Tissues and the Integumentary System

• Specialized cells form tissues, which combine to form organs.
• There are four tissue types: Epithelial, Connective, Muscle, and Nervous.
• Epithelial tissue characteristics: Cellularity, Attachment, Avascularity, Polarity, Innervation, and Regeneration.
• The shape of epithelial cells relates to tissue function; flat cells are for diffusion, tall cells for protection.

Connective Tissues

• All contain specialized cells and ECM
• ECM is composed of ground substance and fibers.
• Loose connective tissues have lots of ground substance in the ECM.
• Examples of loose CT: Areolar (subcutaneous layer of epidermis), Adipose, and Reticular (stroma of the liver).
• Dense CTs have lots of fibers in the ECM.
• The integumentary system includes the skin.
• Key root words: Integ (whole), basal (base), derma (skin), lucid (clear), epi (on top of), rete (net), hypo (below), papill (nipple), cornu (horn).
• Functions of skin: protection, waterproofing, secretion, excretion, thermoregulation, Vitamin D synthesis, storage of lipid reserves.
• Skin thickness ranges from 0.1mm to 1.5mm
• The epidermis is the outer layer of keratinizing stratified squamous epithelium. It is dry because cells moving away from vascularized connective tissue die.

Dermis and Hypodermis

• The dermis is composed mostly of dense irregular connective tissue with some areolar CT closest to the epidermis. It is rich in collagen, blood vessels, sensory receptors, and glands.
• The hypodermis is located deep into the cutaneous membrane and contains adipose tissue.
• The dermis is the vascular layer of the skin.
• The epidermis is composed of keratinized stratified squamous epithelium, with keratin at the surface.
• Mitosis occurs in the deepest region of the epidermis.
• Epidermal ridges and dermal papillae reside between the dermis and epidermis.
• These increase surface area, aid in nutrient supply, and prevent the epidermis from sliding off the dermis.
• The epidermis is the surface layer.
• It is composed of stratified squamous epithelium
• With avascular connective tissue deep into the epidermis that supplies oxygen and nutrients.
• Keratinocytes, melanocytes, Langerhans cells, and Merkel cells are the main epidermal cells.

Epidermal Layers

• The five epidermal layers from superficial to deep: Stratum Corneum, Stratum Lucidum, Stratum Granulosum, Stratum Spinosum, and Stratum Basale.
• Thick skin is located on the heels and palms
• The vascular layer of the skin is the dermis.
• The papillary region makes up 20% of the dermis. It is the top superficial region with dermal papillae.
• Dermal papillae increase surface area between epidermis and dermis.
• Each dermal papilla contains capillaries that supply nutrients to the cells of epidermis. They also house sensory receptors.
• It is composed of areolar CT.
• The reticular layer makes up 80% of the dermis.
• It is composed of dense irregular CT
• This thick layer gives the dermis strength, extensibility and elasticity.
• Thin skin covers most of the body, has a thin epidermis (0.08 mm), and has no stratum lucidum.
• Thick skin is found exclusively on the palms and soles, has a thick epidermis (0.6 to 4.5 mm). Dramatic epidermal ridges and dermal papilla give rise to fingerprints, and has no hair follicles or sebaceous glands.

Hair and Nails

• Hair is composed of keratin and provides protection, communication, and reduces friction.
• Parts of the hair: shaft, root (with hair follicle, arrector pili muscle and sebaceous gland), hair bulb (with vascular "bump" known as the hair papilla and the hair matrix).
• The arrector pili muscle is involuntary smooth muscle.
• Three hair types: Lanugo, Vellus, and Terminal.
• Nails are composed of keratin and protect vulnerable phalanges against mechanical stress.
• The nail matrix is the area of active nail growth.
• Production of the nail occurs because of mitosis
• Merocrine/eccrine sweat glands are found all over the body and produce sweat for evaporative cooling.
• Apocrine sweat glands are associated with hair follicles are found abundantly in groin & axillary regions. They produce viscous sweat, and may contain pheromones.
• Mammary glands are in female breasts, released milk is in response to specific hormonal cues and infant demand.
• Ceruminous glands are located in the ears produce wax to protect/provide from prolonged water exposure.
• Sebaceous glands are associated with hair follicles secrete oily sebum to keep hair healthy and prevent cracking.
• Ducts of exocrine glands such as sweat glands are lined with stratified cuboidal tissue.
• Cerumen waxy protects the ear from water exposure.
• Sweat glands are important for thermoregulation.
• Sweat glands on palms do not release odor compared to sweat glands in axillary region.
• Apocrine glands are most likely to contain pheromones.
• Types of burns: first, second, third degree.

Burns and the Aging Skin

• First-degree: epidermis is damaged, characterized by redness. classic Sun burn
• Second Degree: the epidermis and dermis are involved fluid blisters
• Third Degree: ALL the layers are involved (epidermis, dermis, is a key risk in 3° burns), and damage/loss of nerve function..
• As one ages: Blisters take longer to heal, the blood supply is reduced, and the network of fibers (collagen+elastic) in the dermis is diminished.
• In wound healing, if the dermis is penetrated, blood vessels will be damaged.
• Leukocytes remove bacteria, thrombocytes plug holes and facilitate clot formation.
• Fibroblasts replace damaged collagen fibers, blood vessels regrow, granulation tissue forms.
• Then epithelium regenerates to seal wound, scar tissue (fibrosis) forms.
• Supporting CT is cartilage and one. The ECM is composed of fibers and ground substance.
• Supporting functions of bone and cartilage
• The three types of cartilage are: hyaline, fibrocartilage, and elastic.
• A cartilage cell is called a chondrocyte.
• The two types of bone are compact and spongy.
• A mature bone cell is called an osteocyte.
• Flat bones sternum and ribs.
• Boxy bones patella.
• Long bones: femur, ulna, metacarpal.
• Irregular bones: sphenoid, vertebrae, pelvic girdle.
• Compact bone contains osteons, spongy bone does not.
• Compact bone's ECM collagen and ground substance.