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Human endocrine system is an organization of glands and tissues that are located all over the body. These glands create and secrete hormones, which are chemicals released into the blood to regulate body processes. There are different hormones that regulate different body functions.
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Key Terms: Endocrine, Hormones, Thyroid, Exocrine, Hypothalamus, Secretion
Endocrine System
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The endocrine glands are ductless i.e.they secrete chemicals directly into the bloodstream rather than using ducts for the delivery of substances. The hormones are intercellular messengers and are produced in very low quantities. The organs have receptors that receive and respond to the hormones.
Dedicated endocrine glands in the body are pineal, pituitary, adrenal, parathyroid, thymus, pancreas, and testis (males), and ovaries (females). It regulates and controls various bodily processes, just like the nervous system. The endocrine system uses hormones while the neurological system communicates through nerve impulses and neurotransmitters.
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| Important Concepts | ||
|---|---|---|
| ADH Hormone | Dwarfism | Adrenal Gland |
| Mechanism Of Hormone Action | Symptoms of Thyroid | Goiter |
| Thyroid Cancer | Estrogen Hormone | Cortisol Hormone |
Functions of Endocrine System
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Through the release of hormones, the endocrine system regulates a range of bodily functions. The system also keeps a check on the levels of the hormones in the body and continuously monitors them by controlling their release. The hormones communicate to the target organ or tissue for their functioning.
Some of the significant functions that are controlled by the endocrine system are as follows:
- Growth and development
- Metabolism
- Blood pressure
- Heart rate
- Reproduction and sexual function
- Appetite
- Mood behaviours
- Body temperatur
- Sleep and waking cycles
Different endocrine glands of the human body
Parts of the Endocrine System
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Part of the endocrine system where the hormones are generated, stored, and secreted is called a gland. These glands produce one or more hormones that have different functions and target specific organs and tissues. The glands are present all over the human body. Different glands of the endocrine system are:
- Hypothalamus: Present in the brain, its main function is to control the pituitary gland by producing multiple hormones. It has many neurosecretory cells called nuclei which produce hormones. The hormones originate in the neurons and are released into the nerve endings through axons.
- Pituitary: Located below the hypothalamus, its hormones affect growth and reproduction.
- Pineal: It secretes melatonin which manages sleep cycles.
- Thyroid: This butterfly-shaped gland controls metabolism, growth, and development of Thyroid..
- Parathyroid: Controls the calcium levels in blood and bones useful in the proper functioning of the heart, kidneys, and nervous system.
- Thymus: Produces hormones used in the WBC and T-Cells development.
- Adrenal: Present on the top of each kidney, they produce hormones that control heart rate, stress, and blood pressure.
- Pancreas: Plays an important role in the digestive system. Produces insulin that controls blood sugar levels.
- Testes: Releases testosterone which affects sperm production, sex drive and muscle strength.
- Ovaries: Produce and store ovum and controls menstrual cycle.
Hormones of the Endocrine System
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Hormones of the Endocrine System are tabulated below along with their glands and functions.
| Hormone | Gland | Function |
|---|---|---|
| Gonadotropin-releasing hormone (GnRH) | Hypothalamus | Releases gonadotrophin and stimulates pituitary synthesis. |
| Somatostatin | Hypothalamus | Inhibits growth hormone release from the pituitary. |
| Growth hormone (GH) | Pituitary | Aids in childhood growth and maintains organs and tissues. |
| Prolactin (PRL) | Pituitary | Regulates mammary glands growth. |
| Thyroid Stimulating hormone (TSH) | Pituitary | Involved in the synthesis and secretion of thyroid hormones. |
| Adrenocorticotrophic hormone (ACTH) | Pituitary | Involved in the synthesis and secretion of glucocorticoids. |
| Follicle-stimulating hormone (FSH) | Pituitary | Controls egg and sperm production. |
| Melanocyte-stimulating hormone | Pituitary | Skin protection from UV rays, pigmentation development. |
| Luteinizing hormone (LH) | Pituitary | Controls the production of estrogen and testosterone. |
| Oxytocin | Pituitary | Functions in lactation and childbirth. |
| Vasopressin | Pituitary | Water and electrolytes resorption in kidneys. |
| Melatonin | Pineal | Controls the sleep cycle. |
| Thyroxine (T4), Triiodothyronine (T3) | Thyroid | Regulates basal metabolic rate and formation of RBC, carbohydrates, proteins, fats. |
| Parathyroid hormone | Parathyroid | Controls calcium levels in blood and bones. |
| Thymosin | Thymus | Differentiation of T cells and promotes antibody production. |
| Adrenaline (epinephrine), Noradrenaline (norepinephrine) | Adrenal | Increase heart rate, blood pressure and metabolism in response to stress. |
| Aldosterone | Adrenal | Control salt and water balance. |
| Cortisol | Adrenal | Functions in stress response. |
| Dehydroepiandrosterone sulfate (DHEA-S) | Adrenal | Body hair production during puberty. |
| Glucagon | Pancreas | Helps in increasing blood sugar levels. |
| Insulin | Pancreas | Reduce blood glucose levels. |
| Testosterone | Testis | Regulates the development and function of male accessory sex organs and stimulatory role in spermatogenesis. |
| Estrogen | Ovary | Regulates the menstrual cycle, develops female sex characteristics and helps in pregnancy. |
| Progesterone | Ovary | Prepares the body for pregnancy upon egg fertilization. |
Things to Remember
- Hormones are regulatory chemicals transported via the blood to specific organs to generate an action.
- Endocrine glands are ductless i.e they lack specific channels to transport hormones.
- Endocrine glands are located in the different parts of the body.
- Hypothalamus produces hormones to regulate the pituitary gland.
- GnRH, PRL, TSH, Oxytocin, Thymosin, Insulin, testosterone and estrogen are some of the major hormones produced by the endocrine system.
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Previous Year Questions
- Testosterone is produced by...[NEET 1993]
- The blood calcium level is lowered by the deficiency of...[NEET 2008]
- Rapid increase in the blood sugar level of a patient can be immediately reduced by...[KCET 2008]
- Choose the wrong statement among the following
- The pineal gland secretes
- Farathormone deficiency in blood causes:….[JIPMER 1995]
- The alternative form of gene is called…..[AMUEEE 2015]
- The hormone insulin is secreted by :...[JKCET 2006]
- Which is not a gonadal hormone?...[WBJEE 2007]
- Tetany is caused by...[WBJEE 2011]
- The hormone that controls the level of calcium and phosphorus in the blood is secreted by:...[AFMC 2005]
- During emergency, which one of the following hormone is important?..[UP CPMT 2000]
- Presence of glucose in urine is called
- The amino acid derivative among the following hormone is:
- Gigantism and acromegaly are due to improper functioning of:...[JIPMER 1996]
- Progesterone level falls during...[AMUEEE 2008]
- Regeneration of liver is
- Hypothetical plant hormones are...[AIIMS 2014]
- Aldosterone is secreted by:...[MU OET 2005]
- Which one is a synthetic Auxin:….[UPSEE 2018]
Sample Questions
Ques. What are the differences between endocrine and exocrine glands? (2 Marks)
Ans. Endocrine glands are ductless whereas the exocrine glands have ducts for secretion. Endocrine glands only generate hormones that are directly secreted into the bloodstream to reach the target organ. Enzymes, mucus, sebum, and sweat are secreted by exocrine glands which are released directly onto the surface or an internal organ via a duct.
Ques. What are gonadotropins? (2 Marks)
Ans. Hormones which stimulate the gonads are known as gonadotropins. The anterior lobe of the pituitary gland secretes them. Their function is to regulate ovarian and testicular activity along with growth, reproduction, and sexual development. The follicle-stimulating hormone (FSH) and Luteinizing hormone (LH) are human gonadotropins.
Ques. Differentiate between Diabetes Mellitus and Diabetes Insipidus. (2 Marks)
Ans. Diabetes Mellitus is caused because of the lesser production of insulin by the pancreas. The lesser amount of secretion of ADH vasopressin is the cause of diabetes insipidus. The cells of the islet of Langerhans in the pancreas secrete insulin while vasopressin is secreted by the posterior pituitary gland.
Ques. Why oxytocin is called the birth hormone? (2 Marks)
Ans. The vigorous contractions of the smooth muscles of the uterus are regulated by oxytocin during childbirth hence, it is known as the birth hormone. It is also involved in the production of milk just after childbirth by contractions in the mammary gland.
Ques. List the functions of the pineal gland. (3 Marks)
Ans. The pineal gland serves the following functions -
- It secretes the melatonin hormone, which regulates the sleep cycle.
- It regulates the 24-hour diurnal rhythm.
- It affects metabolism, pigmentation, and the menstrual cycle.
- It reduces the reproductive ability and delays sexual development in some individuals.
Ques. How the menstrual cycle is regulated by the endocrine system. (2 Marks)
Ans. The ruptured Graafian follicle in the ovary is converted into a structure called corpus luteum after ovulation. It is a temporary endocrine gland which secretes the progesterone hormone, which plays an integral part in the menstrual cycle. It also supports pregnancy and acts on the mammary glands.
Ques. What are heterocrine glands? (2 Marks)
Ans. The glands which are partly endocrine and partly exocrine are called heterocrine glands. The endocrine part releases hormones directly into the blood while the exocrine part releases hormones via the associated ducts. These glands are also known as the mixed glands. The Pancreas and the gonads (testes and ovaries) are examples of heterocrine glands.
Ques. List the disorders of the thyroid glands. (3 Marks)
Ans. The disorders of the thyroid glands are -
- Hyperthyroidism: Thyroid hormones are produced in excess.
- Goitre: Hyposecretion of thyroid leading to enlargement of thyroid tissues. The neck protrudes in front known as endemic goitre.
- Myxoedema: Undersecretion of the thyroid cause mucous swelling in adults. Dry skin, hair loss, swelling in the face and slow heart rate are some symptoms of it.
- Cretinism: Extreme hypothyroidism in infancy and childhood. Causes delayed mental and bodily growth, thickening of the skin, and a protruding tongue.
Ques. What are neurohormones? (2 Marks)
Ans. These are produced by neurosecretory cells which are structurally similar to nerve cells. They stimulate the secretion of hormones by the pituitary. They are released into the bloodstream at special regions called neurohemal organs. Examples are oxytocin and ADH.
Ques. What are Leydig’s cells? (2 Marks)
Ans. Also known as interstitial cells, they are present in testes and secrete testosterone. External male sex characteristics like beard and low-pitched voice are stimulated by it. It also aids in sperm formation in the testis.
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