Test1

• Epidermis


  • Keratinised stratified squamous epithelium
• Epidermis cell types


  • Keratinocytes
  • Melanocytes
  • Langerhans cells
  • Merkel cells
• Keratinocytes


  The primary cell type, that produces keratin, a protein that provides strength and waterproofing
• Melanocytes


  Cells that produce melanin, the pigment responsible for skin color and UV protection
• Langerhans cells


  Immune cells that help in fighting against pathogens
• Merkel cells


  Sensory cells associated with touch reception
• Epidermis


  • Avascular: lacks blood vessels and receives nutrients via diffusion from the underlying dermis
  • Stratified: composed of multiple layers of cells to provide better protection
• Epidermis


  The outermost layer of the skin, consisting of multiple layers of cells.
• Stratified


  A term describing a type of tissue composed of multiple layers of cells stacked on top of each other.
• Squamous


  A type of epithelial cell that is roughly cube-shaped under a microscope. Squamous cells are flat and scale-like, which helps to reduce the surface area of the skin while maintaining its strength.
• Fetal period


  Lasts from the ninth week of pregnancy until birth
• Fetal period


  • Involves significant growth, organ maturation, and the development of sensory and physical abilities
  • The fetus prepares for life outside the womb by gaining weight, storing fat, and practicing vital movements and reflexes
• Growth and Maturation


  1. The fetus undergoes significant growth in size and weight

  2. Organs and tissues that formed during the embryonic period continue to develop and mature
• Development of Body Systems

  1. Nervous System: The brain grows rapidly, developing structures and neural connections. The fetus begins to respond to stimuli

  2. Musculoskeletal System: Bones continue to harden, and muscles strengthen, allowing for movement. The fetus practices movements like kicking and stretching

  3. Circulatory System: The heart becomes more efficient, and the blood supply increases to support growing tissues

  4. Respiratory System: The lungs develop, although they are not fully functional until after birth. The fetus practices breathing movements

  5. Digestive System: The digestive organs mature, and the fetus begins to swallow amniotic fluid, which helps develop the gastrointestinal tract

  6. Reproductive System: External genitalia become distinguishable, and the reproductive organs mature
• Formation of External Features

  1. Skin: The skin becomes less transparent, and fat accumulates underneath, providing insulation

  2. Hair and Nails: Fine hair (lanugo) covers the body, and nails start to grow

  3. Face: Facial features become more defined
• Sensory Development


  The senses continue to develop, including touch, taste, hearing, and sight. The fetus can respond to light and sounds from the external environment
• Preparation for Birth


  1. In the final weeks, the fetus gains weight rapidly, stores fat, and prepares for life outside the womb

  2. The head often moves into a downward position, getting ready for delivery
• Importance of Fetal Period

  • Growth: The fetus grows from a few inches in length to a full-term baby, typically around 19-21 inches
  • Organ Maturation: Organs and body systems mature to the point where the fetus can survive outside the womb
  • Development of Abilities: The fetus practices movements and reflexes necessary for survival after birth, such as sucking and swallowing
• Epidermal Maturation


  The layers of the epidermis continue to develop, with the stratum corneum forming a protective outer layer
• Dermal Strengthening


  The dermis becomes more robust with increased collagen and elastin fibers, along with more developed blood vessels and nerves
• Hair and Gland Development

  Lanugo hair covers the body, and sweat and sebaceous glands mature, with sebaceous glands producing the protective vernix caseosa
• Pigmentation


  Melanocytes continue to produce melanin, leading to skin pigmentation
• Fat Accumulation


  Subcutaneous fat develops, aiding in insulation and energy storage
• Continuation of Epidermal Development

  1. Layer Differentiation: The multiple layers of the epidermis that began forming during the embryonic period continue to develop and mature

  2. Stratum Corneum: By the end of the fourth month, the periderm is replaced by the stratum corneum, the outermost layer of dead, keratinized cells that provide a protective barrier

  3. Stratum Granulosum and Stratum Spinosum: These intermediate layers develop between the basal layer and the stratum corneum, adding to the skin's protective and functional properties
• Formation of Dermal Structures

  1. Collagen and Elastin Fibers: The dermis continues to develop, with fibroblasts producing more collagen and elastin fibers, increasing the strength and elasticity of the skin

  2. Blood Vessels and Nerves: These structures continue to grow and expand within the dermis, enhancing the skin's ability to supply nutrients, remove waste, and sense the environment
• Development of Skin Appendages

  1. Hair Follicles: By the fourth to fifth month, hair follicles produce fine, soft hair called lanugo, which covers the fetus's body. Lanugo helps protect the skin and is usually shed before birth

  2. Sweat and Sebaceous Glands: These glands continue to develop and mature. Sweat glands become functional later in fetal development, while sebaceous glands produce sebum, which combines with shed skin cells to form the vernix caseosa
• Vernix Caseosa Formation


  Around the fifth month, the skin is coated with a white, creamy substance called vernix caseosa. This is produced by the sebaceous glands and helps protect the skin from the amniotic fluid, preventing it from becoming chapped or damaged
• Melanocyte Activity


  Melanocytes, which began producing melanin during the embryonic period, continue to increase in number and activity. This leads to the pigmentation of the skin, which becomes more noticeable as the fetus develops
• Subcutaneous Fat Development


  Starting around the seventh month, subcutaneous fat begins to accumulate under the skin. This fat provides insulation and helps with temperature regulation after birth
• Migrant cells


  • Melanocytes: Neural crest-derived cells located in the basal layer of the epidermis. They produce melanin to protect against UV radiation and contribute to skin pigmentation
  • Langerhans Cells: Bone marrow-derived dendritic cells located in the stratum spinosum. They function in immune surveillance and activation of the adaptive immune response
  • Merkel Cells: Cells found in the basal layer of the epidermis, involved in mechanoreception and the sensation of light touch and texture
• Melanocytes


  • Origin: Melanocytes originate from neural crest cells, which are a group of migratory cells that arise from the neural tube during early embryonic development
  • Location: These cells are located in the basal layer of the epidermis, the outermost layer of the skin
  • Function: Pigment Production: Melanocytes produce melanin, the pigment responsible for skin, hair, and eye color. They synthesize melanin in response to ultraviolet (UV) radiation, which helps protect underlying skin cells from DNA damage caused by UV exposure
  • Melanosome Transfer: Melanin is stored in organelles called melanosomes, which are transferred from melanocytes to keratinocytes (the predominant cell type in the epidermis). This transfer provides pigmentation to the skin and hair
• Langerhans Cells


  • Origin: Langerhans cells originate from bone marrow-derived precursors. They are a type of dendritic cell, which are part of the immune system
  • Location: These cells are located in the stratum spinosum layer of the epidermis, as well as in the upper dermis
  • Function: Immune Response: Langerhans cells act as antigen-presenting cells (APCs). They capture and process microbial antigens, then migrate to the nearest lymph node to activate T-cells and initiate an adaptive immune response
  • Skin Surveillance: They play a crucial role in monitoring the skin for pathogens and contributing to the body's immune defense mechanisms
• Merkel Cells


  • Origin: Merkel cells are believed to originate from the neural crest or from epidermal progenitor cells
  • Location: These cells are found in the basal layer of the epidermis, particularly in areas of the skin that are highly sensitive, such as the fingertips, lips, and hair follicles
  • Function: Mechanoreception: Merkel cells are involved in the sensory function of the skin. They are associated with nerve endings and form Merkel cell-neurite complexes
  • Touch Sensation: They are responsible for detecting light touch and texture, contributing to the sense of fine touch or tactile discrimination