Endocrine System Overview

Endocrine System Overview - General Information

• The endocrine system is a messenger system in the body, composed of hormones and glands.
• Hormones are released by glands into the circulatory system and act upon target organs.
• The hypothalamus acts as the central control center for the endocrine system in vertebrates.

Endocrine Glands

• Major endocrine glands include the pituitary, thyroid, parathyroid, adrenal, pancreas, ovaries, and testes.
• The pineal gland and thymus also function as endocrine glands
• The hypothalamus and pituitary glands are part of the neuroendocrine system.

Objectives

• Identify the main functions of the endocrine system.
• Compare endocrine and nervous system signaling.
• Describe how hormones interact with target-cell receptors.
• Discuss the major endocrine glands and their functions.
• Discuss the stress response as an example of neuroendocrine signaling.

Hormones

• Hormones are mediators that regulate cells in other parts of the body.
• Hormones are released in one part of the body and act on target cells elsewhere.
• Hormones have specific receptors on target cells
• Different types of hormones have different target cells.
• Different types of hormones have different effects on target cells.

Local Hormones

• Autocrine hormones act on the same cells that produced them.
• Paracrine hormones act on neighboring cells.

Circulating Hormones

• Circulating hormones are carried through the blood to act on distant target cells.

Neural vs Endocrine Signaling

• Endocrine system uses chemical signals (hormones), can have fast or slow responses (up to 48 hours).
• Endocrine system causes widespread effect throughout the body.
• Nervous system uses electrical and chemical signals (neurotransmitters), always fast (milliseconds).
• Nervous system causes localized specific effects.

Functions of Endocrine System

• Regulates development, growth, and metabolism.
• Maintains blood composition and volume.
• Controls digestive processes.
• Controls reproductive activities.

Pituitary Gland

• Small gland, about the size of a pea, located in the brain.
• Secretes several major hormones, including growth hormone, prolactin, and antidiuretic hormone.
• Growth hormone is important for growth of skeletal muscles and bones.
• Hypo-secretion of growth hormone during childhood can lead to pituitary dwarfism.
• Hyper-secretion of growth hormone during childhood can lead to gigantism.

Pineal Gland

• Located in the brain.
• Produces melatonin, regulating the circadian rhythm, the body’s natural internal 24-hour cycle
• Melatonin levels are highest during sleep and lowest when waking.

Thyroid and Parathyroid Glands

• Thyroid is butterfly-shaped, anterior to trachea, inferior to larynx.

• Produces thyroid hormones (T3 and T4)

• Thyroid hormone regulates metabolism.

• The thyroid hormone controls the rate of glucose oxidation, creating body heat and chemical energy.

• Hypothyroidism occurs when thyroid hormone levels are too low (associated with weight gain, lethargy, intolerance to cold).

• Hyperthyroidism occurs when the thyroid hormone levels are too high (associated with weight loss, hyperactivity, and heat intolerance).

• Parathyroid glands are on the posterior side of the thyroid gland; produce parathyroid hormone.

• Parathyroid hormone regulates calcium levels.

Adrenal Glands

• Located superior to the kidneys.
• Secrete epinephrine and norepinephrine (involved in stress responses).
• Secrete cortisol, the primary stress hormone.

The Stress Response

• Any factor that threatens homeostasis (physiological or psychological)
• Two main responses: sympathetic nervous system activation (fast, fight-or-flight) and the hypothalamic-pituitary-adrenal (HPA) axis activation (endocrine, slower).
• The HPA axis involves several glands working together to produce cortisol.

Pancreas

• Plays dual roles (endocrine and exocrine).
• Endocrine part produces insulin, to lower blood sugar, and glucagon (to raise blood sugar).

Gonads

• Testes secrete testosterone.
• Ovaries secrete estrogen and progesterone.
• These hormones control reproductive processes.

Hypothalamic-Pituitary-Adrenal (HPA) Axis

• Major link between the nervous and endocrine systems.
• Produces corticotrophin-releasing hormone (CRH), which triggers the anterior pituitary gland to produce adrenocorticotropic hormone (ACTH), signaling the adrenal cortex to produce cortisol.

Negative Feedback Control of Cortisol

• High cortisol levels trigger negative feedback on the HPA axis, effectively stopping further cortisol production.
• Chronic stress can disrupt this negative feedback mechanism.

This quiz covers the fundamental concepts of the endocrine system, including its major glands and hormone functions. It explores how hormones interact with target cells and compares endocrine signaling to nervous system signaling. Participants will gain insights into the neuroendocrine system and hormonal regulation in the body.