histology: the integument

the integument is divided into three basic layers: on the surface is the epidermis, then the dermis, then the hypodermis. the epidermis itself has several layers, the deepest of which is called the stratum basale which is on the basement membrane of the epidermis and contains mitotically active keratinocytes, which are epithelial cells containing keratin, which is a sulfur bound protein. also scattered in this layer are other cells such as melaninocytes which produce melanin, Langerhans cells which are antigen presenting cells, and Merkel cells which are involved in light touch perception. the next layer up is the stratum spinosum. which is a thick layer containing keratinocytes that are held together by desmodomes. above the spinosum is a thin layer called stratum granulosum which is composed of dying keratinocytes. the last layer is the stratum corneum, which is basically a thick layer of keratin, of variable thickness depending on the location on the body.

beneath the epidermis is the dermis, and the border between the two contains projections upwards from the dermis called papillary ridges and projections downwards from the epidermis called rete pegs. the dermis has two layers, a thin papillary layer and the reticular layer. the reticular layer makes up the bulk of the dermis and is made of dense irregular CT and is highly vascularized and innervated. inside the dermis are two types of pressure receptors- meissner's corpuscle senses light pressure in the papillary layer and is made from helically wound schwann cells around a nerve axon ending. pacinian corpuscles sense deep pressure in the reticular layer and are made of concentric schwann cell wrappings around the end of the axon.


questions
1. what are the 3 basic layers to the skin?
2. describe the epidermis.
3. describe the dermis.
4. describe the hypodermis.

5. what are the layers of the epidermis?
6. describe the stratum basale.
7. what are the cells that might appear in the stratum basale?
8. describe the stratum spinosum.
9. describe the stratum granulosum.
10. describe the stratum corneum.

11. what are the two layers of the dermis?
12. describe the papillary layer of the dermis.
13. describe the reticular layer of the dermis.
14. what is a meissner's corpuscle?
15. what is a pacinian corpuscle?

16. what is the smooth muscle strip associated with hair follicles?
17. describe the structure of a sweat gland.
18. describe the structure of a sebaceous gland.


answers
1. epidermis, dermis, hypodermis.
2. nonvascularized and minimally innervated, keratinized stratified squamous, made almost entirely of keratinocytes.
3. well vascularized and innervated, mostly dense irregular CT
4. mostly loose CT and adipose tissue.

5. stratum basale, spinosum, granulosum, corneum.
6. single layer of mitotically active cuboidal cells sitting on basement membrane.
7. melanocyte, which produces melanin. langerhans cell, which is an antigen presenting immune cell. merkel cell, involved in light touch sensation.
8. keratinocytes which are held together by extensive desmodomes. form a layer of variable thickness.
9. granular layer a few layers thick with dying keratinocytes.
10. keratinized layer of many dead keratinocytes, sometimes with a clear bottom portion called the stratum lucidum.

11. papillary layer, reticular layer
12. thin, undulating, with upward projections called dermal papillas and downward projections from epidermis called rete pegs.
13. thicker layer with dense irregular CT with elastin, highly vascularized and innervated.

14. touch sensor in dermal papillae. small, helical wound Schwann cells on an axon.
15. a deep pressure and vibration sensor in the deep dermis or hypodermis. large, with concentric layers of schwann cells.

16. arrector pili muscle
17. simple tubular gland extending deep into the dermis.
18. simple acinar gland off of hair follicles that produces sebum.