Animal Tissues

Histology is the study of plants and animal tissues by examining tissues under a light microscope or an electron microscope. A tissue is a group of cells that carry out a particular function. Animals are multicellular organisms with their specialized cells grouped into tissues. In most animals, combinations (group)of various tissues make up functional units called organs, and groups of organs that work together are called systems. For example, the animal digestive system consists of a stomach, small intestine, large intestine, and several other organs, each comprises (cover) of different tissues.

Level of organization in animals: Organs in animals are composed of different types of tissues. Each tissue is composed of cells. Level of organization in animals: Cells Tissues Organs Systems Organism body

Types of Animals Tissues Different types of tissues have different structures and functions. A tissue may be held by a sticky extracellular matrix that bind (link) the cells together in a fabric of fibers (Tissue= cells + extracellular matrix). 1) Epithelial tissue 2) Connective tissue 3) Muscular tissue 4) Nervous tissue Types of tissues

First: Epithelial tissues Characterized by: Cells tightly linked together. The presence of a cell secretion called the basement membrane Covers and lines other tissues and organs. Functions of Epithelium Protection (skin) Absorption (Intestinal villi) Secretion (glandular cells) Glands can be single epithelial cells, such as the goblet cells that found in the stomach and intestines to secrete mucus. Multicellular glands include the endocrine glands

Classification of epithelial tissues Epithelia are classified by the number of cell layers and the shape of cells on the free surface. Classification based on number of cell layers: Simple epithelium is a One layer of cells. Stratified epithelium More than one layer of cells. Pseudostratified epithelium One layer of cells but appear to form two layers. Classification based on cell shape: Cuboidal = cube Columnar = column Squamous = flat حرشفية طبقية حرشفية بسيطة عمودية بسيطة مكعبة بسيطة عمودية طبقية عمودية مهدبة طبقية كاذبة غشاء قاعدي

Second: Connective tissues Characterized by Cells widely separated from each other in a matrix that is produced by the cells (cells are scattered ). The matrix generally consists of fibers The matrix may be solid (as in bone), gelatinous, or liquid (as in blood). The functions of connective tissues are to bind and support other tissues.

Types of Fibers in Connective Tissues There are three types of connective tissues fibers, which are all proteins: 1- Collagenous fibers (white) Are thick and made of collagen and non-elastic 2- Elastic fibers (Yellow) Are long threads of elastin, which provide a rubbery quality. 3-Reticular fibers Are very thin and branched, and composed of collagen.

Types of Connective Tissues 1) Proper connective tissues الأنسجة الضامة الأصيله 2) Skeletal connective tissues الأنسجة الضامة الهيكلية 3) Blood الدم a) Loose الفجوي b) Adipose الدهني c) Fibrous الليفي a) Bone العظم b) Cartilage الغضروف

1- Proper Connective Tissues A- Loose Proper Connective Tissue Binds epithelia to underlying tissues and functions a holding organs in place. It has all three fiber types. It has two cell types: 1- Fibroblasts Are responsible for making the extracellular fibers. 2- Macrophages Are amoeboid cells خلايا أميبية that swallow and digest microbes, and cellular debris بقايا الخلايا الميتة by phagocytosis.

B- Adipose Proper Connective Tissue Function as storage cells for adipose (lipids). Adipose cells contain a large vacuole which in the live cell contains lipids. Cell nucleus and cytoplasm are pushed out to edge حافةof cell membrane.

C- Fibrous Proper Connective Tissue It contains large number of collagenous fibers. The functions of this tissue are to attach muscles to bones (tendons الأوتار), and connect bones to other bones (ligaments الأربطة) at joints المفاصل.