TISSUES

TISSUES

Tissues Tissues are group of associated, similarly structured cells that perform specialized functions for the survival of the organism. Animal tissues are classified into four main groups. • I. EPITHELIAL TISSUES • II. CONNECTIVE TISSUES • III. MUSCLE TISSUES • IV. NERVOUS TISSUES

LINK TO DYNAMIC HUMAN

EPITHELIAL TISSUE • Covering and protecting type of tissue • Epithelial tissue may be: • simple: a single layer of cells • stratified: several layers of cells.

Simple epithelium • Simple epithelium consists of a single layer of identical cells and is divided into four types. • It is usually found on absorptive or secretory surfaces, where the single layer enhances these processes, and not usually on surfaces subject to stress. • The types are named according to the shape of the cells, which differs according to their functions.

Squamous epithelium The squamous is made of a single thin layer of flattened cells with irregular boundaries. They are found in the walls of blood vessels and air sacs of lungs and are involved in a functions like forming a diffusion boundary.

The cuboidal epithelium The cuboidal epithelium is composed of a single layer of cube-like cells. This is commonly found in ducts of glands and tubular parts of nephrons in kidneys and its main functions are secretion and absorption. The epithelium of proximal convoluted tubule (PCT) of nephron in the kidney has microvilli

The columnar epithelium Composed of a single layer of tall and slender cells. Their nuclei are located at the base. Free surface may have microvilli. They are found in the lining of stomach and intestine and help in secretion and absorption. If the columnar or cuboidal cells bear cilia on their free surface they are called ciliated epithelium

Compound epithelium Compound epithelium is made of more than one layer (multi-layered) of cells and thus has a limited role in secretion and absorption . Their main function is to provide protection against chemical and mechanical stresses. They cover the dry surface of the skin, the moist surface of buccal cavity, pharynx, inner lining of ducts of salivary glands and of pancreatic ducts.



Stratified squamous epithelium • This is composed of a number of layers of cells of different shapes representing newly formed and mature cells. • In the deepest layers the cells are mainly columnar and, as they grow towards the surface, they become flattened and are then shed.

Non-keratinised stratified epithelium. • This is found on wet surfaces subjected to wear and tear but are protected from drying, e.g. the conjunctiva of the eyes, the lining of the mouth, the pharynx, the oesophagus and the vagina

Keratinised stratified epithelium • . This is found on dry surfaces subjected to wear and tear, i.e. skin, hair and nails. • The surface layer consists of dead epithelial cells that contain the protein keratin. • This forms a tough relatively waterproof protective layer that prevent drying of the live cells underneath.



Transitional epithelium This is composed of several layers of pear- shaped cells It is found lining the urinary bladder and allow for stretching as the bladder fills.

MEMBRANES EPITHELIAL MEMBRANE SYNOVIAL MEMBRANE 1. Mucous membrane Eg, Lines the cavities of movable Mucosa joints and surrounds the tendons . 2. Serous membrane Eg. Pleura, pericardium and Produces synovial fluid peritoneum.

GLANDS Any structure of animals that produces chemical secretions or excretions. Glands are classified by shape, such as tubular and saccular, or saclike By structure, such as simple and compound. Types of the simple tubular eg. The sweat glands the simple saccular glands Eg. The sebaceous glands .

• Glands are of two types 1. Endocrine : ductless- produces hormone 2. Exocrine: *Tubular- intestinal *Alveolar- intestinal *Sacular-sebaceous *branched tubular- bulbouretral gland *brancehd alveolar-salivary

Nervous tissue Neural tissue exerts the greatest control over the body’s responsiveness to changing conditions. Neurons, the unit of neural system are excitable cells. The neuroglial cell which constitute the rest of the neural system protect and support neurons. Neuroglia make up more than one half the volume of neural tissue in our body.

Connective tissue • Connective tissues support and hold parts of the body together, comprise the: fibrous and elastic connective tissues, the adipose (fatty) tissues, cartilage and bone. • Connective tissues are the most abundant tissues in the body.

Cells of the connective tissue • Fibroblast – secrete Collagen, Elastin, reticulin • Fat cells – Adipose cells • Macrophages:– i. Monocytes – blood ii. Phagocytes – alveoli iii. Kupfer cells – Liver iv. Fibroblasts – lymph node and spleen v. Microglial cells – brain

• Leukocytes - (neutrophils ) • Plasma cells – secrete antibody • Mast cells – heparin, histamine

LOOSE (AREOLAR )CONNECTIVE TISSUE • Most generelised type of connective tissue • Under the skin • Between musles • Supports blood vessels and nerves • Alimentary canal

Adipose tissue • White adipose -20-25% body weight -thermal insulator and energy store. • Brown adipose – newborn – produces more heat.

Dense connective tissue Fibrous tissue Elastic tissue More collagen fibres More elastic tissues Eg. Trachea, Blood vessel Forms ligaments, Periotoneum, coverings, tendons

Blood Fluid connective tissue

Lymphoid tissue (reticular tissue) • Contains reticular tissue, Monocytes and lymphocytes • Found in lymph nodes and organs of lymphatic system.

Cartilage • Cartilage is composed of specialized cells, called chondrocytes, surrounded by a gelatinous matrix of collagen fibres

CARTILAGE Hyaline cartilage fibrocartilage cartilage Elastic fibrocartilage

Hyaline cartilage • Smooth bluish white cartilage. Chondrocyte within the cell nest • At the end of long bones • At the costal cartilage • larynx • Trachea • bronchi

fibro cartilage • Consists of white collagen fibres. • Intervertebral disc • At knee joint • At ball and socket joints • As ligaments

Elastic fibro cartilage • Flexible tissue • Eg. Pinna, Epiglotis Tunica media of blood vessels

Bone • Compact bone • Spongy bone

Muscles • Skeletal muscles • Smooth (visceral muscles ) • Cardiac muscles

Tissue regeneration There are three types of regeneration 1. Labile Cells with continuous replication Eg. Skin, mucous membrane, secretory gland etc 2. Stable cells – retain the ability to replicate but do so infrequently eg. Liver, kidney, pancreas etc 3. Permanent cells – unable to replicate after normal growth is complete. Eg. Nerve cells, cardiac cells, skeletal cells



STRUCTURE OF NEURON →Principle cells of Nervous Tissue →Consist of 3 parts : – CELL BODY (perikaryon/soma) – A single AXON – Multiple DENDRITES →ø 5-150 µm 10/07/2021 37

• Describe the various types of human tissues with diagrams. Mention the functions of tissues.