Presentation on theme: "The marine iguana (Amblyrhynchus cristatus). Common Aspects of Neural and Endocrine Regulation APs are chemical events produced by diffusion of ions through."— Presentation transcript:
Common Aspects of Neural and Endocrine Regulation APs are chemical events produced by diffusion of ions through neuron plasma membrane. Action of some hormones are accompanied by ion diffusion and electrical changes in the target cell. –Nerve axon boutons release NTs. –Some chemicals are secreted as hormones, and also are NTs. In order for either a NT or hormone to function in physiological regulation: –Target cell must have specific receptor proteins. –Combination of the regulatory molecule with its receptor proteins must cause a specific sequence of changes. –There must be a mechanism to quickly turn off the action of a regulator.
Endocrine Glands and Hormones Secrete biologically active molecules into the blood. –Lack ducts. Carry hormones to target cells that contain specific receptor proteins for that hormone. Target cells can respond in a specific fashion.
Endocrine Glands and Hormones (continued) Neurohormone: –Specialized neurons that secrete chemicals into the blood rather than synaptic cleft. Chemical secreted is called neurohormone. Hormones: –Affect metabolism of target organs. Help regulate total body metabolism, growth, and reproduction.
Chemical Classification of Hormones Amines: –Hormones derived from tyrosine and tryptophan. NE, Epi, T 4. Polypeptides and proteins: –Polypeptides: Chains of < 100 amino acids in length. –ADH. –Protein hormones: Polypeptide chains with > 100 amino acids. –Growth hormone.
Chemical Classification of Hormones (continued) Lipids derived from cholesterol. –Are lipophilic hormones. Testosterone. Estradiol. Cortisol. Progesterone.
Chemical Classification of Hormones (continued) Glycoproteins: –Long polypeptides (>100) bound to 1 or more carbohydrate (CHO) groups. FSH and LH. Hormones can also be divided into: –Polar: H 2 0 soluble. –Nonpolar (lipophilic): H 2 0 insoluble. –Can gain entry into target cells. –Steroid hormones and T 4. –Pineal gland secretes melatonin: Has properties of both H 2 0 soluble and lipophilic hormones.
Chemical Classification of Hormones (continued) Steroid hormones- lipid soluble –Synthesize from cholesterol Invertebrates--Molting hormone Vertebrates– gonads and adrenal cortex Peptide and protein hormones-transported via carrier proteins –Invertebrates– gamete-shedding hormones –Vertebrates-- ADH, insulin, growth hormone Amine hormones– –Melatonin, catecholamines, and iodothyronines
Prohormones and Prehormones Prohormone: –Precursor is a longer chained polypeptide that is cut and spliced together to make the hormone. Proinsulin. Preprohormone: –Prohormone derived from larger precursor molecule. Preproinsulin. Prehormone: –Molecules secreted by endocrine glands that are inactive until changed into hormones by target cells. T 4 converted to T 3.
Synergistic: –Two hormones work together to produce a result. –Additive: Each hormone separately produces response, together at same concentrations stimulate even greater effect. –NE and Epi. –Complementary: Each hormone stimulates different step in the process. –FSH and testosterone. Hormonal Interactions
Hormonal Interactions (continued) –Permissive effects: Hormone enhances the responsiveness of a target organ to second hormone. –Increases the activity of a second hormone. »Prior exposure of uterus to estrogen induces formation of receptors for progesterone. –Antagonistic effects: Action of one hormone antagonizes the effects of another. –Insulin and glucagon.
Effects of [Hormone] on Tissue Response [Hormone] in blood reflects the rate of secretion. Half-life: –Time required for the blood [hormone] to be reduced to ½ reference level. Minutes to days. Normal tissue responses are produced only when [hormone] are present within physiological range. Varying [hormone] within normal, physiological range can affect the responsiveness of target cells.
Effects of [Hormone] on Tissue Response (continued) Priming effect (upregulation): –Increase number of receptors formed on target cells in response to particular hormone. – Greater response by the target cell. Desensitization (downregulation): –Prolonged exposure to high [polypeptide hormone]. Subsequent exposure to the same [hormone] produces less response. –Decrease in number of receptors on target cells. »Insulin in adipose cells. –Pulsatile secretion may prevent downregulation.
Mechanisms of Hormone Action Hormones of same chemical class have similar mechanisms of action. –Similarities include: Location of cellular receptor proteins depends on the chemical nature of the hormone. Events that occur in the target cells. To respond to a hormone: –Target cell must have specific receptors for that hormone (specificity). Hormones exhibit: –Affinity (bind to receptors with high bond strength). –Saturation (low capacity of receptors).
Hormones That Bind to Nuclear Receptor Proteins Lipophilic steroid and thyroid hormones are attached to plasma carrier proteins. –Hormones dissociate from carrier proteins to pass through lipid component of the target plasma membrane. Receptors for the lipophilic hormones are known as nuclear hormone receptors.
Nuclear Hormone Receptors Steroid receptors are located in cytoplasm and in the nucleus. Function within cell to activate genetic transcription. –Messenger RNA directs synthesis of specific enzyme proteins that change metabolism. Each nuclear hormone receptor has 2 regions: –A ligand (hormone)-binding domain. –DNA-binding domain. Receptor must be activated by binding to hormone before binding to specific region of DNA called HRE (hormone responsive element). –Located adjacent to gene that will be transcribed.
Mechanisms of Steroid Hormone Action Cytoplasmic receptor binds to steroid hormone. Translocates to nucleus. DNA-binding domain binds to specific HRE of the DNA. Dimerization occurs. –Process of 2 receptor units coming together at the 2 half-sites. Stimulates transcription of particular genes.
Mechanism of Thyroid Hormone Action T 4 passes into cytoplasm and is converted to T 3. Receptor proteins located in nucleus. –T 3 binds to ligand-binding domain. –Other half-site is vitamin A derivative (9-cis-retinoic) acid. DNA-binding domain can then bind to the half-site of the HRE. –Two partners can bind to the DNA to activate HRE. Stimulate transcription of genes.
Hormones That Use 2 nd Messengers Hormones cannot pass through plasma membrane use 2 nd messengers. –Catecholamine, polypeptide, and glycoprotein hormones bind to receptor proteins on the target plasma membrane. Actions are mediated by 2 nd messengers (signal-transduction mechanisms). –Extracellular hormones are transduced into intracellular 2 nd messengers.
Adenylate Cyclase-cAMP (continued) Phosphorylates enzymes within the cell to produce hormone’s effects. Modulates activity of enzymes present in the cell. Alters metabolism of the cell. cAMP inactivated by phosphodiesterase. –Hydrolyzes cAMP to inactive fragments.
Polypeptide or glycoprotein hormone binds to receptor protein causing dissociation of a subunit of G-protein. G-protein subunit binds to and activates adenylate cyclase. ATP cAMP + PP i cAMP attaches to inhibitory subunit of protein kinase. Inhibitory subunit dissociates and activates protein kinase. Adenylate Cyclase-cAMP
Synthesis, storage, and release of hormones Peptide hormones –Synthesized by transcription of DNA, translation and post-translational processing Steroid hormones –Synthesized from cholesterol –Not stored, synthesize on demand –Secreted by diffusion through cell membrane
Figure 14.4 Snapshots of insulin synthesis, processing, and packaging (Part 1)
Figure 14.4 Snapshots of insulin synthesis, processing, and packaging (Part 2)
Pituitary Gland Pituitary gland is located in the diencephalon. Structurally and functionally divided into: –Anterior lobe. –Posterior lobe.
The mammalian pituitary gland Pars nervosa- posterior pituitary –Contains terminals of axons –Secretory cells located in hypothalamus Anterior pituitary –Nonneural endocrine cells –Secretion controlled by hypothalamo- hypophyseal portal system –Separate populations of cells secrete different hormones
Hypothalamic Control of Posterior Pituitary Hypothalamus neuron cell bodies produce: –ADH: supraoptic nuclei. –Oxytocin: paraventricular nuclei. Transported along the hypothalamo- hypophyseal tract. Stored in posterior pituitary. Release controlled by neuroendocrine reflexes.
Figure 14.6 The vertebrate pituitary gland has two parts (Part 1)
Pituitary Hormones (continued) Posterior pituitary: –Stores and releases 2 hormones that are produced in the hypothalamus: Antidiuretic hormone (ADH/vasopressin): –Promotes the retention of H 2 0 by the kidneys. »Less H 2 0 is excreted in the urine. Oxytocin: –Stimulates contractions of the uterus during parturition. –Stimulates contractions of the mammary gland alveoli. »Milk-ejection reflex.
Posterior pituitary(neurohypophysis): –Formed by downgrowth of the brain during fetal development. –Is in contact with the infundibulum. Nerve fibers extend through the infundibulum. Anterior pituitary: –Adenohypophysis –Derived from a pouch of epithelial tissue that migrates upward from the mouth. Pituitary Gland (continued)
Pituitary Hormones Anterior Pituitary: –Trophic effects: High blood [hormone] causes target organ to hypertrophy. Low blood [hormone] causes target organ to atrophy.
Hypothalamic Control of the Anterior Pituitary Hormonal control rather than neural. Hypothalamus neurons synthesize releasing and inhibiting hormones. Hormones are transported to axon endings of median eminence. Hormones secreted into the hypothalamo- hypophyseal portal system regulate the secretions of the anterior pituitary
Figure 14.6 The vertebrate pituitary gland has two parts (Part 2)
Figure 14.6 The vertebrate pituitary gland has two parts (Part 3)
Figure 14.6 The vertebrate pituitary gland has two parts (Part 4)
Figure 14.6 The vertebrate pituitary gland has two parts (Part 5)
Anterior pituitary and hypothalamic secretions are controlled by the target organs they regulate. –Secretions are controlled by negative feedback inhibition by target gland hormones. Negative feedback at 2 levels: –The target gland hormone can act on the hypothalamus and inhibit secretion of releasing hormones. –The target gland hormone can act on the anterior pituitary and inhibit response to the releasing hormone. Feedback Control of the Anterior Pituitary
Feedback Control of the Anterior Pituitary (continued) Short feedback loop: –Retrograde transport of blood from anterior pituitary to the hypothalamus. Hormone released by anterior pituitary inhibits secretion of releasing hormone. Positive feedback effect: –During the menstrual cycle, estrogen stimulates “LH surge.”
Higher Brain Function and Pituitary Secretion Axis: –Relationship between anterior pituitary and a particular target gland. Pituitary-gonad axis. Hypothalamus receives input from higher brain centers. –Psychological stress affects: Circadian rhythms. Menstrual cycle.
Figure 14.7 The adrenal gland consists of an inner medulla and an outer cortex
Figure 14.8 Both hormonal and neural mechanisms modulate the action of the HPA axis
Figure 14.9 Interactions of insulin, glucagon, and epinephrine
Figure 14.10 The mammalian stress response (Part 1)
Figure 14.10 The mammalian stress response (Part 2)
Figure 14.11 The CNS and the immune system interact during the stress response
Cytokines released from certain cells of the immune system –Binds with specific receptor molecules –Travel in the blood to hypothalamus Stimulate CRH neurosecretory cells –Resulting in the physiological responses of the HPA axis Helps fight infection –Glucocorticoids inhibit the production of agents that cause inflammation-modulating the immune response The CNS and the immune system interact during the stress response
Insulin secreted when nutrients molecules are abundant –Hypoglycemic effect- promote uptake of nutrients –Inhibit degradation of glycogen, lipids and proteins Glucagon secreted when glucose level is low –Hyperglycemic effect- stimulate break down of glycogen, triglyceride molecules –Forms glucose from noncarbohydrate sources Growth hormone, glucocorticoids, epinephrine, thyroid hormones play permissive and synergistic roles in nutrient metabolism Endocrine control of nutrient metabolism in mammals
Figure 14.12 Hormone & nutrient levels in blood of healthy humans before & after a meal (Part 1)
Figure 14.12 Hormone & nutrient levels in blood of healthy humans before & after a meal (Part 2)
Figure 14.13 The action of an antidiuretic hormone (Part 1)
Figure 14.13 The action of an antidiuretic hormone (Part 2)
Figure 14.14 The renin–angiotensin–aldosterone system (Part 1)
Figure 14.14 The renin–angiotensin–aldosterone system (Part 2)
Vasopressin (ADH)- peptide neurohormone –Stimulate conservation of water Aldosterone –Stimulate conservation of Na+ –Part of renin-angiotensin-aldosterone system ANP- atrial natriuretic peptide –Stimulate the excretion of Na+ and water Endocrine control of salt and water balance in vertebrates
Figure 14.15 Chemical messengers act over short, intermediate, and long distances
Figure 14.17 The silkworm Bombyx mori goes through holometabolous development
Three hormones control metamorphosis: –Prothoracicotropic hormone – PTTH –Ecdysone –Juvenile hormone JH Secreted by nonneural endocrine cells Prevents metamorphosis in the adult form In adult, stimulates sex-attractant pheromones Additional hormones –Bursicaon – darkening and hardening of the cuticle –Eclosion hormone (EH) –Pre-ecdysis triggering hormone (PETH) –Ecdysis triggering hormone (ETH) –Control stereotyped movements during ecdysis Insect metamorphosis – part 1
Convergent evolution of endocrine and neuroendocrine functions between vertebrate and invertebrate animals Hemimetabolous insects go through gradual metamorphosis Holometabolous insects go through complete metamorphosis Environmental and behavioral signals mediated by the nervous system initiate molting Insect metamorphosis part 2
Neuroendocrine cells in the brain secrete PTTH Stimulates secretion of ecdysone from the prothoracic glands Ecdysone is converted to 20- hydroxyecdysone by peripheral activation Epidermis secrete enzymes required for molting process Insect metamorphosis – part 3
Figure 14.19 Endocrine & neuroendocrine structures involved in control of insect metamorphosis (1)
Figure 14.19 Endocrine & neuroendocrine structures involved in control of insect metamorphosis (2)