Anatomy & Physiology – Tissues

There are four main tissue types in the body: connective, nervous, epithelial, and muscle. Just as different cells make up tissue, different tissues combine to form organs. For example, the heart muscle tissue contracts to enable the heart to beat and pump blood through the veins and the heart’s valves are made up of fibrous tissue.

Connective Tissue

Connective tissue is the most prevalent type of tissue in the human body and it comes in different forms, but every type of connective tissue has the same basic structural makeup:

• Fibers, which provide strength, elasticity, and support
• Cells
• Ground substance, the gel that surrounds the cells and fibers
• Intercellular matrix which is a structural network or solution of non-living intercellular material.

Loose connective tissue fills the spaces between muscle fibers, surrounds blood and lymph vessels, and is present in the lining membranes of the peritoneal, pleural, and cardiac cavities.

Dense Connective Tissue

Dense connective tissue contains relatively few cells but have many more collagen fibers. Dense connective tissue is divided into two sub-categories: dense irregular connective tissue and dense regular connective tissue.

Dense irregular connective tissue, which includes skin, has bundles of relatively randomly ordered collagen fibers.

The fiber bundles in dense regular connective tissue have a defined orientation; fibers running the same direction are what give the tissue its strength. Tendons are the most common occurring dense regular connective tissue. Tendons connect muscles to bones. Similarly, ligaments, which connect bones to bones, are also dense regular connecting tissues. Ligaments have a similar structural arrangement to tendons, but have more elastic fibers in the tissue.

Specialized Connective Tissues

This group includes cartilage, bone, and blood.

Significant Roles of Connective Tissue

Connective tissue is found in almost every organ and makes up a significant percentage of skin, tendons, and muscles. It is the strong material that holds the body’s structures together, provides support and gives shape to organs, stores and transports nutrients, helps to eliminate metabolic waste, and enhances our flexibility.

Metabolism

Adipose tissue, or fat, is a connective tissue that plays a part in the storage, absorption, and disposal of nutrients, vitamins, minerals, and other substances. Fat tissue is found beneath the skin, surrounding internal organs, and within other structures, such as bone marrow and breast tissue.

Since it stores energy, adipose tissue expands when excess food is eaten. A diet high in protein, carbohydrates, and fat will prompt the accumulation of adipose tissue, which is held in reserve for when our bodies need energy.

Healing

When you get a cut, the process of healing is done by connective tissue. To protect the body against infection, platelets are carried by your blood to the wound. Platelets build up and form a temporary covering called a scab. Then fibroblasts produce collagen, which seals the skin beneath dried scabs. If the scab comes off too early or the cut is deep, the collagen becomes a visible scar.

Support

Cartilage is made of collagen and elastic fibers, which create a dense connective tissue that fills the spaces between bones and acts as a cushion when we move. The nose and ears also have cartilage.

There are three primary types of cartilage:

1. Hyaline is the most abundant type and the weakest. It is found in the ears, nose, and at the end of long bones.
2. Elastin maintains shape.
3. Fibrous is the strongest and is found in the pelvis, skull, and vertebral discs.

Tissue Types	Special Cell Types	Unique Cell Characteristics	Special Cell Function	General Tissue Type Function
Bone	Osteon (Haversian System), Central Canal, and Matrix.	Osteoblasts form a cylindrical matrix.	Provide small units of support.	Support for complete structures.
Loose	Elastic, Reticular, Collagenous, Macrophage.	They clear up the area around bone, and they follow the motion of the muscle and bone by connection.	Digest dead cells by phagocytosis.	It binds epithelia to bones and other material. It also holds organs in place.
Fibrous	Fibroblasts	Forms a nonelastic strength.	Formation of the tendons and the ligaments.	Nonelastic stability.
Cartilage	Chondrocytes	Rubbery and elastic.	Provide form and structure without bone.	Structure that does not require bone for support.
Blood	White b. cells, red b. cells, and platelets.	Transport of oxygen, immune defenses, and others.	Immunization of the body and distribution of oxygen from the lungs.	Circulate nutrients, and others.
Adipose tissue	N/A	Contains a fat droplet.	Storage of fat for body fuel.	Storage of fat for body fuel.

 

Nervous Tissue

The brain, spinal cord, and nerves are made of nervous tissue, the most complex tissue in the body. Its function is to transfer electrical impulses throughout the body.

Nervous tissue is organized anatomically into the central nervous system and the peripheral nervous system. The central nervous system is divided into the brain and the spinal cord. The peripheral nervous system is comprised of all the other nervous tissue in the body, which act as a conduit between the central nervous system and the body.

Nerve tissue consists of two types of cells: neurons and neuroglia, or glial cells, which provide support functions for the neurons. All cells exhibit electrical properties, but neurons are designed to transmit electrical impulses from one site in the body to another, and to receive and process information.

Supporting cells such as neuroglia provide physical support, electrical insulation, and metabolic exchange with the vascular system.

Epithelial Tissue

Epithelial tissue is made up of closely packed cells that are arranged in one or more layers. This tissue forms the covering or lining of all internal and external body surfaces to help keep the body organs separate, in place, and protected. Some examples of epithelial tissue are the outer layer of the skin, the inside of the mouth and stomach, and the tissue surrounding the body’s organs. The epithelium acts like a flexible armor plating. Epithelial tissue is avascular meaning it has no blood vessels. Epithelial cells are continually  growing to replenish older or damaged ones through mitosis.

There exists simple epithelial tissue which has a single layer of cells and there exists stratified epithelium which has two or more layers of cells. Epithelial tissue can be further classified by the shape of the cells.

• Squamous has flattened cells which look like cobblestones.
• Cuboidal has sugar cube shaped cells.
• Columnar has cells in the shapes of columns and may have cilia for sensory perception in locations like the lining of the nose.

 

Epithelial Cells Chart

This Epithelial Cells Chart shows the different types of epithelial tissues that are distributed across the organism with their overall functions being protecting and lining the body and internal organs.

Epithelial Tissue Types	Unique Cell Characteristics	Special Cell Function	General Tissue Type Function
Pseudostratified Ciliated Columnar.	These cells contain cilia.	Cilia move the mucous.	Lining the nasal passage and respiratory tract; lining male reproductive tract.
Cuboidal Cells.	No Basement membrane.	N/A	Formation of glands and lining of kidneys.
Stratified columnar.	N/A	N/A	Lines the inner surface of some organs, usually providing extra protection.
Stratified squamous.	These cells reproduce quickly and densely.	N/A	Providing extra layering; quick cell reproduction in specialized organs and regions of the skin.
Simple squamous.	These cells are designed to let materials pass through by diffusion.	Diffusion of chemicals and nutrients.	Providing a thin tissue membrane.
Simple columnar.	Secrete digestive enzymes and absorb nutrients.	Digestion in the intestines.	Lines the stomach and intestines.

Muscle Tissue

Muscle tissue is a specialized tissue that can contract in response to an electrical stimulus sent from the central nervous system, which enables the movement of the body when the muscles are attached to bone. Muscles also control movement of organs, such as the peristaltic movement of food through the digestive tract.

There are three types of muscle tissue: smooth, skeletal, and cardiac.

Skeletal muscles are what make up human flesh and the red meat of a cow or lamb. They are attached to the bones and facilitate movement because of their ability to contract. Because skeletal muscles are under our conscious control, they are considered voluntary muscles.Smooth muscle is found throughout the internal organs of the body, particularly in the digestive tract. Because the contractions of smooth muscle are not under our conscious control, it is considered an involuntary muscle. Compared to skeletal muscle, smooth muscle fibers are much shorter.

Cardiac muscle is found in the wall of the heart. It is also an involuntary muscle.

Muscle Tissue Chart

This Muscle Tissue Chart identifies the muscle tissue types that are located around the skeletal system, pulmonary system, and the cardiovascular system with their overall function being movement of some kind.

Tissue Types	Special Cell Types	Unique Cell Characteristics	Special Cell Function	General Tissue Type Function
Skeletal Muscle.	Muscle Fibers.	Ability to contract muscle in response to a nerve command.	To move the bones so that the organism can move.	Movement
Cardiac Muscle.	Muscle Fibers.	Interlaced discs to ensure a synchronized heartbeat.	Pump blood through the heart.	Pump Blood.
Smooth Muscle.	Muscle Fibers.	Smooth and found in organs.	Special movement of tissues not by muscle-nerve signals.	Part of the digestive tract.

Conclusion