ISSA SN Chapter 12: Anatomy of an Athlete: Cells, Tissues, and Systems

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Chapter Goals:

  • Describe and define the main terms that relate to human anatomy.
  • Know about the structure of cells.
  • Find and understand the main systems we have in our bodies.
  • Describe the varying muscle fiber types and the types of muscle contractions that we can go through.


Anatomy is defined as the structures of the body. 

Physiology is defined as the function of the body.

This chapter will review these concepts as they relate best to sports science.

Cells, Cells, Cells

Our bodies are a biological phenomenon due to the many interdependent systems working together to maintain life. We have systems like the circulatory system, which is needed to nourish the muscular system and also carry away the waste products we produce. The system for digestion is made up of many organs that work to break down things in the body. And we have many more systems that we will discuss throughout, and they are all made up of cells. Cells are designed with different goals and processes in mind.

The Cell – Fundamental Unit of Life

Like every molecule has its own building blocks, our tissues and our structures do too. These are cells. The small units that give us life. We estimate that there are around 100 trillion cells with many different forms and functions spread throughout the average human body. 

One crazy characteristic of cells is that they can reproduce themselves. They can actually only come from cells that existed before. The process starts with one cell in the form of the female’s egg and the other in the form of the male sperm cell. These merge into a zygote, and then through multiplication and order, we get to the trillions of cells we have in our body. 

This process continues automatically, and all we really need to do is provide nutrients through our food.

Cellular Components:

The plasma membrane is like an inflated balloon. It is the outer membrane of the cell. This complex structure is mainly made of proteins and a phospholipid bilayer. The bilayer forms a double walled balloon structure where proteins are embedded within. Proteins provide structure for the membrane, they form channels that allow passage for certain things, they act as receptors for important information, they may function as transports for some materials, and they give a marker for identification of the cells. These are essentially the functions of the plasma membrane.

The Nucleus was discovered over 150 years ago. It is placed in the center of the cell and it has its own membrane. This is the housing center for the DNA of the cell. Those strands of DNA together make up our chromosomes, of which we have 46 in total. These chromosomes contain genetic information that decides how we look and how the body performs. We could call the nucleus the control center of the cell. The liquid between the nuclear and plasma membranes is known as the cytoplasm. 

The ribosomes are an important organelle for cells. They play a role in synthesizing the proteins and cell parts we need. These ribosomes are going to be extremely tiny. They consist of protein and RNA. They are the most numerous organelles found in cells. They are spread throughout the cytoplasm or attached to the endoplasmic reticulum. 

The endoplasmic reticulum is the next organelle to mention. This organelle makes a network of canals in the cytoplasm and is involved in transporting materials. The endoplasmic reticulum has two forms, the rough and the smooth forms. The smooth endoplasmic reticulum appears smooth due to the absence of ribosomes on the outside. And the opposite is true for the rough ER. We also have evidence of some lipid and cholesterol metabolism occurring in liver cells’ endoplasmic reticulums. 

The Golgi apparatus is next. This is made up of stacks of oblong sacs that are embedded in the cytoplasm close to the nucleus. It actively modifies and transports some proteins. Some carbohydrate biomolecules have been seen to be produced through this organelle also. 

The lysosomes are some structures like sacs that have their size and shape changed depending on what activity they will do. They begin as very small, and then we see them increase their size significantly when they are active. They contain many types of enzymes. These are used to carry out varying chemical reactions and break down the components when necessary. These broken down components can then be used to synthesize new molecules by the cells. So, they play a vital role in forming new components. 

The mitochondria are the cells near the nucleus. They are the most discussed organelle of them all. They are often known as the powerhouse of the cell due to their role being the production of energy for everything we do. In different cells, we have varying amounts of these important energy producing organelles. This is all based on if the cell needs to produce energy.


Tissues would be the fundamental units of function and structure if the cells are the fundamental units of life. We define tissues as the aggregation of cells that are bound together and work to perform one common function of some kind. Like our adrenal cortex, for example. We see this working together to produce several related hormones. These are examples of tissue. 

Epithelial Tissues

These are tissues we see throughout our body in the forms of skin, the inner cavities of the body, or the makeup of some of the glands in the body. These tissues work to protect the cells that are underneath them from bacteria, chemicals, and drying. The epithelial tissues have four different groups that they can fall under.

Squamous epithelium is a tissue that is made up of mostly flat cells. It is located in our mouths, the esophagus, and the blood or lymphatic cells. Substances are easily able to diffuse through these. 

Cuboidal epithelium is the second type. These tissues are those that are shaped like cubes and found throughout the tubules of the kidney. 

Columnar Epithelium is the tissue that will look like pillars or columns. They are going to be found in the digestive tract and the respiratory tract mostly. They are used for either secretion or absorption. Some of them even contain some small hair cells known as cilia to increase the surface area of these tissues. 

Glandular Epithelium is the fourth form of these tissues and is specialized for the secretion of mucous and hormones. Examples would be the thymus glands and the salivary glands. 

Connective Tissues

These tissues throughout the body are used for connection and for support. They join things together and comprise cells embedded in a nonliving matrix. The matrix’s nature determines the function of the cells instead of the cells alone. 

Even blood will be considered a connective tissue due to the containing of a fluid matrix and the cells being technically suspended within. 

Connective tissues are made up of many constituents.

Three main fibers are kept in the connective tissues.

Collagen fibers are the strong fibers forming the fibrous parts of skin, tendons, ligaments, and teeth. They are made up of five main amino acids. Collagen will give the connective tissue the versatility it needs to interconnect with the other molecules. These fibers are found in bundles and this gives them exceptional strength. 

Reticular fibers are the second type of fiber. These delicate fibers support the connective tissues found in the networks like the capillaries and the nerve fibers. 

The elastic fibers will be the ones that are extendible and elastic in nature. 

The main connective tissues will be cartilage, bones, tendons, and ligaments. 

Cartilage forms the bone tissue’s foundation. It is found at the bones’ ends and spinal disks. Matured cartilage does now have any nerves or blood vessels in it. We actually have three forms of cartilage in the body. The elastic cartilage in the ear and the Eustachian tubes, the tough fibrous cartilage between bones and the spinal disks, and hard hyaline cartilage at the ends of the bone also, and the nose, larynx, and trachea. 

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Bones are what form our skeleton. This skeleton and the bones in it will act to support and protect the body. The bones resemble and differ from the cartilage. Like cartilage, though, the bone comprises more intracellular substances than cells. These substances are hardened as opposed to the gel like the appearance of cartilage. Collagen fibers are also inside the calcified matrix of bones. Inside this calcified matrix, the cells are quite alive. Many blood vessels are constantly delivering food and oxygen to the cells. 

The tendons and ligaments are grouped together. These are going to be very strong structures that are quite flexible also. They are our strongest tissues in the body, actually. Their intracellular matrix is made up of collagen and reticular fibers that come from surrounding tendons. Tendons are thick and aim to connect the muscles, bones, and many other structures. Ligaments will join the bone to other bones, like in joints. 

Muscle Tissues

Muscle is about 43 percent of the total of a man’s weight and 34 percent for women. There are a total of around 620 muscles that all work together to support the skeletal system and create the motions we do every day. There are around 30 muscles we use to help with food and the digestive system, blood circulation, and the operation of some organs. For this book, the muscles will be primarily talked about as the main source of an operation, energy expenditure, waste generation, and substantial nutrient needs.

A muscle may contract voluntarily or involuntarily. The voluntary muscle and their movements will come from the somatic nervous system, which is all of our skeletal muscles. The involuntary muscle tissues are controlled by the autonomic nervous system, and these cannot be controlled by us. 

We have two forms of muscle tissue that we see when looking under a microscope. These are striated muscles and smooth muscles. We can divide these into three categories. 

Cardiac muscle tissue is striated and involuntary. It composes the heart muscle. It works to contract the heart, which then pumps the blood through the body. 

Smooth Muscle Tissue is smooth, and it is involuntary. It is found in the areas such as the tubular viscera of the digestive, respiratory, and genitourinary tracts. These will function to move substances through their respective systems. They contract slower than other striated muscles will, and thus, they do not fatigue quickly. 

Skeletal muscle is found attached to bones, the eyes, and the upper third of the throat. The skeletal tissue will function to move bones and our eyes or the food we swallow in the first parts of digestion. These muscles have very long cells with many nuclei. They rarely ever contract with one muscle alone. Instead, we see sets of muscles contract to produce movement. The spine and the brain exercise control over these complex movement patterns through the use of nerve fibers. 

Each cell does not have its own line from the CNS. Instead, they combine them into whole groups of these muscles and contract together. 

The special sense organs in our muscles that help with control are called muscle spindles. They essentially measure the amount of strain in the muscle and preset tension. 

The skeletal muscles will contract much more rapidly in response to the CNS system. 

The Mechanics of Muscular Contraction

The external view of the skeletal muscles makes them appear grainy due to the makeup of extremely small fibers. They are divided into bands and look like a stack of coins in a pile. Each fiber has its own sarcolemma, which is a small plasma membrane. Myofibrils are tiny fibrils names. They number from some hundred to several thousand. The sarcoplasm of the muscle cells has many nuclei within it. It also has many mitochondria. 

The fibrils are made out of two different proteins. These are actin and myosin. They work together to contract the muscles.

Fast-Twitch and Slow-Twitch Muscle Fibers

There are these two forms of muscle fibers, fast and slow twitch. 

Slow twitch fibers are the ones that produce power for lower intensity exercise, they have repetitive contractions, and they are mostly used for endurance activities. The athletes in these long distance events and sports are likelier to have a high percentage of slow twitch fibers. 

The fast twitch fibers are the ones that we recruit selectively for heavy workloads where we need maximum strength and power. These are seen more so in athletes in weightlifting, sprinting, and similar sports. 

Muscular Hypertrophy

This is defined as an increase in the size of the muscle fibers. The main mechanism at work will be an increase in the number of myofibrils. 

Hyperplasia is the process of increasing the number of cells that are in the muscles. This is less often but occurs when fibers split.


All of the tissues in our body work together to form the functional units that we call systems. The body is essentially one whole system that is made up of subsystems. We will call these subsystems systems, even if the body is the real ‘system’. 

Skeletal System

This comprises all of the bones in our body and the joints they are attached to or through. The main tissues here will be bones, cartilage, ligaments, and hematopoietic tissue.

Skeletal Muscle System

This is made up of the muscle tissues of our body that are responsible for movement and controlled by the somatic system. The muscles are limited to the storage of proteins in the form of amino acids. Athletes do not want these due to the poor effects on the muscles.

Nervous System

This system comprises all of our neurons, neuroglia, and neurosecretory cells. They provide memory and integrate our bodily functions, control, and our communication.

Respiratory System

This comprises the organs of the nose, lungs, bronchi, trachea, larynx, and pharynx. They all function to connect the gaseous environment with the cells of the human body. 

Cardiovascular (Circulatory) System

This comprises the heart, veins, arteries, and lymphatic system. This is in charge of circulation, which is the movement of fluid, lymph, and blood through the body to carry important things around. 

Digestive system

The five organs hear are the mouth, pharynx, esophagus, stomach, and intestine, both small and large. These work together to control the intake and absorption of nutrients into the body so we can live and thrive.

Urinary System

This consists of the kidneys, the ureters, the bladder, and the urethra. They function to flush the waste from the body in the form of urine. It is a way to keep the body’s homeostasis, which is the tendency to maintain equilibrium. 

Reproductive System

This system has organs that function to make sperm in males and eggs that are fertile in females. 

Endocrine System

This system comprises many organs, all with their own hormones to produce. They function together to provide the body with the needed hormones for its very many functions. 

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Tyler Read - Certified Personal Trainer with PTPioneer

Tyler Read

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