What are macronutrients and micronutrients?

Macronutrients are the body’s major fuel sources used to provide energy, and the raw materials to sustain, grow, and repair the body’s operating systems and infrastructure. The macronutrients consist of proteins, fats, and carbohydrates. Each macronutrient has specific roles and functions that help the body operate at, or near, optimal capacity. Carbohydrates serve four major roles. These roles include central nervous system fuel, primer for metabolism, sparing protein, and an energy source for the body (McArdle, Katch, & Katch, 2016).

Fats also serve four major roles. These roles include suppressing hunger, protection of vital organs and promoting thermal insulation, providing a transportation mechanism for fat soluble vitamins, and acting as a reserve source of energy. Proteins provide important support to the hormonal, transport, metabolic, and tissue synthesis and systems. Proteins provide amino acids, and contribute to cellular, muscular, skeletal, and numerous other internal systems. Together, the three macronutrients provide the body with all of its important needs, in order to operate in a healthy state (McArdle, Katch, & Katch, 2016).

Micronutrients consist of thirteen vitamins and twenty two minerals. Vitamins are categorized into water soluble and fat soluble groups. Each vitamin has specific functions, and all help to maintain the optimal physiological operations of the body. Minerals assist with cellular metabolism, bone and teeth formation, balancing acidity levels, neural functioning, muscle contractions, and heart rhythm (Ahmed, Ali, Islam, Hoque, Hasnat, & Nahar, 2016).

Minerals also assist in the operations of the immune system and other biochemical functions of the body. Both vitamins and minerals assist with antioxidant defense against free radicals and oxidative threats. Together, vitamins and minerals provide a wide variety of essential functions, for all major biological operations and systems of the body (Ahmed, Ali, Islam, Hoque, Hasnat, & Nahar, 2016).

Proteins, fats, and carbohydrates provide many important functions in the body, especially during exercise. Proteins are important for building lean body mass, which includes muscle tissue, connective tissue, and healthy bones. Proteins also help facilitate fat loss, or the loss of fat mass. In emergencies, proteins can be broken down to provide more glycogen to the body. Carbohydrates are the body’s main fuel source during exercise. When carbohydrate levels are sufficient, protein is spared during exercise (Helms, Zinn, Rowlands, & Brown, 2014).

When the body goes through the anaerobic phase, and begins the aerobic phase of exercise, after about two minutes, the carbohydrates become the main fuel. When glycogen stores begin declining after prolonged exercise, fatty acids are broken down into glycogen to sustain the body’s fuel needs. In dire cases of glycogen depletion, fats can break down into ketones to provide fuel. The three macronutrients work in concert to keep the body fueled and strong, throughout whatever stressors that one may face (Helms, Zinn, Rowlands, & Brown, 2014).

Vitamins and minerals are the micronutrients that support numerous chemical, biological, physiological, and metabolic actions, and systems within the body. During exercise the micronutrients play key roles in assisting with the break down and utilization of the macronutrients to provide fuel, and energy. They also assist with defense against free radical damage, muscular contractions, and thermoregulation. Micronutrients are extremely important during all catabolic and anabolic functions of the body. Not only do they provide vital functions in maintaining general health, they are critical components in numerous physiological activities during exercise (Pingitore, Pace, Lima, Mastorci, Quinones, Iervasi, & Vassalle, 2015).

References:

Ahmed, S., Ali, R., Islam, R., Hoque, A., Hasnat, A., & Nahar, Z. (2016). Effect of serum trace elements, macro-minerals and antioxidants in acne vulgaris patients: A case control study. Dhaka University Journal of Pharmaceutical Sciences. Retrieved from https://www.banglajol.info/index.php/JPharma/article/view/30940/20855

Helms, E., Zinn, C., Rowlands, D., & Brown, S. (2014). A systematic review of dietary protein during caloric restriction in resistance trained lean athletes: A case for higher intakes. International Journal of Sport Nutrition and Exercise Metabolism. Retrieved from http://journals.humankinetics.com/doi/abs/10.1123/ijsnem.2013-0054

McArdle, W.D., Katch, F.I., & Katch, V.L. (2016). Essentials of exercise physiology (5th ed.). Philadelphia: Wolters Kluwer.

Pingitore, A., Pace, G., Lima, P., Mastorci, F., Quinones, A., Iervasi, G., & Vassalle, C. (2015). Exercise and oxidative stress: Potential effects of antioxidant dietary strategies in sports. Elsevier Nutrition Journal. Retrieved from http://www.sciencedirect.com/science/article/pii/S0899900715000738

Eric Dempsey

MS, NASM Fitness Nutrition Specialist

Dempseys Resolution Fitness

The sliding filament theory and muscular contraction

Muscular contraction begins with the nervous system sending a stimulus to the muscle fibers. This stimulus occurs at the neuromuscular junction. There is one neuromuscular junction for each muscle fiber. The neuromuscular junction contains structures that include the axon terminal of the neuron, the motor endplate, and the synaptic cleft, or neuromuscular cleft. From this point, the actions of the sliding filament theory begin. The actin and myosin filaments slide past each other, causing the muscle to shorten or lengthen. The filaments do not change in length during this action. Excitatory neurotransmitter acetylcholine (ACh), is released at the neuromuscular junction, after an action potential passes along the length of a neuron. ACh is released into the synaptic cleft between the axon terminal of the neuron and the muscle fiber. This occurs in direct response to the action potential (Coburn & Malek, 2012).

From that point, the Ach binds with ACh receptors, on the motor endplate of the muscle fiber. This occurs after the Ach moves across the synaptic cleft. This causes another action potential to be created. This new action potential moves along the sarcolemma of the muscle fiber. T-tubules are utilized by this action potential to travel to the interior of the muscle fiber. This movement causes the release of stored calcium from the sarcoplasmic reticulum. The calcium is released into the sarcoplasm. Once in the sarcoplasm, the calcium moves to the troponin molecules. The calcium then binds with the troponin molecules. These the troponin molecules are located along the length of the actin filaments. The shape of the troponin changes after the calcium binds to it. Tropomyosin is attached to the troponin. This change in shape causes the tropomyosin to expose the binding sites on actin, to the myosin head (Krans, 2010).

The exposed binding sites on the actin are able to attach to the myosin, forming a cross bridge. This myosin head of attachment pulls the actin filament toward the center of the sarcomere. The effort of the myosin pulling on the actin depletes the energy of the myosin. The depleted myosin must then detach from the cross bridge and reenergize itself. This requires a new adenosine triphosphate (ATP) molecule to be bound to the myosin. Once the ATP molecule is bound to the myosin, it can then detach and energize itself. The energizing of the myosin comes from the enzyme myosin adenosine triphosphatase (ATPase). The ATPase splits the ATP molecule. This energizes the myosin and allows for the cross bridge sequence to occur again. This sequence can continue as long as the muscle fiber is being stimulated to contract, by its motor neuron. The myosin pulling the actin toward the center of the sarcomere shortens the muscle. This process is the muscle contracting. The success or failure of this sequence is determined the external forces pulling against the cross bridge (Szent-Györgyi, 2004).

There are three basic types of contractions that can occur when the sliding filament theory is activated. Muscle contractions are usually pulling against an external force such as a barbell. When the myosin is pulling the actin through the cross bridge, the resistance determines the outcome. The contraction generates more force than the resistance, causing a concentric contraction. The external force is greater than the contraction force, causing a lengthening of the muscle. This is an eccentric contraction. The contraction force is equal to the resistance force, which stalls movement. This is an isometric contraction. The muscle will always attempt to shorten as the myosin pulls on the actin. The resistance level will cause one of the three types of contractions to occur. ATP is the primary fuel source for this sequence (Lefkowith, 2014).

References:

Coburn, J.W., & Malek, M.H. (2012). NSCA’s essentials of personal training (2nd ed.). Champaign, IL: Human Kinetics.

Krans, J. (2010). The sliding filament theory of muscle contraction. Nature Education. Retrieved from http://www.nature.com/scitable/topicpage/the-sliding-filament-theory-of-muscle-contraction-14567666

Lefkowith, C. (2014). What does it all mean: Concentric, eccentric and isometric. Redefining Strength. Retrieved from https://redefiningstrength.com/mean-concentric-eccentric-isometric/

Szent-Györgyi, A. (2004). The early history of the biochemistry of muscle contraction. The Journal of General Physiology. Retrieved from http://jgp.rupress.org/content/123/6/631

Eric Dempsey

MS, ISSA Master Trainer

Dempseys Resolution Fitness

The Difference Between an Endocrine Gland and an Exocrine Gland

There are numerous differences between an endocrine gland and an exocrine gland. To summarize the main differences between the two types of glands in a general sense, the terms internal and external come to mind. Endocrine glands secrete hormones into the body’s internal environment to cause a specific action to occur. Exocrine glands release secretions that follow pathways that lead to external areas (Shier, Butler, & Lewis, 2016).

Endocrine glands secrete hormones into the bloodstream to travel to distant, internal areas and cause specific actions that affect the body’s metabolism and many other processes. Some examples of major endocrine glands include the thyroid, hypothalamus, pituitary, adrenal, testes and ovary. Each endocrine gland secretes specific hormones to effect certain actions within the body. The hormones travel through the bloodstream until they reach their designated target cells to initiate the desired action or effect. An example of a specific action would be the thyroid gland secreting T3 and T4 hormones into the blood stream. These hormones travel through the bloodstream to their target cells. The desired action that results can include enhancing the speed of protein synthesis, lipid breakdown or cellular energy release from carbohydrates (Briers, 2012).

Exocrine glands produce secretions that travel through tubes or ducts to external regions of the body to cause specific effects. Examples of some of the major exocrine glands include sweat, mammary, salivary, tear and mucous. An example of a exocrine gland in action would be the salivary glands which produce saliva in the mouth, to aid in digestion, help prevent bacteria buildup and tooth decay and to enhance the ability to swallow. Another example would be sweat glands secreting sweat droplets on the skin’s surface, to aid in temperature regulation (Crampton, 2016).

While most of the endocrine and exocrine glands have very different, unique roles and functions, there are some glands that pull double duty as a combination of both types of glands. The pancreas produces enzymes which aid in digestion as an exocrine function, while also secreting insulin into the bloodstream, to aid in controlling blood glucose levels, which is an endocrine function. The liver also has a multifaceted capability, in that it produces bile in an exocrine manner, but also secretes plasma proteins into the bloodstream as an endocrine function. These diverse glands have important and amazing roles, in assisting with keeping the human body functioning properly (Davis, 2016).

References:

Shier, D., Butler, J., & Lewis, R. (2016). Hole’s human anatomy and physiology (14th ed.). New York, NY: McGraw-Hill.

Briers, D. (2012). The Difference Between Endocrine and Exocrine Glands. DBriers. Retrieved from http://www.dbriers.com/tutorials/2012/08/the-difference-between-endocrine-and-exocrine-glands/

Davis, K. (2016). Exocrine Pancreatic Insufficiency: What You Need to Know. MNT. Retrieved from http://www.medicalnewstoday.com/articles/310292.php.

Crampton, L. (2016). Interesting Facts about Saliva and Salivary Glands. Owlcation. Retrieved from https://owlcation.com/stem/Interesting-Facts-About-Saliva-and-Salivary-Glands

Photo Credit: http://www.slideshare.net/LadyRixi/endocrine-glands-22547640

Eric Dempsey

MS, ISSA Master Trainer

Dempseys Resolution Fitness