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The endocrine system is a collection of glands that produce hormones - chemical messengers that regulate growth, metabolism, stress response, reproduction, and more. These hormones travel through the bloodstream to specific target cells, ensuring your body works in harmony.
Endocrine vs. Nervous System
Feature
Endocrine System
Nervous System
Messenger Type
Hormones
Electrical impulses
Speed
Slower (seconds–minutes)
Very fast (milliseconds)
Duration
Long-lasting
Short-lived
Communication Path
Bloodstream
Nerve fibers
Types of Hormones
Type
Solubility
Acts On
Example Hormones
Steroid
Lipid-soluble
Inside the cell/nucleus
Cortisol, Estrogen
Non-steroid
Water-soluble
Cell membrane receptors
Insulin, Epinephrine
Hormone Messaging System
First Messenger: Hormone binds to the receptor on the cell membrane.
Second Messenger: Molecules like cAMP, DAG, or IP3 transmit the signal inside the cell.
Result: Enzymes are activated, and a physiological response follows.
Feedback Mechanisms
Type
Description
Example
Negative Feedback
Hormone output reduces future secretion
Thyroid hormone suppresses TSH
Positive Feedback
Hormone output increases future secretion
Oxytocin during childbirth
Major Endocrine Glands and Hormones
1. Hypothalamus & Pituitary Gland
Hypothalamus: Produces releasing hormones (e.g., TRH, CRH) to control pituitary.
Pituitary Gland:
Anterior Lobe: Produces:
GH (growth)
PRL (milk production)
TSH (stimulates thyroid)
ACTH (stimulates adrenal cortex)
LH & FSH (control gonads)
Posterior Lobe: Releases:
Oxytocin (uterine contraction, milk release)
ADH (kidney water retention)
Thyroid and Parathyroid Glands
Gland
Hormone(s)
Function
Thyroid
T3, T4
Increases metabolism, growth
Calcitonin
Lowers blood calcium
Parathyroid
PTH
Raises blood calcium via bone/kidney
Iodine is essential for T3 and T4.
PTH and Calcitonin work as opposites to maintain calcium balance.
Adrenal Glands
Divided into:
Adrenal Cortex: Produces:
Cortisol: Manages stress, raises blood sugar.
Aldosterone: Conserves sodium, raises BP.
Androgens: Secondary sex traits.
Adrenal Medulla: Produces:
Epinephrine and Norepinephrine: "Fight-or-flight" response.
Pancreas
Hormone
Produced By
Function
Insulin
Beta cells
Lowers blood sugar
Glucagon
Alpha cells
Raises blood sugar
Somatostatin
Delta cells
Regulates insulin/glucagon balance
Islets of Langerhans are the endocrine parts.
Insulin and Glucagon maintain blood glucose through negative feedback.
The endocrine system is your body's silent communicator. By understanding its glands and hormones, you gain insight into how your body maintains stability, reacts to stress, regulates metabolism, and manages growth and reproduction. This knowledge will help you tackle any endocrine-related quiz confidently.
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