Standard anatomical position:
Body erect, feet slightly apart, palms forward, thumbs away from body. Remember that “right” and
“left” refer to the patient or the cadaver, NOT THE OBSERVER.
2 Fundamental divisions of body:
Axial part = head, body and trunk
Appendicular part = appendages or limbs attached to axis
There are also regional terms that is used to designate specific areas within axial and appendicular part
Planes / Sections: There are 3 planes
1. Sagittal plane: vertical plane that divide body into left & right parts. NOT RIGHT AND LEFT HALVES:
This is because some planes are parasagittal plane. Where the cut off is not exactly in the middle. In
order to have equal halves, midsagittal or median plane.
2. Frontal plane (Coronal): vertical plane that divide body into anterior and posterior parts.
3. Transverse (Horizontal) plane: horizontal plane that divides body into superior and inferior parts.
(Traverse section = cross-section)
1 more section: Oblique section – plane is cut at an angle.
Anterior (ventral): in front
Posterior (dorsal): behind
Medial: towards middle
Lateral: away from middle
Intermediate: between medial and lateral
Superficial: towards body surface
Deep: away from body surface
Cranial and vertebral cavity. Cranial cavity unclosed by skull and houses the brain. Vertebral cavity
enclosed by the vertebrae and houses the spinal cord. Both cavities are very well-protected. (Very
strong and bony)
Thoracic cavity (superior) and abdominopelvic cavity (inferior)
Thoracic cavity contains 2 lateral pleural cavities (lungs) and central pericardial cavity (heart). Thoracic
cavity is surrounded by ribs and muscles of chest – decent protection.
Abdominopelvic cavity (two parts)
Superior – abdominal (stomach, intestine, spleen, liver) – nothing covering them – no protection
Inferior – pelvic (in bony pelvis, contain urinary bladder, some reproductive organs and rectum) Bony
pelvis sort of protects – protection is basic
Diaphragm separates the thoracic and abdominopelvic cavities, nothing separates the abdominal and
pelvic cavity Skin + derivatives (sweat & oil glands, hair, nails) = integumentary system
Structure of skin:
2 distinct regions:
Epidermis (superficial part of skin) – epithelial layer (thick, keratinized stratified squamous epithelium)
Dermis (deep part of skin) – Connective tissues
There is also the hypodermis, known as superficial fascia because it is superficial to the tough connective
tissue wrapping of skeletal muscles, it consists mostly of adipose tissue– not really skin, but shares the
skins protective functions. Contains areolar CT+ blood vessels, adipose tissue (store fat)
Act as shock absorber, insulator. It thickens when weight is gained. It anchors skin to underlying
structures with ability to slide.
Epidermis isn’t vascularized, dermis and hypodermis is. Epidermis gets nutrition from diffusion.
4 types of epidermal cells:
Keratinocytes: majority of epidermal cells. Main function is to produce keratin – fibrous protein that
helps give the epidermis its protective properties. The lifespan of keratinocyte is 25-45 days.
Melanocytes: spider shaped, creates the pigment melanin. Found in the deepest layer of the epidermis.
As melanin is made, it is accumulated in the membrane bound granules called melanosomes and
brought to the numerous branching processes, they are then taken to the nearby keratinocytes, and
they accumulate on the superficial side of keratinocyte nucleus, forming a shield protecting UV rays.
*Tanning – tanning produce melanin at a faster rate, this is to protect the nucleus from UV rays. Melanin
is a dark colour. Number of melanocytes is the same between people; the difference is half-life,
production rate of melanin etc.
Langerhans cells, also called epidermal dendritic cells: star shaped: They are macrophages: ingest
foreign substances, activate immune system. Migrate to epidermis from bone marrow.
Merkel cells, also called tactile cells: at epidermis/dermis boundary, have disc-like sensory nerve ending
– like touch receptors.
The layers of epidermis (from deep to superficial)
Stratum Basle: attached to dermis, consists of single row of stem cells – youngest keratinocytes. It has
high mitotic index. 10-25% of the cells are melanocytes; also some Merkel cells are present.
Stratum Spinosum: several cell layers thick. Contain web of keratin filaments attached to desmosomes.
Name reflects when the cell is dried and dead – looks like tiny spiked iron balls. Contain keratinocytes
and melanin granules. Also contain Langerhans cells – most abundant in this layer.
Stratum Granulosum: three to five cell layers. Keratinization of cells begins – these cells flatten, their
nuclei/organelles begin to disintegrate, they accumulate two types of granules. The keratohyalin and
lamellated granules. Keratohyaline granules help to form keratin in the upper layers. The lamellated
granules contain water-resistant glycolipids that are a major factor in slowing water loss. Cells are now
struggling to be viable. They are too far from the capillaries, and are cut off from the nutrients by the
Stratum Lucidum: two or three rows of clear, flat, dead keratinocytes – translucent. The Keratohyaline
granules are in parallel arrays. Only found in thick skin. No more nourishment from capillaries. Stratum Corneum: 20 – 30 cell layers thick. They account for ¾ of the epidermal thickness. They are
thickest on palm of hand & soles. They are dead cells filled with keratin fibrils – they are strong,
protective and waterproof.
Thick skins refers to skin that contain all 5 layers, thin skins to skin that contain only 4 layers – no
stratum lucidum. Most of our body are soft skin other than the palm, fingertips, and soles of feet.
Dermis: Strong, flexible connective tissue, the cells are fibroblasts, macrophages, some mast cells and
white blood cells. It is semifluid matrix, embedded with collagen, elastin & reticular fibers – binds entire
Dermis is richly supplied with nerve fibers, blood and lymphatic vessels. Also contain hair follicles, oil &
The dermis contains two layers, the thin superficial papillary layer, and the deep thick reticular layer.
The top 20% of dermis is papillary, and the bottom 80% is reticular.
Fine interlacing collagen and elastic fibers form a loosely woven mat interspersed with small blood
vessels. The looseness of this CT allows phagocytes and other defensive cells to wander freely as they
patrol the area for bacteria. The superior surface is thrown into peg like projections called dermal
papillae that indent the overlying epidermis. On palms of the hands and soles of feet, these papillae lie
atop larger mounds called dermal ridges. Collectively, these skin ridges are called friction ridges,
increase friction and enhance gripping ability of fingers and feet. These create finger prints.
Dense irregular fibrous CT. Network of blood vessels that nourish this layer lies between this layer and
hypodermis – they are called Cutaneous plexus. The bundles of collagen fibers are parallel to the skin.
Separations or less dense regions between these bundles form cleavage or tension lines in the skin.
These externally invisible lines tend to run longitudinally in the skin of the head and limbs and in circular
patterns around the neck and trunk.
*When an incision is made parallel to these lines, the skin gapes less and heals more readily than when
the incision is made across the tension line.
Collagen fibers of the dermis give skin strength and resiliency that prevent most jabs and scrapes from
penetrating the dermis. Collagen also binds to water, helping keep skin hydrated. Elastic fibers provide
the stretch-recoil properties of skin.
In addition to the epidermal ridges and tension lines, a third type of skin marking is flexure lines. They
are dermal folds hat occur at or near joints, where dermis is tightly secured to deeper structures. Since
skin cannot slide easily to accommodate joint movement, the dermis folds and deep skin creases form.
Extreme stretching of stretching such as pregnancy can tear the dermis. This tearing is indicated by
silvery white scars called striae. They are commonly called “stretch marks”.
Short-term but acute trauma (such as burn, or wielding a hoe) can cause a blister, the separation of the
epidermal and dermal layers by fluid-filled pocket. The pigments that contribute to skin colour:
Melanin: Only pigment made in the skin, its two forms range in color from yellow to tan to reddish
brown to black. Skin colour dependent on type, relative amount and keratinocyte retention of the
pigment (how long keratinocyte can hold them).
Carotene: yellow to orange pigment found in plant products (carrot). It accumulates in keratinocytes
(mostly stratum corneum) and in fatty the fatty tissue of the hypodermis. Carotene can be converted to
vitamin A, which is essential for normal vision, as well as for epidermal health.
Hemoglobin: red blood cells circulating through the dermal capillaries, give the pinkish hue to skin.
Cyanosis – decreased oxygen level in hemoglobin, give skin bluish colour. Caucasians have little melanin,
the epidermis is nearly transparent, this allow for the hemoglobin colour to really show.
Hair & Hair follicles
Sense insects, guard head (physical trauma, heat loss, sun), shield eyes, and filter particles from inhaled
Hard keratin (more durable, doesn’t flake)
Hair shaft – Keratization is complete. Hair root – Keratization ongoing
Hair shaft – the shape determines if the hair is straight or curly.
If the shaft is flat, the hair/ribbon like in cross section, the hair is kinky
If the shaft is oval, the hair is silky and wavy
If the shaft is round, the hair is straight and course.
The shaft has three layers
Medulla - consists of large cells and air spaces. Medulla is the only part of the hair that contains soft
keratin. Absent in fine hairs
Cortex – bulky layer surrounding medulla, consists of several layers of flattened keratinocytes, melanin
pigment is here
Cuticle – single layer of overlapping cells (like singles on a roof). It helps to keep neighboring hairs apart.
Most heavily keratinized part of the hair, provides strength and helps keep inner layers compacted.
Split ends occur when the cuticles wear away at the tip of the hair shaft due to abrasion, the keratin
fibrils in the cortex and medulla frizz out. Hair turn gray or white is result of rate of melanin pigment
production is slowing down, and from the replacement of melanin by air bubbles in the hair shaft.
Shaft: Part that projects from skin
Root: part embedded in skin (in hair follicle)
Bulb: deep end of follicle, expanded. Has papilla (contains knot of capillaries that supplies nutrients, and
signals to grow) & root hair plexus (wraps around each bulb, bending the hair stimulates these endings,
contribute to the ability of touch receptors)
Follicle wall: contains outer CT root sheath, derived from dermis. Contains inner CT root sheath, derived
mainly from an invagination of the epidermis. The sheath thins as they reach to the hair bulb.
Hair matrix: fraction of a millimeter above bulb, dividing area of the hair bulb that produces the hair.
Arrector pili muscle: bundle of smooth muscles associated with each hair follicle. Most hair follicles
approach the skin surface at a slight angle. Arrector pili muscle is attached so that its contraction pulls
the hair follicle into an upright position. It dimples skin- cause Goosebumps.
Sebaceous glands: Holocrine (burst) gland that secretes sebum (oily – lubrication & waterproofing;
bactericidal) Whitehead – When sebum keeps producing oil and gets clogged up in follicle
Blackhead – When the oil in whitehead oxidizes and turns black
Acne – Inflammation of the sebaceous glands, usually caused by bacterial infection.
Clinical notes on hair:
Vellus hair – Body of children and adult females – fine hair
Terminal hair – coarser, longer hair of the eyebrows and scalp. Can be darker. At puberty terminal hair
appear in the axillary and public region of both sexes and on the face and chest of males.
Hair growth is affected by hormones such as androgen (male sex hormone, terminal hair). Hair growth is
also affected by nutrition. Conditions that increase local dermal flow may enhance local hair growth
(brick layers who carried their hod on one shoulder all the time developed one hairy shoulder)
Hirsuitism – when adrenal gland or ovarian tumor secretes abnormally large amount of androgens.
Excessive hair in women.
Average rate of hair growth is 2.5mm per week – children grow faster
Each follicle goes through growth cycles. In each cycle there is active phase ranging from weeks to years,
then there is resting phase – during this phase the hair matrix cells die and the follicle base and bulb
shrivel. After the resting phase, the matrix proliferates again and form new hair to replace the old one
that has fallen out or will be pushed out by new hair. Head hair has longer active phase (can grow longer
without falling out) eyebrow hair has shorter active phase (hair can’t grow very long)
Alopecia is a natural process. A hair follicle only has a limited number of cycles, hair are not replaced as
fast – begin balding.
Male pattern baldness – genetically determined, sex influenced condition. Growth cycle becomes so
short that many hairs never emerge from their follicles. This gene “switches on” in adulthood, this cause
the testosterone to turn into DHT. No hormones to help hair growth.
Nails: Also hard keratin like hair, it is a scale-like modification of epidermis - protective and useful tool
Each nail contain free edge, body (visible attached portion) and root (embedded in the skin)
The deeper layers of the epidermis extend beneath the nail as the nail bed, the nail is like the superficial
Nails appear pink because of rich bed of capillaries in the dermis, but the lunula contain more
tissues/cells therefore you can’t see the capillaries and therefore they appear white.
The proximal and lateral borders of the nails are overlapped by skin folds they are called nail folds.
The proximal nail fold is called cuticle or eponychium
The region beneath the free edge of the nail where dirt accumulate is called hyponychium
The proximal portion of the nail bed is called matrix and this makes new nails.
Sweat glands: they are also called sudoriferous glands
They are distributed over skin surface except for the nipples & part of external genitalia. There is
Two types of sweat glands merocrine and apocrine
Merocrine: More common; in palms, soles and forehead. Each is a simple, coiled, tubular gland. The
secretory part lies coiled in the dermis, and the duct extends to open in a funnel-shaped pore at the skin
surface. They secrete sweat – hypotonic solution, 99% water, some salts, and some other solutes.
Normally swear is acidic with pH between 4 and 6. Sweating is regulated by sympathetic division; its major role is to prevent overheating. Sweating first begin on the forehead and then spreads inferiorly
over the remainder of the body. Emotionally induced sweating begins on the palms, soles and axillae
(armpits) and then spreads to other body parts.
Apocrine – 2000/person, in the axillary and the anogential area. They are larger than merocrine; tend to
lie deeper in dermis and even the hypodermis, their ducts empty into hair follicles. Their secretion
contains the same components as sweat, plus fatty substances and proteins. It is more viscous and
sometimes milky or yellowish. The secretion is odorless, but when the organic molecules are
decomposed by bacteria on skin, it develops odor – body odor.
Begin functioning at puberty under the influence of androgens. Not for thermoregulation, are activated
sympathetic nerve fibers during pain and stress. Activity is increased during sexual foreplay, enlarge and
recede with the phases of woman’s menstrual cycle, they might be sexual scent glands.
They are both merocrine glands because they release through exocytosis (exocrine), they use vesicles to
empty into ducts.
Modified apocrine glands:
Cerminous: found in lining of external ear canal, their secretion mixes with sebum to form cerumen or
Mammary: secretes milk
Functions of the skin:
1. Protection: a) chemical (secretions, melanin) b) physical (waterproof, barrier to trauma/bacterial
invasion) c) biological (Langerhans cells in epidermis, macrophage in dermis). Note* not
impermeable to gases, fat soluble vitamins & steroids, plant oleoresins, organic solvents, salts of
heavy metals, penetration enhancers for drug admiration.
2. Excretion: Some N-containing wastes (urea); NaCl & H2O via sweat
3. Body temperature: sweating (0.5-12 L/day), vasoconstriction
4. Cutaneous sensation: feel on skin, pressure on skin, hair follicle receptor on wind, free nerve
ending sense pain, temperature
5. Metabolic: production of vitamin D
6. Blood reservoir: Muscles need blood, can take this blood to muscle. Skin can hold a lot of blood
(5% of body entire volume), it doesn’t need as much blood supply as other body parts.
Burns: can be from heat, electricity, radiation, and chemical (acid)
First concern is dehydration, second concern is infection
First degree – only epidermis
Second degree – epidermis and upper dermis
Third degree – epidermis and dermis
The deeper you go, the more danger you are – you are damaging the cells that cause the repair.
Potential for repair is take skin from other part of the body, and then put it on the damaged skin. Called
skin crafting. Skin might reject this though
Rule of nines: volume of blood lost can be estimated by computing the percent of body surface burned.
Dividing body into 11 areas worth 9% each. 1% for the genitals. Bone: is a living dynamic tissue which responds to its environment.
1. Bone reacts to amount of force applied by increasing the density & amount of roughening on
bone or decreasing density when fore is reduced or eliminated. Deposition (body > bone) vs.
reabsorption (bone > body)
2. Bone stores calcium – resorbed & transferred to bloodstream when needed.
Functions of bone:
1. Support: Supports body when standing, cradles organ
2. Protection: Protects brain, spinal cord, vital organs of thorax
3. Movement: Muscles attach to bones by tendons, use bones as levers to move the body
4. Mineral Storage: Calcium and phosphate
5. Blood Cell Formation: Hematopoiesis occurs in marrow cavities of certain bone
6. Triglyceride (fat) storage: Fat is stored in bone cavities and represents a source of stored energy
for the body.
Compare structure of bony tissues and cartilages:
Cartilage: features between dense CT & bone – it’s tough, but flexible
1. Avascular, no nerve fibers. This is why cartilage take long time to repair – relies on diffusion
2. Ground substance contains of GAG (glucose amino glycan – hold a lot of water) chondroitin
sulfate & hyaluronic acid – also chondronectin (adhesive protein)
3. Collagen fibers – give strength (can have some elastic fibers)
4. Up to 80% H2O, gives it cushioning properties, can spring back to its original shape
Some terms relating to cartilage:
Perichondrium – membranous wrapping around cartilages, act like a girdle to resist outward expansion
when cartilage is compressed. Perichondrium contains the blood vessels from which the nutrients
diffuse to cartilage. In damaged areas, perichondrium can form scar tissues because poorly vascularized
cartilage repairs, badly.
Ossification of cartilage with aging is gradually replacing cartilage with bone (old person’s ribcage is not
flexible, result is not as easy to breathe)
Chondroblasts – high MR, immature cartilage cells – actively form cartilage
Chondrocytes- Low MR: mature cartilage cells – maintain cartilage
Lacunae: localized clusters of chondrocytes in cartilage – in cluster because they get trapped by the
cartilage around them (like wiping a floor)
Types of Cartilage
1. Hyaline cartilage: most abundant, the only fiber found in their matrix is collagen fibers; firm
support + pliability; appear glassy blue-white; chondrocytes only 1-10% of volume.
Location: embryonic skeleton, ends of long bones (epiphyseal plates in growing children), costal
cartilages of ribs, cartilages of nose, trachea, larynx
Function: support & reinforces; resilient cushioning & resists compressive stress.
2. Elastic cartilage: like hyaline cartilage but more elastic fibers in it.
Location: external ear, epiglottis – (in these places because they need the cartilages to be bendy
(for food to go down))
Function: Maintains shape while giving lots of flexibility
3. Fibrocartilage: Rows of chondrocytes alternating rows with thick collagen fibers; structural
intermediate between hyaline cartilage & dense regular CT
Location: intervertebral disks, pubic symphysis, discs of knee joints
Function: tensile strength with ability to absorb compressive shock Bone: calcium salts give hardness & strength for support/protection of softer tissues; cavities for fat
storage & synthesis of blood cells.
Two types: axial and appendicular
Axial: Skull, vertebral column, ribcage – most involved in protecting, supporting, or carrying other body
Appendicular: upper/lower limbs, girdles (attach limbs to axial skeleton) – used for locomotion
Osteoblast – growing bone
Osteocyte – maintain bone
Osteoclast – digesting bone to remove calcium from bone (multi nucleus)
Classification of bones
Bones vary in size and shape, unique shape of each bone fulfills a particular need. Bone is classified by
their SHAPE not their SIZE.
All bones have:
Compact bone provides the external surface
Spongy (trabecular) bone – honeycomb of trabeculae
Types of bones:
1. Long bone – much longer than wide, has a shaft + 2 round ends, mostly compact bone with
hollow centre (marrow cavity); spongy bone is found in the two ends. All limb bones except for
the kneecap, wrist/ankle bones are long bones.
2. Short bone – cube-shaped, primarily spongy bone, with thin outer layer of compact bone. Wrist,
ankle, sesamoid bones are short bones.
3. Flat bone – thin, flattened, sometimes curved. Skull bones, ribs, breastbone are flat bones
4. Irregular bone – Complicated shapes, primarily spongy bone + thin covering layer of compact
bone. Leftover bones – vertebrae & hip bones are irregular bones.
1. Diaphysis – Tubular shaft of long bone = long axis of the bone. Collar of compact bone
surrounding marrow cavity (medullary cavity). In adults, medullary cavity contains fat (yellow
marrow or yellow bone marrow cavity) in babies, medullary cavity contains red blood marrow
instead – as they grow the red blood marrow gets concentrated to epiphyses.
2. Epiphyses – extremities of a long bone; expanded for articulation with other bones. Compact
bones forms thin outer layer; inferior filled with spongy bone. Have a thin layer of hyaline
(articular) cartilage for forming joints.
3. Epiphyseal line – line between diaphysis & each epiphysis – it’s the remnant of epiphyseal plate.
Epiphyseal plate – a disc of hyaline cartilage that grows during childhood – lengthens bone.
When epiphyseal plate becomes line, growth ends.
Membranes cover outer & inner surfaces of long bones.
Periosteum covers the outer surface, contains osteoblasts and osteoclasts.
Endosteum covers the inner surface (lines marrow cavity), and covers each trabeculae; delicate layer of
CT that also contains osteoblasts & osteoclasts Structure of other bone types:
All 3 other types have similar structure
With Compact bone on the outside, spongy bone on the inside
Compact covered with Periosteum & spongy lined with Endosteum.
They are not cylindrical so no shaft, marrow cavity or epiphyses. They do contain bone marrow between
Osteon (Haversian) system: The structural unit of compact bone. Osteon: elongated cylinder orientated
parallel to the long axis of bone.
A single osteon is a group of hollow tubes of bone matrix – like the rings of a tree. Each of the matrix
tube is called lamellar bone. The collagen fiber have a 90*change of orientation with each layer. This
pattern is designed to withstand tension stress; adjacent lamellae reinforce one another to resist
In each core is central canal or Haversian canal, contain small blood vessels and nerve fibers that serve
the needs of osteon cells.
There are also perforating or Volkmann’s canal, perpendicular to long axis bone & Haversian canals that
connect the blood and nerve supply of Periosteum to those in the central canals and medullary cavity.
Osteocytes: mature bone cells; sit within the lacunae within bony matrix in areas where adjacent
Canaliculi: like small version of Volkmann’s canal, connect the lacunae with each other, also connected
to Haversian canal.
Interstitial Lamellae: fill the gaps between osteons or are leftovers of osteons that were partially
destroyed by bone remodelling.
Circumferential lamellae: sheets of bone located just deep to Periosteum; extend around entire
circumference of shaft – resist twisting of long bone.
Contains trabeculae (align precisely along lines of stress and help the bone resist stress), few cells thick,
contain irregularly arranged lamellae and osteocytes interconnected by Canaliculi.
Nutrients diffuse through Canaliculi from the marrow spaces between the trabeculae to reach the
Bone formation and remodeling:
Osteogenesis or Ossification means making something to become bone. This includes formation of bony
skeleton in embryos, growth of bones during childhood & adolescence & remodelling/repair of bones in
1. Intramembranous Ossification: bone develops from fibrous CT membrane containing
mesenchymal (stem) cells. Cranial bones of the skull and clavicles – flat bones. Begins at about 8
weeks of embryonic development.
2. Endochondral Ossification: more common, bone develops via the replacement of hyaline
cartilage. All bones below the skull (other than clavicle). Begins in second month of embryonic
development. More complex because it require the cartilage to break down first before building
*In short bones, only the primary ossification centre are formed; most irregular bones are formed using
several distinct ossification centres. When ossification is complete, hyaline cartilage remains:
1. On the epiphyseal surfaces as the articular cartilage.
2. At the junctions of diaphysis and epiphyses where it forms epiphyseal plates – where long bones
continue to grow.
Mechanisms of bone growth:
During infancy & youth, long bones lengthen entirely by interstitial growth of the epiphyseal plates, and
the bone grows in thickness by appositional growth.
Most bones stop growing during adolescence or early adulthood – some facial bones (jaw, nose)
continues to grow throughout life.
As the long bone lengthens, the shape of the ends must be altered (remodel). As the length increases,
external surface of ends made slimmer while internal surface is thickened.
In summary, bone is destroyed by osteoclasts and laid down by osteoblasts on both the inner and outer
surfaces of growing long bone.
Epiphyseal plate stays roughly the same size throughout childhood & adolescence.
Epiphyseal plate then becomes thinner; the cells multiply more and more slowly.
Longitudinal growth ends when bone of the epiphysis & diaphysis fuses = epiphyseal plate closure (18 in
females, 21 in males). Some hormones cause the epiphyseal plate to close quicker.
Growth in width:
Growth in width = appositional growth.
Layers of bone are laid on top of one another
1. Osteoblasts on periosteal side secrete bone matrix
2. Osteoclasts on the endosteal side remove bone matrix
Osteoblast is quicker than osteoclast, more deposition occurring, bone get thicker slowly.
Parathyroid hormone control:
PTH produced by parathyroid glands, PTH is released when blood is losing calcium. Increased PTH level
stimulate osteoclasts to absorb bone, releasing calcium to blood. Parathyroid glad is posterior to thyroid
gland (4 glands).
Calcitonin is produced by parafollicular cells (in thyroid) – is opposite of PTH.
When bone resorption outpaces bone formation – bone become porous
Some areas of skeleton especially vulnerable: spine, neck of femur.
Estrogen and testosterone promote bone health by restraining osteoclast activity and promoting
deposition of new bone (less of these hormones in adults)
Other factors include: insufficient exercise, poor diet in calcium & protein, abnormal vitamin D
receptors, smoking (reduce estrogen levels) Skeleton: There are 206 bones in skeleton, making up 20% of body weight.
Axial skeleton: segregated into 3 major regions: the skull, vertebral column, and thoracic cage. 80 bones
Skull: most complex. Contain 2 set of bones: cranial + facial = 22 bones.
Most skull bones are flat bones (other than mandible); they are united by sutures (“stiches” –
Facial bone form anterior part of skull & cranial bone form the rest
Skull has eye orbits & paranasal sinuses, houses organs of hearing, 85 openings for nerve, blood vessel,
and spinal cord.
Cranium: Can be divided into vault and base
Vault: forms superior, lateral, & posterior aspects of the skull + forehead
Base: inferior aspect of skull, internally the base is divided into 3 areas: anterior fossa (highest), middle
fossa, posterior fossa (lowest). The brain sits snugly in the cranial fossas.
Cranium surrounds & protects brain and organs of hearing, balance.
Cranium: 8 bones: Paired parietal & temporal bones, unpaired frontal, occipital, sphenoid and ethmoid
bones. The bones are curved, allow them to be self-bracing, can be strong and quite thin (like eggshell)
Dome shaped bone; also forms the roof of the orbits & anterior cranial fossa. It articulates posteriorly
with the parietal bones via the coronal suture.
Supraorbital margins: thickened superior margins of the orbits that lie under the eyebrows – for shading
Supraorbital foramen – Each supraorbital margin is pierced by his, which allows the supraorbital artery
and nerve to pass to the forehead
Glabella: The smooth portion of the frontal bone between the orbits. The areas lateral to the glabella is
riddled internally with sinuses, called frontal sinuses.
Paired, form the superior & lateral aspects of the skull.
Form bulk of the cranial vault.
The 4 largest sutures occur where the parietal bones articulate with other bones.
Parietal – parietal = sagittal suture
2 Parietal – frontal = coronal suture
2 parietal – occipital = lambdoid suture
Parietal – temporal = squamous suture
Single bone at base of skull; helps form posterior aspect of skull, also form walls of the posterior cranial
fossa – supports the cerebellum.
Attaches to 2 parietal & 2 temporal, also attached to sphenoid bone
Foramen magnum –hole at the base of skull – for passage of brain stem – spinal cord.
Occipital condyle – on each side of foramen magnum is the site or articulation with first cervical
vertebra. This permits the nodding motion
External occipital protuberance – it is superior to foramen magnum; knob projection at the back of skull
– more prominent in males. Temporal bone:
Paired, form inferior & lateral aspects of skull and parts of the cranial floor.
Located below the 2 parietal bones – have 4 different areas of region.
1. Squamous region: flattened, touches the squamous suture
Zygomatic process meets zygomatic bone (cheekbone)
Mandibular fossa – small oval – on the inferior surface of the zygomatic process, receives the
condyle of the mandible (lower jawbone). This forms a freely movable joint.
2. Tympanic region: surrounds the external acoustic meatus (external ear canal).
Below the external acoustic meatus is the needle-like styloid process – an attachment site for
many tongue and neck muscles.
3. Mastoid region: contain mastoid process, an anchoring site for some neck muscles.
4. Petrous region – internal aspect of temporal bone (can’t easily be seen)
Contributes to cranial base & houses middle and inner ear cavities.
Jugular foramen – junction of the occipital and temporal bone allows the passage of the internal
jugular vein and 3 cranial nerves.
Carotid canal – Anterior to the jugular foramen, transmits the internal carotid artery into cranial
cavity, The arteries are close to internal ear cavities – explain why we can hear our rapid pulse as
thundering sound when excited.
Internal acoustic meatus – positioned superolateral (top and side) to the jugular foramen,
transmits cranial nerves.
Sphenoid bone: bat-shaped
Complex bone, difficult to visualize; articulates with all other cranial bones. (Keystone bone of the
Forms base of middle cranial fossa, contributes to base of anterior cranial fossa.
Consists of a central body and 3 pairs of processes: greater wings, lesser wings, pterygoid processes
Within the body of the sphenoid are the paired sphenoid sinuses.
Greater wing: project laterally from the sphenoid body, forming parts of the middle cranial fossa, and
the dorsal walls of the orbit.
Lesser wing: horn-like, form part of the floor of the anterior cranial fossa, and part of the medial walls of
Pterygoid process – project inferiorly from the junction of the body and greater wings, they anchor the
pterygoid muscles (for chewing)
Optic foramen (canal) – for optic nerves to pass to the eyes
Superior orbital fi