the endocrine system by Gulshan Athbhaiya

The Endocrine System: The Body's Chemical Messaging Network
The endocrine system is a complex network of glands that produce and secrete hormones, acting as the body's chemical messaging service. These hormones are powerful chemical substances that travel through the bloodstream to target cells and organs, regulating a vast array of bodily functions, including growth and development, metabolism, mood, and reproduction.

Major Glands and Their Hormonal Orchestration
The endocrine system is composed of several key glands, each responsible for producing specific hormones that carry out distinct functions:

1. The "Master Gland" and its Conductor: The Pituitary Gland and the Hypothalamus

Often referred to as the "master gland," the pituitary gland, a pea-sized structure located at the base of the brain, plays a central role in regulating the activities of most other endocrine glands. However, the pituitary itself is under the control of the hypothalamus, a region of the brain to which it is connected. The hypothalamus acts as the crucial link between the nervous system and the endocrine system.

The hypothalamus produces releasing and inhibiting hormones that control the secretion of hormones from the pituitary gland. The pituitary gland is divided into two parts: the anterior and posterior lobes.

Anterior Pituitary: Produces a range of hormones, including:

Growth Hormone (GH): Stimulates growth, cell reproduction, and regeneration.

Thyroid-Stimulating Hormone (TSH): Stimulates the thyroid gland to produce its hormones.

Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal glands to produce cortisol.

Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH): Regulate reproductive functions in both males and females.

Prolactin: Stimulates milk production in females.

Posterior Pituitary: Stores and releases hormones produced by the hypothalamus:

Antidiuretic Hormone (ADH): Regulates water balance in the body.

Oxytocin: Plays a role in childbirth, lactation, and social bonding.

2. The Metabolic Maestro: The Thyroid Gland

Located in the neck, the thyroid gland produces two crucial hormones, thyroxine (T4) and triiodothyronine (T3). These hormones regulate the body's metabolism, influencing heart rate, body temperature, and the rate at which the body uses energy. The thyroid also produces calcitonin, which helps regulate calcium levels in the blood.

3. Responders to Stress: The Adrenal Glands

Situated on top of each kidney, the adrenal glands are composed of two parts: the adrenal cortex and the adrenal medulla.

Adrenal Cortex: Produces steroid hormones, including:

Cortisol: A primary stress hormone that helps regulate metabolism, blood pressure, and the immune system.

Aldosterone: Regulates salt and water balance.

Androgens: Male sex hormones produced in small amounts in both sexes.

Adrenal Medulla: Produces epinephrine (adrenaline) and norepinephrine (noradrenaline), which are involved in the "fight-or-flight" response to s

1. ENDOCRINE SYSTEM By Gulshan Athbhaiya , Assistant Professor, YBN University, Ranchi

2. Father of the endocrine system: Thomas Addison Endocrine system + Nervous system = Neuroendocrine system (Integrating system) Study of the endocrine system, known as endocrinology Development : 0 – 2 weeks: zygote 3 – 8 weeks: endocrine system Hormones are non-nutrient chemicals which act as intracellular messengers and are produced in trace amounts.

3. Hypothalamus : Master of the master gland Origin: Ectodermal Location: Brain (Diencephalon) Specialised cells, which are known as neurosecretory cells. Neuron cell bodies: Directly store, or secrete hormone via the Post. Pituitary gland Secrete hormones via Ant. Pituitary through the hypophyseal portal system

4. Pituitary gland: Enclosed within a cavity called ‘ sella tursica ’ of the sphenoid bone Ectodermal In humans pars intermedia is almost merged with the distalis Pars intermedia has only one hormone MSH Adenohypophysis Neurohypophysis Anterior pituitary Posterior pituitary 75% secretions 25% secretions 2 parts: Pars distalis Pars intermedia Pars nervosa

5. Posterior pituitary: Posterior pituitary does not have any hormone of its own, but it is under direct Neural regulation of the hypothalamus: 2 hypothalamus hormones: Oxytocin and Vasopressin are stored in the posterior fit with axon terminals. Vasopressin Oxytocin ADH : Anti Diuretic hormone Called the birth hormone Helps in water reabsorption from DCT Helps in contraction of uterine muscle during delivery Helps in milk ejection

6. Thyroid gland: Largest endocrine gland Endodermal origin Butterfly-like, present on the ventral side of the trachea with 2 lobes