Chapter 13 The Endocrine System http://ghr.nlm.nih.gov/handbook/illustrations/gh.jpg

Endocrine Functions: Hormones Come from endocrine glands Circulate in the bloodstream Act on specific cells in the body http://www.epc.org/ministries/the-epc-foundation/foundation-services-for-individuals/

Endocrine System Characteristics Access to every cell The exception is the CNS due to the blood – brain barrier Each hormone acts only on specific cells (target cells) Only specific cells have receptors for specific hormones Endocrine control is slower than nervous system Endocrine and nervous systems interact

Classification of Hormones: Steroid Steroid hormones Lipid soluble, chemically derived from cholesterol Enter target cells Activate specific genes to produce specific proteins Slower acting than non-steroid hormones; minutes to hours

Steroid Hormone Action on a Target Cell Figure 13.2

Classification of Hormones: Nonsteroid Nonsteroid hormones Water soluble Bind to receptors on target cell membranes Work through intermediate mechanisms to activate existing enzymes Faster acting than steroid hormones; seconds to minutes

Nonsteroid Hormone Action on a Target Cell Figure 13.3

Role of Negative Feedback Loops Figure 13.4

Hypothalamus and the Anterior Pituitary Gland A link between the nervous system and the endocrine system Monitors the hormones secreted by the pituitary gland Figure 13.7

http://www. clarian. org/ADAM/doc/HealthIllustratedEncyclopedia/2/8883 http://www.clarian.org/ADAM/doc/HealthIllustratedEncyclopedia/2/8883.htm http://www.gopetsamerica.com/anatomy/illustrations/pancreas.jpg The pancreas functions as both an endocrine gland and an exocrine gland (secretions used in digestion) Islets of Langerhans clusters of cells within the pancreas secrete hormones The Pancreas

Roles of Insulin and Glucagon in Regulating Blood Glucose Figure 13.10

Adrenal Glands: Medulla Adrenal medulla Neuroendocrine organ The hormones are synthesized and stored in specialized cells in the adrenal medulla Secretion Sympathetic nervous system The adrenal medulla is innervated with sympathetic nerves Hormones: nonsteroidal Epinephrine and norepinephrine (also serve as neurotransmitters) Enhance function of sympathetic nervous system (fight-or-flight response)

Adrenal Glands: Medulla Figure 13.11

Homeostatic Regulation of Blood Calcium Concentration Figure 13.15a

Homeostatic Regulation of Blood Calcium Concentration (cont.) Figure 13.15b

Thyroid/Parathyroid Glands Calcitonin (secreted from thyroid) Lowers blood calcium levels by inhibiting the action of osteoclasts Parathyroid hormone (PTH): nonsteroidal Removes calcium and phosphate from bone Increases absorption of calcium by the digestive tract Increases renal retention of calcium and excretion of phosphate