Cells, Tissues, Organs, Organ Systems

atomic -> molecular ->  cellular  -> tissue  -> organ  -> organ systems -> organism

In Chemistry and other sciences you would begin studying organisms at the atomic level and move up the chain to the organism itself. In this class, we will look briefly at the cellular and tissue levels, but we will concentrate on organs and organ systems as they relate to the human body.

The discovery of the microscope in the late 1600s by Anton Van Leeuwenhoek opened scientists’ eyes to a previously unseen world. Development of the microscope made it possible to view and study the basic units of life – cells.

In order to simplify a complex concept, just remember that groups of cells form tissues, groups of tissues form organs, groups of organs form organ systems, and groups of organ systems form a living organism, such as a human being.

As the basic unit of life, cells are the smallest element capable of independent life and reproduction. The cell’s nucleus contains all of the genetic material needed for these activities. Although cells might be similar in structure, each cell has a specific task within the body. The human body contains specialized bone cells, blood cells, nerve cells, muscle cells and reproductive cells, just to name a few.

As billions of similar cells group together, they form tissues. There are four basic types of tissue: epithelial, connective, muscle, and nervous.

Epithelial tissue

Epithelial tissue forms the upper layer of the skin. It can also be found in the lining of the digestive system, urinary system, and respiratory system. Epithelial tissue can be one layer of cells, or several layers. If it contains several layers, it is known as stratified. If it is just one layer, it is called simple. There are four primary functions: 1) protection; 2) absorption; 3) secretion; 4) reception of sensory stimuli. (http://bio.rutgers.edu/~gb102/lab_6/601am-epithelial.html). One of the most fascinating features of epithelial tissue is its ability to regenerate very quickly, sometimes in as little as 24-hours.

Connective tissue

Connective tissue includes cartilage, tendons, ligaments, bone, fat, and blood. The primary function of connective tissue is to provide support for organs and hold them in place. Connective tissue is formed by a matrix of cells and can be loosely bound together or dense. For instance, tendons are quite dense and resist stretching in order to provide the necessary stability. Ligaments are also dense, but contain collagen which allows them to stretch (http://bio.rutgers.edu/~gb102/lab_6/603cm-dense.html).

Muscle tissue

There are three types of muscle tissue: smooth, skeletal, and cardiac. Smooth muscle is located in the walls of hollow organs, such as the bladder and intestines. As the name implies, cardiac muscles are found in the heart but are specialized to enable the conduction of electrical impulses. Both cardiac and smooth muscle tissues are considered involuntary, which simply means they perform their functions without conscious thought. Skeletal muscle tissues are connected to bones and joints and are considered voluntary because they are under conscious control.

Nervous tissue

Our body’s nervous tissue is another very specialized type of tissue designed to receive and transmit stimuli. Nervous tissue includes a variety of cell types, including neurons designed to generate and conduct nerve impulses, and neuroglia designed to protect, support, maintain and repair nerve cells.

Organs

Organs are structured from two or more types of tissues that work together to perform a specific function within the body. As we study medical terminology, you will learn the medical terms for the various organs. Some organs are considered visceral, which means they are located within the body. However, other organs, such as the skin and sweat glands, are not located deep inside the body.

There are five organs considered vital for human life: heart, brain, kidney, liver and lungs. If one of these organs stops functioning, the organism will die unless medical intervention is able to restore the organ’s functioning.

Organ Systems

Just like tissues work together to form an organ, two or more organs work together to form an organ system. Each organ system provides a specific function within the body. Some organs are essential to more than one organ system and all organ systems are interconnected. There are 11 major organ systems in the human body: integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, respiratory, lymphatic, digestive, urinary, and reproductive.

Anatomical Position, Body Planes, Quadrants, and Directional Terms

It can be challenging to identify and describe specific areas of the human body. For instance, a patient might refer to his/her right side but the clinician facing the patient might refer to the patient’s right side as the left because it is on the clinician’s left. The anatomical position, body planes, and directional terms were developed to avoid confusion and assist in more specified identification.

Anatomical Position

The anatomical position was developed to eliminate the right/left confusion. In the anatomical position, the patient is standing, facing forward, with arms at the side and the palms of the hands facing forward. The patient’s left side of the body is on the observer’s right. This position is used as a reference, regardless of the patient’s actual position.

Right side                                                                             Left side

Image:  By Connexions – http://cnx.org/content/m47807/latest/, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=29624327

Body Planes

Body planes refer to imaginary lines running through the body from different angles. They are used as points of reference.

In this image, “a” refers to the sagittal plane which divides the body into right and left halves. “b” refers to the frontal or coronal plane which divides the body into front and back halves. “c” refers to the transverse or horizontal plane that divides the body into upper and lower portions.

Image:  “File:Planes of Body labeled.jpg” by Connexions CNXAnatomy & Physiology is licensed under CC BY 4.0

Body Cavities and Quadrants

Image:  “File:Dorsal Ventral Body Cavities.jpg” by Connexions is licensed under CC BY 4.0

The body is also divided into cavities and quadrants. The dorsal cavity is located in the back or posterior of the body. The ventral cavity is located in the anterior or front portion of the body. Each of these general cavity descriptions include other cavities. The dorsal body cavity includes the cranial cavity and the vertebral cavity. The ventral cavity includes the thoracic and abdominopelvic cavities.

The most common division of abdominal quadrants is to divide the region into four quadrants, labeled Right upper quadrant (RUQ), Left upper quadrant (LUQ), Right lower quadrant (RLQ), and Left lower quadrant (LLQ).

Another method for labeling the abdominal regions is to use a nine region grid with the grids labeled (from top to bottom) on the right side labeled as the Right hypochondriac region, Right lumbar region, and Right iliac region; the middle section labeled as the Epigastric region, Umbilical region, and Hypogastric region; and the left side labeled as the Left hypochondriac region, Left lumbar region, and Left iliac region. Please refer to the diagram below.

In both of these methods, the right and left sides are based on the anatomical position.

Image:  “File:Abdominal Quadrant Regions.jpg” by OpenStax is licensed under CC BY 3.0

Directional terms

Directional terms are a very important component of medical terminology and healthcare. These help the clinician accurately identify and label the location of pain, injuries, and treatment/surgeries. Most directional terms are paired with an opposite term. For instance, superior means toward the head or upper portion of the body and inferior means toward the feet or lower portion of the body. At the end of this chapter is a table listing the various directional terms and their meanings. As part of your venture into medical terminology and healthcare, it is important to learn these terms.

When patients are lying horizontal, they are generally considered lying in the supine or prone position. When a patient is in the supine position, he is laying on his back with his face up. In the prone position, the patient is laying on his stomach with his face down.

Supine position

Image:  “File:Supine position 03.JPG” by Saltanat is marked with CC0 1.0

Image:  “File:Directional Terms.jpg” by OpenStax College. Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013. is licensed under CC BY 3.0

List of Directional Terms

The following is a list of directional terms, their common pronunciation, combining form (if applicable) and meaning. Although this list is not inclusive of all directional terms, it does include most of the commonly used terms.

It is important to note that certain specialties may use these terms in different ways. For instance in dentistry, distal refers to the tooth farthest away from the midline of the dental arch (the last tooth on each side, upper or lower).

Term	Pronunciation	Combining Form	Meaning
abduction	ăb-dŭk-shŭn	n/a	Movement toward the side, away from the body (opposite of adduction)
adduction	ă-dŭk-shŭn	n/a	Movement toward the body (opposite of abduction)
anterior	ăn-tēr-ē-ōr	anter/o	Toward or near the front; ventral (opposite of posterior, dorsal)
apex	ā-pĕx	n/a	The pointed tip of a conical or pyramidal structure (opposite of base)
base	bās	n/a	The lower part or bottom; supporting structure (opposite of apex)
bilateral	bī-lăt-ĕr-ăl	n/a	Both sides (opposite of unilateral)
caudal		n/a	Toward the feet or lower part of the body; inferior (opposite of superior)
contralateral	kŏn-trŭh-lăt-ĕr-ăl	n/a	Relating to the opposite side (opposite of ipsilateral)
deep	dēp	n/a	Further into the body; below the surface (opposite of superficial)
distal	dĭs-tăl	dist/o	Farthest away from the center of the body or from the point of origin (opposite of medial)
dorsal	dōr-săl	dors/o	Pertaining to the back; posterior (opposite of ventral, anterior)
eversion	ē-vĕr-zhŭn	n/a	Turning outward (opposite of inversion)
extension	ĕks-tĕn-shŭn	n/a	Movement that straightens or increases the angle between bones; movement in which two ends of any jointed part are pulled away from each other (opposite of flexion)
flexion	flĕk-shŭn	n/a	Movement that decreases the angle between bones; the act of bending (opposite of extension)
inferior	ĭn-fē-rē-ōr	infer/o	Situated below, toward or nearer to the feet; caudal (opposite of superior)
inversion	ĭn-vĕr-zhŭn	n/a	Turning inward (opposite of eversion)
ipsilateral	ĭp-sĭ-lăt-ĕr-ăl	n/a	Referring to the same side (opposite of contralateral)
lateral	lăt-ĕr-ăl	n/a	Toward the side; farther away from the middle (opposite of medial)
medial	mē-dē-ăl	n/a	Toward the middle or midline (opposite of lateral)
posterior	pōst-tē-rē-ōr	poster/o	Toward or near the back; dorsal (opposite of anterior, ventral)
pronation	prō-nā-shŭn	n/a	The act of lying in the prone position; moving the hand so the palm faces downward or backward (opposite of supination)
prone	prōn	n/a	Lying horizontally facing downward (opposite of supine)
protraction	prō-trăk-shŭn	n/a	The act of moving an anatomical part forward (opposite of retraction)
proximal	prŏk-sĭm-ăl	proxim/o	Nearer to the middle or point of attachment (opposite of distal)
retraction	rē-trăk-shŭn	n/a	The act of moving an anatomical part backward (opposite of protraction)
superficial	soo-pĕr-fĭsh-ăl	n/a	Near the surface of the body (opposite of deep)
superior	soo-pē-rē-ōr	super/o	Situated above; nearer to the head (opposite of inferior)
supination	soo-pĭn-ā-shŭn	n/a	The act of lying in the supine position; moving the hand so the palm faces upward (opposite of pronation)
supine	soo-pīn	n/a	Lying horizontally facing upward (opposite of prone)
unilateral	ū-nĭ-lăt-ĕr-ăl	n/a	Pertaining to only one side of the body (opposite of bilateral)
ventral	vĕn-trăl	ventr/o	Pertaining to the front; anterior (opposite of dorsal, posterior)
visceral	vĭs-ĕr-ăl	n/a	Pertaining to internal organs, especially those in the thoracic and abdominal cavities

Abbreviations

Healthcare frequently uses abbreviations in oral and written communications. However, abbreviations have been the cause of medical errors and should always be used cautiously. Each facility should have a list of “authorized” abbreviations and clinicians should not use abbreviations that are not on that list. In addition, the Joint Commission has published a list of “Do Not Use” abbreviations. (https://www.jointcommission.org/-/media/tjc/documents/resources/patient-safety-topics/do_not_use_list_6_28_19.pdf)

At the end of each chapter, you will find a list of abbreviations related to the material in the chapter. As you look at the following list of abbreviations, you may begin to see why caution should always be taken when using abbreviations. The abbreviation PA can represent both posterioanterior (a directional term) and Physician’s Assistant. In non-medical terms, PA can represent Pennsylvania, Panama, Purchasing Agent, Professional Association, Public Affairs, etc. It is easy to see how the use of abbreviations can cause confusion and possibly lead to medical errors.

Abbreviations relating to directional terms include:

Abbreviation	Meaning		Abbreviation	Meaning
abd	Abduction		LLQ	Left lower quadrant
add	Adduction		LUQ	Left upper quadrant
ant	Anterior		med	Medial
AP	Anteroposterior		PA	Posterioanterior
ext	Extension		Pos, post	Posterior
flex	Flexion		R	Right
inf	Inferior		RLQ	Right lower quadrant
L	Left		RUQ	Right upper quadrant
lat	Lateral		Sup	Superior
LE	Lower extremity (leg)		UE	Upper extremity (arm)

Your Turn

Learning all of these terms can be difficult, but the more you practice the easier it becomes.  The following activities are designed to help you begin the memorization process.  In addition, it is highly recommended that you create flashcards or other aids in helping you remember these terms.

Activity 1

1. What is another term for ventral?
2. What is the term that is opposite of deep?
3. What is the term that is opposite of unilateral?
4. What are the two terms that are opposite of posterior?
5. Which term means “toward the middle or midline”?
6. If you scrapped your knee, the provider might describe the wound as ____________.
7. What is the term that describes movement toward the side, away from the body?
8. If you are lying on your back, what position would you be in?
9. Which of these body parts is more distal than the other: the knee or the foot?
10. What is the term that is opposite of medial?

Activity 1 Answers:

1. anterior (both ventral and anterior mean toward or near the front)
2. superficial (superficial means near the surface of the body and deep means further into the body)
3. bilateral (bilateral means both sides; unilateral means one side)
4. anterior and ventral are both opposite of posterior
5. Medial
6. superficial
7. abduction
8. supine
9. The foot is more distal than the knee (distal means farther away from the center of the body or point of origin; in this case, the point of origin is the hip)
10.  lateral