INTEGUMENTARY SYSTEM

• The skin synthesizes vitamin D from a derivative of cholesterol
• The metabolic rate of the skin varies greatly, and depending upon ambient temperature.

NERVOUS SYSTEM

• The aerobic respiration of glucose serves most of the energy needs of the brain.
• Regions of the brain with a faster metabolic rate, resulting from increased brain activity, receive a more abundant blood supply than regions with a slower metabolic rate. This has been used to map brain function by giving subjects radioactively-labeled glucose and observing the glucose uptake with Positron Emission Tomography (however, this method has largely been replaced by functional MRI techniques--for more info see this article on neuroimaging)

ENDOCRINE SYSTEM

• Hormones that bind to receptors in the plasma membrane of their target cells activate enzymes in the target cell cytoplasm.
• Hormones that bind to nuclear receptors in their target cells alter the target cell metabolism by regulating gene expression.
• Hormonal secretions from adipose cells regulate hunger and metabolism
• Anabolism and catabolism are regulated by a number of hormones.
• Insulin stimulates the synthesis of glycogen and fat
• The adrenal hormones stimulate the breakdown of glycogen, fat, and protein.
• Thyroxine stimulates the production of a protein that uncouples oxidative phosphorylation. This helps to increase the body's metabolic rate.
• Growth hormone stimulates protein synthesis.

MUSCULAR SYSTEM

• The intensity of exercise that can be performed aerobically depends on a person's maximal oxygen uptake and lactate threshold.
• The body consumes extra oxygen for a period of time after exercise has ceased. This extra oxygen is used to repay the oxygen debt incurred during exercise.
• Glycogenolysis and gluconeogenesis by the live help to supply glucose for exercising muscles
• Trained athletes obtain a higher proportion of skeletal muscle energy from the aerobic respiration of fatty acids than do non-athletes.
• Muscle fatigue is associated with anaerobic respiration and the production of lactic acid.
• The proportion of energy derived from carbohydrates or lipids by exercising skeletal muscles depends on the intensity of the exercise.

CIRCULATORY SYSTEM

• Metabolic acidosis may result from excessive production of either ketone bodies or lactic acid.
• The metabolic rate of skeletal muscles determines the degree of blood vessel dilation, and thus the rate of blood flow to the organ.
• Atherosclerosis of coronary arteries can force a region of the heart to metabolize anaerobically and produce lactic acid. This is associated with angina pectoris.

RESPIRATORY SYSTEM

• Ventilation oxygenates the blood going to the cells for aerobic cell respiration and removes the carbon dioxide produced by the cells.
• Breathing is regulated primarily by the effects of carbon dioxide produced by aerobic cell respiration.

URINARY SYSTEM

• The kidneys eliminate urea and other waste products of metabolism from the blood plasma.

DIGESTIVE SYSTEM

• the liver contains enzymes needed for many metabolic reactions involved in regulating the blood glucose and lipid concentrations.
• The pancreas produces many enzymes needed for the digestion of food in the small intestine.
• The digestion and absorption of carbohydrates, lipids, and proteins provides the body with the substrates used in cell metabolism
• Vitamin A and D help to regulate metabolism through the activation of nuclear receptors, which bind to regions of DNA

REPRODUCTIVE SYSTEM

• The sperm do not contribute mitochondria to the fertilized oocyte.
• The endometrium contains glycogen that nourishes the developing embryo.

Glycolysis

Glycolysis refers to the conversion of glucose to two molecules of pyruvic acid.

• In the process, two molecules of ATP are consumed and four molecules of ATP are formed. Thus, there is a net gain of two ATP.
• In the steps of glycolysis, two pairs of hydrogens are released. Electrons from these hydrogens reduce two molecules of NAD.
• glycolysis can be considered the 1st step in anaerobic respiration.

When respiration is anaerobic, reduced NAD is oxidized by pyruvic acid, which accepts two hydrogen atoms and is thereby reduced to lactic acid.

• Skeletal muscles use anaerobic respiration and thus produce lactic acid during exercise. Heart muscle respires anaerobically for just a short time, under conditions of ischemia.
• Lactic acid can be converted to glucose in the liver by a process called gluconeogenesis.
• Liver makes and stores glycogen as well as the skeletal muscles.glucigon stimulates breakdown of glycogen.
• when your body needs more energy the skeletal muscles make the glycogen.
• NOTE: The liver release glucose into the bloodstream by breaking down glycogen.The skeletal muscles cannot due to the lack of enzyme to remove phosphate from the glucose (a phosphorylated molecule cannot get through the cell membrane, so even one muscle cell cannot share glucose with a muscle cell next to it).

Glycolysis and the Lactic Acid Pathway
In cellular respiration, energy is released by the stepwise breakdown of glucose and other molecules, and some of this energy is used to produce ATP. The complete combustion of glucose requires the presence of oxygen and yields thirty ATP for each molecule of glucose. However, some energy can be obtained in the absence of oxygen by the pathway that leads to the production of lactic acid. This process results in a net gain of two ATP per glucose.


The expression "lactic acid" is used most commonly by athletes to describe the intense pain felt during exhaustive exercise, especially in events like the 400 metres and 800 metres. When energy is required to perform exercise, it is supplied from the breakdown of Adenosine Triphosphate (ATP). The body has a limited store of about 85 grms of ATP and would use it up very quickly if we did not have ways of resynthesising it. There are three systems used to resynthesise ATP: ATP-PC, lactic acid and aerobic.

• All of the reactions in the body that involve energy transformation are collectively termed metabolism.
  • Metabolism may be divided into two categories: anabolism and catabolism.
  • Catabolic reactions release energy, usually by the breakdown of larger organic molecules into smaller molecules.
    • The catabolic reactions that break down glucose, fatty acids, and amino acids serve as the primary sources of energy for the synthesis of ATP.
  • Anabolic reactions require the input of energy and include the synthesis of large energy-storage molecules, including glycogen, fat, and protein.
• When a molecule is completely broken down to carbon dioxide and water within a cell, the final electron acceptor is always an atom of oxygen. Because of the involvement of oxygen, the metabolic pathway that converts molecules such as glucose or fatty acid to carbon dioxide and water (transferring some of the energy to ATP) is called aerobic cell respiration.
• The breakdown of glucose for energy begins with a metabolic pathway in the cytoplasm known as Glycolysis. (glykys = sweet and lysis = loosening) Glycolysis is the metabolic pathway by which glucose is converted into two molecules of pyruvic acid, or pyruvate.
• The metabolic pathway by which glucose is converted to lactic acid is frequently referred to as anaerobic respiration. The term anaerobic means that oxygen is not used in the process.
  • Red blood cells, which lack mitochondria, can use only the lactic acid pathway; therefore they cannot use oxygen. This spares the oxygen they carry for delivery to other cells.

Aerobic Respiration
Aerobic respiration requires oxygen in order to generate energy (ATP). It is the preferred method of pyruvate breakdown from glycolysis and requires that pyruvate enter the mitochondrion to be fully oxidized by the Krebs cycle. The product of this process is energy in the form of ATP.



Glycogenesis
Glycogenesis is the process of glycogen synthesis, in which glucose molecules are added to chains of glycogen. This process is activated by insulin in response to high glucose levels, for example after a carbohydrate containing meal.

• Glucose is converted into Glucose-6-Phosphate by the action of Glucokinase or Hexokinase.
• Glucose-6-Phosphate is converted into Glucose-1-Phosphate by the action of Phosphoglucomutase, passing through an obligatory intermediate step of Glucose-1,6-Phosphate.
• Glucose-1-Phosphate is converted into UDP-glucose by the action of Uridyl Trasnferase (also called UDP-glucose pyrophosphorylase) and Pyrophosphate is formed, which is converted by pyrophosphatase into 2 molecules of Pi.
• Glucose molecules are collected in a chain by Glycogen synthase, which must act on a pre-existing glycogen primer or glycogenin (small protein that forms the primer).
• Branches are made by Branching enzyme which transfers the end of the chain onto an earlier part via alpha-1:6 glucosidic bond, forming branches, which further grow by addition of more alpha-1:4 glucosidic units

CORI CYCLE
When muscles require energy for short duration or strenuous movements, muscle cells default to anaerobic glycolysis to quickly produce abundant amounts of ATP. The byproduct of anaerobic glycolysis, lactate, diffuses into the blood and is taken up by the liver, where it is converted back into pyruvate by the enzyme lactate dehydrogenase. Pyruvate is then converted back into glucose via gluconeogenesis. The newly formed glucose is released into the blood to be used once again for energy by the red blood cells and muscle.



image: how the cori cycle works in the body.


Krebs Cycle
The first reaction uses an enzyme to remove the acetyl from Acetyl Co-A. This new two carbon molecule can now bond with a four carbon molecule called oxalacetate. This new molecule has six carbons and is called citrate. An isometric conversion takes place and isocitrate forms. From there CO2 is released and NAD picks up a H+ ion. Now the isocitrate has become ketoglutarate. Another CO2 is released from the ketoglutarate, this frees an H+ ion which bonds with a NAD ion making another NADH. The Co-A is now replaced with a phosphate from the matrix now forming Succinyl Co-A and an ADP is bonded with a phosphate to make ATP creating succinate. FAD comes in and takes a H+ ion and becomes FADH2. In doing so succinate turns into Fumarate. Now H20 is added to Fumarate to form Malate. Now another NAD is reduced and Oxalacetate if reformed! The cycle is now ready to be repeated.





Electron Transport Chain
Reduced NAD and FAD donate their electrons to an electron-transport chain of molecules. Each element in the chain becomes oxidized as it donates electrons to the next piece of the chain. This creates the energy for ATP. In the end electrons are given to oxygen which is then reduced to water when two hydrogen atoms are added.



Metabolism Of Lipids and Proteins
I. In lipolysis, triglycerides yield glycerol and fatty acids.
a.Glycerol can be converted to phosphoglyceraldehyde and used for energy.
b. In the process of beta-oxidation of fatty acids, a number of acetyl CoA molecules are produces.
c. processes that operate in the reverse direction can convert glucose to triglycerides.

II. Amino acids derived from the hydrolysis of proteins can serve as sources of energy.
a. through transmination, a particular amino acid (pyruvic acid or one of the Krebs Cycle acids) can serve as substrates to for a new amino acid and a new keto acid.
+it will not change the shape or quality of the enzyme so that it can be recycled and used again.
b. in oxidative deamination, amino acids are converted into keto acids as their amino group is incorporated into urea.

III. Each organ uses certain blood-borne energy carriers as its preferred energy source.
a. the brain has an almost absolute requirement for blood glucose as its energy source.
b. during exercise, the needs of skeletal muscles for blood glucose can be met by glycogenolysis and by gluconeogenesis in the liver.





Uses of different energy sources- all cells in the body could not use the same energy source (for example, glucose) because that energy type would deplete quickly and would result in cellular starvation. Different types of energy sources include glucose, ketone bodies, fatty acids, lactic acid, and amino acids. Even if glucose is the preferred energy source of many organs, these organs will spare glucose in times of fasting and use fatty acids, ketone bodies and lactic acid.

Ketone Bodies are derivatives of fatty acids converted by the liver. A rapid breakdown of fat results in elevated levels of ketone bodies in the blood. This could be due to strict low carbohydrate diets and in uncontrolled diabetes mellitus. The high levels of ketone bodies in the blood is called ketosis. If there are sufficient amounts of ketone bodies in the blood to lower the blood pH, the condition is called ketoacidosis which when severe enough can lead to coma and death.





REVIEW QUESTIONS

1. Ketone bodies are derived from ______.
a. fatty acids
b. glycerol
c. glucose
d. amino acids


2. The conversion of lactic acid to pyruvic acid occurs__________.
a. in anaerobic respiration.
b. in the heart, where lactic acid is aerobically respired.
c. in the liver, where lactic acid can be converted to glucose.
d. in both a and b
e. in both b and c

3. All of the following are formed as a result of the electron-transport chain except:
a. carbon dioxide
b. oxidized NAD
c. water
d. ATP

4. When glucose is catabolized under aerobic conditions, ________ will cross the mitochondrial wall and enter the Krebs cycle.
a. carbon dioxide
b.pyruvate
c. lactate
d. acetyl CoA

5. Anaerobic metabolism of glucose results in an oxygen debt that is the amount of oxygen needed to metabolize the ______ that is produced.
a. carbon dioxide
b. lactic acid
c. glycogen
d. fatty acid

6.Which of the following statements describes the role of the electron transport chain?


8. What percent of Glucose Energy forms ATP bonds?
a. 20%
b. 30%
c. 40%
d. 50%

9. After glycolysis takes place in the cell's cytoplasm, the pyruvic acid molecules travel into the interior of the mitochondrion. Once the pyruvic acid is inside, ___________ is enzymatically removed from each three-carbon pyruvic acid molecule to form acetic acid.
a. oxygen
b. water
c. carbon dioxide
d. ATP

10. The term _________ state is often used to describe the balance of NAD+/NADH and NADP+/NADPH in a biological system such as a cell or organ.
a. oxidation
b. redox
c. anaerobic
d. metabolic

11. How many ATP molecules are produced from one glucose molecule if it went through the whole cellular respiration cycle? (glycolysis, Krebs cycle , and the electron transport chain)
a. 2
b. 12
c. 36
d. 46

12. What organic molecule has to be present in order to to go through the Krebs Cycle and Electron Transport Chain?
a. protein
b. oxygen
c. carbon dioxide
d. sodium

13. At the end of the electron transport chain oxygen accepts the electron and what is produced?
a. hydrogen
b. glucose
c. ATP
d. Water

14. The Cori Cycle is an exchange between what two parts of the body?
a. heart and lungs
b. skeletal muscle and liver
c.brain and kidney
d.heart and stomach

15. What is the difference between oxidation and reduction?
a.oxidation gives ATP reduction takes ATP away.
b. oxidation uses white blood cells and reduction red blood cells.
c. oxidation describes the lost of electrons and reduction described the gain of electrons.
d. none of these above.

16.Aerobic respiration of glucose serves most of the energy needs of the:
a. brain
b. heart
c. hypothalamus
d. lungs
e. bones

17. When skeletal muscles lack sufficient oxygen, there is an increased blood concentration of ____________.
a. pyruvic acid.
b. lactic acid.
c. ATP.
d. glucose.