LEVELS OF ORGANIZATION IN THE HUMAN BODY

The principal systems of the human body interact with each other to create what is known as the training effect. These principal systems are part of an intricate, multi–level organizational structure. The simplest level is the chemical level. The smallest amount of a chemical element is the atom. Atoms can combine to form molecules. About 98 percent of the human body is composed of only six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorous. The next level is the cellular level. Atoms and molecules bind to form the building blocks of the body. Each cell consists of specialized cell parts called organelles. The nucleus, which is the control center of the cell, is an organelle. The next level of organization is the tissue level. A tissue is a group of closely related cells specialized to perform a specific function. The four main tissues in the body are muscle tissue, nervous tissue, connective tissue, and epithelial tissue. These tissues are then organized into organs such as the heart or brain. The organs and tissues work together to perform specific functions of the body’s systems. These body systems make up the human body.

tissue: A collection of similar cells and their intracellular substances.

CELLS

Just as every molecule has building blocks, so do tissues and structures. Cells form the fundamental units of life. Together they somehow organize themselves into the human body. The human body is composed of an estimated 100 trillion cells of various forms and functions. Striated muscle cells can be several inches long and have the unique ability to shorten in length, thereby causing muscle contractions. Fat cells are small and round in shape and function to store fatty acids for energy needs during lean times.

Another magnificent characteristic of cells is that they can reproduce themselves. In fact, cells can only arise from preexisting cells. The complex human body originates from the union of two existing cells: the female egg and the male sperm. These sex cells merge to form one larger cell called the zygote, which is the starting point of a multi-trillion-celled human body. The zygote divides and forms two cells. (Sometimes, these two zygote cells become separated and develop independently of each other, forming twins.) The two zygote cells continue to divide and form four cells. This process continues forever. Even when the total number of cells reaches a relatively fixed amount, cells continue to divide to replace old or dead cells. Throughout life, cells are continually dying and reproducing.

Each type of cell has its own anatomy and physiology. Specialized subcellular structures, called organelles, perform specific functions. Each cell typically contains the following organelles.

Plasma Membrane

Picture the cell as an inflated balloon. The outer boundary is called the plasma membrane, or cell membrane. It is a complex structure made up of mostly proteins and a phospholipid bilayer. The phospholipid bilayer (which is

made up of glycerol, two fatty acids, and a phosphate group) forms a double-walled balloon-like structure with proteins embedded in these bilayer sheets. The nutritional significance of this structure is that the cell membrane is made up of fatty acids, which are part of the phospholipid bilayer. For this reason, fats are an important part of the diet. And while we need to make sure we do not eat too much of it, we do need an appropriate amount to serve the essential building blocks for all cells. Fats are especially important for athletes who are training to gain muscle mass and for long distance athletes whose metabolisms burn up a tremendous amount of fatty acids. (Fats consist mainly of three fatty acids attached to the three carbon glycerol molecules; thus the name triglycerides.)

fatty acid: Any of a large group of monobasic acids, especially those found in animal and vegetable fats and oils.

triglycerides: The storage form of fat made up of three fatty acids and a glycerol group.

The plasma membrane can selectively allow the transport of molecules through it and also actively transport certain compounds across it through special mechanisms. It is therefore referred to as a semipermeable plasma membrane. This semipermeability gives the cell control over the type and amount of a substance it allows inside. In addition, the cell can rid itself of undesirable compounds while retaining desirable ones. Insulin is an important hormone that is responsible for stimulating the uptake of glucose and amino acids across the plasma membrane. Insulin levels increase in the body after a meal to ensure that these vital nutrients get into the cells. You can maximize the function of insulin through supplementation and timing of meals in relation to training.

insulin: A polypeptide hormone functioning in the regulation of the metabolism of carbohydrates and fats, especially the conversion of glucose to glycogen, which lowers the blood glucose level.

glucose: Principal circulating sugar in the blood and the major energy source of the body.

Nucleus

Commonly called the control center of the cell, the nucleus was first discovered in 1830; discovery is credited to the scientist Robert Brown. Usually, the nucleus is situated in approximately the center of each cell and is slightly darker than the surrounding cytoplasm. The nucleus is essentially a cell within a cell, which has a membrane of its own and houses genetic material.

THE NUCLEUS HOUSES THE DEOXYRIBONUCLEIC ACID (DNA) OF THE CELL. Strands of DNA form chromosomes. The human cell contains 46 chromosomes—23 matching pairs. Each parent contributes one set of chromosomes from sex cells; 23 come from the sperm and 23 come from the egg. Chromosomes contain the blueprint for all genetic traits, including eye color, hairline shape, and even predisposition to allergies, among many others. Chromosomes are suspended in a liquid called the nucleoplasm. The liquid between the plasma membrane and nuclear membrane is called cytoplasm, or cytosol.

The nucleus typically functions to initiate production of substances needed by the cell. The process is initiated by an intracellular (within the cell) signal, which causes specific genes on certain chromosomes to produce exact copies of the gene sequence being activated. These pieces of material carrying genetic information are called messenger ribonucleic acid (RNA). The information contained on the messenger RNA strands may be the sequence of amino acids needed for a protein molecule, such as insulin. The messenger RNA is then transported from the nucleus, through pores in the nuclear membrane, and on to the cytoplasm. Once in the cytoplasm of the cell, the strand of messenger RNA is used as a template to make molecules in the cytoplasm. For this event to occur, ribosomes must be connected to the messenger RNA strand. Ribosomes are also organelles and they run along the messenger RNA strands while in the cytoplasm. As the ribosomes go along the messenger RNA strand, they function to connect each code point along the RNA to the corresponding transfer RNA which has an amino acid attached to it. The ribosomes roll along the messenger RNA, recruiting amino acids to produce proteins. If certain amino acids are missing, the

protein chains cannot be completed; protein synthesis can be reduced or temporarily stopped. This is why adequate and effective protein intake is mandatory for human activity. This concept of the limiting nutrient is important to consider. The diet can be abundant in calories But if an essential nutrient is in short supply, it can limit certain reactions needed for the cell—and therefore the active person—to thrive.

The nucleus has another important function: It initiates cell division. During cell division, each chromosome must duplicate itself so that the new cell will contain a full set of 23 pairs of chromosomes.

Ribosomes

Ribosomes are extremely small, spherical organelles made up of protein and RNA. They are the most numerous of cell organelles. They are found scattered throughout the cell’s cytoplasm and also along the surface of another organelle, the endoplasmic reticulum (discussed next). Ribosomes function in pairs as two subunits; one subunit is smaller than the other. Ribosomes are located in the cytoplasm and make various compounds from messenger RNA for local cellular needs. Ribosomes situated on the endoplasmic reticulum synthesize compounds for use outside the cell and can be channeled out of the cell for export, such as with hormones and digestive enzymes.

Endoplasmic Reticulum (ER)

This organelle forms a network of intracellular canals within the cytoplasm. It exists in two forms: rough ER and smooth ER. Rough ER is ER with ribosomes attached. Here is where proteins and other biomolecules can be made and transported through the ER’s canal network to other parts of the cell and outside the cell. Smooth ER is without ribosomes and its function is less clear, although it appears that smooth ER may be the site of steroid synthesis in the testes and adrenal glands. Evidence also indicates that lipid and cholesterol metabolism occur in smooth ER of the liver cells.

Recommended contacts for prayer request and Bible study

Psalm 42:8 NKJV The Lord will command His lovingkindness in the daytime, And in the night His song shall be with me— A prayer to the God of my life.

Psalm 54:2 NKJV Hear my prayer, O God; Give ear to the words of my mouth.

Psalm 55:1 NKJV Give ear to my prayer, O God, And do not hide Yourself from my supplication.

Psalm 55:17 NKJV Evening and morning and at noon I will pray, and cry aloud, And He shall hear my voice.

Psalm 61:1 NKJV Hear my cry, O God; Attend to my prayer.

Psalm 66:19-20 NKJV But certainly God has heard me; He has attended to the voice of my prayer. 20 Blessed be God, Who has not turned away my prayer, Nor His mercy from me!

Psalm 69:13 NKJV But as for me, my prayer is to You, O Lord, in the acceptable time; O God, in the multitude of Your mercy, Hear me in the truth of Your salvation.

Psalm 84:8 NKJV O Lord God of hosts, hear my prayer; Give ear, O God of Jacob! Selah

Psalm 86:6-7 NKJV Give ear, O Lord, to my prayer; And attend to the voice of my supplications. 7 In the day of my trouble I will call upon You, For You will answer me.

Recommended contacts for prayer request and Bible study

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www.adventistontario.org

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breathoflife.tv/

http://www.nadadventist.org/article/15/contact-us

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