ANAPHY 12 LEC.pdf

Chemical Messengers – allow cells to communicate with each other to regulate body activities. Four Classes of Chemical Messengers: (based on source & mode of transport) 79. Autocrine – stimulates the cell that originally secreted it, and sometimes nearby cells of same type (ex: WBC)....

Chemical Messengers – allow cells to communicate with each other to regulate body activities. Four Classes of Chemical Messengers: (based on source & mode of transport) 79. Autocrine – stimulates the cell that originally secreted it, and sometimes nearby cells of same type (ex: WBC). 80. Paracrine – local messengers secreted by one cell type but affect neighboring cells of different types; do not travel in circulation but secreted into extracellular fluid (ex: histamine). 81. Neurotransmitter – secreted by neurons to activate another neuron, muscle cell or glandular cell; secreted into a synaptic cleft (ex: acetylcholine). 82. Endocrine – secreted into bloodstream by certain glands & cells; affect cells distant from the source (ex: epinephrine). Main Regulatory Functions of Endocrine System: 83. Metabolism 84. Control of food intake & digestion 85. Tissue development 86. Ion regulation 87. Water balance 88. Heart rate and blood pressure regulation 89. Control of blood glucose & other nutrients 90. Control of reproductive functions 91. Uterine contractions & milk release 92. Immune system regulation Endocrine System – includes glands & specialized endocrine cells that secrete hormones into the bloodstream. Hormone – a chemical messenger that is secreted into the blood, travels to a distant target tissue, & binds to specific receptors to produce a coordinated set of events in that target tissue. Chemical Nature of Hormones:  93. Lipid-Soluble Hormones – nonpolar; include steroid hormones, thyroid hormones, and fatty acid derivatives such as eicosanoids. o Small molecules; insoluble in water-based fluids (plasma); therefore, attached to binding proteins for transport through bloodstream & protection of hormones. o Gradually removed from circulation; life span ranges from days to several weeks. o Breakdown products are excreted via urine or bile. 94. Water-Soluble Hormones – polar; includes proteins, peptide, & most amino acids derivative hormones. o May circulate as free hormones; large molecules diffuse from blood into tissue spaces slowly; small molecules diffuse rapidly into protein to avoid being filtered out of kidneys. o Relatively short half-lives due to rapid degradation of enzymes (proteases) within bloodstream; hormone breakdown products are then excreted in urine; however, some hormones have chemical modifications, such as adding of carbohydrate groups, which prolongs the hormone’s life span. Type of Stimuli Regulating the Hormone Release Inhibition Hu Directly by blood-borne Companion hormones – secreted with the mor chemicals to hormones that are release of humoral stimuli; oppose the effect al sensitive to levels of particular of secreted hormone & counteract its actions Sti substances (insulin). (glucagon). muli Ne ura Stimulated by action potential, releasing Neurons inhibit target by releasing l neurotransmitter from neurons into inhibitory neurotransmitter causing the Sti synapse with cell producing hormones target endocrine gland to not secrete mu (epinephrine). its hormone. li Hor Hormone is secreted to Common mode; release of hormones to mon stimulate the secretion of other prevent secretion of other hormones al hormones (tropic hormones of (inhibiting hormones from hypothalamus Stim anterior pituitary gland). prevent the secretion of tropic hormones). uli Major Mechanism that Maintain Hormone Levels in Blood: (See process figure 10.5, page 268)  Negative Feedback: prevents further hormone secretion once a set point is achieved. Positive Feedback: self-promoting system whereby the stimulation of hormone secretion increases over time. Receptors – proteins where the hormones bind. Receptor Site – location on the cell where the hormone binds; each characteristic allows only a specific type of hormone to bind to it. Specificity – tendency for each type of hormone to bind to one type of receptor. (See figure 10.6, page 268) Classes of Receptors: (See process figure 10.7-10.11, pages 269-272) 95. Nuclear Receptors – often found in the cell nucleus where the lipid-soluble hormones bind; cannot respond immediately because it takes time to produce mRNA and the protein. o Hormone-Response Elements – fingerlike projections that recognize & bind specific nucleotide sequence in DNA; found in receptors that bind to DNA. o Transcription Factor – forms from the combination of hormone and its receptors. The hormone-receptor complex activates genes, which in turn activates the DNA to produce mRNA. o The mRNA increases the synthesis of certain proteins that produce the target cell’s response. 96. Membrane-Bound Receptors – proteins that extend across the cell membrane where water-soluble hormones bind; with hormone-binding sites exposed on cell membrane’s outer surface. o Activate responses in two ways: i. Alter the activity of G proteins (α, β, and γ) at the inner surface of the cell membrane. The α subunit of G proteins opens/closes ion channels & causes them to open or change the rate of synthesis of intracellular mediators, such as cAMP (cyclic adenosine monophosphate) or others. ii. Alter the activity of intracellular enzymes directly to initiate the cellular response referred to.  These activations elicit second messenger activities that rapidly activate already existing intracellular messenger systems. o Second Messenger Systems – means that a single hormone activates many second messengers, each of which activates only one final product. o There is a signal amplification, which means that the single hormone activates many second messengers, each of which activates only one final product. Pituitary Gland / Hypophysis – small gland that rests in the sella turcica which is controlled by the hypothalamus; connected to hypothalamus by infundibulum; divided into two parts: (See table 10.2, page 274 and figure 10.12, page 273) 97. Anterior Pituitary – made of epithelium from embryonic oral cavity (See process figure 10.13, page 275). o Secretions are controlled by hormones that pass through Hypothalamic- Pituitary Portal System (capillary beds and veins that transport the releasing and inhibiting hormones). ▪ Hormones released by the anterior pituitary are controlled by hormones (See figure 10.15, page 275). 98. Posterior Pituitary – extension of the brain & composed of nerve cells (See process figure 10.14, page 276). o Hormones secreted are controlled by action potentials carried by axons that pass from the hypothalamus (Direct Innervation).