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Chapter 10 Internal Regulation. Temperature Regulation. Temperature affects many aspects of behavior. Temperature regulation is vital to the normal functioning of many behavioral processes.
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Temperature Regulation • Temperature affects many aspects of behavior. • Temperature regulation is vital to the normal functioning of many behavioral processes. • Homeostasis refers to temperature regulation and other biological processes that keep certain body variables within a fixed range.
Temperature Regulation • A set point refers to a single value that the body works to maintain. • Examples: Levels of water, oxygen, glucose, sodium chloride, protein, fat and acidity in the body. • Processes that reduce discrepancies from the set point are known as negative feedback. • Allostasis refers to the adaptive way in which the body changes its set point in response to changes in life or the environment.
Temperature Regulation • Temperature regulation is one of the body’s biological priorities. • Uses about two-thirds of our energy/ kilocalories per day. • Basal metabolism is the energy used to maintain a constant body temperature while at rest.
Temperature Regulation • Poikilothermic refers to the idea that the body temperature matches that of the environment. • Amphibians, reptiles and most fish. • The organism lacks the internal, physiological mechanisms of temperature regulation. • Temperature regulation is accomplished via choosing locations in the environment.
Temperature Regulation • Homeothermic refers to the use of internal physiological mechanisms to maintain an almost constant body temperature. • Characteristic of mammals and birds. • Requires energy and fuel. • Sweating and panting decrease temperature. • Increasing temperature is accomplished via shivering, increasing metabolic rate, decreasing blood flow to the skin, etc.
Temperature Regulation • Mammals evolved to have a constant temperature of 37˚ C (98˚ F). • Muscle activity benefits from being as warm as possible and ready for vigorous activity. • Proteins in the body break their bonds and lose their useful properties at higher temperatures. • Reproductive cells require cooler temperatures.
Temperature Regulation • Body temperature regulation is predominantly dependent upon areas in the preoptic area/ anterior hypothalamus (POA/AH). • The POA/AH partially monitors the body’s temperature by monitoring its own temperature. • Heating the POA/AH leads to panting or shivering; cooling leads to shivering. • Cells of the POA/AH also receive input from temperature sensitive receptors in the skin.
Temperature Regulation • Bacterial and viral infections can cause a fever, part of the body’s defense against illness. • Bacteria and viruses trigger the release of leukocytes which release small proteins called cytokines. • Cytokines attack intruders but also stimulate the vagus nerve.
Temperature Regulation (Continued) • The vagus nerve stimulates the hypothalamus to initiate a fever. • Some bacteria grow less vigorously in warmer than normal body temperature. • However, a fever of above 39˚ C (103˚ F) does the body more harm than good.
Thirst • Water constitutes 70% of the mammalian body. • Water in the body must be regulated within narrow limits. • The concentrations of chemicals in water determines the rate of all chemical reactions in the body.
Thirst • Mechanisms of water regulation vary for humans. • Water can be conserved by: • Excreting concentrated urine. • Decreasing sweat and other autonomic responses. • Most often water regulation is accomplished via drinking more water than we need and excreting the rest.
Thirst • Vasopressin is a hormone released by the posterior pituitary which raises blood pressure by constricting blood vessels. • helps to compensate for the decreased water volume. • Vasopressin is also known as an antidiuretic hormone because it enables the kidneys to reabsorb water and excrete highly concentrated urine.
Thirst • Two different kinds of thirst include: • Osmotic thirst – athirst resulting from eating salty foods. • Hypovolemic thirst – a thirst resulting from loss of fluids due to bleeding or sweating. • Each kind of thirst motivates different kinds of behaviors.
Thirst • Osmotic thirst occurs because the human body maintains a combined concentration of solutes at a fixed level of .15 M (molar). • Solutes inside and outside a cell produce osmotic pressure, the tendency of water to flow across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration. • Occurs when solutes are more concentrated on one side of the membrane.
Thirst • Eating salty food causes sodium ions to spread through the blood and extracellular fluid of the cell. • The higher concentration of solutes outside the cell results in osmotic pressure, drawing water from the cell to the extracellular fluid. • Certain neurons detect the loss of water and trigger osmotic thirst to help restore the body to the normal state.
Thirst • The brain detects osmotic pressure from: • Receptors around the third ventricle. • The OVLT (organum vasculosum laminae terminalis) and the subfornical organ (detect osmotic pressure and salt content). • Receptors in the periphery, including the stomach, which detect high levels of sodium.
Thirst • Receptors in the OVLT, subfornical organ, stomach and elsewhere relay information to areas of the hypothalamus including: • the supraoptic nucleus • paraventricular nucleus. • Both control the rate at which the posterior pituitary releases vasopressin. • Receptors also relay information to the lateral preoptic area which controls drinking.
Thirst • When osmotic thirst is triggered, water that you drink has to be absorbed through the digestive system. • To inhibit thirst, the body monitors swallowing and detects the water contents of the stomach and intestines.
Thirst • Hypovolemic thirst is thirst associated with low volume of body fluids. • Triggered by the release of the hormones vasopressin and angiotensin II, which constrict blood vessels to compensate for a drop in blood pressure. • Angiotensin II stimulates neurons in areas adjoining the third ventricle. • Neurons in the third ventricle send axons to the hypothalamus where angiotensin II is also released as a neurotransmitter.
Thirst • Animals with osmotic thirst have a preference for pure water. • Animals with hypovolemic thirst have a preference for slightly salty water as pure water dilutes body fluids and changes osmotic pressure. • Sodium-specific hunger, a strong craving for salty foods. • develops automatically to restore solute levels in the blood.
Hunger • Animals vary in their strategies of eating, but humans tend to eat more than they need at the given moment. • A combination of learned and unlearned factors contribute to hunger.
Hunger • The function of the digestive system is to break down food into smaller molecules that the cells can use. • Digestion begins in the mouth where enzymes in the saliva break down carbohydrates. • Hydrochloric acid and enzymes in the stomach digest proteins.
Hunger • The small intestine has enzymes that digest proteins, fats, and carbohydrates and absorbs digested food into the bloodstream. • The large intestine absorbs water and minerals and lubricates the remaining materials to pass as feces.
Hunger • At the age of weaning, most mammals lose the intestinal enzyme lactase, which is necessary for metabolizing lactose. • Lactose is the sugar found in milk. • Milk consumption after weaning can cause gas and stomach cramps. • Declining levels of lactase may be an evolutionary mechanism to encourage weaning.
Hunger • Most human adults have enough lactase to consume milk and other dairy products throughout the lifetime. • Nearly all people in China and surrounding countries lack the gene that enables adults to metabolize lactose. • Only small quantities of dairy products can be consumed.
Hunger • A carnivore is an animal that eats meat and necessary vitamins are found in the meat consumed. • Herbivores are animals that exclusively eat plants. • Omnivores are animals that eat both meat and plants.
Hunger • Herbivores and omnivores must distinguish between edible and inedible substances to find sufficient vitamins and minerals. • Selecting foods to eat is usually accomplished via imitation of others.
Hunger • Other strategies of selecting food include: • Selecting sweet foods and avoiding bitter foods. • Preferring things that taste familiar. • Learning from consequences that happen after a food is consumed. • A conditioned taste aversion is a distaste for food that develops if the food makes one ill.
Hunger • The brain regulates eating through messages from the mouth, stomach, intestines, fat cells and elsewhere. • The desire to taste and other mouth sensations, such as chewing, are also motivating factors in hunger and satiety. • Sham feeding experiments,in which everything an animals eats leaks out of a tube connected to the stomach or esophagus, do not produce satiety.
Hunger • The main signal to stop eating is the distention of the stomach. • The vagus nerve conveys information about the stretching of the stomach walls to the brain. • The splanchnic nerves convey information about the nutrient contents of the stomach.
Hunger • The duodenum is the part of the small intestine where the initial absorption of significant amounts of nutrients occurs. • Distention of the duodenum can also produce feelings of satiety. • The duodenum also releases the hormone cholecystokinin (CCK), which helps to regulate hunger.
Hunger • Cholecystokinin (CCK) released by the duodenum regulates hunger by: • Closing the sphincter muscle between the stomach and duodenum and causing the stomach to hold its contents and fill faster. • Stimulating the vagus nerve to send a message to the hypothalamus that releases a chemical similar to CCK.
Hunger • Glucose, insulin, and glucagon levels also influence feelings of hunger. • Most digested food enters the bloodstream as glucose, an important source of energy for the body and nearly the only fuel used by the brain. • When glucose levels are high, liver cells convert some of the excess into glycogen and fat cells convert it into fat. • When low, liver converts glycogen back into glucose.
Hunger • Insulin is a pancreatic hormone that enables glucose to enter the cell. • Insulin levels rise as someone is getting ready for a meal and after a meal. • In preparation for the rush of additional glucose about to enter the blood, high insulin levels let some of the existing glucose in the blood to enter the cells. • Consequently, high levels of insulin generally decrease appetite.
Hunger • Glucagon is also a hormone released by the pancreas when glucose levels fall. • Glucagon stimulates the liver to convert some of its stored glycogen to glucose to replenish low supplies in the blood. • As insulin levels drop, glucose enters the cell more slowly and hunger increases.
Hunger • If insulin levels constantly stay high, the body continues rapidly moving blood glucose into the cells long after a meal. • Blood glucose drops and hunger increases in spite of the high insulin levels. • Food is rapidly deposited as fat and glycogen. • The organism gains weight.
Hunger • In people with diabetes, insulin levels remain constantly low, but blood glucose levels are high. • People eat more food than normal, but excrete the glucose unused and lose weight.
Hunger • Long-term hunger regulation is accomplished via the monitoring of fat supplies by the body. • The body’s fat cells produce the peptide leptin, which signals the brain to increase or decrease eating. • Low levels of leptin increase hunger.
Hunger • High levels of leptin do not necessarily decrease hunger. • Most people are obese because they are less sensitive to leptin. • Some people are obese because of a genetic inability to produce leptin.
