The Endocrine System and Chemical Messengers
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This document discusses the endocrine system and chemical messengers. It begins by comparing the nervous and endocrine systems, noting that the endocrine system uses slower chemical messengers. It then describes the evolution of these messengers and the five major types: local chemical messengers, neurotransmitters, neuropeptides, hormones, and pheromones. The document provides examples of these messengers in both invertebrates and vertebrates. It also explains the mechanisms of hormone action, feedback control systems, and gives specific examples of endocrine systems in groups like molluscs, arthropods, and crustaceans.
The Endocrine System and Chemical Messengers
- 1. T H E E N D O C R I N E S Y S T E M A N D C H E M I C A L M E S S E N G E R S B Y NAVEED AKHTAR ASSISTANT PROFESSOR OF ZOOLOGY Communication III
- 2. Comparison of Nervous and Endocrine System
- 3. Introduction The nervous and sensory systems work together to rapidly communicate information and maintain homeostasis in an animal’s body. In addition, many animals have a second, slower form of communication and coordination—the endocrine system with its chemical messengers. Evolution of Chemical Messenger: Some scientists suggest that chemical messengers may initially have evolved in single-celled organisms to coordinate feeding or reproduction. As multicellularity evolved, more complex organs also evolved to govern the many individual coordination tasks, but control centers relied on the same kinds of messengers that were present in the simpler organisms.
- 4. Chemical messengers have an ancient origin and must have been conserved for hundreds of millions of years “old” messengers are adapted to new purposes. For example, some ancient protein hormones are in species ranging from bacteria to humans One key to the survival of any group of animals is proper timing of activity so that growth, maturation, and reproduction coincide with the times of year when climate and food supply favor survival. It seems likely that the chemical messengers regulating growth and reproduction were among the first to appear. These messengers were probably secretions of neurons. .
- 5. Later, specific hormones developed to play important regulatory roles in molting, growth, metamorphosis, and reproduction in various invertebrates. Chemical messengers and their associated secretory structures became even more complex with the appearance of vertebrates
- 6. A chemical messenger is a substance secreted by a cell or tissue and it regulate activities of body functions. Types of Chemical Messengers: There are five major types of Chemical messengers; 1. Local Chemical Messenger (LCM) 2. Neurotransmitters 3. Neuropeptides 4. Hormones 5. Pheromones
- 7. 1. Local Chemical Messenger (LCM) Many cells secrete chemicals that alter physiological conditions in the immediate vicinity Autocrine agents :Most of these chemicals act on the same cell or adjacent cells Vertebrate examples include some of the chemicals called lumones that the gut produces and that help regulate digestion. In a wound, mast cells secrete a substance called histamine that participates in the inflammatory response.
- 8. 2. Neurotransmitters. neurons secrete chemicals called neurotransmitters (e.g., nitric oxide and acetylcholine) that act on immediately adjacent target cells These chemical messengers reach high concentrations in the synaptic cleft, act quickly, and are actively degraded and recycled.
- 9. 3. Neuropeptides or Neurohormones Some specialized neurons (called neurosecretory cells) secrete neuropeptides (neurohormones). The blood or other body fluids transport neuropeptides to nonadjacent target cells, where neuropeptides exert their effects In mammals, for example, certain nerve cells in the hypothalamus release a neuropeptide that causes the pituitary gland to release the hormone oxytocin, which induces powerful uterine contractions during the delivery of offspring.
- 10. 4. Hormones Secretions of endocrine glands that are released into the blood to be transported to a target organ to show its effect. Example : Insulin 5. Pheromones. Pheromones are chemical messengers released to the exterior of one animal that affect the behavior of another individual of the same species
- 13. How do hormones and neurotransmitters differ?
- 14. HORMONES AND THEIR FEEDBACK SYSTEMS What are hormones? A hormone (Gr. hormaein, to set in motion or to spur on) is a specialized chemical messenger that an endocrine gland or tissue produces and secretes. Hormones circulate through body fluids and affect the metabolic activity of a target cell or tissue in a specific way. By definition, a target cell has receptors to which chemical messengers either selectively bind or on which they have an effect
- 15. Endocrinology :The study of endocrine glands and their hormones is called endocrinology Biochemistry of Hormones:
- 16. Amount of Hormones: Hormones are effective in extremely small amounts. Only a few molecules of a hormone may be enough to produce a dramatic response in a target cell. In the target cell Working of Hormones: Hormones influence cellular functions byaltering rates of biochemical processes intarget cells Change membrane permeability to increase or decrease the diffusion rate of a substance Affect enzyme synthesis and activity to alter cell metabolism Stimulate release of hormones from other glands This is a dynamic process that must be regulated, not just activated
- 17. Feedback Control System of Hormone Secretion
- 20. MECHANISMS OF HORMONE ACTION Hormones modify the biochemical activity of a target cell or tissue. Two basic mechanisms are involved. The first, the fixed-membrane-receptor mechanism, applies to hormones that are proteins or amines Because they are water soluble (hydrophilic) and cannot diffuse across the plasma membrane, these hormones initiate their response by means of specialized receptors on the plasma membrane of the target cell. The second, the mobile-receptor mechanism, applies to steroid hormones. These hormones are lipid soluble (lipophilic) and diffuse easily into the cytoplasm, where they initiate their response by binding to cytoplasmic receptors
- 24. SOME HORMONES OF INVERTEBRATES
- 25. The first hormones were probably neurosecretions. 1. Porifera The porifera (sponges) do not have classical endocrine glands. Because sponges do not have neurons, they also do not have neurosecretory cells 2. Cnidarians The nerve cells of Hydra contain a growth-promoting hormone that stimulates budding, regeneration, and growth. For example, when the hormone is present in the medium in which fragments of Hydra are incubated, “head” regeneration is accelerated. This so-called “head activator” also stimulates mitosis in Hydra.
- 26. 3. Platyhelminthes Neurosecretary Cells Cerebral ganglion Neuropeptides: regeneration, asexual reproduction, and gonad maturation Example: neurosecretory cells in the scolex of some tapeworms control shedding of the proglottids 4. Nemerteans Nemerteans have more cephalization than platyhelminthes and a larger brain, composed of a dorsal and ventral pair of ganglia connected by a nerve ring. The neuropeptide that these ganglia produce appears to control gonadal development and regulate water balance
- 27. 5. Nematodes No classical endocrine system Only neurosecretory cells Control ecdysis or moulting The neuropeptide is released after a new cuticle is produced and stimulates the excretory gland to secrete an enzyme (leucine aminopeptidase) into the space between the old and new cuticles. The accumulation of fluid in this space causes the old cuticle to split and be shed
- 28. 6. Molluscs The ring of ganglia that constitutes the central nervous system of molluscs is richly endowed with neurosecretory cells. The neuropeptides that these cells produce help regulate heart rate, kidney function, and energy metabolism. The intestines of some bivalves have been found to produce insulin, which may have a carbohydrate-regulating role similar to that of insulin in vertebrates
- 29. In certain gastropods, such as the common land snail Helix, a specific hormone stimulates spermatogenesis; another hormone, termed egg-laying hormone, stimulates egg development; and hormones from the ovary and testis stimulate accessory sex organs. In all snails, a growth hormone controls shell growth In cephalopods, such as the octopus and squid, the optic gland in the eyestalk produces one or more hormones that stimulate egg development, proliferation of spermatogonia, and the development of secondary sexual characterists
- 30. 7. Annelids A well-developed and cephalized nervous system, a well-developed circulatory system, and a large coelom demands well developed endocrine system The various endocrine systems of annelids are generally involved with morphogenesis, development, growth, regeneration, and gonadal maturation. For example, in polychaetes, juvenile hormone inhibits the gonads and stimulates growth and regeneration
- 31. Another hormone, gonadotropin, stimulates the development of eggs, whereas the hormone annetocin (related to vertebrate oxytocin) elicits egg-laying behavior. In leeches, a neuropeptide stimulates gamete development and triggers color changes. Osmoregulatory hormones have been reported in oligochaetes, and a hyperglycemic hormone that maintains a high concentration of blood glucose has been reported for the oligochaete Lumbricus.
- 32. 8. Arthropods: The endocrine systems of crustaceans and insects are excellent examples of how hormones regulate growth, maturation, and reproduction. Much is known about hormones and their functioning in these animals The endocrine system of a crustacean, such as a crayfish, controls functions such as ecdysis (molting), sex determination, and color changes.
- 33. X-Organ: X-organs are neurosecretory tissues in the crayfish eyestalks Associated with each X-organ is a sinus gland that accumulates and releases the secretions of the X-organ. Y -Organ: Other glands, called Y-organs, are at the base of the maxillae Mechanism of Ecdysis: X-organs and Y-organs control ecdysis as follows. In the absence of an appropriate stimulus, the X-organ produces molt-inhibiting hormone (MIH), and the sinus gland releases
- 34. Control of Ecdysis (Molting) in Crustaceans.
- 35. Control of Ecdysis (Molting) in Crustaceans.
- 36. The target of this hormone is the Y-organ. When MIH is present in high concentrations, the Y-organ is inactive. Under appropriate internal and external stimuli, MIH release is prevented, and the Y-organ releases the hormone ecdysone, which leads to molting
- 37. Control of Ecdysis (Molting) and Development (Metamorphosis) in an Insect. The sequence of events in insects is similar to that of crustaceans, but it does not involve a molt-inhibiting hormone. The presence of an appropriate stimulus to the central nervous system activates certain neurosecretory cells (pars intercerebralis) in the optic lobes of the brain These cells secrete the hormone ecdysiotropin, which axons transport to the corpora cardiaca (a mass of neurons associated with the brain). The corpora cardiaca produces thoracotropic hormone, which is carried to the prothoracic glands, stimulating them to produce and release ecdysone, which induces molting —in particular, the reabsorption of some of the old cuticle and the development of a new cuticle.
- 38. Bursicon Hormone: Other neurosecretory cells in the brain and nerve cords produce the hormone bursicon. Bursicon influences certain aspects of epidermal development, such as tanning (i.e., hardening and darkening of the chitinous outer cuticle layer). Tanning is completed several hours after each molting.
- 41. Juvenile hormone (JH): Another hormone, juvenile hormone (JH), is also involved in the morphological differentiation that occurs during the molting of insects. Just behind the insect brain are the paired corpora allata These structures produce JH. High concentrations of JH in the blood of an insect inhibit differentiation. In the absence of an appropriate environmental stimulus, the corpora allata decrease JH production, which causes the insect larva to differentiate into a pupa. The pupa then forms a cocoon to overwinter. In the spring, a final surge of ecdysone, in the absence of JH, transforms the pupa into an adult moth.
- 42. 9: Echinoderms: Because echinoderms are deuterostomes, they are more closely allied with chordates than the other invertebrates. However, the endocrine systems of echinoderms provide few insights into the evolution of chordate endocrine systems, because echinoderm hormones and endocrine glands are very different from those of chordates. the radial nerves of sea stars contain a neuropeptide called gonad-stimulating substance. When this neuropeptide is injected into a mature sea star, it induces immediate shedding of the gametes, spawning behavior, and meiosis in the oocytes. The neuropeptide also causes the release of a hormone called maturationinducing substance, which has various effects on the reproductive system
- 44. AN OVERVIEW OF THE VERTEBRATE ENDOCRINE SYSTEM