Tissues Tissues Definition a group of closely associated

Tissues

Tissues Definition: a group of closely associated cells that perform related functions and are similar in structure n Between cells: nonliving extracellular material n Four basic types of tissue…function n ¨ Epithelium…covering ¨ Connective tissue…support ¨ Muscle tissue…movement ¨ Nervous tissue…control

Cell Junctions n Tight Junctions: Contain web like strands of transmembrane proteins that fuse outer layers of adjacent plasma membranes together. These retard passage of liquids between cells. They prevent leakage and keep certain tissues more or less water tight. Would you expect to see these in tissue of the urinary bladder? Why?

Cell Junctions n Adherences Junctions: Contain plaque, which is a dense layer of proteins inside of the plasma membrane which attaches to the cytoskeleton and to the plasma membrane proteins. Adherences junctions help epithelial surfaces resist separation.

Cell Junctions n Desmosomes also contain plaque. They serve such purposes as keeping cardiac muscle fibers from separating during contraction and keeping epithelial cells from separating under tension.

Cell Junctions Hemidesmisomes anchor cells to basement membranes (we’ll talk more about this later). n They look like “half desmisomes” but are structured differently (chemically). n

Cell Junctions Gap Junctions: contain proteins called connexins that produce tiny fluid filled tunnels called connexons. These allow the cells in tissues to communicate with one another. n In embryos, these may allow exchange of electrical and chemical info important in differentiation. n

Gap junctions (continued) These also enable nerve and muscle impulses to spread rapidly among cells n This is a process that is important for normal operation of some parts of the nervous system, for the contraction of the heart muscle and the muscles in the gastrointestinal (GI) tract. n

Cell Junctions n Tight junctions ¨ n Adherens junctions ¨ n So close that are sometimes impermeable Transmembrane linker proteins Desmosomes Anchoring junctions ¨ Filaments anchor to the opposite side ¨ n Gap junctions ¨ Allow small molecules to move between cells

Germ Layers All tissues of body develop from 3 primary germ layers that form in a human embryo. n Mesoderm gives rise to all connective tissues and most muscle tissues as well as some epithelial tissue n Ectoderm gives rise to nerve tissue and epithelial tissue. n Endoderm gives rise to epithelial tissue. n

Epithelia (plural) n n n Epithelium: sheet of cells that covers a body surface or lines a body cavity; also form most of the body’s glands Roles: as interfaces and as boundaries Functions: Protection Absorption Sensory reception Ion transport Secretion Filtration Formation of slippery surfaces for movement

Special characteristics of epithelia n n n Cellularity Specialized contacts Polarity ¨ Free upper (apical) surface ¨ Lower (basal) surface contributing basal lamina to basement membrane n n Support by connective tissue Avascular but innervated ¨ Without vessels ¨ With nerve endings n Regeneration

Classification of epithelia n According to thickness ¨ “simple” - one cell layer ¨ “stratified” – more than one layer of cells (which are named according to the shape of the cells in the apical layer) n According to shape ¨ “squamous” – wider than tall ¨ “cuboidal” – as tall as wide ¨ “columnar” - taller than wide

to protect

where diffusion is important where tissues are involved in secretion and absorption: larger cells because of the machinery of production, packaging, and energy requirements

“ciliated” literally = eyelashes (see next page)

Stratified: regenerate from below

Rare…

Rare…

Endothelium A simple squamous epithelium that lines the interior of the circulatory vessels and heart Mesothelium Simple squamous epithelium that lines the peritoneal, pleural and pericardial cavities and covers the viscera

Glands Epithelial cells form them n Production & secretion of needed substances n Are aqueous (water-based) products n The protein product is made in rough ER, packed into secretory granules by Golgi apparatus, released from the cell by exocytosis n

Classification of glands n By where they release their product ¨ Exocrine: external secretion onto body surfaces (skin) or into body cavities ¨ Endocrine: secrete messenger molecules (hormones) which are carried by blood to target organs; “ductless” glands n By whether they are unicellular or multicellular

Exocrine glands unicellular or multicellular Unicellular: goblet cell scattered within epithelial lining of intestines and respiratory tubes Product: mucin mucus is mucin & water

Multicellular exocrine glands Epithelium-walled duct and a secretory unit

Examples of exocrine gland products Many types of mucus secreting glands n Sweat glands of skin n Oil glands of skin n Salivary glands of mouth n Liver (bile) n Pancreas (digestive enzymes) n Mammary glands (milk) n

Endocrine glands n Ductless glands n Release hormones into extracellular space ¨ Hormones n are messenger molecules Hormones enter blood and travel to specific target organs

Epithelial surface features n Lateral surface ¨ Adhesion proteins ¨ Tongue and groove wavy contours ¨ Cell junctions: see next slide n Basal surface ¨ Basal lamina: noncellular sheet of protein together with reticular fibers form basement membrane n Apical surface

Apical surface features n Microvilli – maximize surface area ¨ Fingerlike extensions of the plasma membrane of apical epithelial cells ¨ On moist and mucus secreting epithelium ¨ Longest on epithelia that absorb nutrients (small intestine) or transport ions (kidneys) (continued)

n Cilia ¨ Whiplike motile extentions of the apical surface membranes n Flagellum ¨ Long isolated cilium ¨ Only found as sperm in human

n Four basic types of tissue ¨Epithelium ¨Connective tissue n Connective tissue proper (examples: fat tissue, fibrous tissue of ligaments) n Cartilage n Bone n Blood ¨Muscle tissue ¨Nervous tissue

Classes of Connective Tissue: note the cell types and great variety of subclasses

Connective Tissue n n Originate from embryonic tissue called mesenchyme Most diverse and abundant type of tissue Many subclasses (see previous slide) Function: to protect, support and bind together other tissues ¨ Bones, ligaments, tendons ¨ Areolar cushions; adipose insulates and is food source ¨ Blood cells replenished; body tissues repaired n Cells separated from one another by large amount of nonliving extracellular matrix

Extracellular Matrix explained n n Nonliving material between cells Produced by the cells and then extruded Responsible for the strength Two components 1. Ground substance ¨ ¨ 2. Of fluid, adhesion proteins, proteoglycans Liquid, semisolid, gel-like or very hard Fibers: collagen, elastic or reticular

Basic functions of connective tissue reviewed Support and binding of other tissues n Holding body fluids n Defending the body against infection n ¨ macrophages, n plasma cells, mast cells, WBCs Storing nutrients as fat

Classes of Connective Tissue *

Classes of Connective Tissue *

Classes of Connective Tissue *

Classes of Connective Tissue *

Classes of Connective Tissue *

Membranes that combine epithelial sheets plus underlying connective tissue proper (see next slide) n Cutaneous membranes ¨ Skin: n epidermis and dermis Mucous membranes, or mucosa ¨ Lines every hollow internal organ that opens to the outside of the body n Serous membranes, or serosa ¨ Slippery membranes lining the pleural, pericardial and peritoneal cavities ¨ The fluid formed on the surfaces is called a transudate n Synovial membranes ¨ Line joints

(a) Cutaneous membrane (b) Mucous membrane (c) Serous membrane

n Four basic types of tissue ¨Epithelium ¨Connective tissue ¨Muscle tissue n Skeletal n Cardiac n Smooth ¨Nervous tissue

n Four basic types of tissue ¨Epithelium ¨Connective tissue ¨Muscle tissue ¨Nervous tissue n Neurons n Supporting cells

Tissue response to injury n n Immune: takes longer and is highly specific Inflammation ¨ Nonspecific, local, rapid ¨ Inflammatory chemicals ¨ Signs: heat, swelling, redness, pain n Repair – two ways ¨ Regeneration ¨ Fibrosis n n and scarring Severe injuries Cardiac and nervous tissue

Tumors (neoplasms): abnormal growth of cells Adenoma – neoplasm of glandular epithelium, benign or malignant n Carcinoma – cancer arising in an epithelium (90% of all human cancers) n Sarcoma – cancer arising in mesenchymederived tissue (connective tissues and muscle) n

STEM CELLS…. ______ Inner cell mass becomes the baby STEM CELLS