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Pituitary Gland

• The pituitary gland is composed of two lobes: anterior (adenohypophysis) and posterior (neurohypophysis)
• Anterior pituitary: made of simple cuboidal epithelium, produces hormones, and releases them into the bloodstream
• Posterior pituitary: neural tissue, stores and releases hormones produced by the hypothalamus
• Hypophyseal portal system: a circulatory system that allows the hypothalamus to regulate hormone secretion by the anterior pituitary

Posterior Pituitary Hormones

• Oxytocin: stimulates uterine contractions during childbirth, triggers milk ejection, and plays a role in sexual arousal and orgasm
• Antidiuretic Hormone (ADH): regulates water retention in the kidneys, increases blood pressure, and is inhibited by alcohol

Anterior Pituitary Hormones

• Growth Hormone (GH): stimulates protein synthesis, promotes fat use for fuel, and targets bone and skeletal muscle
• Thyroid-Stimulating Hormone (TSH): stimulates the release of thyroid hormones
• Adrenocorticotropic Hormone (ACTH): stimulates the release of cortisol from the adrenal cortex
• Follicle-Stimulating Hormone (FSH): targets ovaries and testes, regulates sperm production and egg maturation
• Luteinizing Hormone (LH): targets ovaries and testes, regulates testosterone production and ovulation
• Prolactin: stimulates lactation and is involved in milk production

Thyroid Gland

• The thyroid gland is the largest endocrine gland, producing triiodothyronine, thyroxine, and calcitonin
• Thyroid hormones: T₃ and T₄, regulate cellular metabolism
• Hypothyroidism: a condition characterized by low thyroid hormone levels, resulting in cretinism in children and myxedema in adults
• Hyperthyroidism: a condition characterized by high thyroid hormone levels, resulting in Grave's disease

Parathyroid Glands

• The parathyroid glands are located in the posterior aspect of the thyroid gland
• Parathyroid Hormone (PTH): regulates calcium levels, stimulates osteoclast activity, and targets osseous tissue, kidneys, and intestines
• Hypoparathyroidism: a condition characterized by low PTH levels, resulting in low calcium levels and muscle twitching
• Hyperparathyroidism: a condition characterized by high PTH levels, resulting in high calcium levels and bone weakening

Adrenal Glands

• The adrenal glands are paired, pyramid-shaped organs located on top of the kidneys
• Adrenal cortex: produces corticosteroids, including aldosterone, cortisol, and androgens
• Adrenal medulla: produces epinephrine and norepinephrine, which regulate the "fight or flight" response

Pancreas

• The pancreas is a triangular gland located behind the stomach
• Pancreatic islets (islets of Langerhans): produce glucagon, which increases blood glucose levels
• Glucagon: stimulates glycogenolysis and gluconeogenesis

Endocrine System

• The endocrine system acts with the nervous system to coordinate and integrate body cell activities
• Endocrine glands: pituitary, thyroid, parathyroids, adrenals, and pineal gland
• The endocrine system influences metabolic activities through hormones transported in the blood### Insulin and Diabetes
• Produced by beta cells in the pancreas, insulin lowers blood glucose levels by targeting the liver and most cells.
• Insulin inhibits glycogen breakdown and promotes glycogen synthesis.
• Diabetes Mellitus (DM) occurs due to hyposecretion or hypoactivity of insulin, resulting in signs such as:
  • Polyuria (excessive urine output)
  • Polydipsia (excessive thirst)
  • Polyphagia (excessive hunger and food consumption)
  • Hyperinsulinism (causes hypoglycemia)

Pineal Gland and Melatonin

• Located in the brain, the pineal gland produces melatonin from serotonin through pinealocytes.
• Melatonin regulates sleep/wake cycles, increasing in the evening to induce sleepiness.
• Sunlight inhibits melatonin release, and its deficiency can cause Seasonal Affective Disorder (SAD).

Gonads and Sex Hormones

• Female gonads (ovaries) produce estrogen and progesterone, responsible for:
  • Maturation of reproductive organs
  • Appearance of secondary sex characteristics (e.g., adipose tissue in breasts and buttocks)
• Estrogen specifically:
  • Causes breast development
  • Initiates cyclic changes in uterine mucosa
• Male gonads (testes) produce testosterone, necessary for:
  • Maturation of male reproductive organs
  • Appearance of secondary sexual characteristics and sex drive
  • Sperm production

Placenta and Human Chorionic Gonadotropin (HCG)

• The placenta produces HCG, which:
  • Maintains uterine thickness
  • Maintains corpus luteum
  • Elevates progesterone levels

Thymus and Thymosin

• The thymus gland produces thymosin, involved in the normal development of T-lymphocytes.
• The thymus gland is large in infants and children, but diminishes in size throughout adulthood.

Hormones and Chemical Messengers

• Hormones are long-distance chemical signals that travel in the blood or lymph.
• Autocrines are hormones that exert effects on the same cells that secrete them.
• Paracrines are locally acting hormones that affect cells other than those that secrete them.
• There are two main classes of hormones, with varying chemical structures and functions.