Controlling your Homeostasis The Endocrine System Controlling your Homeostasis

Basics Network of glands that secrete hormones which travel through blood to affect target cells Paracrine secretions act locally Autocrine secretions act on the cells that produce them Exocrine glands secrete to the outside of the body through tubes or ducts

Functions Control metabolic processes Control rates of reaction, aid in transport across membranes, regulate balances of substances Vital in reproduction, development and growth

Types of Hormones Steroid – formed from cholesterol Ex. Estrogen, testosterone, aldosterone, cortisol

Types of Hormones Nonsteroid – formed from amino acids Amines, peptides, and proteins Not lipid soluble Nonsteroid Hormone Action Combine with receptors in the target cell membrane Receptors have binding site and activity site Hormone-receptor complex signals a G protein to stimulate a membrane protein (adenylate cyclase) to induce formation of second messenger protein w/ the help of ATP

Types cont. Hormone action cont. The second messenger associated with one group of hormones is known as cyclic adenosine monophosphate (cAMP) The cAMP activates another set of enzymes (protein kinases) which transfer phosphate groups from ATP to substrate molecules The series of reactions that follows induce the cellular changes associated w/ the hormone’s actions

Cont.

Feedback Mechanisms Negative feedback Positive feedback An increase in concentration of a hormone triggers activities that inhibit further secretion Positive feedback An increase in concentration of a hormone triggers activities that stimulate further secretion

Hypothalamus and Pituitary

Hypothalamus Region in the forebrain Contains hormone-secreting cells Interacts closely with pituitary gland Releases hormones that affect pituitary activities Primary function: monitor internal organs and states related to organ functioning

Pituitary Gland Master gland of the endocrine system Pea-sized gland at base of hypothalamus Two lobes Posterior lobe stores and secretes hormones that were synthesized in the hypothalamus Anterior lobe produces and secretes its own hormones Summarized in Table 11.3

Anterior Pituitary Adrenocortitropic (ACTH) Steroids Control secretions from adrenal cortex Thyroid Stimulating (TSH): Thyroid Follicle Stimulating (FSH): Ovaries, Testes Stimulates production of sex cells Luteinizing (LH): Ovaries, Testes Promotes secretion of sex hormones; role in releasing egg in females Prolactin (PRL): Mammary Tissue Sustains milk production after birth Growth (GH): all cells

Abnormalities GH Output Gigantism: overproduction during childhood Pituitary dwarfism: underproduction Acromegaly: too much in adulthood

Thyroid Two lobes connected by isthmus Produces: Thyroxine (T4) – contains 4 iodine atoms Increases rate of metabolism Triiodothyronine (T3) – 3 atoms of I Same as above, but 5 times more potent Calcitonin – lowers blood calcium and phosphate ion concentrations by inhibiting release from bones and increasing excretion of these in kidneys

Parathyroid Located on posterior side of thyroid Parathyroid hormone (PTH) Increases blood calcium concentration and decreases blood phosphate ion concentration Affects bones, kidneys, and intestines Negative feedback mechanism: increased blood calcium inhibits PTH production

Adrenal Glands Closely associated with kidneys Two portions: Adrenal medulla – central portion Adrenal cortex – outer portion

Adrenal Medulla Epinephrine (adrenalin) Norepinephrine (noradrenalin) Both… Increase: heart rate, breathing rate, force of cardiac muscle contraction, blood pressure, blood glucose Decrease: digestive activity Produced in response to stress Preparation for “fight or flight responses”

Adrenal Cortex Aldosterone – regulates concentration of extracellular electrolytes by conserving sodium ions and excreting potassium ions Cortisol – decreases protein synthesis, increases fatty acid release (fat used for energy instead of glucose), and stimulates glucose synthesis from noncarbohydrates Maintains blood glucose levels between meals Controlled by ACTH from ant. pit.

Pancreas Glucagon – produced by alpha cells, stimulates liver to break down glycogen into glucose  raising blood sugar When blood sugar gets too high, beta cells detect and secrete insulin Insulin – promotes movement of glucose into certain cells, stimulates formation of glycogen from glucose  lowering blood sugar

Pineal Gland Located deep between cerebral hemispheres Melatonin – produced in response to light conditions  may help control circadian rhythm

Thymus, Testes, Ovaries Thymosin Testosterone Estrogen

Stress Condition of the body in response to a stressor – change in external environment Stressors can be physical (extreme heat/cold, injuries, infections etc) or psychological (thoughts about danger, personal loss, unpleasant social interactions)

Stress cont. Short term “fight or flight” Long term adjustment Adrenal medulla secretes epi and norepi See info under epinephrine Long term adjustment Ant. Pit. Secretes ACTH which stimulates adrenal cortex to release cortisol See info under cortisol Fig. 11.17