Hormones Definition and Function

Hormone Definition and Production

• A hormone is produced in an endocrine gland, secreted into the bloodstream, and transported to target cells, where it binds to receptors and exerts its effect.
• Hormones are produced in endocrine glands, released into the bloodstream, and transported to target cells, where they bind to receptors and exert their effect.

Nervous System vs. Endocrine System

• The nervous system and endocrine system work together to regulate body functions.
• The nervous system stimulates a body function, and the endocrine system responds by releasing hormones.
• The nervous system is faster, but its effects are short-term, while the endocrine system is slower, but its effects are long-term.

Hormone Stimulation

• An endocrine gland can be stimulated to produce and release hormones through:
  • Nerve impulses directly on the cell
  • Stimulation from a higher-level hormone
  • Chemical stimulation
  • Physical stimulation

Antagonism

• Antagonism is the interaction of two substances with opposing effects.
• Example: Parathyroid hormone (regulates calcium levels in the blood) and calcitonin (antagonist) have opposing effects on calcium levels.

Hypothalamus

• The hypothalamus is located in the stalk of the brain, connected to the pituitary gland through the infundibulum.
• It gives orders to the pituitary gland and enables it to respond to nerve impulses.

Pituitary Gland

• The pituitary gland is located in the stalk of the brain, connected to the hypothalamus through the infundibulum.
• It is divided into an anterior lobe (adenohypophysis) and a posterior lobe (neurohypophysis).
• The anterior lobe releases 7 hormones, while the posterior lobe releases 2 hormones.

Hormone Functions

• FSH and LH stimulate the gonads to produce sex hormones.
• TSH stimulates the thyroid gland to produce thyroxine and triiodothyronine.
• ACTH stimulates the adrenal cortex to produce cortisol and sex hormones.
• Growth hormone stimulates the liver to produce growth factors.
• Prolactin stimulates the mammary glands.
• MSH stimulates melanocytes.
• ADH stimulates water conservation and blood pressure increase.
• Oxytocin stimulates uterine contractions.

Thyroid Gland

• The thyroid gland is located in front of the trachea, below the laryngeal prominence.
• It is composed of small follicles.
• It produces thyroglobulin, which is converted to T3 and T4 under the influence of TSH.
• It also produces calcitonin, which lowers calcium levels.

Thyroid Hormone Functions

• T3 and T4 stimulate the body's metabolism.
• They increase the sensitivity of the sympathetic nervous system.
• Calcitonin lowers calcium levels.

Parathyroid Glands

• There are 4 parathyroid glands located behind the thyroid gland.
• They produce parathyroid hormone, which regulates calcium levels in the blood by:
  • Extracting calcium from bones
  • Increasing calcium reabsorption in the kidneys
  • Activating vitamin D
  • Increasing calcium absorption from food

Insulin and Glucagon

• Insulin and glucagon are produced in the Langerhans islets of the pancreas.
• Insulin is produced in beta cells and lowers blood sugar levels.
• Glucagon is produced in alpha cells and raises blood sugar levels.