Temperature, Thirst, and Hunger

• Internal regulation involves temperature regulation, thirst, and hunger

Temperature Regulation

• Temperature significantly influences behavior
• Temperature regulation is critical for normal behavioral processes
• Homeostasis maintains body variables within a fixed range through temperature regulation and other biological processes

Set Point and Feedback

• Set point: A single value the body aims to maintain
• Examples of set points: water, oxygen, glucose, sodium chloride, protein, fats, and acidity levels
• Negative feedback: Processes that reduce deviations from a set point
• Aliostasis: The body's adaptive change of the set point in response to life or environmental changes

Biological Priorities and Energy Use

• Temperature regulation is a key biological priority
• Around two-thirds of daily energy/kilocalories are used for temperature regulation
• Basal metabolism: Energy used to keep a constant body temperature at rest

Poikilothermic Organisms

• Poikilothermic: Body temperature matches the environment, seen in amphibians, reptiles, and most fish
• These organisms lack internal physiological temperature regulation mechanisms
• Temperature regulation is achieved by selecting specific locations in the environment

Homeothermic Organisms

• Homeothermic: Use internal physiological mechanisms to maintain a nearly constant body temperature
• Mammals and birds are homeothermic
• Homeothermic characteristics: requires energy and fuel, sweating and panting lowers temperature, shivering and increased metabolic rate increases temperature

Mammalian Temperature

• Mammals maintain a constant temperature of 37°C (98°F)
• Benefits of warmth: muscle activity readiness
• Drawbacks of excess heat: proteins break down and reproductive cells require cooler temperatures

Brain Areas and Temperature Regulation

• Body temperature regulation relies on areas in the preoptic area/anterior hypothalamus (POA/AH)
• The POA/AH monitors body temperature
• Heating the POA/AH causes panting or shivering, while cooling leads to shivering

Temperature Receptors

• POA/AH cells receive input from temperature-sensitive receptors in the skin

Fever

• Bacterial and viral infections can cause fever, which is a defense against illness
• Bacteria and viruses trigger leukocytes to release cytokines
• Cytokines stimulate the vagus nerve after attacking intruders
• The vagus nerve stimulates the hypothalamus to start a fever
• Some bacteria grow less in warmer temperatures
• Fevers above 39°C (103°F) are more harmful than beneficial

Thirst

• Water accounts for 70% of the mammalian body
• Water in the body must be regulated within strict limits
• Chemical concentrations in water determine the rate of bodily chemical reactions
• Water regulation mechanisms vary in humans

Water Conservation

• Water can be conserved by excreting concentrated urine and reducing sweat/autonomic responses
• Water regulation consists of drinking more water than needed and excreting the rest
• Vasopressin, released by the pituitary gland, increases blood pressure by constricting blood vessels

Antidiuretic Hormone

• Antidiuretic hormone: Another name for vasopressin
• Vasopressin enables the kidneys to reabsorb water and excrete concentrated urine

Thirst Types

• Osmotic thirst: Thirst due to eating salty foods
• Hypovolemic thirst: Thirst due to fluid loss (bleeding or sweating)
• Each type of thirst triggers different behaviors

Osmotic Thirst

• Occurs because the body maintains a solute concentration of 0.15 M (molar)
• Solutes inside and outside cells produce osmotic pressure
• Osmotic pressure: Water's tendency to flow across a semi-permeable membrane from low to high solute concentration
• Occurs when solutes are more concentrated on one side of the membrane

Sodium and Osmotic Pressure

• Eating salty foods causes sodium ions to spread through blood and the extracellular fluid
• This results in osmotic pressure and draws water from cells to the extracellular fluid
• Osmotic thirst is triggered when certain neurons detect the loss of water

Brain Detection of Osmotic Pressure

• The brain detects osmotic pressure via receptors around the third ventricle
• Including the organum vasculosum laminae terminalis (OVLT) and subfornical organ
• Peripheral receptors, including in the stomach, can also detect high levels of sodium
• Receptors in the OVLT, subfornical organ, stomach and elsewhere relay information to areas of the hypothalamus

Nucleus Involvement in Drinking

• The supraoptic nucleus and paraventricular nucleus control vasopressin release from the pituitary gland
• Receptors relay information to the lateral preoptic area, controls drinking

Thirst Inhibition

• When osmotic thirst is triggered, water must be absorbed through the digestive system
• The body monitors swallowing and detects water content in the stomach and intestines to inhibit thirst

Hypovolemic Thirst

• Hypovolemic thirst is associated with having a low volume of bodily fluids

Angiotensin and Blood Pressure

• Hypovolemic thirst is triggered by the hormones vasopressin and angiotensin II, which constrict blood vessels to increase blood pressure
• Angiotensin II stimulates neurons near the third ventricle and is released as a neurotransmitter in the hypothalamus

Thirst and Water Preference

• Animals with osmotic thirst prefer pure water
• Animals with hypovolemic thirst prefer slightly salty water because it dilutes body fluids and changes osmotic pressure
• Sodium-specific hunger is a strong craving for salty foods that automatically develops to restore blood solute levels

Hunger

• Animals vary their strategies of eating, but humans typically eat more than needed
• Hunger is influenced by a combination of learned and unlearned factors
• The digestive system breaks down food into smaller molecules for cell use

Digestion

• Digestion starts in the mouth where saliva enzymes break down carbohydrates
• Hydrochloric acid and enzymes digest proteins in the stomach
• The small intestine's enzymes digest proteins, fats, and carbohydrates; it also absorbs digested food into the bloodstream
• The large intestine absorbs water and minerals and lubricates remaining materials to pass as feces

Lactose Metabolism

• The intestinal enzyme lactase metabolizes lactose
• After weaning, most mammals lose lactase
• Lactose: the sugar found in milk
• Milk consumption after weaning can lead to gas and stomach cramps
• Declining lactase levels is one evolutionary mechanism to encourage weaning
• Most human adults have enough lactase to consume milk and other dairy products throughout life

Diet Types

• Carnivores eat meat and necessary vitamins from the meat consumed
• Herbivores eat plants only
• Omnivores eat both meat and plants
• Herbivores and omnivores distinguish between edible and inedible substances to find necessary vitamins and minerals

Food Selection

• Imitation of others is one means of selecting foods to eat
• Other strategies: select sweet foods and avoid bitter, prefer familiar tastes, and learn from the consequences of consuming the food
• Conditioned taste aversion: A distaste for food that develops if the food makes one ill

Brain Regulation of Eating

• The brain regulates eating through signals from the mouth, stomach, intestines, fat cells
• Desire to taste influences hunger and satiety
• Sham feeding experiments: Allowing animals to eat, but not digest, prevents satiety from developing

Stomach and the Vagus Nerve

• The main signal to stop eating is the stomach distention
• The vagus nerve allows information about the stomach walls
• The splanchnic nerves allow information about the nutrient contents of the stomach

Duodenum and Hormone Release

• Duodenum: Part of the small intestine where initial absorption of nutrients occurs
• The duodenum produces satiety
• The duodenum releases cholecystokinin (CCK), which assists with regulating hunger
• CCK manages hunger by closing the sphincter muscle to hold contents in the stomach longer and fill faster

Role of Hormones

• Stimulation of the vagus nerve sends a message to the hypothalamus that releases a chemical similar to CCK
• Glucose, insulin, and glucagon
• Glucose: the main source of energy for the body and the brain
• Digest food enters the bloodstream as glucose

Glucose Metabolism

• When glucose levels are high, liver cells convert glucose into glycogen and fat cells convert it into fat
• When glucose levels are low, the liver converts glycogen back into glucose
• Insulin: a pancreatic hormone that enables glucose to enter the cell
• Insulin levels increase while you prepare for a meal or eat a meal
• High insulin lets existing blood glucose enter cells in preparation of new glucose
• Consequently, high levels of insulin generally decreases appetite.

Glucose Metabolism II

• Glucagon, a hormone released by the pancreas when glucose levels fall
• Glucagon stimulates the liver to convert glycogen to glucose
• As insulin levels drop, glucose enters the cell more slowly and hunger increases
• Body continues rapidly moving blood glucose into cells even after meal if insulin levels constantly stay high
• In this case, blood glucose drops and hunger grows, food is deposited a fat and glycogen, and the organism gains weight
• In people with diabetes, insulin is low but blood glucose is high, people eat more but glucose is unused and lose weight

Leptin and Satiety

• Long-term hunger regulation is accomplished via the monitoring of fat supplies
• Leptin, produced by fat cells, signals the brain to adjust eating
• Low leptin levels increase hunger
• High leptin levels do not necessarily decrease hunger, due to decreased sensitivity or genetic inability to produce leptin

Nucleus Integration

• Information from the body integrates into two kinds of cells in the arcuate nucleus

Arcuate Nucleus

• The arcuate nucleus is located in the hypothalamus containing two sets of neurons, related to both hunger and to satiety signals
• Those related to hunger, receive input from taste pathways and axons releasing the neurotransmitter ghrelin
• Ghrelin is released to trigger stomach contractions
• Satiety cells in the arcuate nucleus receive signals for both long-term and short-term satiety
• Distention in the intestine triggers neurons release to release the neurotransmitter, CCK
• Blood glucose increases from increased body fat levels

Nucleus Output

• Some neuron cell release a peptide releases to insulin as a transmitter
• Lepton provides additional input in this, from the arcuate nucleus
• Output goes through the from the paraventricular nucleus and hypothalamus, which is important for both satiety ad hunger

Hunger and Eating Regulation

• Axons from the satiety cells, deliver information to the satiety nucleus that triggers satiety
• Input from Hunger cells is inhibitory to the satiety cells, in satiety cells

Neurotransmitters

• Inhibitory transmitters include neuropeptide (NPY) an appetite stimulator
• Inhibitory Y are inhibitory transmitters in this case, and provoke overeating

Hypothalamus Connection

• Output from the paraventricular nucleus is connected to the hypothalamus
• Insulin signals contribute to responsiveness
• The animals may starve to death unless the area is directly fed

Roles of the Lateral Hypothalamus

• The lateral hypothalamus is used to detect and respond to hunger
• The cerebral cortex is released to signal taste and other bodily functions
• Pituitary secretions related to insulin increase, related to secretions

Ventromedial Damage

• Damage can occur to those leading to weight gain, can lead to over eating if extended outside
• Usual frequency meals can occur as a result
• Insulin production and fat storage increases, related to hormones

Hunger and Genetic Influence

• Mutated Gene in receptors increases overeating
• Melanocrotin increase peptides for hunger
• Wills syndrome, and increase retardation
• Peptide levels are increased related to genetic conditions

Genetics of Obesity

• A single gene cannot be identified, but is linked with obesity contributing factors
• Conditions include diet and American populations, related to changes
• Life style changes are also influential related to fastfood for example

Appetite Treatments

• Weight loose or difficult to treat and may not agree, with exercise
• Appetite suppressant has medication and can block similar food related neurotransmitters
• Drug use must follow specific fat rules
• Nervosa increases hunger from needs to eat
• Clear genetic are difficult

Hunger Issues

• Fear is not a disinterest in food, in anoxia
• Biochemical abnormalities may not cause weight
• Nervosa can be associated in between normal diet
• May result from neurotransmitters related issues