Endocrine system

Secretion of hormones act on tissues as:

1. Autocrine (same cell)
2. Paracrine (cells in immediate vincity)
3. Endocrine (distant cells via blood)

Hormones divided into:

1. Signaling molecules (1st messengers act on cell surface receptors)
   • Peptides – Growth hormone, insulin
   • Amino acid derived molecules – epinephrine, histamine
2. Steroids (diffuse across cell membrane and interact with intracellular receptors)
   • Estrogen
   • Progesterone
   • Glucocorticoids
   • Thyroxine
   • Retinoic aid

Feedback inhibition: Increased activity of target-tissues → act as stimulus to down regulate secretary glands

Major pituitary function – controlled by hypothalamus

Anatomical region	Cell type	Hormones secreted	Target organ
Anterior pituitary/adenohypophysis	Somatotrophs	Growth hormone (GH)	All body systems
	Lactotrophs	Prolactin	Breasts
	Corticotrophs	1.Adrenocorticotropic hormone (ACTH) 2.Proopiomelanocortin 3.Melanocyte stimulating hormone (MSH) 4.Endorphins 5.Lipotropin	Adrenal glands Melanocytes Brain cortices Adipocytes
	Thyrotrophs	Thyroid stimulating hormone (TSH)	Thyroid glands
	Gonadotrophs	1.Follicle stimulating hormone (FSH) 2.Luteinizing hormone (LH)	Ovaries
Posterior pituitary/neurohypophysis	Glial cells/pituicytes	Oxytocin	Uterus, breasts
		Vasopressin	Liver (glycogen breakdown)
		Antidiuretic hormone (ADH)	Renal system for fluid/electrolyte balance

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1. Acromegaly
2. Hyperparathyroidism
3. Hypoparathyroidism
4. Hypophosphatasia
5. Hypothyroidism
6. Infantile cortical hyperostosis – Caffey’s disease
7. Osteitis deformans – Paget’s disease
8. Osteogenesis imperfecta
9. Osteoporosis
10. Osteopetrosis
11. Renal osteodystrophy and rickets
12. Scurvy

Bone disease of unknown etiology:

• Langerhans cell histiocytosis