Skin Structure and Epidermis Quiz

Skin Structure

• Skin consists of two main layers: the epidermis and the dermis.
• The epidermis is a superficial layer of stratified squamous epithelium.
• The dermis is a deep layer of connective tissue, containing collagen and elastic fibers.
• The hypodermis, also called the subcutaneous layer, is a layer of areolar and adipose connective tissue that lies deep to the dermis.
• The hypodermis is not considered part of the skin.

Epidermis

• The epidermis has layers, from deep to superficial: basale, spinosum, granulosum, lucidum (in thick skin only), and corneum.
• Stratum basale (germinativum) is the deepest layer, where continuous cell division occurs, producing the other layers.
• Stratum spinosum is the layer above basale, with 8-10 layers of keratinocytes.
• Stratum granulosum contains keratohyalin and lamellar granules.
• Stratum lucidum is only present in thick skin (palms, soles, fingertips).
• Stratum corneum is composed of many layers of flat, dead keratinocytes called corneocytes. These cells are continuously shed and replaced.

Epidermal Cells

• Keratinocytes (90%): Produce keratin, a tough fibrous protein for protection.
• Melanocytes: Produce melanin for protection against UV radiation.
• Langerhans cells: Involved in the immune response, originate from red bone marrow.
• Merkel cells: Function in the sensation of touch, along with adjacent tactile discs.

Types of Skin

• Thick skin: Found on palms, soles, and corresponding surfaces of fingers and toes. It contains all five epidermal strata and is hairless.
• Thin skin: Covers most of the body, has a thinner stratum corneum, and lacks stratum lucidum. It has only four epidermal strata.

Dermis

• The dermis is a dense layer of irregular connective tissue containing collagen and elastic fibers.
• It varies in thickness.
• It's rich in nerves, blood vessels, hair follicles, sebaceous glands, and sweat glands.
• Contains hair follicles, arrector pili muscles, sebaceous glands, and sweat glands.

Hair

• Hairs are filaments arising from hair follicles, which are modified parts of the stratum corneum.
• Arrector pili muscles attach the follicle to the superficial dermis.

Sebaceous Glands

• Sebaceous glands are holocrine glands, where cells rupture during secretion.
• Secrete sebum to prevent dryness.

Sweat Glands

• Sweat glands are tubular structures, with a highly coiled end, lined by cuboidal epithelium.
• Typical sweat glands are merocrine glands (watery secretion secreted by exocytosis).

Fascia

• Fascia is a collection of connective tissues.
• Two types of fascia are superficial and deep fascia.

Lymphatic System

• The lymphatic system is a combination of cells, tissues, and organs that protect the body from invasions from foreign cells, microbes, viruses, and parasites.
• Lymph is a colorless fluid derived from body tissues.

Lymphoid Organs

• Primary lymphoid organs are where antigen-dependent proliferation and differentiation of lymphocytes occur.
  • Thymus: centrally located, behind the sternum. Functions in maturation of T lymphocytes.
  • Bone Marrow: site of B lymphocyte maturation.
• Secondary lymphoid organs are where functional lymphocytes eventually reach (final destination).
  • Lymph nodes
  • Spleen
  • Tonsils
  • Peyer's patches

Spleen

• The spleen is covered by a connective tissue capsule with trabeculae extending inward.
• It is composed of white pulp (lymphoid nodules containing B lymphocytes) and red pulp (splenic cords and sinuses, containing all types of white blood cells).

Tonsils

• Tonsils are incompletely encapsulated lymphoid nodules.
• Palatine tonsils are located in the oral cavity, covered by stratified squamous non-keratinized epithelium; crypts and underlying connective tissue barrier exist.
• Pharyngeal tonsils (adenoids) are centrally located and have ciliated pseudostratified columnar epithelium; no crypts.

Limb Development

• Upper limb buds appear before lower limb buds.
• Limb buds develop opposite specific spinal cord segments.
• Limb buds initially have a core of mesenchymal tissue derived from somatic mesoderm, which will give rise to bones and connective tissues—covered by a layer of ectoderm.
• A circular constriction separates the hand and foot plates from the proximal segment.
• The limb buds rotate in the 7th week of gestation.

Congenital Anomalies

• Amelia is a condition of complete absence of a limb, developing during the early 4th week.
• Meromelia is a condition of partial limb absence, related to differentiation and growth disturbances during the 5th week.
• Causes can be genetic, chromosomal abnormalities, or environmental factors like thalidomide.
• Congenital clubfoot (Talipes equinovarus) is a condition where the foot is turned medially and inverted, more common in males. The cause is multifactorial.

Test your knowledge on the structure of skin, focusing on the various layers of the epidermis and its functions. Understand the differences between the epidermis, dermis, and hypodermis, and learn about the unique features of each skin layer. This quiz will solidify your understanding of skin anatomy.