The Integumentary System

I know we've only covered two out of the four types of tissue, but that will be enough to start looking at some of the systems of the human body. We will start with the one that is easiest to see, the integumentary system. This is made up of the skin and hair and nails, as well as certain glands. It's actually quite a remarkable system, so let's learn all about this now.

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[prasanth]

**Skin Structure:**
- Made up of epidermis (outer layer) and dermis (inner layer).
- Epidermis is avascular and made of keratinized stratified squamous epithelium.
- Dermis is vascularized connective tissue.
- Below dermis is subcutaneous layer (hypodermis) made of adipose tissue.

**Epidermis Layers:**
1. Stratum basale: Single row of rapidly dividing keratinocytes, contains melanocytes and tactile cells.
2. Stratum spinosum: Several layers of spiky cells connected by desmosomes, contains dendritic cells.
3. Stratum granulosum: 4-6 cell layers, beginning of keratinization.
4. Stratum lucidum: 2-3 cell layers of clear, dead keratinocytes.
5. Stratum corneum: 20-30 cell layers of dead, anucleated keratinocytes.

**Dermis:**
- Strong, flexible connective tissue.
- Papillary layer: Thin, areolar connective tissue with dermal papillae.
- Reticular layer: Dense fibrous connective tissue with blood vessels.

**Skin Pigmentation:**
- Melanocytes produce melanin, determining skin color and protecting from UV radiation.
- Other pigments include carotene (yellow-orange) and hemoglobin (red when oxygenated).

**Skin Appendages:**
1. Hair: Made of dead, keratinized cells, produced by hair follicles.
2. Nails: Modified epidermis made of hard keratin.
3. Glands: Sweat glands (eccrine and apocrine), sebaceous glands (oil glands).

[yaseminnursahin]

1) Collagen and elastic fibers are seen in the papillary layer of dermis.
2) Reticular tissue is made of irregular dense connective tissue.
3) Melanocytes are seen in the stratum basale of epidermis.
4) Eccrine/Merocrine sweat glands release their watery secretion directly to the epidermis.
5) Apocrine sweat glands release their secretion through the hair follicles on certain areas(armpits and outer genital areas) and cause body odor.

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