FR1-Energy Balance Flashcards
All energy used by cells is ultimately provided by
Food intake
What is External work?
the energy expended when skeletal muscles contract to move external objects or to move the body in relation to the environment
What is Internal work?
Internal work encompasses two types of energy-dependent activities:
constitutes all other forms of biological energy expenditure that do not accomplish mechanical work outside the body
(1) skeletal muscle activity used for purposes other than external work, such as the contractions associated with postural maintenance and shivering
(2) all energy-expending activities that must go on all the time just to sustain life e.g. pumping blood and breathing, the energy required for active transport of critical materials across plasma membranes, and the energy used during synthetic reactions essential for the maintenance, repair, and growth of cellular structures—in short, the “metabolic cost of living
What are the laws of thermodynamics in realation to metabolic input and output?
Energy cannot be created or destroyed, but it can be converted from one form to another.
The energy in nutrient molecules not used to energize work is transformed into thermal energy, or heat
During biochemical processing, how much of the energy in nutrient molecules is transferred to ATP?
When the cells expend ATP, how much of the energy derived from ingested food becomes heat?
- During biochemical processing, only about 50% of the energy in nutrient molecules is transferred to ATP; the other 50% of nutrient energy is immediately lost as heat
- When the cells expend ATP, another 25% of the energy derived from ingested food becomes heat.
- Therefore, not more than 25% of nutrient energy is available for work, either external or internal. The remaining 75% is lost as heat
Of the energy actually captured for use by the body, almost all expended energy eventually becomes heat, give an example
Why can this heat be useful?
- Energy expended by the heart to pump blood is gradually changed into heat by friction as blood flows through the vessels.
- Energy used in synthesizing structural protein eventually appears as heat when that protein is degraded during the normal course of turnover of bodily constituents.
- Even in performing external work, skeletal muscles convert chemical energy into mechanical energy inefficiently; as much as 75% of the expended energy is lost as heat
- This heat is not entirely wasted energy, however, because much of it is used to maintain body temperature
Define metabolic rate
- The rate at which energy is expended by the body during both external and internal work is known as the metabolic rate:
- Metabolic rate 5 energy expenditure/unit of time
- Because most of the body’s energy expenditure eventually appears as heat, the metabolic rate is normally expressed in terms of the rate of heat production in kilocalories per hour
What is the basic unit of heat energy?
the calorie, which is the amount of heat required to raise the temperature of 1 g of H2O by 1°C
How many kilocalories of heat energy are released when 1 g of glucose is oxidized or “burned,” whether the oxidation takes place inside or outside the body?
Four kilocalories of heat energy are released when 1 g of glucose is oxidized or “burned,” whether the oxidation takes place inside or outside the body
What is the factor that can increase metabolic rate to the greatest extent?
Increased skeletal muscle activity
Even slight increases in muscle tone notably elevate the metabolic rate, and various levels of physical activity markedly alter energy expenditure and heat production
Why is metabolic rate measured at rest?
many variables can alter metabolic rate as possible
The BMR is measured under the following specified conditions:
- The person should be at physical rest, having refrained from exercise for at least 30 minutes to eliminate any contribution of muscular exertion to heat production.
- The person should be at mental rest to minimize skeletal muscle tone (people “tense up” when they are nervous) and to prevent a rise in epinephrine, a hormone secreted in response to stress that increases metabolic rate.
- The measurement should be performed at a comfortable room temperature so that the person does not shiver. Shivering can markedly increase heat production
- The subject should not have eaten any food within 12 hours before the BMR determination to avoid diet-induced thermogenesis (thermo means “heat”; genesis means “production”), or the obligatory, short-lived (less than 12-hour) rise in metabolic rate that occurs as a result of the increased metabolic activity associated with processing and storing ingested nutrients.
Methods of Measuring the Basal Metabolic Rate: Directly
To directly measure heat production, the person sits in an insulated chamber with water circulating through the walls. The difference in the temperature of the water entering and leaving the chamber reflects the amount of heat liberated by the person and picked up by the water as it passes through the chamber
Methods of Measuring the Basal Metabolic Rate: Indirectly
Food + O2 ► CO2+ H2O +energy (mostly transformed into heat)
Accordingly, a direct relationship exists between the volume of O2 used and the quantity of heat produced
- Although carbohydrates, proteins, and fats require different amounts of O2 for their oxidation and yield different amounts of kilocalories when oxidized, an average estimate can be made of the quantity of heat produced per liter of O2 consumed on a typical mixed diet.
- This approximate value, known as the energy equivalent of O2, is 4.8 kcal of energy liberated per liter of O2 consumed.
- Using this method, the metabolic rate of a person consuming 15 liters/hour of O2 can be estimated as follows:
- 15 liters/hr =O2 consumption= 15 x 4.8 kilocalories/liter = energy equivalent of O2. 72 kilocalories/hr estimated metabolic rate
What is is the primary but not sole determinant of the rate of basal metabolism?
As thyroid hormone increases, the BMR increases correspondingly.
Epinephrine also increases the BMR.
Is the BMR is not the body’s lowest metabolic rate?
The rate of energy expenditure during sleep is 10% to 15% lower than the BMR, presumably because of the more complete muscle relaxation that occurs during the paradoxical stage of sleep
What are the 3 possible states of energy balance?
■ Neutral energy balance. If the amount of energy in food intake exactly equals the amount of energy expended in performing external work plus the basal internal energy expenditure that eventually appears as body heat, then energy input and output are exactly in balance, and body weight remains constant.
■ Positive energy balance. If the amount of energy in food intake is greater than the amount of energy expended, the extra energy taken in but not used is stored in the body, primarily as adipose tissue, so body weight increases.
■ Negative energy balance. If the energy derived from food intake is less than the body’s immediate energy requirements, the body must use stored energy to supply energy needs, and body weight decreases accordingly
What is the most important factor in longterm maintenance of energy balance and body weight?
regulation of food intake
(blood-borne chemical factors that signal the body’s nutritional state, such as how much fat is stored or the feeding status, are important in regulating food intake)
Role of the Arcuate Nucleus: NPY and Melanocortins
- The arcuate nucleus of the hypothalamus plays a central role in both long-term control of energy balance and body weight and short-term control of food intake from meal to meal.
- The arcuate nucleus is an arc-shaped collection of neurons located adjacent to the floor of the third ventricle.
- Multiple, highly integrated, redundant pathways crisscross into and out of the arcuate nucleus, indicative of the complex systems involved in feeding and satiety.
- Feeding, or appetite, signals give rise to the sensation of hunger, driving us to eat.
- By contrast, satiety is the feeling of being full. Satiety signals tell us when we have had enough and suppress the desire to eat.
The arcuate nucleus has two subsets of neurons that function in an opposing manner:
Are NPY and melanocortins the final effectors in appetite control?
- One subset releases neuropeptide Y, and the other releases melanocortins derived from pro-opiomelanocortin (POMC), a precursor molecule that can be cleaved in different ways to produce several hormone products
- Neuropeptide Y (NPY), one of the most potent appetite stimulators ever found, leads to increased food intake, thus promoting weight gain.
- Melanocortins, a group of hormones that have been shown to exert an unexpected role in energy homeostasis in humans. Melanocortins, most notably a-melanocytestimulating hormone (a-MSH) from the hypothalamus, suppress appetite, thus leading to reduced food intake and weight loss.
- Melanocortins’ major importance in our species, however, is the role of hypothalamic a-MSH in toning down appetite.
- NPY and melanocortins are not the final effectors in appetite control.
- These arcuate-nucleus chemical messengers influence the release of neuropeptides in other parts of the brain that exert more direct control over food intake
Regulatory Inputs to the Arcuate Nucleus in LongTerm Maintenance of Energy Balance: Leptin
Is adipose tissue considered an endocrine gland?
What other adipokines are released from oth adipocytes and from immune cells such as mactrophages?
Adipose tissue secretes several hormones, collectively termed adipokines, that play important roles in energy balance and metabolism.
Thus, adipose tissue is now considered an endocrine gland and is the largest hormone-secreting organ in the body.
Some adipokines are released only from adipocytes, an example being leptin, which plays an important role in energy balance.
Some, like tumor necrosis factor (TNF) and interleukin 6 (IL-6), are released from adipocytes and from immune cells such as macrophages (large stationary phagocytes) that reside in abundance in excessive adipose tissue
What is the newly identified link between obesity-induced inflammation and its metabolic consequences called?
metaflammation
Is subcutaneous fat more harmful than visceral fat?
Visceral fat is more likely to be chronically inflamed and is associated with increased heart disease and other disorders, in contrast to the more superficial and less harmful subcutaneous fat that is deposited under the skin
What adipokine helps protect against type 2 diabetes?
What adipokine promotes type 2 diabetes?
- Adiponectin increases sensitivity to insulin (which helps protect against Type 2, or adult-onset, diabetes mellitus (Type 1 diabetes)
- Resistin, which is released primarily in obesity, leads to insulin resistance (thus increasing the risk of developing Type 2 diabetes)
What adipokine is essential for body weight regulation?
- Leptin (means “thin”)
- The amount of leptin in the blood is an excellent indicator of the total amount of triglyceride fat stored in adipose tissue: The larger the fat stores, the more leptin released into the blood
- This blood-borne signal, discovered in the mid-1990s, was the first molecular satiety signal identified
- Leptin suppresses appetite, thus decreasing food consumption and promoting weight loss, by inhibiting hypothalamic output of appetite-stimulating NPY and stimulating output of appetitesuppressing melanocortins
- The leptin signal is generally considered the dominant factor responsible for the long-term matching of food intake to energy expenditure so that total body energy content remains balanced and body weight remains constant
Another blood-borne signal besides leptin that plays an important role in long-term control of body weight is insulin:
- Insulin, a hormone secreted by the pancreas in response to a rise in the concentration of glucose and other nutrients in the blood following a meal, stimulates cellular uptake, use, and storage of these nutrients .
- Thus, the increase in insulin secretion that accompanies nutrient abundance, use, and storage appropriately inhibits the NPY-secreting cells of the arcuate nucleus, thus suppressing further food intake
There are two hypothalamic areas are richly supplied by axons from the NPY and melanocortin-secreting neurons of the arcuate nucleus:
What are these second-order neuronal areas involved in energy balance and food intake?
lateral hypothalamic area (LHA) and paraventricular nucleus (PVN)
- The LHA and PVN release chemical messengers in response to input from the arcuate nucleus neurons.
- These messengers act downstream from the NPY and melanocortin signals to regulate appetite.
- The LHA produces orexins (ore-EKS-ins), which are potent stimulators of food intake (orexis means “appetite”).
- NPY stimulates and melanocortins inhibit the release of appetite-enhancing orexins. By contrast, the PVN releases chemical messengers, for example, corticotropin-releasing hormone, that decrease appetite and food intake
- Melanocortins stimulate and NPY inhibits the release of these appetite-suppressing chemicals
Short-Term Eating Behavior: Ghrelin and PYY3-36 Secretion
- Two blood-borne peptides secreted by the digestive tract that are important in regulating how often and how much we eat in a given day are ghrelin and peptide YY3-36 (PYY3-36), which signify hunger and fullness, respectively. Ghrelin (GRELL-in), the so-called hunger hormone, is a potent appetite stimulator produced by the stomach and regulated by the feeding status (ghrelin is the Hindu word for “growth”). Secretion of this mealtime stimulator peaks before meals and makes people feel like eating, and then it falls once food is eaten.
- Ghrelin stimulates appetite by activating the hypothalamic NPY-secreting neurons. PYY3-36 is a counterpart of ghrelin. The secretion of PYY3-36, which is produced by the small and large intestines, is at its lowest level before a meal but rises during meals and signals satiety.
- This peptide acts by inhibiting the appetite-stimulating NPYsecreting neurons in the arcuate nucleus.
- By thwarting appetite, PYY3-36 is an important mealtime terminator.
What is the satiety center in the brain stem known as?
- The nucleus tractus solitarius (NTS) processes signals important in the feeling of being full and thus contributes to short-term control of meals.
- Not only does the NTS receive input from the higher hypothalamic neurons involved in energy homeostasis, but it also receives afferent inputs from the digestive tract (for example, afferent input indicating the extent of stomach distension) and elsewhere that signal satiety
Name the mode of action of an important satiety signal
- Cholecystokinin (CCK), one of the gastrointestinal hormones released from the duodenal mucosa during digestion of a meal, is an important satiety signal for regulating meal size
- CCK is secreted in response to the presence of nutrients in the small intestine.
- Through multiple effects on the digestive system, CCK facilitates digestion and absorption of these nutrients
- . It is appropriate that this blood-borne signal, whose rate of secretion is correlated with the amount of nutrients ingested, contributes to the sense of being filled after a meal has been consumed but before it has been digested and absorbed.
- We feel satisfied when adequate food to replenish the stores is in the digestive tract even though the body’s energy stores are still low.
- This explains why we stop eating before the ingested food is made available to meet the body’s energy needs. Other related, more recently discovered gut peptides released in response to a meal that serve as satiety signals include glucagon-like peptide 1 (GLP-1) and oxyntomodulin
Psychosocial and Environmental Influences on appetite
- Frequently, we eat out of habit (eating three meals a day on schedule no matter what our status on the hunger–satiety continuum) or because of social custom (food often plays a prime role in entertainment, leisure, and business activities)
- Even well-intentioned family pressure—“Clean your plate before you leave the table”—can affect the amount consumed.
- Furthermore, the amount of pleasure derived from eating can reinforce feeding behavior; eating foods with an enjoyable taste, smell, and texture can increase appetite and food intake. Stress, anxiety, depression, and boredom have also been shown to alter feeding behavior in ways unrelated to energy needs.
- People often eat to satisfy psychological needs rather than to satisfy hunger.
- Furthermore, environmental influences, such as the amount of food available.
Give a summary of the effects of involuntary regulatory signals on appetite
How does obesity occur?
- Obesity occurs when, over time, more kilocalories are ingested in food than are used to support the body’s energy needs, with the excessive energy being stored as triglycerides in adipose tissue
- Each fat cell can store the maximum of about 1.2 mg of triglycerides. Once existing fat cells are full, if people continue to consume more calories than they expend, they make more adipocytes
Scientists have identified variations in more than 20 genes that predispose people to gaining excess weight easily:
Give an example
The FTO gene (the polite acronym now used instead of the less flattering original name “fatso gene”). T
here are two versions of the FTO gene: the “normal” T variant and the “faulty” A variant. Individuals who have one A version and one T version are 30% more likely to be obese than those who have two T copies of the gene.
For people who have two A copies of FTO, the risk of becoming obese jumps to 70%
What are some influences that are linked to obesity?
- Disturbances in the leptin-signaling pathway
- An abundance of convenient, highly palatable, energy-dense, relatively inexpensive foods
- Differences in extracting energy from food (For example, slimmer individuals have more uncoupling proteins, which allow their cells to convert more of the nutrient calories into heat instead of fat)
- Composition of colonic bacterial communities. Studies demonstrate that obese people have a greater proportion of a type of bacteria in their colon that breaks down indigestible fiber more efficiently for absorption
- Lack of exercise
- Differences in the “fidget factor.” Nonexercise activity thermogenesis (NEAT)
- Certain endocrine disorders such as hypothyroidism
- Emotional disturbances in which overeating replaces other gratifications
- Stress or too little sleep
- One study showed that the cold virus adenovirus-36 might lead to obesity by transforming adult tissue-specific stem cells into fat-storing adipocytes
