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Lesson 5 - Integument Accessory Structures - Glands

Student Performance Objectives
1. List 4 different exocrine glands found in the integument.
2. Explain the difference between exocrine and endocrine glands.
3. Explain the difference in function of the eccrine and apocrine sweat glands.
4. List 3 functions for sebaceous gland secretions.

Lesson Outline
Glands - the glands associated with the skin are exocrine glands - glands with ducts that carry
     the gland's secretion to a specific location.
A. Sweat glands - these occur in two types. The glands contain modified epithelial cells
    that secrete their product, sweat, and other epithelial cells modified so that they can
    contract and thereby push the secretion to the skin's surface through the gland's duct.
    These contracting epithelial cells are called myoepithelial cells.
    1. Eccrine sweat glands produce a watery secretion that cools us. They can
        secrete without us noticing it (insensible perspiration) or can produce enough
        secretion for us to notice the moisture accumulation (sensible perspiration).
        a. There are 2-5 million of these glands in the skin with the greatest
            density occurring in the palms, soles and forehead.
        b. Their method of secretion is merocrine meaning that the sweat leaves
            the intact cells of the gland by exocytosis from vesicles produced by
            the Golgi apparatus.
        c. The gland itself is a coiled, tubular structure located in the dermis with
            a long, slender duct that passes up through the dermis and epidermis to
            the skin exterior where the sweat is deposited.
    2.  Apocrine sweat glands produce a secretion thicker than that of the eccrine
         glands that passes through a duct that leads not to the skin surface directly, but
         to the space in a hair follicle where the hair itself is located. The secretion then
         exits at the skin surface at the same opening the hair utilizes to protrude from
         the surface.
         a.  These glands are found mainly in the axillary and inguinal areas and
             develop during puberty.
        b.  Their secretion contains odorless pheromones that can attract or repel
             other individuals in a sexual sense. The secretion also contains
             substances (fatty acids) that can be metabolized by surface bacteria into
             odorous molecules we associate with a gym locker room, a nervous
             person, or an unbathed individual.
       c.  The gland is coiled and tubular, located in the dermis with a duct
            extending toward the skin surface, and the method of secretion is
            merocrine, like the eccrine glands.
B.  Sebaceous glands
     1. These glands secrete an oily product, called sebum, into the hair follicle. It
         functions to soften the keratinized cell layers making up the hairs, it
         contains substances inhibitory to the growth of bacteria and helps to soften
         the skin. Some sebaceous glands secrete directly onto skin without passing
         first into the hair follicles.
     2.  Sebaceous glands secrete by the holocrine method which means that cells
         accumulate the gland's product and then those specific cells rupture and die
         but release the secretion into the gland's duct. New cells form to take the
         place of the lost cells.
     3. The secretory product is pushed to the surface through the contraction of the
         arrector pili muscle.
     4. Sebum is very important when you are a fetus because it mixes with shedding
         epithelial cells and lanugo to produce the thick, oily coating (called vernix
         caseosa) seen on the newborn baby. This coating protects the delicate fetal
         skin during the months of immersion in amniotic fluid.
    5.  Modified sebaceous glands, called Meibomian glands, are located along the
         inner margins of the eyelids. These secrete oil that prevents the eyelids
         from sticking to each other and helps to keep tears within the eye surface.
C.  Mammary glands - these milk-producing glands are modified apocrine sweat glands
      located in a woman's breasts. The gland's secretion is directed into a nipple for
      easy delivery to the nursing infant.
     1. These glands develop only during pregnancy and lactation.
     2. The developed gland consists of 15 to 20 lobes, each drained by a lactiferous
         duct, all of which drain into a lactiferous sinus that leads to the nipple.
     3. The mammary glands develop in the subcutaneous, pectoral fat pad.
D.  Ceruminous glands - these modified sweat glands secrete their product into the
     external auditory canal. Here it mixes with sebum from sebaceous glands to form
     earwax that helps to waterproof the ear canal, traps small insects that might try to
     crawl inside, and is bactericidal.