embryology

early stages

(ovary) graafian follicle --> (fallopian tube) postovulatory ovum --> fertilization at the ampulla --> zygote formation -> first segmentation --> 2 cell stage (30 hours) --> morula stage (day 3) --> entry into the uterine cavity --> blastocyte (day 4-5) --> implantation (day 5-6)

five segments of juvenile and neonate sacrum

- 21 separate primary centers - intervertebral fusion begins in childhood - fusion of centra delayed until adulthood, requires many years to complete - female sacroccygeal joint often remains unfused throughout life

atypical vertebrae

- base of occipital bone forms from somites as if it were a vertebra - C2 body and neural arch develop from two half somites like most vertebrae - transverse process C7 shows homology to ribs most obviously

primary ossification

- bone formation in primary ossification centers begins before birth

septum transversum

- contributes to diaphragm - farthest from axis so pushed furthest after cranial fold - the septum transvedsum is a block of mesoderm - initially it forms at the cranial end of the embryonic disc - the septum transvedsum is farthest from the cranial fold axis so it is pushed farthest posteriorly - it will not bisect the gut tube but it compresses the intraembryonic coelom and participates in dividing it - drags motor neurons

urinary bladder and urethra

- derived from endoderm just like rectum and anal canal

dens

- despite its position, the dens isn't the atlas centrum - the dens is in the position of a centrum of C1, but at no point is it fused to other parts of the atlas - C2 body and neural arch develop from two half somites like most vertebrae

cervical neural arches

- expand ventrally to form lateral parts of vertebral bodies - thoracic transverse process element becomes transverse process and rib - centrum element of lumbar vertebral body enlarges greatly

secondary ossification

- five secondary ossification centers appear by puberty - tips of transverse processes (2), superior and inferior end plates of vertebral body (2), tip of SP - begins after birth - begins first in the atlas and axis and last in sacrum and coccyx

meningocele

- fluid in empty space above vertebra (subarachnoid space containing cerebrospinal fluid) - protrudes out/ covered by skin

physiological herniation of midgut

- hematopoiesis: in late embryo, liver is large - its size crowds the midgut into the umbilical cord (what anchors it?) - week 10/11: the midgut tube returns to the abdominal cavity - the gut tube folds and rotates as it returns, folding arranges the small intestine across the abdominal cavity - rotating locates the colon around the abdominal cavity

anal canal

- hind gut meets body wall at pectinate line (above pecten aka proctodeum) - above pectinate line: endoderm surface, portal venous system - below pectinate line: ectoderm surface, (inferior vena) caval system

completion of lateral folding

- neural crests develop - somatic mesoderm pushes out and around dragging ectoderm with it forming intraembryonic body cavity - splanchnic mesoderm pushes down and pinches yolk sac - part of the former yolk sac is pinched into the gut tube - the tube is surrounded by mesoderm (splanchnic mesoderm) - gut tube is connected to mesoderm layer via dorsal mesentery

myeloschisis

- open spinal cord - no fusion of neural arch + split of spinal cord

formation of typical vertebral body

- parts of two scleretomes makes a typical vertebral body and disc - cranial and caudal half scelertomes from adjacent somites merge to form each vertebra and disc caudal to C2 - a spinal nerve that ran though a somite passes between vertebrae via the IVF

divisions of the intraembryonic coelom

- peritoneal space - left pleural space - pericardial space - right pleural space - peritoneal space

intermediate mesoderm

- relatively slender - develops into organs of the urogenital tract

pericardioperitoneal canals

- right/left pleural sacs - parts of intraembryonic coelom - the cranial fold puts the bend in the intraembryonic coelom between the pericardioperitoneal canals and the midline "pericardial area" - the cranial fold displaces the "pericardial area" ventrally and caudally - part of the intraembryonic coelom - midline intraembyronic coelom becomes pericardial sac

intraembryonic coelom within the lateral plate mesoderm

- somatic mesoderm layer = somatopleure --> body wall and limbs - splachnic mesoderm layer = splanchnopleure --> soft tissues surrounding the gut tube and lungs - intraembryonic coelom --> various cavities of the trunk (anterior portion appears closed, posterior portion opens laterally to right and left) - initial formation of intraembryonic cavity is made by lateral folding - splanchnic mesoderm is the medial margin of the intraemryonic coelom) surrounds the gut tube

somite elaboration

- somitomeres and somites develop from paraxial mesoderm - somites are distinct blocks of tissue - each somite is a clump of cells that will be associated with a segmental nerve and vasculature - somites divide into regions with exclusive fates: dermomyotome, sclerotome, dermatome, myotome - cranially located somitomeres are less distinct

monozygotic twins

- splitting of inner cell mass - shared placenta and chorion

chorion

- surrounds amniotic cavity which surrounds fetus

human embryo at end of week 4

- the connecting stalk approaches the yolk stalk - the extaembryonic coelom is crowded away by the amniotic cavity - septum transversum, heart bulge, yolk sac, connecting stalk

identifying homologous elements in various vertebrae

- the thoracic transverse process has no rib element contribution unless you say the rib is part of the TP - facet joint is always part of neural arch - rib element is always anterior to transverse process - neural arch always contributes to vertebral body

spina bifida occulta

- tuft of hair on skin that covers unfused vertebral arch

dizygotic twins

- two fertilizations in one cycle - separate placentas and membranes

myelomingocele

- worst than meningocele - displaced spinal cord in subarachnoid space bulging out of skin (creating membranous sac)

end plate epiphysis

-forms distinct rim of compact bone - may remain evident in adult bone

dividing the mesoderm

. Discuss division of embryonic mesoderm into columns of somites and somitomeres in the paraxial mesoderm, a line of intermediate mesoderm and a region of lateral plate mesoderm. - paraxial mesoderm (somites (thicker clumps more caudal, associated with thoracic nerves, lateral to neural crest, more vertebra = more somites) and somitomeres (thinner by neuropore - associated with cranial nerves), many body wall tissues) - intermediate mesoderm (thin column, forms urogenital organs) - lateral plate mesoderm ( intraemryonic coelom, body wall and viscera) - folding of the embryonic sic (cranial and caudal folding, lateral folding)

development of the diaphragm

. First list the four embryonic structures that fuse to form the diaphragm: septum transversum, dorsal mesentery of esophagus, pleuroperitoneal membranes and lateral thoracic wall, then explain the neuroanatomical consequences of the contributions from the septum transversum and thoracic wall. - dorsal esophageal mesentery - pleuroperitoneal membrane - septum transversum - thoracic body wall

clinical anatomy

ANTERIOR BODY WALL DEFECTS. Distinguish two distinct congenital defects of body wall closure: gastroschisis and omphalocele. gastroschisis: -intestine protruding through abdominal wall defect - improper fusion of lateral folds - can include stomach and intestinal loops - herniation may not include the umbilicus - typically accompanies other congenital anomalies - often incompatible with life omphalocoele: - abdominal viscera herniating into base of umbilicus - congenital umbilical herniation - amnion covers the herniated viscera - good surgical prognosis

formation of placenta

Describe growth of the cytotrophoblast and the changes in the endometrium to show how the placenta forms as a combination of extraembryonic tissues and maternal tissues. a. The placenta is connected to the fetus by the umbilical cord, which contains the umbilical artery and umbilical veins. It supplies oxygen and other nutrients to fetal blood, and it removes CO2 and other waste from fetal blood. It is the only means of nutrient supply and waste removal for the fetus. b. The placenta grows throughout the pregnancy, and it weighs about 500 grams at birth. c. The surface of the placenta that is exposed to the uterine lumen itself is composed of syncytiotrophoblast cells. That surface is covered by the amniotic layer, with the total covering being amniochorion just like all of the rest of the gravid uterine cavity. d. The functional part of the placenta is composed of a combination of "fetal" chorionic tissue (chorion frondosum) and tissue from the maternal uterine endometrium. e. The chorionic tissue grows into the maternal endometrium by forming chorionic villi. These are microscopic extensions of cytotrophoblast and extraembryonic mesoderm that consume the endometrium and anchor the developing placenta to the uterine wall.

yolk sac

Describe the changes that the yolk sac undergoes in early stages of development, and associate those changes with development of the vitelline duct and vitelline vessels. a. Think first about how the combination of the cranial fold, caudal fold and lateral folds brings the amniotic cavity completely around the embryo that is newly formed as a tubular or elongated structure (it has lost its original disc shape). b. Prior to that, where was the yolk sac relative to the trilaminar embryonic disc? under the endoderm surface c. When the tubular embryo is formed by folding, what happens to that sac? the middle part of it becomes a thin tube, the yolk stalk d. Is any part of it still in contact with endoderm? If so, where is that? yes, it is inside the embryo, forming the gut tube e. What extraembryonic structure of late embryonic life and all of fetal life is produced as a result of all of that folding and by manipulation of the yolk sac? umbillical cord f. We have to add a new term to say what part of the structure named in the answer to the previous question is a part of the former yolk sac. vitelline duct g. Notice that the blood vessels there take the same name. What are they called? vitelline artery and vitelline veins h. That story concerned changes that happen to the definitive yolk sac in placental mammals. Now go back in time to earlier stages. What development caused the primitive yolk sac to divide into a remnant and the secondary yolk sac? expansion of the extra embryonic coelom

caudal fold of the embryo

Discuss the caudal fold of the embryonic disc and its effects on development of the abdominal wall and pelvis. - major consequences of caudal fold: position and contents of umbilical cord - caudal fold brings allantois and connecting stalk ventrally - cloacal membrane tucks ventral to coccyx (tail) - develops heart bulge

clinical anatomy: fetal membranes

Discuss the causes and consequences of polyhydramnios, oligohydramnios and amniotic bands. a. This objective means "Name some conditions that cause polyhydramnios and oligohydramnios, discuss the clinical consequences of polyhydramnios and oligohydramnios, and know a little bit about amniotic bands, too." b. b. Polyhydramnios is too much amniotic fluid. It is not intrinsically harmful to the mother or fetus. c. c. Oligohydramnios is insufficient amniotic fluid. That limits fetal movement and growth, so it is intrinsically harmful. Severe cases of oligohydramnios can be fatal to the fetus and create serious ailments for the neonate. d. d. Ultrasound is useful in the diagnosis for both, and both have, very roughly speaking, about 1% incidence. e. e. Two of the various possible causes of polyhydramnios are decreased fetal swallowing and increased fetal urine output. f. f. When polyhydramnios is present, you must consider the possibility of atresia of the upper digestive tract (usually the esophagus), which prevents swallowing. Gut tube atresia is not something we have studied directly. Find out about it, and explain it using knowledge you gained by mastering these embryology objectives. g. g. Two of the various possible causes of oligohydramnios are decreased fetal urine output and ruptured fetal membranes. h. h. Why is limitation of fetal movement harmful to a neonate? i. i. Amniotic bands limit the movements and growth of the fetus, and problems ensue. Are those problems more like polyhydramnios or more like oligohydramnios? j. E3.09. CLINICAL ANATOMY: FETAL MEMBRANES k. f. The foregut that derives from the embryonic gut tube goes through an early stage when it is entirely blocked with epithelioid cells, then it recannulates. (It starts as a tube, fills in, then becomes a tube again.) If the esophagus does not reopen properly, the fetus cannot swallow amniotic fluid. Inability to swallow causes very severe problems for the neonate, but the excess amniotic fluid is not very serious. l. h. Inadequate respiratory muscle function and rib movement at birth. m. i. Olioghydramnios.

cranial fold of the embryo

Discuss the cranial fold of the embryonic disc and its effects on development of the head and thorax. - major consequences of cranial fold: positions of mouth and thoracic organs - cranial fold is caused by expansion of the head (mostly brain) - brings structures ventrally and caudally - parts that are most cranial end up in the middle of the trunk (these tissues go to thorax) - axis of the cranial fold is near the buccopharyngeal membrane (tissues around the axis become mouth and face)

timing of prenatal events

Discuss the sequence and staging of specific events in embryonic development and fetal life in the context of the eight week embryonic period of Homo sapiens and a full term pregnancy. a. We have already mastered some of this objective. b. Let's not add any new material, but just recognize that this makes any of the timings we have already discussed fully testable.

neurolation

E2.01. NEURULATION. Describe the prerequisites, processes and outcomes of neurulation of the ectoderm layer of the trilaminar embryonic disc including induction of the neural plate, formation of neural crest cell masses and closing of the neural tube. - neural plate induced by notochord - neural plate forms near midline only - development inhibited laterally by BMP-4 molecule - the plate folds upward bilaterally - neural grooves form between neural folds - neural crest forms from the lateral part of the neural plate - the notochord is cranial to the primitive pit, so the neural tube is cranial to the coccyx neural plate --> neural crest --> (fuse) --> neural tube - mesoderm growth from primitive streak

clinical anatomy: nueral tube defect (NTDs) processes

EXAM explain how neural tube defects occur form failures normal processes of neurulation - Schisis (looks split, right and left sides of neural tube don't fuse properly) defects: what has failed to fuse (spina bifida (not proper spinus process), spina bifid a occulta (skin closed over lesion nicely, can't see the problem,hair), myeloschisis (inside the spinal cord split, spina biffida + split spinal cord) -Cystic defects: what fills the bulge (meningocele (just fluid in space of meninges,bulge), myelomeningocele (spinal cord in the cyst or bulge even skin not over it, worse than menigocele), encephalocele (failure of cranial neural pore to close, brain protruding in a closed area))

timeline

Embryogenesis (establish systems and detect pregnancy): conception 0-1 weeks, implantation week 1 - 2, bilaminar disc week 2-3 , trilaminar disc/neurulation weeks 3-8 (embryo forms) Organogenesis (grow and elaborate established systems, detect defects): fetus forms week 8-38

thoracic cavities

Explain how barriers that divide the intraembryonic coelom of the developing trunk of an embryo produce the pericardial sac, the pleural spaces and the peritoneal cavity.

dividing the cloaca

Explain how dividing the distal part of the hindgut lengthwise with the urorectal septum forms a pair of parallel endoderm-lined canals (urinary bladder and urethra, rectum and anal canal) in the pelvis. - cloacal membrane is exposed to yolk sac and amniotic cavity - allantois is cephalic to cloacal membrane - caudal fold brings allantois and connecting stalk ventrally - urorectal septum arcs toward the cloacal membrane - urorectal septum divides cloaca (between urogenital sinus and distal hindgut, contacts cloacal membrane - anal part of cloacal membrane soon degenerates

basic vertebrate body plan

How does a row of nerves between bones develop from a row of somites, each with a nerve growing into its middle? - muscles and nerves between ribs - nerve into muscle from spinal cord

umbilical cord

List the extraembryonic structures that form the umbilical cord, describe the process of their joining, list the parts that remain in the later fetal stages, and discuss the functions of those parts. . The umbilical cord forms when the caudal fold shifts the connecting stalk ventrally and cranially to meet the yolk stalk. b. Elements that contribute to the core of the umbilical cord: connecting stalk; yolk stalk containing vitelline duct, vitelline arteries, vitelline veins. c. What forms the external lining of the umbilical cord? amnion - connecting stalk and yolk stalk fuse to make umbilical cord - embryo bathes in amniotic fluid - eurtherian mammals get little nutrition form the yolk sac ( the placenta will provide the necessary ongoing nourishment) - funcitonally, intervillous spaces replace the lacunae - 3 fetal layers between maternal blood and fetal blood

fetal membranes

Organize the layering of the amnion and the chorion by recognizing their relationships to the embryonic discs and by reasoning through the topographical changes they must undergo as the trilaminar disc becomes an embryo and the embryo grows to become a fetus. a. What space gets partially incorporated into the embryo as a result of folding? yolk sac b. What space necessarily comes to surround the embryo (and later the fetus) as a result of folding? What is the name of the membrane or tissue layer (epithelium with supporting connective tissue) that forms the external surface of that space? amniotic cavity. amnion c. What space had been external to that? extraembryonic coelom d. The layer that surrounded that outermost space is the chorionic membrane. As the outermost space is exceeded by the space surrounding the fetus, their membranes contact and become more or less fused, and they are in direct contact with the walls of the uterus. e. The combined membranes are the amniochorionic membrane. f. Name the fluid that bathes the fetus. amniotic fluid g. The fetus urinates into the fluid surrounding itself. That is an important source of volume for the fluid. The fetus also drinks the fluid and eventually breathes it, too. These are essential exercises for the fetus in preparation for birth, and they regulate fluid volume. This, by the way, is another "key point" such as we discussed in Objective 1.09. It is memorable because it seems a little strange, and it leads on to two clinical conditions in the next objective.

physioanatomy: placenta

PLACENTA. Relate the structure of the placenta to its role in exchange of nutrients and waste between the fetal circulation and maternal circulation. a. Recall that maternal blood flows from the endometrial capillary sinusoids into lacunae, so maternal blood contacts the syncytiotrophoblast directly. b. In higher primates (monkeys, apes, Homo sapiens) and various other mammals, the placenta is hemochorial--maternal blood has direct contact with chorion cells of villi without an intervening maternal cell layer. Normally, there is no direct sharing of blood because three fetal layers intervene. c. Those three layers are trophoblast epithelium, placental connective tissues and endothelium lining the fetal blood vessels. The fetal blood remains sealed in its circulatory system in a way that the maternal blood is not. d. Additionally, the endometrium is richly nourished and able to donate nutrients released from its own cells. e. Maternal IgG antibodies, most maternal hormones, and some microbes can cross the maternal-fetal barrier. f. What about prescription drugs or over-the-counter drugs given to or taken by the mother? some can cross, some cannot g. Alcohol? yes h. Name at least one fetally produced hormone that affects the mother. chorionic gonadotropin, somatomammotropin

early gut tube development

Recognize how physiological herniation of the midgut during the transition from embryo to fetus brings together anatomy of the vitelline duct, development of the intestines and closure of the body wall d. And the word "anatomy" for the vitelline duct is intended to remind us to think of "source, course and destination." What is the vitelline duct attached to at its distal end? yolk sac e. What is the vitelline duct attached to at its fetal end? We need that attachment to tell the story. (midgut?) - vitelline duct distinguishes midgut from foregut and hindgut - foregut most cephalic/rostral - hindgut most dorsal, dorsal to yolk sac - foregut has ventral and dorsal mesenteries - esophagus, stomach, proximal small intestine, liver, panceras - midgut phsyiological herniation - distal small intestine, proximal large intestine - hindgut - the urorectal septum divides the cloaca, perforation of the cloacal membrane - distal colon, rectum, anal canal

lateral folds of the embryo

Show how lateral folding of the trilaminar disc forms the enclosed cylindrical shape of the embryo. - major consequences of lateral folding: gut tube's shape, external surface of embryo, umbilical cord - completion of lateral folding forms the yom stalk - the disc becomes an embryo and it is surrounded by amniotic cavity covered in ectoderm which fuses together to form a cavity and pinches the yolk sac into the gut tube (which runs the vertical length of embryo) - the yolk stalk only exists near the region where the umbilicus will form - ectoderm around circumference (lateral edges)

somite destination

State the adult tissues or regions for which the sclerotome, myotome and dermatome are the embryonic sources.

intraembryonic coelom

Understand how the shape and position of the intraembryonic coelom allow it to be divided into the pleural cavities, the pericardial cavity and the peritoneal cavity in different parts of the developing trunk. - empty space in the mesoderm - opens into extra embryonic coelom - has horseshoe or U shape - midline cranial pat is anterior to the prechordal plate - caudal ends of the U open into the extra embryonic coelom - lateral folding brings caudal ends together to form peritoneal cavity -LATERAL PLATE (3 layers): - somatic mesoderm closer to ectoderm - intraembryonic coelem (horse shoe around rostral end (buccopharyngeal end) then opens at caudal end like a tunnel, tubular (connects caudally to extra embryonic coelem, closes after lateral fold) - makes pericardial sac, greater and lesser sac, peritoneal sac) - splachnic mesoderm layer closer to yolk sac (make soft tissues surrounding around lungs and gut tube, splanchnic means "guts")

mesoderm defects (VACTERL)

Vertebral defects Anal atresia Cardiac defects Tracheo-Esophageal fistula Renal defects Limb defects (bone/muscle)

trophoblast differentiation

associated with implantation (late in week 1) trophoblast differentiation: syncytiotrophoblast - an invasive outer multinucleate mass of cytoplasm inner cuboidal cells of cytotrophoblast - source cells for synctiotrophoblast and for early membranes placenta is made tom syncytiotrophoblast

early infolding at primitive streak

begins crowding out hypoblast cells and replaces it with forming endoderm

neural crest

bi lateral to the neural tube and formed from lateral part of the neural plate starts in the location of the dorsal root ganglion meninges (dura, arachnid, pia), melanocytes, nerve ganglia, adrenal medulla, heart valves from neural crest (contributes little to CNS)

neuroectoderm (neural plate)

brain (neurohypophysis, CNS neurons, oligodendrocytes, astrocytes, ependymal cells, pineal gland), retina and optic nerve, spinal cord think CNS

elaboration of the bilaminar germ disc

caudal end of membrane - cloacal membrane rostral/cranial end - buccopharyngeal membrane both membranes consist of tightly bound epi and hypoblast squamos cells two places within germ disc where mesoderm cells cannot be pushed (create asymmetry in trilaminar disc)

teratogen

cause severe birth defects

sclerotome

centrum - drift ventrally - makes the IV disc - mesenchyme cells of the sclerotome that remain near the notochord form vertebral bodies lateral parts of the sclerotome grow dorsally to form the neural arch

chodnrification and ossification

chondrification: - mesenchymal cells of sclerotomes differentiate into chondroblas cells that will make cartilage - separate chondrification centers merge to form cartilaginous models of whole bones 0ssification: - occurs at specific times and specific sites called ossification centers - week 6

embryology

classical - descriptive (good starting point) experimental embryology - as physiology of growth molecular biology and developmental biology - genes and environments, lilies "great paradox" ( comparitive biology - indications of a shared heritage, staging of embryos

vertebral unit developmetn

describe how division of each sclerotome into a cranial section and a caudal section followed by fusion of those segments locates spinal nerves between bones but within myotomes and dermatomes - development of individual vertebrae: typical vertebrae, atlas, axis and sacrum - parts of two sceleotomes make typical vertebral body and disc - cranial and caudal "half" sclerotomes from adjacent somites merge to form each vertebra caudal to C2 - the caudal portion of one somite and the cranial portion of the next somite = vertebra and disc

dermatome

develops into epaxial and hypaxial dermis (not epidermis)

myotome

develops into epaxial muscles (dorsal muscles of back, nuchal region) and hypaxial muscles (ventral muscles of neck, trunk and limbs; some muscles of head)

dermomyotome

divides to form the dermatome and myotome

dizygotic vs monozygotic

dizygotic - 2 oocytes released and both are fertilized monozygotic - single inner cell mass splits in 2

cell paths

early cells are totipotent restriction events lead to pleuripotency and ultimately to determination determined cells differentiate to reach the definitive state the ability to express specific genes underlies these cellular states

middle of week 2 (embyroblast)

embryoblast becomes bilaminar germ disc which floats in the extra embryonic coelom (expanding cavity in the trophoblast tissue) amniotic cells along the amnion cavity which is superior to epiblast layer which is superior to hypoblast layer which surrounds primitive yolk sac columnar epiblast cells and cuboidal hypoblast cells will form entire organism polarity of inner cell mass set by prechordal plate

bilaminar disc

epiblast, hypoblast 2 weeks = 2 layers

ectoderm

epidermis, lens of eye, epithelial linings of oral cavity, sensory organs of ear, olfactory epithelium, sweat, mammary glands

mesoderm

expands from primitive streak

chorionic villus sampling

f. You will be reading about risks and benefits of chorionic villus sampling, a biopsy procedure, as part of the Doctoring course. - invasive removal of chorionic tissue to assess genetic disorders - results are returned quickly because ample DNA is removed - primarily used for rare or suspected disorders - not recommended before 10 weeks of gestation - less than 3% rate of fetal loss - transabdominal approach for CVS is less risky than transcervical

later infolding at primitive streak

forms mesenchyme epiblast layer becomes ectoderm mesenchymal cells form between amniotic cavity and yolk sac (mesoderm) endoderm begins replacing hypoblast (crowds it out) (all three layers ecto, mess, endoderm from epiblast later)

allantois

goes into connecting stalk (part of bilaminar disc)

endoderm

gut tube epithelium(including anal canal above the pectinate line), most of urethra, luminal epithelial derivatives (lungs, liver, gallbladder, pancreas, eustachian tube, thymus, parathyroid, thyroid follicular cells)

basic vertebrate body plan: the process

how does a row of nerves between bones develop from a row of somites, each with a nerve growing into its middle? 1. sclerotome divides into a caudal and cranial half 2. cranial half of Sc2 splits into 2 halves (1/4s) - caudal half of Sc1 merges with half of the Sc2 (other half becomes intrevertebral disc) cranial half (1/4 portion of Sc2) to make a vertebra 3. caudal half of the cranial half of Sc2 remains unmerged and forms intervertebral disc 4. due to the merging of adjacent sclerotome segments a spinal nerve can run between the forming vertebrae and exit the intervertebral disc via and spinal cord via an intervertebral foramen

week 2 (events peripheral to the organism)

implantation continues trophoblast grows larger than the embryoblast as it forms membranes, spaces, and tissues which will nourish the germ cells while allowing them to grow and change

uterus

internal lining of the uterus is the endometrium or decidua oocyte released into peritoneal cavity once a month from ovary and goes into the oviduct via finger like projections called fimbriae and into the infundibulum. fertilization usually occurs just further into the uterine tube in the ampulla

extraembryonic coelom

makes room for folding the disc to form the embryo and becomes the chorionic cavity

chorionic gonadotropin

molecular structure similar to luteinizing hormone (LH) stimulates progesterone and estrogen secretion by maternal ovary stimulates testosterone secretion in male fetuses syncytiotrophoblast begins secreting chorionic gonadotropin in week 2 hCG detected in blood or urine for pregnancy test: must distinguish between LH and FSH molecules, super high levels, highly reliable by 6 weeks post last menstruation

misplaced implantation: ectopic pregnancy

most common: uterine tube interstitial uterine tube and cervical: improper locations within the uterus signs/symptoms: first trimester bleeding or pain consider history that results in limiting passage through uterine tube transvaginal ultrasound aids diagnosis

mesoderm

muscle, bone, connective tissue, serous linings of body cavities (peritoneum), spleen (derived from foregut mesentery), cardiovascular structures, lymphatics, blood, wall of gut tube, vagina, kidneys, adrenal cortex, dermis, testes, ovaries

neurulation

neural plate induced by notochord plate rises (crests) and folds upward bilaterally forms neural tube notochord inferior to neural tube neuropore - openings of neural tube at both ends (rostral/cranial and caudal)

fertilization

occurs in the ampulla of the oviduct fertilization of the oocyte by a spermatid produces a zygote cell with a full complement of nuclear DNA

Hox genes

often expressed where anatomical elements are laid out in craniocaudal series different combination of hox genes are expressed in primordial of each vertebra but similar combinations of Hox genes are expressed in adjacent vertebra - different Hox genes are expressed along the spinal column

ready for ovulation

one follicle within one ovary has matured to macroscopic size and migrated to the edge of the ovary

derivatives of embryonic tissues

or any adult gross anatomical structure, state whether each of its component tissues derives from endoderm, mesoderm, neural plate ectoderm, neural crest ectoderm or surface ectoderm, and discuss the functional or clinical relevance of these associations. a. State whether the following structures or tissues are derived from surface ectoderm, neural tube, neural crest, mesoderm or endoderm 1. epithelial lining of oral cavity (lips, gums and cheeks). ectoderm 2. epithelial lining of pharynx. endoderm 3. epithelial lining of esophagus and stomach. endoderm 4. epithelial lining of glands secreting into stomach and intestine (e.g., pancreas). endoderm 5. external surface of tympanic membrane ("eardrum"). ectoderm 6. connective tissue and small blood vessels within tympanic membrane. mesoderm 7. epithelial lining of auditory tube (Eustachian tube), tympanic cavity and internal surface of tympanic membrane. endoderm 8. preganglionic parasympathetic neuron in sacral region of spinal cord. neural tube 9. neuron in parasympathetic ganglion in descending colon. neural crest 10. smooth muscle in wall of descending colon. mesoderm 11. right upper molar tooth. ectoderm (enamel), mesoderm (deeper components) 12. brain neurons, for those who have any left. neural tube 13. mesothelial lining of pericardium, pleura or peritoneum. mesoderm 14. epidermis on dorsum of left hand. ectoderm 15. dermis on dorsum of left hand. mesoderm 16. sweat gland on dorsum of left hand. ectoderm 17. smooth muscle in wall of superficial vein on dorsum of left hand. mesoderm 18. endothelial lining of superficial vein on dorsum of left hand. mesoderm 19. red blood cells in superficial vein on dorsum of left hand. mesoderm 20. primary sensory neuron delivering sense of touch from dorsum of left hand. neural crest 21. left third metacarpal bone. mesoderm 22. left thumbnail. ectoderm b. Here are questions for some general principles that support the information you provided in the 22 points of "a" above. c. Where does ectoderm end and where does endoderm begin in the alimentary canal? between the cheek lining (oral vestibule) from the throat (pharynx) d. What structure that is present in the embryo but not in the fetus determines this location? buccopharyngeal membrane e. What source provides cells for the lining of gut tube extensions (i.e., auditory tube, airway and lungs, liver and other glands)? endoderm f. Nowhere do ectodermal and endodermal surfaces lie atop each other without an intervening layer of mesoderm (points 5, 6 and 7 above). g. What is the source of cells in nerve ganglia (e.g., dorsal root ganglia, sympathetic and parasympathetic ganglia)? neural crest h. The meninges and supporting cells of the peripheral nervous system derive from the same source, and also adrenal medulla and various other cells. i. Teeth have more complicated development than we care to study. j. The surface ectoderm is very thin. It has a few roles in addition to the epidermis of the skin: hair, nails and glands, lens and other eye parts, lining of oral cavity. k. Almost all vascular structures are derived from mesoderm (or from neural crest mesenchyme in the head and neck). l. Please define endothelium and endoderm relative to each other. m. Did you know that neural crest contributes to heart valves?

placenta

primary site of nutrient and gas exchange cytotrophoblast makes cells of placenta syncytiotrophoblast - secretes hCG

primitive streak

primitive node and streak are near the caudal pole in epiblast layer in what will become the midline of the disc primitive streak is limited to one end of the disc, but it will send cells broadly the node is slightly mounded borders around small indented primitive pit

trilaminar disc (gastrulation)

primitive streak, notochord, mesoderm and its organization, and neural plate begin to form 3 weeks = 3 layers

vertebral column development

recognize that formation of individual bones gives fine examples of interaction between genes and environment in development, and discuss how morphological differences between vertebrae are formed by modifications of homologous parts that were less distinct in the fetal or juvenile skeleton - formation of the spinal column: gene/environemnt interactions, dividing of somites, merging of sclerotomes, chondrification and ossification - regulatory genes and internal environment (internally generated mechanical forces, externally generated mechanical forces, internal chemical environment) both contribute to OSSEOUS MORPHOLOGY

development interaction between genes and environement

size and shape of bone is influenced by the internal strain environment bone growth is affected by the forces that are applied to the bone (muscle forces and gravity) before birth and after birth

blastocyte

superficial to deep: degenerating zone pellucida (to allow for growth and implantation), outer cell ring (trophoblast), inner cell mass (embryoblast), blastocoele (blastocyst cavity) expansion coincides with rupture of zone pellucida inner cell mass defines the blastocyts embryonic pole pleuripotency: trophoblast becomes membranes and placenta; embyroblast becomes embryo

development of placenta

syncytiotrophoblast erode maternal edothelium capillary sinusoids and the lacunae develop within the syncytiotrophoblast maternal blood makes contact with fetal tissue directly via lacunae and initial nutrient exchange occurs via diffusion without fetal circulation ultimately felt blood will be separated from maternal blood by fetal endothelium, cytotrophoblast connect tissue and cytotrophoblast cells

neural tube

the dorsal part of the tube develops from a different coding source than the ventral part which produces the spatial boundary of sensory input and motor output of the CNS - BMP (bone morphogenetic Proteins) are at caudal and rostral ends of neural plate - SHH (sonic hedge hog is at middle of plate)

buccopharygneal membrane and coacal membrane folding

the membranes start with amniotic sac and yolk sac, however they then become exposed to external and internal surfaces their yolk sac surfaces will be exposed to gut tube and the amniotic surfaces will remain relatively external

notochordal process and notochord

unique and distinct distinct tube of cells grows anteriorly on the midline between epiblast and endoderm limited anteriorly by the prechordal plate and buccopharyngeal membrane expansion is simultaneous with endoderm and mesoderm expansion the notochord develops form the tubular notochordal process

clinical anatomy: neural tube defect depths

use appropriate terminally to discuss the different manifestations of neural tube defects of varying depths

clinical anatomy: neural tube defect regions

use appropriate terminology to discuss manifest ions of neural tube defects in different regions of the head and vertebral column

vertebra formation

vertebra: - top half of one somite + bottom half another somite + nerves in the middle - make bone first in cartilage (chondrification) then ossify the cartilage (not grow like vertebra) - intramemrbanous bone (can grow/stretch) membrane (like skull) - primary ossificaiton ? - secondary ossifcation ?

Graafian follicle

will rupture through the ovary wall and its oocyte will be embraced by the fimbriae of the oviduct

mitotic division

zygote divides mitotically while encased in the zone pellucida (zone pellucida will not allow cell to grow larger and thus will need to degrade before the morula can become the blastocyst) cells are totipotent: can produce any of the cell lines of the embryo, membranes or placenta 8 divisions - sixteen cells - morula