• Cells of similar type and function
• Typically clustered into layers, sheets or groups

• Tissues are classified into the following four primary types:

1.Epithelial tissue

• Covers and lines tissue sheets or organs

2.Connective tissue

• Provides structure, support, protection

3.Muscle tissue

• Specialized for movement

4.Nervous tissue

• Controls the work of muscles, modulates function by secretions

• Sheets of cells that cover and line other tissues
• Protect underlying tissues and may act to filter biochemical substances
• May absorb, secrete, or excrete biochemical substances
• May play a role in the reception of sensory input

• Each epithelial cell has an apical surface and a basal surface
• Apical surface faces the lumen or outside of the organ 
• Basal surface faces the basal lamina and blood vessels
• Lateral surfaces  are connected to neighboring cells by junctional complexes.
• Epithelial cells are avascular. 
• Most epithelial cells are innervated.

• Three major types of cellular junctions 

1. Tight junctions

• Formed by the fusion of the outermost layers of the plasma membranes of adjoining cells 

• Found in tissues in which there can be no leaks (urinary bladder, digestive tract)

2. Desmosomes

• Mechanical coupling formed by filaments that interlock with one another
• Tonofilaments extend from the plaque into the cytoplasm.
• Found in tissues that undergo repeated episodes of tension and stretching (skin, heart, uterus) 
• Hemidesmosomes link epithelial cells to the basement membrane

3. Gap junctions

• Tubular channel proteins (connexons) that extend from the cytoplasm of one cell to the cytoplasm of another 
• Allow exchange and passage of ions and nutrients 
• Found in intestinal epithelial cells, the heart, and smooth muscle tissue

• Nonliving meshwork of fibers that cements the epithelial cell to the underlying connective tissue 
• Also called basal lamina
• Varies in thickness 
• Helps prevent the cell from being torn off by intraluminal pressures
• Acts as a partial barrier between the epithelial cell and the underlying connective tissue

• Surfaces of epithelial cells vary depending on where they are located and what role they play in the function of the tissue
• Smooth
• Microvilli (brush border)
• Cilia
• Keratin.

• Number of layers of cells: Simple or stratified
• Shape of the cells: squamous, cuboidal, and columnar
• Presence of surface specializations: Cilia, keratin, etc.

• Fragile and thin 
• Found lining surfaces involved in the passage of either gas or liquid 
• Flat and smooth

• Single layer of cube-shaped cells 
• Round, dark-staining nuclei aligned in a single row 
• Occurs in areas of the body where secretion and absorption take place

• Elongated and closely packed together
• Nuclei aligned in a row at the base of the cell near the basement membrane
• Found in many excretory ducts as well as in the digestive 
• 2 types: absorptive cell and goblet cell

• Multilayered 
• Occur in areas of the body subject to mechanical and chemical stresses such as oral cavity and esophagus
• Protect underlying tissues

• Usually two layers of cuboidal cells
• Found primarily along large excretory ducts, such as mouth, salivary glands and ducts
• Protects underlying tissues

• Found only in select parts of the respiratory, digestive, reproductive systems and along some excretory ducts
• Function in secretion and protection

• Cell nuclei are found at different levels across the length of the tissue
• Some cells do not reach the luminal surface 
• Found in respiratory tract and in portions of the male reproductive tract

• Stratified epithelium with a basal layer of cuboidal or columnar cells and a superficial layer of cuboidal or squamous cells
• Found in areas of the body required to expand and contract as part of their normal function, such as kidney, urethra, bladder

• Groups of cells that manufacture and discharge a secretion
• Classification of glands

1. Presence or absence of ducts 
2. Number of cells that compose them 
3. Shape of the secreting ducts
4. Complexity of the glandular structure
5. Type of secretion they produce
6. Manner in which the secretion is stored and discharged

• Glands that do not have ducts or tubules and whose secretions are distributed throughout the body
• Produce and secrete hormones into the bloodstream or the lymphatic system
• Part of a complex, biochemical network known as the endocrine system
• The endocrine pancreas

• Discharge secretions via ducts directly into local areas (except for goblet cell)
• Unicellular or multicellular
• The exocrine pancreas

• Unicellular exocrine gland 
• Ductless and composed of modified columnar epithelial cell 
• Found among columnar cells of the respiratory and digestive tracts and the conjunctiva of the eye 
• Secretes mucin

• Composed of a secretory unit and a duct 
• Secretory unit is usually surrounded by connective tissue rich in blood vessels and nerve fibers 
• May be surrounded by myoepithelial cells that assist with the discharge of secretions into the glandular duct

• Ducts:
• Simple: main duct is unbranched 
• Compound: main duct is branched
• Shape of secretory portions 
• Tubular: secretory cells form a long channel of even width
• Alveolar or acinar: secretory unit forms a rounded sac
• Tubuloalveolar, or tubuloacinar: secretory units possess both tubular and alveolar qualities

• Merocrine glands package their secretions  and release them via exocytosis as they are manufactured. 
• Apocrine glands store their secretions and then release the top part of the cell (apex) into the duct system
• Holocrine glands store their secretions and then release the entire contents of the cell

• Serous secretions 
• Watery 
• Contain a high concentration of enzymes
• Mucous secretions 
• Thick, viscous
• Composed of glycoproteins
• Mixed exocrine glands contain both mucous and serous components.

• Functions
• Forms metabolic and structural connections between other tissues
• Forms a protective sheath around organs and helps insulate the body
• Acts as a reserve for energy
• Provides the frame that supports the body
• Composes the medium that transports substances from one region of the body to another 
• Plays a role in the healing process and in the control of invading microorganisms

• Extracellular matrix
• Extracellular fibers
• Ground substance
• Cells 

• Medium through which cells exchange nutrients and waste with the bloodstream
• Amorphous, homogeneous material 
• Ranges in texture from a liquid or gel to a calcified solid
• Acts to protect the more delicate cells it envelopes
• Serves as an effective obstacle for invading microorganisms

• Collagenous fibers
• Strong, thick strands of collagen
• Organized into bundles of long, parallel fibrils composed of bundled microfibrils
• Variable density and arrangement of fibers
• Found in tendons and ligaments
• Reticular fibers
• Thin, delicate, branched networks of collagen
• Provide support for highly cellular organs  (endocrine glands, lymph nodes, spleen, bone marrow, and liver) 
• Also found around blood vessels, nerves, muscle fibers, and capillaries
• Elastic fibers 
• Branched networks composed primarily of the protein elastin
• Composed of coiled bundles of microfibrils
• Occur in tissues commonly subjected to stretching (vocal cords, lungs, skin, and walls of blood vessels)

• Fixed Cells: involved in production and maintenance of the matrix
• Fibroblasts, chondroblasts, osteoblasts, adipocytes, reticular cells
• Transient Cells: involved in the repair and protection of tissues
• Leukocytes, mast cells, macrophages

• Loose connective tissue 
• Areolar
• Adipose
• Reticular 
• Dense connective tissue 
• Dense regular
• Dense irregular
• Elastic

• Loose connective tissue 
• Fibers and cells suspended in a thick, translucent ground substance 
• Predominant cell is the fibroblast
• Manufactures the elastic, reticular, and collagenous fibers
• Surrounds every organ; forms the SQ layer that connects skin to muscle; envelopes blood vessels, nerves, and lymph nodes; present in all mucous membranes

• Loose connective tissue
• Areolar tissue in which adipocytes predominate 
• Highly vascular
• Acts as an energy storehouse, a thermal insulator, and a shock absorber

• Loose connective tissue 
• Network of thin reticular fibers. 
• Contains loosely arranged fibers and many fibroblasts suspended in a supportive ground substance
• Forms the stroma (framework of several organs)

• Composed of tightly packed, parallel collagen fibers 
• Relatively avascular 
• Makes up the tendons and ligaments 
• Can be found in fascial sheets that cover muscles

• Composed primarily of collagen fibers arranged in thick bundles 
• Fibers are interwoven to form a single sheet 
• Found in the dermis of the skin and in the fibrous coverings of many organs
• Forms the tough capsule of joints

• Primarily composed of elastic fibers
• Fibers may be arranged parallel or in interwoven patterns with fibroblasts and collagenous fibers interspersed
• Found in spaces between vertebrae and in areas of the body that require stretching (walls of arteries, stomach, bronchi, bladder, etc.)

• Cartilage
• Hyaline cartilage
• Elastic cartilage
• Fibrocartilage
• Bone
• Blood

• Found in joints and in the ear, nose, and vocal cords 
• Forms a framework on which bone is formed
• Avascular, no innervation
• Cells: 
• Chondrocytes
• Matrix:
• Ground substance
• Collagen fibers are most commonly found in the matrix, but elastic fibers are also present in varying amounts.

• Most common type of cartilage found in the body
• Composed of closely packed collagen 
• Found in joints at the ends of long bones, growth plates of long bones, tracheal rings, and connections of the ribs to the sternum 
• Composes most of the embryonic skeleton 
• Enclosed within a perichondrium

• Contains elastic fibers in dense branching bundles 
• Flexible: can withstand repeated bending 
• Found in the epiglottis of the larynx and in pinnae of ears of animals

• Usually found merged with hyaline cartilage and dense connective tissue 
• Contains thick bundles of collagen fibers with fewer chondrocytes than hyaline cartilage
• Lacks a perichondrium 
• Found in spaces between vertebrae of the spine, between bones in the pelvic girdle, and in the knee joint

• Matrix is a combination of organic collagen fibers and inorganic calcium salts
• Well vascularized
• Haversian canal contains both a vascular and a nerve supply 
• Canaliculi: channels within the matrix support passage of blood vessels into deeper portions of tissue
• Osteoblasts: manufacture the fibers that are part of the matrix
• Lacunae and canaliculi are created as the osteoblasts manufacture the bony matrix. 
• Osteocytes reside in lacunae. 
• Cellular extensions pass through the canaliculi.

• Matrix: 
• Ground substance: plasma 
• fibrous component: protein 
• Cells
• Erythrocytes 
• Leukocytes 
• Thrombocytes

• Collaboration between epithelial and connective tissue
• Thin, protective layers that line body cavities, separate organs, and cover surfaces
• Epithelial tissue coated in wed solution of liquid mucus (or urine, in the bladder)
• 4 common types of membranes:
• Mucous
• Serous
• Cutaneous
• Synovial 

• Mucous membranes (mucosae)
• Line organs with connections to the outside environment (mouth, intestines, nasal passages, etc.)
• Usually composed of either stratified squamous or simple columnar epithelium covering a layer of loose connective tissue 
• Submucosa : connective tissue layer that connects the mucosa to underlying structures
• May contain goblet cells or multicellular glands 
• Can produce large quantities of mucus 
• Mucus  consists primarily of water, electrolytes, and the protein mucin
• Some mucosae also can absorb (e.g., the epithelial layer in the intestine)

• Serous membranes (serosae)
• Line walls and cover organs of body cavities 
• Consist of a continuous sheet doubled over on itself to form two layers 
• The portion of the membrane that lines the cavity wall is called the parietal layer.
• The portion of the membrane that covers the outer surface of organs is called the visceral layer.
• In abdominopelvic cavity, visceral layers of serosa merge to form mesenteries.

• Also called integument (or, more simply, skin) 
• Composed of an outer keratinized stratified squamous epithelium, or epidermis
• Epidermis is attached to an underlying layer of dense irregular connective tissue called the dermis. 
• Dermis contains collagenous, reticular, and elastic fibers which enable skin to be both strong and elastic

• Line the cavities of joints 
• Composed of loose connective tissue and adipose tissue covered by a layer of collagen fibers and fibroblasts 
• Manufacture the synovial fluid that fills the joint spaces

• Composed of actin and myosin fibers
• Three types of muscle tissue

1. Skeletal
2. Smooth
3. Cardiac

• Large cells that contain hundreds of nuclei and mitochondria
• Usually controlled through conscious efforts (voluntary muscle)
• Skeletal muscle cells are striated
• Skeletal muscle cells are bundles of fibers held together by loose connective tissue
• The collagen fibers that surround the cells merge with the collagen fibers in tendons

• Composed of small, spindle-shaped cells that lack striations
• Muscle contractions cannot be consciously controlled (nonstriated involuntary muscle)
• Found in the walls of hollow organs, in exocrine glands, and along the respiratory tract 
• Responsible for peristalsis in gastrointestinal tract, constriction of blood vessels, and emptying of urinary bladder

• Found only in the heart 
• Contains specialized pacemaker cells that supply signal for heart to contract at regular intervals 
• Entirely involuntary and striated
• Cardiac muscle cells connected to one another via intercalated disks

• Found in the brain, spinal cord, and peripheral nerves 
• Composed of two general cell types:
• Neurons 
• Supporting neuroglial cells
• Neurons:
• Longest cells in the body
• Three primary parts:

1. Perikaryon 
2. Dendrites 
3. Axons 

• Neuroglial cells 
• Support the neurons

• Inflammation: initial response to injuries 
• Goal: limit further damage and eliminate any harmful agents 
• Repair: involves organization of granulation tissue and regeneration of lost tissue or formation of scar tissue

• Inflammatory Phase
• Pain is felt
• Cell damage and infection is dealt with
• Proliferative Phase
• Chemical mediators released to recruit required cell response
• Remodeling Phase

• Nonspecific reaction to injury or disease
• Steps

1. Vasodilation
2. Swelling
3. Clot formation
4. Phagocytosis
5. Capillaries return to normal size, blood flow and fluid leakage into the affected area abate

• Tissue that forms beneath the overlying blood clot or scab 
• Composed of a layer of collagen fibers infiltrated with capillaries (that have branched off existing capillaries in deeper layers of damaged tissue)
• Granulation tissue is slowly replaced by fibrous scar tissue.

• Clean Wound
• A “wound” made under aseptic conditions
• Clean Contaminated Wound
• A wound with either contamination that is easily removed or comes from another organ’s contents during surgery
• Contaminated Wound
• Gross aspects of foreign debris, bite wounds, GI tract contents in a surgery site
• Infected Wound
• Site is inflamed, has microorganisms present, pus and fibrin

• First intention:
• Edges of wound held in close apposition 
• Skin forms a primary union without formation of granulation tissue or significant scarring 
• Second intention: 
• Edges  of wound separated from each another
• Granulation tissue forms to close gap; scarring results
• Third intention:
• Contaminated wound left open until contamination is reduced and inflammation subsides; later closed by first intention; also called delayed primary closure

A group of tissues which perform a specific function