Lecture 25 - The Endocrine System

The Endocrine System Overview of the Endocrine System ▪ System of ductless glands that secrete hormones ▪ Hormones are “messenger molecules” ▪ Circulate in the blood ▪ Act on distant target cells ▪ Target cells ...

The Endocrine System Overview of the Endocrine System ▪ System of ductless glands that secrete hormones ▪ Hormones are “messenger molecules” ▪ Circulate in the blood ▪ Act on distant target cells ▪ Target cells respond to the hormones for which they have receptors ▪ The effects are dependent on the programmed response of the target cells ▪ Hormones are just molecular triggers ▪ Basic categories of hormones ▪ Amino acid based: modified amino acids (or amines), peptides (short chains of amino acids), and proteins (long chains of amino acids) ▪ Steroids: lipid molecules derived from cholesterol 2 Endocrine Organs ▪ Purely endocrine organs ▪ Pituitary gland ▪ Pineal gland ▪ Thyroid gland ▪ Parathyroid glands ▪ Adrenal: 2 glands ▪ Cortex ▪ Medulla ▪ Endocrine cells in other organs ▪ Pancreas ▪ Thymus ▪ Gonads ▪ Hypothalamus Mechanisms of hormone release (a) Humoral: in response to changing levels of ions or nutrients in the blood (b) Neural: stimulation by nerves (c) Hormonal: stimulation received from other hormones Learn the 3 endocrine organs on this slide: Hypothalamus Pituitary (hyophysis) Pineal Hypothalamus Anterior pituitary Posterior pituitary (adenohypophysis) (neurohypophysis) Hypothalamus Pituitary (hypophysis) The Pituitary Sits in hypophyseal fossa: depression in sella turcica of sphenoid bone Pituitary secretes 9 hormones Two divisions: ▪ Anterior pituitary (adenohypophysis) 1. TSH 2. ACTH 3. FSH 4. LH 5. GH 6. PRL 7. MSH The first four are “tropic” hormones, they regulate the function of other hormones ▪ Posterior pituitary (neurohypophysis) 8. ADH (antidiuretic hormone), or vasopressin 9. Oxytocin What the letters stand for… ▪ TSH: thyroid-stimulating hormone ▪ ACTH: adrenocorticotropic hormone ▪ FSH: follicle-stimulating hormone ▪ LH: luteinizing hormone ▪ GH: growth hormone ▪ PRL: prolactin ▪ MSH: melanocyte-stimulating hormone ▪ ADH: antidiuretic hormone ▪ Oxytocin Hypothalamus controls anterior pituitary hormone release ▪ Releasing hormones (releasing factors) Secreted like neurotransmitters from neuronal axons into capillaries and veins to anterior pituitary (adenohypophysis) TRH-----turns on TSH CRH-----turns on ACTH GnRH (=LHRH)---turns on FSH and LH PRF-----turns on PRL GHRH----turns on GH ▪ Inhibiting hormones PIF-----turns off PRL GH inhibiting hormone ---turns off GH ...........................................................................continued............................................................................