Tissues Chapter 13

Differential Cell Affinities Cells alter cell surface during development to change affinities. This allows different interactions and movements. Cell surface interactions determine strength and specificity of cell-cell binding. Also involves the cytoskeleton and extracellular matrix (ECM).

Remove different regions of embryo. Dissociate cells using alkaline solution and mix together. Cells sort out according to type. Final position reflects original position

Thermodynamic Sorting Model B Thermodynamic Sorting Model If A-A adhesion is stronger than A-B or B-B, A cells will be in the center with B on the outside. If A-A is equal to A-B there will be no sorting out If A-A and B-B are MUCH GREATER than A-B they will separate out.

Cells and Tissues Cells are arranged as tissues Tissues are held together by cell adhesion molecules (CAMs). Cadherins IgSuperfamily CAMs Integrins All are transmembrane proteins

Cell Adhesion Molecules Cadherins IgSuperfamily CAMs Appendix A.7 Integrins

Cell Adhesion Molecules Cadherins Ca++-dependent adhesion molecules. Single-pass transmembrane glycoproteins Homophilic binding--bind to the same type on other cells Cytoplasmic region interacts with the actin cytoskeleton via proteins called catenins. Examples: E cadherin– mainly epithelial N cadherin– mainly neural P cadherin-- placental

Integral Membrane Proteins

Cell Adhesion Molecules Ig Superfamily CAMs Ca++-independent adhesion molecules. Single-pass transmembrane glycoproteins; extracellular region has disulfide loops similar to Igs. Many show homophilic binding Example: N CAM L1 CAM

Cell Adhesion Molecules Integrins Heterodimers of alpha and beta chains Act as receptors for extracellular matrix (ECM) molecules Associate with the cytoskeleton on the inside Transmit information about the outside to the inside for a response (cell movement, cell shape, differentiation, etc.)

Cell Junctions Tight junctions Desmosomes and Adherens junctions seal epithelial cells to prevent molecules moving between cells polarize cells (apical and basal sides different) Desmosomes and Adherens junctions Include cadherins to hold cells together Gap Junctions Allow cell-cell communication

Epithelial Tissues Sheets of cells with an underlying basement membrane (basal lamina) Cells have polarity-- basal side by basement membrane and apical side opposite. Tight junctions prevent leakage between cells and maintain membrane polarity Adherens junctions and desmosomes contain CAMS to hold cells together. Adherens junctions and hemidesmosomes also hold cells to basement membrane

Epithelial Tissues Fig 13.1

Epithelial Tissues May be derived from any tissue layer Most coverings are ectodermal Epithelial linings such as intestines are endodermal Some sheets of muscle are epithelial

Types of Epithelial Tissue Fig 13.2

Types of Epithelial Tissue Simple epithelial--single layer Stratified- multiple layers Pseudostratified-- looks like multiple layers but each cells extends from apical to basal

Types of Epithelial Cells Cuboidal Squamous-- flattened Columnar

Types of Epithelial Tissue Fig 13.2

Epithelial Glands Many epithelial tissues form glands Glands may be simple or branched Exocrine glands secrete into ducts Endocrine glands secrete hormones into the bloodstream or surrounding tissue. Examples? Exocrine– sweat glands, salivary glands, mammary glands, liver—bile, pancreas—digestive enzymes into small intestine Endocrine– hormones; adrenal glands, thyroid glands, pituitary, hypothalamus, etc.pancreas-- insulin

Connective Tissues Consist mainly of fibroblast cells and the extracellular matrix they secrete (and sometimes other cells). Most are of mesodermal origin Dermis of the skin Adipose tissues Cartilage Bone Blood (sometimes considered separately)

Connective Tissues Collagen is most common extracellular matrix of connective tissues Also hyaluronan, fibronectins, elastins, and proteoglycans

Collagen Main component of ligaments and tendons Great tensile strength and elasticity Consists of woven fibers

Fibronectin http://www.ks.uiuc.edu Fibronectin in the extracellular matrix binds to integrins which are associated with actin filaments of the cytoskeleton.

Muscle Tissues Fig 13.3

Muscle Tissues Skeletal formed from myotome of somites Consist of multinucleate myofibers formed from fusion of myocytes Arranged as sarcomeres which appear striated Voluntary muscles

Muscle Tissues Smooth Cardiac From lateral plate mesoderm Surround blood vessels, intestines, ducts from some glands Mononucleate cells, not arranged as sarcomere Cardiac Heart muscle, also from lateral plate Consists of individual cells held together by junctions Has myofibers and is striated.

Muscle Tissues Fig 13.3

Neural Tissue

Neural Tissue Neural tube is induced by notochord in the ectoderm and forms as a neuroepithelium. Neural tube cells form neurons and glial cells Neurons send impulses; glial cells are support cells Neural crest cells migrate from the neural folds to form many different kinds of cells

Blood Vessels Fig 13.4

Circulatory system Sometimes considered connective tissue Hematopoietic stem cells produce many types of blood cells Arteries and veins consist of inner endothelial layer a smooth muscle layer Outer fibrous connective tissue layer Capillaries are a single cell layer thick with endothelial cells and a basal lamina.

Examples of importance of change in cell adhesion 1º and 2º mesenchyme cells of sea urchins Compaction Formation of the neural tube

Examples of importance of change in cell adhesion 1º and 2º mesenchyme cells of sea urchins 1º lose affinity for hyaline and each other and gain affinity for ECM components 2º gain affinity for fibronectin Compaction Formation of the neural tube

Examples of importance of change in cell adhesion 1º and 2º mesenchyme cells of sea urchins Compaction Formation of the neural tube

Compaction involves rearrangement of CAMs (E Cadherins) to sites of cell-cell contact-- holds cells tightly together.

Examples of importance of change in cell adhesion 1º and 2º mesenchyme cells of sea urchins Compaction Formation of the neural tube

Neural tube separates out from the epidermis above it.

Neural tube tissue stops expressing E-cadherins and begins expressing N-CAMs and N-cadherins. If expression of CAMs is experimentally manipulated, the tube will not sort out correctly.