Endocrine System and Homeostasis

Study Notes

Endocrine System Overview

The body has two primary control systems for homeostasis: endocrine and nervous.
The endocrine system regulates metabolic activity via hormones, which are chemical messengers that travel through the blood to specific target cells.
Hormones can be categorized into amino acid-based or steroid-based types.
Endocrine components, including cells, tissues, and organs, are dispersed throughout the body and typically operate more slowly with prolonged effects.

General Characteristics of Endocrine System

Endocrine glands are primarily composed of epithelial cells and have a cuboidal shape.
These glands are ductless, releasing hormones directly into extracellular fluid (ECF) or bloodstream.

General Anatomy of Endocrine System

Endocrine tissue can take various forms:
- Whole glands (e.g., parathyroid and thyroid)
- Partial glands (e.g., anterior and posterior pituitary)
- Partial organs (e.g., islets of the pancreas)
- Patches of tissue within organs (e.g., gastrin-releasing cells in the stomach)
- Neuroendocrine tissues (e.g., hypothalamus, adrenal medulla)
- Malignant tissue (e.g., lung cancer)

Thyroid Gland

Shaped like a butterfly, located in the anterior neck, on the trachea below the larynx.
Responsible for releasing thyroid hormones (T3 and T4) which regulate metabolism.
Thyroid can be palpated when swallowing due to its movement.

Thyroid Gland Histology

Consists of follicles, which are hollow and may contain colloid (protein).
Follicular cells form the follicle walls; they are typically cuboidal or squamous in shape.
Parafollicular cells, located between the follicles, produce calcitonin which lowers blood calcium levels.

Thyroid Gland Hormones

Follicles release stored thyroid hormones by utilizing colloids.
T3 (active form) and T4 (thyroxin) synthesized by follicular cells increase metabolic rate and cellular oxidation.
Parafollicular cells secrete calcitonin for calcium regulation.

Parathyroid Glands

Composed of four bean-shaped glands, located on the posterior aspect of the thyroid.
The number of parathyroid glands can vary across individuals.

Parathyroid Histology

Contains chief cells, which stain blue-purple and release parathyroid hormone (PTH) to elevate blood calcium levels.
Larger oxyphil cells are lighter in color, with an unknown function.

Pancreas

Functions in chemical digestion and is located partially behind the stomach.
Comprises both endocrine (islets of Langerhans) and exocrine glands (acinar cells).

Pancreas Histology

Islets of Langerhans appear as round, lighter-stained clusters of endocrine cells, accounting for about 2% of pancreatic cells.
Acinar cells are darker exocrine cells surrounding the islets.

Islets of Langerhans

Consist of alpha cells (secrete glucagon to raise blood glucose, found at periphery), beta cells (secrete insulin to lower blood glucose, appear grey-blue), and delta cells (secrete somatostatin).

Pituitary Gland

Known as hypophysis, located within the sphenoid bone, features two major lobes: anterior (glandular tissue) and posterior (mainly neural tissue).

Anterior Pituitary

Also called Adenohypophysis; its activity is regulated by the hypothalamus via chemical signals.
Produces and releases six protein hormones, four of which are tropic hormones targeting other endocrine glands to stimulate hormone secretion.
Composed of acidophilic cells that typically stain orange/brown, producing growth hormone (GH) that targets liver, muscle, bone, and cartilage.

Description

Explore the role of the endocrine system in maintaining homeostasis in the body. This quiz covers the functions of hormones, their types, and how they influence metabolic activity. Test your knowledge on the mechanisms of hormonal control and their effects on target cells.