Endocrine System (True or False)

The Endocrine System

• The endocrine system utilizes hormones as chemical messengers to regulate various bodily functions.
• The endocrine system often works slower than the nervous system.
• The endocrine system has a wider reach than the nervous system.
• The nervous system and the endocrine system collaborate as an integrated “supersystem.”

Hypothalamus and Pituitary Gland

• Pituitary gland, sometimes referred to as the "master" endocrine gland, secretes crucial hormones controlling other glands.
• The hypothalamus, strategically located below the thalamus in the brain, is the primary link between the nervous and endocrine systems.
• The hypothalamus produces hormones that play roles in growth, development, metabolism, and homeostasis.

Pituitary Gland

• The pituitary gland is a pea-sized structure situated in the sella turcica of the sphenoid bone.
• It comprises two main portions: the anterior and posterior pituitary.
• The infundibular stalk connects the pituitary gland to the hypothalamus.

Anterior Pituitary

• The anterior pituitary, also known as the adenohypophysis, is composed of epithelial tissue and accounts for 75% of the gland's weight.
• The anterior pituitary secretes several hormones that regulate numerous bodily functions, including growth and reproduction.

Hormones Secreted by the Anterior Pituitary

• Growth Hormone (GH), secreted by somatotrophic cells, stimulates general body growth and controls aspects of metabolism.
• Thyroid Stimulating Hormone (TSH), produced by thyrotrophic cells, regulates thyroid gland secretions and activities.
• Folicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH), secreted by gonadotrophic cells, act on the gonads (testes and ovaries). In men, they promote sperm production and testosterone secretion, while in women, they stimulate oocyte maturation and estrogen and progesterone production.
• Prolactin (PRL), secreted by prolactin cells, initiates milk production in the mammary glands.
• Adrenocorticotropic Hormone (ACTH), secreted by corticotrophic cells, stimulates the suprarenal cortex to secrete glucocorticoids like cortisol.
• Melanocyte-Stimulating Hormone (MSH), also secreted by corticotrophs, plays a role in skin pigmentation.

Posterior Pituitary

• The posterior pituitary, or neurohypophysis, is composed of neural tissue and harbors axons and axon terminals from hypothalamic neurosecretory cells.

Hormones Released from Posterior Pituitary

• The posterior pituitary does not synthesize hormones but instead stores and releases two hormones from the hypothalamus:
  • Oxytocin (OT): This hormone stimulates uterine contractions during labor and milk ejection.
    • Also plays a role in feelings of sexual pleasure.
  • Antidiuretic Hormone (ADH)/Vasopressin: This hormone reduces urine production by promoting water retention.
    • Alcohol inhibits ADH secretion, leading to increased urination.
    • ADH also regulates blood pressure.

Thyroid Gland

• The thyroid gland, butterfly-shaped and located below the larynx, is composed of right and left lobes connected by an isthmus.
• Microscopic spherical sacs called thyroid follicles, composed of follicular cells (T thyrocytes), make up the thyroid gland.

Thyroid Hormone Production

• Follicular cells produce two hormones:
  • Thyroxine (T4): Contains four iodine atoms.
  • Triiodothyronine (T3): Contains three iodine atoms.

Functions of Thyroid Hormones

• The thyroid hormones (T3 and T4) regulate:
  • Metabolism
  • Growth and Development
  • Body temperature regulation
• T3 and T4 increase metabolism, heart rate, and blood pressure.
• They also play crucial roles in nervous system development and bone growth.

Suprarenal Medulla

• The suprarenal medulla, a modified sympathetic ganglion, is located within the suprarenal gland.
• This region produces hormones that intensify sympathetic responses.

Hormones Secreted by the Suprarenal Medulla

• Chromaffin cells in the suprarenal medulla secrete:
  • Norepinephrine/adrenaline/noradrenaline: 80%
  • Epinephrine: 20%

Pancreas

• The pancreas functions as both an endocrine and exocrine gland.
• It is a flattened organ situated in the curve of the duodenum.

Exocrine Function of the Pancreas

• Pancreatic acini, clusters of exocrine cells, constitute 99% of the pancreas.
• They produce digestive enzymes that reach the digestive canal through a network of ducts.

Endocrine Function of the Pancreas

• Pancreatic islets/Islets of Langerhans, about 1-2 million small clusters of endocrine cells, are scattered among the pancreatic acini.
• Pancreatic Islets contain four types of hormone-secreting cells:
  • Alpha (A) cells (17%): Secrete glucagon.
  • Beta (B) cells (70%): Secrete insulin.
  • Delta (D) cells (7%): Secrete somatostatin.
  • F cells (very low percentage): Secrete pancreatic polypeptide.

Explore the fascinating components of the endocrine system, including the critical roles played by the hypothalamus and pituitary gland. This quiz delves into how hormones act as messengers and the interaction between the endocrine and nervous systems. Test your knowledge on the functions and significance of this vital biological system.