2 - Skin Derivatives PDF

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Skin Appendages Reference pages: 503-510 “Histology a Text and Atlas” Dr. S. McLean, [email protected], MSB 203 Office hours: Mondays 9-11 am LEARNING OBJECTIVES: By the end of this lecture you should be able to: 1. Describe the structure of the hair follicle and explain the role of matrix cells in the production of hair 2. List the structural components of nails and their functions 3. Explain the structure of sebaceous glands and how sebum is produced 4. Compare and contrast eccrine and apocrine sweat glands in terms of structure and function Case Study: Rupert McLean

OVERVIEW OF SKIN APPENDAGES Skin appendages are so-named because they are derived from downgrowths of epidermal epithelium. They include: 1) hair follicles and hair involved in heat regulation 2) nails protection (?) 3) sebaceous glands and sebum lubrication, antimicrobial (?) 4) eccrine sweat glands and sweat thermoregulation 5) apocrine sweat glands and “sweat” pheromone secretion (?) HAIR: Is composed of keratinized cells: develop from hair follicles all skin, with minor exceptions, has hair. Hair development is heavily influenced by hormones: facial and pubic hair production occurs during puberty male pattern baldness  changes in sex hormone levels with age There are two kinds of hair: terminal hair (thick), and vellus hair (difficult to see). colour comes from melanin

Notes: Hair Structure:

The hair follicle is responsible for the production and growth of the hair. It has a fairly uniform diameter, except at the base of the hair where it is expanded to form the hair bulb. The hair bulb has two important components: 1. Dermal papilla- vascularized tuft of loose connective tissue 2. Matrix cells- matrix cells are the cells that divide and account for the growth of the hair. They are keratinocytes.

You will find developing hair.

in the hair bulb, which lend pigment to the

Bulb gives rise to the internal root sheath (which is discontinued after the hair leaves the epidermis). Contains keratinocytes which form soft keratin. The bulb also gives rise to the hair itself, composed of consists of 3 layers: (from inside of hair to outside of hair)

keratin, and

1. inner medulla 2. cortex 3. outer cuticle

*note: you may not see the medulla in histological sections of vellus hair Outside of hair: down growth of epithelium called the external root sheath. It is surrounded by basement membrane called the “glassy membrane”. Also associated with the hair follicle is the muscle, which is involved under autonomic nervous system control. NAILS: Nails consist of: 1) Nail plate (hard keratin, highly sulphated) 2) Nail bed consisting of stratum basale and stratum spinosum of the epidermis. 3) Nail matrix: gives rise to root of nail, where keratinocytes undergo keratinization in region of the lunula (opaque in appearance). The lunula is opaque as the cells in this area are not completely keratinized. The process of keratinization is different than that for soft keratin formation that is found in the skin. The edge of the skin fold covering the nail root is called the eponychium or . It does not undergo desquamation as it is composed of hard keratin. Lower junction of the epidermal layer is called and attaches the nail plate to the fingertip. Notes/Questions: SEBACEOUS GLANDS:

Develop as a growth off the side of the hair follicle. Secrete sebum by holocrine secretion. Basal cells renew, and cells fill up with lipid secretion until the cell dies and all is secreted into the hair follicle. Process takes approximately 8 days Well developed

for production of lipids.

Unlike apocrine and eccrine sweat glands, they contain no

cells.

ECCRINE SWEAT GLANDS Consist of simple coiled tubular glands (apocrine may be compound) Eccrine sweat glands are found throughout the body except in the lips and certain regions of the external genitalia. Their secretion is “sweat” as we know it and is involved in thermal regulation. The sweat that is produced is essentially a more dilute form of urine. Eccrine sweat glands consist of a secretory and duct portion. Secretory portion The secretory portion is found in deep dermis or hypodermis and consists of 3 types of cells, all of which rest on the basement membrane. i. clear cells: portion of secretion (moth eaten appearance), usually found close to base of acini ii.dark cells: portion of secretion (darker moth eaten appearance), usually found closer to lumen iii.myoepithelial cells: squeeze out the secretions. Found at the base cells in the secretory portion. In eccrine sweat glands, the secretions are stored inside the secretory cells. Duct portion The duct portion consists of stratified cuboidal epithelium (2 layers) Compared to the secretory portion, the cells are dark staining with prominent nuclei and are smaller. Some salts are as secretion passes through. The secretion is released on the skin’s surface, not in a hair follicle. Lining of duct consists of epidermis once the duct reaches the surface. Notes/Questions: APOCRINE SWEAT GLANDS:

Apocrine sweat glands are found in axilla, and genital region. Similar to eccrine sweat glands, their secretory portion is found deep in dermis or in the hypodermis. Apocrine sweat glands release their secretion partly in response to stress. The secretion is “sweat-like” except it has a higher protein concentration and may also contain . Secretory portion 2 types of cells: 1- secretory basal cells 2- myoepithelial cells: similar to eccrine myoepithelial cells, help expel the secretion. Unlike eccrine ducts, the secretions are stored in lumen of secretory units. Duct portion Duct portion is composed of stratified cuboidal epithelium. Duct opens into hair follicle above sebaceous gland; the secretion is released through the hair follicle. Secretory product not altered in duct i.e. no reabsorption occurs in apocrine ducts....