BIO 3324 1st Edition Lecture 4 Outline of Last Lecture I. concurrent effects II. Membrane electrical statesIII. Local signalingIV. Signal transductionV. Control systemsVI. Response loopsOutline of Current Lecture II. System reflexIII. Steroid hormonesIV. Pituitary glandsV. Regulating HypothalamicVI. Effect of hormonesCurrent LectureSystem reflex speed, duration, and intensity:• Neural reflexes are much faster than endocrine reflexesNeurons transmit electrical signals very fast (~120 m/s)Neurotransmitter need only travel a short distance between cells• Endocrine reflexes last longer than neural reflexesNeurotransmitters are quickly removed/destroyed once released (milliseconds to seconds)Second messengers systems last seconds to hoursDe novo protein synthesis lasts hours to days • Nature of the signal determines intensityNeurons transmit signals of the same magnitude, thus to indicate a stimulus intensity, the frequency of the signal is increasedEndocrine signals reflect intensity of stimuli by adjusting the amount of hormone releasedHormones:• A chemical secreted by a cell or group of cells into the blood for transport to a distant target where it exerts its effects at very low concentrations• The boundaries between hormonal and nonhormonal activity is rather blurred due to advances in research• Origin of secretionMost secreted by glands, tissue derived from epitheliumThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Some secreted by individual cells, neurons (neurohormones), and immune system (cytokines)• SecretionMost hormones are secreted into the blood streamEctohormones are special class of hormones that serve as signal molecules secreted into the external environment; ex: pheromones• TargetsCan act locally or at a distance away depending on the location of target cells• ConcentrationsAct in the nano- (10-9) to picomolar (10-12) rangesComplexity of hormone action:• A single endocrine gland may produce more than one hormoneAnterior pituitary produces 6 different hormones• A single hormone may be secreted by more than one endocrine glandSomatostatin: hypothalamus and pancreas• A single hormone can have more than one type of target cellInsulin can act on muscles, liver and fat (as well as other tissues)• Rate of secretion of some hormones varies considerably over the course of time in a cyclic patternCircadian rhythms and menstrual cycleComplexity of endocrine function:• A single target cell may be influenced by more than one hormoneInsulin & glucagon on hepatic cellsProgesterone and estrogen on uterine cells• A chemical messenger may be either a hormone or a neurotransmitter depending on its source and method of deliveryNorE is secreted by adrenal medulla (hormone) and by sympathetic postganglionic fibers• Some organs are exclusively endocrine while others perform non-endocrine functionsEndocrine: anterior pituitaryMultifunctional: testis (makes testosterone and produces sperm)Hormone classifications:• Can be classified in multiple waysSource of secretionMechanism of action (type of receptor used)Solubility in H2OChemical classesPeptide/protein hormonesSteroid hormones (derivatives of cholesterol)Amine hormones (modified amino acids)Peptide/protein Hormones:• Synthesis, storage and releaseLarge precursor proteins (preprohormones) are synthesized in ERProcessed in the Golgi apparatus into a second stage inactive form (prohormone)Packaged into secretory vesicles and processed (post-translational modification) into the active form (hormone) and stored until signaled to be releasedSecretion of the vesicular contents (hormones + peptide fragments) by exocytosis into the bloodstream• TransportPeptide hormones are water-soluble (lipophobic) and thus dissolve easily into the ECFShort half-lifes• Mechanism of actionLipophobic thus must bind a cell surface receptor and usually act through a second messenger systemShort lag time between binding and responseSteroid hormones:• Synthesis, storage and releaseStored cholesterol undergoes a series of enzymatic reactions that modify the basic cholesterol molecule in the Smooth ERThe enzymes that produce specific hormones are only present in specialized steroidogenic cellsTherefore, specialized steroidogenic organs may only produce specific steroidsOnce synthesized, lipophilic steroids diffuse through the plasma membrane and enter the blood• TransportNot water-soluble thus must be bound by a carrier moleculeSpecific carriers; e.g. corticosteroid-binding proteinNon-specific carriers; albuminBinding to the carrier molecules extends the half-life but blocks the entry of steroid into cellsDynamic balance between bound and unbound hormone; obeys the law of mass action to maintain the ratio of bound to unbound hormone so that plasma concentrations stay constant• Mechanism of actionBind to intracellular receptors located in the cytosol or nucleus which act as transcription factorsResults in gene activation (or inactivation) and thus de novo protein synthesis; aka genomic effectLong lag time between binding and response(some bind to cell surface receptors similar to protein hormones)Amine hormones:• Derived from the amino acid tyrosine or tryptophanTryptophan: melatoninTyrosine: catecholamines and thyroid hormone• Mechanism of actionCatecholamines act like peptide hormones and bind to cell surface receptors and work through second messengersThyroid hormone acts like steroid hormones and bind intracellular receptors and activate gene transcriptionSimple endocrine reflexes:• A simple negative feedback loop• The endocrine cell directly senses the stimuli and responds by secreting the hormoneNeurohormones:• Three major classesCatecholamines – produced by modified neurons of the adrenal medullaHypothalamic neurohormones – produced in the hypothalamus and secreted from the posterior pituitaryHypothalamic neurohormones – regulate the release of hormones from the anterior pituitaryThe pituitary gland (hypophysis):• Has two anatomically and functionally distinct lobesAnterior pituitary (glandular)Posterior pituitary (neural)• Hormones released by the pituitary are directly controlled by the hypothalamusAnterior pituitary (vascular link)Posterior pituitary (neural pathway)Posterior pituitary:• Neurosecretory neuron cell bodies located in the hypothalamus (supraoptic & paraventricular