Chapter 21 (metabolism)

is insulin secreted during absorptive state or postabsorptive state?

Insulin secretion is stimulated during absorptive state and inhibited during the postabsorptive state. .Insulin is an Anabolic hormone: promotes the synthesis of storage molecules. .Its secreted by the Beta cells of the pancreas.

Gluconeogenesis:

(Catabolic action) Is the generation of NEW glucose from the liver, derived from non-carbohydrate sources, (which means making those glucose from fats and proteins)

(Extra) formula to obtain the Basal metabolic rate:

(Ml of O2 per hour)/(weight in kg ) -Ml of O2 per hour: refers to the amount of Oxygen in milliliters that a person consumes in one hour. Then divide this amount over: -weight in Kg; which refers to the whole weigh of the person in kilograms. Example using a laboratory rat:

-Glycolysis:

(anabolic action) is the process of breaking down glucose (for cellular energy (ATP))., so that we can use glucose for energy (instantly or during the absorptive state).

Glycogenesis:

(anabolic action) is the process of making glycogen from glucose molecules. (and storage it to use later during the Postabsorptive state)

Glycogenolysis:

(catabolic action) The brake down of glycogen into glucose molecules. (mostly at the liver)

Proteolysis:

(catabolic action) Is the breakdown of proteins into amino acids. -During prolonged starvation, the body tissues can undergo proteolysis (atrophy(brake) of skeletal muscle) .Only as a last resort, the body will catabolized a significant amount of proteins.

Lipolysis:

(catabolic action) is the breakdown of Triglycerides (TGA) into fatty acids (FA).

postabsorptive state: at the liver

(glucagon action at postabsorptive state is catabolic) -does glycolysis and release of glucose into bloodstream. (after breaking down the glycogen into glucose, the glucose are released into the bloodstream) -does Gluconeogenesis and release glucose into blood stream. (after gluconeogenesis is made, the new glucose are released into the blood stream) -Ketogenesis: process of converting fatty acids (FA) into ketone. while in prolonged fasting, the CNS can use ketone bodies instead of glucose (although the CNS can somehow get used to ketones, it is not recommended) ( I can think that when the body goes in starvation for a very long period of time, the last resources for energy are; to use ketones for energy for the brain and amino acid from braking proteins for energy for the body)

Lipogenesis:

(is anabolic action) is the process by which fat is made from nonlipid nutrients (using excess carbohydrates is the most common way). (any excess of the 3 substrates for energy can be converted into fat= lipogenesis)

what is the function of the lipoprotein enzyme Lipase?

- Lipoprotein lipase (LPL) will convert TGA(triglycerides) into FA (fatty acids)+ monoglycerides in the capillaries (basically LPL enzyme brakes the triglyceride into monoglycerides and fatty acids). .Monoglycerides will remain in the blood and are metabolized (brake and used) by the liver, while FA will enter into the body cells.

Energy Balance:

Body balance, what comes into the body and what is produced by the body should equal what is used by the body and what is eliminated by the body. Input + production = utilization + output

Absorptive state metabolism: at the skeletal muscles

Skeletal muscles: -Use glucose and Fatty acids for its own needs (it does not like to share, and its reason is because skeletal muscle cells use more energy than the rest of the cells of body) -glycogenesis: it converts glucose into glycogen. (to store the glucose in the form of glycogen. this glycogen is to be used by the skeletal muscle in the future.) -Stores amino acids in the form of proteins (proteins are made up of amino acids= protein synthesis)

Is the absorptive state anabolic or catabolic?

anabolic ( because is building big macromolecules for storage of energy and also using energy) (also building fat)

- Triglycerides(TGA) energy content:

are the most dense. they have 9 kilocalories per 1 gram.

post absorptive Dilemma:

post absorptive Dilemma: the glucose levels in blood must remain constant for the nervous system to function properly and glycogen stores will only last for a few hours, how do we survive between meals and through out the night? The liver can synthesize new glucose: gluconeogenesis. . liver makes the new glucose from breaking down triglycerides (TGA).

Amino acids:

will enter into the cells, in the form of amino acids. These amino acids can be: 1- Used to synthesize proteins (in translation) 2-used for energy (instantly) 3- Stored as proteins in skeletal muscle. (amino acids are the stored form of proteins ) -Proteolysis: Is the breakdown of proteins into amino acids. -During prolonged starvation, the body tissues can undergo proteolysis (atrophy(brake) of skeletal muscle) .Only as a last resort, the body will catabolized a significant amount of proteins.

-Glucose (CHO) energy content:

have 4 kilocalories pre 1 gram.

-Proteins energy content:

have 5 to 6 kilocalories per 1 gram.

what happens while in absorptive state:

while in absorptive state: - we are in positive energy balance. -during this period Glucose serves as primary energy substrate for all the cells. -during this period Fatty acids (FA), amino acids (AA), and excess glucose are stored as macromolecules by anabolic process. (glucose is converted into glycogen, Fatty acids converted into triglycerides, and amino acids into proteins) by the liver skeletal muscles and adipose tissue. -this process is anabolic

what happens to Fat after we eat it?

-Fat is transported through the blood as lipoproteins(since is fat, if can not travel in blood, so it need transporters), but will enter into the cells as fatty acids (FA). - Lipoprotein lipase (LPL) will convert TGA(triglycerides) into FA (fatty acids)+ monoglycerides in the capillaries (basically LPL enzyme brakes the triglyceride into monoglycerides and fatty acids). .After TGA are broken down by LPL: the FA will go into the cells and the Monoglycerides will remain in the blood and are metabolized (brake and used) by the liver.

Fat:

-Fat is transported through the blood as lipoproteins(since is fat, if can not travel in blood, so it need transporters), but will enter into the cells as fatty acids (FA). - Lipoprotein lipase (LPL) will convert TGA(triglycerides) into FA (fatty acids)+ monoglycerides in the capillaries (basically LPL enzyme brakes the triglyceride into monoglycerides and fatty acids). .Monoglycerides will remain in the blood and are metabolized (brake and used) by the liver. FA will enter into the cells. 3 fates (destinies) for fatty acids (FA) 1- used as energy by the cells (by all cells that are not part of the CNS) 2-Stored as TGA (triglycerides) in adipocytes(fat cells) for later usage. 3- When needed, the TGA will be broken into fatty acids (FA) and Glycerol which will be released into the blood.(then single amino acids can go into the cells of the body). Lipolysis: is the breakdown of Triglycerides (TGA) into fatty acids (FA). Lipogenesis: is the process by which fat is made from non-lipid nutrients (using excess carbohydrates is the most common way).(any excess of the 3 substrates for energy can be converted into fat)

Absorptive state metabolism: At Adipocytes (adipose tissue)

-It stores triglycerides (TGA) made from fatty acids (FA) (these triglycerides can come from VLDL and chylomicrons) -Excess glucose that enters the adipocytes is also converted into Triglycerides. the body can only store a limited amount of glucose and proteins, but it can store an almost unlimited supply of fat: - All nutrients in excess are converted into triglycerides. -20% to 30% of normal body weight is fat, but can be as high as 80%. -If we had to rely on glycogen stores, we would survive only a few hours (specially if we are exercising); but we can survive approximately 2 months in our fat stores.

what is metabolic rate modulated(regulated) by: (6things )

-Metabolic rate is modulated by: -Genetics -activity level -age -gender -body surface area -ambient temperature.

What is Metabolic Rate (MR)

-Metabolic rete: is the amount of energy expended per unit time. -Metabolic rate is modulated by: Genetics, activity level, age gender, body surface area, and ambient temperature. -Basal metabolic rate (BMR): is the energy expended by a person who has fasted for 12 hours and is awake, laying down, and is relaxed. .BMR is estimated by measuring the person's rate of oxygen utilization and c accounting for body weight. .Oxygen is always used to break down nutrients(substrates) .Why to account for body weight? because energy requirements are higher in larger subjects (they have more surface area and more tissue mass.) (Extra) formula to obtain the Basal metabolic rate: (Ml of O2 per hour)/(weight in kg )

how do we maintain energy balance?

-The endocrine system ensures that there is a steady supply of nutrients available to all cells; uninterrupted energy expenditure. -Energy comes from 2 sources: 1-eating 2-mobilization(breakdown) of energy stores.(this process is during the postabsorptive state, since all the energy stores are being braking down during this process)

why the glucose that is stored during absorptive state, is used only by the CNS ?

-because during the postabsorptive state the hormone that is active is glucagon. and in order for the cells of the body to use glucose they need insulin to induce the cell of the body to make glucose transporters in their plasma membrane(so that the glucose can go in through the glucose transporters). -The CNS cells have glucose transporters in their plasma membrane/ soma body/axon all the time; therefore the cells of the brain (CNS) can be doing glycolysis all the time( obtaining and using the glucose all the time). The cells of the body (which are not CNS cells) need insulin to be able to get the insulin into the cells. and as we know insulin hormone is active during the absorptive state only; therefore, during absorptive state all the cells of the body and CNS can have glucose, but during the postabsorptive state; only the CNS cells can.

postabsorptive state: at the adipocytes

-does lipolysis and release Fatty acids and glycerol into bloodstream. . then the Glycerol can be converted into glucose by the liver. .and The fatty acids can utilized by other tissues to spare(reserve) the glucose for the CNS.

postabsorptive state: at skeletal muscles

-glycogenolysis but can not release glucose; it releases pyruvate or lactate (lactate will go to the liver to be broken down further, so that it can be used as energy) -Proteolysis: it converts(brake) proteins into amino acids and will release these AA into the bloodstream (will only do this in small amounts, not enough to breakdown muscle)(it wont affect the muscle tissue, unless is for a prolonged time of starvation, then the muscle will brake a bunch of proteins as a last resource)

how is BMR estimated?

.BMR is estimated by measuring the person's rate of oxygen utilization and accounting for the person's body weight as well. .Oxygen is always used to break down nutrients(substrates) .Why to account for body weight? because energy requirements are higher in larger subjects (they have more surface area and more tissue mass.)

what modulates(regulates) insulin secretion? (4 things)

1- High levels of glucose in plasma blood will stimulate glucose secretion. . Glucose can stimulate insulin directly. 2-Plasma Amino acids concentration: high concentration of AA is in plasma blood, will stimulates insulin secretion. 3-Glucose-dependent insulinotropic peptide (GIP) which is secreted by the GI tract (GIP releases is triggered by food in the GI tract) it stimulates insulin secretion. 4- Parasympathetic drive will increase it, sympathetic drive will decrease it. (its just opposite to glucagon) (Parasympathetic drive= rest and digest, so it need insulin to digest the glucose and store the left over glucose)

6 Actions of insulin:

1- It promotes energy storage: storage of Fatty acids into triglycerides, Amino acids into proteins, and glucose into glycogen. 2-it opposes catabolic process: It inhibits the break down of energy stores and gluconeogenesis.(since gluconeogenesis means to break triglycerides to make new form of glucose) 3-it stimulates the uptake of Amino acids by most cells (except for the CNS, since the CNS only uses glucose and ketones, but no AA) 4-it stimulates the uptake of glucose by most cells by upregulating glucose transporters (transcription and translation of glucose transporters is enhanced) 5-It promotes growth; must be present for Growth hormone (GH) to be effective (is the permissive hormone). 6- It promotes protein synthesis, DNA synthesis, and cell division.

How can we obtain positive energy balance? (2 ways):

1- Take in more dietary energy 2- exercise less.( it just means food)

How can we obtain negative energy balance? (2 ways):

1- exercise (this increase the work produced and the heat released) 2- Take in less dietary energy.( it just means food)

3 types of cellular work that is done through the use of ATP (from energy from energy released from the breaking own of substrates):

1- mechanical work: generate movement. . Muscle contraction 2-Cheical work: formation of bonds during chemical reactions. .Conversion of glucose to glycogen. 3-Transport work: used to move a molecule across the plasma membrane. .Na+/K+ ATPase pumps .Endocytosis and exocytosis

3 fates (destinies) for fatty acids (FA):

1- used as energy by the cells (by all cells that are not part of the CNS since the CNS cell prefer glucose as fuel) 2-Stored as TGA (triglycerides) in adipocytes(fat cells) 3- When needed, the TGA will be broken into fatty acids (FA) and Glycerol which will be released into the blood.(then single amino acids can go into the cell of the body).

3 energy substrates of our diet (byproduct that is transported in the blood)

1-Carbohydrates, which is made up of many things but specially glucose (CHO) 2-Proteins, which which are made up of amino acids. (insulin mediates A.A intake into the cell) 3-Lipids, which will use lipoproteins to travel in the blood plasma. (lipids can be in the form of fatty acids or triglycerides; however lipids travel through the blood plasma in the form of fatty acids and use lipoproteins to travel)

how does the 3 energy substrates go into our system? (4 steps)

1-First, we ate the meal, 2-Then, the GI tract digest the food. 3-then, the nutrients(the 3 energy substrates) are absorbed by the epithelial cells of the GI tract and are transported into the blood. 4-Then, they are delivered to the tissues.

what modulates( regulates) Glucagon secretion? (4 things)

1-High levels of glucose in plasma blood will inhibit glucagon secretion. 2-Certain Amino acid levels: high levels of AA will stimulate glucagon secretion (THIS effect is the same as insulin) .It prevents the decrease in glucose levels following a meal that is low-carb(since low carb food, will release very little glucose). .high protein meals will protect the glucose supply to the brain.(, so we still need glucose to supply the body cells energy, since the protein its been reserve for the CNS) 3- Sympathetic drive will increase glucagon, and parasympathetic drive will inhibit glucagon. .Increases blood glucose levels to support fight or flight response (usually during fight or flight, we are not eating, that's why we need glucagon to release more glucose from glucose stores.) 4- glucagon is inhibited by somatostatin.

3 fates(destinies) for the 3 energy substrates:

1-They can be used as energy instantly. 2-They can be used to synthesize other molecules 3-They can be stored to use them later: .Ex: glucose is stored as glycogen, and fats are stored as triglycerides (TGA) (triglycerides are the storage form of fat) (these 3 fates happen during absorptive state)

4 actions of Glucagon:

1-it promotes Glycogenolysis (braking down of glycogen into glucose monomers) 2-It promotes Gluconeogenesis (breaking down triglycerides and form glucose. these glucose then can be used for energy.) 3-It promotes lipolysis. (breaking down lipids into fatty acids and glycerol. then the fatty acids can be converted by the liver into ketones for energy or just go into the cell as FA and be use for energy as well ,and the glycerol into glucose) 4- it opposes glycogenesis and protein synthesis. (because making glycogen and proteins would be in the absorptive state; when we are actually eating)

absorptive and postabsorptive states: absorptive state

Absorptive state: is from mealtime to 3-4 hours after meal, during this time nutrients are absorbed. -Fallowing the absorptive state, absorption will cease (stop) until the next meal. while in absorptive state: - we are in positive energy balance. -during this period Glucose serves as primary energy substrate for all the cells. -during this period Fatty acids (FA), amino acids (AA), and excess glucose are stored as macromolecules by anabolic process. (glucose is converted into glycogen, Fatty acids converted into triglycerides, and amino acids into proteins) by the liver skeletal muscles and adipose tissue. -this process is anabolic

Anabolic action (anabolism)

Convert nutrients into storage energy molecules following a meal. (extra) anabolism includes: -Glycolysis: break glucose, to be used as energy. -Glycogenesis: storing glucose in the form of glycogen. -Lipogenesis: the formation of triglycerides to storage fat. -protein synthesis: making proteins from amino acids (to storage AA) -Anything that is anabolic uses insulin .(insulin signal the cells to use glucose. .it also induces the cells of the liver and skeletal muscles to store glucose as glycogen. .it causes proteins to be manufactured from AA. It causes fat to be stored into triglycerides)

when nutrients are oxidized, energy becomes available for use:

Energy content: is how much energy is contained in a given substrate: - Triglycerides(TGA) energy content: are the most dense. they have 9 kilocalories per 1 gram. -Proteins energy content: have 5 to 6 kilocalories per 1 gram. -Glucose (CHO) energy content: have 4 kilocalories pre 1 gram. Energy intake: means, the total energy of all nutrients absorbed. (regardless of the amount of kilocalories; every kilocalories that are not used will be converted into fat)

is Glucagon secreted during absorptive state or postabsorptive state?

Glucagon secretion is stimulated during the postabsorptive state and is inhibited during the absorptive state. . Glucagon is secreted by the Alpha cells of the pancreas. . Glucagon is a catabolic hormone: it promotes the breakdown of energy stores into usable energy; it metabolizes energy sources.

Endocrine control during absorptive and postabsorptive states: Glucagon

Glucagon secretion is stimulated during the postabsorptive state and is inhibited during the absorptive state. . Glucagon is secreted by the Alpha cells of the pancreas. . Glucagon is a catabolic hormone: it promotes the breakdown of energy stores into usable energy; it metabolizes energy sources. 4 actions of Glucagon: 1-it promotes Glycogenolysis (braking down of glycogen into glucose monomers) 2-It promotes Gluconeogenesis (breaking down triglycerides and form glucose. these glucose then can be used for energy.) 3-It promotes lipolysis. (breaking down lipids into fatty acids and glycerol. then the fatty acids can be converted by the liver into ketones for energy or just go into the cell as FA and be use for energy as well ,and the glycerol into glucose) 4- it opposes glycogenesis and protein synthesis. (because making glycogen and proteins would be in the absorptive state; when we are actually eating)

glucose:

Glucose will enter into the cell through glucose transporters (which are specific receptors for glucose) -These 2 things can happen to glucose after it goes from the blood into the cells: 1-Glycolysis: which is the process of breaking down glucose to convert it into cellular energy (ATP).(to be used instantly) 2-Glycogenesis: which is the process of converting glucose into glycogen for storage (glycogenesis occurs primarily in the liver and skeletal muscle. glycogen can be used for energy later). Glucose terminology: -Glycolysis: is the process of breaking down glucose (for cellular energy (ATP)). -Glycogenesis: is the process of making glycogen from glucose molecules. -Glycogenolysis: The brake down of glycogen into glucose molecules. -Gluconeogenesis: Is the generation of NEW glucose from the liver, derived from non-carbohydrate sources, (which means making those glucose from fats and proteins but not from carbohydrates)

body weight

If the energy input and output are not balanced, we gain or loose weight; this means that we are NOT in energy balance. -Positive energy balance: energy is stored ( energy stores are growing) (probably getting fat) -Negative energy balance: energy stores are shrinking(breaking) (probably getting thin) -How can we obtain negative energy balance? (2 ways): 1- exercise (this increase the work produced and the heat released) 2- Take in less dietary energy.( it just means food) -How can we obtain positive energy balance? (2 ways): 1- Take in more dietary energy( it just means food) 2- exercise less.

positive energy balance vs negative energy balance:

If the energy input and output are not balanced, we gain or loose weight; this means that we are NOT in energy balance. -Positive energy balance: energy is stored ( energy stores are growing) (probably getting fat) -Negative energy balance: energy stores are shrinking(breaking) (probably getting thin)

Energy Balance Equation

Input + produced = utilization + output

Endocrine control during absorptive and postabsorptive states: Insulin

Insulin secretion is stimulated during absorptive state and inhibited during the postabsorptive state. .Insulin is an Anabolic hormone: promotes the synthesis of storage molecules. .Its secreted by the Beta cells of the pancreas. 6 Actions of insulin: 1- It promotes energy storage: storage of Fatty acids into triglycerides, Amino acids into proteins, and glucose into glycogen. 2-it opposes catabolic process: It inhibits the break down of energy stores and gluconeogenesis.(since gluconeogenesis means to break triglycerides to make new form of glucose) 3-it stimulates the uptake of Amino acids by most cells (except for the CNS, since the CNS only uses glucose and ketones, but no AA) 4-it stimulates the uptake of glucose by most cells by upregulating glucose transporters (transcription and translation of glucose transporters is enhanced) 5-It promotes growth; must be present for Growth hormone (GH) to be effective (is the permissive hormone). 6- It promotes protein synthesis, DNA synthesis, and cell division.

What is anabolism?

Is the synthesis of large molecules from smaller molecules, generally requires energy. (it causes building and storage of energy, always uses insulin) (think of it as a process that: signals cell to use glucose, to store glucose as glycogen, causes proteins to be manufactured, and causes fat to be stored.)

What is the postabsorptive state?

Is the time between meals, when nutrients are not being obtained.

Postabsorptive state metabolism

Postabsorptive state: Is the time between meals, when nutrients are not being obtained. While in Postabsorptive state: -we are in negative energy balance -energy stores are mobilized(broken-down to use them for energy) -glucose is reserved for CNS usage. other cells will utilize fatty acids. (from triglycerides) -this process is Catabolic. post absorptive Dilemma: the glucose levels in blood must remain constant for the nervous system to function properly and glycogen stores will only last for a few hours, how do we survive between meals and through out the night? The liver can synthesize new glucose: gluconeogenesis. . liver makes the new glucose from breaking down triglycerides (TGA).

what happens in the Postabsorptive state:

While in Postabsorptive state: -we are in negative energy balance -energy stores are mobilized(broken-down to use them for energy for the body cells and CNS cells) (the glucose for the CNS cells and the tatty acids and proteins for the rest of the cells) -glucose is reserved(put apart) for CNS usage. other cells will utilize fatty acids. (from triglycerides) -this process is Catabolic.

are Insulin and Glucagon antagonist hormones?

Yes. insulin and glucagon are antagonist hormones. -Whenever insulin secretion is stimulated, glucagon is inhibited. -Whenever insulin secretion is inhibited, glucagon is stimulated. -Both work together to maintain normal levels of blood glucose. (which is supposed to be 70-110 mg/dl) through negative feedback loops .

(extra) What is the difference between absorptive and postabsorption?

absorptive state is the state that digests foods and absorbs nutrients into our bloodstream while the postabsorptive state is the state in which the nutrient absorption does not occur, and the body relies on the energy reserves for energy.

Catabolic action (catabolism)

convert energy stores into usable energy.(brake down the storages of energy to be used) (extra) catabolic actions includes: -Glycogenolysis: break down glycogen into glucose. -Gluconeogenesis: making glucose from braking triglycerides or proteins but not from carbohydrates. -Lipolysis: break down triglycerides into amino acids. -Proteolysis: is break triglycerides into glycerol and fatty acids. -Anything that catabolic: is done through glucagon.

postabsorptive state: at CNS

does glycolysis in both states. absorptive state and post absorptive state.

what is the absorptive state?

is from mealtime to 3-4 hours after meal, during this time nutrients are absorbed.( this happens at the Gi track) -Fallowing the absorptive state, absorption will cease (stop) until the next meal.

Energy content:

is how much energy is contained in a given substrate:

What is Basal metabolic rate (BMR):

is the energy expended by a person who has fasted for 12 hours and is awake, laying down, and is relaxed. .BMR is estimated by measuring the person's rate of oxygen utilization and accounting for body weight as well. .Oxygen is always used to break down nutrients(substrates) .Why to account for body weight? because energy requirements are higher in larger subjects (they have more surface area and more tissue mass.)

Absorptive state metabolism: At the liver

liver: -does glycogenesis(storing glucose in the form of glycogen) (is is to be used by the brain in the future) -it can convert glucose into Fatty acids (FA) -it can convert the fatty acids into triglycerides (TGA)(Triglycerides are NOT stored in the liver. They are transported to adipose tissue for storage by very low density lipoproteins (VLDLs)) . VLDLs (very low density lipoproteins). .Fatty acids cannot be free in plasma. they require carriers to be or travel on plasma. . VLDL are degraded by lipoprotein lipase (LPL) and fatty acids enter into the cell . -Amino acids (AA) are used to synthesize proteins (plasma proteins, such as albumin)

Energy intake:

means, the total energy of all nutrients absorbed.

can catabolism and anabolism be on at the same time?

no ( one inhibits the other one. anabolism uses insulin and catabolism uses glucagon; glucagon and insulin are antagonists of each other and also of its effects.)

what does the body uses energy for??

the body can use the energy to do work or as heat: -60% of all calories consumed are utilized as heat to maintain the body temperature. -40% is used to synthesize ATP which is used to do cellular work. Whenever the body breaks down nutrients, it either releases energy as heat or uses this obtained energy to do work.

what does the body uses energy for?

the body can use the energy to do work or as heat: -60% of all calories consumed are utilized as heat to maintain the body temperature. -40% is used to synthesize ATP which is used to do cellular work. Whenever the body breaks down nutrients, it either releases energy as heat or uses this obtained energy to do work. 3 types of cellular work that is done through the use of ATP (from energy from energy released from the breaking own of substrates): 1- mechanical work: generate movement. . Muscle contraction 2-Cheical work: formation of bonds during chemical reactions. .Conversion of glucose to glycogen. 3-Transport work: used to move a molecule across the plasma membrane. .Na+/K+ ATPase pumps .Endocytosis and exocytosis

What is catabolism?

the breaking down of large molecules into smaller molecules, generally releasing energy (glucagon is on during this process)

What is the greatest dilemma in regards to metabolism?

the dilemma: is that the body requires a steady supply of energy, despite of the fact that we are not constantly obtain nutrients(we are not eating all the time) -The body must adapt to changes in eating habit:(ex: eating at different times of day, skipping meals some times, eating large amounts of food sometimes, etc). -The brain needs a constant supply of glucose as fuel so the body must maintain the blood glucose levels at a right point to be able to ensure proper brain function. .Glucose is the sole(only) fuel for the brain. except during prolonged starvation. The brain consumes about 120g (420 Kcal) per day. It is incapable of storing glucose, it also uses 60% of its glucose to maintain Na+ and K+ gradients(levels). -The body must expend energy continuously to remain alive. -The body must adapt to different physiological states: ex: growth, pregnancy, lactation, exercise, etc.

what regulates metabolism?

the whole body metabolism is primarily regulated by hormones.