Understanding the Endocrine System and Hormone Regulation
The Endocrine System
The endocrine system produces and releases hormones according to the needs of the body. These substances are capable of triggering effects in other tissues.
Glandular Organs
Glandular organs produce and release substances capable of carrying out specific functions.
Types of Glands
Exocrine Glands
Exocrine glands have ducts that allow them to release or secrete their products on the internal or external surfaces of our body.
- Salivary glands: Produce and release saliva.
- Sweat glands: Produce sweat on the skin.
- Mammary glands: Can produce milk.
- Stomach: Releases substances such as hydrochloric acid.
- Liver: Produces bile and releases it into the intestine.
Endocrine Glands
Endocrine glands are specialized structures that produce and secrete hormones, which pass directly into the bloodstream without passing through any type of duct.
- Pituitary gland: With its three lobes: anterior, intermediate, and posterior.
- Hypothalamus: An endocrine gland that is part of the diencephalon and is situated below the thalamus.
- Thyroid: Regulates metabolism.
- Parathyroid glands: Located in the neck, usually at the poles of the thyroid gland, they produce parathyroid hormone or parathormone.
Mixed Glands
Mixed glands produce compounds that flow outward and are discharged internally. For example, the gonads (testes and ovaries) are mixed glands that produce gametes (external secretion) and hormones (internal secretion) that exert their action on organs involved in reproductive function.
Functions of Hormones
- Influence many chemical reactions in the body.
- Regulate bodily actions.
- Control sexual functions.
Types of Hormones
- Steroids: Derived from cholesterol. Examples include testosterone (produced by the testes), estrogen and progesterone (secreted by the ovaries), cortisol, aldosterone, and androgens (secreted by the adrenal cortex).
- Amine Hormones: Amino acid derivatives. Examples include thyroid hormone (secreted by the thyroid) and adrenaline or epinephrine (secreted by the medulla of the adrenal glands).
- Proteins: Made up of chains of amino acids. Examples include insulin (secreted by the pancreas), oxytocin and antidiuretic hormone (secreted by the posterior pituitary), calcitonin (produced by the thyroid), and parathyroid hormone (produced by the parathyroid gland).
Feedback Mechanisms
Example of Negative Feedback
When we remove our hand from a fire because we are burning.
Example of Positive Feedback
When we are thirsty, we drink a glass of water and realize that it quenches our thirst, so we continue drinking water. (The same example serves for negative feedback when we stop drinking water because we are no longer thirsty).
Main Endocrine Glands of Our Body
- Pituitary gland: With its three lobes: anterior, intermediate, and posterior.
- Pineal gland: Also located at the base of the brain.
- Gonads: Ovaries in females and testes in males.
- Adrenal glands: Situated on top of the kidneys.
- Thyroid: Regulates metabolism.
- Parathyroid glands: Located behind the thyroid.
- Endocrine pancreas: Located below the stomach.
- Thymus: Located behind the breastbone and between the lungs.
Hormones are chemicals produced by tissues or organs that regulate, activate, inhibit, or excite. They are normally released into the blood in small quantities.