Transcript Ch4-5.Tissues.Skin.Lecture

TISSUES (cont.) & THE
INTEGUMENTARY SYSTEM
Hair
Skin
Nails
Sonya Schuh-Huerta, Ph.D.
Human Anatomy
Glands
• Ducts carry products of exocrine glands to
epithelial surface
• Include the following diverse glands
–
–
–
–
Mucus-secreting glands
Sweat & oil glands
Salivary glands
Liver & pancreas
Unicellular Exocrine Glands:
The Goblet Cell
• Goblet cells produce mucin
– Mucin + water  mucus
– Protects & lubricates many internal body
surfaces
– Goblet cells are a unicellular exocrine gland
Goblet Cells
Microvilli
Secretory
vesicles
containing
mucin
Rough ER
Golgi
apparatus
Nucleus
Multicellular Exocrine Glands
• Have 2 basic parts
– Epithelium-walled duct
– Secretory unit
• Classified by structure of duct
– Simple
– Compound
• Categorized by secretory unit
– Tubular
– Alveolar
– Tubuloalveolar
Lateral Surface Features: Cell Junctions
• Factors binding epithelial cells together
– Adhesion proteins link plasma membranes
of adjacent cells
– Contours of adjacent cell membranes
– Special cell junctions
Lateral Surface Features: Cell Junctions
• Tight junctions – close off intercellular space
– Found at apical region of most epithelial tissue types
– Some proteins in plasma membrane of adjacent cells
are fused
– Prevent certain molecules from passing between cells
of epithelial tissue
Tight Junction
Interlocking
junctional
proteins
Intercellular
space
(a) Tight junctions: Impermeable junctions
prevent molecules from passing through
the intercellular space.
Lateral Surface Features: Cell Junctions
• Adhesive belt junctions (zonula adherens) =
anchoring junction
– Transmembrane linker proteins attach to actin
microfilaments of the cytoskeleton & bind adjacent
cells
• With tight junctions, these linker proteins form the
tight junctional complex around apical lateral
borders of epithelial tissues
Lateral Surface Features: Cell Junctions
• Desmosomes = main junctions for binding cells
together
– Scattered along abutting sides of adjacent cells
– Cytoplasmic side of each plasma membrane has a
plaque
• Plaques are joined by linker proteins
– Intermediate filaments extend across the cytoplasm
and anchor at desmosomes on opposite side of cell
– Are common in cardiac muscle & epithelial tissue
Desmosome
Intercellular
space
Plaque
Intermediate
filament
(keratin)
Linker
glycoproteins
(cadherins)
(b) Desmosomes: Anchoring junctions bind
adjacent cells together and help form an
internal tension-reducing network of fibers.
Lateral Surface Features: Cell Junctions
• Gap junctions = passageway between 2
adjacent cells
– These let small molecules move directly between
neighboring cells
– Cells are connected by hollow cylinders of protein
– Function in intercellular communication!
Gap Junction
Intercellular
space
Channel
between cells
(connexon)
Gap junctions: Communicating junctions
allow ions and small molecules to pass
from one cell to the next for intercellular
communication.
Basal Feature: The Basal Lamina
• Non-cellular supporting sheet between the
epithelial tissue & the connective tissue deep to it
• Consists of proteins secreted by epithelial cells
Basal Feature: The Basal Lamina
• Functions:
– Acts as a selective filter, determining which molecules
from capillaries enter the epithelium
– Acts as scaffolding along which regenerating
epithelial cells can migrate
• Basal lamina & reticular layers of the
underlying CT deep to it form the basement
membrane
Epithelial Surface Features
• Apical surface features
– Microvilli = fingerlike extensions of plasma
membrane
• Abundant in epithelia of small intestine & kidney
• Maximize surface
area across which
small molecules
Microvillus
enter or leave
• Act as stiff knobs
Actin
that resist abrasion
filaments
Epithelial Surface Features
• Apical surface features
– Cilia = whiplike, highly motile extensions of apical
surface membranes
• The apical surface contains a core of 9 pairs of
microtubules encircling one middle pair
– Axoneme – a set of microtubules
– Each pair of microtubules are arranged in a
doublet
• Microtubules in cilia – arranged similarly to
centrioles
• Movement of cilia – in coordinated waves
A Cilium
Outer
microtubule
doublet
Central
microtubule
Dynein arms
Cross-linking
proteins inside
outer doublets
Radial spoke
Plasma
membrane
Power, or
propulsive,
stroke
The doublets
also have
attached motor
proteins, the
dynein arms.
The outer
microtubule
doublets and
the two central
microtubules
are held
together by
cross-linking
proteins and
radial spokes.
1
2
3
4
Recovery stroke, when
cilium is returning to
its initial position
5
6
7
(b) Phases of ciliary motion
Layer of mucus
Cilium
Cell surface
Basal body
(centriole)
(a) Structure of a cilium
(c) Traveling wave created by the activity
of many cilia acting together propels
mucus across cell surfaces.
Connective Tissue
• Most diverse & abundant tissue
• Main classes:
–
–
–
–
Connective tissue proper
Cartilage
Bone tissue
Blood
• Cells separated by a large amount of
extracellular matrix
• Extracellular matrix is composed of ground
substance & fibers
• Common embryonic origin – mesenchyme
Mesenchyme
(a) Embryonic connective tissue: mesenchyme
Description: Embryonic connective
tissue; gel-like ground substance
containing fibers; star-shaped
mesenchymal cells.
Function: Gives rise to all other
connective tissue types.
Mesenchymal
cell
Ground
substance
Location: Primarily in embryo.
Fibers
Photomicrograph: Mesenchymal tissue, an embryonic
connective tissue (600); the clear-appearing background is
the fluid ground substance of the matrix; notice the fine,
sparse fibers.
Structural Elements of Connective
Tissue
• Connective tissues differ in structural properties
– Differences in types of cells
– Differences in composition of extracellular matrix
• However, connective tissues all share structural
elements
• Loose areolar connective tissue
– Will illustrate connective tissue features
Structural Elements of Connective
Tissue
• Cells – primary cell type of connective tissue
produces matrix
– Fibroblasts
• Make protein subunits (protein fibers)
• Secrete molecules that form the ground substance
– Chondroblasts – secrete matrix in cartilage
– Osteoblasts – secrete matrix in bone
– Blood cells – an exception
• Do not produce matrix
Areolar connective tissue: A model
connective tissue
Cell types
Macrophage
Extracellular
matrix
Ground substance
Fibers
Collagen fiber
Elastic fiber
Fibroblast
Reticular fiber
Lymphocyte
Fat cell
Mast cell
Neutrophil
Capillary
Structural Elements of Connective
Tissue
• Fibers – function in support
– Collagen fibers – strongest; resist tension
– Reticular fibers – bundles of special type of
collagen
• Cover & support structures
– Elastic fibers – contain elastin
• Recoil after stretching; give resilience
Structural Elements of Connective
Tissue
• Ground substance
–
–
–
–
–
Is produced by primary cell type of the tissue
Is usually gel-like
Cushions & protects body structures
Holds tissue fluid
Blood is an exception
• Plasma is not produced by blood cells
Connective Tissue Proper
• Has 2 subclasses:
– Loose connective tissue
• Areolar, adipose, & reticular
– Dense connective tissue
• Dense irregular, dense regular, & elastic
Areolar Connective Tissue
• Areolar connective tissue:
– Underlies epithelial tissue
– Surrounds small nerves & blood vessels
– Has structures & functions shared by other CT
– Borders all other tissues in the body
Major Functions of Connective Tissue
• Structure of areolar connective tissue reflects its
functions
–
–
–
–
Support & binding of other tissues
Holding body fluids (interstitial fluid  lymph)
Defending body against infection
Storing nutrients as fat
Areolar Connective Tissue
• Description:
– Gel-like matrix with all 3 fiber types
– Cells of areolar CT
• Fibroblasts, macrophages, mast cells, & WBCs
• Function:
– Wraps & cushions organs
– Holds & conveys tissue fluid (interstitial fluid)
– Important role in inflammation
• Locations:
– Widely distributed under epithelia
– Packages organs
– Surrounds capillaries
Areolar Connective Tissue
(b) Connective tissue proper: loose connective tissue, areolar
Description: Gel-like matrix with all
three fiber types; cells: fibroblasts,
macrophages, mast cells, and some
white blood cells.
Function: Wraps and cushions organs;
its macrophages phagocytize bacteria;
plays important role in inflammation;
holds and conveys tissue fluid.
Location: Widely distributed under
epithelia of body, e.g., forms lamina
propria of mucous membranes;
packages organs; surrounds capillaries.
Epithelium
Lamina
propria
Elastic
fibers
Collagen
fibers
Fibroblast
nuclei
Photomicrograph: Areolar connective tissue, a soft packaging
tissue of the body (360).
Areolar Connective Tissue
• Tissue fluid (interstitial fluid)
– Watery fluid occupying extracellular matrix
– Tissue fluid derives from blood
• Ground substance
– Viscous, spongy part of extracellular matrix
– Consists of sugar & protein molecules
– Made & secreted by fibroblasts
Areolar Connective Tissue
• Main battlefield in fight against infection
• Defenders gather at infection sites
–
–
–
–
Macrophages
Plasma cells
Mast cells
White blood cells
• Neutrophils, lymphocytes, & eosinophils
Adipose Tissue
• Function:
– Provides reserve fuel
– Insulates against heat loss
– Supports & protects organs
• Location:
– Under skin
– Around organs
– Behind eyeballs, within
abdomen, & in breasts
– Hypodermis
Adipose Tissue
• Description:
– Closely packed adipocytes
– Have nucleus pushed to one side by fat droplet
– Richly vascularized
Adipose Tissue
(c) Connective tissue proper: loose connective tissue, adipose
Description: Matrix as in areolar, but
very sparse; closely packed adipocytes,
or fat cells, have nucleus pushed to the
side by large fat droplet.
Function: Provides reserve food fuel;
insulates against heat loss; supports
and protects organs.
Location: Under skin in the hypodermis;
around kidneys and eyeballs; within
abdomen; in breasts.
Adipose
tissue
Nucleus of
fat cell
Vacuole
containing
fat droplet
Photomicrograph: Adipose tissue from the subcutaneous
layer under the skin (500).
Mammary
glands
Reticular Connective Tissue
• Description – network of reticular fibers in loose
ground substance
• Function – forms a soft, internal skeleton
(stroma); supports other cell types
• Location – lymphoid organs
– Lymph nodes, bone marrow, & spleen
Reticular Connective Tissue
(d) Connective tissue proper: loose connective tissue, reticular
Description: Network of reticular
fibers in a typical loose ground
substance; reticular cells lie on
the network.
Function: Fibers form a soft internal
skeleton (stroma) that supports other
cell types including white blood cells,
mast cells, and macrophages.
Location: Lymphoid organs (lymph
nodes, bone marrow, and spleen).
White blood cell
(lymphocyte)
Reticular
fibers
Spleen
Photomicrograph: Dark-staining network of reticular connective
tissue fibers forming the internal skeleton of the spleen (555).
Dense Connective Tissue
• Dense irregular connective tissue
• Dense regular connective tissue
• Elastic connective tissue
Dense Irregular Connective Tissue
• Description:
– Primarily irregularly arranged collagen fibers
– Some elastic fibers & fibroblasts
• Function:
– Withstands tension
– Provides structural strength
• Location:
– Dermis of skin
– Submucosa of digestive tract
– Fibrous capsules of joints & organs
Dense Irregular Connective Tissue
(e) Connective tissue proper: dense connective tissue, dense irregular
Description: Primarily irregularly
arranged collagen fibers; some elastic
fibers; major cell type is the fibroblast.
Function: Able to withstand tension
exerted in many directions; provides
structural strength.
Location: Fibrous capsules of organs
and of joints; dermis of the skin;
submucosa of digestive tract.
Nuclei of
fibroblasts
Collagen
fibers
Fibrous
joint
capsule
Photomicrograph: Dense irregular connective tissue from the
dermis of the skin (600).
Dense Regular Connective Tissue
• Description:
– Primarily parallel collagen fibers
– Fibroblasts & some elastic fibers
– Poorly vascularized
– Forms fascia surrounding muscles
Dense Regular Connective Tissue
• Function:
– Attaches muscle to bone
– Attaches bone to bone
– Withstands great stress in one direction
• Location:
– Tendons & ligaments
– Fascia around muscles
– Aponeuroses
Dense Regular Connective Tissue
(f) Connective tissue proper: dense connective tissue, dense regular
Description: Primarily parallel collagen
fibers; a few elastic fibers; major cell
type is the fibroblast.
Function: Attaches muscles to bones
or to muscles; attaches bones to bones;
withstands great tensile stress when
pulling force is applied in one direction.
Collagen
fibers
Location: Tendons, most ligaments,
aponeuroses.
Nuclei of
fibroblasts
Shoulder
joint
Ligament
Photomicrograph: Dense regular connective tissue from a
tendon (270).
Tendon
Elastic Connective Tissue
• Description:
– Elastic fibers predominate
• Function: allows recoil after stretching
• Location:
– Within walls of arteries, in certain ligaments, &
surrounding bronchial tubes
Elastic Connective Tissue
(g) Connective tissue proper: dense connective tissue, elastic
Description: Dense regular connective
tissue containing a high proportion of
elastic fibers.
Function: Allows recoil of tissue
following stretching; maintains
pulsatile flow of blood through
arteries; aids passive recoil of lungs
following inspiration.
Elastic
fibers
Location: Walls of large arteries;
within certain ligaments associated
with the vertebral column; within the
walls of the bronchial tubes.
Aorta
Heart
Photomicrograph: Elastic connective tissue in the wall of
the aorta (85).
Cartilage
•
•
•
•
Firm, flexible tissue
Contains no blood vessels or nerves
Matrix contains up to 80% water
Cell type  chondrocyte
• Types of Cartilage:
1.) Hyaline cartilage
2.) Elastic cartilage
3.) Fibrocartilage
Hyaline Cartilage
• Description:
– Imperceptible collagen fibers (hyaline =
glassy)
– Chondroblasts produce matrix
– Chondrocytes lie in lacunae
• Function:
– Supports & reinforces
– Resilient cushion
– Resists repetitive stress
Hyaline Cartilage
• Location:
– Fetal skeleton
– Ends of long bones
– Costal cartilage of ribs
– Cartilages of nose, trachea,
& larynx
Hyaline Cartilage
(h) Cartilage: hyaline
Description: Amorphous but firm
matrix; collagen fibers form an
imperceptible network; chondroblasts
produce the matrix and when mature
(chondrocytes) lie in lacunae.
Function: Supports and reinforces;
has resilient cushioning properties;
resists compressive stress.
Location: Forms most of the
embryonic skeleton; covers the ends
of long bones in joint cavities; forms
costal cartilages of the ribs; cartilages
of the nose, trachea, and larynx.
Chondrocyte
in lacuna
Matrix
Photomicrograph: Hyaline cartilage from the trachea (720).
Costal
cartilages
Elastic Cartilage
• Description:
– Similar to hyaline cartilage
– More elastic fibers in matrix
• Function:
– Maintains shape of structure
– Allows great flexibility
• Location:
– Supports external ear
– Epiglottis
Elastic Cartilage
(i) Cartilage: elastic
Description: Similar to hyaline
cartilage, but more elastic fibers
in matrix.
Function: Maintains the shape
of a structure while allowing great
flexibility.
Location: Supports the external ear
(pinna); epiglottis.
Chondrocyte
in lacuna
Matrix
Photomicrograph: Elastic cartilage from the human ear pinna;
forms the flexible skeleton of the ear (980).
Fibrocartilage
• Description:
– Matrix similar, but less firm than hyaline cartilage
– Thick collagen fibers predominate
• Function:
– Tensile strength & ability to absorb compressive
shock
• Location:
– Intervertebral discs
– Pubic symphysis
– Discs of knee joint
Fibrocartilage
(j) Cartilage: fibrocartilage
Description: Matrix similar to but
less firm than that in hyaline cartilage;
thick collagen fibers predominate.
Function: Tensile strength with the
ability to absorb compressive shock.
Location: Intervertebral discs; pubic
symphysis; discs of knee joint.
Chondrocytes
in lacunae
Intervertebral
discs
Collagen
fiber
Photomicrograph: Fibrocartilage of an intervertebral
disc (180). Special staining produced the blue color seen.
Bone Tissue
• Function:
– Supports & protects organs
– Provides levers & attachment
sites for muscles
– Stores calcium & other minerals
– Stores fat
– Marrow is site of blood cell
formation
• Location:
– Bones
Bone Tissue
• Description:
– Calcified matrix containing many collagen
fibers
– Osteoblasts – secrete collagen fibers &
matrix
– Osteocytes – mature bone cells in lacunae
– Well vascularized
Bone Tissue
(k) Others: bone (osseous tissue)
Description: Hard, calcified matrix
containing many collagen fibers;
osteocytes lie in lacunae. Very well
vascularized.
Function: Bone supports and protects
(by enclosing); provides levers for the
muscles to act on; stores calcium and
other minerals and fat; marrow inside
bones is the site for blood cell
formation (hematopoiesis).
Location: Bones
Central
canal
Lacunae
Lamella
Photomicrograph: Cross-sectional view of bone (190).
Blood Tissue
• An atypical connective tissue
• Develops from mesenchyme
• Consists of cells surrounded by nonliving matrix
Blood Tissue
• Description:
– Red & white blood cells in a fluid matrix
• Function:
– Transport of respiratory gases, nutrients, &
wastes; immune system
• Location:
– Within blood vessels
Blood Tissue
(l) Others: blood
Description: Red and white blood
cells in a fluid matrix (plasma).
Plasma
Function: Transport of respiratory
gases, nutrients, wastes, and other
substances.
Location: Contained within blood
vessels.
Neutrophil
Red blood
cells
Lymphocyte
Photomicrograph: Smear of human blood (1785); two white
blood cells (neutrophil and lymphocyte) are seen surrounded by
red blood cells.
Covering & Lining Membranes
• Combine epithelial tissues & connective tissues
• Cover broad areas within body
• Consist of epithelial sheet plus underlying
connective tissue
3 Types of Membranes
• Cutaneous membrane  skin
• Mucous membrane
– Lines hollow organs that open to surface of body
– An epithelial sheet underlain with layer of lamina
propria
• Serous membrane
– Simple squamous epithelium lying on areolar
connective tissue
– Lines closed cavities
• Pleural, peritoneal, & pericardial cavities
Covering & Lining Membranes
Cutaneous
membrane
(skin)
Mucosa of
nasal cavity
Mucosa of
mouth
Esophagus
lining
Mucosa of
lung bronchi
(a) Cutaneous membrane (the skin)
covers the body surface.
(b) Mucous membranes line body cavities
open to the exterior.
Covering & Lining Membranes
Parietal
peritoneum
Parietal
pleura
Visceral
peritoneum
Visceral
pleura
Parietal
pericardium
Visceral
pericardium
(c) Serous membranes line body cavities
closed to the exterior.
Muscle Tissue
• Skeletal muscle tissue
• Cardiac muscle tissue
• Smooth muscle tissue
Skeletal Muscle Tissue
• Description:
– Long, cylindrical cells
– Multi-nucleate
– Obvious striations
• Function:
– Voluntary movement
– Manipulation of environment
– Facial expression
• Location:
– Skeletal muscles attached to bones (occasionally to
skin) all throughout body
Skeletal Muscle Tissue
(a) Skeletal muscle
Description: Long, cylindrical,
multinucleate cells; obvious striations.
Striations
Function: Voluntary movement;
locomotion; manipulation of the
environment; facial expression.
Nuclei
Location: In skeletal muscles
attached to bones or occasionally
to skin.
Part of
muscle
fiber (cell)
Photomicrograph: Skeletal muscle (300).
Notice the obvious banding pattern and the
fact that these large cells are multinucleate.
Cardiac Muscle Tissue
• Description:
– Branching cells, striated
– Generally uninucleate
– Cells interdigitate at
intercalated discs
• Function:
– Contracts to propel blood into circulatory
system
• Location:
– In walls of heart
Cardiac Muscle Tissue
(b) Cardiac muscle
Description: Branching, striated,
generally uninucleate cells that
interdigitate at specialized junctions
(intercalated discs).
Striations
Intercalated
discs
Function: As it contracts, it propels
blood into the circulation; involuntary
control.
Nucleus
Location: The walls of the heart.
Photomicrograph: Cardiac muscle (600);
notice the striations, branching of cells, and
the intercalated discs.
Smooth Muscle Tissue
• Description:
– Spindle-shaped cells with central nuclei
– Arranged closely to form sheets
– No striations
• Function:
– Propels substances along internal passageways
– Involuntary control
• Location:
– Mostly walls of hollow organs
Smooth Muscle Tissue
(c) Smooth muscle
Description: Spindle-shaped cells
with central nuclei; no striations;
cells arranged closely to form sheets.
Smooth
muscle
cell
Function: Propels substances or
objects (foodstuffs, urine, a baby)
along internal passageways;
involuntary control.
Nuclei
Location: Mostly in the walls of
hollow organs.
Photomicrograph: Sheet of smooth muscle (220).
Nervous Tissue
• Description:
– Main components – brain, spinal cord, & nerves
– Contains 2 types of cells
• Neurons  excitatory cells
• Supporting cells  neuroglial cells
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Nervous Tissue
• Function:
– Transmit electrical signals from sensory
receptors to effectors
• Location:
– Brain, spinal cord, & nerves
Nervous Tissue
Nervous tissue
Description: Neurons are branching
cells; cell processes that may be
quite long extend from the nucleuscontaining cell body; also contributing
to nervous tissue are nonirritable
supporting cells (not illustrated).
Neuron processes
Axon
Nuclei of
supporting
cells
Cell body
Cell body
of a neuron
Dendrites
Function: Transmit electrical signals
from sensory receptors and to effectors
(muscles and glands) which control
their activity.
Neuron
processes
Location: Brain, spinal
cord, and nerves.
Photomicrograph: Neurons (200)
Tissue Response to Injury
• Inflammatory response
– Nonspecific, local response
– Limits damage to injury site
• Immune response
– Takes longer to develop & very specific
– Destroys particular microorganisms at site of
infection
Inflammation
• Acute inflammation
– Heat
– Redness
– Swelling
– Pain
– Chemicals signal nearby blood vessels to
dilate
• Histamine increases permeability of capillaries
Inflammation
• Edema – accumulation of fluid
– Helps dilute toxins secreted by bacteria
– Brings oxygen & nutrients from blood
– Brings antibodies from blood to fight infection
Repair
• Organization
– Clot is replaced by granulation tissue
• Regeneration
– Replacement of destroyed tissue with same
type of tissue
• Fibrosis
– Proliferation of scar tissue
Tissue Repair of a Skin Wound
Scab
Blood clot in
incised wound
Epidermis
Regenerating
epithelium
Regenerated epithelium
Area of
granulation
tissue
ingrowth
Vein
Fibroblast
Macrophage
Inflammatory Migrating Artery
chemicals
white
blood cell
1
Inflammation sets the stage:
• Severed blood vessels bleed.
• Inflammatory chemicals are released.
• Local blood vessels become more
permeable, allowing white blood
cells, fluid, clotting proteins, and
other plasma proteins to seep
into the injured area.
• Clotting occurs; surface dries and
forms a scab.
Fibrosed area
2
Organization restores the blood
supply:
• The clot is replaced by granulation
tissue, which restores the vascular
supply.
• Fibroblasts produce collagen fibers
that bridge the gap.
• Macrophages phagocytize cell debris.
• Surface epithelial cells multiply and
migrate over the granulation tissue.
3
Regeneration and fibrosis effect
permanent repair:
• The fibrosed area matures and
contracts; the epithelium thickens.
• A fully regenerated epithelium with
an underlying area of scar tissue
results.
Capacity for Regeneration
– Good to excellent:
• ET, bone CT, areolar CT, dense irregular CT, &
blood forming CT
– Moderate:
• Smooth muscle, dense regular CT
– Weak:
• Skeletal MT, cartilage
– None or almost none:
• Cardiac MT, Nervous Tissue
The Tissues Throughout Life
• At the end of 2nd month of
development:
– Primary tissue types
– Major organs in place
• Adulthood
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– A few tissues regenerate
– Many tissues still retain populations of stem cells
The Tissues Throughout Life
• With increasing age:
– Epithelia thin
– Collagen decreases
– Bones, muscles, & nervous
tissue begin to atrophy
– Poor nutrition & poor
circulation lead to poor
tissue health
Part II: The Integumentary System
The Skin & The Hypodermis
• Skin  our largest organ
– Accounts for 7% of body weight
– Varies in thickness from 1.5–4.4 mm
– Divided into 2 distinct layers:
• Epidermis
• Dermis
– Hypodermis  lies deep to the dermis
(covered in skin chapter, but not really part of skin)
Skin Structure
Hair shaft
Dermal papillae
Subpapillary vascular
plexus
Epidermis
Papillary
layer
Dermis
Pore
Appendages of skin
Eccrine sweat gland
Arrector pili muscle
Sebaceous (oil) gland
Hair follicle
Hair root
Reticular
layer
Hypodermis
(superficial fascia)
Nervous structures
Sensory nerve fiber
Lamellar (Pacinian)
corpuscle
Hair follicle receptor
(root hair plexus)
Dermal vascular plexus
Adipose tissue
The Skin & Hypodermis
• Functions:
1. Protection  cushions organs and protects
from bumps, chemicals, water loss, UV
radiation
2. Regulation of body temperature
3. Excretion  urea, salts, and water lost
through sweat
4. Production of vitamin D
5. Sensory reception  keeps us aware of
conditions at body’s surface
Epidermis
• Contains 4 main cell types:
– Keratinocytes
• Location: stratum spinosum; produce
keratin (a fibrous protein)
– Melanocytes
• Location: basal layer; manufacture &
secrete pigment
Epidermis
• 4 main cell types (cont.)
– Tactile epithelial cells
• Location: basal layer; attached to sensory
nerve endings
– Dendritic cells
• Location: stratum spinosum; part of
immune system; macrophage-like
Epidermis
• Keratinocytes – most abundant cell type in
epidermis
–
–
–
–
Arise from deepest layer of epidermis
Produce keratin, a tough fibrous protein
Produce antibodies & enzymes
Keratinocytes are dead at skin's surface
Layers of the Epidermis
•
•
•
•
•
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum (only in thick skin)
Stratum corneum
Epidermal Cells & Layers of the Epidermis
Stratum corneum
Most superficial layer; 20–30 layers of dead cells
represented only by flat membranous sacs filled
with keratin. Glycolipids in extracellular space.
Stratum granulosum
Three to five layers of flattened cells, organelles
deteriorating; cytoplasm full of lamellated granules
(release lipids) and keratohyaline granules.
Stratum spinosum
Several layers of keratinocytes unified by
desmosomes. Cells contain thick bundles of
intermediate filaments made of pre-keratin.
(a)
Stratum basale
Deepest epidermal layer; one row of actively mitotic
stem cells; some newly formed cells become part of
the more superficial layers. See occasional
melanocytes and dendritic cells.
Dermis
Epidermal Cells & Layers of the Epidermis
Keratinocytes
Stratum corneum
Most superficial layer; 20–30 layers of dead cells
represented only by flat membranous sacs filled
with keratin. Glycolipids in extracellular space.
Stratum granulosum
Three to five layers of flattened cells, organelles
deteriorating; cytoplasm full of lamellated granules
(release lipids) and keratohyaline granules.
Stratum spinosum
Several layers of keratinocytes unified by
desmosomes. Cells contain thick bundles of
intermediate filaments made of pre-keratin.
Stratum basale
Deepest epidermal layer; one row of actively
mitotic stem cells; some newly formed cells
become part of the more superficial layers. See
occasional melanocytes and dendritic cells.
Dendritic cell
Dermis
Melanin
granule
Desmosomes
Melanocyte
Tactile epithelial
cell
Sensory
nerve
ending
Layers of the Epidermis
• Stratum basale
– Deepest layer of epidermis
– Attached to underlying dermis
– Cells actively divide
– Stratum basale contains:
• Merkel cells – associated with sensory nerve
ending
• Melanocytes – secrete the pigment melanin
-gives skin its color!
Layers of the Epidermis
• Stratum spinosum (spiny layer)
– “Spiny” appearance caused by:
• Artifacts of histological preparation
– Contains thick bundles of intermediate
filaments (tonofilaments)
• Resist tension
• Contain protein prekeratin
– Contains star-shaped dendritic cells
• A type of macrophage
• Function in immune system
Layers of the Epidermis
• Stratum corneum (“horny” outer layer)
– Thick layer of dead keratinocytes & thickened
plasma membranes
– Protects skin against abrasion & penetration
Thick Skin
Epidermis
Stratum
corneum
Stratum
lucidum
Stratum
granulosum
Stratum
spinosum
Stratum
basale
Dermis
Papillary
layer
Reticular
layer
Dermis
•
•
•
•
2nd major layer of the skin
Strong, flexible connective tissue
Richly supplied with blood vessels & nerves
Has 2 layers:
– Papillary layer – includes dermal papillae
– Reticular layer
• Deeper layer – 80% of thickness of dermis
• Flexure lines
– Creases on palms
2 Regions of the Dermis
Dermis
(b) Papillary layer of dermis, SEM (570)
(a) Light micrograph of thick skin
identifying the extent of the
dermis, (100)
(c) Reticular layer of dermis, SEM (430)
Dermal Modifications
Friction ridges
Openings of
sweat gland ducts
Flexion
creases
on digit
(a) Friction ridges of finger
tip (SEM 20)
Flexion
creases
on the
palm
(b) Cleavage lines in the
reticular dermis
(c) Flexure lines of
the hand
Hypodermis
•
•
•
•
Deep to the skin – also called superficial fascia
Contains areolar & adipose CT
Anchors skin to underlying structures
Helps insulate the body
Skin Color
• 3 pigments contribute to skin color:
– Melanin
• Most important pigment – made from tyrosine
– Carotene
• Yellowish pigment from carrots & tomatoes
– Hemoglobin
• Caucasian skin contains little melanin
• Allows crimson color of blood to show through
• Do light-skinned people have fewer melanocytes or
what?...
Nails
• Nails = scale-like modification of epidermis
– Made of hard keratin
– Parts of the nail
•
•
•
•
•
Free edge
Body
Root
Nail folds
Eponychium (cuticle)
Structure of a Nail
Lunule
Free edge
of nail
Lateral
nail fold
Body Eponychium
Root of nail
of nail (cuticle)
Proximal
Nail
nail fold
matrix
Nail bed
Phalanx (bone of fingertip)
Appendages of the Skin: Hair
• Hair
– Flexible strand of dead,
keratinized cells
– Hard keratin – tough & durable
– Chief parts of a hair
• Root  imbedded in the skin
• Shaft  projects above skin
Hair
• Hair has 3 concentric layers of keratinized cells
– Medulla  central core
– Cortex  surrounds medulla
– Cuticle  outermost layer
Cross Section of a Hair
Follicle wall
Connective tissue
root sheath
Glassy membrane
External epithelial
root sheath
Internal epithelial
root sheath
Hair shaft
Hair
Cuticle
Cortex
Medulla
Arrector
pili
Sebaceous
gland
Hair root
Follicle wall
Connective tissue
root sheath
Glassy membrane
Hair bulb
External epithelial
root sheath
Internal epithelial
root sheath
Hair
Cuticle
Cortex
Medulla
(b) Photomicrograph of a cross section
of a hair and hair follicle (185)
Hair
• Hair follicles
– Extend from epidermis into dermis
• Hair bulb
– Deep, expanded end of the hair follicle
• Root plexus
– Knot of sensory nerves around hair bulb
Longitudinal Section of Base of Follicle
Hair shaft
Arrector
pili
Sebaceous
gland
Hair root
Follicle wall
Connective
tissue root sheath
Glassy membrane
External epithelial
root sheath
Internal epithelial
root sheath
Hair root
Cuticle
Cortex
Medulla
Hair bulb
Hair matrix
Hair papilla
Melanocyte
Subcutaneous
adipose tissue
(c) Diagram of a longitudinal view of the expanded hair
bulb of the follicle, which encloses the matrix
Follicle wall
Connective
tissue root sheath
Glassy membrane
External epithelial
root sheath
Internal epithelial
root sheath
Hair root
Cuticle
Cortex
Medulla
Hair matrix
Hair papilla
Subcutaneous
adipose tissue
(d) Photomicrograph of longitudinal view
of the hair bulb in the follicle (130)
Hair Follicle
• Wall of hair follicle
– CT root sheath
– Epithelial root sheath
• Arrector pili muscle
– Bundle of smooth muscle
– Hair stands erect when arrector pili contracts
Types & Growth of Hair
• Vellus hairs
– Body hairs of women & children
• Terminal hairs
– Hair of scalp
– Axillary & pubic area (at puberty)
• Hair thinning & baldness
– Due to aging – loss of follicle stem cells
– Male pattern baldness – genetics
Sebaceous Glands
• Occur over entire body
– Except palms & soles
• Secrete sebum  an oily substance
– Simple alveolar glands
– Holocrine secretion – entire cell breaks up to form
secretion
– Most are associated with a hair follicle
• Functions of sebum
– Collects dirt; softens & lubricates hair & skin
Sebaceous Glands
Sweat
pore
Dermal
connective
tissue
Sebaceous
gland duct
Sebaceous
gland
Hair in
hair follicle
Eccrine
gland
Secretory cells
(a) Photomicrograph of a sectioned
sebaceous gland (140)
Sweat Glands
• Sweat glands (sudoriferous glands) widely
distributed on body
• Sweat  is a blood filtrate
– 99% water with some salts
– Contains traces of metabolic wastes
• About 2% urea
Sweat Glands
Sweat
pore
Eccrine
Gland
(sweat gland)
Sebaceous
gland
Duct
Dermal connective
tissue
Secretory cells
(b) Photomicrograph of a sectioned
eccrine gland (140)
Sweat Glands
• 2 types of sweat gland
– Eccrine gland
• Most numerous – these produce true sweat
– Apocrine gland
• Confined to axillary, anal, & genital areas
• Produce a special kind of sweat
– Musky odor  attracts a mate?
– Signal information about a person’s immune system, MHC
• Ceruminous glands & mammary glands
– Are modified apocrine glands
Burns
• Classified by severity
– First-degree burn – only upper epidermis is
damaged
– Second-degree burn – upper part of dermis
is also damaged
• Blisters appear
• Skin heals with little scarring
– Third-degree burn
• Consumes thickness of skin
• Burned area appears white, red, or blackened
Estimating Burns Using the Rule of 9s
Anterior values
1st degree burn
Totals
41⁄2%
Anterior and posterior
head and neck, 9%
Anterior and posterior
upper limbs, 18%
2nd degree burn
41⁄2% Anterior 41⁄2%
(a)
Skin bearing partial thickness burn
(first- and second-degree burns)
3rd degree burn
trunk, 18%
Anterior and posterior
trunk, 36%
9%
(Perineum, 1%)
9%
Anterior and posterior
lower limbs, 36%
100%
(b) Skin bearing full thickness burn
(third-degree burn)
(c)
Rule of nines; used to estimate
extent of burns
Skin Cancer
• Basal cell carcinoma
– Least malignant & most common
• Squamous cell carcinoma
– Arises from keratinocytes of stratum spinosum
• Melanoma
– A cancer of melanocytes
– The most dangerous type of skin cancer
• The ABCDE rule of skin cancer…
Skin Cancer
The Skin Throughout Life: Embryo
• Epidermis
– Develops from embryonic ectoderm
• Dermis & hypodermis
– Develop from mesoderm
• Melanocytes
– Develop from neural crest cells
The Skin Throughout Life: Fetus
• Fetal skin
– Well-formed after the 4th month
– At 5–6 months, the fetus is
covered with lanugo (downy hairs)
– Fetal sebaceous glands produce
vernix caseosa
The Skin Throughout Life: Adult
• Middle to old age
– Skin thins & becomes less elastic
– Shows harmful effects of environmental damage
– Skin inflammations become more common
Questions…?
What’s Next?
Lab: Tissues & Skin
Wed Lecture: Review
Wed Lab: Lab Exam 1
Mon Lecture: Lecture Exam 1