Integumentary System Functions

Functions of the Integumentary System

• Keratohylain granules and lamellar bodies contribute to physical protection by secreting lipid-rich substances in the stratum granulosum, forming a hydrophobic barrier that prevents water loss and pathogen entry.
• Langerhans cells, as antigen-presenting cells, play a role in innate immunity by presenting microbial antigens, migrating to lymph nodes, and activating T-cells.
• Defensins and cathelicidins are antimicrobial peptides that disrupt bacterial membranes.
• Melanosomes transfer to keratinocytes, forming a protective cap around the nuclei, which absorbs UV radiation, minimizing DNA damage.
• UVB radiation (280–315 nm) interacts with 7-dehydrocholesterol in the stratum basale and stratum spinosum, converting it into previtamin D3.
• Previtamin D3 undergoes thermal isomerization into cholecalciferol (vitamin D3).
• Hepatic hydroxylation via CYP2R1 converts cholecalciferol into 25-hydroxyvitamin D3 in the liver.
• 25-hydroxyvitamin D3 converts to 1,25-dihydroxyvitamin D3 (calcitriol).
• Vitamin D synthesis deficiency can lead to rickets (in children) or osteomalacia (in adults) due to impaired bone mineralization.
• Meissner’s corpuscles, found in the papillary dermis, detect low-frequency vibrations and light touch, rapidly adapting and are abundant in fingertips and lips.
• Pacinian corpuscles, located in the reticular dermis and hypodermis, respond to high-frequency vibrations and deep pressure, utilizing lamellar structures to amplify mechanical stimuli.
• Merkel cells, present in the basal epidermis, are slow-adapting receptors that mediate fine touch discrimination via synaptic-like vesicles that release neurotransmitters into afferent neurons.
• TRPV1 receptors detect heat (above 43°C) and are activated by capsaicin.
• TRPM8 receptors detect cold stimuli (below 25°C) and are activated by menthol.
• Free nerve endings detect mechanical, thermal, and pain stimuli.
• Ruffini Endings are slow-adapting type II mechanoreceptors found in the dermis, subcutaneous tissue, and joint capsules, featuring elongated spindle-shaped structures with collagen fibers interwoven with nerve endings.
• Krause End Bulbs are encapsulated mechanoreceptors with special structures found in mucous membranes and dermal regions that respond to cold sensation.
• Vasodilation, triggered by hypothalamic activation, increases heat loss and contributes to thermoregulation.
• Vasoconstriction and piloerection reduce convective heat loss, conserving heat.

Skin Color, Skin Texture, and Effects of Aging on Skin

• Eumelanin is a brown/black pigment dominant in darker skin.
• Pheomelanin is a yellow/red pigment found in lighter skin, lips, and hair.
• Oxygenated hemoglobin gives a red hue to the skin.
• Deoxygenated hemoglobin causes a bluish hue in cyanosis.
• Carotenoids are yellow-orange pigments from dietary sources like carrots, and sweet potatoes, stored in subcutaneous fat.
• Collagen provides strength, whereas elastin allows recoil and flexibility.
• Reduced collagen/elastin content results in wrinkles and sagging.
• Sun exposure disrupts collagen and increases MMP activity, which degrades dermal components, leading to UV-induced photoaging.
• Aging affects epidermal renewal, dermal integrity, and subcutaneous fat distribution, leading to structural and functional changes.
• Elastin fibers become disorganized and clumped, reducing skin elasticity (solar elastosis in sun-exposed areas).
• Type I collagen decreases by ~1% per year after age 20.
• Sebum production decreases (~60% decline by age 80), leading to dry, flaky skin.

Cellular Components of Cutaneous Immune System

• The dermis includes eosinophils, mast cells, helper CD4 T cells, and natural killer cells.
• The epidermis includes IL-1, which activates dendritic cells.
• Chemokines activate neutrophils, macrophages, and T-cells.
• Activated T-cells return to the site of infection.

Joint Types and Muscle Attachments

• Fibrous joints are fixed or immovable, lacking a joint cavity, and are held together by dense connective tissue, such as sutures (skull), gomphoses (teeth), and syndesmosis (between radius & ulna).
• Cartilaginous joints are partially movable and held together by cartilage, classified as synchondrosis (temporary joints that fuse over time, like epiphyseal plates) and symphysis (permanent joints with limited movement, like the pubic symphysis).
• Synovial joints are highly movable with a joint cavity filled with synovial fluid, classified based on their articulating surfaces.
• Plane joints have flat surfaces that allow gliding movements.
• Hinge joints have cylindrical surfaces that allow flexion and extension.
• Pivot joints feature a cylindrical bone rotating within a ring-like structure.
• Condyloid joints have oval-shaped surfaces that allow up-and-down, side-to-side, and rotational movements.
• Saddle joints have two concave-convex surfaces that allow multidirectional movements.
• Ball and socket joints have a spherical surface fitting into a cup-shaped socket, allowing for a wide range of motion.
• Synarthrosis joints are immovable, like fibrous joints.
• Amphiarthrosis joints are slightly movable, like cartilaginous joints.
• Diarthrosis joints are freely movable, like synovial joints.

Functions of the Muscular System

• The Muscular System facilitates movement.
• The Muscular System maintains posture.
• The Muscular System stabilizes joints.
• The Muscular System generates heat through muscle contractions.