CH. 5- Integumentary System

1. Protection- oily sebum keeps the skin soft and controls bacterial growth.
2. Body Temperature Regulation- increasing sweat gland secretions to cool the body
3. Cutaneous Sensation- contain receptors that sense touch.
4. Metabolic Functions- synthesis of vitamin D in dermal blood vessels
5. Blood Resevoir- skin blood vessels store up to 5% of the bodys blood volume.
6. Excretion- limited amounts of nitrogenous wastes are eliminated from the body in sweat.

2 Major regions of the Skin
Epidermis-(outermost superficial region), composed of epithelial tissue.
Dermis-(vascularized middle layer), composed primarily of connective tissue, with nervous and muscle tissues.

3rd
Hypodermis/Subcutaneous-(deepest region) Not technically a part of our skin. Adipose or areolar tissue for fat storage.

Epidermis- composed of keritanized stratified squamous epithelium, There are four distinct cell types: keratinocytes (90%), melanocytes (8%), Dendritic cells/Langerhan's cells, Tactile/Merkel Cells

Epidermal layers:
Stratum Basale/Stratum germinativum (base layer)- Deepest layer firmly attached to the dermis, Single row of youngest keratinocytes, rapid cell division pushes up new cells into more superficial layer above (and differentiates into mature keratinocytes)

Stratum Spinosum (prickly layer)- 8-10 layers of closely packed keratinocytes, provides strength and fleixibility to the skin, melanin granules and dendritic cells are abundant in this layer.

Stratum Granulosome (granular layer)- 4-6 cell layers of flat dying cells, keratinization of keratinocytes begins, transition between the deeper, metabolically active layers and the dead cells of the more superficial layers.
Cells begin to break down concentrate two types of granules:
Keratohyaline- forms keratin which assembles into intermediate filaments--for protection of deeper layers.
Lamellated- releases lipid-rich secretions that contribute to further water repellent properties

Stratum Lucidum (clear layer)- 2-3 layers of clear, flat, dead cells. Only present in fingertips, palms and soles of feet (thick skin), reduces friction and shear forces.

Stratum Corneum (horny layer)- most superficial layer, 25-30 layers of tightly packed, flattened, dead Anucleate cells filled with keratin and surrounded by lipids (water repellent), are continuously shed and replaced by cells and replaced by cells from deeper layers, barrier to injuries, heat, water, chemicals and microbes.

Keratinization + Epidermal Growth a process that takes between 2 and 4 weeks, Stem cells in the basal layer divide to produce keratinocytes.
As keratinocytes move farther away from the blood supply, they receive less and less nutrients and eventually die.

Psoiriasis is a skin condition in which this keratinization process is greatly accelerated (7-10 days), produces abnormal keratin, casuses flakiness

Dermis- composed of strong, flixible connective tissue containing fibers (collagen and elastic), and cells (fibroblasts, macrophages, adipocytes and sometimes mast cells and WBC)
2 Major regions in Dermis-
1. Papillary Region (top 20%)
2. Reticular Region (bottom 80%)

Papillary Region (top 20%)- comprised of areolar connective tissue (loosely woven collagen and elastic fibers), and blood vessels. Anchors the epidermis to the dermis. Dermal Papillae project up into the epidermis and create friction ridges, provide gripping ablility on fingers and feet (sense of touch)

Dermal Papillae- contain capillary loops-supply the epidermis. touch receptors (Meissner's corpuscules) pain receptors (free nerve endings)

Reticular Region (bottom 80%)

dense regular connective tissue, collagen fibers for strength and resiliency, elastic fibers provide extensibility, also contains adipose tissue, hair follicles, nerves etc

Hypodermis- subcutansous layer deep to the skin, composed of adipose and areolar connective tissue.