Digestion at the Cellular and Molecular Level

When the term digestion is mentioned, it is natural to think about the actions of the mouth, stomach, and small intestine in the processing of food for energy. While these actions are no doubt important in the breakdown of food, they actually are the result of complex processing mechanisms at the cellular level. This chapter will examine the physiology of the digestive system at the organ level. However, to effectively understand the structure and function of the digestive system, we must first understand the cellular and molecular basis of nutrient processing.

The purpose of digestion is to process food by breaking the chemical bonds that hold the nutrients together. This is necessary so that the body has an adequate source of energy for daily activity, as well as materials for the construction of new cells and tissues. Since these nutrients arrive in the digestive system as the tissues of previously living organisms, they are rarely in the precise molecular structure needed by a human body. For example, the blood of cows and chickens has evolved over time to meet the precise metabolic needs of the organism. When the tissues of these animals are consumed, our bodies must chemically alter the proteins and other nutrients found in the animal’s blood to form human blood proteins such as hemoglobin.

As is the case with almost all the nutrients (with the exception of water, minerals, and some vitamins), the body breaks down the nutrient into its fundamental building blocks, transports the digested nutrient into circulatory and lymphatic systems, and eventually uses these nutrients in the cells of the body for either energy or metabolic processes.

Cardiac Muscle

The heart is made out of cardiac muscle (also known as myocardium), a tissue that is unlike the smooth or striated muscle seen elsewhere in the human body. Striated muscle is the tissue that a person uses to move his or her legs or fingers. Because the individual can control it, it is also known as voluntary muscle.

This tissue has light and dark bands, called striations, which give skel etal muscle yet another name: striated muscle. Smooth muscle, like that in blood vessels, is known as involuntary muscle, because a person cannot direct its movements like he or she can control skeletal muscle. Instead, the autonomic nervous system controls its action.

Falling somewhere in the middle of these two types of tissue is cardiac muscle. Cardiac muscle has the striations seen in skeletal muscle, but it takes its direction from the autonomic nervous system like the smooth muscle does. Unlike either stri ated (also known as skeletal) or smooth muscle, cardiac muscle cells are very closely linked to one another and have fibers that interconnect one cell to the next. As will be shown in the section on electrical activity later in this chapter, this is vital in making the heart beat as a unit. In addition, cardiac muscle does not tire out like skeletal muscle does, and it requires a shorter resting time between contractions. It is easy to assume that skeletal muscle can contract for a very long time, especially when considering how a body maintains muscle tone. A closer look reveals that different groups of skeletal muscle alternately shorten to give the appearance of constant contraction, even when the muscle cells are individually contracting and relaxing. In the heart, conversely, all of the cardiac cells contract at the same time.

Capillary System

Although the capillaries are the smallest vessels in the circulatory system, they represent the main exchange site between the blood and the tissues. They can be viewed as both the ultimate destination of the arterial system and the starting point of the venous system. From the heart, blood travels through the arteries to the arterioles, and then to the capilla ries, where exchange occurs.

Nutrients, oxygen, and other materials carried by the blood are traded for waste products from tissue cells. Blood contin ues down the capillaries, soon entering the venules and then the veins on its return trip to the heart.



Comprised of building blocks known as amino acids, proteins contain car bon, hydrogen, oxygen, nitrogen, and sometimes sulfur. One of the most important functions of proteins is their role as enzymes or catalysts. Enzymes accelerate chemical reactions in the body without additional energy, such as heat.

There are specific enzymes for specific reactions. The digestive system provides some excellent examples. The enzymes that react to digest starches are different from those that digest lipids in food.

Because there are many thousands of different chemical reactions going on in the body at one time, there are many thousands of different enzymes.


Oxygen and Carbon Dioxide in body

We are continuously inhaling the gas known as oxygen-without it, we would die. Oxygen plays a vital role in breaking down nutrients such as glucose that need to be transported to various locations to provide the body with energy. This process is known as cell respiration.

The energy produced through cell respiration is contained in a molecule that is called ATP, which stands for adenosine triphosphate. ATP can be thought of as the fuel required for various cellular processes to occur throughout the body.

In addition to producing ATP, cell respiration also produces carbon dioxide. So while oxygen is inhaled, carbon dioxide is exhaled, and is con sidered a waste product. It is exhaled because it is a waste product of cell respiration. Like other waste products that are covered throughout this book, carbon dioxide must leave the body. If carbon dioxide builds up in the body, it can disrupt the chemical balance in the body. This can cause acidosis, when fluid becomes too acidic, which can result in calcium deposits in the body’s soft tissue. Carbon dioxide buildup in the body is toxic to the heart.


Water in body

Water, which scientists estimate comprises approximately 60 to 75 percent of the human body, is important for three primary reasons: it acts as a solvent, it acts as a lubricant, and because it changes temperature slowly, it is vital in regulating the body’s temperature. The first reason because it is a solvent-means that many substances can dissolve in it, which allows nutrients and other vital components to be transported throughout the body. This is because the body’s main transportation systems, blood, are largely composed of water.

Therefore, substances like glucose (which comes from food) that are needed for energy in the body can be dissolved in the blood and then delivered to the heart and cells. Another important function is the elimination of waste. Materials that the body does not need, called waste products, are dissolved in the water component of urine and then flushed out of the body through the urinary system.

In addition to acting as a solvent, water is a lubricant, which means it prevents friction between the various surfaces inside the body, such as bones and blood vessels. One example of water acting as a lubricant is in the diges tive system. One of the fluids present in this system is the fluid mucus, which, like blood, is primarily made up of water. Mucus enables food to move through the intestines and be digested, providing the body with fuel.

The third function of water in the body is that of a temperature regulator. The temperature of water does not change quickly-it has to absorb a lot of heat or lose a lot of heat before the temperature increases or drops. This property enables the body to stay at a fairly constant temperature. In addition, water does an important cooling job for the body in the form of perspiration. When the body is absorbing an excess amount of heat, sweat forms on the skin, which allows the heat to escape the body without damaging any cells.


Short series – 7 The Reproductive System

The Reproductive System: The role of this system is to carry out the process of sexual reproduction, which is necessary to continue the human species that contains genetic information that determines a person’s physical characteristics, but also their resistance to certain mutations also ensures the future of the species.

This system is unique because there are distinct sets of organs for females and males. In addition, there are internal and external organs in the male and female, with the internal organs located inside the body and external organs located outside the body. Some examples of the internal female reproductive system include the cervix, vagina, and fallopian tubes; external organs include the mammary glands or breasts. For males, internal organs include the ejaculatory ducts and urethra; external organs include the penis and testicles.





10 Characteristics of a Mentally Strong Person

We all face times in our lives where our emotional endurance is put to the test. A poisonous friend or colleague, a dead-end career, or a strained friendship are all possibilities. Whatever the challenge, you must be strong, see it from a different perspective, and take decisive steps if you are to overcome it. It appears to be easy. Good friends, good work, and good relationships are all things we want.

But it isn’t.

Mentally healthy people aren’t born with the emotional muscles they need to confront their anxiety, overcome self-doubt, and take constructive steps. Through dedicated practice, they learned the skills that help them control their emotions, feelings, and behaviour.

It’s difficult to be physically tough when you’re trapped. Only the most emotionally strong people possess the extra grit, daring, and spunk needed to crack the mould and lead a brave new path. Building mental strength takes a lot of hard work and commitment, but it’s the key to your greatest potential. All of our life experiences make us stronger and better people.

Mentally strong people have good routines. They can control their desires, feelings, and actions in ways that position them for life success. Being optimistic, taking control of your own life and not feeling sorry for the situations we can not control are some of the characteristics that mentally strong people possess.

  • They embrace change:
    A mentally strong person is flexible and adaptive. They know that the fear of change is one of the major threat to their success and happiness. They look for change that is hiding just around the corner, and they form a plan of action for changes when they occur.

  • They focus on things they can control:
    If you are mentally strong, you try to stay productive and effective by focusing on the things you have control over. Instead of wasting energy on worrying about the difficult times, you invest your efforts into preparing for it the best you can.

  • They set healthy boundaries for themselves:
    If you need to grow, you need to create a healthy emotional and physical environment for yourself. A mentally strong person doesn’t want anyone to go over the boundaries they’ve developed, and they respectfully but firmly inform people of those boundaries.

  • They learn from their mistakes:
    Mentally healthy people don’t try to hide their mistakes or justify their actions. They learn from their mistakes and become a better version of themselves.

  • They see difficulties as opportunities:
    Every obstacle and every problem you face is an opportunity for you to grow. People usually get annoyed by difficult situations, but mentally strong people accept those challenges and become better.

  • They don’t let anyone limit their joy…
    You are no longer the master of your happiness if your sense of joy and fulfilment comes from comparing yourself to others. When emotionally tough people are proud of what they do, they will not allow others’ views or successes to diminish their pride.

  • …they don’t limit the joy of others:
    Mentally tough people don’t judge others and understand that everyone has something valuable to contribute, and they don’t need to put others down to feel good for themselves.

  • They try to improve their skills instead of showing them off:
    People, in general, want acceptance from others. Mentally strong people, on the other hand, focus on improving their skills rather than attracting attention.

  • They don’t please everyone:
    Mentally strong individuals understand that they should not have to appease them all of the time. They aren’t afraid to say no or speak up when something isn’t working. They make an effort to be kind and truthful, but they are also capable of dealing with other people’s dissatisfaction if they are unable to make them happy.

  • They don’t dwell on the past:
    Mentally strong people do not spend time reminiscing or longing for things to be different. They are aware of their experience and can articulate what they have learned from it. They don’t, though, endlessly relive painful memories or fantasise about happier times. Rather, they live in the moment and make plans for the future.

Mental endurance is not a natural trait that only a few people possess. It is possible to attain and love. Everyone has a level of mental toughness, and there’s still space for growth.

What else does it take to make a person mentally tough? How many of these 10 characteristics apply to you?





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Short series – 6 The Respiratory System

The Respiratory System: The primary organs are located in two areas: the upper and lower respiratory tracts. The upper tract contains the nose and nasal cavity (also known as the nasal passage), the pharynx (or throat), and the larynx (or voice box).

The lower respiratory tract contains the trachea (windpipe), the bronchi, the alveoli, and the lungs. This system’s major responsibility is to control and regulate the breathing process, which involves moving air into and out of the lungs.


Short series – 5 The Nervous System

The Nervous System: The primary organs of the nervous system are the brain and spinal cord. Through the nervous system’s two divisions, the central nervous system (CNS) and the peripheral nervous system (PNS), stimuli and other information is processed into the form of reaction and activity.

In addition to the endocrine system, the nervous system is known as one of the body’s key communication centers. This communication is done through nerve impulses that travel through the body’s nerve fiber system.