Tissues

Groups of cells similar in structure and function

Come from the same part of the embryo

Carry out a specific function for the body typically as part of an organ

Four major tissue types:

Epithelial

Connective

Muscle

Nervous

Tissues are organized into organs that carry out specific functions * at least 2 different types of tissues to be an organ

Epithelial

Locations:

Skin

Lining the body surfaces that open to the outside (nasal, oral)

Lining internal body cavities

Covering organs

Glands ( sweat, salivary, endocrine)

Functions:

Protection (skin)

Sensation ( tactile cells in S. basale)

Absorption and filtration ( EPI of small intestine absorbs nutrients) (EPI of kidneys filters the blood)

Secretion ( EPI of stomach secretes acid- endocrine glands secrete hormones)

Gas exchange ( across respiratory surfaces of lungs across capillaries)

General structure of EPI

Cells fit tightly

On lower surface, EPI cells are attached to and supported by an adhesive basement membrane

EPI are avascular *capillaries in underlying connective tissue only

EPI tissues have on free surface, apical surface

EPI is very good at regenerating itself, if well-nourished ***via stem cells

Specialization of structure

Microvilli ( small intestine)

Cilia (airway of lung)

Goblet cell = unicellular glands that produces mucus

Classification of epithelial tissue

Cell shape:

Squamous

Functions:

Flat, thin shape makes it ideal for the rapid diffusion of substances

Provides smooth surface to reduce friction

Locations:

Gas-exchange sites of lungs, lining of blood vessels and body cavities

Cuboidal

Function:

Absorption and secretion

Location:

Kidneys tubules, certain glands (thyroid)

Columnar (may contain goblet, may be ciliated)

Functions:

Absorption, secretion ( esp. Of mucus), movement of egg

Locations:

Lining of small intestines

Oviducts

Stratified squamous- two types

Keratinized (dry) - outermost layers consist of dead cells packed with keratin

Nonkeratinized (wet) - outer layers are living and not filled with keratin

Function: protection from abrasion and pathogens

Location: skin, cornea, body cavities that open to outside

Stratified cuboidal

Function: secretion and some protection

Location: sweat and salivary gland ducts

Stratified columnar (*rare)

Function: secretion and protection

Location: larynx, mammary gland ducts, parts of male urethra

^^^ 6 main types

Pseudostratified columnar

Function: secretion and movement of mucus

Location: lining of nasal cavity, trachea... upper respir. Tract

• in the respiratory tract, mucus... traps debris

• beating cilia move mucus to the throat called the... " mucus escalator"

Effects of smoking:

The dryness of and chemicals in smoke paralyze the cilia

w/o cilia function, mucus builds up

Heat eventually burns the cilia off and damages the EPI * tissue responds by producing more mucus, but it can be removed only by ***smokers cough

Transitional epithelium (urothelium)

Function:

Allows structures to stretch as they are filled with urine

Protection from chemicals in urine

Location: ureters, bladder, urethra

Number of layers: simple cuboidal, stratified cuboidal

Glandular EPI

Exocrine glands

Have ducts (tubes) through which their secretions travel to the apical surface ( lacrimal glands, sweat, mammary)

Endocrine

Ductless (lose them early in development)

Hormones diffuse outward into extra cellular fluid (ECF) (pituitary, thyroid, ovary...)

Specialized junctions between EPI cells

Gap junctions

Cells are held together by interlocking proteins called connexons

The connexon has a hollow space through its center

This allows small molecules and ions to pass directly from cell to cell

• gap functions are common between ciliated EPI cells

Desmosomes

Cells held together by proteins and "glue"

Proteins are anchored to "dense areas" which attach to the cells skeleton

Very strong, resists stretching/ tearing * common between superficial skin cells

Tight junctions

Long stretch of interlocking proteins tightly connects the two cell membranes

Such that the adjacent lipids are fused

Blocks the passage of substances between the cells * common between superficial intestinal cells

Two cells can be joined by a mixture of different types of junctions * and these junctions also occur in other types of tissue (cardiac muscle, lens of eye, desmosomes in cervix of uterus)

Connective Tissue

Major functions

Connects structures (ligaments, tendons)

Protection and support (bones, CT capsules around organs Areolar CT ((supports the EPI above it)

Acts as filler material ( fills space between EPI ducts: and separates nerves from muscle)

Transports gas (blood)

Stores energy (adipose tissue)

Structure of connective tissue

Cells

The young unspecialized cells( ex. Fibroblasts, chondroblasts, osteoblasts) (suffix- blast)

Once mature, the cells live in the matrix and they have made (suffix- cyte)

Extracellular matrix

Ground substances

Fibers *(three types)

Collagen fibers (major protein collagen I)

Great tensile strength, but flexible

Reticular fibers (collagen II)

Thinner fibers, often from ornate, sponge-like shapes

Elastic fibers (elastin)

Thinnest, highly elastic (enables lungs to stretch/ contact)

Ground substance: material that fills the space between cells and holds the fiber – made up mostly of complex carbohydrates and proteins

Acts like glue

Holds lots of water

Often syrupy/ rubbery consistency

Classification of CT

Depends on:

Predominant cell type

% of each fiber type present

Amount of ground substance

Types of CT

Mesenchyme (embryonic CT)

Arise early in embryonic development

Eventually gives rise to all the other CT types

Connective tissue proper ( two types)

Loose CT (vascularized, fibers packed loosely)

Areolar

Syrupy ground substance

May contain all 3 fiber types loosely arranged

Function:

Soft packing material

Reservoir of water and salts

Play important role in inflammation

Location

Widely distributed underneath EPI tissue -Major part of hypodermis

Adipose

Fibroblasts predominate but also has

Fat cells (adipocyte)

Most of cell vol. Is occupied by a vacuole containing oil (triglycerides)

Mature fat cells cannot divide

Unlike other CT, it has little matrix

Macrophages (what's attacking pathogens)

mast cells- initiate the local inflammatory response by releasing histamine

Function

Long-term energy storage

Cushions joints/internal organs

Insulation

Heat generation (B.A.T)

Reticular (lymph nodes)

Contains only reticular fibers, loosely arranged

Function: forms a soft, ornate, internal skeleton that supports the working cells of the organ

Location: found in lymphoid organs (spleen, lymph nodes, bone marrow, liver)

Ex. Reticular CT forms an internal skeleton for the spleen – macrophages attach to this skeleton and recycle old/broken rbc's as they pass by

Dense CT (poorly vascularized, fibers densely packed)

Dense regular

The collagen fibers are mostly parallel to the direction in which they are pulled

Function:

Resists stretching along one direction

Locations:

tendons, ligaments

Dense irregular

Collagen fibers form a network and thus resist stretching from multiple directions

Location:

Dermis

Protective sheaths around cartilage, bone, and nerves

Protective capsules around kidneys, spleen

Cartilage

Tougher than dense CT, but not as tough as bone

Chondrocytes are the major cell type (chondrocytes live in lacuna)

Avascular

Matrix contains lots of collagen fiber and lots of water

Most cartilage is covered with a sheath of dense irregular CT called the perichondrium

Three major type of cartilage:

Hyaline

Lots of very thin collagen fibers

Firmest of the cartilage

Function

Firm support with some flexibility

Location

Tip of nose

Tracheal rings

Costal cartilages

Capping long bones

Fibrocartilage

Mainly thick collagen fibers with little ground substance

Functions to absorb shocks

Also pads the knee joint

Elastic

Most common

Most elastic, least firm

Functions to give structures great flexibility without losing original shape

Location: external ear, epiglottis

Bone

Blood

Structure

Atypical CT but it does meet all requirements

Has cells

Surrounded by a matrix (=plasma)

Even has fibers but these are only visible during clotting

Function

Transportation of gases, nutrients, wastes, hormones, heat

Reservoir of fluid

Hemophilia

Refers to several disorders in which a person's blood doesn’t clot normally

Far more common in males, since malfunctioning gene is on X chromosome