Endocrine part 3 Stimuli for Control of Hormone

Endocrine, part 3

Stimuli for Control of Hormone Release • Hormone levels in the blood are maintained mostly by negative feedback • A stimulus or low hormone levels in the blood trigger the release of more hormone • Hormone release stops once an appropriate level in the blood is reached What stimuli would release a positive feedback mechanism, for example, the secretion of Oxytocin? © 2018 Pearson Education, Inc.

Stimuli for Control of Hormone Release • The stimuli that activate endocrine glands fall into three major categories 1. Hormonal – RELEASES HORMONES IN RESPONSE TO ANOTHER HORMONE LIKE A DOMINO EFFECT. 2. Humoral – “HUMOUR” MEANS BODY FLUIDS, LIKE BLOOD. RESPONSE TO CHANGES IN EXTRACELLULAR FLUIDS. 3. Neural – “NEURO” PERTAINS TO NERVOUS SYSTEM – SHORT-TERM STRESS RESPONSES. © 2018 Pearson Education, Inc.

Stimuli for Control of Hormone Release • Hormonal stimuli • Most common category of stimulus • Endocrine organs are activated by other hormones – TROPIC (INFLUENCED BY OTHER HORMONES) • Example: • Hormones of the hypothalamus stimulate the anterior pituitary to secrete its hormones © 2018 Pearson Education, Inc.

(a) Hormonal stimulus Figure 9. 2 a Endocrine gland stimuli. 1 The hypothalamus secretes hormones that… Hypothalamus 2 …stimulate the anterior pituitary gland to secrete hormones that… Thyroid gland Anterior pituitary gland Adrenal cortex Gonad (testis) 3 …stimulate other endocrine glands to secrete hormones

Stimuli for Control of Hormone Release • Humoral stimuli – “VASCULAR”, IN THE BLOOD AND FLUIDS • Changing blood levels of certain ions and nutrients stimulate hormone release • Humoral indicates various body fluids, such as blood and bile • Examples: • Parathyroid hormone and calcitonin are produced in response to changing levels of blood calcium levels • Insulin is produced in response to changing levels of blood glucose levels © 2018 Pearson Education, Inc.

(b) Humoral stimulus Figure 9. 2 b Endocrine gland stimuli. 1 Capillary blood contains low concentration of Ca 2+, which stimulates… Capillary (low Ca 2+ in blood) Thyroid gland (posterior view) Parathyroid glands PTH 2 …secretion of parathyroid hormone (PTH) by parathyroid glands

Stimuli for Control of Hormone Release • Neural stimuli – SENSES FOR EXTERNAL, CNS/PNS FOR INTERNAL • Nerve fibers stimulate hormone release • Most are under the control of the sympathetic nervous system • Examples: • Sympathetic stimulation of the adrenal medulla to release epinephrine and norepinephrine © 2018 Pearson Education, Inc.

(c) Neural stimulus Figure 9. 2 c Endocrine gland stimuli. 1 Preganglionic sympathetic fiber stimulates adrenal medulla cells… CNS (spinal cord) Preganglionic sympathetic fibers Medulla of adrenal gland Capillary 2 …to secrete catecholamines (epinephrine and norepinephrine)