BSC 2086 1st Edition Lecture 5 Outline of Last Lecture I. Equilibrium and HearingII. Intro to Endocrine SystemIII. Intercellular Communication in the Endocrine System Outline of Current Lecture I. HormonesII. Pituitary Gland Current LectureI. Hormones a. Can either travel freely or attached to special carrier proteins b. Amino acid derivatives i. Structurally related to amino acidsii. Derivatives of Tyrosine:1. Thyroid hormones 2. Catecholamines (epinephrine and norepinephrine)iii. Derivatives of Tryptophan1. Used to make many hormones and neurotransmitters2. Dopamine, melatonin (pineal gland) and serotonin c. Peptide Hormonesi. Chains amino acids synthesized as prohormones 1. “Pro”- means inactive2. Converted to active hormones before or after secretionii. Glycoproteins1. More than 200 amino acids long with carb side chains chains2. Thyroid-stimulating hormone (TSH)3. Luteinizing hormone (LH)4. Follicle-stimulating hormone (FSH)iii. Short chain polypeptides – antidiuretic hormone (ADH) and oxytocin (OXT)1. Each 9 amino acids longiv. Small proteins1. Growth hormone (GH) and prolactin (PRL) 2. GH = 191 amino acids3. PRL = 198 amino acidsd. Lipid Derivativesi. Eicosanoids: 20 carbon fatty acid derived from arachidonic acid1. Paracrine factors that coordinate cell activities and play a role in enzymatic processes such as blood clotting 2. Prostaglandins: direct local cell activities a. Sometimes converted to thromboxanes and prostacyclinsii. Steroid hormones 1. Originate from cholesterol2. Released as:a. Androgens by testesb. Estrogens and progestins by the ovariesc. Corticosteroids by adrenal glandsd. Calcitriol by the kidneys 3. Remain in circulation longer than peptide hormones because they are bound to specific transport proteins e. Secretion and distribution of free hormonesi. Go out of bloodstream and bind to target cell receptorsii. Cells in liver or kidneys, as well as enzymes in plasma membrane or in interstitial fluids, break down and absorb the free hormonesf. Thyroid and steroid hormonesi. Stay in circulation longer due to more than 99% of them binding to carrierproteinsii. Intracellular receptors: affect rate of DNA transcription in nucleus which will change pattern of protein synthesis1. Affects metabolic activity and structure of target cell g. Mechanisms of Hormone Actioni. Hormone receptors1. Hormonal sensitivity determined by presence or absence of receptors different tissues have different receptor combinations2. One cell can respond to different hormones as long as they have receptors for itii. Catecholamines and peptide hormones1. Cant penetrate plasma membrane not lipid soluble2. Bind to extracellular receptors on outer surface of plasma membrane iii. Eicosanoids 1. Can penetrate plasma membrane2. Bind to intracellular receptors iv. First and Second Messengers 1. First messenger (hormone) must stimulate second messenger to cause change in a cell 2. Use intermediary to have effect on activities within target cell3. Second messengers include:a. Cyclic-AMP (cAMP)i. ATP which has been converted into cyclic formb. Cyclic-GMP (cGMP)c. Calcium Ions i. Important in muscle systems4. G Proteins – involved in the link between first and second messenger a. Adenylate cyclase (enzyme): activated when hormone binds to receptor and changes concentration of cyclic AMP i. Increased cAMP = acceleration of metabolic activityii. Converts ATP to cAMP b. G proteins and calcium ionsi. Activated G protein opens calcium ion channels which released calcium ionsii. G protein activates phospholipase C (PLC) which is an enzyme triggers receptor cascadeiii. Calmodulin may be activated which will cause morechanges v. Amplification 1. Binding of small amount of hormone molecules to receptors which leads to thousands of second messengers 2. Amplifies the effect of the hormonevi. Regulation1. Down regulation: when there is a high presence of a hormone which leads to decreased sensitivity and less hormone receptors a. Ex. Cocaine usage need more and more to get the same high2. Up regulation: when there is a low presence of hormones which leads to increased sensitivity and more hormone receptors h. Hormone Control by Endocrine Reflexes i. Counterpart of neural reflexesii. Usually controlled by negative feedback stimulus triggers hormone production, the effects of the hormone will reduce intensity of stimulusiii. Can be triggered by:1. Humoral stimuli : different signals found in blood which cause change in composition of extracellular fluid2. Hormonal stimuli: Addition or removal of specific hormone3. Neural stimuli: signal coming from nervous system through neurotransmitters at neuroglandular junctions iv. Types: 1. Simple endocrine reflex: only one hormone involved a. Controls secretion of hormones by the heart, digestive system, pancreas and parathyroid gland2. Complex endocrine reflex: two or more hormonesv. Hypothalamus = highest level of endocrine controlvi. Neuroendocrine Reflexes: both neural and endocrine componentsvii. Complex commands are given by changing amount of hormone secreted and the pattern of release 1. Pituitary and hypothalamic hormones are released in random bursts II. Pituitary Gland a. Also known as hypophysis b. Located within sella turcica of the sphenoid bone and is connected to the infundibulum under the hypothalamus i. Sellar diaphragm: holds pituitary in position and isolates it from the cranial cavity c. Releases 9 important peptide hormones which bind to intracellular receptors i. cAMP = second messengerd. Anterior Lobe i. Aka. adenohypophysis ii. Endocrine glands and other organs are turned on by hormonesiii. Tropic hormone: causes release of other hormones by endocrine glands iv. Hypothalamic control1. Releasing hormones (RH)a. Promotes synthesis and secretion of one or more hormones at anterior lobe 2. Inhibiting hormones (IH)a. Prevents synthesis and secretion of hormones from anterior lobe 3. Secretion rate controlled by negative feedback v. Hormones 1. Thyroid stimulating hormone (TSH)a. “thyrotropin”b. Increases secretion of TH by thyroid gland2. Adrenocorticotropic hormone (ACTH) a. “corticotropin”b. Stimulates release of steroids from adrenal cortex3. Follicle stimulating hormone (FSH)a. “follitropin”b. Promotes follicle development and estrogen secretion in women4. Luteinizing hormone (LH)a. “lutropin” b. Starts ovulation and secretion of estrogens and progestins in women 5. Growth hormone (GH) a.
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