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
Merocrine secretion
Merocrine secretion is when secretory components are packaged into secretory vesicles that are delivered to apical plasma membrane and then exocytosed. Typical exocytosis is in merocrine secretory mechanism
Eccrine sweat glands in H and E
At low magnification in H and E, find circular darker stained loops of cross sectional profiles. Location is reticular dermis and hypodermis.
Can see holes in epidermis, which is where the duct inserts itself
The resorptive duct stains darker compared
to the secretory coil. This is an exception compared to other exocrine glands; Other exocrine glands have a darker part for the portion that secretes and the resorptive duct is lighter.
Eccrine sweat gland segments
Gland has resorptive duct portion near the top that is thinner. There is secretory coil below the resorptive duct and the secretory coil is thicker
The resorptive duct stains darker compared
to the secretory coil.
Secretory coil of eccrine sweat gland
At the bottom of the gland surrounded by secretory coil, H20 and NaCl enter the gland
Secretory coil has several cell types that make sweat. Sweat is mostly made of water and electrolytes but also has other proteins and urea. This is produced in secretory coil
Resorptive duct of eccrine sweat gland
The resorptive duct absorbs NaCl and removes some of the NaCl so we get hypotonic sweat where the sweat cools us off.
Resorptive duct allows NaCl absorption into the skin
Cystic fibrosis and sweat
If there is issue with NaCl absorption in resorptive duct of eccrine sweat gland, we secrete hypertonic sweat, which is often found in cystic fibrosis.
Cystic fibrosis is mutated chloride channel that misfunctions, so chloride and sodium resorption are impaired.
Sometimes, mothers will diagnose cystic fibrosis in their babies early on b/c they sense that the scent of the child is very salty.
Resorptive duct and secretory coil of eccrine sweat gland in H and E
Resorptive duct - stratified cuboidal epithelium (2 cell layers). Lots of nuclei and stains darker. Lots of nuclei
Secretory coil - pseudostratified epithelium (2 cell layers). Larger, lighter-stained.
- Clear cells stain lighter, they produce water and sodium chloride (NaCl)
- Dark cells stain darker, they have secretory granules within the cytoplasm; dark cells make urea, glycoproteins; made in merocrine fashion
Myoepithelial cells in H and E
The darker pink layer on the outside of the secretory portion of the eccrine sweat glands are myoepithelial cells.
You can see elevated bumps of eosinophilic material, lots of contractile proteins and can sometimes see longitudinal or grazing section.
Myoepithelial cells function
Myoepithelial cells form meshwork of contractile epithelial cells and are within the basement membrane. Myoepithelial cells are contractile and ensure the secretion leaves the gland. They contract and squeeze the content out to the surface.
Secretory coils and ducts are surrounded by contractile Myoepithelial Cells. They contract upon hormonal and nervous stimulation and move secretory products through the duct system.
Myoepithelial cells stained for F-actin
If you take part of the eccrine sweat gland and stain for F-actin, you can see that the myoepithelial cells form a star-shaped interwoven network that allow for 3D squeezing of the content out of the gland. This activity is under the influence of the nervous system and hormonal stimulation (i.e when u get nervous).
Apocrine sweat gland
Simple tubular, merocrine secretion
- Are associated with hair follicles, but are not evenly distributed in the body
- Found in axilla, mons pubis, circumanal region
- Opens into hair follicles
- Secretory coil with large lumen; these glands secrete highly protein rich secretions, which they store within their secretory duct
- Activity starts at puberty
- Odor produced by bacterial breakdown of secretion
- Have myoepithelial cells
Apocrine sweat gland in H and E
In H and E, you see a lot of spaces, which are all secretions stored in the apocrine sweat gland.
Pheromones from apocrine sweat gland
In other mammals, apocrine sweat gland has important functions. For cats and dogs (and
other mammals), they mark their territory. They secrete pheromones by pee or rub their circumanal gland onto areas to release their material.
Human pheromones are released through
apocrine sweat glands. The ones in the axilla produce the “locker room smell”. The secretion is not odorous, but the breakdown of all the protein components within the sweat via bacteria causes the smell.
If you leave sweaty things in gym bag for a long time, it becomes smellier b/c bacteria has time to break stuff down
Male axilla sweat has a signal function on females
The name ‘apocrine’ sweat gland is a misnomer
the name apocrine sweat gland is a misnomer. they are not secreting by
an apocrine mechanism (apocrine mechanism is only found in mammary
gland and a little bit in prostate). apocrine means where lipid
components are squeezed out of surface of cell and the lipid droplet
is released and leaves with a little bit of cytoplasm of the cell. BUT
apocrine sweat glands secrete by merocrine mechanism and NOT by
apocrine mechanism
Mammary glands
Mammary glands are a version or modification of apocrine sweat glands
Epithelium types of secretory coil and duct of apocrine sweat gland
Secretory coil: simple cuboidal epithelium
Duct: stratified cuboidal epithelium
