Anatomy Lecture 4 LO.pdf

Lecture Learning Objectives 1. List the main functions of the integument​ Functions: 1.Protection: Physical barrier, Initiates immune response 2.Sensory 3.Thermoregulation 4.Metabolic: Vitamin D synthesis, Energy storage, Removal of electrolytes in sweat 5.Sexual signaling: indicators o...

Lecture Learning Objectives 1. List the main functions of the integument​ Functions: 1.Protection: Physical barrier, Initiates immune response 2.Sensory 3.Thermoregulation 4.Metabolic: Vitamin D synthesis, Energy storage, Removal of electrolytes in sweat 5.Sexual signaling: indicators of health, Sex pheromones 2. Describe the epidermis, dermis, and subcutaneous layers regarding the tissues (epithelium/CT), specialized cells, and specific layers that comprise them​ Epidermis - Epithelial layer derived from ectoderm, its Avascular, and forms Accessory organs of the integument (sweat glands, hair follicles) Dermis - Connective tissue derived from mesoderm, vascular supply to epidermis Two layers: 1. Papillary Layer: ○ Location: The uppermost layer of the dermis, directly beneath the epidermis. ○ Structure: Made up of loose connective tissue, including collagen and elastin fibers, which give it a soft, flexible structure. It contains dermal papillae, which are small, finger-like projections that extend into the epidermis and help increase the surface area for nutrient exchange. ○ Function: This layer contains capillaries that supply nutrients to the epidermis and house sensory receptors (such as Meissner’s corpuscles) for touch. The papillary layer also plays a role in temperature regulation and contributes to the formation of fingerprints. 2. Reticular Layer: ○ Location: The deeper, thicker layer of the dermis. ○ Structure: Composed of dense irregular connective tissue, packed with thick collagen fibers and elastin, which provide the skin with strength, resilience, and elasticity. It also contains larger blood vessels, sweat  glands, sebaceous glands, and deep pressure receptors (like Pacinian corpuscles). ○ Function: The reticular layer provides structural support to the skin, houses important skin appendages (hair follicles, sweat, and oil glands), and contributes to the skin’s toughness and flexibility. Subcutaneous layer (superficial fascia) - Loose areolar CT and adipose CT, Binds skin to underlying tissue, Not part of integument but greatly involved Epidermis is made up of Stratified squamous epithelium - Composed of keratinocytes: cell’s cytoplasm is replaced with keratin proteins as cells progress superficially, cells at surface die Epidermis receives Nutrients and oxygen via diffusion from dermal vessels, with the deeper layers receiving the most Epidermis is Connected to dermis via the basement membrane Epidermis and dermis are interlocked via projections called the epidermal ridges and dermal papillae - Epidermal ridges: most visible on surface as finger/foot prints and purpose is grip Dendritic cells (Langerhans cells): Exist In stratum spinosum and granulosum, extend between keratinocytes of all layers, Play a role in immune defense, APCs Tactile cells (Merkel cells): Located in stratum basal, Release chemicals that stimulate sensory nerve endings when compressed Mechanoreceptors: merkel cells that sense gentle touch Melanocytes: Specialized cells derived from neural crest cells located in the basal layer of the epidermis that produce melanin. These cells have long dendritic extensions that transfer melanin to nearby keratinocytes, helping to protect the skin from UV radiation. Melanin: A pigment produced by melanocytes that gives skin, hair, and eyes their color. It also plays a crucial role in absorbing and dissipating ultraviolet (UV) radiation, providing protection against DNA damage caused by UV exposure. There are two main types of melanin: eumelanin (brown/black) and pheomelanin (red/yellow). Melanosomes: Organelles within melanocytes where melanin is synthesized, stored, and transported. Once formed, melanosomes are transferred from melanocytes to keratinocytes, distributing pigment throughout the skin. The number, size, and distribution of melanosomes determine skin color. 3. Identify the primary characteristics of each specific layers of the epidermis, focusing on the process of keratinization​ “Come Lets Get a Sun Burn” Stratum Basale (Basal Layer): a. Location: Deepest layer, Directly contacts dermis via hemidesmosomes b. Cell Types: Single layer of keratinocyte stem cells, along with melanocytes and Merkel cells. c. Function: Keratinocytes in this layer are mitotically active, continuously dividing to produce new cells that will move up through the layers. Forms epidermal ridges and has many mitotic nuclei Stratum Spinosum (Spiny Layer): d. Location: Above the stratum basale, thickest layer of epidermis e. Types: Keratinocytes, Langerhans cells (immune cells). f. Function: Cells in this layer are connected by desmosomes, giving them a "spiny" appearance. Keratinization begins here as cells start producing keratin and become more flattened. Langerhans cells help in immune defense. Stratum Granulosum (Granular Layer): g. Location: Above the stratum spinosum, 3-5 layers of keratinocytes, last layer that is ALIVE h. Cell Types: Flattened keratinocytes containing keratohyalin granules and lamellar bodies.  i. Function: Cells undergo keratinization, accumulating keratohyalin granules, which help in forming keratin. Lamellar bodies release lipids that contribute to the formation of a waterproof barrier. Stratum Lucidum (Clear Layer): j.Location: Present only in thick skin (palms of the hands, soles of the feet). k. Cell Types: Dead, flattened keratinocytes. l. Function: This layer provides an additional barrier to friction, with cells appearing translucent due to the presence of eleidin, a precursor to keratin. 4. Stratum Corneum (Horny Layer): a. Location: Outermost layer. 15-20 layers of squamous, keratinized cells on surface b. Cell Types: Dead, flattened, fully keratinized cells, with no nucleus (anucleate). c. Function: This layer provides a strong, protective barrier against environmental damage via desmosomes. The cells are continuously shed as groups and replaced, completing the keratinization process. 5. Describe albinism and how it relates to melanocytes​ Albinism is a genetic condition characterized by a lack or significant reduction of melanin production, resulting in very light skin, hair, and eyes. It affects individuals of all ethnic backgrounds and can involve both the skin and the eyes (oculocutaneous albinism) or just the eyes (ocular albinism). How Albinism Relates to Melanocytes: - Melanocytes are present in individuals with albinism, but they are unable to produce sufficient melanin due to mutations in genes that control melanin synthesis, such as the TYR gene (which encodes tyrosinase, an enzyme crucial for melanin production). - In albinism, although the number of melanocytes is typically normal, the defective production pathway means these cells are unable to convert tyrosine into melanin efficiently.  - As a result, the melanosomes in melanocytes either produce very little or no melanin, leading to the characteristic pale skin, light hair, and vision problems associated with albinism. Vitiligo: acquired condition that involves depigmentation, occurs in patches, due to loss or decreased activity of melanocytes. May be due to environmental, genetic, or autoimmune conditions 6. List the sensory roles played by the integument​ Exteroceptors: respond to stimuli outside the body Nerve fibers in skin: Control blood flow, Adjust gland secretion rates, Monitor sensory receptors in dermis and epidermis Sensory neurons in epidermis: Free nerve endings: pain and temperature Merkel cells: light touch Sensory neurons in dermis- Meissner corpuscles: light touch Ruffini endings: pressure Krause bulbs: pressure and vibration Pacinian corpuscles: touch, pressure, and vibration 7. Give examples of the metabolic, reservoir, and disposal function played by the integument​ 1. Metabolic Functions: Vitamin D Synthesis: The skin plays a crucial role in the production of vitamin D. When exposed to UV radiation from sunlight, the skin converts 7-dehydrocholesterol to cholecalciferol (vitamin D3), which is then activated by the liver and kidneys to help regulate calcium and phosphate levels, essential for bone health.  Lipid Metabolism: The skin is involved in synthesizing and storing certain lipids, including ceramides, which are important for maintaining the barrier function of the skin. 2. Reservoir Functions: Blood Reservoir: The dermis contains a rich supply of blood vessels that can hold about 5% of the body's total blood volume. Nervous system constricts blood vessels to supply more blood to other systems Fat Storage: The hypodermis (subcutaneous layer) stores fat, which serves as a reservoir for energy, insulates the body, and provides cushioning against mechanical injury. 3. Disposal Functions: 8. Excretion of Wastes: The skin helps eliminate metabolic wastes through sweat. Detoxification: By sweating, the skin also aids in removing toxins from the body, including small amounts of heavy metals and other environmental toxins, playing a role in detoxification. 4. Keratinocyte enzymes play a role in the immune systems - Cancer – convert chemicals into carcinogens or disarm carcinogenic chemicals - Inflammation- activate steroids with anti-inflammatory properties 9. Describe the early development of the integument​ 1. Epidermis Development: Origin: The epidermis arises from the ectoderm, the outermost germ layer formed during gastrulation. Early Formation: ○ Around the 4th week of development, the surface ectoderm forms a single layer of simple cuboidal cells. ○ By the end of the second month, these cells proliferate and form a periderm, a temporary protective layer, above the underlying basal layer (which eventually becomes the stratum basale).  ○ Periderm will undergo keratinization and desquamation (shedding in scales) and is replaced by basal layers Stratification and Specialization: ○ Basal layer becomes stratum germinativumàbecomes stratum basal and will create all other epidermal layers via mitosis 2. Dermis Development: Origin: The dermis is derived from the mesoderm, that arises mostly from the somatic layer of the lateral plate mesoderm. Early Formation: ○ Collagen and elastic CT fibers are produced by mesenchymal cells ○ Through vasculogenesis and angiogenesis, blood vessels form and grow from mesenchyme 3. Neural crest cell --> Melanocytes - Migrate to mesenchyme of dermis and differentiate into melanoblasts in stratum basal 4. Vernix Caseosa: a waxy coating called the vernix caseosa covers the fetal skin. It is composed of sebum (from sebaceous glands), dead skin cells, and lanugo hair. This coating protects the delicate fetal skin from amniotic fluid.