slide 2:Homeostasis is the tendency to oppose change to maintain a stable internal environment. (1)Homeostasis involves negative feedback loops which counteract the changes. This is known as set points. (1)On the other hand, positive feedback loops expand their initiating stimuli. This moves the system away from its initial state. (1)slide 3:Negative feedback loops are the most common way of maintaining homeostasis. They work by opposing the stimulus which triggers them. An example of this is if the body temperature is too high, the negative feedback loop will bring it back down towards the set point. (1)It works by the sensors detecting the high temperature. These sensors are usually the primarily nerve cells which end in the skin and brain, which are then sent to a temperature-regulatory control centre in the brain. The control centre processes the information and activates the effector. In this case, it is the sweat glands whose job is to oppose the stimulus by bringing the temperature down. (1)slide 5:Positive feedback loops usually occur in biological systems by amplifying the starting signal. They usually occur in processes that need to be pushed to completion rather than the existing conditions needing to be maintained. (1)During childbirth, a positive feedback loop occurs. The baby’s head presses on the cervix where the baby must emerge and activates neurons in the brain. The neuron sends a signal which releases a hormone called oxytocin from the pituitary gland. Oxytocin increases uterine contractions and therefore, pressure on the cervix, which then causes more oxytocin to be released and produces stronger contractions. This continues till the baby is born. (1)slide 7:The exocrine system is a system of glands that protect or lubricate the body by producing and secreting substances. An example is sweat and is located in the dermis of the skin. Sweat is secreted by the exocrine glands. (2)The glands travel through ducts depositing their substances onto epithelial surfaces. The epithelial surfaces which substances are deposited to are the ones which line the cavities and surfaces of blood vessels and organs throughout the body. (2)slide 8:Exocrine gland secretions lead to the exterior of the body. Therefore, the inner surface of the glands and the ducts which drain them are similar to the skin. Although the exocrine system is considered a system, the glands work independently. They each have their own jobs and respond to the body’s needs at any particular time. (2) slide 9:Infections, ulcers, cancer, tumours, obstruction of any kind, genetic conditions and cysts can all affect the exocrine system. As the exocrine and endocrine system are closely linked, some disorders in the endocrine system can also affect the exocrine system. (2)One disorder of the exocrine system is thyroidism. Hyperthyroidism is a disorder in which an overactive thyroid produces too much thyroxine. On the other hand, hypothyroidism is a disorder in which an underactive thyroid produces too little thyroxine. (2)slide 10:The endocrine system is a collection of glands that produce hormones. Growth and development, tissue and sexual function, sleep and mood are all bodily functions which are regulated by these hormones. (3)The endocrine system works by a gland removing the materials which it needs from the blood. These materials are them processed and then it secretes the finished product for use somewhere else in the body. Each type of hormone is intended for specific organs and tissues. (3)slide 11:The hypothalamus is a part of the brain which is responsible for the production of hormones. The hypothalamus’ main function is homeostasis. The hormones released in the hypothalamus include thyrotropin, gonadotropin and dopamine hormones. These hormones are released into the blood through the capillaries and travel to the pituitary gland. (4)The hypothalamus uses a set-point to regulate the systems. It receives inputs from the body and then makes the appropriate changes. (4)slide 12:A pituitary gland is a pea-sized structure located at the base of the brain. (3) The pituitary gland is made up of 2 distinct areas. The anterior pituitary gland, also known as adenohypophysis, is a hormone-producing gland made of glandular epithelia. On the other hand, the posterior pituitary gland, also known as neurohypophysis, is an addition of nervous tissues from the hypothalamus. It stores and releases 2 hormones produced in the hypothalamus. (5)The superior hypophyseal artery provides blood flow to capillaries around the hypothalamus and the infundibulum. Hormones produced by the hypothalamus are secreted into these capillaries and then carried by the hypophyseal vein to the capillaries around the anterior pituitary. These hormones are used to control the number of hormones released by the anterior pituitary. The blood and hormones are returned to the heart and the rest of the body through the anterior hypophyseal veins. (5)slide 13:A thyroid gland is a butterfly-shaped gland that sits low on the front of the neck. (3) It releases hormones that control the way the body uses energy (metabolism). The thyroid is part of the endocrine system which is made up of glands that produce, store, and release hormones into the bloodstream so that hormones can reach the body’s cells. Triiodothyronine (T3) and Thyroxine (T4) is produced by the thyroid gland by using the iodine from the foods eaten. (6)The hypothalamus produces TSH releasing hormone (TRH) which signals the pituitary to tell the thyroid gland to produce more or less T3 and T4. This is done by either increasing or decreasing the release of a hormone called thyroid stimulating hormone (TSH) When T3 and T4 are low in the blood, the pituitary gland releases more TSH to tell the thyroid gland to produce f=more thyroid hormones. On the other hand, if T3 and T4 are high, the pituitary gland releases less TSG to the thyroid gland to slow production of the hormones. (6)slide 15:The parathyroid glands are four tiny glands located in the neck which control the body’s calcium levels. (3) The parathyroid gland produces a hormone called parathyroid hormone (PTH). This hormone raises the blood calcium levels by breaking down the bone and causing the calcium to release. This is because the bone is where most of the body’s calcium is stored. It also raises the calcium levels by increasing the body’s ability to absorb calcium from food and also increasing the kidney’s ability to hold on to calcium that would otherwise be lost in the urine. (7)When the blood calcium level is too low, PTH is released to bring the calcium levels back to normal. When the calcium level is normal or gets a little too high, normal parathyroids will stop releasing PTH. Calcium balance is important for a normal functioning of the heart, nervous system, kidneys and bones. (7)slide 16:Problems arise in the endocrine system when the hormone levels go too high or low, or the body doesn’t respond to the hormones appropriately. Diabetes is a common endocrine disease. This is a condition in which the body does not properly process glucose (a simple sugar). (3)Endocrine disorders are typically grouped into 2 categories. One category is when a gland produces too much or little of an endocrine hormone resulting in a hormone imbalance. Another category is due to the development of lesions (tumours etc) in the endocrine system. This may or may not affect hormone levels. (8)slide 17:The pancreas is about 15 cm long and sits across the back of the abdomen behind the stomach (3) Functioning as an exocrine gland, the pancreas secretes enzymes to break down the proteins, lipids, carbohydrates and nucleic acids in food. Also, to function as an endocrine gland, the pancreas secretes the hormones insulin and glucagon to control blood sugar levels. (9)The liver acts as an exocrine gland, secreting bile into the intestine. But it is also an endocrine gland and filters the blood. (10) The liver produces bile from the conversion of substrates from the digestive tract, pancreas, and spleen. This is its exocrine function. Its endocrine function includes the release of substances produced by the liver cells into the blood. (11)slide 18:Osmoregulation is physiological processes that organisms use to maintain water balance. Their job is to compensate for water loss and avoid excess water gain and maintain osmotic concentration of the body fluids. (12)The brain and kidneys regulate the amount of water excreted by the body. When the blood volume is low, the concentration of solutes in the blood is high. The hypothalamus senses the low blood volume and it synthesized ADH (Antidiuretic hormone). The pituitary gland then releases ADH into the bloodstream which causes the kidneys to retain water by concentrating the urine and reducing urine volume. (13)Water retention boosts blood volume. Increased blood volume prevents the release of ADH, therefore, the kidneys retain less water, this dilutes the urine and increases urine output. As fluid leaves the body, blood volume decreases and osmolarity increases. This stimulates the release of ADH and the cycle begins anew. (13)slide 19:The renin-angiotensin-aldosterone system is responsible for keeping sodium and water balance in check and to maintain healthy blood volume and blood pressure. A bundle of capillary blood vessels found in the kidney (glomeruli) senses a drop in blood flow or sodium and therefore, secretes an enzyme called renin into the bloodstream. The renin moves toward the liver where it converts the inactive peptide angiotensinogen to angiotensin I. This then travels to the lungs where another enzyme converts it to angiotensin II. It makes its way to the adrenal glands at the top of the kidneys where it stimulates the production of aldosterone. This helps the kidneys conserve sodium and water, leading to increased fluid volume and sodium levels. (13)slide 20:When blood volume and blood pressure increases, the stretched atria releases Atrial Natriuretic Peptide (ANP) which is a cardiac hormone. It promotes natriuresis by shutting down the renin-angiotensin-aldosterone system and causing vasodilation. As the blood vessels expand, urine excretion of sodium and water increases, stabilising blood volume and blood pressure. (13)slide 21:Glucose is needed by cells for respiration, therefore, it is important for the concentration of glucose in the blood to be maintained at a constant level. Insulin is a hormone which is produced by the pancreas that regulates glucose levels in the blood. When the glucose level is too high, insulin is secreted into the blood by the pancreas. Then the liver converts the glucose into glycogen and the glucose levels go down. When the glucose levels are too low it has an opposite effect on the pancreas and liver. (14)slide 22:Islets of Langerhans are irregularly shaped patches of endocrine tissues located inside the pancreas. The islets consist of 4 distinct cell types. Three of which are alpha, beta, and delta cells which produce important hormones. The fourth component is c cells which have no known function. (15)Beta cells produce insulin which regulates the metabolism of carbohydrates, fats and proteins. It also promotes the uptake and metabolism of glucose and prevents the release the release of glucose by the liver. It causes muscle cells to take up amino acids and inhibits the breakdown and release of fats. The release of insulin from the beta cells can be triggered by a growth hormone called somatotropin or by glycogen. (15)The alpha cells produce an opposing hormone called glucagon which releases glucose from the liver and fatty acids from fat tissue. Glucose and free fatty acids release insulin and inhibit glucagon being released. The delta cells produce somatostatin which is an inhibitor of somatropin, insulin, and glucagon. (15)slide 24:Glycogenesis- when the blood glucose levels in the body rise, excess sugar needs to be swept out. It does this by glycogenesis which is the process in which glycogen is created. This is the name given to stored glucose. Glycogen is stored in the liver and in the muscles. (23)Glycogenolysis- before the blood glucose levels get too low, the body wants to add glucose to the body. It does this by glycogenolysis, which is the breakdown of glycogen into glucose. Now the glucose molecules are free, they are able to move into the bloodstream, maintaining normal blood glucose levels. (23)Gluconeogenesis- this is the reversal of glycolysis. Instead of using carbohydrates to produce glucose, the body converts the non-carbohydrate sources such as amino acids in the liver into glucose. The glucose made is then used in maintaining the blood sugar at a constant level. (24)slide 25:Body temperature is controlled by the thermoregulatory centre in the hypothalamus. There are two sets of thermoreceptors which the hypothalamus receives input from. The receptors in the hypothalamus itself monitor the temperature of blood as it passes through the brain. There are also receptors in the skin which monitor the external temperature. Both sets of information are needed so that the body can make appropriate adjustment. (16)The bodies first response to changes in temperature is voluntary. This is when extra clothes are put on when it gets too cold. When these responses are not enough, the thermoregulatory centre is stimulated. The responses are involuntary as there is part of the autonomic nervous system. (16)slide 26:The smooth muscles in arterioles in the skin respond to low temperature by the muscles contracting causing vasoconstriction. Therefore, less heat is carried from the core to the surface of the body which maintains the core temperature. In extremities, they can turn blue and can even be damaged. On the other hand, when the temperature is high, the muscles relax causing vasodilation. Therefore, more heat is carried from the core to the surface, so can be lost by convection and radiation. Conduction occurs when in water. The skin can also turn red. (16)The sweat gland responds to high temperature by secreting sweat onto the surface of the skin, where it evaporates. As a result of water having a high latent heat of evaporation, it takes heat from the body.high humidity and tight clothing made of manmade fibres reduce the ability of the sweat evaporating. On the other hand, when the temperature is low, no sweat is produced. (16)slide 27:The arrector pili muscles in the skin respond to low temperature by contracting the muscles, which raises the skin. This traps an insulating layer of warm air next to the skin. To respond to high temperature, the muscles relax which lower the skin hairs and allow air to circulate over the skin. This encourages convection and evaporation. (16)The skeletal muscles respond to low temperature by shivering, the muscles contract and relax repeatedly which generates heat by friction and from metabolic reaction. When the temperature is high no shivering occurs. (16)The adrenal and thyroid gland secrete adrenaline and thyroxine when the temperature is low. This increases the metabolic rate in different tissues such as the liver to generate heat. On the other hand, when the temperature is high, the glands stop secreting adrenaline and thyroxine. (16)slide 29:A decrease in water can lead to dehydration. Dehydration can occur when the body starts sweating whilst carrying out exercise. Sweat is released to cool the body temperature down. It is important to replenish the fluid as if this is not done the sweating might stop to respond to the dehydration. To manage dehydration, fluids need to be taken regularly. (17)Hyperthermia occurs when the heat gain exceeds the ability of the body to lose heat, the temperature of the body, therefore, increases above normal levels.this can be as a result of exposure to hot environments, exercise, fever and anaesthesia. Being exposed to hot environments normally activates the heat loss mechanisms and the body temperature is maintained back to normal. Prolonged exposure to hot environments can result in heat exhaustion. The normal negative-feedback mechanisms for controlling body temperature are operating but isn’t able to maintain normal temperature. Heavy sweating results in dehydration, decreased blood volume, decrease blood pressure and increased heart rate.treatment includes moving to cooler environments and restoring blood volume by drinking fluids. (18)slide 30:Hypoglycemia is caused by a reduction in plasma glucose concentration. It usually arises due to abnormalities in the mechanisms involved in glucose homeostasis. To manage hypoglycemia frequent meals/ snacking is advised and also avoiding simple sugars and carbohydrates. Medicines such as dextrose, glucagon and streptozocin can also be taken. (17)Hypothermia takes place when the heat loss exceeds the ability of the body to produce heat, body temperature decreases below normal levels. Hyperthermia occurs when the body temperature falls below 35 degrees Celsius. It usually occurs due to prolonged exposure to cold environments. The individual’s thinking can become sluggish and movements may be uncoordinated as a result of hypothermia. (18)The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is continued secretion or action of the antidiuretic hormone arginine vasopressin (AVP) despite normal or increases plasma volume, which results in impaired water excretion. Symptoms such as chronic pain or excessive fluid intake can occur. (19)slide 31:Hormones regulate the activity of body cells. The release of the hormones in the blood is controlled by a stimulus. For example, the stimulus either causes an increase or decrease in the amount of hormone secreted. Then the response to a stimulus changes the internal conditions and may itself become a stimulus. (20)Hormones regulate various homeostases, such as glucose and calcium homeostasis. Homeostasis is maintained by the endocrine system which secretes hormones. The gut hormones regulate glucose homeostasis. After eating, multiple gut peptides help with the uptake and storage of energy from food, gut hormones communicate with organs to manage energy intake and absorption. Certain hormones work to regulate calcium homeostasis. The parathyroid hormone works to increase concentrations of calcium in the blood and calcitonin is a hormone that works to reduce blood calcium levels when needed. Hormones work together and with nutrients such as vitamin D to regulate calcium levels. (21)slide 32:If the body temperature falls too low or goes too high, hypothermia or heat stroke may occur, which are both life-threatening. If homeostasis does not work, it may become difficult for the body to produce heat from the nutrients which are taken in or from the outside environment. In extreme heat, the body may be unable to cool down leading to heat strokes. Hyperthermia may also lead to seizures and unconsciousness. On the other hand, if the body is exposed to extremely cold temperatures, the body temperature could fall which could lead to hypothermia. This can slow organ function, producing confusion and fatigue. (22)If the body is unable to maintain its energy balance, development of obesity or diabetes may occur. Hunger is the brain’s way of telling the body to eat food so that the body is able to convert into energy. The stomach releases a hormone ghrelin, which affects your brain and increases appetite. Leptin hormone is also produced by fat cells which counter ghrelin, inducing a sense of satiety or fullness. If the brain stops responding to ghrelin, the body may always feel hungry and if leptin is not produced, the body may never feel satisfied from a meal. The results are overeating which can result in obesity and diabetes. (22) slide 33:If the amount of calcium in the blood becomes too low or too high, there is a risk of hypocalcemia or hypercalcemia occurring. Calcium ions are important for proper nerve and muscle function. The thyroid parathyroid glands regulate blood calcium levels. The thyroid gland causes a decrease in blood calcium levels, while the parathyroid gland helps increase calcium in the blood. If calcium drops too low, it can result in hypocalcemia which can cause seizures, muscle spasms or an abnormal heart rhythm. When there is too much calcium in the body, the individual may experience nausea, vomiting, abdominal pain, constipation and other symptoms such as loss of appetite. (22)If water balance becomes a problem, the individual may become dehydrated or hyper-hydrated. Water balance is important for proper functioning of nerves and other organs. The brain detects the amount of water in the blood and the kidney senses the blood pressure which determines the degree by the volume of the blood. When water levels in the body are low, the individual becomes dehydrated. The brain induces thirst and signals the kidneys to retain more water. This prevents kidney damage, hear cramps, shock or even coma. Drinking too much water can result in hyperhydration. It can induce weakness, confusion, irritation and seizures. (22)
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