Hormones and Feedback Mechanisms Chapter16 How the endocrine system controls everything

The Endocrine System

ES and Homeostasis Homeostasis

Feedback Mechanisms Stimulus Response change in homeostatic environment signal sent to CNS Response signal sent from CNS produce effect body returns to homeostasis

Basic ES cont. ES and NS = 2 main control systems of body Endocrine organs located throughout body Actions mediate all tissues Control of ES through feedback mechanisms

II. ES anatomy basics Exocrine gland Ducts Lumen and surfaces Ex: Sudoriferous, salivary Endocrine gland Chemical messengers Blood stream Ex: Testosterone, Estrogen, Thyroxin

C. Hormones Chemical messenger Secreted by endocrine gland Specific to target Activate cellular change

Hormone + Receptor

Where are Hormones Made ?

The H-P-A Hypothalamic-Pituitary Axis Most feedback loops run through this axis HPA mediates growth, metabolism, stress response, reproduction. is secondarily in charge of almost everything else.

Why is the Hypothalamus so Important? Secretes regulatory hormones RH (releasing) RIH (inhibiting) "Directs" pituitary

(Release-Inhibiting Hormone) STIMULUS Hypothalamus Releasing Hormone (Release-Inhibiting Hormone) Pituitary Stimulating Hormone Gland Hormone Target

E. Pituitary gland MASTER GLAND Anterior and posterior portions Posterior connected to hypothalamus by infundibulum Anterior connected via blood stream

2. Anterior Pituitary Hormones TARGET FUNCTION Thyroid (TSH) Stimulating Thyroid gland TH synthesis & release Growth (GH) Many tissues growth Adrenocortico- Tropin (ACTH) Adrenal cortex Cortisol release (androgens) Prolactin (Prl) Breast Milk production Follicle (FSH) Gonads Egg/sperm prod. Luteinizing (LH) Sex hormones

III.Control of Endocrine Function Positive or Negative Feedback mechanisms Self-regulating system

A. Positive Feedback Not common Classic example: Action of OXYTOCIN on uterine muscle during birth.

B. Negative Feedback Most common control mechanism Level of hormone in blood or body’s return to homeostasis shuts off loop at hypothalamus and pituitary Ex: Thermostat controls and thyroxin (thyroid hormone)

Thyroid Problems What would happen if the thyroid could no longer produce T3 and T4? No negative feedback to hypothalamus and anterior pituitary

Goiter

Hyper-secretion of TSH or TH

B. Growth Hormone Stimulus = Tissue growth/ repair Seen during infancy, toddler, adolescent stages.

What happens with too much GH?

GH = pituitary dwarfism

Too many steroids

Adrenal glands responsible for Hormone Adrenaline, which gives you the rush when presented with a fight or flight situation. The pancreas is responsible for producing insulin. Regulation determines if person is classified as diabetic or not.

Developmental Aspects Levels of hormones decrease as the individual ages. Gonads undergo significant changes especially in females. The ability to bear children decrease along with egg production. In males, testosterone decreases in testes, but the effect is not seen until very old age.