Epithelial and Connective Tissues

Cutaneous Membrane

Skin, Epithelial Tissue (epidermis), Connective Tissue (dermis), Dry membrane

Mucous Membranes

Lines all body cavities open to the environment, Epithelial tissue (stratified sqamous or simple columnar) , Connective Tissue (areolar lamina propria), moist membrane

Serous Membranes

In closed body cavities, made of epithelial tissue (simple squamous), connecti

Serous membranes are what

moist membranes of the closed ventral body cavity

ventral body cavity

a large fluid-filled space located on the front (anterior) side of the human body that houses and protects major internal organs.

Skins Properties

Sensation: monitors temperature, touch, and pressure via nerve endings

Thermoregulation: optimal body temp

Excretion: excretes salts, water wastes (via glands)

Physical Barrier: defense against pathogens + foreign substances

• bound together by tight junctions, acid mantle (lower pH)(thin film on the surface of the skin that protects against bacteria)

Barrier to water and light:

• Keratinized cells prevent gain/loss of water

• Melanin of cells prevent UV damage from sun

Why is sun exposure necessary

Vitamin D Synthesis by cholesterol

What are the two main regions of the skin

Epidermis, Dermis

Epidermis

most outermost layer, made up of stratified squamous epithelial tissue, keratinized, made up of tightly joined together cells by tight junctions and desmosomes

Dermis

Connective tissue layer, made up of:

• collagen, elastic and reticular fibers

• muscle (arrector pili - a tiny smooth muscle attached to a hair follicle that pulls the hair upright when it contracts)

• blood and nerve supply

• glands opening onto surface

Hypodermis

subcutaneous layer, fat layer under dermis:

• composed of adipose and areolar connective tissues

• anchors and insulates

• fat is not uniformly distributed (low levels on scalp, high levels in abdomen)

• not technically a skin layer

Stratum Corneum

first layer of epidermis, made up of 20+ layers of dead keratinocytes tightly joined by desmosomes

• flattened cells with protein packed lipid envelope

• water resistant lipid covering

barrier to water, not water proof

Stratum Granulosum

second layer of skin, made up of 1-5 layers of flat cells, water resistant

Stratum Spinosum

3rd layer of epidermis, thickest layer, 8-10 layers of cells filled with pre-keratin filaments

• cells flatten as they approach the top of the spinosum layer

• dendritic cells present (immune cells)

Stratum basale (germinativum)

fourth layer of epidermis, Basement layer, miotic (produces keratinocytes)

• includes stem cells, tactile cells, melanocytes

• epidermal ridges extends into the dermis

What is the stratum lucidum?

located in thick skin under the stratum corneum, pale featureless cells packed with eleidin (clear intracellular protein) and keratin

Colleen Likes Good Soup Bowls (CLGSB)

Corneum, Lucidum, Granulosum, Spinosum, Basale

Keratinocytes

most numerous in epidermis, 30-45 day lifespan, anchored together by desmosomes and tight junctions

• produced in basale layer and pushed upward

• as keratinocytes migrate up the skin layer, they become more resilient - accumulates melanin to protect against UV damage

• packed with keratin filaments to provide resistance and protection

• coats surface with lipids to resist water

• undergoes apoptosis when it reaches the top of the epidermis

Stem Cells

divides to generate keratinocytes

• confined to the basal layer (stratum basale), in direct contact with cell tissue beneath

Melanocytes

Located in basal layer (basement layer)

• branches protrude between keratinocytes

Produces melanin

• releases melanin from surface in granules, melanin pigments picked up by keratinocytes and accumulate on outward facing edge on cell (sunny side up)

Dermis

the connective tissue that is deep to the epidermis, the connective tissue layer is made of collagen, elastic and reticular fibers, has extenside blood and nerve supply (which provides O2 and nutrients and processes stimuli)

involved in immune defense which includes:

macrophages

white blood cells

mast cells

Fibroblasts

produces semifluid matrix, deposits collagen

Papillary Layer

Loose connective tissue - Areolar (collagen and elastic fibers) - Good for immune defense - Many small blood vessels

Dermal Papillae

extends to epidermis, includes Capillaries, nerve endings, and touch receptors

Epidermal Ridge

downward projections of epidermis

How are friction ridges made

dermal papillae + epidermal ridges

Messiner’s corpuscles

Specialized mechanoreceptors located near the epidermal : dermal border (mainly in hairless skin- fingertips, palms)

• detect light touch

• encapsulated nerve ending, not a nerve

• surrounded by flattened Schwann cells (protects nerve ending)

reticular layer

extends from the papillary layer to the subcutaneous layer

made of Dense irregular connective tissue - Thicker collagen fibers for strength and stability - Fewer cells than in papillary layer - Elastic fibers for stretch and recoil - Adipose tissue

cleavage lines

made of Collagen fibers and elastic fibers form parallel bundles

• Perpendicular cuts take longer to heal and are pulled apart by elastic fibers

• Cuts parallel heal more quickly with less scaring

collagen fibers

provide strength

elastic fibers

provide structure/stretch and recoil (think of a rubber band)

Strech Marks

generated by tears in dermis

• Stretch exceeds elastic limits

• Wrinkles/creases- don’t go away

Pacinian corpuscles

deep pressure mechanoreceptors in the reticular layer of the dermis

Pacinian corpuscles are deep pressure mechanoreceptors

• Detect pressure and vibrations

• Generally oval shaped

• Looks like slices of onion

Myelinated nerve enters corpuscle and loses myelination

Interstitum

a fluid filled space in between other cellular structures and tissues that drains into the lymph nodes and is supported by a complex network of thick collagen bundles.