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Zygote
A one-celled organism formed by the union of a sperm and an egg.
4 basic cell functions
multiply, move, signal, differentiate
Spermatogenesis
Formation of sperm
Oogenesis
formation of egg, each division produces a polar body so that there is lots of cytoplasm in the oocyte so it can survive
fertilization
12-24 hours after ovulation
First stages of life order
fertilization 2) one cell stage (zygote) 3) first cleavage
first week
cells undergo cleavage using energy from cytoplasm (costly) to create blastocyst
blastocyst
has cell differentiation
Embryoblast
inner cell of blastocyst (future embryo)
trophoblast
outer layer of blastocyst (supportive structure)
second week
blastocyst gains access to uterine wall (blood) and embryoblast divides in to two
epiblast
top layer of embryoblast division (future embryo)
hypoblast
bottom layer of embryoblast division (yolk sack)
Gastrulation
begins with a primitive then three germ layers: ectoderm, mesoderm, endoderm
ectoderm
originally the epiblast/ will form head, nervous system, epidermis
primitive streak
an invagination that develops along midline on dorsal side starting from caudal end formed from inward migration and rapidly dividing and differentiating epiblast cells (first hypoblast cells are replaced and epiblast cells form endoderm then they form mesoderm)
mesoderm
mid section formed by migrating epiblast cells/ skeletal, muscle, lymph, reproductive systems
endoderm
formed from epiblast cells that replace hypoblast/ digestive, respiratory, most of endocrine
notochord
hardened rod down central axis formed from mesoderm
third week
embryo has three layers
Neuralation
the process of forming the neural tube which will become the CNS
neural folds
ends of stiffened ectoderm that rise and cause neural groove
neural groove
depression caused by neural folds
neural tube
made from ectoderm, will become CNS
somites
segmented swells of mesoderm along the notochord.. will form repetitive structures such as vertebrae
lateral mesoderm parts
splanchnic (lower) and somatic (higher)
visceral peritoneum
formed from the splanchnic mesoderm and lines the external surface of organs
parietal peritoneum
formed from the somatic mesoderm and lines the internal body wall
mesentries
formed by connection of left and right splanchnic mesoderm/ double layered/ used to tether organs to body
coelome
big empty space between gut tube/splanchnic mesoderm and somatic mesoderm which will develop in to the abdominal cavity
neural plate
folds to create neural tube.
Blind Watchmaker Analogy
evolution by natural selection is agentless (blind) so how could something so complex have no "guide"
solutions to blind watchmaker problem
many steps to make changes 2. the process of development promotes and permits evolution because there is lots of integration between many modules
evolutionary change
descent with modification (development is hierarchical)
Somite differentiation
sclerotome and dermomyotome
sclerotome
gives rise to the vertebrae
Dermomyotome differentiation
dermatome and myotome
Afferent neurons
neural crest cells sent out on dorsal side (sensory receptors to CNS)
efferent neurons
neural crest cells sent out on ventral side (CNS to motor receptors)
myotome cells
mesoderm cells that form muscle and migrate and bring neurons with them
epaxial
myotome nerve cells on dorsal side
hypaxial
myotome nerve cells on ventral side
Vertebra formation
each vertebra is half of one segment plus half of another so that spinal nerves emerge between vertebrae and muscles cross over.
Primitive Fins
specialized flaps of the body wall (lateral plate mesoderm). Muscle splits on either side in to elevators and depressors
bud
beginning of a limb in lateral plate mesoderm. position is determined by somite signaling
apical ectodermal ridge
organization center on the most lateral part of the bud that sends out signals causing cell differentation
Head key facts
heads like limbs are evolutionary novelties 2. many distinct modules become highly integrated 3. lots of opportunity for integration
neural tube segments
forebrain, midbrain, hindbrain, spinal cord
neural crest cells
migratory, pluripotent (can differentiate into many types), go over head like hoodie and form face or become branchial arches
Branchial Arches
streams of neural crest cells that go over sides like collar and form gills or neck. They have a nerve, blood vessel, ectoderm, endoderm, and mesoderm.
cleft
neural crest cells fail to fuse at midline
functional roles of the skeleton
stiffness 2) strength 3)mineral (Ca++) homeostasis, 4) make blood 5) permit movement around joint
purpose of skeleton
oppose gravity, allow muscles to generate movement, protect organs
strength
maximum force before failure
stiffness
resistance to deformation (force over change in length)
hinge joints
one axis of rotation
metacarpo-phalangeal joint
two axis of rotation
ball and socket joint
three axis of rotation
Epiphysis
ends of bone - mostly trabecular
metaphysis
between diaphysis and epiphysis
diaphysis
shaft of bone mainly compact bone
compact bone
hard and dense bone tissue (in diaphysis)
trabecular bone
spongy bone mainly in epiphysis, arranged in layered plates and reduces bone mass while maintaining strength
Bone is a two phase tissue because
this allows bone to be strong, stiff, and tough
organic layer of bone
collagen type 1, arranged in a criss cross formation
mineral layer of bone
calcium phosphate
circumferential lamallae
layers around surface of bone
osteonal
tube-like layers around a vascular channel (bone is well vascularized to supply cells)
appositional modeling
changes to bone tissue only happen on preexisting surfaces
other connective tissue
cartilage, ligament, tendon, muscle
osteoblasts
bone forming cells (become osteocyte in mineralized tissue)
chondroblast
cartilage forming cells (become chondrocyte in mineralized tissue)
fibroblasts
tendon and ligament forming cells?
chondroclasts
cartilage destroying cells
osteoclasts
Bone-destroying cells: 1) secrete H+ ions which form HCl and use lysosomes to dissolve collagen 2) reabsorb dissolved material and release in to blood
two step synthesis of bone
osteoblasts lay down extracellular collagen matrix 2) mineralization
mesenchyme
undifferentiated progenitor cells (mesoderm)
intramembrous bone formation
membrane changing into bone (skull and mandible)
endochondral bone formation
cartilage model as starting point
cartilage
flexible tissue that allows for both internal and surface growth (early embryonic skeletal growth is more rapid)
growth plate
allows increased in bone length via cartilage
adaptive bone remodeling
adding mass when there is more force, mostly for animals because humans peak bone mass occurs 28-30
Osteoporosis
occurs with aging, effects trabecular bone, occurs when bone resorption is faster than bone deposition
major factors affecting bone health
exercise, smoking, pregnancy, genetics, calcium
3 major systems integrating body functions
endocrine, immune, and nervous systems
endocrine glands
secrete hormones into the bloodstream
hormones
specialized chemical messengers secreted into bloodstream which travel to specific organs or cells to exert physiological control
amplification (endocrine system)
hormones secreted in small and amounts and are effective in low concentrations because of amplification due to intracellular cascades
Peptide hormone mechanisms of action
first messenger in blood and second messenger in cell, this first and second messenger situation leads to cascades
steroid hormone mechanisms of action
hormone passes into membrane and binds to receptor then this complex enters the nucleus and triggers gene transcription (gene transcription leads to amplification)
breadth (endocrine system)
breath of hormone action: broad effect
broad effect (hormone)
many cells have receptors for this hormone (thyroid hormone)
narrow effect (hormone)
only some cells have receptors for this hormone (oxytocin)
receptor selectivity (endocrine system)
hormones only act on cells that have the receptors for them
glands (endocrine system)
can secrete more than one hormone
hormones (endocrine system)
secreted by more than one gland and can have other functions in the body
permissiveness (endocrine system)
two hormones may both be needed to produce an effect
peptide/protein hormones
amino acid chains, receptors on cell membrane
steroid hormones
small lipid soluble structures that have receptors in the cytoplasm of cells
Note 
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