HORMONES & METABOLISM Option D.5 (AHL)

U: Endocrine glands secrete hormones directly into the bloodstream Endocrine glands = secrete hormones directly into blood (no ducts) Hormones = chemical messengers transported through blood to target cell ~Can be lipid or peptide ~ aka steroid or non-steroid

U: Steroid hormones bind to receptor proteins in cytoplasm of target cell to form receptor-hormone complex Lipid hormones (steroids) can cross directly by simple diffusion across plasma membrane & nuclear membrane Bind to receptor proteins in cytoplasm Receptor-hormone complex attaches to DNA Serves as promotor or inhibitor of transcription of a certain gene E.g. estrogen

U: The receptor-hormone complex promotes the transcription of specific genes Examples: Calciferol (vitamin D) binds to receptor in nucleus Promotes expression of calbindin (Ca+2 transport protein) in small intestine Cortisol (stress hormone) Binds to receptor in cytoplasm In liver, promotes gluconeogenesis (converting fat and protein into glucose), raising blood glucose In body cells, inhibits insulin receptor gene, preventing glucose from being stored in cells, raising blood glucose In pancreas, inhibits transcription of insulin genes

U: Peptide hormones bind to receptors in the plasma membrane of the target cell Protein hormones (non-steroid) can’t pass through plasma membrane (hydrophilic) Bind to surface receptors Trigger reactions mediated by “second messengers”

U: Binding of hormones to membrane receptors activates a cascade mediated by a second messenger inside cell Second messengers = small, water-soluble molecules Can quickly spread through cytoplasm Relay signals throughout cell Most common: ~Ca+2 ~cAMP (cyclic adenosine monophosphate) e.g. Mechanism of action of epinephrine

U: Hormones secreted by the pituitary control growth, developmental changes, reproduction & homeostasis Hormones of anterior pituitary: 1. hGH = human growth hormone 2. FSH = follicle stimulating hormone 3. LH = luteinizing hormone 4. PRL = prolactin 5. TSH = thyroid-stimulating hormone 6. ACTH = adrenocorticotropic hormone Hormones of posterior pituitary: 1. ADH = anti-diuretic hormone 2. Oxytocin

c

U: The hypothalamus controls hormone secretion by the anterior & posterior lobes of the pituitary gland Nervous & Endocrine systems function in homeostasis! Posterior pituitary: hormones produced in neurosecretory cells of hypothalamus, travel down axons where they are stored, until secretion is stimulated by nerve impulse Anterior pituitary: hypothalamus secretes releasing factors, which are carried from hypothalamus to anterior pituitary by a portal vein Note: a portal vein connects one capillary bed to another

NOS: Cooperation & collaboration between groups of scientists: The International Council for the Control of Iodine Deficiency Disorders includes a number of scientists who work to eliminate the harm done by iodine deficiency Thyroid hormone = regulates metabolism Consists of: Triiodothyronine (T3) = contains 3 iodine atoms Tetraiodothyronine (T4) = contains 4 iodine atoms Consequences of iodine deficiency: Goiter = enlargement of thyroid due to constant stimulation from anterior pituitary During pregnancy, can affect fetal nervous development (mental retardation) ICCIDD (non-govt organization) partnered with UNICEF, WHO, national govts, and universities in a worldwide effort to eliminate iodine deficiency through universal iodization of salt

App: Control of milk secretion by oxytocin an prolactin prolactin Produced in anterior pituitary Stimulates growth of mammary glands & production of milk Nursing stimulates continued creation of prolactin During pregnancy, high levels of estrogen: Increases prolactin production Inhibits production of milk from mammary glands During delivery, drop in levels of estrogen & progesterone: Inhibition of milk production is removed oxytocin Produced by neurosecretory cells of hypothalamus and stored in posterior pituitary Stimulates contraction of cells that surround milk glands, allowing ejection of milk Nursing stimulates release of oxytocin

App: Some athletes take growth hormone to build muscles GH Peptide (non-steroid) hormone Produced in anterior pituitary Target organ: liver Stimulates release of insulin-like growth factor which circulates in blood and stimulates bone and cartilage growth Additional effects: increase in muscle mass Produced using GMOs (E.coli) Has been used as a performance enhancing drug (banned by most international sporting federations) Correlation between muscle size & strength; causation unclear Claims of perf enhancing drug: Allows short bursts of great strength Allows tired muscles to recover more quickly Scientific research suggests the benefits are small or non-existent compared to risks

Risks involved with taking hGH Possible side effects of HGH use include: Nerve, muscle, or joint painjoint pain Swelling due to fluid in the body's tissues (edema)edema Carpal tunnel syndrome Numbness and tingling of the skinskin High cholesterol levelscholesterol levels Increased risk of diabetes and cancer