Lecture Exam 2 Notecards

Integumentary and Skeletal Systems

Accessories of the integumentary system

hair, nails, sweat glands, sebum glands.

functions of the integementary system

protection, water balance, body temp regulation, cutaneous sensation, metabolic functions, blood reservoir, excretion

Skin as a barrier: protection → physical barrier

keratin and glycolipids

Skin as a barrier: protection → chemical barrier

antibacterial growth; acid mantle (low pH secretions), defensins (antimicrobials), protects DNA from UV rays (damages DNA backbone)

Skin as a barrier: protection → biological barrier

dendritic cells and macrophages

Why is the skin an incomplete barrier?

There’s a limited penetration of the skin, such as lipid-soluble substances, salts of heavy metals, organic solvents, etc.

Skin as body temperature regulation

when too hot, dilation of dermal vessels, increased sweat gland activity; however, we also loose 500mL of water a day in insensible perspiration

Skin as a means of cutaneous sensations

temperature, touch, pain

metabolic functions of the skin

Vitamin D3 precursor produced here, collagenase (destroys collagen so its not inflexible), melanin production here

Skin as a blood reservoir

contains areolar and DICT, which are highly connective tissues

Skin as a mode of secretion

nitrogenous (urea) wastes and salts via sweat

Two distinct regions of the skin

Epidermis and Dermis

Epidermis

made of epithelial tissue (keratinized stratified squamous epithelium)

Dermis

made of areolar CT, DICT, and most fibrous

hypodermis

mostly adipose tissue, underneath the dermis but not part of the integumentary system

True or false, the epidermis is a stratified squamous vascularized epithelium

false - epithelial tissue is not vascularized

Five layers of the epidermis (superficial to deep)

Stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, stratum basale (come, lets get some bagels)

cells of the epidermis: keratinocytes

can differentiate into corneocytes → S. spinosum (second deepest layer) keratinocytes produce keratin and Vit D precursor

cells of the epidermis: melanocytes

produce melanin (important in UV protection), 10-25% of cells in S. Basale (deepest cell layer → protects cells undergoing hyperplasia).

cells of the epidermis: epidermal dendritic cells

Langerhans cells, phagocytic activity (immune system) → branch out to sense if pathogens are present

cells of the epidermis: Merkel cells

sensory nerve fibers (allow us to feel things)

Stratum basale

deepest layer (1-3 rows of 3 cell types)

cell types of S. basale

basal stem cells → keratinocytes (differentiation), which are mitotically active, tactile (Merkel cells), linked to sensory neurons, and melanocytes

How is the S. Basale attached?

to each other via desmosomes, to the basal lamina through hemidesmosomes (journey from basal layer to surface is 25-25 days)

Stratum Spinosum (Prickly layer) - 2nd deepest

8-10 layers of cells, metabolically active, produce intermediate prekeratin filaments and Vit D precursour (chemical)

Stratum Spinosum components

desmosome junctions, melanin granules (melanosomes) that protect the cells in the S. Basale from UV damage, dendritic cells, Immune cells of the epidermis (Langerhans cells).

Vitamin D Biosynthesis: Calcitriol

Pre Vit-D is produced by keratinocytes and ingested by food → happens via UVB rays from the sun that cause the keratinocytes to produce the precursor

Vitamin D function

essential for CA2+ homeostasis and healthy bones!! Thus, we need to protect our keratinocytes as much as possible from harmful UV rays (melanocytes)

Stratum granulosum

4-6 layers of cells, granules include keratohyalin and keratin, lamellated (water-resistant gylcolipid) → cell begins to die here! Nucleus and organelles start to disintegrate b/c very few molecules are able to diffuse from the basal layer

Stratum lucidum (clear layer)

only in thick skin of the palms, digits, and soles → few roles of flat, dead keratinocytes → contains sweat glands but lacks hair, sebaceous glands, and smooth muscle.

Functions of keratinocytes

1. forms strong impenetrable mesh superficially in epidermis

2. Produces precursor to vitamin D

3. serves as the internal immune system in the epidermis

Stratum corneum (horny layer)

15-30 rows of head, flat cells, no nucleus, organelles, mostly proteins (keratin), all contained by plasma membrane, ¾ of epidermal thickness → dead cells shed, loss of junctions

Stratum corneum functions

protects from abrasion and penetration (keratin and plasma membrane), waterproofs skin (glycolipids), and physical barrier from inside to outside.

Which cells in the epidermis serve as the resident macrophages, surveilling the epidermis, as its resident immune system?

Keratinocytes

Melanin and Melanocytes

melanocytes produce melanin, which is transported in melanosomes (vesicles) which are then incorporated in the keratinocytes of the S. spinosum to protect mitotic basal stem cells (underneath), allowing them to continue mitosis

melanin and skin pigment

different versions and amounts of melanin lead to different skin pigmentation/color

Sunlight → good or bad?

metabolically, sun provides vitamin D3 precursor (cholecalciferol), but carcinogenically, the sun creates thymine dimers (melanin protects the DNA from mutations).

Dermis composition

strong, flexible connective tissues (vascularized, support epidermis), fibroblasts, macrophages, and occasionally mast/white blood cells, has smooth muscle and skeletal muscle (voluntary → facial expressions!)

layers of the dermis

Papillary layer, Reticular layer

Papillary layer (dermis)

areolar CT (20% of dermis), blood vessels, dermal papillae (nipple shaped protrusions that inc. SA between the dermis and epidermis).

Dermal Papillae (papillary layer)

most contain capillary loops, some have tactile (Meissner’s) corpuscles for touch, other have free nerve endings (pain receptors), IN THICK SKIN, there are dermal ridges (fingerprints)

Capillary loops function

component of dermal papillae that give blood supply to epithelial tissues (epidermis)

Reticular layer (dermis)

80% of the dermis thickness, DICT → elastic fibers provide stretch-recoil properties, collagen fibers provide strength/resiliency, immune cells, highly vascularized (able to heal quickly)

special parts of the reticular layer

Pacinian/lamellar corpuscles (vibration), Ruffini’s corpuscles (stretch), hair, arrector pili muscles, glands, etc.

Repair of localized injuries to the skin

occurs through regeneration and fibrosis

regeneration

replacement of original tissue and structures (regain elasticity, skin pigmentation, etc).

fibrosis

scar tissue, structures might not all be replaced (not the same tissues/elasticity as before)

Blood vessels are ruptured in the skin (step 1 to healing)

bleeding occurs, damaged cells release inflammatory chemicals → mast cells, histamine (closes blood vessels), heparin (prevents bacteria from coming in)

Positive feedback loop of localized skin injuries

body sense blood, makes platelets and immune cells, which stop bleeding and clear up and repair the wound (moving away from homeostasis because we want liquid blood, not clotted blood).

capillary bed

where gas and nutrient/waste exchange occurs

capillary bed during an inflammatory response

increased permeability of capillary vessels; intact capillaries around injury support repair with immune cells

blood clotting (step 2 to healing)

blood in contact with collagen in air begins to dry and harden, making a scab appear

Skin repair (step 3 to healing)

blood clots become replaced with granulation tissue → mast cells release their pro-healing granules (growth factors), which causes new CT, blood vessels and cell division, stem cells at s. Basale migrate, macrophages clean

re-epithelization

occurs during skin repair, epithelial cells from stratum basale migrate to edges of wounds.

Skin regeneration in the epidermis (final step)

regeneration of the epithelial tissues

Skin regeneration in the dermis (final step)

fibroblasts proliferate, collagen and elastin fibers by fibroblasts reinforce the area (decreased elasticity, fewer blood vessels) → may not replace OG structures lost

Keloids

overgrowth of granulation tissues, leading to too much collagen in the wound and a raised bump

Accessories of the skin → types

Sweat exocrine glands, Oil glands, hairs and hair follicles, nails

types of sweat exocrine glands

eccrine/merocrine sweat glands, and apocrine glands, which include apocrine sweat glands, ceruminous, mammary, and Moll’s glands

Gland

one or more cells that make and secrete an aqueous or oily fluid

How are glands classified?

site of product release, relative number of cells forming the gland (uni or multicellular), mode of secretion

Site of product release - glands

endocrine (to blood) or exocrine (to outside)

modes of secretion → glands

merocrine (exocytosis), apocrine (not observed), holocrine (whole cell)

Endocrine glands

ductless glands directly to blood (capillaries), secrete hormones (travel through lymph or blood to target organs)

examples of endocrine glands

hypothalamus, pancreas, adrenal

exocrine glands

ducts to body surfaces (skin) or body cavities

exocrine glands examples

goblet cells, mucous, serous, sweat, oil, salivary, mammary glands, pancreas

merocrine mode of secretion (aka, eccrine)

products are secreted by exocytosis

apocrine mode of secretion

product is pinched off from cell → NOT observed in humans (apocrine sweat glands are merocrine secretions)

holocrine mode of secretion

products are secreted by rupture of gland cells

Sweat (sudoriferous) glands: eccrine glands

merocrine mode of secretion, duct to the outside, skin surface, release directly into skin itself *NOT HAIR), simple tubular coiled, in the reticular layer of the dermis, widely distributed in body, present on palms of hands, soles of feet, forehead

Sweat (sudoriferous) glands: apocrine glands

merocrine mode of secretion; duct to the hair follicle, simple tubular coiled, deeper dermis, most are present are birth but only a few remain during puberty (axilla, anal region,)

apocrine gland sections vs. eccrine gland secretions

apocrine glands secrete sweat (water + ions) + fatty substances and proteins, while eccrine glands secrete 99% water, na+, cl-, antibodies, metabolic waste

specialized apocrine glands

ceruminous glands (ear wax), mammary glands (lactation), and Moll’s glands (eyelids)

Sebaceous oil glands

widely distributed (except in thick skin), most develop from hair follicles, secrete sebum via holocrine secretion

what is sebum?

oily secretion, bactericidal, softens hair and skin (additional layer of protection)

Why don’t we have oil glands where we have thick skin?

want to maintain our ability to have traction/grip things

Skin structures: hair → functions

awareness, environmental protection from physical trauma, heat loss, and sunlight → associated with arrector pili muscle (smooth muscle, involuntary)

Skin structures: hair → distribution

except palms, soles, lips, nipples, and portions of external genitalia

Components of hair

keratinized cells (hard keratin), melanins in medulla, pilus includes the hair bulb, root, and shaft (part that sticks out)

Hair follicles (from dermis to epidermal surface)

Hair bulb, hair papilla (vessels), arrector pili muscle (smooth muscle)

hair bulb

has the hair follicle receptor (root hair (nervous) plexus), and is where the hair matrix is, which allows for hair growth (cell division)

Arrector pili muscle → description

1 muscle/hair follicle, bundle of smooth muscle cells → motor nerve signals from the sympathetic nervous system (involuntary)

Arrector pili muscle → functions

traps air → heat insulation, self defense (to increase size appearance and reduce access to skin)

Types of hair

lanugo, vellus, terminal

lanugo hair

fetal and newborn hair, thin, soft, sheds pre or around birth

vellus hair

thermal insulation and cooling

terminal hair

secondary sex characteristic (sexual selection) → stronger, thicker hairs

Skin structures: Nail

scalelike modification of the epidermis, contains nail matrix (cell division), root → body → free edge, lunule is moon at the bottom, cuticle is on top of the tail

The origin of the cells that form the nail is…

Basal stem cells of the epidermis at the nail matrix

moles

benign accumulation of melanocytes → melanomas

pressure ulcers

bedsores in bedridden patients due to lack of blood flow → hypoxia and anoxia → tissues die

Acne

blocked sebaceous glands → bacteria infection, cystic acne

Alopecia areata

patches/total loss of hair (autoimmune)

albinism

congenital absence of melanin

Causes of burns

heat, electrical current, friction, cold, radiation, and corrosive chemicals

First degree burns

localized to just the epidermis, some redness, edema, and pain

superficial second degree burns

Epidermis and part of the dermis, skin adnexa remain; heals by re-epithelization, moist, red, blanching, blisters, very painful (activated the free nerve endings)

do superficial burns leave scars?

usually no if healed properly without infection → tissue regeneration

deep second degree burns

damage to deeper dermis, less moist, less blanching, less pain, heal by scar deposition, contraction and limited re-epithelization