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Six Levels of the Human Body: Level 3 – TISSUE

Six Levels of the Human Body:  Level 3 – TISSUE

(Part two in a three part series)

In part one of my series on the 6 Levels that make-up the human body we discussed the rolls of: atoms. molecules, and cells; and also their rolls as it relates to athlete performance.  In part two I will discuss the third level: Tissues.

Have you ever seen a science program about the planet earth and our solar system where they start with a close up of the earth and then pan out?  Imagine starting at the surface of the earth and moving away.  Next you see the continents, then the plant earth, then our solar system. Farther yet you see the Milky Way, then our galactic companions, then the local supercluster.  You start at the microscopic level and finish at the macroscopic level.  You can take that same concept and use it on the human body.  Starting at the cellular level and reaching the final organism we call the human body.  There are six levels that make up the human body, they are:

The Six Levels of the human body are:

1) The Chemical Level: consisting of atoms and molecules

2) The Cellular Level: consisting of a cell and its nucleus (organelle)

3) Tissue Level: such as muscle and connective tissue

4) Organ Level: example is the heart

5) The Body System level: There are 10 principles systems in our body.  One example is the Central Nervous System (CNS).

6) The Organism Level: the human being.

In a Nutshell How all These Systems Work Together

The atom is the smallest amount of chemical elements and they combine to form molecules.  The human body is 98 percent composed of only six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorous.  Atoms and molecules bind together to build the basic building blocks of our body.  Tissue is considered a group of closely related cells working together to perform a specific function.  The four main tissues in our body are: 1) muscle tissue, 2) nervous tissue, 3) connective tissue, and 4) epithelial tissue.  These tissues then organize themselves into organs such as the heart and the brain.  Then the organs perform specific functions in our body’s system, and all these systems combined together form our human body.


In the first part of this series we learned that cells are the fundamental unit of life, where tissues are the fundamental units of function and structure for our body.  Tissues are defined as the aggregation of cells bound together and working to perform a common function. Tissues can be broken down into four basic groups: epithelia tissues, connective tissues, muscle tissues, and nervous tissues.  Let’s take a look at each and the rolls they play in our body.

Epithelia Tissues

Epithelia tissues are found throughout our body.  They are the the external layer covering your whole body (the skin), they are found on most of the bodies internal cavities, and make up our body’s several glands.  On the outside of our body, epithelia tissues function is to protect the underlying cells.  On the inside of our body the function is for absorbing and secreting tissues (an example is the digestive system glands such as the pancreas and the gallbladder).  The epithelia tissues are divided into four groups:

Squamous epithelia: this tissue is composed of one layer of flat cells.  It can be found in the mouth, esophagus, blood, and lymphatic vessels.

Cuboidal epithelia:  cells in a single layer of cube-like cells with large, spherical central nuclei. Simple cuboidal epithelia are found on the surface of ovaries, the lining of nephrons, the walls of the renal tubules, and parts of the eye and thyroid. On these surfaces, the cells perform secretion and absorption.*

Columnar epithelia: these tissues have the shape of a column or pillar and are found widespread throughout the body.  They form such things as the lining of the digestive tract and respiratory tract.  They function as secretive and absorptive cells.

Glandular: these tissues relate to the specific gland they comprise of and the secretions of that gland.

Connective Tissues

The connective tissues discussed will be the ones most important to athletes (cartilage, bone, tendons, and ligaments).  As the name implies, connective tissues serve to connect structures in your body.  Simple examples are the connect tissues that connect bone to bone, or muscle to bone.  Connective Tissues are composed of cells embedded in a non-living matrix.  The makeup of the matrix rather than the makeup of the cells themselves determine the function of the particular type of connective tissue.  As athletes, it is important to note that connective tissues consists mostly of intercellular material interspersed among relatively very few cells.

The Connective Tissues


Why is this important to know?  Because damage to these structures is a serious injury.  Connective tissue only consists of a few cells and mostly non-living matrix.  From part one of this series we learned that cells can only regenerate from other cells.  Since there are very few cells within connective tissues they have a very limiting capacity to regenerate new cells for healing themselves.  Most often when an injury occurs in connective tissues surgery is necessary for repair.  It is important to note that as athletes we have an advantage over the sedentary person such that proper nutrition and exercise can help build strong connective tissues that will become more resultant to injury.

Connective tissues are made up of many different components such as: salts, water, protein, and carbohydrates.  Within these substances there are embedded cells and fibers.  The three fibers are: 1) Elastic Fibers for elasticity; 2) Collagen Fibers for strength; and 3) Reticular Fibers for support, microphages and white blood cells to fight infection, fat cells for storage of energy, and plasma cells to product antibodies.  Connective tissues will contain one or more of the three fibers (collagen, reticular, and elastic). The connective tissues that are most important to an athlete are: cartilage, bone, tendons, and ligaments.


Cartilage forms the foundation of bone tissue and it is found at the bone ends, in spinal disks, and in the nose.  Mature cartilage does not contain any blood vessels or nerves.  The nutrients that cartilage needs are provided  through small holes where the nutrients seep in.  There are three different types of cartilage and they are classified by their consistency.  They are: elastic, fibrous, and hyaline.


Bones form our skeleton and serves as the support structure and as a protective structure for our body.  Bone and cartilage are similar in that they consist more of intercellular substances than cells.  The difference is that in bones the intercellular substance is calcified as opposed to cartilage.

Tendons and Ligaments

Tendons and Ligaments of the knee joint

Tendons and ligaments are very strong and flexible.  They are the strongest of the connective tissues in our body.  Tendons function to connect muscles to bone, or muscles to other structures.  Ligaments join bone to bone.

Muscle Tissues

Muscle tissue make up about 43 percent of a man’s bodyweight, and about 34 percent of a woman’s bodyweight.  Within our body there are 600 muscles that work together to support the skeletal system and to create motion.  As athletes, muscles are the main operating tissue.  They expend energy, generate wastes, and require substantial nutrition.

Nervous Tissues

Nervous Tissue


Nervous tissue are made up of many different cells that are responsible for controlling our bodily functions.  Nervous Tissues are found in the brain, spinal cord, and nerves; and they are called: neurons, neuroglia, and neurosecretory cells.

Neurons: Neurons conduct nerve impulses, register sensory impulses, and conduct motor impulses.

Neuroglia: They are the delicate network of branched cells in the Central Nervous System (CNS).

Neurosecretory cells: secrete substances that may have an effect somewhere else in the body.


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