Human endocrine system - Functions & Overview

What is the Endocrine System?

The endocrine system is defined as the system of glands that secrete their secretion directly into the bloodstream and not through a duct. These endocrine glands control the body system and produce hormones that help regulate all the body functions of our cells and tissues.

Hormones are defined as the chemicals that affect the body's functions, which range from hunger to reproduction to even the growth of the body. The hormones also control the emotions and behaviour of a human being. When we talk about the exocrine glands in our bodies, they secrete their secretion in the ducts. These usually contain earwax and sebaceous glands that usually secrete oil, and sweat glands that usually secrete sweat.

Definition of Endocrine and Exocrine Glands

The body contains two kinds of glands: exocrine glands and endocrine glands. Exocrine glands (exo meaning outside) secrete their products into ducts that carry the secretions into body cavities, into the lumen of an organ, or to the outer surface of the body. Exocrine glands include sweat, sebaceous (oil), mucous, and digestive glands.

Endocrine glands (endo meaning within) secrete their hormones into the interstitial fluid rather than into ducts. From the interstitial fluid, hormones diffuse into blood capillaries and blood carries them to target cells throughout the body. The endocrine glands include the pituitary, thyroid, parathyroid, adrenal, and pineal glands. In addition, several organs and tissues are not exclusively classified as endocrine glands but contain cells that secrete hormones. These include the hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, and placenta.

Parts and Organs of the Endocrine System

The endocrine system consists of a network of glands and organs that produce hormones to regulate various body functions. These glands are scattered throughout the body and are responsible for controlling processes like growth, metabolism, reproduction, and stress response. Key components include the hypothalamus, pituitary gland, thyroid, parathyroid, adrenal glands, pineal gland, pancreas, ovaries, and testes, all with unique roles in maintaining balance and coordination in the body. There are several diverse glands in the endocrine system, each having specific kinds of hormones secreted.

Hypothalamus

• Located in the brain, below the thalamus.

• The hypothalamus acts as a link between the endocrine and nervous systems.

• Produces hormones that regulate the pituitary gland, such as releasing and inhibiting hormones.

• Controls body functions like temperature, thirst, hunger, and emotions.

• Helps regulate sleep cycles and the body's internal clock.

Pituitary Gland

• The pituitary gland is a pea-shaped gland at the base of the brain, below the hypothalamus.

• Divided into anterior and posterior lobes, each releasing different hormones.

• The anterior lobe of the pituitary produces growth hormone (GH), thyroid-stimulating hormone (TSH), and adrenocorticotropic hormone (ACTH).

• The posterior lobe of the pituitary stores and releases hormones produced by the hypothalamus, which include oxytocin and antidiuretic hormone (ADH).

• Coordinates the functions of other endocrine glands.

Thyroid Gland

• The thyroid gland is found in the neck, surrounding the trachea.

• Produces hormones such as thyroxine (T4) and triiodothyronine (T3), which regulate metabolism.

• Regulates energy production, heart rate, and digestion.

• Requires iodine to manufacture thyroid hormones.

• It aids in the proper growth and development of the brain, particularly in children.

Parathyroid Gland

• These are four small glands located at the back of the thyroid gland.

• The parathyroid hormone, PTH, regulates calcium and phosphorus in the blood.

• This hormone maintains the proper functioning of muscles, nerves, and bones.

Adrenal Glands

• Two triangular glands sit on top of each kidney.

• Adrenal glands consist of two parts: adrenal cortex and adrenal medulla.

• The adrenal cortex secretes cortisol, which regulates metabolism and stress, and aldosterone, which controls salt and water balance.

• The adrenal medulla secretes adrenaline, also known as epinephrine, and noradrenaline, which enables the body to respond to stress.

• Involved in the fight or flight reaction.

Pineal Gland

• Pineal Gland is a tiny, pea-sized gland located in the brain between the two hemispheres.

• Produces melatonin, a hormone which helps control the sleep-wake cycles.

• Regulates seasonal biological rhythms in some animals.

Pancreas

• A long, flat organ located behind the stomach.

• The pancreas is both an endocrine and exocrine gland.

• It produces insulin, which lowers blood sugar, and glucagon, which raises blood sugar.

• It maintains blood sugar levels within a normal range.

• It also produces digestive enzymes to help break down food.

Ovaries

• Two almond-shaped organs are located in the pelvic cavity.

• Ovaries produce female sex hormones like estrogen and progesterone.

• It regulates the menstrual cycle and ovulation.

• Facilitate pregnancy and secondary sexual development, for example, growth of mammary glands in females.

Testes

• Two oval-shaped structures contained within the scrotum

• Produced testosterone, which is the most important male sex hormone.

• Regulate male sexual organ development and accessory reproductive structures, including changes in deep voice and pubic and facial hair growth

• Fundamental in the formation of sperm as well as in fertility.

Structure of the Endocrine System

The endocrine system is distributed throughout the body and is different from all other systems. The parts of the endocrine system can act independently in regulating various functions of the body. For instance, the pineal gland within the brain synthesizes melatonin depending on the level of light it detects. The reproductive glands, however, respond to totally different signals, showing the vast difference in their functions.

The hypothalamus and thyroid control other glands to keep the body going. Many glands release numerous hormones at the same time, which work differently and create different effects. All these make the endocrine system one of the more complex systems in the human body.

Functions of the Endocrine System

Endocrine glands are a group of ductless glands that control the body. They usually act on the body by secreting some of the chemical substances that are termed hormones. Hormones usually act on all the nearby tissues of the body from where they are secreted, and they are transported through the bloodstream to act on the specific target organs. Human endocrine systems use hormones to keep track of all the coordinated systems in the body. These glands are located in the human system and in many different locations. Endocrine glands usually coordinate with the neural system of the human body and help with control and coordination activities.

Hormonal Regulation in the Human Body

Hormones regulate various physiological activities.

• Metabolism: Thyroid hormones control the rate of metabolism

• Growth and Development: It is controlled through the growth hormone

• Stress Response: The reaction of the body to stress is controlled by the adrenal hormones

Human Endocrine System NEET MCQs

Q1. Ductless glands are called

1. Alveolar glands

2. Tubular glands

3. Exocrine glands

4. Endocrine glands

Correct answer: 4) Endocrine glands

Explanation:

As we have learned: Endocrine Glands:

• Endocrine glands lack ducts and are hence called ductless glands.

• Their secretions are called hormones.

• The classical definition of the hormone is a chemical produced by endocrine glands and released into the blood and transported to a distantly located target organ.

• Hormones are non-nutrient chemicals that act as intercellular messengers and are produced in trace amounts.

Hence, the correct option is 4) Endocrine glands.

Q2. Which of the following statements is correct?

1. Endocrine glands regulate neural activity, but not vice versa.

2. Neurons regulate endocrine activity, but not vice versa.

3. Endocrine glands regulate neural activity, and the nervous system regulates endocrine glands.

4. Neither hormones control neural activity nor the neurons control endocrine activity.

Correct answer: 3) Endocrine glands regulate neural activity, and the nervous system regulates endocrine glands.

Explanation:

Endocrine glands and the nervous system are intimately connected to uphold homeostasis, exemplifying neuroendocrine integration.

Endocrine Regulation of Neural Activity:
Endocrine glands secrete hormones that can modulate brain function and neural processes. Instances include:
1. Cortisol from adrenals influencing stress-related brain regions.
2. Thyroid hormones impact mood, cognition, and energy utilization, thereby affecting brain function.

Neural Control of Endocrine Glands:
The brain's hypothalamus governs pituitary hormone release, which in turn regulates endocrine glands such as the thyroid, adrenals, and gonads.
Neural signals, like those during stress, activate the hypothalamus-pituitary-adrenal axis, prompting hormone secretion.

Hence, the correct answer is option 3) Endocrine glands regulate neural activity, and the nervous system regulates endocrine glands.

Q3. Peptidal hormone is/are

1. Insulin

2. Cortisol

3. Pituitary Hormone

4. More than one correct answer

Correct answer: 4) More than one correct answer

Explanation:

Four major classifications could classify the chemical nature of hormones:
Peptides, Polypeptides, and Protein Hormones Contain amino acids such as insulin or glucagon.
Steroid Hormones: Lipid-soluble hormones derived from cholesterol, such as cortisol and testosterone.
Iodothyronines: Thyroid hormones required for metabolic regulation.
Amino Acid Derivatives: Hormones from single amino acids, such as epinephrine. Each group has distinct functions and modes of action in the body.

Hence the correct answer is Option (4) More than one correct answer.

Also Read:

• MCQs on Introduction to Endocrine System

• Hormones of Heart, Kidney and Gastrointestinal Tract

• Pancreas Function in Human Body

FAQs on Human Endocrine System

What do you mean by an endocrine system?

The endocrine system is a network of ductless glands that secrete hormones directly into the bloodstream. These hormones act as chemical messengers that regulate vital functions such as growth, metabolism, reproduction, mood, and homeostasis. Unlike the nervous system, which works through rapid electrical impulses, the endocrine system controls body functions more slowly but with long-lasting effects. It plays a central role in maintaining internal balance and coordinating body activities.

Which are the major endocrine glands?

The human body has several major endocrine glands, including the hypothalamus, pituitary, thyroid, parathyroid, adrenal, pineal gland, pancreas, ovaries, and testes. The hypothalamus and pituitary act as the master controllers, regulating the activity of other glands. The thyroid regulates metabolism, adrenal glands control stress responses, and the pancreas regulates blood sugar. The gonads (ovaries and testes) produce sex hormones that influence reproduction. Each gland has specialized hormones for specific body functions.

Which hormone regulates metabolism?

Metabolism is primarily regulated by thyroxine (T4) and triiodothyronine (T3), secreted by the thyroid gland. These hormones control the rate of cellular respiration and energy production. They influence processes like protein synthesis, fat metabolism, and carbohydrate utilization. An imbalance in these hormones leads to disorders such as hypothyroidism and hyperthyroidism. Proper thyroid function is essential for growth, brain development, and energy balance.

What is the difference between endocrine and exocrine glands?

The key difference lies in their mode of secretion. Endocrine glands are ductless and release hormones directly into the blood e.g., thyroid, adrenal, pituitary. These hormones travel to target organs and regulate specific functions. In contrast, exocrine glands secrete their products through ducts onto surfaces or into body cavities e.g., sweat glands, sebaceous glands, salivary glands. While endocrine glands maintain internal regulation, exocrine glands mainly assist in digestion, lubrication, and protection.

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