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Biology 30 Module 2 Lesson 9 Body Actions and Systems: Maintaining Life Chemical Control and Coordination Copyright: Ministry of Education, Saskatchewan May be reproduced for educational purposes Biology 30 267 Lesson 9 Biology 30 268 Lesson 9 Lesson 9 Transport Systems Directions for completing the lesson: Text References for suggested reading: Read BSCS Biology 8th edition Sections 17.7 – 17.10, pages 443-450 OR Nelson Biology Chapter 10, pages 223-236 Study the instructional portion of the lesson. Review the vocabulary list. Do Assignment 9. Biology 30 269 Lesson 9 Vocabulary ACTH ADH adrenal cortex adrenal glands biofeedback diabetes mellitus endocrine estrogen exocrine FSH glucagons gonads HGH hypothalamus insulin Islets of Langerhans Biology 30 LH MSH neurosecretory cells ovaries oxytocin parathyroid pheromones pituitary gland progesterone prolactin testes testosterone thymus thyroid TSH 270 Lesson 9 Lesson 9 – Chemical Control and Coordination Introduction Studies of the internal natures of living organisms have indicated the ongoing actions of different processes. Gas exchanges during respiration, food and waste processing and movements, internal transport and body movements, are just some of the life-sustaining actions. Usual methods of study have been to look at these individually. In doing so, one may form a mistaken impression that all of these processes are going on at the same time, but independently of each other. Yet, just the opposite relationship exists. All the different systems and processes are closely tied in with each other and variations in individual ones almost always affect the others. Increased muscular action in a vertebrate animal brings about a higher respiration rate, increased heart action and circulatory movement, production of more wastes and many other changes. The ability of individual systems to work closely together requires some sort of close communication with each other. How some communication occurs has already been looked at in the lesson on nervous and sensory systems. Many organisms have other or additional ways of having their cells or body parts interact. Changes in rates of cell or body respiration as well as in various body developments take place continuously. Variations in developments and processes are commonly highlighted by differences in the growths and behaviors of organisms during their daily and life cycles. An animal's body processes may be directed to growth and maintenance for much of a year. During part of that year, the same animal could experience changes in body activities during a reproduction phase which sharply alter both body appearance and behavior. The exact manners in which changes in cell or body actions occur are not always clear. However, the main mechanisms or agents bringing about those changes are known. Coordination and regulation of metabolic rates and body processes take place by means of "messengers". In an animal, a nervous system helps to detect surrounding conditions or stimuli and then to carry out appropriate responses by sending impulses along nerve networks. Coordination of body systems within an animal also relies on the uses of chemicals produced by certain cells and released to travel to other locations. This particular lesson will concentrate on coordination and regulation by hormones. Biology 30 271 Lesson 9 After completing this lesson you should be able to: Biology 30 • explain the importance of regulating metabolic rates and coordinating body systems. • name the two major mechanisms involved in controlling body processes. • describe the general nature of hormones and explain how they may affect cell and body actions. • indicate some of the major differences between controls in animal bodies. • distinguish between duct and ductless glands. • explain the role of neurosecretory cells. • describe the locations and functions of various endocrine glands in a vertebrate body system. • explain some of the ways in which hormonal actions are coordinated. 272 Lesson 9 Hormones Hormones are organic chemicals or chemical "messengers" which can affect certain cell processes. They are produced within cells. In multicellular organisms, they are produced either in specialized cells or in particular areas of the organisms. Molecular structures of these chemicals vary considerably, but for the most part they are modifications of the same amino acids and lipids used in forming other organic matter (proteins and fats). In a multicellular plant or animal, a hormone is commonly released from one area and moves by diffusion or through an existing transport system to affect another area. Not all cells or tissues are affected by a hormone, even though all are exposed to it. Instead, there are "target" areas where only certain cells react in some way. Target cells have receptors or molecules which combine with specific hormones. These receptor or attaching molecules can be located on the surface membranes of cells or they can be inside cells, either in the cytoplasm or right in nuclei. Many researchers think that hormones, as chemical "messengers", simply start a certain sequence of already planned events or responses in target cells. A comparison sometimes used is that a hormone merely pushes a "starter button" for some reaction. Pushing a certain button in a poultry feeding operation may cause a hopper to dump a measured amount of feed onto a conveyor belt. The button could also have started the conveyor belt in motion past a series of bird cages. As the conveyor moves along, it deposits measured amounts of feed in front of or into each cage. After a certain programmed time, the system may shut itself off. How hormones push the "starter buttons" or begin events may vary. A particular hormone may attach to the receptor molecule in the membrane of a certain (target) cell. The receptor-hormone combination could activate a particular enzyme, causing a second messenger to be produced in the cytoplasm. This second compound can then initiate the production of other proteins or it can enter the nucleus. Inside a nucleus this messenger or even a hormone itself could attach to other receptors in specific regions of DNA or chromatin. The messenger-receptor or hormone-receptor combination can then either activate or shut down the actions of some genes and the cell processes which those genes control. Biology 30 273 Lesson 9 A hormone may also affect a cell membrane's permeability to certain substances. By doing this, enzymes may enter to start various metabolic actions. The sizes or complexities of the hormone molecules could determine which actions take place. Larger, more complex polypeptide (protein-based) hormones are more likely to remain on the outside of cell membranes. Steroid or lipid hormones can pass fairly easily through membranes and their effects are more likely to be initiated right in a cell's cytoplasm or nucleus. Regardless of the way in which reactions are started or stopped, only extremely small amounts of hormones need to be present. Many are effective in concentrations of just a few parts per million. Chemical Messengers in Animals Coordination of metabolic rates and body processes is probably more critical in animals than it is in plants. The ability to move about results in changes which often occur more rapidly or to a greater degree both internally and externally for animals. Animals have adapted by developing an additional "messenger" system in the form of nerves and nerve networks. However, chemical messengers or hormones still play major roles in body functions. In vertebrates, hormones are involved in some way in almost all body actions. Not only are hormones involved in what could be considered as moment-by-moment ongoing actions, but they are also responsible for the various developmental stages from embryo to old age. Some of the more obvious results of this are the developments of secondary sexual characteristics in organisms and the distinct reproductive cycles of species. Biology 30 274 Lesson 9 The Endocrine System Plant hormones are produced in various organs by cells which are the same as other cells in that tissue. That is, there are no cells in plants which are specifically adapted or designed for producing hormones. This is different in multicellular animals, as there are secretory cells specialized for hormone production alone. In addition, the more complex multicellular organisms have these cells in distinct groupings or glands which are located in specific areas of bodies. There are two common types of glands: endocrine and exocrine glands. Endocrine glands are ductless glands, that is they do not have any tubes or ducts leading out of them to other body areas or to transport systems. Endocrine glands secrete hormones directly into the bloodstream by diffusion. Most often, these hormones enter circulatory systems and are eventually transported to all body areas. Glands have blood vessels running through them so that hormones do not find it difficult to enter the circulatory system. All the ductless glands, whose hormones remain inside a body, make up an endocrine system. In contrast, exocrine glands utilize ducts or tubes to transport their secrections to specific areas of the body, which could include outside surfaces. Examples are sweat glands, salivary glands and tear glands. The secrete such substances as sweat, milk, digestive enzymes and other materials. The Nerve-Endocrine Relationship Coordination of cellular and body functions is accomplished by the nervous and endocrine systems working very closely together. Although there are direct attachments of nerves to glands in only two instances, the two systems affect one another indirectly in many ways. For the most part, nerves receive external and internal stimuli and transmit them to various parts of the body, with the most important being the brain. Parts of the brain, the hypothalamus in particular, can "interpret" the various stimuli and send directions to response networks like the endocrine glands. The glands of the endocrine system then regulate many of the internal responses which the body makes to these stimuli. The light-dark interval, or photoperiodism, affects hormonal and behavioral changes in many animals, just as it does in plants. Migratory and reproductive behaviors, growing more fur or shedding it and changing fur colors, are some events resulting from nerve-endocrine interactions. Biology 30 275 Lesson 9 Neurosecretory Cells An important "indirect" link between the nervous and endocrine systems is the presence of neurosecretory cells. These are nerve cells which produce secretions at their ends. The nerve ends are long fibres which are close to, or are even embedded in, capillary networks. The secretions or hormones produced by the nerves can diffuse into the circulatory system and be carried throughout the body. These hormones can either affect other glands or can affect certain cells directly. Insects, annelids (worms), mollusks and other invertebrates regulate internal body conditions almost entirely with neurosecretory cells. Well-defined glands are not apparent in these groups. Most of the neurosecretory cells are concentrated in the brain areas of these organisms. Light stimulations received by the eyes and transferred to the neurosecretory cells in the brains of octopuses and squids, cause cells to release hormones into the circulatory systems. The hormones cause various pigment bodies in skin cells to expand or contract, changing the colors of the organisms. Neurosecretory cells and hormones are responsible for other actions such as periodic molting of exoskeletons and the timing of the different parts of reproductive and life cycles. Biology 30 276 Lesson 9 Neurosecretory cells are also present in vertebrates. In this group, nerves, neurosecretory cells and glands of the endocrine system are closely connected. Stimulations and responses can take place both ways between nerves and hormones. An important linking area in vertebrates occurs in the hypothalamus. There is a concentration of neurosecretory cells in this area of the brain. The cells release a number of hormones which affect an adjacent pituitary gland. This gland, in turn, affects almost all the other endocrine glands. Biology 30 277 Lesson 9 The Vertebrate Endocrine System The types of endocrine glands present, the kinds of hormones they produce and the effects these have on bodies, are very much the same in all vertebrates. Therefore, the human example will be used as an illustration of the system. INSERT DIAGRAM OF ENDOCRINE SYSTEM HERE Hypothalamus The hypothalamus is not an endocrine gland itself, but is a portion of the brain just above the pituitary gland. There are actual nerve connections between the hypothalamus and part of the pituitary. Neurosecretory cells provide a chemical link between the hypothalamus and the other portion of the pituitary. The hypothalamus is sensitive to various body conditions, including chemical concentrations, and can transmit neural or chemical signals to the pituitary and other glands to control these. Biology 30 278 Lesson 9 The Pituitary Gland About the size of a pea, the structure of this gland has three parts with: an anterior lobe, an intermediate part and a posterior lobe. In adults, the intermediate portion has almost disappeared. The lobes or parts indicate different origins during their formation. The posterior lobe developed as an apparent extension of a portion of the hypothalamus. This is probably why there are neural connections between the two. The anterior lobe developed from a different kind of embryonic tissue and is considered as a true endocrine gland (while the posterior lobe is not generally considered as such). Approximately eight hormones have been recognized as being produced by the pituitary gland and are as follows: Hormones produced in Pituitary Released by Biology 30 Human Growth Hormone (HGH) anterior pituitary Gonadotrophic hormones such as FSH and LH anterior pituitary Prolactin anterior pituitary Thyroid-stimulating hormone (TSH) anterior pituitary Adrenocorticotrophic hormone, (ACTH) anterior pituitary Melanocyte-stimulating hormone (MSH) anterior pituitary Oxytocin posterior pituitary Antidiuretic hormone, (ADH or vasopressin) posterior pituitary 279 Lesson 9 With the exception of oxytocin and ADH which are released by the posterior pituitary, the hormones are secreted by the anterior pituitary. The release of these hormones into the blood is controlled by the hypothalamus. Neurosecretory cells in the hypothalamus add releasing chemicals to blood vessels which pass through the hypothalamus and the anterior pituitary. These neurosecretions cause the anterior lobe to release various amounts of its hormones into the circulatory system. Most of the pituitary hormones influence other glands, causing them to produce and release secretions. For this reason, the pituitary is often called the "master gland", even though the hypothalamus usually initiates responses. When hormones appear to be involved in "messenger" roles to other glands, they are referred to as trophic or tropic hormones. That term will be at the endings of the names. For instance, gonadotrophic hormone is produced by the pituitary gland and it affects the ovaries (or gonads). A closer look at the hormones produced in the Pituitary 1. Human Growth hormone indirectly controls skeletal and muscular development. An excess of this hormone can lead to a pituitary giant (sometimes called giantism or gigantism), with individuals ranging in height from two and one-half to nearly 3 meters. A deficiency of the hormone results in dwarfism, with individuals being about one meter tall. Excess HGH in adults produces acromegaly, symptoms of which include excessive thickening of bone tissue, leading to abnormal growth of head, hands and feet. 2. Gonadotrophic hormones act upon the sex organs (gonads) of females and males. A number of sex hormones have been recognized. FSH (Follicle-stimulating hormone) stimulates the formation of sperm producing tubules in testes. In females, FSH promotes follicle development in ovaries (for egg development) and also estrogen secretions. Estrogen is responsible for secondary female sex characteristics and also affects female reproductive cycles. Luteinizing hormone (LH) induces ovulation, or release of eggs, from the ovary and acts with FSH in causing estrogen secretions. In males, LH acts upon cells in the testes causing them to release other sex hormones. In humans, these sex hormones lead to the onset of puberty and the development of secondary sexual characteristics – such as growth of extra body hair and a deepening voice. In other male animals, the sex hormones lead to seasonal or annual changes in sexual behavior and possibly even appearance. 3. Prolactin in mammals is produced during and after pregnancy. It stimulates the development of mammary glands and milk production. In non-mammals, it seems to bring about some reproductive behaviors in females (such as broodiness in hens). Biology 30 280 Lesson 9 4. TSH (Thyroid-stimulating hormone) activates the thyroid gland. The thyroid gland will be examined in more detail later. 5. ACTH (Adrenocorticotrophic hormone) activates the cortex of the adrenal gland. 6. MSH (melanocyte-stimulating hormone) affects cells containing a black pigment called melanin. In humans, it seems to play minor roles in the development of freckles or the darkening of some body areas under conditions such as pregnancy. MSH is much more important in the reptilian and amphibian groups. The hormones can cause melanin to be concentrated in small areas of cells or spread throughout. These, respectively, cause lighter and darker skin colors, enabling organisms to better blend in with their surroundings. This is why fish or frogs change colors. The posterior pituitary functions as a storage area for the neurosecretions from the hypothalamus. 7. Oxytocin hormone stimulates smooth muscle contraction. In female mammals, this hormone causes contraction of the uterine walls during birth and the contraction of muscle fibres in the mammary glands during nursing. 8. ADH or Antidiuretic hormone (sometimes called vasopressin), causes contraction of arterial walls. This increases blood pressure. ADH, as the name implies, also acts as an antidiuretic. It increases the permeability of the kidney tubules, causing the kidneys to reabsorb much of the water originally removed from the blood. Occasionally, the pituitary may not form and release very much of this hormone. If this happens, there would not be very much reabsorption of water by the kidney. A person would be excreting or urinating large amounts of fluids. This action would lead to body dehydration and excessive thirst. Such a condition is called Diabetes insipidus. This should not be confused with the more commonly known Diabetes mellitus, which will be described shortly and relates to blood glucose levels. Even if a pituitary is functioning properly under ordinary circumstances, consumption of alcohol will begin suppressing the production of ADH. This is what increases the frequency of urination when a person drinks alcohol, and is not merely due to the intake of fluids. The resulting dehydration can be evident in a person's thirst and drinking of larger amounts of water some time after an (alcohol) drinking session. Biology 30 281 Lesson 9 The Thyroid Gland The thyroid gland is a two-lobed structure which encircles the trachea near the larynx. Thyroxine is an iodine-containing hormone which controls the rate of body metabolism. Often, this hormone may be undersecreted or oversecreted, leading to medical complications. Hypothyroidism: undersecretions of thyroxine. This may be caused by iodine shortages in the environment and diet, leading to reduced body developments in young animals. Amphibians may never develop beyond the larval or tadpole stage. Some varieties of salamanders even become sexually active and reproduce in these larval or axolotl forms. Undersecretion or hypothyroidism in humans also stops physical development. Cretinism, where an individual remains very short, is the resulting abnormality or disease. Individuals are not only small physically, but are poorly developed mentally (a difference from pituitary dwarfism). Shortages of the hormone after adulthood has been reached also result in abnormalities. Conditions such as being overweight, being mentally and physically sluggish and showing puffiness or coarsening of features could develop. Hyperthyroidism: overproduction of thyroxine. Excessive amounts of the hormone may lead to a doubling of the metabolic rate. Individuals may be hyperactive or irritable, unable to sleep and show such body symptoms as trembling, sweating, weight losses and protruding eyes. Often, a malfunction of the pituitary gland and its TSH is the problem. Goiter, or swelling of the thyroid gland, can be associated with either hypothyroidism or hyperthyroidism. Hypothyroid goiter can occur when there is not enough thyroxine to turn off TSH production. Hyperthyroid goiter can occur when the thyroxine levels are high, the feedback mechanisms fail to tell the thyroid cells to stop thyroxine production. Diagnosing thyroid problems is frequently carried out by measuring oxygen consumption. Since metabolic rates, cellular respiration and respiration are all related, excessively high or low metabolic rates would be reflected in high or low oxygen use. Biology 30 282 Lesson 9 The Parathyroids Embedded within the thyroid gland itself are four parathyroids. Parathyroid hormone tries to maintain a particular concentration of calcium ions in the blood. The hormone causes cells to release calcium into surrounding blood vessels. Calcium ions are used in bone formation and are also particularly important in muscle contractions and nerve impulses. Low calcium levels can lead to muscle twitchings, convulsions and death. A reduced amount of calcium in the diet causes parathyroid hormone to remove more of the mineral from the bones. This can cause the bones to be weak, deformed and prone to breaking easily. The Thymus Gland A two-lobed gland, which is prominent in the early years but becomes reduced in size in adulthood, is the thymus gland. This gland is located high in the chest area, just over the heart. Testings and observations indicate that this gland is important in the early development years when the body is first setting up an immune system. Hormones from the thymus may stimulate the formation of antibody-producing lymphocytes in lymph glands. The Pancreas and the Islets of Langerhans The pancreatic organ, next to the stomach, was mentioned for its part as a duct gland in the process of digestion. Pancreatic juice makes its way from the gland and into the duodenum. There are isolated clusters of cells throughout the pancreas, called islets of Langerhans, which function as ductless glands. Two kinds of cells make up the islets of Langerhans: Biology 30 One type produces the hormone glucagon. Glucagon stimulates a particular enzyme to convert glycogen, carbohydrates and fats into glucose, which enters the blood stream. 283 Lesson 9 The second kind of cell releases the hormone insulin. This hormone alters the permeability of membranes to glucose, allowing extra amounts of it to be absorbed by cells and to be metabolized into glycogen for storage or for incorporation into other organic compounds. In most diabetics, there is a shortage of insulin (although an excess of glucagon is also possible) and the body begins excreting abnormal amounts of blood sugar through the urine. The high sugar concentration of blood through the kidneys also reduces the abilities of these organs to reabsorb water from the nephrons back into the body system. Therefore, an individual is losing high amounts of both glucose and water. At the same time, glycogen and organic compounds in body tissues are being broken down into glucose which enters the blood. The breaking down or catabolism of carbohydrates, fats and proteins produces high levels of toxic matter, which can be the actual cause of diabetic coma and death. Diabetes mellitus, the condition commonly resulting from a shortage of insulin, is treated with injections of insulin from animal extracts. Taking insulin too soon after strenuous physical activity or after a long time without nourishment or simply in too large a quantity, can create another problem called insulin reaction or shock. In this situation, low blood-sugar levels are decreased even further, leading to collapse, loss of consciousness and possible coma. Diabetics or people associated with diabetics should be familiar with the differences between diabetic coma and insulin shock. Symptoms leading up to diabetic coma are excessive thirst, nausea, vomiting and breathing difficulty. Symptoms prior to insulin shock are hunger, sweating, irritability and fatigue. The Adrenal Glands An adrenal gland is located on the top of each kidney. A darker central area or adrenal medulla is surrounded by a lighter outer part called the adrenal cortex. These two parts have different origins and functions. Biology 30 284 Lesson 9 1. The adrenal cortex produces many secretions which are steroid in nature. The hormone, ACTH (adrenocorticotrophic hormone), that is produced in the anterior pituitary, is sent out to the adrenal cortex to regulate these secretions. Steroids are in the same group as lipids and other fat-related compounds. The chemicals which make up the steroids are generally called corticoids and these can be divided into three groups according to function. Glucocorticoids promote the conversion of fats and amino acids or proteins into glucose and glycogen. Cortisol is the main glucocorticoid steroid hormone secreted by the adrenal cortex. The steroids thus provide bodies with extra energy. Under natural conditions, physical or emotional stresses can cause rapid drops in blood glucose levels and blood pressure. This is when the adrenal cortex is signalled by the ACTH of the pituitary gland to release glucocorticoids into the blood and bring glucose levels up. Steroids, such as cortisone, are sometimes used to reduce swellings or inflammation by their actions on membranes (which are based on fat or lipid structures.) Mineralocorticoids encourage reabsorption of sodium and chlorine ions from the kidneys into the blood. This is done by Aldosterone, the main mineralocorticoid steroid hormone secreted by the adrenal cortex. These ions help to keep blood volume and pressure up. A deficiency of these hormones cause excessive excretions of the salts in the urine. At the same time, the blood draws phosphate and potassium ions from body tissues. These ions make the blood acidic. Undersecretions of the hormones can cause Addison's disease, which is marked by a low blood pressure, weakened muscles and a listless condition. Applying cortical steroids or ACTH can help to maintain a normal life. Lack of treatment generally leads to death in one to two years. There are a number of cortical sex hormones (sex steroids) produced which may add their effects to those of the sex hormones produced by ovaries or testes. An overactive adrenal cortex can lead to early sexual development in young animals and children. In human females, overactivity can result in the appearance of secondary sexual characteristics normally associated with males. These may include extra facial hair and a deeper voice. 2. The central adrenal medulla may have originated from nerve cells and is under the control of the nervous system (by neurosecretory cells). This is the "emergency gland" which produces hormones in response to "fight or flight" situations. In conditions of anger, fear, pain or other kinds of stress, the medulla releases two hormones: adrenaline (epinephrine) and noradrenaline (norepinephrine). Both of these hormones induce changes or conditions designed to prepare a body for some type of action. The liver converts glycogen into glucose and releases it into the blood, as an available source of energy. Breathing rates increase, with pulmonary bronchi increasing in diameter to allow the passage of more air. Blood vessels to "non-emergency" areas or organs (skin and digestive system) constrict, sending blood to the heart, liver and muscles where it is needed more. Vessels to these particular areas expand slightly and the heart rate goes up. Biology 30 285 Lesson 9 The Gonads Female or male gonads are normally associated with the production of either eggs or sperm. While this is so, ovaries and testes also have cells which produce and release hormones. The hormones from these ductless gland cells may contribute to the formation of eggs or sperm, but they also give rise to secondary sexual characteristics. The Testes When testes are stimulated by the LH or lutenizing hormone from the pituitary gland, they produce and release a number of hormones called androgens. One of the more important of these is a steroid called testosterone. This hormone leads to a further development of the male gonads and to a development of the "male" features common to a species. In many species, the hormone also initiates a reproductive drive in male animals, which could include aggressive behaviors. Livestock producers commonly emasculate or castrate many male animals at a young age. This changes their growth patterns so that musculature (meat) is different and the animals have subdued temperaments, in addition to being sterile. Some synthetic androgens or steroids are sometimes utilized by human athletes to promote the development of extra musculature and strength. The Ovaries Estrogens and progesterones are two types of hormones produced by the ovaries when they are influenced by the FSH (follicle-stimulating hormone) and LH (lutenizing hormone) from the pituitary gland. Estrogens lead to the development of secondary sexual characteristics of female mammals. These hormones also take part in regular reproductive cycles of females during their fertile periods. Estrogens are released by the follicle cells in which eggs develop. The hormones cause the uterus to begin adding more glandular cells and blood vessels, in preparation for the possibility of a fertilized egg embedding in its wall. Once the follicle ruptures and the egg is released (ovulation), the follicle is transformed into a group of glandular cells called the corpus luteum. Biology 30 286 Lesson 9 The corpus luteum now releases the hormone progesterone which has two main actions. It completes the preparation of the uterus. It also prevents the development of any other follicles (and eggs). If fertilization does not occur, progesterone and estrogen production begins to decline and the corpus luteum begins to break down, as does the lining of the uterus. The inner uterine lining is then discharged during a four or five day period of menstruation. Even as this occurs, the level of progesterone will have fallen so that another follicle will have begun developing to repeat the cycle. In the fertile human female this cycle occurs about once every 28 days, unless there is a pregnancy or if there is some irregularity. These cycles continue until an individual is about 42 to 52 years of age. During this time period, follicles are affected less and less by FSH and LH and they release less estrogen. Ovulations and menstruations become irregular and finally stop at a time known as menopause. Other Glands and Hormones The endocrine glands described so far are some of the major or more noticeable ones (especially during a malfunction). However, there are other gland cells which are part of other tissues or organs and are scattered throughout various parts of the body. The placenta of a pregnant mammal has cells which also produce the hormones estrogen and progesterone, which affect the uterine wall. Gland cells in the stomach and small intestine produce hormones involved with digestion. A small pineal gland in the brain may produce hormones in animals which regulate reproductive cycles according to photoperiods or light-dark intervals. A group of lipid-like hormones called prostaglandins, initially isolated from semen, are produced in a number of body areas. Original studies showed these prostaglandins to be responsible for smooth muscle contractions. Further research is revealing these chemicals to be responsible for many more actions, including regulations of blood pressure, pain levels and immune responses. Certain cells in the heart muscle have been found to release a hormone affecting kidneys and their elimination of sodium (salt) and water. Some kidney cells also release a hormone which affects red blood cell formation by bone marrow. Expectations are that continuing investigations will reveal more hormone-producing cells in tissues and organs previously regarded as nonendocrine. A summary of glands, their hormones and actions are presented in the following table. Biology 30 287 Lesson 9 Endocrine Gland Pituitary Gland: Posterior lobe Pituitary Gland: Anterior lobe Hormone Major Functions Oxytocin Stimulates smooth muscle contraction. ADH - Antidiuretic hormone Promotes reabsorption of water in the kidneys. ACTH - Adrenocorticotropic hormone TSH - Thyrotrophic hormone (also called Thyroid Stimulating Hormone) GH - Growth hormone LH - Lutenizing hormone Stimulates adrenal cortex Stimulates thyroid and production of thyroxin. Stimulates growth - especially of skeleton. Stimulates follicle in ovary and stimulates the corpus luteum. Stimulates testes in males. Stimulates milk production in mammaries. Regulates pigment concentrations in skin cells. Prolactin MSH - Melanophore stimulating hormone Thyroid Thyroxin Increases metabolic rate. Suppresses TSH. Parathyroid Parathyroid hormone Increases calcium levels in the blood. Thymus Thymus hormone May be responsible for development of lymphocytes and therefore, antibody production. Pancreas: Islets of Langerhans Insulin Enables body cells to convert glucose to (storable) glycogen. Causes body cells to convert glycogen to glucose. Glucagon Adrenal cortex Corticoid (steroid) hormones Regulate metabolism of carbohydrates, water and minerals. Affect connective tissue. Stimulate appearance of secondary sex characteristics. Adrenal medulla Adrenaline, Noradrenaline Stimulate actions designed to prepare body for "fight or flight". Testes Androgens (testosterone) Stimulate metabolism (respiration) and blood circulation. Promote development of male secondary sex characteristics. Stimulate reproductive or sex drive. Inhibits FSH. Ovaries: Follicle Estrogen Corpus luteum Progesterone Stimulate development of uterine lining. Promote development of female secondary sex characteristics. Inhibits FSH. Encourages ovulation. Promotes and maintains uterine lining before and after pregnancy. Inhibits LH. Stomach Gastrin Stimulates secretion of gastric juices. Duodenum Secretin Stimulates secretion of pancreatic and bile juices. Biology 30 288 Lesson 9 Balancing Hormonal Actions The concept of a steady state or homeostasis has been continually emphasized in the descriptions of cell and body processes. Actions involving the production and interplay of hormones is no different. Hormones are the chemical messengers for controlling body actions and a fine balance often exists between too little stimulation or too much. Going too far in either direction can result in poor functioning, disease and even death. A number of different conditions are responsible for controlling gland actions: 1. Stimuli received. All glands regulate their production of hormones by the stimuli which they receive. Some glands respond to stimuli which have nothing to do with other glands. These may come from: external stimuli. Many animals have photoperiodic responses or behaviors, just as plants do. (Some scientists feel that photoperiods are among the most important external stimuli for most animals.) As an example, in following through on the reproductive behaviors of organisms, the following sequence likely occurs in many species. Biology 30 289 Lesson 9 Light-dark intervals of particular amounts, which occur over a certain period of time, will stimulate some nerve centers in organisms' brains. These nerve stimulations eventually reach the hypothalamus portion of the brains. A hypothalamus has cells which produce chemicals that affect one of the more central glands in the body – the pituitary. In this way, an external stimulus (which is light in this instance) triggers a response in the pituitary gland. internal body conditions Some glands also respond to internal stimuli. Some of these internal stimuli are "triggering" or trophic hormones from other glands. The illustration on light-dark effects on reproductive behavior shows that after the pituitary is stimulated, it sends out (trophic) hormones which affect the testes or ovaries of individuals. These gonads are prompted to produce their own hormones which then bring about various changes in reproductive characteristics. In whitetail deer, androgens in bucks increase the sizes of testes and cause the production of sperm. (Most bucks are actually infertile for much of a year.) These male hormones cause a swelling of the neck muscles and of scent glands on the legs. Behavior is sharply modified as bucks enter a "rutting" or reproductive behavior. This includes an expansion of territorities, active searching for does and possible aggressive actions towards other animals, especially rival males. Internal stimuli could also include the levels or concentrations of particular substances in the blood or tissues. The amount of glucose in the blood affects the islets of Langerhans and their production of the hormones insulin and glucagon. Higher amounts of glucose will result in a greater production of insulin, which causes some cells to take up glucose and convert it to glycogen (in the liver and muscles) and fat (in body cells). Low glucose levels in the blood cause a drop in insulin production and a release of glucagon. Glucagon reverses the actions of insulin, causing cells to form glucose and release it into blood vessels. Biology 30 290 Lesson 9 Glucose levels in blood demonstrate yet another way in which regulation of hormone production and body activities occurs. Some hormones exist as antagonistic pairs. The levels of some substances in the body could be very critical. The body is very sensitive to the amounts of glucose in the blood and severe damage to cells and tissues can occur if there are excesses or shortages. If insulin alone controlled glucose levels, increasing or decreasing the production of that hormone probably would not bring about fast enough adjustments. The other hormone produced by the pancreas has an opposing action, or negative feedback, to insulin. When glucose levels in the blood become low due to the actions of insulin, glucagon tries to negate or to correct the imbalance. Its actions cause liver and muscle cells to convert glycogen and, if necessary, amino acids and fats into glucose. The antagonistic actions between such pairs of hormones are able to bring about faster adjustments. Imbalances between such pairs of hormones or in the glands themselves could lead to malfunctions, such as Diabetes mellitus which was described earlier. Blood – Glucose Cycle Insulin and glucagons function together to maintain a fairly stable level of blood glucose Again, the type of action in which a hormone causes the production of another hormone and then this second hormone suppresses the first, illustrates a feedback action. To be more precise, it is negative feedback. Feedback actions occur on a continuous basis. The hypothalamus part of the brain is sensitive to many of these feedbacks. The hypothalamus then passes on neurosecretions or neural messages to the pituitary gland which changes its own actions. A more careful examination of the human female reproductive cycle and its illustration of negative feedback will be looked at more closely in Lesson 11. Biology 30 291 Lesson 9 Biofeedback The "feedback" described with respect to hormones should not be confused with another term or action called biofeedback. Biofeedback refers to techniques or actions where some individuals try to consciously control internal body actions normally under the influence of the autonomic nervous system. Individuals try to (develop techniques to) control various body conditions by using monitoring devices. By observing and concentrating on such things as his or her own blood pressure, heart rate, electrical impulses (on electroencephalographs) or other conditions, a person tries to consciously regulate those very conditions. Any success in achieving any degree of extra control could possibly be used in treating high blood pressure, migraine headaches, epileptic seizures or other undesirable conditions. The difficulties in trying to explain how or why conscious controls could work, or how to measure if they really do work, make biofeedback an uncertain area of study. Pheromones Pheromones are a group of chemicals that are designed to affect other members of the same species. These chemicals are secreted by duct glands and are released to the outside. The chemicals which had been previously described were hormones which are distributed internally and affect internal actions of an individual. Pheromones are especially noticeable in social insect groups. A queen bee releases a pheromone from glands in her body into the atmosphere around her. This chemical affects the female worker bees and prevents any of them from developing an egg-laying ability. Ants can leave pheromone "trails" on the ground behind them and use these to retrace their way or to serve as "markers" for others to follow. Ants also release another type of pheromone from glands in their heads when they are alarmed. In smaller concentrations, the chemical attracts others toward it. In larger concentrations, the chemical causes concern and alarm in others and induces them to scurry about looking for the source of disturbance. If the disturbance has disappeared, the chemical eventually loses its concentration in the air and the ants resume normal activities. Biology 30 292 Lesson 9 Pheromones are also released by individuals during reproduction, enabling males and females to locate each other over long distances. (Scientists have duplicated some of these to use as lures in attracting some organisms to traps.) Just as hormones can be looked at as chemicals which co-ordinate and regulate individual internal actions, pheromones can be regarded as chemicals which regulate activities among a group of organisms. For some species – especially social groups, close communications or regulations among individual members by means of pheromones are important in maintaining group numbers and social structures. Pheromones may be just as important for group survival as hormones are for individual survival. Summary To sustain living conditions, organisms must be able to respond to external and internal stimuli. A response, however, does not necessarily ensure survival. It must be the right response, in such things as timing and possibly direction and degree or level of reaction. As the complexities of organisms increase, there are increasing numbers of body processes going on at the same time. While some may appear to function independently, many complex interrelationships are actually present. This makes responses much more complex than what they may seem to be. An action of one body part or in one area may mean a whole series of actions in other parts or systems. Simply being startled by a loud noise could result in responses or changes in heart rate, breathing rate, glucose levels in the blood, sizes of blood vessels and blood pressure. The ability to make proper responses, which occur at the right times and in harmony with each other, has to be under some sort of control. Coordination and regulation of responses in animal bodies is carried out, in part, by chemical messengers. In an animal body, these hormones are produced in secretory cells usually organized into distinct groupings to make up endocrine glands. Ductless, these glands release their hormones into the blood which then transports them around the body. While hormones may have some effect on all body cells, specific ones generally have a "target" area or a group of cells on which they have more influence. Hormones have some control in almost all body actions or responses. A question which often arises has to do with what "turns the glands on or off" or what determines their level of output. External stimuli can do this through their stimulation of nerve cells and neurosecretory cells in the hypothalamus or other areas. The hypothalamus can also respond to internal stimuli, particularly to the levels of substances in the blood or tissues. Once certain glands are stimulated to release hormones, those hormones may themselves serve as triggering agents for other glands. Some hormones can exert negative feedback by suppressing the production of the agent which caused their formation in the first place. All these influences on hormone production mean that there is usually a fine line or balance between too little or too much. Extremes in either direction can lead to consequences ranging from "mild" body disturbances to possible death. Biology 30 293 Lesson 9