Lecture 26 Flashcards
What is hair associated with?
Hair has hair shaft (outside of skin) and hair root (inside of skin). Hair follicle is at the innermost part of the hair and inside of skin. Hair is anchored via hair follicles
Each hair is associated with sebaceous gland, which makes sebum. Hair is lubricated by sebaceous gland. Sebaceous gland secretes material towards hair shaft
Each hair is associated with arrector pili muscle, which is bundle of smooth muscle. This muscle is activated when ur cold. Goosebump is contraction of this muscle, which lifts the hair up
There is sensory nerve fiber in skin and next to the hair
Sweat gland is tubular and open on surface of skin to release water, electrolytes and urea; we pee through our skin
Within the dermis, there is pacinian corpuscle, which is pressure-sensitive and senses vibration
Pacinian corpuscle basics
Pressure, vibration
Onion-shaped structure sitting at border b/w dermis and hypodermis. Pressure-sensitive, gives diffuse pressure that is not localized due to compression of liquid b/w schwann cells and fibroblasts surrounding the nerve endings of pacinian
Meissner’s corpuscle basics
Touch receptors, dermal papillae, thick skin
Meissner’s corpuscles are in dermal papillae, are barrel-shaped with schwann cells,
surround unmyelinated nerve ending, allows us to sense fine touch
Merkel Cells basics
Mechanoreceptors, mostly thick skin
Merkel is incorporated in basal layer of skin, also mechanoreceptors, allows us to sense fine touch
Free nerve endings basics
Temperature
Free nerve endings are temperature-sensitive, its endings end in the stratum spinosum
Ruffini corpuscles basics
Stretch and torque
Ruffini is structurally similar to pacinian in terms of size and organization. The nerve ending breaks up into many diff branches. For stretch and torque; if you stretch or twist the skin, then ruffini senses it
Pacinian corpuscle
- Senses pressure, vibration
- Ovoid, encapsulated, over 1 mm in size
- Concentric lamellae of Schwann cells
- Central nerve fiber
Usually found in hypodermis, but sometimes found a little higher up.
Fibroblasts are found further out within the pacinian, and schwann cells are found further in within the pacinian
They secrete a liquid that is “compressible” and conveys the compression all the way to the central nerve fiber in the centre
Lots of _____ tissue in hypodermis
Adipose tissue
Papillary vs reticular layer of dermis
Papillary layer of dermis: right underneath epidermis, has loose CT
Reticular layer of dermis: right underneath papillary layer of dermis, collagen is thicker, DICT with fewer cells
Meissner’s corpuscle
Located in dermal papillae.
- Senses touch
- Papillary layer of hairless skin
- Composed of unmyelinated nerve fibers surrounded by Schwann cells
Eccrine sweat gland vs apocrine sweat gland vs sebaceous gland
Eccrine sweat gland
- Simple tubular
- Merocrine secretion
Apocrine sweat gland
- Simple tubular
- Merocrine secretion
Sebaceous gland
- Holocrine secretion (holocrine cells die and break apart)
Epidermis contribution to hair
Hair arises from downgrowth of epidermis; Epidermis dips down and forms a layer of the hair itself; The outer layer is epidermis and is continuous with the epidermis, and continues into a hair bulb/ hair follicle. There are special cells that rapidly divide to form the hair. The layer of epidermis that goes down surrounds the hair at diff levels until the hair protrudes outwards
Apocrine and eccrine sweat glands contribution to hair
Sweat glands surround the hair.
Eccrine sweat glands secrete watery fluids. Apocrine sweat glands secrete protein rich fluids.
Hair bulb location
At bottom of hair
Layers of epidermis + root sheath + hair
Epidermis is stratified squamous epithelium and comes from the top. Epidermis forms an external root sheath that goes all the way around the hair.
Special stem cells divide and the progeny cells move upwards to form the hair.
The layers from outside to inside: External root sheath (formed by epidermis), internal root sheath, cuticle, cortex and medulla. The hair shaft is composed of the medulla (core of cells) and cortex. The hair shaft is pigmented. Internal root sheath stops at the level where the hair emerges out of the skin
Sometimes, the medulla disappears and the hair can become hollow.
Follicular bulge
Adjacent to the hair shaft is region called follicular bulge that is part of the hair follicle. Follicular bulge is where stem cells live; The stem cells that generate the hair are born in follicular bulge.
The stem cells can move upwards to make sebaceous glands or move downwards
towards a region of the hair that called the hair matrix. Hair matrix is part of hair follicle where cells divide and
differentiate
Dermal papilla of hair
Surrounded by hair bulb and beside hair matrix cells, but is not part of the hair
6 layers that make up a hair (outer layer to inner)
External root sheath (not part of hair)
Internal root sheath (part of hair)
- Henle layer (squamous epithelial cells)
- Huxley layer (made of cuboidal epithelial cells)
- Internal root sheath cuticle
Hair shaft (part of hair)
- Hair cuticle (covers hair on outside)
- Cortex (forms wall of hair)
- Medulla
Nail anatomy
Phalanx (finger bone) is covered by loose CT and DICT of the dermis. The dermis is covered by the epidermis.
Underneath the outer free edge of the nail is the hyponychium, which is located right underneath the nail plate.
All cells that make the nail are located in the nail matrix. The nail matrix is near the nail root.
The nail plate covers an epidermis called the nail bed.
The eponychium is the cuticle. The lunula is the crescent moon shape on the nail plate, located right next to the cuticle.
Sebaceous gland appearance in H and E
Sebaceous gland looks like white bags of material right next to shaft of hair
Sebaceous glands near nipples
There is 1 type of sebaceous gland not associated with hair follicle, and this is found on the nipple. Nipple is lubricated by
sebaceous glands that do not open up to hair follicles. Sebaceous gland present, but not hair follicle.
There is quality of secretion of the nipple; they secrete pheromones that the baby can smell and it guides the baby to the place of nourishment.
Sebum secreting cells
- Stores oily secretion
- Undergoes apoptosis
- Release sebum by disintegrating
- Located below hair follicle. Surrounded by basal cells that divide and accumulate lipids
These cells are arranged in branched acinar glands, there is no duct system. An acinus is a bag of cells.
At the bottom of hair follicle are nuclei sitting on basement membrane, and these
cells are the sebum secreting cells that divide and move upwards. As these cells move upwards, they differentiate and fill the
secretory granules. The secretory granules contain a lot of lipids, protein, carbohydrates and oily substances that lubricate the hair. This material is constantly made so the cells are constantly moving upwards. As the cells fill with the secretions, they undergo apoptosis.
The nuclei in histological section become pyknotic and very dense, but then they disappear. The bags of oily material do not stain with H and E; it has lots of lipids, mucins and sugar molecules within it. The cells die and break apart and all the material they have inside will move up to surround the hair.
If you don’t wash your hair…
If you don’t wash hair, it gets very oily. It has protective function, keeps us from being infiltrated from water
Eccrine sweat glands
Simple tubular gland, Merocrine secretion
Eccrine sweat glands are invaginations from the surface epidermis into the underlying reticular dermis and hypodermis
