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

peripheral connective tissue (fibrous sheath)

the connective tissue sheath is derived from the dermis; forms the external layer of the follicle wall 

glassy membrane

at the junction of the fibrous sheath and the epithelial root sheath. the basement membrane of the follicle epithelium

2 components of the epithelial root sheath

1. external root sheath: direction continuation of the epidermis

2. internal root sheath: derived from the matrix cells

components of a the wall of a hair follicle 

1. peripheral connective tissue 

2. glassy membrane 

3. epithelial root sheath

how does hair grow

the cells in the bulb of the follicle divide rapdily

how are hair matrix cells replenished as they divide

by stem cells that migrate down to the bulb from a region closer to the skin surface called the hair bulge

arrector pili muscle attachment 

its contraction pulls the upright and dimples the skin surface to produce goosebumps

arrector pili muscle function

contractions force sebum out of hair follicles to the skin surface where it acts as a skin lubricant

vellus hair

body hair of children and adult women

terminal hair 

coarser, longer hair of eyebrows, eyelashes, and scalp 

androgen

male sex hormones

hair follice growth cycles

an active growth phase is followed by a resting phase in which the hair matrix is inactive and the follicle shrinks somewhat 

male pattern baldness

a genetically determined, gender-influenced conditions that change the response of the hair follicles to androgens

drugs used to treat male pattern baldness functions

1. inhibit the production of androgens

2. increase blood flow to the skin and hair follicles

structure of nail 

1. proximal root (embedded in skin)

2. nail plate or body (visible attached portion)

3. free edge

nail bed

contains the deeper layers of the epidermis; where the nail rests upon

nail matrix

thickened proximal portion of nail bed

nail matrix function 

responsible for nail growth 

lunule

the region that lives over the thick nail matrix

hyponychium

the thickened region beneath the free edge of the nail where dirt and debris tend to accumulate

hyponychium function 

secures the free edge of the nail plate at the tip of the finger or toe 

2 types of sweat glands

1. eccrine

2. apocrine

what regulates sweating

autonomic (involuntary) nervous system

eccrine sweat glands structure

simple, coiled, tubular gland; secretory part lies coiled in the dermis, and the duct extends to open in a tunnel-shaped pore at the skin surface

eccrine sweat glands secretion

sweat

sweat

hypotonic filtrate of blood that passes through the secretory cells of the sweat glands and is released by exocytosis

sweat composition 

99% water, traces of metabolic wastes (urea, uric acid, ammonia), and dermicidin 

dermicidin

microbe-killing peptide

sweat function

prevent the body from overheating

apocrine sweat glands location 

axillary and urogenital areas 

apocrine sweat gland secretion

sweat, fatty substances, and proteins (bacteria decomposing can lead to BO)

when do apocrine glands begin functioning 

at puberty 

3 lines of evidence that suggest that apocrine glands are the human equivalent of animal’s sex scent glands

1. sexual foreplay increases their activity

2. enlarge and recede with the phases of a women’s menstrural cycle

3. may act as pheromone

2 types of modified apocrine glands

1. ceruminous glands

2. mammary glands

ceruminous glands 

modified apocrine glands found in the lining of the external ear canal; secretion mixes with sebum to form earwax 

mammary glands

secrete milk

sebaceous glands structure

simple branched alveolar glands

sebaceous glands secretion 

sebum

sebum function

softens and lubricates the hair and skin, slows water loss from the skin, prevents hair from becoming brittle, bactericidal action

acne 

active inflammation of the sebaceous glands accompanied by pimples, whiteheads, or blackheads 

functions of the skin

1. protection

2. BT regulation

3. cutaneous sensation

4. metabolic functions

5. blood reservoir

6. excretion

3 barriers of the skin

1. chemical

2. physical

3. biological

acid mantle 

low pH of skin secretions

defensins

skin cell secretion; natural antibiotic

eathelicidins

protective peptides that prevent infection by group A streptococcus bacteria; secreted by wounded skin

substances that penetrate the skin in limited amounts 

1. lipid-soluble substances: O2; CO2; vits A, D, G, K; steroids (estrogens)

2. oleoresins of certain plants (poison ivy)

3. organic solvents: acetone

4. salts of heavy metal (lead and mercury)

5. drug agents called penetration enhancers that help ferry other drugs into the body

biological barriers

1. dendritic cells in epidermis

2. macrophages in dermis

dendritic cells

part of immune system; engulf foreign invaders that have penetrated the epidermis; leave the skin and migrate to the recent lymph node where they display their prey to immune cells—triggers immune response

dermal macrophages 

dispose of viruses and bacteria that manage to penetrate the epidermis; initiate immune response

insensible perspiration

routine and unnoticable sweating

sensible perspiration

noticable output of sweating

constriction of dermal blood vessels function 

allows warm blood to bypass the skin temporarily and allows skin T to drop to that of the external environment