Unit 2: Tissues

a group of cells with similar origin and function

–Epithelial tissues: cover surfaces, line cavities, form secretory parts of glands 

–Connective tissues: connect other tissues, support, protect, transport (blood), insulate (fat)

–Muscle tissues: movement

–Nervous tissue: recognizing and responding to stimuli (changes in environment), transfer information

by embryonic stem cells that arise 13-14 days after fertilization

–Ectoderm (outer) – forms skin and nervous system 

–Mesoderm (middle) – forms muscle, bone and blood vessels

–Endoderm (inner) – forms lining of digestive tract and derivatives

•Closely packed cells (cell junctions) 

•Little extracellular matrix

•Single (simple) or multi-layered (stratified)

•Associated with underlying connective tissue

•Avascular (no blood vessels)

•Regeneration (mitotic cell division)

•Polarity

•Apical surface - free edge exposed to body exterior or cavity 

• •Basal surface - attached to basement membrane
• --specialized type of extra- cellular material secreted by epithelial & connective cells 
• --important to tissue repair

• Number of layers:      Shape of cells:
• Simple                           Squamous
• Stratified                       Cuboidal 
•                                     Columnar

• Simple Tissue 
• Simple Squamous*
• Simple Cuboidal*
• Simple Columnar*
• Pseudostratified Columnar*

• Stratified Tissue
• *Defined by the shape of the outer cells

• Stratified Squamous*
• Stratified Columnar
• Stratified Cuboidal
• Transitional*

Function: filtration, diffusion, secretion, protection 

• Location:
• •endothelium (lining of blood and lymphatic vessels, heart)
• •mesothelium (serous membranes of ventral body cavity)
• •kidneys, lungs

• Function: 
• •secretion 
• •absorption 

• Location:
• •kidneys 
• •glands

• Function: 
• •secretion 
• •absorption 

• Location:
• •digestive, respiratory & reproductive systems 

• Modifications:
• •Cilia - movement of materials; e.g., uterine tubes 
• •Microvilli - increase surface area for absorption; small intestine 
• •Goblet cells - secrete mucous for lubrication; GI

• •false (pseudo) layers 
• •nuclei at different levels give appearance of being multilayered 
• •all cells rest on basement membrane but NOT all reach free surface 

Function: secretion

Location: respiratory system

• Modifications:
• –cilia - respiratory system 
• –goblet cells - respiratory system

• Function:
• •protection against abrasion

• Location:
• •Keratinized (epidermis of skin)
• –contains keratin (water-proof protein)

• •Non-keratinized (mouth, esophagus, vagina, anus)
• –lacks keratin

• Function: 
• •protection
• •absorption
• •secretion

• Location:
• •ducts of sweat & salivary glands

• Function: 
• •protection 
• •secretion 

• Location:
• •male urethra
• •mammary gland ducts

• •Stretched - uppermost cells are squamous 
• •Relaxed - uppermost cells are cuboidal 

• Function:
• •capable of  stretching to accommodate fluctuations in fluid volume

• •Location:
• –urinary system

• Tight junctions - tight seals between cells 
• •prevent movement of substances
• •stomach & urinary bladder

• Desmosomes - disc-shaped structures
• •resist stretching & twisting 
• •skin epidermis, heart 

• Gap junctions - protein channels 
• •allow transfer of ions à electric signaling between cells 
• •cardiac & smooth muscle tissue

• a)fibroblasts 
• b)a rich vascular supply
• c)cilia
• d)dense microvilli

TRUE/FALSE

•Composed primarily of epithelium with supporting network of connective tissue 

Endocrine glands secrete hormones into blood (by way of interstitial fluid)

• •e.g., pituitary gland, adrenal gland, pancreas
• *will be covered in Unit XI & XII

• Exocrine glands secrete products into ducts 
• •classified by shape & complexity 
• •classified by mode of secretion

• –merocrine glands - secrete product; sweat glands
• –apocrine glands – secrete product + fragments of cells; mammary glands
• –holocrine glands – product + entire cell; oil glands

• •well-innervated 
• •highly vascular (except cartilage) 
• •few cells embedded in large amount of extracellular (outside the cell) matrix 
• •structural elements: matrix and cells 
• –each type of CT has its own associated cell type & matrix
• •all CT arise from mesenchymal cells

= consists of ground substance, fibers and fluid 

• Ground substance
• •shapeless
• •contains nonfibrous proteins (hyaluronic acid and proteoglycans) 
• •consistency varies from rock-hard (bone) to watery fluid (plasma)

• •Collagen 
• –thick, most abundant fibers
• –Strong, resists pulling tension

• •Reticular
• –fine strands of collagen
• –form network around blood vessels, soft organs, basement membrane

• •Elastic (elastin)
• –stretch and recoil without breakage
• –skin, lungs, blood vessels

•Blasts – create matrix (mitotically active) 

• What does it mean?
• –e.g., fibroblasts, osteoblasts

• •Cytes – maintain matrix (mature cell)
• –e.g., adipocytes, osteocytes

• •Clasts – break down (reabsorb) matrix
• –e.g., osteoclasts

• Embryonic CT 
• •Mesenchyme (irregularly shaped osteoblasts & semifluid matix)
• •Mucous (support umbilical cord blood vessels)

• Adult CT
• •Connective tissue proper – Loose and Dense
• •Supporting CT – Cartilage and Bone
• •Fluid CT – Blood and Hematopoietic tissue

•areolar, adipose and reticular 

• Areolar *Table 4.8
• •contains three types of fibers
• •cells: fibroblasts, macrophages, mast cells

• What is the function of each cell type?
• •water and solute reservoir
• •associated with most epithelial membranes
• –forms lamina propria of mucous membranes
• –forms papillary layer of dermis

• •adipocytes, fibers & small extracellular matrix 
• •insulates, stores energy, absorbs shock
• •subcutaneous areas & around organs
• •liposuction

• •network of reticular fibers irregularly arranged 
• •cells – dendritic (immune) cells, microphages
• •forms framework of spleen, liver, lymph nodes, bone marrow

• •Dense Regular 
• –Collagenous
• –Elastic

• •Dense Irregular
• –Collagenous
• –Elastic

•densely packed parallel collagen fibers 

•function: provides strength & resists tension in one direction

•location: tendons (muscle-bone); ligaments (bone-bone), aponeuroses (wide tendons)

• •abundant elastic fibers (elastin=yellow color) 
• •parallel bundles of collagen fibers

•function: stretch and recoil

•location: elastic ligaments of vocal folds and between vertebrae

• •randomly oriented fibers 
• •withstand stretching in all directions

• Dense Irregular Collagenous
• •collagen fibers - provide strength
• •dermis 
• •fibrous capsules around some organs, e.g., kidneys, testes, heart (fibrous pericardium) 
• •perichondrium, periosteum

•Tissues change (as a result of changing cells) affects organ function and structure that decrease: 

• –Lung capacity by 50%
• –Muscle strength by 45% 
• –Kidneys by 30% 

Why?

•Collagen & elastin decrease --> tissue stiffer, less elastic --> less efficient

• •Fat content changes
• –Male – increases until age 60, then gradually decreases
• –Female – fat accumulates continuously

•Total amount of water decreases --> slower metabolism --> slower response to drugs

•Tissue atrophy --> decrease in mass of most organs

–Would it affect function of the organ?

• •avascular 
• •perichondrium = dense irregular CT surrounding cartilage (supplies blood)
• •lack innervation
• •cells = chondroblasts (during cartilage formation) and chondrocytes (mature) found in lacunae (lacuna) 

• •types:
• Hyaline Cartilage 
• Elastic Cartilage 
• Fibrocartilage 

• •most abundant 
• •collagen fibers (not visible) make it strong, yet pliable 
• •tip of nose, respiratory system, epiphyseal plate (growing bone), fetal skeleton, articular cartilage, ribs 

•Which part of a bone is covered with the articular cartilage?  Explain why.

• •thick bundles of collagen fibers 
• •compressible and tough
• •intervertebral disks, menisci (knee), symphysis pubis

• •elastic fibers 
• •provides rigidity and flexibility
• •allow recoil after bending
• •external ear (pinna), epiglottis and auditory tubes

• Functions: 
• •forms the skeletal system
• •provides support,
• •movement (muscle attachment),
• •protection,
• •hemopoiesis ( hematopoiesis)= blood cell formation

• Features:
• •osteocytes in hard matrix (calcium, magnesium and phosphate salts);
• •collagen fibers and other proteins

• •Cancellous (spongy) bone 
• –plates of bone called trabeculae
• –spaces between trabeculae are filled with bone marrow and blood vessels
• –found in interior of bones of the skull, vertebrae, sternum, pelvis, and ends of long bones.

• •Compact bone
• –based on osteon (haversian system)
• –outer portion of all bones and shafts of long bones

• •cells & cell fragments (suspended in matrix-plasma) 
• –leukocytes = white blood cells (WBCs)
• –erythrocytes = red blood cells (RBCs) 
• –platelets (cell fragments) 

•contains solutes (ions, nutrients, wastes) and suspended substances, e.g., large proteins

• Functions
• •fights diseases 
• •transports substances, 
• e.g., nutrients, wastes, hormones, respiratory gasses

• •Function & location: 
• –forms blood cells (red bone marrow)
• –stores lipids (yellow bone marrow)

• •high  metabolic rate 
• •highly vascular (needs good supply of oxygen & nutrients when active) 
• •produce movement of body parts including movement of materials through tubes 
• •cells = muscle fibers 

• •types:
• –Skeletal
• –Cardiac
• –Smooth

• •Location - attached to bones 
• •Function - voluntary movement of skeleton & control of sphincters  
• •Cells 
• –large, long, cylindrical & striated
• –multinucleate (develops from union of cells)

• •Location - myocardium (heart) 
• •Function –pumps blood through the body
• •Cells
• – striated,  involuntary, branching
• –uninucleate
• •Intercalated disks (cell to cell junctions) allow rapid spread of impulses from one cell to another

•Location - walls of hollow organs 

• •Function:
• –regulates size of organs
• –forces substances through tubes

• •Cells
• –tapered ends, no visible striations
• –involuntary
• –uninucleate

• Functions: 
• •recognize environmental changes 
• •integrates sensory inputs and motor outputs 
• •controls motor outputs (muscle contraction, glandular secretion) 

• Neurons 
• •conduct information (sensation, motor impulses)

• •Neuroglia
• protect, insulate, support neurons

• a.Cartilage tissue 
• b.Fibrocartilage tissue
• c.Osseous tissue
• d.Areolar tissue

(TRUE/ FALSE) 

• Consist of: 
• •epithelial tissue and 
• •connective tissue (CT) 

• Three types:
• •Cutaneous Membrane (“dry” membrane)
• •Mucous Membranes (“wet” membranes)
• •Serous Membranes (“wet” membranes)

•forms skin

• •consists of:
• –keratinized stratified squamous epithelium (epidermis)

• –connective tissue (dermis)
• •areolar CT forms papillary layer, and
• •dense irregular CT forms reticular layer

•line body cavities open to the outside (digestive, respiratory, reproductive, and urinary tracts) 

•non-keratinized stratified squamous epithelium or stratified columnar, or simple columnar

• •protect, absorb, secrete
• –some contain goblet cells or mucous glands (mucus)

• •Line cavities not open to the exterior (except pelvic cavity) 
• –parietal layer - lines wall of cavity 
• –visceral layer - overlies organs

•Secrete serous fluid (lubricates to prevent friction)

• •Consist of:
• –simple squamous epithelium (mesothelium) 
• –areolar CT

• Ventral body cavities and organs: 
• •pericardium - surrounds and covers heart
• •pleura - covers lungs and lines thoracic cavity
• •peritoneum - abdominal cavity and organs

Inflammation of serosa due to irritation and/or disease

• •pleurisy - in pleural cavity
• •peritonitis - in abdominal cavity 
• •pericarditis - in pericardium

•The serous membrane that lines the peritoneal cavity is called __________.

• •modified connective tissue 
• •covers all internal joint surfaces that are not covered by hyaline cartilage
• •produces fluid rich in hyaluronic acid (facilitate smooth movement within joints)

•Epithelial tissues usually repair/regenerate well 

•Connective tissues are often replaced by fibrous connective tissue (fibrosis=scar tissue)

• Events of tissue repair, e.g., skin repair
• •inflammation (WBC, clotting proteins, fluid)
• •blood clot formation
• •new epidermis is formed– epithelium grows into wound
• •granulation tissue is formed – fibroblasts proliferate
• •granulation tissue is replaced with dermis

• Answer 1: 
• •Composed of dense regular connective tissue
• •Few cells and vascular supply is poor

• Answer 2:
• •Occurs when wounds are very deep and cannot close

Connective tissue fills in the space before epithelial tissue can cover it