By Regina Bailey, About.com

What are Tissues?

The word tissue is derived from a Latin word meaning to “weave.” Cells that make up tissues are sometimes “woven” together with extracellular fibers.

Likewise, a tissue can sometimes be held together by a sticky substance that coats its cells.

There are four main categories of tissues: epithelial, connective,muscle and nervous. Let’s take a look at epithelial tissue.

Epithelial Tissue

Epithelial tissue covers the outside of the body and lines organs and cavities. The cells in this type of tissue are very closely packed together and joined with little space between them.

With a tightly packed structure we would expect epithelial tissue to perhaps serve some type of barrier and protective function and that is certainly the case.

Epithelial tissue helps to protect organisms from microorganisms, injury, and fluid loss.

In an epithelium, the free surface is usually exposed to fluid or the air while the bottom surface is attached to a basement membrane.

Classifying

Epithelia are commonly classified based on the shape of the cells on the free surface, as well as the number of cell layers. Sample types include:

Simple Epithelium: A simple epithelium has a single layer of cells.

Stratified Epithelium: A stratified epithelium has multiple layers of cells.

Likewise, the shape of the cells on the free surface can be:

Cuboidal

Analogous to the shape of dice.

Columnar

Analogous to the shape of bricks on an end.

Squamous

Analogous to the shape of flat tiles on a floor.

By combining the terms for shape and layers, we can derive epithelial types such as stratified squamous epithelium or simple columnar epithelium.

Animal Tissue Types

To learn more about animal tissues, visit:

• Connective Tissue
• Muscle Tissue
• Nervous Tissue
• Nervous Tissue – Glial Cells

http://biology.about.com/od/anatomy/a/aa121407a.htm

By Regina Bailey

The heart is the organ that supplies blood and oxygen to all parts of the body. It is about the size of a clenched fist, weighs about 10.5 ounces and is shaped like a cone. The heart is located in the chest cavity just posterior to the breastbone, between the lungs and superior to the diaphragm. The heart is surrounded by a fluid filled sac called the pericardium. Blood is pumped away from the heart through arteries and returns to the heart through veins. The major artery of the body is the aorta and the major veins of the body are the vena cava.

Image courtesy of MedValet

Chambers

The heart is divided by a partition or septum into two halves. The halves are in turn divided into chambers. The upper two chambers of the heart are called atria and the lower two chambers are called ventricles. Valves allow blood to flow in one direction between the chambers of the heart.

Heart Wall

The heart wall is divided into three layers:

• Epicardium

• Myocardium

• Endocardium

Cardiac Conduction

Cardiac conduction is the rate at which the heart conducts electrical impulses. Cardiac muscle cells contract spontaneously and are coordinated by nodal tissue, specifically the sinoatrial node. There are other factors that influence heart rate as well. These include endocrine hormones, body temperature and exercise.

Cardiac Cycle

The cardiac cycle is the sequence of events that occur when the heart beats. There are two phases of this cycle:

• Diastole – Ventricles are relaxed.

• Systole – Ventricles contract.

http://biology.about.com/library/weekly/aa062801a.htm

By Regina Bailey, About.com

Biology, the study of life, can be fascinating and wondrous. However, certain biology topics can sometimes seem incomprehensible. The best way to get a clear understanding of difficult biology concepts is to study them at home, as well as at school. Students should use quality biology homework help resources when studying. Below are some good resources and information to help you answer some of your biology homework questions.

Biology Homework Help Resources

Anatomy of the Heart
Learn about this amazing organ that supplies blood to the entire body.

Animal Tissues
Information on the structure and function of animal tissue types.

Bio-Word Dissections
Learn how to “dissect” difficult biology words.

Brain Basics
The brain is one of the largest and most important organs of the human body. Weighing in at about three pounds, this organ has a wide range of responsibilities.

Cell Division
An introduction to the process of asexual and sexual reproduction, mitosis, and meiosis.

Cellular Respiration
Learn about this process by which cells harvest the energy stored in food.

Characteristics of Life
Learn about the basic characteristics of life.

Journey into the Cell
Explore the structure and function of the parts of a eukaryotic cell.

Macromolecules
A look at macromolecules and molecular diversity.

Mendelian Genetics
Learn about Mendel’s law of segregation and independent assortment.

Plant Cells and Tissues
A look at the structure and function of plant cells and tissues.

Organ Systems
The human body is made up of several organ systems that work together as one unit. Learn about these systems and how they work together.

Science Fair Project Help
Here are some great ideas for biology related science fair projects for students, teachers, and parents.

The above information provides a basic foundation for various biology topics. If you find that you still have problems understanding the material, don’t be afraid to request assistance from an instructor or tutor.

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