Chemical Coordination And Integration 

• The neural and endocrine systems work together to control and manage the body's physiological functions. Neural coordination acts quickly, is highly precise, and has short-term effects. 
• In contrast, chemical coordination tends to be slower, more extensive, and long-lasting. Since not all body cells are connected to nerve fibers, yet require constant regulation, a unique form of coordination is necessary. Hormones fulfill this role by ensuring continuous regulation of cellular functions.

1.0Endocrine Glands and Hormones

• Endocrine glands do not have ducts and are therefore known as ductless glands. They release chemicals known as hormones. 
• A hormone is a substance produced by endocrine glands, released into the bloodstream, and transported to a distant target organ.
  

Chemical Nature of Hormones

2.0Human Endocrine System

• The endocrine system is made up of various endocrine glands and hormone-producing tissues or cells scattered throughout the body. 
• Major endocrine glands include the pituitary, pineal, thyroid, adrenal, pancreas, parathyroid, thymus, and gonads (testes in males and ovaries in females). Additionally, organs such as the gastrointestinal tract, liver, kidneys, and heart also produce hormones. 

1. Hypothalamus

• The hypothalamus, located at the base of the diencephalon in the forebrain, plays a crucial role in regulating various body functions. 
• It contains numerous neurosecretory cells known as nuclei that produce neurohormones. 
• These neurohormones control the production and release of hormones from the pituitary gland.

2. Pituitary Gland

• Based on development, the pituitary gland is completely ectodermal. 
• It is located in the sphenoid bone's sellatursica (bony cavity). 
• This gland is attached to the hypothalamus through a stalk called an infundibulum. 
• It is divided anatomically into an adenohypophysis (anterior pituitary) and a neurohypophysis (posterior pituitary). 
• Dwarfism is a medical condition characterized by short stature, generally due to genetic or medical factors. 
• Growth Hormone Deficiency - Growth hormone (GH) is an essential substance that plays a vital role in promoting the growth and development of children.

Know more about: Pituitary Gland

3. Thyroid Gland

• The thyroid gland comprises two lobes on either side of the trachea. 
• Both lobes are interconnected with a thin flap of connective tissue called isthmus (non-glandular part). 
• Origin: Endodermal 
• Position: Located in the neck between the trachea and larynx. 
• Structure: 'H' shape, Largest Endocrine gland. 

Function of Thyroid Gland:

• Regulates basal metabolic rate (BMR) of the body. (Calorigenic Hormone) 
• Supports the process of red blood cell formation. (Erythropoiesis) 
• This hormones control the metabolism of carbohydrates, proteins and fats. 
• Thyroid hormones also influence the maintenance of water and electrolyte balance. 
• It is responsible for physical, mental and sexual growth. 
• They are required for the development of the nerve fibres and their myelination. 
• It stimulates the metamorphosis of tadpole larvae in amphibians. When it is deficient, larvae do not metamorphose into adults.

Thyroid Disorders:

• Cretinism – Hypothyroidism during pregnancy can lead to impaired development and maturation of the growing baby, resulting in stunted growth (cretinism), mental retardation, low intelligence quotient, abnormal skin, and deaf-mutism, among other issues.
• Multinodular Goitre - Multinodular goitre (MNG) is a commonly encountered condition characterized by an enlarged thyroid gland with multiple areas of nodularity. 
• Exophthalmic Goitre - Exophthalmic goitre, commonly known as Graves' disease, is an autoimmune disorder directly affecting the thyroid gland. 

4. Parathyroid Gland

• Origin: Endodermal 
• Position: Present on the backside of the thyroid gland. Four in number (One pair for each lobe of the thyroid gland).
• The parathyroid gland secretes parathyroid hormone (PTH), Collip's hormone, or parathormone. 
• It is a polypeptide in nature.

Functions of Parathyroid Gland:

• An increase in blood calcium level causes Hypercalcemia 
• A decrease in blood phosphate level causes Hypophosphatemia 
• Parathormone is essential for survival as it is critical in maintaining homeostasis by regulating calcium and phosphate ion levels in the extracellular fluid (ECF).

5. Adrenal Gland

• They are also called suprarenal glands or glands of emergency. 
• Our body contains a pair of adrenal glands, one positioned on top of each kidney. Each gland is made up of two distinct types of tissues:

(i) The centrally located tissue is called the adrenal medulla 

(ii) Outside this lies the adrenal cortex

Control of Adrenal Secretion:

• ACTH of the anterior pituitary controls the secretion of the adrenal cortex (mainly glucocorticoids). 
• Secretion of mineralocorticoids is controlled by Renin (Kidney). 
• The nervous system controls adrenal medullary hormones.

6. Thymus Gland

• Origin :- Endodermal 
• Position:- The thymus gland is a lobular structure (bilobed) located between the lungs behind the sternum on the ventral side of the aorta. 
• Hormone secrete:- Thymosin. 
• Nature of thymosin:- Proteinaceous.

7. Pineal Gland

• Origin:- Ectodermal 
• Position: It is located on the dorsal side of the forebrain (the Dorsal side of the Diencephalon) and is also known as the Epiphysis cerebri. 
• Nature of hormone:- Amino acid derivative 
• A hormone secreted is melatonin. Light reduces melatonin formation. Its maximum concentration is at midnight, and its minimum is at noon.

8. Pancreas

• Origin: Endodermal Position: Elongated organ situated between the limbs of the 'C' shaped duodenum. 
• Nature: Heterocrine / Mixed / Composite gland / Compound (exocrine and endocrine). 
• The exocrine portion secretes an alkaline pancreatic juice containing enzymes, and the endocrine portion secretes hormones, insulin and glucagon.

9. Gonads and Other Organs

Gonads (In Male - Testis):

• A pair of testis is present in male individuals' scrotal sac (outside abdomen). 
• The testis serves dual roles as both a primary sex organ and an endocrine gland. It is composed of seminiferous tubules and interstitial (or stromal) tissue.

Gonads (In Female - Ovaries):

• Females possess a pair of ovaries located in the abdomen, which serve as the primary female sex organs. 
• Each ovary produces one ovum per menstrual cycle and generates two groups of steroid hormones: estrogen and progesterone. 
• The ovary consists of ovarian follicles and stromal tissues. 
• Estrogen is primarily synthesized and secreted by the developing ovarian follicles. Following ovulation, the ruptured follicle transforms into a structure known as the corpus luteum, which predominantly secretes progesterone.

3.0Mechanism of Hormone Action

• There are two types of hormones: (i) water-soluble hormones and (ii) lipid-soluble hormones. 
• Hormones exert their effects on target tissues by binding to specific proteins known as hormone receptors, which are found only in those tissues. Receptors located on the cell membrane of target cells are called membrane-bound receptors, while those located inside the target cell are known as intracellular receptors, often found in the nucleus. 
• When a hormone attaches to its receptor, it creates a hormone-receptor complex. Each receptor is specific to a single hormone, ensuring precise interactions. The formation of this complex triggers biochemical changes in the target tissue, thereby regulating its metabolism and overall physiological function.

4.0Properties of Hormones

Hormones have several key properties that define their function and action in the body:

1. Specificity: Each hormone binds to specific receptors on target cells, leading to a particular response. This specificity ensures that hormones exert their effects only on the appropriate tissues or organs.

2. Regulation: Hormone levels are tightly regulated through feedback mechanisms. This regulation maintains homeostasis by adjusting hormone secretion based on the body's needs.

3. Transport: Hormones are often transported in the bloodstream. Some are soluble in water and can travel freely in the blood, while others are lipid-soluble and require carrier proteins for transport.

4. Action: Hormones can act through different mechanisms:

• Direct Action: Hormones can directly influence cellular functions by binding to receptors on the cell membrane or inside the cell.
• Indirect Action:  Hormones may stimulate the release of other hormones or substances that then act on target cells.

5. Potency: Hormones can have significant effects even at very low concentrations. Their actions are typically powerful and can lead to profound physiological changes.

6. Duration: The effects of hormones can be short-lived or long-lasting, depending on their nature and the mechanisms involved. Some hormones act quickly and have brief effects, while others have prolonged actions.

7. Secretion Patterns: Hormones can be released in a pulsatile manner, in response to specific stimuli, or on a continuous basis. Their secretion patterns can influence their effects and regulation.

8. Excretion: Hormones are eventually broken down and excreted by the body. This process usually occurs in the liver or kidneys and ensures that hormone levels remain balanced.

5.0Chemical Corordination and Integration NEET Questions

Multiple Choice Questions (MCQs)

1. Which hormone is known as the "fight or flight" hormone? 

a. Insulin b. Thyroxine c. Adrenaline d. Oxytocin

Answer: c. Adrenaline

2. The hormone that regulates the sleep-wake cycle is produced by the: 

a. Pituitary gland b. Pineal gland c. Adrenal gland d. Pancreas

Answer: b. Pineal gland

3. Which of the following hormones is involved in the regulation of calcium levels in the blood? 

a. Thyroxine b. Parathyroid hormone c. Insulin d. Glucagon

Answer: b. Parathyroid hormone

4. The posterior pituitary gland secretes: 

a. Oxytocin and vasopressin b. Prolactin and growth hormone c. Thyroxine and calcitonin d. Cortisol and aldosterone

Answer: a. Oxytocin and vasopressin

Short Answer Questions

Q.1 Explain the role of insulin and glucagon in the regulation of blood glucose levels.

Ans. Insulin and glucagon are hormones secreted by the pancreas that play crucial roles in managing blood glucose levels. Insulin decreases blood glucose by aiding in glucose absorption into cells and encouraging its storage as glycogen in the liver. 

Q.2 How does the hormone aldosterone regulate electrolyte balance?

Ans. Aldosterone, produced by the adrenal cortex, helps regulate electrolyte balance by increasing sodium and water reabsorption and potassium excretion in the kidneys. This action helps maintain blood pressure and fluid balance in the body.