Understanding the Endocrine System

• The endocrine system consists of glands producing hormones, which are chemical messengers carrying instructions between cells.
• It influences almost every cell, organ, and bodily function.

Endocrine System Functions

• Endocrine glands release hormones into the bloodstream, allowing them to travel to cells throughout the body.
• Hormones control mood, growth, development, organ function, metabolism, and reproduction.
• The endocrine system regulates the amount of each hormone released.
• Both the nervous and endocrine systems coordinate bodily functions.
• The nervous system is responsible for quick responses to stimuli.
• The endocrine system controls slower, long-lasting changes.
• The body signals the endocrine system to release specific hormones when there is a need such as hunger, stress, or danger.

Glands

• Exocrine glands secrete substances onto body surfaces through ducts, such as sweat, saliva, or ear wax.
• Endocrine glands release hormones directly into the bloodstream; these are ductless.
• Hormones in the bloodstream travel to target organs with dedicated receptors.
• Glands release hormones when a need arises.
• Hormone production stops once the need is met.

Feedback

• Positive feedback continues hormone production when a need persists.
• Negative feedback halts hormone production once the need is satisfied.

Secretion

• Hypersecretion/Hyperfunctioning involves excessive hormone production and release without a need.
• Hypofunctioning involves decreased or insufficient gland function.

Primary Glands

• Primary endocrine glands include the pituitary, thyroid, parathyroid, adrenal, endo-pancreas, and pineal glands.
• The pineal gland regulates the sleep/wake cycle.

Secondary Glands

• Secondary endocrine glands are not primarily part of the endocrine system, with the exception of the gonads.
• Gonads (ovaries/testes) are endocrine glands.
• Ovaries produce estrogen and progesterone.
• Testes produce testosterone.
• Other secondary glands include the heart, kidneys, fat tissues, and small intestines.

Pituitary Gland

• The pituitary gland is divided into the posterior and anterior lobes.
• The posterior pituitary lobe stores and secretes hormones produced by the hypothalamus.
• Neurohypophysis is a brain part playing a key role in hormone regulation.
• The anterior pituitary produces its own hormones and regulates various physiological processes.
• The hypothalamus controls hormone release from the anterior pituitary.
• Adenohypophysis is responsible for the production and secretion of various hormones.
• The posterior pituitary stores and releases oxytocin and vasopressin.

Anterior Pituitary Hormones

• Growth hormone (GH) promotes protein synthesis and bone growth.
• Pituitary dwarfism results from insufficient GH.
• Gigantism is abnormal growth due to excess GH during childhood.
• Acromegaly occurs when the body makes too much GH.

Tropic Hormones

• Tropic hormones stimulate the production and secretion of other hormones.
• Examples include thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH).

Calcium Regulation

• Elevated blood calcium triggers the thyroid gland to secrete calcitonin into the blood.

Calcium Regulation

• Decreased blood calcium triggers the parathyroid glands.
• Parathyroid hormone (PTH) moves calcium from the bones to the bloodstream.

Adrenal Medullary Function

• The adrenal medullary function supports the alarm phase of the stress response or "fight-or-flight".
• It is a rapid, short-term response that increases heart rate, blood pressure, plasma glucose, and dilates airways, increasing energy for muscles.

Pancreas

• The pancreas responds directly to plasma glucose.
• Glucagon, produced by alpha cells, increases plasma glucose.
• Insulin, produced by beta cells, decreases plasma glucose.
• T3 is tri-iodothyronine.
• T4 is thyroxine.