 These cover surfaces, line body cavities, and form protective sheets around organs  Two main types: ◦ Epithelial membranes (cutaneous, mucous, and serous membranes) and are considered to be simple organs ◦ Connective tissue membranes (synovial membranes)

 Otherwise known as the skin  Superficial epidermis is composed of a keratinizing (hardening) stratified squamous epithelium  Underlying dermis is mostly dense connective tissue  Since it is exposed to the air, it is considered to be a dry membrane  (More to come later)

 Also known as mucosa  Used for absorption and secretion  Epithelium resting on loose connective tissue called lamina propria  Lines all body cavities that open to the exterior, such as the hollow organs of the respiratory, digestive, urinary, and reproductive tracts  They are considered to be wet (moist) membranes

 Also known as serosa  Simple squamous epithelium resting on a thin layer of areolar connective tissue  Line body cavities that are closed to the exterior

 Different areas have different names: ◦ Around the abdominal cavity organs – peritoneum ◦ Around the lungs – pleura ◦ Around the heart - pericardium  Occur in pairs as it folds in on itself ◦ Parietal layer – outer wall (fused to cavity wall) ◦ Visceral layer – inner wall (touches organ) ◦ Space between contains a little bit of a thin, clear liquid called serous fluid (lubricant).  (Remember the balloon and fist model)

 Composed of just areolar connective tissue.  Line the fibrous capsules surrounding the joints, small sacs called bursae, and tubelike tendon sheaths  Provide a smooth surface and secrete a lubricating fluid to cushion organs during physical activities

And the Integumentary system (the skin and its appendages Some of the basic functions are…

 Mechanical Damage ◦ How? It makes a physical barrier. Outer layers has cells that contain keratin, which toughens the cells and has pressure receptors, which alert the body of potential damage  Chemical Damage ◦ How? Once again the keratinized cells block chemicals and pain receptors alert the body

 Bacterial Damage ◦ How? Block the bacteria, but also the skin’s secretion are acidic (inhibit growth) and skin cells have phagocytes (eat the bacteria)  Ultraviolet Radiation ◦ How? Contains melanin that offers protection from UV damage  Thermal Damage ◦ How? Contains hot, cold, and pain receptors that alert the body  Desiccation (Drying Out) ◦ How? Contains waterproofing glycolipid and keratin

 Aids in heat loss (activates sweat glands and allows blood to flow closer to surface) and heat retention (stops blood from rushing to surface)  Aids in excretion of urea and uric acid (makes up some of your sweat)  Synthesizes vitamin D (uses sunlight to convert some cholesterol molecules to vitamin D)

 Epidermis – “top layer” of skin, made up of stratified squamous epithelium that is capable of keratinizing  Dermis – “bottom layer” of skin, made of dense connective tissue  Hypodermis or Subcutaneous tissue – not a layer of skin, but connects skin to organs, mostly adipose tissue and acts as a shock absorber

 Stratum Basale – lies closest to the dermis and therefore the blood supply, they are constantly dividing and pushing cells up to the surface  Stratum Spinosum – become flatter and fuller of keratin  Stratum Granulosum – keep getting flatter and fuller  Stratum Lucidum – cells die and form this clear layer  Stratum Corneum – cells are completely dead and full of karetin. About the top cell layers thick. Layer closest to surface

 Papillary Layer ◦ upper dermal region ◦ Contain fingerlike projections called dermal papillae, which may contain capillary loops to help nourish the epidermis, pain receptors (nerve endings) and touch receptors (Meissner’s corpuscles) ◦ On hands and feet they are arranged in a specific pattern. The result? Fingerprints.

 Reticular Layer ◦ Deepest Layer of the skin ◦ Contains blood vessels, sweat and oil glands, phagocytes, and deep pain receptors called Pacinian corpuscles ◦ Contains both collagen (for toughness and water retention) and elastic fibers (for stretchiness) ◦ Contains blood vessels for heat control ◦ Contains nerves for responsiveness