LECTURE #5

Cutaneous appendages are all derivatives of the epidermis.

Eccrine (merocrine) sweat glands are simple, coiled, tubular glands that are widely distributed over the body. Secretory portions are tightly coiled and consist of a single layer of columnar-like pyramidal cells. They deep extend with in the dermis or hypodermis, where they are surrounded by myoepithelial cells, which aid in the discharge of secretion by contraction.

Duct portions, composed of two cuboidal cell layers, are corkscrew-shaped and open onto the epidermal surface. The luminal diameter of the duct is less than that of the secretory coil. These glands are important in thermal regulation. When hypotonic sweat is released onto the body surface, heat is lost by water evaporation.

Control of the eccrine glands is mainly by the innervation of choli-nergic fibers.

Apocrine sweat glands are also simple, coiled, tubular glands but are much less abundant in their distribution than eccrine glands. They can be found in the axillary, areolar, and anal regions.

Secretory portions of these glands are composed of a single layer of cuboidal or columnar cells. They are larger and have a much wider luminal diameter than eccrine sweat glands. Myoepithelial cells surround the secretory cells within the basement membrane and contract to facilitate secretion.

Duct portions are similar to those of eccrine sweat glands but open onto hair follicles instead of onto the epidermal surfaces.

Functions of these glands in humans is not at all clear. In other mammals, apocrine sweat glands are widely distributed over the body and serve a variety of functions related to olfaction and behavior. Specialized apocrine glands in the ear canal (ceruminous glands) produce a secretion in conjunction with adjacent sebaceous glands to form the protective earwax (cerumen). Apocrine sweat is normally odorless when secreted but becomes noticeable due to the activity of cutaneous bacteria. Control of the apocrine glands is hormonal and via the innervation of adrenergic fibers. These glands do not begin to function until puberty.

Sebaceous glands are simple, branched holocrine acinar glands. They usually discharge their secretions onto the hair shaft within hair follicles. These glands are found in the dermis throught the skin, except on the palms and soles.

Secretory portions consist of peripherally located, flattened stem cells that resemble basal keratinocytes. Toward the center of the acini, enlarged differentiated cells are engorged with lipid. Death and fragmentation of cells nearest the duct portion result in the holocrine mechanism of secretion.

Duct portions of sebaceous glands are composed of stratified squamous epithelium that is continuous with the hair cat and epidermal surface.

Functions involve the lubrication of both hairs and cornified layers of the skin, as well as resistance to desiccation.

Control of sebaceous glands is hormonal. Enlargement of the acini occurs at puberty.

Hairs are long, filamentous projections consisting of dead keratin-zed epidermal cells. Each hair derives from an epidermal invagination called the hair follicle, which possesses a terminal hair bulb, located in the dermis or hypodermis, from which the hair shaft grows. Bundles of smooth muscle cells, called arrector pili muscles, are attached to the hair follicle at one end and the papillary dermis at the other. Contraction of these muscles raise the hairs and dimple the epidermis ("goose flesh"). The follicles and associated sebaceous glands are known as pi-losebaceous units.

Nails, like hair, are a modified stratum corneum of the epidermis. They contain hard keratin that forms in a manner similar to the formation of hair. Cells continually proliferate and keratinize from the stratum basale of the nail matrix.

new words

cutaneous - skin

appendace - cover

coiled

tubular - tubular

widely - widely

to distribute - distribute

columnar-like - columnar-like

pyramidal - pyramidal

surface - the surface

duct portions

corkscrew-shaped - corkscrew-shaped

luminal - luminal

thermal - thermal

innervation - innervation

abundant - in abundance

to facilitate - facilitate

Often, at the first mention of an object, however, it is not recommended to use the definite article before it:

1) if the mentioned item is the only one in the world:

E. g. The sun is shining brightly;

2) if this subject is specific to the situation:

E. g. Put the book on the table.

Insert the article where necessary.

1. What's... weather like today? -... the weather is fine.

2... sun is yellow.

3... sky is gray today.

4... earth is... planet.

5. We had... English lesson yesterday... teacher asked me many... questions... questions were difficult.

6. Where is your... brother? - He is at... home. He is in his... room. He is sitting at... table. He is doing his... homework... homework is difficult.

7. Our... cat is sitting on... sofa.

8. It is very dark in... room. Turn on... light, please.

9. Nick went into... bathroom, turned on... water and washed his hands.

10. This is... good... book. Take... book from... table. Put this... book into... bookcase.

11... weather is fine today... sky is blue... sun is shining brightly in... blue... sky.

12. This is... boy... boy is... school. He is... pupil.

13. This... boy is my... brother's friend.

14. He has... cat, but he has no. dog.

15. He likes his...cat.

16. He doesn't give. cat...milk every day.

17. Yesterday I received... letter from my... friend... letter was interesting.

18. We live in... big house. I like... house very much.

19. Are you. worker? - No, I am... student.

20. Is this... table? - Yes, this is a table.

Answer the questions.

1. What are all derivatives of the epidermis?

2. What do secretory portions consist of?

3. How much do secretory portions extend?

4. What are duct portions composed of?

5. In what regulation are the glands important?

6. What is surrounded by myoepithelial cells?

7. What is the result in the holocrine mechanism of secretion?

8. What are duct portions of sebaceous glands composed of?

9. What does each hair derive from?

10. What does hard keratin contain?

Make the sentences of your own using the new words (10 sentences).

Find the definite and indefinite articles in the text.

Find one word, which is a little bit different in meaning from others (find one word that is slightly different from others in meaning):

1) a) cutaneous; b) skin; c)face;

2) a) cold; b) heat; c) thermal;

3) a) mouth; b) nose; c)arm;

4) a) nail; b) hair; c) skin;

5) a) neck; b) head; c) string.

Author: Elena Belikova

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