Tissue

Definition A tissue is a group of usually similar cells, which together with their intercellular substance, perform a particular function. The study of tissue is Histology. Cells, cytoskeletal filaments and the extracellular matrix are major components of tissue

The Extracellular Matrix Secreted by cells Provides supportive tissue their strength In some cases, the ECM provides cells a medium by which cells can be bound together However, cells can be connected directly to each other. Details on cell junctions to come

Animal Tissue Animals are predators and must be strong and agile Means that tissue must possess characteristics of capable of rapid movement and the cells that make up the tissue must be able to generate and transmit forces and change shape quickly

Animal Tissue II Epithelial tissue Connective Tissues Muscular Tissue Nervous Tissue

Animal Tissue Connective tissue

Connective Tissue I Characteristics Extremely varied Tough and flexible Tendons Dermis of the skin Hard and dense Bone Resilient and shock-absorbing Cartilage Soft and transparent Jelly that fills interior of the eye

Connective Tissue II Functions Supporting function Cartilage Bone Transport function Blood

Connective Tissue III Bulk of this tissue is composed of extracellular matrix Tensile strength provided by the fibrous protein collagen

Connective Tissue IV Collagen There are 20 different variations of the protein Chief proteins in bone, tendon and skin Make up 25% of the total protein mass in a mammal More than any other type of protein Collagen is long, stiff and a triple stranded helical structure Collagen fibrils 10-300nm in diameter

Connective Tissue V Collagen Homework Question How does procollagen and the extracellular enzyme collagenase relate to the formation of collagen? What is the result of a genetic disorder that results in the deficit of the enzyme collagenase? Procollagen to collagen-collagen fibrils do not assemble correctly Hyperextensible skin

Connective Tissue VI Connection to and Movement of Cells Within the ECM Cells move by pulling on the matrix and crawl over it Hence cells must attach to the matrix Actin filament (cell) (binds)Adaptor protein (cell) Integrin (plasma membrane) Fibronectin (ECM) Collagen (ECM) Integrin—receptor protein found in the plasma membrane

Muscular tissue

Muscular Tissue All muscle cells can contract Voluntary Skeletal Muscle The main type found in mammals Composed of Myofibrils Made up of myofilaments Actin Myosin Responsible for striped appearance

Nervous tissue

Nervous Tissue Has highly developed properties of irritability and conductivity. Composed of packed nerve cells known as neurons.

Epithelial tissue

Epithelial Tissue Acts as a protective barrier There are more than 200 visible cell types in the body of a vertebrate Acts as a protective barrier May have complex biochemical functions and secrete specialized products Hormones Milk Tears Absorb nutrients Lining of the gut Detect signals Photoreceptors of the eye Auditory hair cells of the ear

Epithelial Tissue II Form Cells joined together, side to side, to form multicelluar sheets Thick sheets (many cells) Stratified Epidermis covering of the skin One cell thick Simple Lining of the gut

Epithelial Tissue III Form Cells may be tall Columnar Cells may be cubed shape Cuboidal Cells may be “flat” Squamous

Epithelial Tissue IV Since epithelial tissue are in the form of sheets, they have two sides (faces) Apical surface Free and exposed to the air or to a watery fluid Basal surface Rests on some other tissue Usually connective tissue Basal lamina The basal lamina (often confused with the basement membrane, and sometimes used inconsistently in the literature, see below) is a layer on which epithelium sits and which is secreted by the epithelial cells.

Epithelial Tissue V Columnar epithelium Tall narrow cells often with cilia Used in transporting mucus and other particles Found in Nasal cavities Trachea Oviducts Ventricles of the brain

Epithelial Tissue VI Squamous epithelium Called “pavement epithelium” Flattened single layer of thin nucleated cells Found where rapid diffusion takes place Bowman’s capsule Alveoli Endothlium

Epithelial Tissue VII Compound (Stratified Epithelium) Many layers of cells Ones nearest to the basement are normally flattened and dead Impregnated with keratin Found where there is considerable mechanical stress Epidermis of skin Esophagus Anal cavity Vagina

Epithelial Sheets And Cell to cell connections

Introduction Epithelial cell junctions can be classified according to their function Prevent leakage of molecules Provide strong mechanical attachments Provide a special type of intimate chemical communication In most epithelia, all types of junctions are present together

Tight Junctions Sealing function in invertebrates Seal neighboring cells together so that water-soluble molecules cannot easily leak between the cells Make the epithelium leak proof Separate the apical and basal surfaces

Desmosome Considered as a “spot weld,” anchors intermediate filaments in one cell to those in a neighboring cell Specifically keratins, an intermediate filament, found in epithelia Anchorage is mediated by integrin proteins in the basal plasma membrane of epithelial cells

Gap Junction Allows passage of small water-soluble ions and molecules Found in most epithelial cells and many other types of tissue Identical plasma membranes found in opposite cells Connexons Gap junctions, found between heart muscle cells, provide the electrical coupling that allows electrical waves of excitation to spread through the tissue, triggering coordinated contraction of the cells.

Plant Tissue

Plant Tissue Plants are sedentary in comparison to animals Tissue is more, or less, rigid Cells, when taken into isolation, are weak and fragile The strength of plants rise from the cell walls Cell wall Type of extracellular matrix, that the cell secrete around itself, allows “wood” to be thick and hard or thin and flexible in a leaf

Cell to Cell Connection Plasmodesmata Found in plant tissue Cytoplasms of adjacent plant cells are connected via minute communicating channels called plasmodesmata Lined with plasma membrane common to the two connected cells. Contains a fine tubular structure, desmotubule, derived from the smooth endoplasmic reticulum Allows restricted range of ions and small molecules to pass Similar to gap junctions found in animal tissue

Plasmodesmata

Plant Tissue Three Tissue Systems Dermal Tissue Vascular Tissue Plant’s protective covering in contact with the environment Facilitates water and ion uptake in roots Regulates gas exchange in leaves and stems Vascular Tissue Xylem & phloem Conducts water and solutes between organs Provides structural support Ground Tissue Packing and supportive tissue Food manufacturing and storage

Dermal Tissue Epidermis Primary outer protective, usually of one layer of cells, covering of the plant Cells of epidermis have thick primary cell walls and are covered by a special cuticle. Modified cells, of the epidermis, form hairs of various kinds and stomata

Dermal Tissue II Stomata Openings in the epidermis Regulate gas exchange in the plant Formed by two specialized epidermal cells Guard cells Regulate the diameter of the pore Distributed in species-specific pattern within each epidermis

Dermal Tissue III Hairs Appendages derived from epidermal cells Trichomes Appendages derived from epidermal cells Function in protection, absorption and secretion Cotton seed Single hair cells developing the epidermis if cotton seed Walls will be secondarily thickened with cellulose to form cotton fibers Root hairs are used to take up water and ions from the soil

Trichomes

Ground Tissue Three main types of cells Parenchyma Collenchyma Sclerenchyma

Ground Tissue Cell Types

Parenchyma Cells Unspecialized cells, with a variety of functions, that are a major component of ground tissue. Apical and lateral meristematic cells of shoots and roots provide new cells required for growth Storage Food production and storage occur in the photosynthetic cells of the leaf Mesophyll cells Storage parenchyma cells form the bulk of most fruits and vegetables Present in vascular tissues Tissue used in the movement of substances through the plant

Collenchyma Cells Similar to parenchyma cells except that the cell walls are thicker and are usually elongated and packed into ropelike fibers Primary cell wall is thickened with cellulose and pectin but not lignin Capable of stretching and provide mechanical support in the ground system of the elongating regions of the plant Common in the subepidermal regions of stems Function in supporting younger cells where plasticity is necessary to allow for changing growth requirements Pits are present in the cell walls

Collenchyma Cells

Sclerenchyma Cells Strengthening and supporting functions Usually dead cells with thick lignified secondary cell walls Forms supporting tissue with a secondary cell wall, composed of lignin, deposited on the primary cell wall of cellulose Two basic types Sclerids Short and unbranched cells found in seed coats and fruit Fibres Form long bundles Found often in the vascular bundles of dicotyledons or around the vascular bundles of monocotyledons Jute Hemp Flax

Xylem Primary xylem is doemed from the embryo and the resultant meristems Secondary xylem, which develops later, is formed during secondary thickening Four main elements Vessels Cells have more than one perforation at each end so that water can move easily from cell to cell Tracheids Cells have no open ends and the pits occur in pairs so that the water can pass easily through the thin pit membrane

Xylem II Fibres Parenchyma Long cells whose secondary walls are commonly lignified. Pits frequent Used for support Parenchyma

Phloem Primary phloem develops from the procambium Secondary phloem develops from the vascular cambium Four main elements Sieve tubes Highly specialized phloem cells Companion cells Form from sieve tubes early in their development Contains a nucleus where the sieve tube does not Walls between two are thin and densely pitted Sclerenchyma Parenchyma