Unit 5: Integumentary System

integumentary system 

the skin and its appendages that make up a complex set of organs that serve several function 

layers of skin

1. epidermis

2. dermis

epidermis

composed of epithelial cells, the outermost protective shield of the body

dermis

makes up the bulk of the skin; tough, leathery layer composed of mostly dense connective tissue

hypodermis/subcutaneous tissue

lies deep to the skin; superficial to the tough connective tissue wrapping (fascia) of skeletal muscles

4 cell types of the epidermis

1. keratinocytes

2. melanocytes

3. dendritic cells

4. tactile epithelial cells

keratinocytes

produce keratin, the fibrous protein that helps give the epidermis its protective properties

epidermal growth factor

peptide produced by various cells throughout the body 

melanocytes

spider-shaped epithelial cells that synthesize the pigment melanin

melanocytes location

deepest layer of the epidermis

where are melanocytes synthesized

in granules called melanosomes and are then transferred through the cell processes to nearby keratinocytes

dendritic cells

star-shaped cells that arise from bone marrow and migrate to the epidermis

dendritic cells function

ingest foreign substances and are key activators of the immune system

tactile epithelial cells (merkel cells)

present at the epidermal-dermal junction; associated with a sensory nerve ending

tactile epithelial cells function

sensory receptor for touch 

thick skin

covers the palms, fingertips, and soles of the feet

5 layers of epidermis (thick skin) *thin skin does not have stratum lucidum

1. stratum correum

2. stratum lucidum

3. stratum granulosum

4. stratum spinosum

5. stratum basale

stratum basale 

deepest epidermal layer that is actively mitotic

stratum spinosum

several cell layers thick; cells contain thick bundles of intermediate filaments, which consist of a tension-resisting protein, pre-keratin

stratum granulosum

1-5 cell layers in which keratinocyte appearance changes drastically, and the process of keratinization begins

2 types of granules that cells accumulate in keratinization

1. keratohyaline granules help form keratin in upper layers 

2. lamellar granules

lamellar granules

contain a water-resistant glycolipid that is secreted into the extracellular space; glycolipid slows water loss across the epidermis

how does the epidermis receive its nourishment?

from the capillaries in the dermis

stratum lucidum 

few rows of flat, dead keratinocytes

stratum correum

broad zone of 20 to 30 cell layers that accounts for up to ¾ of the epidermal thickness

desomsomes

help to hold the cells together during abrasion and stress

4 cell types of the dermis 

1. fibroblasts

2. macrophages

3. mast cells

4. WBCs

2 layers of the dermis

1. papillary

2. reticular

papillary dermis

areolar connective tissue in which fine interlacing collagen and elastic fibers form a loosely woven mat with many small blood vessels

dermal papillae

projections that indent the overlying epidermis

contents of the dermal papillae

capillary loops or free nerve endings (pain receptors) and touch receptors called tactile corpuscles

reticular dermis

dense irregular connective tissue; network of blood vessels that nourish this layer; dermal vascular plexus lies between this layer and the hypodermis; ECM contains thick bundles of interlacing collagen fibers

flexure lines

dermal folds that occur at or near joints, where the dermis is tightly secured to deeper structures

melanin 

polymer of AA tyrosine 

2 forms of melanin

1. reddish yellow

2. brownish black

melanin transport

from the melanocytes to the basal keratinocytes

why is melanin pigment only found in the deeper layers of the epidermis?

lysosome break down the melanosomes

carotene

yellow to orange pigment; stratum correum; can be converted to vit A

hairs or pili

flexible strands produced by hair follices and consist largely of dead, keratinized cells

hair follicles 

tubular invaginations of the epidermis from which the hairs grow 

advantages of hard keratin (hair, nails) over soft keratin (epidermal cells)

1. tougher and more durable

2. individual cells do not flake off

chief regions of hair

root and shaft

3 connective layers of keratinized cells 

1. medulla

2. cortex

3. cuticle

medulla

central core; consists of large cells and air spaces; soft keratin; is absent in fine hairs

cortex

bulky layer surrounding the medulla, consists of several layers of flattened cells

cuticle 

outermost part formed from a single layer of cells overlapping one

hair pigment synthesis

made by melanocytes at the base of the hair follicle and is transferred to the cortical cells

papilla of a hair follice

protrudes into the hair bulb