. Epinephrine, also known as adrenaline, interacts with membrane-bound receptors in response to stress, increasing heart rate and blood pressure, among other effects. Progesterone, relaxin, and estrogen are steroid hormones that interact with intracellular receptors rather than membrane-bound receptors.

Hence, the correct answer is option 2) Two.

Q3. Proteins perform many physiological functions. For example, some functions as enzymes. Which of the following represents an additional function that some proteins discharge?

1. Antibiotics

2. Pigment conferring colour to skin

3. Pigments making colours of flowers

4. Hormones

Correct answer: 4) Hormones

Explanation:

Antibiotics that contain enzymes do not possess proteins, but many antibodies might not have proteins or enzymes. Moreover, pigments are not proteins. Hormones can be categorized chemically as either proteins or steroids. Except for sex hormones and those derived from the adrenal cortex, every hormone in the human body is a protein or a protein derivative.

Hence, the correct answer is option 4) Hormones.

Also Read:

• MCQs on Introduction to Endocrine System

• Disorders of Pituitary Gland

• Hormones Receptors

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