Lecture 2

Question 1

Intercellular Attachment

Cells are joined by _____

Answer 1

cell junctions

Question 2

Cell junctions…

Answer 2

prevent unwanted movement through the epithelium

Question 3

Intercellular Attachement: Adhering Junction

Answer 3

Attach cells to one another

TIGHT JUNCTION (occluding) - at apex, keeps cells tight and close together

• brings plasmalamallae of adjacent cells together (like ziploc bag) with “interlocking membrane proteins”
• seals intercellular space, forcing materials to move through the cells (with a process that requires energy) vs between the epithelial cells
  i. e. small intestine –> prevents digestive enzymes that degrade molecules from moving bt ep and connective tissue

ANCHORING - link two adjacent cells at lateral surface or link epidermal cell to basal lamina

• very strong linkages that resist stretching and twisting
• occur via “cell adhesion molecules” (CAMS) which bind to each other and other extracellular materials and “proteoglycans” that link the opposing membranes and form a junction with the cytoskeleton wi adjoining cells
• neighbouring cells separated by small space spanned b fine web of protein filaments that anchor to thickened protein plaque (dense area) at the internal surface of the plasma membrane
• on cytoplasmic side, intermediate filaments of cytoskeleton penetrate plaque to extend throughout cell for support and strength

Two Types of Anchoring Junctions:

• zonae adherens (adhesion belt) - sheet-like anchoring junction that stabilizes non-epithelial cells
• macula adherens (desmosome) - provides small localized spot-like anchoing junctions that stabilize adjacent ep cells, like button or snap, with each cell contributing to half of the ‘snap’

Question 4

Intercellular Attachment: Communication Junction / Gap Junctions

Answer 4

in the middle bt base and apex of cell, there are channels (aka gaps) made of structures called connexions

• connexions consist of 6 transmembrane proteins arranged in a circle to form tiny fluid filled tunnel so cells can communicate with each other
• ions, glucose, amino acids, regulatory molecules, and other small solutes pass through
• common in epithelial cells where they help coordinate beating of cilia and in muscles where they coordinate muscle contraction

Question 5

The integumentary system is composed of:

Answer 5

Skin
Hair
Nails
Sweat glands
Oil glands
Mammary glands
Integument = skin, uses two types of tissue
- epithelial –> on surface, protects underlying body layers or lines body caivities, composed of one or more layers of packed cells, little/no extracellular matrix cells and no blood vessels
- connective tissue –> most diverse, abundant and widely distributed, designed for support, protect and bing organs; under the epithelium and contains blood vessels that provide nutrients

Question 6

The integumentary system function

Answer 6

• physical protection
• regulation of body temperature
• excretion of products (waste and sweat)
• synthesis of products (keratin and vitamin d)
• sensation
• absorption
• immune defense

Question 7

Integumentary Structure and Function

Answer 7

Skin (cutaneous membrane)
- epidermis = most superficial
- dermis = deep to epidermis
Hypodermis (subcutaneous layer) deep to the dermis
Accessory structures = hair, nails, exocrine glands

Question 8

The Epidermis

Answer 8

Region that deals w friction

Thickest of soles of feet and thinnest of eyelids and behind ears

Like deck of cards; each flexible but together tough to tear

Derived from ECTODERM germinal layer

Bottom/basal (deepest) layer is most important

Question 9

Layers of the Epidermis

Answer 9

Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum

Question 10

Epidermal ridges

Answer 10

Stratum basale forms epidermal ridges

• Ridges (dermal papillae) extend into the dermis
• Creates ridges we call fingerprints

• The study of finger prints is called dermatoglyphics (derma = skin, glyph = carving) the ridges are
formed by the 4th month of fetal development and are unique to each individual, most common are arches, loops, whorls or a combination

Question 11

Stratum basale

Answer 11

Deepest layer, single layer of cuboidal cells which divide rapidly to produce the cell layers
above (germinal (epidermal stem cell) layer

o Cells produced in this layer move superficially toward skin surface

Everyone has about the same number of melanocytes but melanocyte activity
and colour of the melanin produced by these cells varies among individuals and
races resulting in different skin tones

The melanin forms in vesicles called melanosomes which eventually are
destroyed by lysosomes, the melanosomes are destroyed and release melanin in
deeper layers in fair skinned individuals and more superficially in darker skinned
individuals

Moles (nevus) are harmless localized overgrowths of melanin-forming cells, most
people have at least a few of these

Melanin pigments help prevent skin damage by absorbing ultraviolet (UV)
radiation in sunlight. A small amount of UV is necessary because the skin requires it to convert a cholesterol-related steroid precursor into Vitamin D
hormones. Vitamin D is required for normal calcium and phosphorus absorption
by the small intestine; too much UV absorption can damage the skin

is also the location of Merkel cells
§ Specialized epithelial cells that are sensitive to touch and release chemicals that
stimulate sensory nerve endings known as tactile discs (Merkel’s disc), providing
information about objects touching the skin, highly sensitive

Question 12

Stratum spinosum

Answer 12

once cell division occurs in the stratum basale, one daughter cell remains
in the stratum basale, while the other daughter cell is pushed up into the next more superficial
layer, the stratum spinosum (spiny layer), where the new cell will begin to differentiate into a keratinocyte

all keratinocytes in the stratum spinosum are tied together by a network of interlocked 
macula adherens (desmosomes) and tonofibrils (bundles of protein filaments)

o Langerhans cells (dendritic/immune cells) are common in this layer

o Langerhans cells play an important role in initiating an immune response against
pathogens that have penetrated the superficial layers of the epidermis and epidermal
cancer cells

Question 13

Stratum granulosum (granular layer)

Answer 13

this is the most superficial layer of the epidermis which
all the cells still possess a nucleus (keratinisation starts – ie. cells filling with keratin)

o The keratinocyte is the principle cell type, produce the proteins keratohyalin and keratin
that toughen and waterproof the skin, they are produced in the stratum basale and
gradually move farther away from the O2 and blood supply of the layers below and their
nuclei and organelles degenerate and become filled with keratin, when the reach the surface they resemble dead flat cells

o Takes 15-30 days for new skin to reach the top layer

o Keratin – basic structural component of hair and nails in humans, claws, horns, feathers,
baleen and snake scales in other vertebrates

Question 14

Stratum lucidum (clear layer)

Answer 14

only present in very thick skin (ie. skin of palms and soles of
feet)

o Cells in this layer lack organelles and nuclei, are flattened, densely packed, and filled with
keratin filaments that are oriented parallel to the surface of the skin

Question 15

Stratum corneum

Answer 15

most superficial layer of both thick and thin skin

o Consists of 15-30 layers of flattened dead cells that possess a thickened plasmalemma

No organelles or nucleus; keratinized (or cornified – cornu =horn), normally relatively dry
and water resistant making the surface unsuitable for growth of microorganisms

Question 16

Skin color

Answer 16

Due to:
• Thickness of stratum corneum

• Various concentrations of carotene and melanin

o Carotene – a yellow/orange pigment acquired in the body by yellow/orange vegetables
(eg. Carrots, corn, squash), accumulates inside the keratinocytes in stratum corneum

o In the body carotene is converted into Vitamin A, important for vision, also has a role in
reducing potentially dangerous molecules formed during metabolic activity and in
improving immune cell number and activity

Question 17

The Dermis consists of two layers

Answer 17

Papillary layer -Superficial dermis
o Consists of:
§ Dermal papillae
§ Capillaries
§ Nerve axons

o Reticular layer -Deep dermis
o Consists of:
§ Interwoven network of dense irregular connective tissue
§ Accessory Structures
§ Hair follicles
§ Sweat glands
§ Sebaceous glands

Question 18

The Subcutaneous Layer

Answer 18

The subcutaneous layer (hypodermis) is deep to the dermis

• Not technically considered a part of the integument

o Helps stabilize the integument

Consists of:
• Adipose tissue
• Major blood vessels
o Due to the location of the vessels, we have terms such as:
§ Hypodermic needles
§ Subcutaneous injections

Question 19

Accessory Structures

Answer 19

Hair - made of keratin
• Hair follicles - Cells are layered in concentric rings
• Hair papilla - a small peg of connective tissue containing capillaries and nerves
• Hair bulb – epithelial cells surrounding the papilla

Question 20

Types of Hair

Answer 20

• Vellus - covers most of the body
• Intermediate - covers arms and legs
• Terminal - covers the head
• No hair on lips, palms or soles of feet

Question 21

Functions of Hair

Answer 21

Protection from UV light
• Insulation
• Guards entrance to nose and ears
• Movement of the hair sends impulses via nerves to the brain, such as when a bug is crawling on
your arm
• Facial expression
• Visual identification
• eyebrows
• Chemical signalling (pheromone dispersal) – in places with good blood supply
• Contraction of the arrector pili muscles results in goose bumps (muscles pilling follicles elevates
hairs) – fight or flight, hairs stand up, response to cold or fear/rage

Question 22

Hair color

Answer 22

Due to: Variation in melanin production by the melanocytes

• Melanin production decreases with age

• Influenced by:
o Genetics
o Hormones
o Environmental factors

Question 23

Hair growth

Answer 23

• Active phase
  • Regression phase
  • Resting phase
  • Reactivation phase

Question 24

Accessory Structures: Exocrine vs endocrine glands

Answer 24

Glands in the skin
• Sebaceous glands
• Sweat glands

Gland function:
• Lubricates the epidermis, excretes waste, assists in thermoregulation

Sebaceous glands
• Secrete sebum (oily fluid) to lubricate the skin
• Found all over the body except for the palms and soles
• Found in high concentrations on the forehead, face, and upper back
• If the ducts become blocked, acne may occur

Sweat glands
• Apocrine glands
o High concentration in the armpit , pubic and nipple regions
o Produce an odorous secretion (BO – body odour)
o Secretions may contain pheromones
o These are the secretions that babies smell in order to detect and “feel safe” with mom
o Males have these secretions as well
• Mammary glands
o special type of apocrine gland
o Produce milk under the control of hormones from the pituitary gland
Ceruminous glands
o A special type of apocrine gland
o Found only in the ear canal
o Produce cerumen (ear wax)
o Provide minimal protection associated with the ear
Merocrine glands
o Also known as eccrine glands
o Found all over the body
o Found in high concentrations on the palms and soles
o Contains antibiotics
o Produce sweat for cooling purposes – watery non-viscous
o Everyday produce about ½ litre of sweat (much more when exercising or very hot), sweat
turns to vapour to cool off body (salty H2O)

Question 25

Accessory Structures: Nails

Answer 25

Function - provide protection for the tips of the fingers and toes

Structure
• Free edge
• Lateral nail fold – boundary of nail
• Lunula – pale crescent on nail 
• Eponychium (cuticle) – portion of stratum corneum of the nail fold that extends 
over the exposed nail root
• Hyponychium – thickened portion of the stratum corneum that the free edge of 
the nail extends ove