Summary
Highlights
The video introduces the three main accessory structures of the integumentary system: hair, exocrine glands, and nails. These structures will be discussed in detail.
The anatomy of hair and hair follicles is explored, including the stratum corneum, epidermis, dermal root sheath, epithelial root sheath, and sebaceous glands. The arrector pili muscle is introduced as a smooth muscle responsible for making hair stand up, triggered by cold temperatures or fear. The hair papilla, a capillary bed providing nutrients to the hair follicle, and the hair root nerve plexus, a sensory neuron system detecting hair movement, are also explained.
The matrix within the hair root is identified as the site of active cell division and hair production, where melanocytes also transfer pigments. Hair growth occurs in asynchronous cycles, with each follicle having a growth stage and a resting stage. The duration of these stages varies depending on the body location, such as eyelashes with a 30-day growth and 105-day resting cycle, versus scalp hair with a 3-year growth and 1-2 year resting cycle. Approximately 90% of scalp hair is in the growing stage, and an average person loses about 100 hairs per day.
Four types of exocrine glands are discussed, starting with sebaceous glands (oil glands). These glands, found in the dermis surrounding hair follicles, produce sebum through holocrine secretion. Sebum lubricates skin and hair and possesses antimicrobial properties. Sebaceous glands are concentrated on the face, back, chest, and male sex organs, and are sensitive to sex hormone levels, leading to conditions like acne during puberty.
Sweat glands are detailed, including eccrine and apocrine types. Apocrine sweat glands, despite their name, release products via eccrine methods. Their secretions, found in areas like armpits and genitalia, contribute to body odor when metabolized by microbes. Eccrine sweat glands are widely distributed, particularly on the palms and soles, and release a watery perspiration that cools the body through evaporation. Up to 1 gallon of sweat can be lost per hour, necessitating fluid replenishment to prevent electrolyte imbalances.
Ceruminous glands, modified apocrine sweat glands in the ear canal, produce cerumen (earwax). Cerumen protects the eardrum and traps insects, preventing deeper penetration and potential infections. Mammary glands are also modified apocrine sweat glands, found in the breast, that produce milk through apocrine secretion. They develop in females during pregnancy and lactation.
The final accessory structure, nails, are described as flattened claws made of hard keratin. The nail matrix is the site of new nail cell production, pushing out older cells to form the nail body. Key anatomical features include the eponychium (cuticle) and hyponychium, both composed of stratum corneum, and the lunula, a white area due to limited underlying blood supply.