Tissue

Tissue is a word used to describe a group of similar cells found in the body. Cells within a tissue share a common embryonic origin. 

There are 4 types of tissue

-Epithelial

-Connective

-Muscle

-Nervous

Epithelial Tissue is basically any tissue that covers something or lines something

     -Ex: Skin or stomach lining

Connective Tissue supports and binds things together

     -There are four major types of connective tissue

          -Adipose Tissue - a type of loose connective tissue that stores lipids. Known as fat

          -Cartilage - A hard yet flexible tissue used for support

               -Like human ears or the whole skeleton of a shark

          -Bone Cells - Made of calcium phosphate and calcium carbonate making it very hard

          -Blood - a connective tissue in which fluid called plasma suspends special cells (blood cells)

Muscle Tissue allows movement

     -There are three kinds of muscle tissue

          -Skeletal muscles are the ones associated with movement

          -Smooth muscle has a turning motion. It is the type that moves food around and expands the bladder

          -Cardiac muscles cause the heart beat

Nervous tissue is for communication

     -There are lots of types

          -Neurons - Impulse conducting

          -Neuroglia - Protection, support, and nourishment

          -Peripheral glial cells - Form sheaths to protect the peripheral nervous system

Tissue Layers

Humans have 3 tissue layers. These tissue layers refer to the embryonic stage of development, not the fully developed human. At the blastula stage there are 3 layers of cells:

Ectoderm (ecto = outer)

Mesoderm (meso = middle)

Endoderm (endo = inner)

The cells in these tissue layers give rise to all the cells that will become the complete human.

Epithelial tissue arises from all 3 tissue layers. 

Epithelial tissue that arises from the endoderm is called endothelium and is the thin lining of the lymphatic and cardiovascular system, the lungs, kidneys, etc.

Epithelial tissue that arises from the mesoderm is called mesothelium and is the protective covering of most organs.

Epithelial tissue that arises from the ectoderm is simply called epithelium or epithelial and is the thick protective layer for normal biological wear and tear.

Epithelial Cells

Epithelial tissue is usually the bodies first line of defense against the crazy outside world. Epithelial tissue can be protective against outside invaders and dirt, it can also be the gatekeeper that allows some things in. Many epithelial cells are capable of secretion, such as sweat and oils.

Cells of Epithelia are closely connected unlike other cells. Because epithelia cells are the covering of many organs, the cells must be "woven" tightly.

Here are examples of epithelia cell junctions.

Classification of Epithelial Tissues

Epithelial Tissues are classified based on their shape and the number of layers. 

Squamous and flattened and thin

Cuboidal are boxy, as wide as they are tall

Columnar are rectangular, taller than they are wide

When the epithelial tissue is in one layer, it is called simple

When the epithelial tissue is in multiple layers, it is called stratified

-Simple squamous epithelium tissue is thin and used to line the inside of many organs. Thin tissue is needed anywhere there needs to be absorption or molecules passing through the tissue. 

-Simple cuboidal epithelium is used for secretion and also absorption. Found lining the kidneys

-Simple columnar epithelium is used in areas where there is a lot of absorption like the digestive system

-Stratified epithelium is used in areas where a thicker tissue is needed like skin or more protective lining. 

Student Activity:

Open your coloring book to page 8 and follow the coloring instructions

Connective Tissue

Connective tissue is just like it sounds. It is tissue used to connect other types of tissue in the body. The entire body is connected through different types of connective tissue. Some of these tissues connect muscle to bone, some transport fluids through the body, and others are used as energy storage and insulation. 

All connective tissue derives from the middle embryonic layer, the mesoderm. The connective tissue comes from a multipotent stem cell layer called mesenchyme. Mesenchyme cells are scattered throughout the adult body and used to repair any torn or damaged connective tissue.

Classification of Connective Tissue

There are 3 broad categories of connective tissue

1. Connective Tissue Proper

          a. Loose connective tissue - Adipose Tissue (fat)

                    Found all around organs to absorb shock. Also binds tissues together.

          b. Dense connective tissue

2. Supportive Connective Tissue - Cartilage and Bone

3. Fluid Connective Tissue - Blood and Lymph

Students Read:

Connective Tissue: Tendinitis

Your opponent stands ready as you prepare to hit the serve, but you are confident that you will smash the ball past your opponent. As you toss the ball high in the air, a burning pain shoots across your wrist and you drop the tennis racket. That dull ache in the wrist that you ignored through the summer is now an unbearable pain. The game is over for now.

After examining your swollen wrist, the doctor in the emergency room announces that you have developed wrist tendinitis. She recommends icing the tender area, taking non-steroidal anti-inflammatory medication to ease the pain and to reduce swelling, and complete rest for a few weeks. She interrupts your protests that you cannot stop playing. She issues a stern warning about the risk of aggravating the condition and the possibility of surgery. She consoles you by mentioning that well known tennis players such as Venus and Serena Williams and Rafael Nadal have also suffered from tendinitis related injuries.

What is tendinitis and how did it happen? Tendinitis is the inflammation of a tendon, the thick band of fibrous connective tissue that attaches a muscle to a bone. The condition causes pain and tenderness in the area around a joint. On rare occasions, a sudden serious injury will cause tendinitis. Most often, the condition results from repetitive motions over time that strain the tendons needed to perform the tasks.

Persons whose jobs and hobbies involve performing the same movements over and over again are often at the greatest risk of tendinitis. You hear of tennis and golfer’s elbow, jumper's knee, and swimmer’s shoulder. In all cases, overuse of the joint causes a microtrauma that initiates the inflammatory response. Tendinitis is routinely diagnosed through a clinical examination. In case of severe pain, X-rays can be examined to rule out the possibility of a bone injury. Severe cases of tendinitis can even tear loose a tendon. Surgical repair of a tendon is painful. Connective tissue in the tendon does not have abundant blood supply and heals slowly.

While older adults are at risk for tendinitis because the elasticity of tendon tissue decreases with age, active people of all ages can develop tendinitis. Young athletes, dancers, and computer operators; anyone who performs the same movements constantly is at risk for tendinitis. Although repetitive motions are unavoidable in many activities and may lead to tendinitis, precautions can be taken that can lessen the probability of developing tendinitis. For active individuals, stretches before exercising and cross training or changing exercises are recommended. For the passionate athlete, it may be time to take some lessons to improve technique. All of the preventive measures aim to increase the strength of the tendon and decrease the stress put on it. With proper rest and managed care, you will be back on the court to hit that slice-spin serve over the net.

Watch this animation to learn more about tendonitis, a painful condition caused by swollen or injured tendons.