Notes on the Web
Integumentary System

Bruce G. Stewart
Images like this were taken from slides actually used in your MSC lab exercises. More can be view from links in these notes. Some are at least partially labeled to help you review the lab histology materials..

Related Textbook Readings

Selected Images of Histological Materials From Laboratory Studies

This project of preparing images is ongoing. More may be added as time allows. See also the link to another web site at the end of these notes for integumentary system images that may aid you in your understanding of this system.

Lecture Outline

I. Integumentary System - general information

    A. Definition - the skin and its derivatives

  1. dermatology (derma=skin; logos= study of)

  2. derivatives include hair, nails, glands, and receptors

    B. General physiological roles

  1. regulation of body temperature

  1. protection

  1. reception of stimuli

  1. excretion

  1. synthesis of vitamin D (actual acts as a hormone)

    C. General Structure - a two-layered structure over a "subcutaneous layer"

  1. epidermis – the outer layer

  • keratinocytes - most common cells

  • produce keratin which helps waterproof and protect following keratinization

  • melanocytes - found in basal parts of the epidermis

  • produces melanin - a pigment which plays roles in skin color and absorption of UV radiation

  • nonpigmented granular dendrocytes - arise from bone marrow and migrate to epidermis or other areas with stratified squamous epithelium

  •  role in - immune reponses involving T-cells

  • stratum basale (= stratum germinativum of some authors)

  • single layer of cuboidal to columnar-shaped cells

  • capable of continuous mitosis

  • cells pushed to surface which later causes degeneration of nuclei and gradual cell death

  • in hairless skin, this layer also has tactile discs (Merkel's discs)

  • stratum spinosum - means 'prickly'

  • 8-10 (but varies) rows of polyhedral-shaped cells

  • spine-like projections of cytoplasm function to join cells together tightly

  • stratum granulosum

  • 3-5 (but varies) rows of flattened cells that contain granules of keratohyalin (1st step in keratin formation)

  • nuclei show various stages of degeneration because of distances from capillaries

  • stratum lucidum – (lucidum means 'clear')

  • location - normally evident under a light microscope from "thick skin" of palms and soles

  • 3-5 (but varies) rows of clear, flat, dead cells that contain droplets of eleidin (2nd step in keratin formation; formed from convertion of keratohyalin)

  • stratum corneum (cornified or "horny" layer)

  • 25-30 (but varies) rows of flat, dead cells

  • completely filled with keratin (produced by conversion of eleidin)

  • dead cells slough off due to wear and abrasion

  • locally produced "epidermal growth factor" influences base rate of mitosis and growth of epidermal cells

  • growth involves a series of events/changes as follows:  mitosis --> growth and filling of cell with keratohyalin --> conversion of keratohyalin to eleidin --> conversion of eleidin to keratin --> cell death --> sloughing off of old worn out cells.

  • approximate time of series - two weeks to 1.5 months

  1. dermis – the inner (deep) layer

  1. Hypodermis - this layer lies just below the dermis and has strong supporting connective tissue that provides support for blood vessels, nerves, adipose cells, etc. It anchors the skin to the underlying body structure (e.g. muscles). In fact, voluntary striated muscle fibers interdigitate with connective tissue fibers and are visible on some of our lab microscope slides. When you wrinkle your nose (for example) you are activating muscles that insert in the hypodermis and move the overlying skin.

Instructions for Study of Skin Histology and Including Instructions Pertaining to Lab Work and Diagram Coloring for the Remainder of the Semester

LAB INSTRUCTIONS:

At this point we will study histological preparations of human skin tissue. I will place the slides out for your use with the microscopes. I will present an illustrated overview of the slides you will be studying by using a videomicroscope that will allow me to project actual microscope views onto a screen.

You are to use proper care and safety techniques with the expensive lab equipment at all times. After you finish, return the slides to the exact same storage tray from which they came. You are to keep the microscope lense and the slides clean with lens paper which are available in the lab.

Ask me for help after and only after you have made an honest attempt to identfy what you can by:referring to:

At that point I will be more than willing to respond to questions on an individual or small group basis as fast as I can. Teamwork is a requirement, not an option in our lab studies. You must be willing to share what you are observing with others, especially if I announce some like, "Jane has found a very good example of ____." Step back from your scope and let others observe. Likewise, you must be willing to observe what others have found on their slides. This will help everyone make efficient use of lab time, and it is critical to fully understanding the variation in appearances of the various slide preparations. Remember that you could study a single slide so thoroughly that you know every single visible structure by name, yet you might well flunk a practical exam if you cannot recognize those structures in other slide preparations or images!

Examine a skin preparation. Find and be able to identify on sight the following level of detail (and, of course, know any more general names for combinations of these structures):

Color all features on Plates 18 and 19 of your Human Anatomy Coloring Book. You are responsible for recognizing these structures on any diagram. The structures have certain recognizable features. If you know these distinguishing features, then you will be able to interpret diagrams you have not previously seen.

Follow the instructions given on each plate with reference to colors to be used.

The names of the structures are to be colored, keying them to corresponding structures on the diagram and in colors as suggested in the plate's instructions. Do not simply "washed across" the words. Make this activity a spelling practice in addition to structural study.

Out-of-class study will be required to commit the lab subject matter to your long-term memory. Two compound microscopes have been placed in the library for in-library use. One or two examples of the slides examined in lab are also on hold there. Ask for them at the library desk.

Video Histology Series - Skin
Dr. David Moran - Colorado State University

At this point we will view an excellent video histology presentation by Dr. David Moran. You can consider him to be a "visiting lecturer" throughout the semester since we will view video histology presentations by him on almost all major tissue types found in the human body systems we cover. We will always view these after we have completed our own lab exercises so that you will be better prepared to understand the presentations. Do not take these lightly since they can add a useful perspective on tissue structure, and Dr. Moran presents images taken with types of microscopes we do not have (e.g. scanning electron, transmission electron, Nomarski interference contrast, and phase contrast microscopes). He also shows images of materials prepared with different histological stains and techniques that enhance the quality of images.

Lecture Outline (Continued)

    D. Skin Color - caused by both skin and non-skin pigments

  1. primary pigment - melanin

  • genetically controlled by gene codes in DNA

  • activity increased by UV exposure

  • albinism

  • vitiligo

  • freckles

  1. a secondary pigment - carotene

  1. a respiratory pigment carried in dermal capillaries - hemoglobin

    E. Surface Topography of the Skin

  1. ridges of feet and hands

  1. grooves - aid in bending of skin

    F. Epidermal Derivatives (= "Appendages" of the Skin of Marieb)

  1. Hair - heavily keratinized layers of cells that project from skin

  •  surrounding structure - hair follicle

  • connective tissue – outer layer

  • epithelial root sheath – includes stratum basale & stratum spinosum layers and an inner layer of proliferating cells

  • shape of base of hair follicle - bulblike

  • stratum basale including melanocytes folds upward into the bulb around a dermal papilla which projects upward into the bulb

  • the matrix of epidermal cells around the papilla is the major area of growth for the hair

  • concentric layers develop in the growth zone area and are clearly evident in a cross-section of the shaft

  • medulla - center

  • cortex - band of keratinocytes around medulla and contains melanin they received from melanocytes in the bulb

  • cuticle - outer band of heavily packed, highly keratinized cells

  • muscle - arrector pili - evolutionary vestigial muscle organ formerly useful to thicken fur for insulation and to change appearance for social communication (e.g. anger)

  • glands - sebaceous glands (over most of body) and apocrine sweat glands (only where they occur in axial regions)

  • sensory structures - hair root plexes

  • types include vellus (fine, light-colored & over most of body) and terminal [coarser, longer & found in eyebrows, scalp, axilla, and pubic areas plus (in males) face, chest, arms & legs]

  • growth - factors that affect growth include hormones (androgens), diet, health, stress, and genetics

  • growth cycles - replacement is natural at, say, 90 scalp hairs per day (but varies); alternate resting versus active periods vary among the follicles of different hair types.

  • special conditions

  • common baldness (=male-pattern baldness) due to heredity & hormones (especially testosterone)

  • minoxidil (e.g. Rogaine) works to stimulate follicles in some men

  1. glands - another type of epidermal derivative

  • location - haired skin

  • product - sebum

  • functions - waterproofing and keeping the hair soft

  • a clinical condition related to these glands - cystic acne

  • apocrine - a type that is relatively limited in distribution

  • location - axilla and pubic areas

  • design - discharge into hair follicles in selected regions

  • behavioral and evolutionary aspects - probable pheromone function
    Example of Recent Research Related to Human Apocrine Glands
    Source Journal: Cellular and Molecular Life Sciences. Vol. 58, No. 9, Aug 2001

    Authors: G. Rothardt and K. Beier


    Abstract

    The products of the human apocrine axillary glands contain volatile steroids which act as pheromones. The steroidal structure of these pheromones implies that the axillary glands should be able to synthesize cholesterol which is the essential precursor of these molecules. Since important steps in cholesterol synthesis are localized within peroxisomes, we investigated the occurrence and the putative role of peroxisomes in the axillary glands at protein and mRNA levels by immunocytochemistry, Western blotting, and RT-PCR. Numerous peroxisomes were localized in the cells of the apocrine glands by immunocytochemistry, and the presence of catalase was confirmed by Western blotting and RT-PCR. Additionally, RT-PCR revealed the presence of mRNAs of two peroxisome-associated enzymes of the cholesterol biosynthetic pathway, mevalonate kinase and farnesyl diphosphate synthase. The results suggest that the peroxisomes in the human apocrine axillary glands may play a pivotal role in the biosynthesis of pheromones.

  • eccrine - a widespread and more common type

  • design - simple, coiled tubular

  • locations - over most of body except lips, nails, parts of pubic area

  • areas of highest density - thick skin

  • ceruminous - a type of modified sudoriferous gland

  • location - external ear canal (auditory meatus)

  • production - cerumen

  • function - antibacterial and waterproofing

  • mammary glands - a type of reproductive/nutritional gland

  • evolutionary history - developed in stages from secretory glands of hair of belly (e.g. duck-billed platypus) to distinctly organized organs.

  1. nails - still yet another type of epidermal derivative

    G. Skin Wound Healing

  1. epidermal wound healing - a sequence of events

  1. deep wound healing - lacerations & incisions are more complex

  • blood clot forms

  • epidermal cells begin migration

  • vasodilation occurs and capillary walls become more permeable to neutrophils and monocytes which help with attack on microbes and disposal of tissue fragments; mesenchyme cells arrive for fibroblast building.

  • clot becomes a scab (clot without the water)

  • epithelial cells continue migration beneath scab

  • fibroblasts migrate along fibrin threads (which are a part of the scab) and synthesize scar tissue

  • granular tissue - type of scar tissue formed

  • period of intense growth and repair

  • scab sloughs off, fibers become more organized and fibroblasts disappear

  • blood vessels restored to some degree

  1. fibrosis - process of scar formation

    H. Homeostatic Imbalances

  1. wrinkles – due to wear and changes in connective tissue fibers of dermis; folds of dermis also show in surface of epidermis

  1. burns: severity based on depth

  • 1st degree – involves only surface epidermis

  • appearance – redness but no blisters

  • scarring - none

  • healing – two-three days

  • 2nd degree – epidermis and upper parts of dermis

  • appearance – redness, blisters, edema

  • scarring – mild to moderate

  • regeneration and healing time – cells from follicles and glands provide source of new epidermal cells; seven days to four weeks

  • 3rd degree – destroys epidermis, dermis, and skin derivatives

  • appearance – white to dark charred dry wounds; extensive edema

  • healing and treatment – slow and dangerous; often requiring skin graphs and extended hospital stays; scarring severe

  1. severity based on percent of body burned

The Lund-Browder Method of Estimating Burn Coverage

Body Area

<1 year

1 year

5 years

10 years

15 years

adult

Front or Back of Head

9. 5%

8.5%

6.5%

5.5%

4.5%

3.5%

Front or Back of Thigh

2.75%

3.25%

4%

4.25%

4.5%

4.75%

Front or Back of Leg

2.5%

2.5

2.75%

3%

3.25%

3.5%

Front or Back of Neck

1%

1%

1%

1%

1%

1%

Top or Bottom of One Foot

1.75%

1.75%

1.75%

1.75%

1.75%

1.75%

Front or Back of One Hand

1.25%

1.25%

1.25%

1.25%

1.25%

1.25%

Front or Back of One Upper Arm

2%

2%

2%

2%

2%

2%

Front or Back One Forearm

1.5%

1.5%

1.5%

1.5%

1.5%

1.5%

Perineum

1%

1%

1%

1%

1%

1%

  1. examples of other homeostatic imbalances -

  • hormonal affects – testosterone but also adrenal and ovarian hormones

  • onset – usually at puberty when secretions increase

  • an especially severe type – cystic acne produces scarring

  • caused by chronic deficiency of blood to tissue overlying a pressure point

  • cause – over exposure to UV radiation

  • affects – 1st degree burns (sometimes worse); skin cancers

  • basal cell carcinomas

  • source cells – basal cells of epidermis

  • risk factors – skin type, sun exposure (most important), family history, age, immunologic status

  • danger & prevalence – rarely metastasize; over 75% of skin cancers

  • squamal cell carcinomas

  • specific source cells - keratinocytes of stratum spinosum

  • risk factors – same as other skin cancers

  • danger and prevalence– variable rates of metastasization; about 20% of skin cancers

  • malignant melanoma

  • specific source cells - melanocytes

  • cause – same as other skin cancers

  • danger and prevelance – metastasizes rapidly to surrounding lymph and blood vessels; about 5% of skin cancers

I. Related Clinical Terms/Medical Terminology – Learn all of the related clinical terms from your assigned textbook chapter..

Reminder about Textbook Study

As with other topics, your textbook has excellent presentations of the materials on the endocrine system. While you should focus on the specific material in the Notes on the Web, you should always use your textbook as a resource for illustrations and for understanding content that your notes cover. Also, your Notes on the Web sometimes refer you to specific materials to learn from your book (i.e. the clinical terms noted previously).

As with all materials throughout the semester, you will have opportunities to ask questions or ask that any relevant material from your assignments be discussed in class. Please do not hesitate to seek help.

Related Internet Resources

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