A_P_Lab_Exercise_1_-_Endocrine_System__2024_.docx

Objectives

• Identify major endocrine organs in the human body.

• Relate histology of the pituitary gland to its function as an endocrine regulator.

• Describe the function of the thyroid gland with cellular details based on histology.

• Identify unique areas of the adrenal gland and the hormones produced in each region.

• Understand anatomy and histology of the endocrine pancreas.

Introduction to the Endocrine System

• Composed of glandular tissues communicating information through hormones.

• Hormones: chemical messengers secreted into the bloodstream, affecting target tissues at a distance.

• Target cells must have specific receptors to respond to hormones, limiting effects on unintended tissues.

• Endocrine system communicates slower than the nervous system but reaches various cells throughout the body.

Hypothalamus-Pituitary-Axis

• Pituitary gland controlled by the hypothalamus through releasing factors.

• Example: Hypothalamus secretes corticotropin-releasing hormone (CRH), stimulating the anterior pituitary to produce adrenocorticotropic hormone (ACTH), which stimulates the adrenal cortex to produce cortisol.

Pituitary Gland

• Divided into two parts: anterior (adenohypophysis) and posterior (neurohypophysis).

• Anterior Pituitary (Pars Distalis):

  • Contains glandular epithelial cells, secreting hormones like ACTH, LH, FSH, GH, TSH, and PRL.

• Posterior Pituitary:

  • Composed of nerve termini from hypothalamic neurons; secretes oxytocin and anti-diuretic hormone (ADH), produced in the hypothalamus.

Thyroid Gland

• Responds to thyroid-stimulating hormone (TSH) by secreting T3 and T4, which regulate cellular metabolism.

• Structure: bilobed, located at the anterior trachea, with large thyroid follicles storing colloid (viscous hormone material).

  • Follicular Cells: Secrete T3 and T4.

  • Parafollicular Cells: Secrete calcitonin, regulating blood calcium levels.

Parathyroid Glands

• Typically four glands on the posterior face of the thyroid.

• Secretes parathyroid hormone (PTH), which increases serum calcium levels.

  • Chief Cells: More abundant, intensely stained, responsible for PTH secretion.

  • Oxyphil Cells: Larger, lighter-stained, function unknown.

Adrenal Glands

• Located superior to each kidney, covered by a collagen capsule.

• Cortex Layers:

  • Zona Glomerulosa: Produces aldosterone (mineralocorticoid) for blood pressure regulation.

  • Zona Fasciculata: Produces cortisol in response to ACTH during stress, identifiable by long cord-like structures.

  • Zona Reticularis: Produces dehydroepiandrosterone (DHEA), identified by shorter, anastomosing cords.

• Medulla: Contains chromaffin cells, which produce epinephrine (adrenaline) and norepinephrine (noradrenaline).

Pancreas

• Functions as both an endocrine and exocrine organ; exocrine functions discussed later.

• Anatomy: Divided into head, body, and tail; pancreatic duct collects digestive secretions.

• Islets of Langerhans: Contains endocrine cells:

  • Beta Cells: Secrete insulin (most abundant).

  • Alpha Cells: Secrete glucagon.

  • Delta Cells: Secrete somatostatin.

  • Insulin and glucagon regulate blood glucose levels; dysfunction leads to diabetes.