Histology Final - new material only

New histology content for final only

What is the largest, single organ of the body

Skin

How much of total body weight does skin account for?

15-20%

What else is the skin known as?

integument, or cutaneous layer

Epidermis

An epithelial layer of ectodermal origin

Dermis

layer of mesodermal CT

Dermal papillae

projections at the irregular junction between the dermis and epidermis

What do dermal papillae interdigitate with?

invaginating epidermal ridges to strengthen adhesion of two layers

Epidermal derivatives

hairs, nails, sebaceous and sweat glands

Subcutaneous tissue AKA hypodermis

LCT layer containing pads of adipocytes, lies beneath the dermis

What is the function of the hypodermis

binds the skin loosely to the underlying tissues

What are the strata of Epidermis?

Layers of the skin

Where do ducts from a sweat gland enter the epidermis?

From a dermal papilla, and coils to a surface pore through all the strata

__ has coarse bundles of collagen

Dermis

What are important nonkeratinocyte cells in the epidermis?

melanocytes, langerhans cells, tactile Merkel cell

What do nonkeratinocyte cells mean?

Not skin cells

How is the dermis of THIN skin different?

more cellular, well vascularized, has elastin, less coars bundles of collagen

Epidermis of thin skin usually has how many layers?

4 layers

What are the 4 layers found in thin skin epidermis?

S. Basale, S. Spinosum, S. Granulosum, S. Corneum

Stratum Basale

one-cell thick containing most MIOTIC cells

Stratum Spinosum

synthesis of much keratin and other proteins take place

Stratum Corneum

consists of dead squames composed of mostly keratin

Epidermal S. Spinosum of thick skin have keratinocytes with what?

numerous short cytoplasmic projections

What type of junctions are present between keratinocytes in the epidermis?

Desmosomes

What are intermediate filaments?

cytoskeleton structures

Keratohyaline Granules

large, amorphous masses of protein

How do granules in the S. Granulosum stain?

Basophilic

Keratin filaments are cross-link with what protein?

Filaggrin

What is Filaggrin?

filament associated protein

What happens when tight bundles fill the cytoplasm in the S. Granulosum?

flattening of cells

What small organs can be found in the S. Granulosum?

lamellar granules

What so lamellar organs undergo?

exocytosis

What do lamellar granules secrete?

lipid-rich layer

What is important about the lipid-layer around our skin cells

makes the epidermis impermeable to water

The lipid envelope and the keratin-filled cells determine what?

Physical properties of the epidermis

S. Lucidum

dense, thin layer of differentiated cells from the S. granulosum

What do S. Corneum lose?

nuclei and cytoplasm (meaning that the cells are dead)

Do squames like water?

NO, they are hydrophobic

What are squames bound by?

hydrophobic, lipid-rich intercellular cement

What makes up the S. Corneum?

flattened, keratinized structures called squames

What happens to thick skin at the surface?

they are worn away

What happens to thin skin at the surface?

they flake off

Where are melanocytes found?

are present in the epidermal basal layer

What are the function of melanocytes?

synthesize melanin granules

Where do the melanin granules usually travel?

into neighboring keratinocytes of the basal and spinous layers

How do melanocytes stain?

pale-staining on the BM, with lower melanin content than the keratinocytes

How do melanocytes transfer melanin to nearby keratinocytes?

through their irregular, cytoplasmic processes

What important cell organelle do melanocytes have?

Golgi complexes

What do the golgi complexes do in melanocytes?

they make the vesicles in which the melanin is synthezied

What do vesicles become as they fill with melanin?

Melanin granules

Where do melanin granules accumulate before transfer?

tips of dendritic cytoplasmic extensions

What are Langerhans cells?

dendritic, APCs of the epidermis

What are the functions of Langerhan cells?

comprise an important defense against pathogens and environmental insults

Where do Langerhan cells develop?

bone marrow (after they migrate into blood then into skin)

Where can Langerhans cells be found?

in hair follicles and throughout epidermis

What color do follicles and keratin of epidermis stain?

green

_____ of Langerhans cells detects invading microorganisms

network

How do Langerhans carry out their immune response?

they activate lymphoctyes to mount a collective immune response

Merkel cell

have high tactile sensitivity and function as mechanoerceptors

Where are merkel cells found?

basal epidermal layer

What is the general structure of Merkel cells?

mass of dense-core cytoplasmic granules near the basolateral cell membrane

What are cytoplasmic granules in Merkel cells connected with?

nerve endings

What are the cytoplasmic granules in Merkel cells similar to?

granules of neuroendocrine cells

Elastic fibers decrease in diameter as they approach what?

the epidermis (then insert into the BM)

How do elastic fibers of the epidermis stain?

darkly, distributed aomng the eosinophilic collagen bundles

Skin contains servel types of ____ receptors

sensory

What type of nerve endings are foundin the epidermis?

free

What are the purpose of epidermal free nerve endings?

detect pain and temperature

Root hair plexus

present around the bases of hair follicles in the dermis, detect light touch or movement of hair

Tactile receptors

Meissner corpuscles, Lamellated (pacinian corpsuscles), Krause end bulbs, Ruffini corpuscle

Purpose of Meissner corpuscle

light touch

Purpose of Lamellated (pacinian) corpuscles

detecting pressure and high-frequency vibration

Purpose of Karise end bulbs

for low frequency vibrations/movements

Purpose of Ruffini corpuscles

detecting tissue distortion

Where do hair follicles derived from? Where do they extend into?

epidermis, deep into dermis

Major parts of hair and its follicle

vascularized, nutritive hair dermal papilla, arrector pili

What does the arrector pili muscle do?

pulls the hair erect

Parts of hair structure

Matrix, Medulla, cortex (in root), epithelial and connective tissue sheaths

what is the outermost layer of the hair

thin cuticle

What is the hair cuticle made up of

shingle-like cells

How do Sebocytes undergo terminal differentiation?

filling with small lipid droplets, and then disintergrating near the ducts opening at the hair shaft

Small progenitor cells

more specific than stem cells, they differentiate into a cell having specific function

Where do small progenitor cells proliferate?

Just inside the capsule

Lumen size of eccrine sweat glands?

small lumens

What appearance do eccrine sweat glands have?

irregular, stratified cuboidal appearance

What do apocrine sweat glands produce?

protein-rich secretion with pheremonal properties

Lumen size of apocrine sweat glands

larger than eccrine glands

Where do aprocrine sweat glands open into?

Hair follicles

Major stages of cutaneous wound healing

1. cut blood vessels bleed into wound, 2. blood clot forms, leukocytes clean wound, 3. blood vessels regrow and granulation tissue forms, 4. epithelium regenerates and CT fibrosis occurs

Fibrosis

phenomena where parenchymal tissue is replaced by CT, involves extensive tissue remodeling

Psoriasis

T cells attack healthy skin cells by mistake, as if to heal a wound or to fight an infection

What are mostly prescribed for psoriasis, and what do they do?

topical corticosteroids, they reduce inflammation and relieve itching

Immune system

provides defense or immunity against infecions agents ranging from viruses to multicellular parasites

What does our immune system consist of?

large, diverse population of leukocytes

Where are leukocytes located?

every tissue of the body and lymphoid organs

Primary lymphoid organs

thymus, bone marrow

Secondary lymphoid organs

adenoids, tonsils, lymph nodes, spleen, peyer's patches, appendix

What happens in the primary lymphoid organs?

Lymphocytes are formed initially

What happens in the secondary lymphoid organs?

lymphocyte activiation and proliferation

MALT cells are?

immune cells located in digestive, repisratory and urogenital mucosae

Lymphoid nodules

small and spherical, contain proliferating B lymphocytes in the secondary structures of MALT