Endocrine System: Maintaining Internal Body Homeostasis

Endocrine, Exocrine, and Mixed Glands

The endocrine system is composed of glands that secrete hormones. Hormones are chemical messengers that travel through the blood and exert specific actions on certain organs, known as target organs.

• Endocrine glands discharge hormones directly into the bloodstream.
• Exocrine glands discharge substances onto the body's surface through excretory ducts.
• Mixed glands combine the features of both endocrine and exocrine glands.

Endocrine System Functions

Hormones are key regulators of metabolism, reactions, and responses to states of alarm.

Endocrine Gland Characteristics

• Lack excretory ducts
• Generally small in size
• Act in small doses
• Can be formed as independent bodies, arranged in clusters, or within other organs

Pituitary Gland

Location: Pituitary fossa of the sella turcica on the upper body of the sphenoid bone.

Structure

• Anterior lobe (adenohypophysis): Secretes hormones such as:
  • Somatotropic hormone
  • Adrenocorticotropic hormone
  • Thyrotropin
  • Follicle-stimulating hormone
  • Luteinizing hormone
• Posterior lobe (neurohypophysis): Reservoir for neurosecretions like:
  • Oxytocin
  • Vasopressin

Regulatory factors also play a role.

Epiphysis (Pineal Gland)

The epiphysis secretes tropins, adenoglomerulotropin, and melatonin. It participates in the circadian cycle and sexual function.

Mammary Gland

The mammary gland is an organ unique to mammals, situated between the 3rd and 7th ribs. It is separated from the chest wall by a lower sulcus. The central part features the nipple, into which the galactose ducts open. The nipple is surrounded by a darker, circular area of skin called the areola, where small areolar glands are observed.

In men, the mammary gland is atrophic.

Adrenal Gland

Location: Posterior part of the retroperitoneum, above and within the fascia surrounding the kidney, but independent of it.

Structure

• Fibrous capsule: Envelops the gland.
• Cortex: Peripheral part.
• Medulla: Softer, central part.

Irrigation: Supplied by three pedicles.

Venous drainage: Occurs directly into the inferior vena cava on the right side and into the renal vein on the left side.

Innervation: Sympathetic nervous system.

Gland Secretions

• Cortex:
  • Mineralocorticoids (affect mineral metabolism)
  • Glucocorticoids (affect general metabolism, especially renal)
  • Gonadocorticoids (sex hormones: testosterone in men, estrogen in women)
• Medulla:
  • Epinephrine (adrenaline, noradrenaline)

Thymus

The thymus is a gland that reaches its maximum development at puberty and then atrophies.