By: Abagail Brooke Rupe
What is a Tissue?
Tissue is a cellular organizational level intermediate between cell and a complete organism. A tissue is an ensemble of similar cells from the same orgin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues.
What are the Four Types of Tissue?
I. Muscle Tissue
A. Contract for Movement & Support
B. Skeletal muscle
1. voluntary (works when you want it to)
C. Cardiac Muscle
1. Only found in the heart
2. Involuntary (works all the time)
D. Smooth Muscle
1. involuntary (works all the time)
II. Nerve Tissue
A. Gives signals to muscles, informs us of environmental conditions (hot, cold, humid)
B. ex. Brain, Spinal Cord, Nerves
III. Epithelial Tissue
A. Lines our organs
B. ex. Stomach lining, skin
IV. Connective Tissue
A. Connects, supports, and protects other tissues
1. ligaments, tendons, cartilage, bone, blood, fibers (organ walls)
Tissues are groups of similar cells that perform a common function. There are four categories of tissues in the human body: epithelial, connective, nervous, and muscle.
Epithelial tissue protects your body from moisture loss, bacteria, and internal injury. There are two kinds of epithelial tissues:
- Covering and lining epithelium covers or lines almost all of your internal and external body surfaces; for example, the outermost layer of your skin and other organs, and the internal surface lining of your lymph vessels and digestive tract.
- Glandular epithelium secretes hormones or other products such as stomach acid, sweat, saliva, and milk.
Connective tissue generally provides structure and support to the body. There are two types of connective tissue:
- Loose connective tissue holds structures together. For example, loose connective tissue holds the outer layer of skin to the underlying muscle tissue. This tissue is also found in your fat layers, lymph nodes, and red bone marrow.
- Fibrous connective tissue also holds body parts together, but its structure is a bit more rigid than loose connective tissue. Fibrous connective tissue is found in ligaments, tendons, cartilage, and bone.
Nervous tissue forms the nervous system, which is responsible for coordinating the activities and movements of your body through its network of nerves. Parts of the nervous system include the brain, spinal cord, and nerves that branch off of those two key parts.
Nervous tissue consists of two kinds of nerve cells:
- Neurons are the basic structural unit of the nervous system. Each cell consists of the cell body, dendrites, and axon.
- Neuroglia, or glial cells, provide support functions for the neurons, such as insulation or anchoring neurons to blood vessels.
Muscle tissue differs from other tissue types in that it contracts. Muscle tissue comes in three types: cardiac, smooth, and skeletal. Those muscle tissues are made up of muscle fibers. The muscle fibers contain many myofibrils, which are the parts of the fiber that actually contract. There are three kinds of muscle tissues:
- Skeletal muscle is attached to bones and causes movements of the body.
- Cardiac muscle is found in the heart.
- Smooth muscle lines the walls of blood vessels and certain organs such as the digestive and urogenital tracts.
1. Epithelium- lines and covers surfaces
2. Connective tissue- protect, support, and bind together
3. Muscular tissue- produces movement
4. Nervous tissue- receive stimuli and conduct impulses
Special Characteristics of Epithelium
Epithelium generally has the characteristics below:
~Except for glandular epithelium, epithelial cells fit closely together to form continuous sheets. Neighboring calls are bound together at many points by cell junction, including desmosomes and tight junctions.
~The membranes always have one free surface or edge. This so-called apical surface is exposed to the body's exterior or to the cavity of an internal organ. The exposed surfaces of some epithelia are slick and smooth, but others exhibit cell surface modifications, such as mircovilii or cilia.
~The lower surface of an epithelium rests in a basement membrane, a structure-less material secreted by the cells.
~Epithelial tissues have no blood supply of their own and depend on diffusion from the capillaries in the underlying connective tissue for food and oxygen.
~If well nourished, epithelial cells regenerate themselves easily.
Example where the types of tissues can be found
1. Epithelial: Occurring in sheets of tightly packed cells. Covers the outside of the body,and lines organs and cavities of the body. In most cases the cells are held together by tight junctions. The cells are attached to a basal membrane.
2.Connective: Functions mainly to bind and support other tissues. They contain a sparse population of cells surrounded by a nonliving matrix. This matrix can be fibrous, liquid or jellylike.
3.Muscle Tissue: Composed of long contractile cells. The cells are composed of long microfilaments made of the proteins actin and myosin. There are 3 types of muscle tissue: Striated or skeletal, cardiac, and visceral or smooth.
4. Nervous Tissue: Senses stimuli and sends signals from one part of the body to another. The cells are called neurons. The neuron consists of a cyton ( cell body), dendrites (many branches that carry impulses to the cyton), and an axon (long filament that carries impulses away from the cells.