Integument

Learning Objectives:

o Define the integument and its functions

o Identify the principal layers of skin and the light microscope level and understand the functions and specializations of each layer

o Describe the major cellular events that take place in each layer during the process of keratinization

o Identify melanocytes and explain the process of pigmentation of the skin

o Identify and differentiate Meissner's and Pacinian corpuscles

o Compare eccrine and appocrine sweat glands, as well as sebaceous glands

o Identify the components of the pilosebaceous apparatus

SLU Slide 5: Thick Skin; Slide 92, Thin skin

Iowa Virtual Slidebox: Skin-Sole of foot (297); Skin (274)

Make a labeled sketch or screenshot comparing sections of thick skin and thin skin, paying close attention morphological changes in a keratinocyte in each layer. Which of these layers is continuously being replaced? Which layers contain sensory nerve endings? Where is adipose tissue concentrated?

Your sketch of thick skin should include the following layers of epidermis:

Stratum basale – A single layer of columnar cells

Stratum spinosum – polyhedral cells with numerous desomosomes that make them look “spiny” or prickly.

Stratum granulosum – flattened cells with numerous keratohyalin granules that make them stain more darkly (hence the name!)

Stratum lucidum in thick skin – Narrow, relatively lightly stained zone with flattened cells without nuclei

Stratum corneum – Flakey, flattened cells without nuclei or organelles, filled with keratin. The outer layers may be separated from the inner layers.

Deep to the epidermal layers, you should sketch the dermis, comprising stratum papillare and stratum reticulare in both thick and thin skin. Deeper yet is the hypodermis with adipocytes (which is not actually part of the “skin.”

Sensory nerve endings and glands are discussed below, but you may also add them to your sketch or to another summary sketch or table.

Iowa Virtual Slidebox: Pigmented skin (217)

Compare this slide with the less pigmented skin present in slide 274, noting any observations below.

Describe the process by which keratinocytes receive pigmentation. In which layer does this occur? How can you (or can you?) identify melanocytes in an H&E preparation?

· Premelanosomes emerge from the Golgi

· Melanin is produced from tyrosine and accumulates in the melanosomes

· Melanosomes (containing melanin granules) moves to the processes/arms of melanocytes

· Keratinocytes phatocytize the tips of melanocyte processes that contain mature melanosomes

· Melanosomes released into the cytoplasm of the keratinocyte

Melanocytes are located in the stratum basale, but send processes up through the stratum spinosum. They are identified in H&E by their clear cytoplasm and elongated nuclei, but are difficult to pick out from the surrounding basal keratinocytes.

Iowa Virtual Slidebox: Skin: Axilla (219)

This section demonstrates both eccrine and apocrine sweat glands. Describing their lumens and the epithelium that forms them, how can you distinguish between these two? How can you distinguish between the secretory and ductal portions? (Draw/screenshot and label them if you want!) What do they secrete and by which mechanism?

Eccrine sweat glands are smaller in diameter, with smaller lumens. The secretory portion of these glands is a simple cuboidal to columnar epithelium, which transitions to a stratified cuboidal or columnar epithelium in the duct portion. The ducts of eccrine sweat glands are also more deeply basophilic. You may also see some myoepithelial cells. Eccrine sweat glands release a watery secretion rich in electrolytes directly onto the surface of the skin.

Apocrine sweat glands are enlarged and have large, open lumens. Their ducts are similar to those of eccrine sweat glands, except that they are typically found associated with a hair follicle. Apocrine sweat glands secrete a viscous secretion with organic compounds/proteins which are then acted on by bacteria to produce an odor (i.e,, stinky sweat).

SLU Slide 6: Scalp

Iowa Virtual Slidebox: Skin of scalp (218)

Draw or screenshot and label the structure of a hair follicle. Include the hair medulla, cortex, and cuticle, as well as the inner and outer epithelial root sheath and the hair bulb.

In Which layers of the skin are portions of the hair found?

Hair is an invagination of the epidermis and is found within that layer. It also penetrates the dermis and hypodermis as well. Hair is not, however, found in some thick skin, called “glabrous” skin.

This section demonstrates many sebaceous glands. How can you differentiate these glands from eccrine or apocrine sweat glands? What do they secrete and by which mechanism of secretion? In which layer of the skin will you find the secretory portion of these glands?

Sebaceous glands secrete sebum, an oily, waxy substance, holocrine secretion. In holocrine secretion, entire cells and their contents are secreted. This is demonstrated in the anatomy of the sebaceous gland by the fact that the entire lumen of alveoli of these glands are filled with large, pale-staining cells with small, sickly-looking (pyknotic) nuclei. This is especially true at the center of the alveolus. You will find the secretory alveoli of sebaceous glands in the dermis of the skin (along with hair follicles).

Describe the process by which a person gets “goosebumps.” What structures are involved, and what do they look like? In general terms, do you know the innervation for those structures? Add arrector pili to your sketch above if you wish.

Goosebumps happen with smooth muscle fibers that are associated with hair follicles – arrector pilli – contract. They can contract in response to cold temperatures, or in response to sympathetic stimulation.

SLU Slide 005: Thick Skin

Iowa Virtual Slidebox: Fingertip (220)

Examine these slides to identify a Meissner’s corpuscle and a Pacinian (lamellar) corpuscle. Draw each below, including annotations indicating where in the skin each is located, and an indication of their relative size.

Your drawing of a Meissner’s corpuscle should be situated papillary layer of the dermis, in a dermal papilla. Your lamellar corpuscle should be large, in the reticular layer of the dermis, and feature many concentric layers (like an onion or tree rings)

SLU Slide 75: Finger Joint (look at nail bed)

Iowa Virtual Slidebox: Nail (221)

Describe the specializations of the epithelium that form a fingernail. Where does production of new fingernail cells take place?

You can also observe the difference in distribution of dermal papillae and Meissner’s corpuscles in this section.

The nail plate (fingernail) is a specialized version of the stratum corneum that produces hard keratin.

Nail beds are specialized versions of the stratum granulosum and spinosum.

The nail matrix, located at the proximal end of the nail plate, is where production of new cells occurs.