Anatomy and Cell Biology 3309 Lecture Notes - Lecture 2: Apocrine Sweat Gland, Eccrine Sweat Gland, Arrector Pili Muscle
15 May 2018
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Lecture 2 – Skin Derivatives
Skin derivatives
- Sebaceous glands and sweat glands are skin derived appendages
- Hair and nails are keratin based like the skin
o Hair: mostly hard keratin but there is still parts of soft keratin in hair
o Nails: hard keratin
o Hard keratin is due to the cross linkages of sulfur groups
- Eccrine, apocrine: result in expression in different types of sweat
- If there is a hair follicle, it is thin skin
o Do not grow hair on thick skin
- Eccrine sweat gland: tubular structure with loops on its way up through the dermis to the
surface of the epidermis
o More coiled than apocrine sweat gland
- Apocrine sweat glands: secretions are continuous with the hair follicle
o Secretions get released from where the hair is protruding into the skin
o When hair comes out of head it is dead
o There are parts of the hair that have stem cells that contribute to the growth of the
hair (similar to what it is seen in the skin)
- Sebaceous gland: secretes contents along the hair shaft → secrete sebum
- Arrector pili muscle: muscle associated with each hair follicle
o Activated when scared or emotional = goosebumps
o In mammals such as cats or dogs, muscle pulls the hair shaft up
o Hair standing on end
o Defense mechanism in animals so they look bigger and can scare something off
o Emotional response in humans
- Hair shaft: when it comes out of the epidermis
- Sebaceous gland and apocrine is in close approximation to the hair
- Terminal hair (pubic, head, axillary); vellous is fine hair
- A hair is strand made of keratinized cells. Root = part of hair in the skin; shaft = part of hair
that projects from the skin
- Hair follicle is a tubular invagination of the epidermis from which the hairs grow
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Hair follicles and hair
- Hair follicle is responsible for growth and production of hair
- Infundibulum: from opening of the surface to opening of sebaceous gland
o Sebaceous gland is in close proximation to the hair follicle
o Opening of the sebaceous gland to the opening of skin from which hair shaft
protrudes
- Isthmus: from indfundibulum to arrector pili muscle insertion
o If muscle is contracted, it makes the hair stand on end
- Hair shaft:
o Hair is made of hard keratin
o Cuticle: outer most part
o Outer cortex
o Inner medulla
- Won’t see medulla in fine vellus hair
o There is terminal hair and fine vellus hair
o Vellus hair: hair on cheeks, on inner part of forearm, etc. → very fine strands of hair
o Not a terminal hair like what is on our head
- Hair bulge region:
o Source of epidermal stem cells
o During wound healing, stem cells from here can contribute to forming new skin
▪ Can migrate in, proliferate and form new skin
- Hair bulb:
o Made of the dermal papilla and matrix cells
o There is some innervation and a blood supply
o If pull a hair out of your head – it hurts because there is innervation
o If cut your hair, it does not hurt because there is no innervation/ blood supply there
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o Dermal papilla and matrix cells give rise to the internal root sheath
o Internal root sheath does not contribute to the hair itself
▪ = it is not apart of the hair shaft
o Proliferation of cells occurs here
o Where melanocytes are found that give pigment to hair
- Outer root shealth:
o Part of the external root sheath
o Caused by a down growth of epithelium
o Epithelium during development has a down growth and that is going to contribute
to the outer root sheath
- Crime scenes:
o Need some of the hairs that are from the bulb in order to extract DNA
o Cells of hair are mostly keratin (not cells at that point – like skin)
Hair – bulb
- In order to understand how hair is made, have to look at deepest part of the follicle...
- Deep end of the hair follicle is expanded, forming the bulb
- Image: cross section
- Deepest part of the hair follicle forms the bulb
- Matrix zone: growth zone in hair bulb
- Melanocytes: give pigment to the hair shaft as it is being produced
o Found within the growth zone area
- Dermal papilla: protrusion of dermis into the bulb
o Important because it carries the blood supply that supports the hair bulb
o If there are cells that are undergoing proliferation, they need a blood supply to
provide oxygen, glucose and other nutrients
- Overlying the papilla is a layer of keratinocytes that form the hair and melanocytes which
distribute pigment into hair
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Sebaceous glands and sweat glands are skin derived appendages. Hair and nails are keratin based like the skin: hair: mostly hard keratin but there is still parts of soft keratin in hair, nails: hard keratin, hard keratin is due to the cross linkages of sulfur groups. Eccrine, apocrine: result in expression in different types of sweat. If there is a hair follicle, it is thin skin: do not grow hair on thick skin. Eccrine sweat gland: tubular structure with loops on its way up through the dermis to the surface of the epidermis: more coiled than apocrine sweat gland. Sebaceous gland: secretes contents along the hair shaft secrete sebum. Arrector pili muscle: muscle associated with each hair follicle: activated when scared or emotional = goosebumps. In mammals such as cats or dogs, muscle pulls the hair shaft up (cid:498)hair standing on end(cid:499: defense mechanism in animals so they look bigger and can scare something off, emotional response in humans.
