Exam 1-body membranes, skin, skin health and skeletal system Flashcards
apical surface
an upper free surface exposed to the body exterior or the cavity of an internal organ
basal surface
The bottom layer of epithelial tissue that attaches to the basement membrane
endocrine glands
Glands of the endocrine system that release hormones into the bloodstream
exocrine glands
secrete chemical substances into ducts that lead either to other organs or out of the body
connective tissue and the 4 main types
Has lots of extracellular matrix, fewer cells
-Connective tissue proper
*Cartilage
*Bone
*Blood
cells of connective tissue
-cytes are mature cells of connective tissue,
-blasts are mitoctically active and secretory cells
–Also: fat cells, immune system cells (some phagocytes, mast cells
Cells of connective tissue proper
Fibroblasts
Adipocytes
Melanocytes
Macrophages/phagocytes
Mast cells
Lymphocytes
types of connective tissue proper
loose and dense
loose connective tissue
areolar, adipose, reticular (found in spleen)
Dense connective tissues (AKA fibrous connective tissues)
*Dense regular (regular collagen fibers)
*Dense irregular (more irregular collagen fibers)
*Elastic (elastin)
structure of dense connective tissue
-mainly collagen fibers; it is what is mostly visible
-ground sub. is the what medium that is behind the collagen and fibroblasts
-fibroblasts are the dark purple circles
dense CT is the deepest layer of skin and it is in thick skin (feet, hands)
exocrine glands
secrete chemical substances into ducts that lead either to other organs or out of the body
structure of dense connective tissue
mainly collagen fibers; it is what is mostly visible
-ground sub. is the what medium that is behind the collagen and fibroblasts
-fibroblasts are the dark purple circles
dense CT is the deepest layer of skin and it is in thick skin (feet, hands)
Cartilage
Avascular
•Receives nutrients from surrounding membrane
3 types of connective tissue
Hyaline, Elastic, Fibrocartilage
Have at least two primary tissue types
epithelium + connective tissue)
Three types of Covering and Lining Membranes
Cutaneous membranes (dry, surface)
•Mucous membranes (moist, line cavities open to the outside)
•Serous membranes (moist, in closed ventral body cavity)
Mucous membrane
on trachea and near lungs
has goblet cells
loose CT
mucous
Pseudostratified epithelium
Cutaneous membrane
on hands
has epidermis that is keratinized stratified squamous epithelium
has dermis
has dense and loose CT
serous membrane
Membrane that lines a cavity without an opening to the outside of the body
tissue damage gives rise to tissue repair
what are the types of tissue repair
fibrosis
regeneration
Regeneration
the regrowth of missing tissues or organs
- replace damaged tissue with original cells (in mouth)
Fibrosis
the thickening and scarring of connective tissue, usually as a result of injury
replace damaged tissue with scar tissue (connective tissue- fibroblasts)
example of regeneration
burn mouth: cells die, cells are replaced by epithelial cells
example of fibrosis
injure area with damaged cells, the cells die, cells are replaced with collagen fibers and fibroblasts
integumentary system
the largest organ of the body that forms a physical barrier between the external environment and the internal environment that it serves to protect and maintain; Consists of the skin, mucous membranes, hair, and nail
Two types of skin
thick = non-hairy skin = glabrous skin = acral
and
thin = hairy skin = non-glabrous skin
thick skin
found on sole of feet and palms of hands
-specialized for discriminative touch (texture/shape/grip), hair follicles
-has extra layer of cells compared to the thin skin
the skin is…
the cutaneous membrane of the body. it is the largest organ of the body
cutaneous membrane
skin- covers the body surface
functions of integumentary system
- Protection
- Body Temperature Regulation
- Cutaneous Sensation (touch)
- Metabolic Functions
- Blood Reservoir
- Excretion
- skin keeps In H20
How skin regulates body temperature
Hot: Sweating, the evaporation of the sweat cools off the skin
Cold: Shivering, the muscles and bone shake to generate heat
how skin is involved in metabolic functions
skin producing necessary materials (ex: vitamin D production)
Two distinct regions of the skin
Epidermis
•Epithelial tissue, avascular, superficial region
Dermis
•Fibrous connective tissue, vascularized, underlies epidermis (deep to epidermis)- mostly fibrous connective tissue
Hypodermis is not part of the skin
hypodermis- subcutaneous layer of deep to skin
mostly adipose tissue that absorbs shock & insulates
anchors skin to underlying structures (mostly muscles) not part of skin but shares some functions
Subcutaneous fluids
fluids placed in the hypodermis and slowly absorbed by the body
cutaneous membrane includes
Epidermis and dermis not the hypodermis
what cells are found in the epidermis
stratified squamous cells
epidermis is made of
keratinized stratified squamous epithelium
5 layers of skin
- stratum basale - deepest
- stratum spinosum
- stratum granulosum
- stratum lucidum
- stratum corneum - most superficial
4 major cells types of the epidermis
keratinocytes (skin cells that shed)
melanocytes (produce pigment; give skin color)
dendritic cells (part of immune system -> langerhans, came from the bone marrow, traveled through the blood)
Merkel (tactile) cells (sensation)
cells of the epidermis
keratinocytes, melanocytes, langerhans cells, merkel cells
Keratinocytes
The most abundant epidermal cells, function mainly to produce keratin.
make significant boundaries from bacteria, toxins, and from H20 being lost
and found: on top of the epidermis and below the stratum basale before the basal
Melanocytes
cells that produce melanin
produce pigments; helps protect cells from DNA damage
found: in the stratum basale
Merkel cells
touch receptors
found in stratum basale
dendritic cells
immune system
aka langerhans
stratum basale
also called the germinativum
firmly attached to dermis
stem cells are in the stratum basale
stem cells
unspecialized cells that are able to renew themselves for long periods of time by cell division
where is the stratum basale
Deepest part of the epidermis
Stratum Spinosum (Prickly Layer)
Several cell layers thick
Keratinocytes
abundant melanosomes
dendritic cells
stratum granulosum (granular layer)
-thin; four to six cell layers
- cells flatten
- nuclei and organelles disintegrate
- keratinization begins, becomes bag of keratin
- cells release glycolipids
Glycolipids
Membrane carbohydrates that are covalently bonded to lipids.
what is it that glycolipids do?
help to mold cells together
-hydrophobic layer so H20 does not leave or come in
stratum corneum
protective layer
-three-quarters of epidermal thickness
-most superficial layer; 20-30 layers of dead cells, essentially flat membranous sacs filled with kera
Melanosomes
A melanosome is an organelle found in animal cells and is the site for synthesis, storage and transport of melanin, the most common light-absorbing pigment
Melanocyte
mature melanin-forming cell, especially in the skin.
Where are keratinocytes found?
Epidermis
Where are melanocytes found?
stratum basale of epidermis
Where are dendritic cells found?
stratum spinosum
Where are tactile cells found?
basal layer of epidermis
stratum basale
Dermis contains
-nervous system components (neurons etc..)
-blood + lymph
-hair follicles
-sebaceous glands (oil glands), other sweat glands
dermis cells types
fibroblasts
macrophages
sometimes mast cells & white
blood cells (immune cells)
Dermis two layers
papillary- next to the epidermis; nipple shaped; has capillaries which has O2 that will diffuse to the epidermis
and
reticular- deep to the epidermis
structure of dermis
dermal papillae
capillaries
papillary layer
reticular layers
epidermis
dermal papillae
tactile corpuscles
collagen fibers
lamellated corpuscles
blood vessels
Pieces of skin (appendages)
epidermis
dermis
hypodermis (not part of skin)
sensory receptors
arrestor pili muscle
blood vessel
apipose tissue
sweat gland
sebaceous gland
hair
dermal papillae
-most contain capillary loops
-the dermal papillae in hairless skin contain meissner’s corpuscle (AKA tactile corpuscles)
-some contain pain receptors
Layers of the Dermis: Reticular Layer
Accounts for approximately 80% of the thickness of the skin
appendages of skin embedded into the reticular layer
innervated- nervous tissue components
reticular layers contains dense fibrous connective tissue- elastic fibers and collagen fibers
what do elastic fibers allow for
stretch and snap back to their original length
What does collagen provide?
flexibility and strength in resisting tension
sensory receptors in skin
cutaneous receptors, pain, touch, pressure, temperature
Mechanoreceptors
Receptors that respond to pressure, stretch, or vibration, and change the position of receptors in the skin
Where are mechanoreceptors found?
Skin- dermis
types of mechanoreceptors
Merkel cell fibers
-Tactile corpuscles (meissner’s corpuscle’s)
-Ruffini endings (bulbous corpuscles)
-Lamellated corpuscles
Types of receptors
thermoreceptors- sense temp.
prurireceptors- itch
nocioreceptors- pain
mechanoreceptors- touch
Meissner’s corpuscles
sensitive touch receptors in the dermis
Pacinian corpuscles
respond to deep pressure and vibration
three pigments that contribute to skin color
melanin- only pigment made in the skin, produced by melanocytes
carotene- diet
hemoglobin- blood
Appendages of the skin
Hair, hair root, nails, sweat glands, arrestor pili muscle and oil glands
Two types of sweat glands
eccrine and apocrine
what do sweat glands have
myoepithelial cells to help them contract
eccrine sweat glands
respond primarily to elevated body temperature; the evaporation of the sweat helps you to cool down
-abundant in palm, soles, forehead
apocrine sweat glands
Found in armpits, around nipples, and groin; Secrete products into hair follicles; Produce sticky, cloudy secretions; Break down and cause odors;
what is in the sweat in eccrine glands
99% water, salts, vitamin C, antibodies, dermicidin (microbe killing peptide)
they play the thermoregulation role in homeostasis
type of sweat in apocrine glands
viscous, milky or yellowish, odorless
but produces an odor when the bacteria (that comes at puberty) mixes with it
apocrine sweat glands location
axillary and anogenital areas, function at puberty
ducts empty into hair follicles or directly onto surface
their secretion is sweat + fatty substances + proteins
modified apocrine glands
ceruminous glands (ear wax) and mammary glands
sebaceous glands
found all over skin except palms and soles; develop from and empty into hair follicle; produce sebum; inactive until hormonal stimulation at puberty
hair
dead cells of hard keratin
everywhere except soles of feet, palms, lips, nipples,
function of hair
cushion and keep in heat
hair follicles are part of what
part dermis, part epidermis
hair bulb
Lowest part of a hair strand; the thickened, club-shaped structure that forms the lower part of the hair root.
hair follicle receptors
sensory nerve endings around each hair bulb; simulated by bending a hair; detect light touch
hair matrix
actively dividing area of the hair bulb that produces the hair
arrestor pili
tiny muscle fibers attached to the hair follicles that cause the hair to stand erect
Smoot muscle attached to hair
some functions of the integumentary system
sensation- mechanoreceptors
excretion- metabolic waste, thermal
blood reservoir- how to send more (hot temp.) or less (cold temp.) blood to the skin depending on temp
metabolic functions- vitamin D production
protection
Vitamin D production
UV light and cholesterol makes vitamin D precursor and this is modified in the liver and fully activates in the kidney
protective functions of integumentary system
physical barrier and protection against infection
what can and cannot get through the skin?- physical barrier
can- hydrophobic things
cannot- hydrophilic things
all due to phospholipid bilayer of cells
protection against infection of skin
what protects us from pathogenic bacteria infection?
lots of bacteria normally live on our skin
what protects us from pathogenic bacteria?- topical medicine in the form of a lipid to get though the skin
general phases of wound repair
1- blood + lymphocytes flow into the wound= brings in lots of signaling molecules, so does the damaged tissue
2- hemostasis- blood clotting + construction of blood vessels, clot is provisioned scaffold/structure
3- cells migrate in –> white blood cells, fibroblasts, tissue specific cells (ex: skin, have keratinocytes coming in)
Two types of tissue repair
regeneration and fibrosis
why is a wound a medical concern
because it can introduce bacteria and lead to infection so immune system is always patrolling
what does the immune system do for skin health
physical and chemical barriers
- innate immunity
- adaptive immunity
physical and chemical barriers of the immune system
cutaneous membrane (skin) = various epithelia, secretions
innate immunity
nonspecific response, but very quick - body recognizes foreigner
adaptive immunity
the ability to recognize and remember specific antigens and mount an attack on them- cells recognize type of pathogen
phases of wound repair
hemostasis, inflammation, proliferation, remodeling
The first line of defense
First line of defense
Physical and chemical barriers contribute to this first line of defense how?
producing mucus, defensins, pH, Only when a pathogen (illness-causing thing) gets by these initial defenses does it encounter biological barriers
What materials do not penetrate the skin?
H2O
Hydrophillic substances
charged particles (do not get thru plasma membrane)
What materials get through the barrier in limited amounts?
hydrophobic substances
heavy metals
hydrophobic substances
heavy metals
sweat and sebum from glands
skin cells
sweat and sebum from glands
skin cells
dermicidin
sebum is antimicrobial
sweat is acidic
From skin cells themselves:
defensin
*(Wounded skin also releases protective peptides that prevent some bacterial infection.)
innate immunity cells
nonspecific response, but very quick - body recognizes foreigner
adaptive immunity
the ability to recognize and remember specific antigens and mount an attack on them- cells recognize type of pathogen
phases of wound repair
hemostasis, inflammation, proliferation, remodeling
First line of defense
is the epithelial layers (barriers)
Physical and chemical barriers contribute to this first line of defense how?
producing mucus, defensins, pH, Only when a pathogen (illness-causing thing) gets by these initial defenses does it encounter biological barriers
innate immunity cells
macrophages (patrol in solid tissue like skin)
dendritic cells (patrol in solid tissue like skin)
neutrophils (patrol in blood stream)
adaptive immunity cells
B and T cells
Antigen
any protein or particle that can elicit an immune response
Macrophages and Dendritic Cells patrol
patrol
solid tissue for foreign invaders
what do Macrophages and Dendritic Cells do
These cells eat the invaders, destroying them. They send out signals that there is a foreign invader to additional immune system players on “billboards” called MHC molecules
In the Epidermis: dendritic cells are
Antigen-Presenting Cells
function of hair
cushion and keep in heat
in the Dermis: Macrophages can
also, be APCs- antigen-presenting cells
autoimmune disease
a disease in which the immune system attacks the organism’s own cells
*Some autoimmune disorders of the skin:
*Vitiligo (mature melanocytes are destroyed)
*Psoriasis
*Atopic dermatitis (AKA eczema)
*Scleroderma (hardening of connective tissue
*Most epithelial skin tumors are
benign (not cancerous) and do not metastasize (spread)
Risk factors of skin cancer
Overexposure to UV radiation
•Frequent irritation of skin
•Genetic factors
•Previous chemical or thermal burns
•Potentially, viral infectionThree major types of cancer
Three major types of skin cancer
Basal cell carcinoma
•Squamous cell carcinoma
•Melanoma
Very rare:
•Merkel cell (tactile cell)
metastasize
the process by which cancer spreads from one place to another
basal cell carcinoma (BCC)
malignant tumor of the basal layer of the epidermis; the most common type of skin cancer
•Least malignant; most common
•occurs in Stratum basale cells
•What do you know about these cells?- in the basal layer of the dermis
•proliferate and slowly invade dermis and hypodermis
•Cured by surgical excision (cutting out) in 99% of cases
squamous cell carcinoma (SCC)
Second most common type
•According to the American Cancer Institute, ~680,000 cases diagnosed/year
•(incidences are also not required to be reported to cancer registries)
•Stratum spinosum keratinocytes
•What do you know about these cells?- these are cells in the stratum spinosum layer that produce keratin
•Usually scaly &/or reddened papule on scalp, ears, lower lip, and hands
•(Forms plaques that bleed or ulcerate)
•Does metastasize
•Good prognosis if treated by radiation therapy or removed surgically
Melanoma
Most dangerous
•Highly metastatic and resistant to chemotherapy
•Estimated new cases and deaths from melanoma in the United States in (2022, from the National Cancer Institute): New cases: 99,780 (5.2% of all new cancer cases) Deaths: 7650 (1.3% of all cancer deaths)
•Melanocytes
Common treatment: wide surgical excision accompanied by immunotherapy
immunotherapy
use of immune cells, antibodies, or vaccines to treat or prevent disease
Merkel Cell (Tactile Cell) Carcinoma
Currently treatment options include excision, radiation, immunotherapy, chemotherapy
Merkel Cells originally thought to be origin of this cancer, but emerging evidence may suggest otherwise
Merkel Cell polyoma virus found in most (but not all) patients with disease (MCPyV)
Most people have been exposed to this by adulthood, but only causes symptoms in these rare Merkel Cell Carcinoma situations
UV light exposure and age
Burns
Tissue damage caused by heat, electricity, radiation, certain chemicals
•Denatures proteins (“unfolds”)
•Kills cells
what is the threat of burns
Dehydration and electrolyte imbalance
•Leads to renal (kidney) shutdown and circulatory shock (organs and tissues don’t receive enough blood)
first- burns the epidermis and second- burns the epidermis and half of the dermis degree burns
Partial-thickness burns
Full thickness burns
Third degree- burn the epidermis, dermis and hypodermis
Cellulitis
Bacterial infection - deep dermis, subcutaneous tissue
•Organisms usually only identified in 15% of cases
•In those cases: Strep and Staph are common
•Life-threatening if not treated
•Systemic treatment
MRSA
Bacterial infection, can be community or hospital-acquired
•Methicillin-resistant Staphylococcus aureus
•May lead to cellulitis
- keep safe when going to gyms and locker rooms, that is how they spread
Ringworm (times corporsus)
Fungal infection (not a worm!)
•Related to athlete’s foot (tinea pedis), jock itch (tinea cruris)
•Zoonotic
•Topical or systemic treatment
Anchoring junctions have these general components:
1)Transmembrane proteins that interact with each other or extracellular matrix
-2) Intracellular proteins that connect the transmembrane adhesion proteins to the cytoskeleton.
-3) Cytoskeleton components
eg. Intermediate filaments, or actin filaments
the hemidesmosomes that anchors intermediate filaments in a cell to ECM is disrupted
Epidermolysis bullosa —> hemidesmosome problems
Epidermolysis bullosa
derm- skin
lysis- breaking apart
Kindler syndrome —> focal adhesion complex problems
action-linked cell-matrix adhesion anchors actin filaments in cell to ECM
Epidermal replacement slows
•Decreased sebaceous gland activity
•Subcutaneous fat and elasticity decrease
•Decreased numbers of melanocytes and dendritic cells
What happens to skin as we age?
oss-/ost-
Bone
trophy
Enlargement
Plasia
growth via new cells, mitosis
-genesis
To form
Chon-
cartilage
Mesenchyme
embryonic connective tissue
mesenchymal cells
multipotent stem cells arising from mesenchyme (daughter cells can become many things)
Ossification
bone formation (hardening)
Hydroxyapatite
hard body matrix
calcium-phosphate mineral
How do we know what we know about Anatomy?
observational based
-compare lots of different subjects
-as tech. improves, so does our understanding, CAT, PET, MRIs
How do we know what we know about physiology?
observation, non-invasively by urinalysis, blood chemistry, EKG, Sonography, animal-model studies (does not fully capture what is happening in humans), comparative studies between groups of people
compact bone
osteon/haversian system
osteons
Layer of bone tissue having many small spaces and found just inside the layer of compact bone.
looks like a sponge!
Spongy bone
Function of skeletal system
support, protection, movement, fat storage, blood cell formation, mineral storage and acid-base homeostasis
Protection of the skeletal system
skeleton protects vital organs such as the brain and also the heart and lungs are within the rib cage
mineral storage and acid-base homeostasis of the skeletal system
Bone stores minerals such as Ca2+ & PO43-, which are necessary for electrolyte & acid-base balance
example of negative feedback (if the Ca+ goes up in the blood then it is absorbed by the bone, if the Ca+ goes down then bone releases it into the blood)
blood cell formation of the skeletal system
red bone marrow is the site of blood cell formation
red and white blood cells
for kids: every bone has red bone but adults have red and yellow bone (which is in the medullary cavity)
fat storage of the skeletal system
yellow bone marrow stores triglycerides
movement of the skeletal system
muscles produce body movement via their attachment to bones
support of the skeletal system
Supports weight of the body
Bones are classified by
Shape
bone is about as long as it is wide
ex: trapezium (carpal bone)
Short bone
Long bone
bone is longer that it is wide
ex: humerus
Flat bone
bone is broad, flat, and thin
ex: sternum
Irregular bone
bones shape does not fit into other classes
ex: vertebrae
Sesamoid bone
round, flat bones found within tendons (e.g., the patella)
Bones are
living tissue
there are blood and nerve supplies- have cells that need O2
coverings of the bone
Periosteum and endosteum
periosteum
Lining around the bone
Endosteum
Lining that lines the medullary cavity
hyaline (articular) cartilage of the bone
on the part of the bone that connects to other parts of the bone
perforating fibers
-fibers that connect periosteum to bone
-a matrix of connective tissue consisting of bundles of strong collagen fibres connecting periosteum to bone
Nutrient Foramen
a small tunnel through the cortex of a long bone containing a nutrient artery which supplies the bone with nutrients
nutrients- nutrients in the form of blood (O2, Ca+)
foramen- opening
Diaphysis (shaft)
Compact bone collar surrounds medullary (marrow) cavity
Medullary cavity in adults contains fat (yellow marrow)
Epiphysis
Ends of a long bone
Epiphyseal bands
growth bands
Medullary cavity
the hollow part of bone that contains bone marrow
Nutrient artery
large artery that enters compact bone near the middle of the diaphysis
Yellow bone marrow
fatty tissue found in the medullary cavity of most adult long bones
Red bone marrow
produces blood cells, found in spongy bone
Compact bone definition
Hard, dense bone tissue that is beneath the outer membrane of a bone
Where is bone marrow found
medullary cavity for yellow but on the epiphyses for red
can be red for kids and adults and yellow for only adults
Foramen
Hole
circumferential Lamellae (compact bone)
The lamellar; Layers of bone matrix that go all the way around the bone.
Interstitial lamellae (compact bone)
fill the spaces between osteons. the circumferential lamellae (L) run around the circumference of the bone.
Perforating canals
structures through which blood vessels enter and exit the bone shaft.
Central canal
Canal running up and down, carrying blood vessels, is in the center of the osteon
components of the periosteum
outer fibrous layer and inner cellular layer which contains osteoblasts
Lacunae
small cavities that contain osteocytes
collagen fibers in the bone
provides flexibility and strength;; remove it then the bone is brittle because it is not able to bend but if you only have it then the bone will only bend a lot and not remain stiff
Channels in bone that contain blood vessels and nerves
What is in the Haversian canal?
Subunits of spongy bone
Trabeculae
What is in the trabeculae
lacunae with osteocytes
-canaliculi
-osteoblasts of the endosteum
-lamellae
-osteoclasts
Composition of bone
organic and inorganic components
organic components of bone (make up 1/3 of bone- 33% of bone by mass)
bone cells
osteoid
ground substance
collagen fibers
Red bone marrow
what is in between the trabeculae
Hydroxyapatites (mineral salts)
inorganic components of bone
(makes up 2/3 of bone- 65% of bone by mass)
the calcium phosphate mineral of the bone is from
the blood
derived from blood by osteoblasts
secreted from osteoblasts
Osteoid
bones without organic matrix sUch as collagen, ground substance, osteoids, bone cells
brittle and shatters quickly
probably due to lack of collagen which provides strength
Bones without inorganic material
cannot resist compression, so bends easily
What are the bone cells
osteoblasts, osteocytes, osteoclasts
Osteoblasts
bone forming cells
Osteocytes
mature bone cells
Osteoclasts
Bone-destroying cells
bone-resorbing cell
Osteoblasts
are secretory cells; secrete unmineralized bone matrix (collagen and Ca2+binding proteins = osteoid); play role in mineralization, too.
osteocalcin
What hormone do osteoblasts secrete
Osteocytes maintain
bone matrix
Important to communicate stress info to osteoblasts and osteoclasts (for bone remodeling)
Osteogeneic cells
bone stem cell that can become an osteoblast
Where does bone genesis occur
in the periosteum
Osteogenesis in the periosteum
1- osteogenic cells differentiating into osteoblasts
2- osteoblasts deposit bone until they are trapped-they become surrounded by bone matrix
3- osteoclasts secreting chemicals required for bone maintenance- they are suspended in the extracellular fluid in lacuna and trapped between the bone ECM
Chondroblast
cartilage-forming cell
Chondrocyte
mature cartilage cell (trapped in lacunae)
The human skeleton starts out as cartilage
what type of cartilage?
Hyaline cartilage
the skeleton, which is cartilage in babies, will be replaced by bone one of two ways:
endochondral ossification and intramembranous ossification
Below the level of the skull bones (with a few skull bone exceptions), bones form by
endochondral ossification
(this is also used by long bones to achieve adult height)
The skull (and also clavicles) form by ______________________.
intramembranous ossification
Fetal primary ossification centers
At 12 weeks
endochondral ossification steps
- Chondrocytes grow, die, leave cavities
- blood vessels grow, perichondrium cells -> osteoblasts, bone collar forms
- vessels penetrate, fibroblasts -> osteoblasts, spongy bone forms in primary ossification center
- osteoclasts erode trabeculae = medullary cavity, increases in length & diameter
- secondary ossification centers in epiphyses
- articular cartilage on ends, epiphyseal cartilage at metaphysis
endochondral ossification
Process of transforming cartilage into bone.
Epiphysis plate
the main site of longitudinal grepiphysis plates of long bonesowth of the long bones. At this site, cartilage is formed by the proliferation and hypertrophy of cells and synthesis of the typical extracellular matrix. The formed cartilage is then calcified, degraded, and replaced by osseous tissue.
in young child the carpal bones
are not visible because ethyl have not completed endochondral ossification
Structure of epiphyseal plate
- Ossification Zone
- Calcification Zone
- Hypertrophic Zone (enlarge)
- Growth Zone (division)
- Resting zone
intramembrane ossification
Creation of bone from the periosteum
why does a newborn have “soft spots” (fontanelles) on their head when they are born?
heads needs to be able to squeeze through the birth canal of the mother
- and also the brain needs space and flexibility of the skull in order to expand and grow- grow tthe most during the first 2 years of life
Parts of newborn skull
-frontal suture
-ossification center
-posterior fontanelle
-parietal bone
-anterior fontanelle
-occipital bone
-sphenoidal fontanelle
-mastoid fontanelle
-temporal bone
- Osteoblasts develop in the primary ossification center
- Osteoblasts secrete organic matrix, which calcifies
- Early spongy bone is formed
- Early compact bone is formed
process of intramembranous ossification
Function of osteocytes
regulates mineral content in the matrix; aids in bone repair
Bone remodeling
ongoing replacement of old bone tissue by new bone tissue
Remodeling units
Osteoblasts & osteoclasts at periosteum and endosteum
Stem cell Daughter cells may differentiate into osteoblasts.
Osteogenic cell role in bone remodeling
osteoblast cell role in bone remodeling
Matrix-synthesizing
cell responsible for
bone growth
Osteoblasts are responsible for laying bone matrix
osteoclast cell role in bone remodeling
-Bone-resorbing cell
-responsible for breaking down matrix
(they secrete enzymes and low pH material to digest collagen and dissolve calcium phosphate)
bone resorption
the removal of minerals and collagen fibers from bone by osteoclasts
Bone Deposition (Mineralization)
Osteoid laid down by osteoblasts.
•Hydroxyapetite may form spotaneously and catalyze new crystal formation
•Proteins and enzymes from osteoblasts needed for mineralization
Bone resorption - demineralization
Osteoclasts secrete lysosomal enzymes (remember the lysosome?)
•They also secrete low acid solution to break apart matrix.
•Osteoclasts transfer broken down material to blood.
•When finished, they undergo apoptosis (remember apoptosis?)
absolutely necessary for normal bone development!
•Mechanical stress determines where remodeling occurs
Mechanical stress is
circumferential lamellae
Layers of bone matrix that go all the way around the osteon
interstitial lamellae
fill the spaces between osteons
what does collagen provide the bone
it is organic material that provides flexibility and strength for the bone; without it the bone will not be very strong or flexible so it will wqq
what does collagen provide the bone
it is organic material that provides flexibility and strength for the bone; without it the bone will not be very strong or flexible so it will snap and break easily and will be brittle; will not be able to be flexy; the bone will be all ca+ so it will be very resistant to bending and snap very easily and be very very hard
what does ca+ inorganic composite for the bone provide the bone
it provides resistance to compression and bending; if no ca+ , then the bone will be completely collagen it will be very bendy and flexible and will not resist the bending and compression, the bone will then be very soft and not hard
the human skeleton starts out as cartilage
it is hyaline cartilage
what two processes replace the hyaline cartilage?
endochondral ossification
intramembranous ossification
below the level of the skull bones (with a few skull exceptions) bones form by
endochondral ossification, also used by long bone to get adult height
the skull (and also clavicles) form by
intramembranous ossification
where does intramembranous ossification happen
in the fontanelles of the baby skull; it is connective tissue (mostly mesenchymal cells)
where does longitudinal growth of the bone occur
at the epiphyseal plates
is longitudinal growth regulated by
growth hormone is a big player
also thyroid hormones (testosterones)
how does longitudinal growth mimic endochondral oss.
organized array of proliferating and mineralizing chondrocytes lead bone formation and growth
structure of epiphyseal plate
deepest- zone of reserve cartilage– where chondrocytes are
zone of proliferation– chondrocytes begin to undergo mitosis
zone of hypertrophy and maturation— the chondrocytes stop dividing (amitotic) and get bigger–chondrocytes that reach the next zone enlarge and mature
zone of calcification— chondrocytes begin to die and their matrix begins to calcify as calcium salt is deposited in their matrix–
zone of ossification– the chondrocytes is now turned into bone– calcified cartilage is replaced with bone
direction of growth in which new bone is added+
up from the epiphyseal plate
so new bone will be added above the epiphyseal plate which is cartilage
epiphyseal growth
The growth plate, is a thin layer of cartilage where the growth of long bones takes place.
process of intramembranous oss.
1- the mesenchymal cells in the primary ossification cells begin to differentiate into osteoblasts
2- the osteoblasts in the primary ossification center begin to secrete organic matrix (osteoid, ground sub. + collagen), the blood vessels bring the calcium from the blood
3- the osteoblasts become osteocytes once they are encased in their secreted organic matrix that is now calcified due to the calcium
4- the osteoids surround blood vessels, forming trabecular/cancellous/spongy bone. These vessels will eventually form the red bone marrow.
5- Mesenchymal cells on the surface of the bone (around the primary ossification center) form a membrane called the periosteum.
6- Cells on the inner surface of the periosteum differentiate into osteoblasts and secrete osteoid parallel to that of the existing matrix, thus forming layers. These layers are collectively called the compact bone on towards the periosteum and the spongy bone towards the inner part
mechanical stress for bones
-necessary for bone growth
- determines where remodeling occurs
- Wolff’s law: bone grows or remodels in response to demands placed on it
vigorous exercise can strengthen bone
-added bone matrix counteracts added stress, so the more stress added, the more bone matrix developed which is strong
-bone, unlike cartilage, have a better blood supply- this is why it is worse to break a tendon
endochondral oss. literal meaning
endo- inside
chondral- cartilage
oss.- bone
inside cartilage bone formation
types of cartilage replaced by bone
hyaline
where does endo. ossi. happen
all bones below the skull except the clavicle
general process of endo. ossi.
1- start with cartilage
2- chondrocytes stop proliferating, get larger and die
3- osteoblasts secrete organic matrix and calcify the cartilage. the organic matrix will become the bone after the calcification is done
4- lots of endo. ossi. is finished by birth, but not all of it. the epiphyseal plates do not completely close (finish ossifying) until late teens or early 20s
where do osteoblasts come from?
-at bone collar:: chondroblasts or osteogenic cells differentiate into osteoblasts
-at primary and secondary ossi. centers: osteoblasts may be brought in via the blood (along with other cells)
intramembranous oss. literal meaning
bone formation inside the membrane
what membrane- the fontanelles of the infant head
where does intramem. ossi happen
in th ebaby skull
in the fontanelles
general process of intra. mem. ossi.
in the fontanelles tehre are mesenchymal cells that become osteoblasts that lay down matrix
Mesenchymal cells differentiate into osteoblasts and group into ossification centers
Osteoblasts become entrapped by the osteoid they secrete, transforming them to osteocytes
Trabecular bone and periosteum form
Cortical bone forms superficially to the trabecular bone
Blood vessels form the red marrow
when do fontanelles close
do not become fully ossified until 2 years of age
what do these types of bone formation have in common
they are both closely linked with angiogenesis or blood vessels formations.
some of the same growth factors (likehai growth factor VEGF) are necessary for both to occur
many of the same signals are likely used for both
hair structure
medulla- middle or center
cortex- outer to the medulla
cuticle- very outer part
hair structure part 2
melanocyte
hair papilla
matrix
cortex
cuticle
medulla
dermal root sheath
epithelial root sheath
hair follicle- a tube-like structure (pore) that surrounds the root and strand of a hair
