a common function in the body. The tissues of the human body can be categorized into four major types:

Transcription

1 Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university Types of Tissues A tissue is composed of similarly specialized cells that perform a common function in the body. The tissues of the human body can be categorized into four major types: epithelial tissue, which covers body surfaces and lines body cavities; connective tissue, which binds and supports body parts ; muscular tissue, which moves body parts; nervous tissue, which receives stimuli and conducts impulses from one body part to another Epithelial Tissue Epithelial tissue, also called epithelium, consists of tightly packed cells that form a continuous layer or sheet lining the entire body surface and most of the body s inner cavities. On the external surface, it protects the body from injury, drying out, and possible pathogen (virus and bacterium) invasion. On internal surfaces, epithelial tissue may be specialized for other functions in addition to protection. For example, epithelial tissue secretes mucus along the digestive tract and sweeps up impurities from the lungs by means of cilia (sing.,cilium). It efficiently absorbs molecules from kidney tubules and from the intestine because of minute cellular extensions called microvilli.there are various types of epithelial tissue Squamous epithelium is composed of flattened cells and is found lining the lungs and blood vessels. Cuboidal epithelium contains cube-shaped cells and is found lining the kidney tubules. Columnar epithelium has cells resembling rectangular pillars or columns, and nuclei are usually located near the bottom of each

2 Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university cell. This epithelium is found lining the digestive tract. Ciliated columnar epithelium is found lining the oviducts, where it propels the egg toward the uterus. An epithelium can be simple or stratified. Simple means the tissue has a single layer of cells, and stratified means the tissue has layers of cells piled one on top of the other. The walls of the smallest blood vessels, called capillaries,are composed of a single layer of epithelial cells. The permeability of capillaries allows exchange of substances between the blood and tissue cells. The nose, mouth, esophagus,anal canal, and vagina are all lined by stratified squamous epitheliumthe outer layer of skin is also stratified squamous epithelium, but the cells have been reinforced by keratin, a protein that provides strength Pseudostratified epithelium appears to be layered; however,true layers do not exist because each cell touches the baseline. The lining of trachea, is called pseudostratified ciliated columnar epithelium. A secreted covering of mucus traps foreign particles, and the upward motion of the cilia carries the mucus to the back of the throat, where it may either be swallowed or expectorated.smoking can cause a change in mucus secretion and inhibit ciliary action, and the result is a chronic inflammatory condition called bronchitis. basement membrane often joins an epithelium to underlying connective tissue. We now know that the basement membrane is glycoprotein, reinforced by fibers that are supplied by connective tissue. An epithelium sometimes secretes a product, in which case it is described as glandular. A gland can be a single epithelial cell, as in the case of mucus-secreting goblet cells found within the columnar epithelium lining the digestive tract, or a gland can contain many cells. Glands that secrete their product into ducts are called exocrine glands, and those that secrete their product directly into the bloodstream are called endocrine glands. The pancreas is both an exocrine gland, because it secretes digestive juices into the small intestine via ducts, and an endocrine gland, because it secretes insulin into the bloodstream

3 Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university

4

5 Connective Tissue Connective tissue binds organs together, provides support and protection, fills spaces, produces blood cells, and stores fat. As a rule, connective tissue cells are widely separated by a matrix, consisting of a noncellular material that varies in consistency from solid to semifluid to fluid. The matrix may have fibers of three possible types: white collagen fibers contain collagen, a protein that gives them flexibility and strength. Reticular fibers are very thin collagen fibers that are highly branched and form delicate supporting networks.yellow elastic fibers contain elastin, a protein that is not as strong as collagen but is more elastic Loose Fibrous and Dense Fibrous Tissues Both loose fibrous and dense fibrous connective tissues have cells called fibroblasts that are located some distance from one another and are separated by a jellylike matrix containing white collagen fibers and yellow elastic fibers. Loose fibrous connective tissue supports epithelium and also many internal organs Its presence inlungs, arteries, and the urinary bladder allows these organs to expand. It forms a protective covering enclosing many internal organs, such as muscles, blood vessels, and nerves

6 Dense fibrous connective tissue contains many collagen fibers that are packed together. This type of tissue has more specific functions than does loose connective tissue. For example, dense fibrous connective tissue is found in tendons, which connect muscles to bones, and in ligaments, which connect bones to other bones at joints. Adipose Tissue In adipose tissue the fibroblasts enlarge and store fat. The body uses this stored fat for energy, insulation, and organ protection. Adipose tissue is found beneath the skin,around the kidneys, and on the surface of the heart. Reticular Connective Tissue Reticular connective tissue forms the supporting meshwork of lymphoid tissue present in lymph nodes, the Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university spleen, the thymus,and the bone marrow. All types of blood cells are produced in red bone marrow, but a certain type of lymphocyte (T lymphocyte) completes its development in the thymus.the lymph nodes store lymphocytes. Specialized connective tissue Cartilage In cartilage, the cells lie in small chambers called lacunae (sing., lacuna), separated by a matrix that is solid yet flexible.unfortunately, because this tissue lacks a direct blood supply, it heals very slowly. There are three types of cartilage,distinguished by the type of fiber in the matrix. 1-Hyaline cartilage the most common type of cartilage, contains only very fine collagen fibers. The matrix has a white, translucent appearance. Hyaline cartilage is found in the nose and at the ends of the long bones and the ribs, and it forms rings in the walls of respiratory passages.the fetal skeleton also is made of this type of cartilage. Later,the cartilaginous fetal skeleton is replaced by bone

7 Elastic cartilage has more elastic fi bers than hyaline cartilage. For this reason, it is more fl exible and is found, for example, in the framework of the outer ear. Fibrocartilage has a matrix containing strong collagen fi bers. Fibrocartilage is found in structures that withstand tension and pressure, such as the disks between the vertebrae 2-Bone Bone is the most rigid connective tissue. It consists of an extremely hard matrix of inorganic salts, notably calcium salts.these salts are deposited around protein fi bers, especially collagen fi bers. The inorganic salts give bone rigidity. The protein fi bers provide elasticity and strength, much as steel rods do in reinforced concrete. Cells called osteoblasts and osteoclasts are responsible for forming the matrix in bone tissue. Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university a-compact bone makes up the shaft of a long bone It consists of cylindrical structural units called osteons The central canal of each osteon is surrounded by rings of hard matrix. Bone cells are located in lacunae between the rings of matrix. In the central canal, nerve fi bers carry nerve impulses,and blood vessels carry nutrients that allow bone to renew itself. Thin extensions of bone cells within canaliculi (minute canals) connect the cells to each other and to the central canal. b-the ends of the long bones are composed of spongy bone covered by compact bone. Spongy bone also surrounds the bone marrow cavity. This, in turn, is covered by compact bone forming a sandwich structure. Spongy bone appears as an open, bony latticework with numerous bony bars and plates. These are separated by irregular spaces. Although lighter than compact bone, spongy bone is still designed for strength. Just as braces are used for support in buildings, the solid portions of spongy bone follow lines of stress 3-Blood Blood represents a fl uid connective tissue. Blood, which consists of formed elements and plasma, is located in blood vessels. Blood transports nutrients and oxygen to tissue fl uid. Tissue fl uid bathes the body s cells and removes carbon dioxide and other wastes. Blood helps distribute heat and also plays a role in fl uid, ion, and ph balance. The systems of the body help keep blood composition and chemistry within normal limits.

8 4-Lymph Lymph is also a fl uid connective tissue. Lymph is a clear (sometimes faintly yellow) fl uid derived from the fl uids surrounding the tissues. It contains white blood cells. Lymphatic vessels absorb excess tissue fl uid and various dissolved solutes in the tissues. They transport lymph to particular vessels of the cardiovascular system. Lymphatic vessels absorb fat molecules from the small intestine. Lymph nodes, composed of fi brous connective tissue, occur along the length of lymphatic vessels. Lymph is cleansed as it passes through lymph nodes, in particular, because white blood cells congregate there. Lymph nodes enlarge when you have an infection.. Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university Muscular Tissue Muscular (contractile) tissue is composed of cells called muscle fi bers. Muscle fi bers contain fi laments made of proteins called actin and myosin. The interaction of actin and myosin accounts for movement. The three types of vertebrate muscular tissue are skeletal, smooth, and cardiac 1-Skeletal muscle is also called voluntary muscle It is attached by tendons to the bones of the skeleton. When it contracts, body parts move. Contraction of skeletal muscle is under voluntary control. Skeletal muscle fi bers are cylindrical and long sometimes they run the length of the muscle. The nuclei are located at the periphery of the cell, just inside the plasma membrane. The fi bers have alternating light and dark bands that give them a striated, or striped, appearance. These bands are due to the placement of actin fi laments and myosin filaments in the cell. 2-Smooth (visceral) muscle is so named because the cells lack striations The spindle-shaped cells each have a single nucleus. These cells form layers in which the thick middle portion of one cell is opposite the thin ends of adjacent cells. Consequently, the nuclei form an irregular pattern in the tissue. Smooth muscle is not under conscious or voluntary control. Therefore, it is said to be involuntary. Smooth muscle is found in the walls of viscera (intestine, bladder, and other internal organs) and blood vessels..

9 . Cardiac muscle is found only in the walls of the heart. Its contraction pumps blood and accounts for the heartbeat. Cardiac muscle combines features of both smooth and skeletal muscle. Like skeletal muscle, it has striations, but the contraction of the heart is involuntary for the most part. Cardiac muscle cells also differ from skeletal muscle cells in that they usually have a single, centrally placed nucleus. The cells are branched and seemingly fused, one with another. The heart. Cardiac muscle cells are separate and individual, but they are bound end to end at intercalated disks.

10 Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university Nervous tissue consists of nerve cells, called neurons, and.neuroglia, the cells that support and nourish the neurons First: Neurons A neuron is a specialized cell that has three parts: dendrites, a cell body, and an axon. A dendrite is an extension that receives signals from sensory receptors or other neurons. The cell body contains most of the cell s cytoplasm and the nucleus An axon is an extension that conducts nerve impulses. Long axons are covered by myelin, a white fatty substance. The term fi ber1 is used here to refer to an axon along with its myelin sheath, if it has one. Outside the brain and spinal cord.fi bers bound by connective tissue form nerves The nervous system has three functions: sensory input integration of data, and motor output. Nerves conduct signals from sensory receptors to the spinal cord and the brain, where integration, or processing, occurs. Second : Neuroglia In addition to neurons, nervous tissue contains neuroglia Neuroglia are cells that outnumber neurons nine to one and take up more than half the volume of the brain. primary function of neuroglia is to support and nourish neurons,research is being conducted to determine how much they directly contribute to brain function. Neuroglia do not have long extensions (axons or dendrites).

11 Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university neuroglia found in the brain are microglia, astrocytes, and oligodendrocytes Microglia,in addition to supporting neurons, engulf bacterial and cellular debris. Astrocytes provide nutrients to neurons and produce a hormone known as glial-derived neutrophic factor (GDNF). This growth factor is currently undergoing clinical trials as a therapy for Parkinson disease and other diseases caused by neuron degeneration. Oligodendrocytes form the myelin sheaths around fi bers in the brain and spinal cord. Outside the brain, Schwann cells are the type of neuroglia that encircle long nerve fi bers and form a myelin sheath

12 Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university The skin The skin has two regions: the epidermis and the dermis The Epidermis The epidermis is made up of stratifi ed squamous epithelium. New epidermal cells for the renewal of skin are derived from stem (basal) cells. The importance of these stem cells is observed when there is an injury to the skin. Two types of specialized cells are located deep in the epidermis. 1- Langerhans cells are macrophages, white blood cells that phagocytize infectious agents and then travel to lymphatic organs. 2-Melanocytes, lying deep in the epidermis,produce melanin. This is the main pigment responsible for skin color. The number of melanocytes is about the same in all individuals, so variation in skin color is due to the amount of melanin produced and its distribution. When skin is exposed to the sun, melanocytes produce more melanin. This protects the skin from the damaging effects of the ultraviolet (UV) radiation in sunlight Dermis The dermis is a region of dense fi brous connective tissue beneath the epidermisthe dermis contains The dermis also contains blood vessels that nourish the skin.collagen and elastic fi bers Blood vessels in the dermis play a role in temperature regulation. If body temperature starts to rise the blood vessels in the skin will dilate. As a result, more blood is brought to the surface of the skin for cooling. If the outer temperature cools, the blood vessels constrict, so less blood is brought to the skin s surface The sensory receptors primarily in the dermis are specialized for touch, pressure, pain, hot, and cold. These receptors supply the central nervous system with information about the external environment Nails, hair, and glands are structures of epidermal origin, even though some parts of hair and glands are largely found in the dermis

13