Chapter 4 Tissue Level of Organization

Tissues are… Groups of similar cells and extracellular products that carry out a common function providing protection facilitating body movement Study of tissues is histology

4 primary types of tissues in the body epithelial connective muscle nervous today later, dude

Epithelial Tissue Epithelial tissue covers or lines every body surface and body cavity Epithelium is composed of one or more layers of closely packed cells between two compartments

Characteristics of Epithelial Tissue Cellularity: composed almost entirely of cells (with some extracellular matrix and sometimes other structures)

Characteristics of Epithelial Tissue Apical (free) surface Epithelium Lateral surface Basement membrane Polarity: has specific top and bottom apical surface exposed to external environment or internal body space, and basal surface attached to underlying connective tissue, plus lateral surfaces connected by intercellular junctions Basal surface Connective tissue Blood vessel (a) Epithelium–connective tissue junction

Characteristics of Epithelial Tissue Attachment: basal surface bound to basement membrane Avascularity: no blood vessels; receive nutrients across apical surface or by diffusion Innervation: lots of nerve endings High regeneration capacity: epithelial cells are frequently damaged or lost to abrasion, so they are replaced quickly

Functions of Epithelial Tissue Physical protection: protect exposed and internal surfaces from dehydration, abrasion, destruction Selective permeability: act as gatekeepers to let some substances in and keep others out Sensation: sense changes in the environment Some also do secretion: contain glands that release sweat, scents, hormones, etc.

Specialized structures of Epithelial Tissue Epithelium Basement membrane Basement layer is extracellular layer between epithelium and connective tissue often visible with microscope Basal surface Connective tissue (a) Epithelium–connective tissue junction

Specialized structures of Epithelial Tissue Fig. 4.1 Specialized structures of Epithelial Tissue In some epithelial tissue, basal cells anchored to basement membrane with junctions called hemidesmosomes Hemidesmosome

Intercellular Junctions Fig. 4.1 Intercellular Junctions Junctions between cells in epithelium Tight junctions anchor cells to each other prevents substances from passing between cells materials must move through cells, or are blocked from moving past cells found in intestinal lining Tight junction

Intercellular Junctions Fig. 4.1 Intercellular Junctions Adhering junctions often deep to tight junctions Form all the way around a cell Support apical surface Allows passage between cells below apical surface Adhering junction

Cell-Cell Attachment Desmosomes attach cells to each other Bind epithelium together Bind muscle cells Resist shear forces

Cell-Cell Communicating Attachment 2 Cell 1 Cytosol Channel proteins Intercellular space Gap junctions tunnel between two plasma membranes Found in muscles Enables sharing of ions and proteins Enables fast communication between cells Cell membrane

Cell-Cell Communicating Attachment Gap junctions are communicating junctions. Gap junctions tunnel between two plasma membranes Found in muscles Enables sharing of ions and proteins Enables fast communication between cells Clusters of gap junctions Freeze fracture of cell membrane

Classifications of Epithelial Tissue Apical surface Lateral surface Basement membrane Basal surface Number of cell layers simple = one cell layer thick stratified = >2 cell layers thick Simple epithelium Apical surface Lateral surface Basement membrane Basal surface Stratified epithelium

Classifications of Epithelial Tissue Nucleus Squamous cell Nucleus Cell shape squamous = flattened cuboidal = basically cube-shaped or roundish columnar = long and thin (like a column) Cuboidal cell Nucleus Columnar cell

Simple squamous epithelium Simple cuboidal epithelium Table 4.3a-1 LM 400x Simple squamous cell Amnion Kidney tubules Simple cuboidal cell LM 1000x Simple squamous epithelium Simple cuboidal epithelium

Table 4.3b-2 Cilia Nonciliated simple Simple columnar columnar cell LM 100x Uterine tube Simple columnar epithelial cell LM 400x Mucosa of small intestine Nonciliated simple columnar cell Nonciliated simple columnar epithelium Ciliated simple columnar epithelium

Table 4.4a-1 Vagina Epidermis of skin Squamous epithelial cell Nonkeratinized stratified squamous epithelium LM 125x LM 100x Epidermis of skin Keratinized stratified squamous epithelial cells Living stratified

Table 4.4b-1 Male urethra Duct of sweat gland Columnar cell LM100x Columnar cell Cuboidal cell Stratified cuboidal epithelium Stratified columnar epithelium

Table 4.5a Nasal cavity lining Pseudostratified columnar epithelium looks stratified, but is actually one layer of cells all cells in contact with basement membrane stratified look because nuclei are at different levels in cells may be ciliated or nonciliated Cilia Pseudostratified ciliated columnar epithelium Columnar cell Basal cell

Transitional epithelium is made of cells that can stretch Table 4.5b Urinary bladder lining Transitional epithelium is made of cells that can stretch cells look cuboidal when relaxed; look squamous when stretched found in lining of urinary bladder Binucleated epithelial cell Transitional epithelium (relaxed)

Connective tissue Supports, protects, and binds organs Includes tendons and ligaments, body fat, cartilage, skeleton, blood

Connective tissue Contains specific types of cells protein fibers ground substance nonliving material of protein and carbohydrate molecules Each type of connective tissue has a specific function Develops from mesenchyme type of stem cell from which all other connective tissues arise first arises in developing embryo form extracellular matrix (stuff outside and around cells, produced by cells)

Ground substance Elastic fibers Extracellular matrix Collagen fibers Fig. 4.7 Ground substance Elastic fibers Extracellular matrix Collagen fibers Protein fibers Reticular fibers Mesenchymal cell Blood vessel Macrophage Adipocyte (fat cell) Fibroblast

Loose connective tissue Fewer cells and protein fibers than dense connective tissue protein fibers loosely connected

Areolar connective tissue Table 4.9a-1 Papillary layer of dermis Provides cushioning to overlying tissues Fibroblasts are most visible cells cells with tapered ends produce fibers and ground substance Has collagen fibers fibers of protein collagen strong, flexible, resistant to stretching Has elastic fibers fibers of protein elastin (thinner than collagen) stretch and recoil easily Elastic fiber Fibroblast Collagen fiber Ground substance LM 240x

Adipose connective tissue Table 4.9a-2 Adipose connective tissue Subcutaneous layer (hypodermis) AKA “fat” contains large cells filled with a droplet of lipid nucleus pushed to the side cushions structures from shocks acts as insulation storage of energy for the body adipocytes can’t divide, but mesenchyme can make more if needed Adipocyte Blood vessel Adipocyte nucleus LM 250x LM 200x

Dense connective tissue Primarily protein fibers lots of collagen fibers Less ground substance than loose connective tissue 3 types: dense regular tendons dense irregular reticular layer of dermis elastic wall of aorta

Dense, regular connective tissue Table 4.10a-1 Dense, regular connective tissue Tendon Found in tendons and ligaments Collagen fibers packed tightly, arranged in parallel to force applied Few blood vessels Ground substance Collagen fibers Fibroblast nucleus LM 250x

Dense, irregular connective tissue Table 4.10a-2 Reticular layer of dermis Collagen fibers arranged in clumps and bunches scattered throughout tissue Withstands stress in all directions Found around cartilage and bone Forms capsule around some internal organs Collagen fiber bundles Fibroblast nucleus Ground substance LM 200x

Elastic connective tissue Table 4.10b-1 Aorta wall Elastic connective tissue Ground substance Branching elastic fibers provide resilience and ability to return to shape after being deformed Lots of fibroblasts Collagen fibers packed close Fibroblast nucleus Elastic fibers