Andrews Flashcards
Describe apocrine gland in more detail
Apocrine is a term used to classify exocrine glands in the study of histology. Cells which are classified as apocrine bud their secretions off through the plasma membrane producing membrane-bound vesicles in the lumen. This method is also called decapitation secretion. The apical portion of the secretory cell of the gland pinches off and enters the lumen.
Apocrine secretion is less damaging to the gland than holocrine secretion (which destroys a cell) but more damaging than merocrine secretion (exocytosis).
An example of true apocrine glands are mammary glands, responsible for secreting breast mil
Adrenergic innervation:
Excretion is episodic/ pulsatile, but secretion is continuous
No known function in humans; do not begin to function until puberty
Give examples of apocrine glands
Axilla, areola, anogenital, external auditory canal (ceruminous glands), eyelids (glands of Moll-on margin of eyelids next to lashes; anterior to Meibobian glands; they empty into adajcent lashes; secrete lipds that makes up tear film; blockage results in a stye)
Describe modes of secretion: apocrine, decapitation, merocrine.
Aprocrine/Decapitation: see above
Merocrine: Merocrine is a term used to classify exocrine glands and their secretions in the study of histology. A cell is classified as merocrine if the secretions of that cell are excreted via exocytosis from secretory cells into an epithelial-walled duct or ducts and thence onto a bodily surface or into the lumen.
Merocrine is the most common manner of secretion. The gland releases its product and no part of the gland is lost or damaged (compare holocrine and apocrine).
The term eccrine is specifically used to designate merocrine secretions from sweat glands (eccrine sweat glands)
Holocrine: Holocrine secretion is the most damaging type of secretion, with merocrine secretion being the least damaging and apocrine secretion falling in between.
Examples of holocrine glands include the sebaceous glands of the skin and the meibomian glands (The meibomian glands (or tarsal glands) are a special kind of sebaceous gland at the rim of the eyelids inside the tarsal plate, responsible for the supply of meibum, an oily substance that prevents evaporation of the eye’s tear film) of the eyelid. The sebaceous gland is an example of a holocrine gland because its product of secretion (sebum) is released with remnants of dead cells
What is the innervation of apocrine glands?
Adrenergic innervation:
Excretion is episodic/ pulsatile, but secretion is continuous
No known function in humans; do not begin to function until puberty
When do hair and sebaceous glands develop?
Hair follicle/sebaceous gland primordia: 9-12 weeks
What biochemical factors are necessary to initiate hair growth?
Ectodysplasin A & noggin are essential for the development of primary hair follicles & induction of secondary follicles
Describe the anatomy of a hair follicle
Infundibular segment
Uppermost portion from epidermis to sebaceous duct
Isthmus
Between sebaceous duct and arrector pili insertion
Inferior segment
Bulb, dermal papilla
What segment of the hair follicle fully keratinizes?
IRS fully keratinizes and sheds within isthmus
What are the layers of the hair follicle from inside to outside?
Medulla → Cortex → Cuticle → Cuticle →Huxley → Henley–>outer root sheath
Hair shaft – 3 components
Medulla: central, citrulline containing proteins
Cortex: forms bulk of hair, hair keratins, ↑ sulfur & glycine/tyrosine packing
Cuticle
Inner root sheath
Cuticle: 2nd layer cornified, protects cortex (like stratum corneum)
Huxley’s layer: Trichohyalin granules (substrate for citrulline rich proteins)
Henle’s layer: 1st to be cornified
Outer root sheath – most peripheral of cellular components
What is the length of time for each of the three hair cycles?
Anagen: 3-5 years, ACTIVE growth phase
85-90% all scalp hairs; growth rate 0.37mm/day
Pigmented bulb (laser hair removal)
Catagen: 3 weeks, INVOLUTION phase
1% of hairs normally
Many apoptotic cells in outer root sheath
Telogen: 3-5 months, RESTing
13-20% of hairs normally
Non-pigmented bulb
Sebaceous glands are what type of gland?
Holocrine
Where are the following sebaceous glands found? Fordyce spots Meibomian glands Zeiss glands Tyson glands Montgomery tubercle
Fordyce spots-lips Meibomian glands-eyes (eyelids; tarsal plate; chalazion) Zeiss glands-eyes (eyelids; hordoleon) Tyson glands-penis Montgomery tubercle-breasts
What are the contents of sebum?
Wax esters and squalene are unique secretory products of sebaceous glands
How fast to finger and toe nails grow?
Fingernails
Growth rate 0.1mm/day (~3mm/month)
About 4-6 months to replace complete plate
Toenails: slower growth rate
Growth rate 0.03mm/day (~1mm/month)
12-18 months to replace great toe
Facts about nails…
Little melanin little photoprotection in nail bed
Lack of stratum granulosum
No sebaceous glands
No SQ- dermis directly on bone
UVA penetrates normal nails more readily than it penetrates normal skin
