Where is tissue found

Note the regularly arranged bundles of closely packed collagen fibers running in the same direction, which results in flexible tissue with great resistance to pulling forces. Because it is made up a single layer of scale-like cells, simple squamous epithelium is well suited for rapid diffusion and filtration. These cells look hexagonal in surface view but when viewed from the side as shown in the image of the model above , they appear flat with bulges where nuclei are located.

Simple squamous epithelium forms the inside walls of blood vessels endothelium , the wall of Bowman's capsule of the kidney, the lining of the body cavity and viscera parietal and visceral peritoneum and the walls of the air sacs alveoli and respiratory ducts of the lung. Simple cuboidal epithelial cells are usually six-sided cube shaped , but they appear square in side view as shown on the above image of the model and polygonal or hexagonal when viewed from the top.

Their spherical nuclei stain darkly and often give the layer an appearance of a string of beads. This type of tissue is adapted for secretion and absorption. It can be found in such areas as the kidney tubules, the covering of the ovary and as a component of the ducts of many glands.

Simple columnar epithelium is composed of tall columnar cells that are closely packed together. Viewed from the surface they appear hexagonal but when viewed from the side as shown on the image of the model above , they appear as a row of rectangles with the elongated nuclei frequently located at the same level, usually in the lower part of the cell.

Simple columnar epithelial cells may be specialized for secretion such as the goblet cells that secrete a protective layer of mucus in the small intestine , for absorption or for protection from abrasion.

Columnar epithelial cells line a large part of the digestive tract, oviducts and many glands. The image to the left shows a model of pseudostratified columnar epithelium. This type of tissue consists of a single layer of cells resting on a noncellular basement membrane that secures the epithelium. The tissue appears stratified occurring in several layers because the cells are not all the same height and because their nuclei shown as black oval structures are located at different levels.

Pseudostratified ciliated columnar epithelium lines the trachea windpipe and larger respiratory passage ways. Although it is often activated by reflexes that function in automatically in response to an outside stimulus, skeletal muscle is also called voluntary muscle because it is the only type subject to conscious control.

Because skeletal muscle fibers have obvious bands called striations that can be observed under a microscope, it is also called striated muscle. Note that skeletal muscle cells are multinucleate, that is, each cell has more than one nucleus.

Smooth muscle is the simplest of the three kinds of muscle. It is found where slow, sustained, involuntary contractions are needed such as in the digestive tract, reproductive system and other internal organs.

Smooth muscle cells are long and spindle shaped with a single, centrally located nucleus. Smooth muscle is often arranged in two layers that run perpendicular to one another, a circular layer whose fibers appear in cross section as shown on the model above and a longitudinal layer whose fibers appear like the ends of a cut cable when viewed on-end.

Cardiac muscle is striated like skeletal muscle but adapted for involuntary, rhythmic contractions like smooth muscle. The myofibrils are transversely striated, but each cell has only one centrally located nucleus.

Note the dark blue transverse bands on the model called intercalated disks that mark the boundaries between the ends of the muscle cells. This model shows a cross section of compact bone. Observe that the matrix of the bone is deposited in concentric layers that are called lamellae 5. The basic unit of structure in this type of bone is the Haversian system, or osteon. In each of these osteons, the lamellae are arranged around a central Haversian canal 1 housing nerves 4 and blood vessels 2, 3 in living bone.

Osteocytes or bone cells, 6 are located in spaces called lacunae 7 that are connected by slender branching tubules called canaliculi 8. The image above is that of a greatly enlarged multipolar neuron, the most common type of neuron found in humans. Notice that the cell body 1 contains the nucleus 2 with its conspicuous darkly staining nucleolus 3.

Branching from the cell body are cytoplasmic extensions called nerve cell processes. In motor neurons which conduct nerve impulses toward muscle cells , these processes consist of a single, long axon 4 and many of shorter dendrites 5.

Note in this magnified view of an axon that it is surrounded by specialized cells called Schwann cells 1 whose plasma membranes form a covering of the axon called the neurilemma 2 , which is shown in brown on the model. These Schwann cells secrete a fatty myelin sheath 3 , which is shown in yellow on the model, that protects and insulates nerve fibers from one another and increases the speed of transmission of nerve impulses.

Adjacent Schwann cells along an axon do not touch one another, leaving gaps in the sheath called nodes of Ranvier at regular intervals 4. Home Zoo-lab. Introduction to histology Part 1 Tissues are composed of similar types of cells that work in a coordinated fashion to perform a common task, and the study of the tissue level of biological organization is histology.

Introduction to histology Part 2 Connective tissue performs such diverse functions as binding, support, protection, insulation and transport. Muscle tissue is specialized for contraction.

There are three kinds of muscle tissue: Smooth muscle designed for slow, sustained, involuntary contractions is made up of spindle-shaped cells with one nucleus per cell. Skeletal , or striated muscle , which is associated with voluntary contractions, contains cylindrical cells with many nuclei per cell arranged in bundles. Cardiac heart muscle is striated like skeletal muscle, but each cell contains only one nucleus.

Introduction to histology Part 3 Nervous tissue is specialized for the reception of stimuli and conduction of nerve impulses. Organs are the body's recognizable structures for example, the heart, lungs, liver, eyes, and stomach that perform specific functions. An organ is made of several types of tissue and therefore several types of cells Cells Often thought of as the smallest unit of a living organism, a cell is made up of many even smaller parts, each with its own function.

Human cells vary in size, but all are quite small. For example, the heart Biology of the Heart The heart and blood vessels constitute the cardiovascular circulatory system. The heart pumps the blood to the lungs so it can pick up oxygen and then pumps oxygen-rich blood to the body The eye Structure and Function of the Eyes The structures and functions of the eyes are complex.

Each eye constantly adjusts the amount of light it lets in, focuses on objects near and far, and produces continuous images that are instantly Even an organ as apparently simple as the gallbladder Gallbladder and Biliary Tract The gallbladder is a small, pear-shaped, muscular storage sac that holds bile and is interconnected to the liver by ducts known as the biliary tract.

See also Overview of the Liver and Gallbladder Merck and Co. From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world. Just as knowing the structure and function of cells helps you in your study of tissues, knowledge of tissues will help you understand how organs function. The epithelial and connective tissues are discussed in detail in this chapter.

Muscle and nervous tissues will be discussed only briefly in this chapter. The zygote, or fertilized egg, is a single cell formed by the fusion of an egg and sperm. After fertilization the zygote gives rise to rapid mitotic cycles, generating many cells to form the embryo. The first embryonic cells generated have the ability to differentiate into any type of cell in the body and, as such, are called totipotent , meaning each has the capacity to divide, differentiate, and develop into a new organism.

As cell proliferation progresses, three major cell lineages are established within the embryo. Each of these lineages of embryonic cells forms the distinct germ layers from which all the tissues and organs of the human body eventually form. Figure 2 shows the types of tissues and organs associated with the each of the three germ layers.

Note that epithelial tissue originates in all three layers, whereas nervous tissue derives primarily from the ectoderm and muscle tissue from mesoderm. A tissue membrane is a thin layer or sheet of cells that covers the outside of the body for example, skin , the organs for example, pericardium , internal passageways that lead to the exterior of the body for example, abdominal mesenteries , and the lining of the moveable joint cavities.

There are two basic types of tissue membranes: connective tissue and epithelial membranes Figure 3. Figure 3. Tissue Membranes. The two broad categories of tissue membranes in the body are 1 connective tissue membranes, which include synovial membranes, and 2 epithelial membranes, which include mucous membranes, serous membranes, and the cutaneous membrane, in other words, the skin. The connective tissue membrane is formed solely from connective tissue.

These membranes encapsulate organs, such as the kidneys, and line our movable joints. A synovial membrane is a type of connective tissue membrane that lines the cavity of a freely movable joint. For example, synovial membranes surround the joints of the shoulder, elbow, and knee.

Fibroblasts in the inner layer of the synovial membrane release hyaluronan into the joint cavity.