Block 1 Review Flashcards
Spontaneous Generation Theory
began i.e. “new life arises from slime and decaying matter.
Held from the time of Galen for nearly 1500 years.
Suggested life came from inanimate objects
Preformation Theory
founded i.e., “sperm or ovum contain a germ that is completely formed bu minute and invisible and expands to visible size and form during development”
Suggested that there was a pre-formed individual in every gamete
Epigenesis Theory
founded, i.e., “egg lacks internal organization and develop into a new organism
Germ Layer Theory
founded i.e., “all animal embryos are composed of three primary germ layers, ectoderm, mesoderm, and endoderm”
Recapitulation Theory
founded, i.e. “ontogeny Recapitulates Phylogeny”
Embryo
the developing individual from fertilized until the end of the second month (8th week inclusive)
Fetus
the developing individual in utero from the end of the 2nd month (8th week) until birth
Zygote
the first diploid cell formed by the union of sperm and ovum
Gestation
the period of development prior to birth
Congenital Abnormalities
abnormalities or malformations detected at birth, or shortly thereafter
Anomaly
marked deviation from the average or normal standard. A congenital defect. May be structural or metabolic
Malformation
a morphological defect that results from an abnormal developmental process and usually causes a functional deficit
Variation
a morphological deviation from an assumed standard that causes no functional deficit
Syndrome
a “package” of congenital abnormalities that occurs in several organ systems as a result of a single factor
True Age
38 weeks (266 days) counting from the time of fertilzation or conception Embryologists use true age and it is the age used in Gross and Developmental Anatomy
Ovulation Age
True age + 1 day
because that oocyte has to be ovulated first and start its travel down the fallopian tube before it is normally fertilized
Copulation Age
True Age + 1 to 3 days
1 to 3 days represents the time period that a sperm is viable in the tract
Menstrual “Gestational” Age
True age + 14 days (290 days)
Obstetricians use menstrual age since this is the most practical from the clinical viewpoint. Two thirds of all deliveries occur 280 +/- 11 days from the onset of the mother’s LMP
Ovulation would have occurred about halfway through the female’s cycle - total cycle averages 28 days, so that extra 14 days is the time from LMP until ovulation
Mitosis vs. Meiosis
Mitosis: gives rise to two daughter cells, which are genetically identical to the parent cell
Meiosis: Process of reduction division of chromosomes
Takes place only in germ cells
Reduces number of chromosomes from a diploid (2N) to a haploid (1N) state
- Consists of two divisions
Spermatogenesis
Spermatogonium (2n) - @ puberty, increase in # by Mitosis They enlarge into primary spermatocytes (2n) -Meiosis I takes place- Secondary spermatocytes (1n) -Meiosis II takes place- Spermatids (1n) -Spermatogenesis- 4 mature sperm (1n)
spermiogenesis
when spermatids mature into mature sperm:
morphologic changes, including development of the acromosome and tail and an increase int he # of mitochondria
Oogenesis
Oogonium (2n) during early fetal life proliferate by mitosis [5,000,000 oogenia @ 12 weeks]
They enlarge into primary oocytes (diploid)
-[2,000,000 primary oocytes @ birth]
-Begin meoisis I (before birth)-
Completely meisos I (before ovulation) forming secondary oocyte (1n) and 1st polar body
-begin meiosis II at ovulation-
[300 needed and produced in lifetime]
Completely meiosis II at sperm penetration forming mature oocyte (1n) and 2nd polar body
Process of Fertilization
Passage of sperm through the corona radiate
Penetration of the zona pellucida
Fusion of plasma membranes of the two gametes
Completion of 2nd meiotic division of oocyte with formation of female pronucleus
Fusion of pronuclei, forming 2n zygote
Results of Fertilization
Completion of the 2nd meiotic division of the secondary oocyte (at fertilization)
Restoration of the 2n number of chromosomes in the zygote
Mixing of the ateral and maternal chromosomes to insure diversity of species
Determination of chromosomal sex
Initiation of cleavage
Normal site of fertilization
ampulla of the uterine (fallopian) tube
Normal site of implantation
posterior wall of the uterus
Most common site for abnormal implantation
within the fallopian tube near the ampulla
During week 2, trophoblast differentiates into:
cytotrophoblast and syncytiotrophoblast
During week 2, the embryoblast differentiates into:
epiblast and hypoblast
During week 2, the mesoderm differentiates into:
the somatic (epiblast) and splanchnic (hypoblast) mesoderm
Primary Chorionic Villi
solid primary villi composed of a cytotrophoblast core covered by syncytium
secondary chorionic villi
mesenchyme grows into primary chorionic villi to form a mesenchymal core
-cover the entire chorionic sac at this time
tertiary chorionic villi
mesenchyme differentiates into capillaries and blood cells
Hydatiform Moles
Secrete high levels of hCG
Sometimes the trophoblast develops and forms placental membranes with little or no embryonic tissue present
Degenerating chorionic villi that form cystic swellings after embryonic death form hydatiform moles
look like grape like projections
Placenta
“afterbirth”
the primary site of nutrient and gas exchange between the mother and the fetus
Two components:
-fetal part - develops from chorionic sac (chorion frondosum)
-Maternal part - develops from the endometrium of the uterus (decidual basalis)
Functions: protection, respiration, nutrition, excretion, hormone production
Extraembryonic mesoderm + syncytiotriphoblast + cytotrophoblast = chorion
Decidua
the functional layer of the uterine endometrium in a pregnant woman
“falling off”
Three regions:
Decidua basalis: deep to the conceptus - forms the maternal part of the placenta - between teh chorionic vesicle and the myometrium
Decidua capsularis: superficial part of the decidua overlying the conceptus
Decidua parietalis: remaining endometrium lining the main cavity of the uterus
Decidual reaction: cellular and vascular changes in the endometrium as the blastocyst implants
Placenta Accreta
abnormal adherence of chorionic villi to the myometrium
Placenta Percreta
when the chorion villi penetrate the full thickness of the myometrium to or through the perimetrium (peritoneal covering)
- Abnormally tight connection between the placenta and uterine wall
- more difficult to separate this plcenta from the uterus after birth; may require going in to scrape it out
Placenta previa
most common
when the blastocyst implants close to or overlying the internal os of the uterus
Considered an ectopic site of implantation
May result in late pregnancy bleeding (3rd trimester)
Battledore Placenta
insertion of the umbilical cord at the placental margin
Accessory Placenta
can develop from a patch of chorionic villi that persisted a short distance from the main placenta
-Inspect maternal surface of placenta after birth to make sure that any portion (like a cotyledon) was not left inside the uterus - may cause bleeding it not all removed
Velamentous insertion of umbilical cord
cord is attached to the membranes (amnion and chorion), not to the placenta; umbilical vessels leave the cord and run between the amnion and chorion before spreading to the placenta
-Vessels can be easily torn in this location, which would cause the fetus to lose blood supply
Amniotic sac
surrounds the embryo/fetus
Enlarges to obliterate the chorionic cavity and forms the epithelial covering of the umbilical cord
Amniotic Band Syndrome
various defects related to constriction of parts of the embryo/fetus by encircling amniotic bands; can wrap around an extremity, causing it to die or disappear
Oligohydramnios
low volume of amniotic fluid for gestational age
May result from:
-placental insufficiency with diminished placental blood flow
-Preterm rupture of the amniochorionic membrane
-Renal agenesis or obstructive uropathy
Polyhydramnios
high volume of amniotic fluid
May be associated with:
-severe anomalies of the CNS - improper innervation to muscles involved in the swallowing mechanism can be preventing fetus from swallowing the fluid
Esophageal atresia- fetus is unable to swallow the amniotic fluid if the esophagus does not form correctly
-Multiple gestations
Amniocentesis
invasive prenatal diagnostic procedure
- Amniotic fluid is sampled by inserting a needle through the mother’s anterior abdominal and uterine walls into the amniotic cavity, requiring piercing of the chorion and amnion
- Usually performed between 15 and 18 weeks of gestation
- common for detecting genetic disorders
Dizygotic twins
results from fertilization of two oocytes
- always have two amnions and two chorions, but the chorions and placentas may be fused
- shows a hereditary tendency
Monozygotic twins
most developed from one zygote by division of the embryoblast
- have separate amnions
- have a single chorionic sac
- share a placeta
Discordant twins
twin-twin transfusion syndrome can cause this - there is a shunt of arterial blood from one twin through arteriovenous anastomoses into the venous circulation of the other twin
Monozygotic conjoined twins
embryonic disc does not divide completely or adjacent discs fuse
Stages of labor
Dilation
Expulsion
Placental stage
Recovery
Three major processes of Gastrulation
Formation of the primitive streak
Development of notochord
Differentiation of three germ layers (endoderm, mesoderm, ectoderm)
Primitive streak
a thickened band of epiblast cells on the dorsal surface of the embryonic disc
-the first sign of gastrulation
Formation of the primitive streak establishes:
Craniocaudal axis of the embryo
Right/Left side of the embryo
Dorsal/ventral surfaces of the embryo
Sacrococcygeal teratoma
tumors that contain tissue derived from all three germ layers i incomplete stages of differentiation
-Most common tumor in newborns
Notocord
defines the primordial cranialcaudal axis of the embryo
- provides some rigidity to the developing embryo
- serves as the basis for development of the axial skeleton (bones of the head and vertebral column)
- indicates the future site of the vertebral bodies
- in part, persists as the nucleus pulposis of the intervertebral discs
- functions as the primary inductor in the early embryo
Neurulation
the process involved in the formation of the neural plate and neural folds and closure of the folds to form the neural tube
Neurulation accomplished three major things:
- It creates the neural tube, which gives rise to the CNS
- It creates the neural crest, which migrates away from the dorsal surface of the neural tube, and gives rise to a diverse set of cell types
- It creates the definitive epidermis, which covers over the neural tube once it is created
Primary neurulation
formation of the neural tube at the dorsal midline
Secondary neurulation
secondary cavity formation at the caudal end of the neural tube to form the sacral spinal cord
First organ system to be laid down
CNS = brain and spinal cord
Fate of the neural tube:
Walls become brain and spinal cord
Space in the middle becomes the ventricular system of the brain and central canal of spinal cord
Neural Crest Cells
Neural Crest Cells
involved with spetation of the heart (among other things)
Neopores
neural tube is open at each end
Rostal neuropore = closes ~ day 25
Caudal neuropose = closes ~ day 27
Closure of the neuropores coincides with establishment of vascular system
Neurofibramatosis
von Recklinghausen disease
peripheral nerve tumors
Waardenburg syndrome
Autosomal dominant
Extremely pale blue eyes or heterochromia (two different colored eyes)
Partial albinism - white forelock (poliosis) of hair or early graying of hair
CHARGE Symdrome
Coloboma Heart defects Atresi choanae Retardation of growth and development Genitourinary problems Ear abnormalities
Alar plate
associated with secondary sensory neurons
Gives rise to dorsal horn of spinal cord
**We know dorsal horn is involved with sensory fibers*
Basal plate
Associated with motor neurons
Gives rise to ventral horn of spinal cord
Sulcus limitans
groove separating dorsal sensory from ventral motor
-This goes all the way to the medulla of the brain
Lumbar cistern
enlarged area of subarachnoid space in lumbar region
-Important for lumbar punctures L4/L5
All ganglia come from __________.
Neural Crest Cells
Spinal Cord Termination Levels
Adult: Intervertebral discs between L1/L2
Newborn: L3
Somite Differentiation
Initially differentiates into dermomyatomes and sclerotomes
-then to dermatomes, myotomes, and sclerotomes
Dermatome
Dermis of skin
Myotome
myoblasts (develop into muscle)
Sclerotome
Will form vertebrae and ribs; loosely organized mseenchyme
Sclerotome cells found in three main areas:
- On either side of notochord
- Surrounding neural tube
- In the body wall (form ribs)
Genes controlling somite differentiation
Sonic Hedgehog (Shh) causes the ventral part of the somite to form sclerotome
Two parts of Sclerotomes that are surrounding the notochord
- cranial - loosely arranged part
- caudal - densely arranged part
- Caudal portion will with combine with loosely arranged cells of next caudal sclerotome to form central body of vertebrae (centrum)
Notochord goes on to form:
nucleus pulposis
Mesenchyme around neural tube forms _______.
vertebral (neural) arch
Mesenchyme in the body walls form _______.
Coastal processes that form ribs in the thoracic region
Napoleonic vertebrae
three bony parts;
referring to ossification enters (7 weeks)
Spina Bifida
problem with development of the nervous system and skeletal system
Spina Bifida Occulta
cannot see it (occulta - Latin for “hidden”
- Mildest form of spine bifida
- May be indicated by tuft of hair or dimple
Spina Bifida Cystica
indicated by high levels of alpha-fetoprotein (AFP)
Spina Bifida Cystica with Meningocele
protruding sac contains meninges and CSF
-No neurological deficits because nerves are still in proper places
Spina Bifida Cystica with Meningomyelocele
Cord is included in sac
-Associated with neurological deficits because nerve roots are stretches at the level of herniation
Spina Bifida Cystica with Myeloschisis
Most severe type
-Open neural plate exposed so that the neural folds didn’t form
Cervical Rib Syndrome
rib on C7 may put pressure on brachial plexus and/or subclavian vessels and produce symptoms (like parasthesia)
Congenital hemivertebra
occurs if one of the two chondrification centers on either side of the centrum fails to develop
- Mutation of the HOX (homobox) genes may cause
- Can be a cause of scoliosis
Anomalies of sternum development
“pigeon chest” - sternu protrudes anteriorly
Cleft sternum - worst case scenario: ectopic cardis (heart develops outside body)
Notching o the xiphoid process - xiphoid process can be naturally bifurcated
Sternal foramen
Four Sources of Limb Tissue Development
Lateral Plate Mesoderm: gives rise to skeleton, tendons, ligaments, vasculature Somites (Dermo-myotome): Musculature Neural Crest: rise to Schwann cells, Dorsal root ganglia, sensory axons Neural Tube: gives rise to motor axons
All muscles of the body develop from ______.
Mesoderm
Epaxial Division of Myotome
supplied by dorsal primary ramus of a spinal nerve (epimere)
-Intrinsic (true) back muscles
Hypaxial Division of Myotome
supplies by ventral primary ramus of a spinal nerve (hypomere)
-Muscles of body wall (intercostals, abdominal muscle)
Straited muscle of the trunk develops from ______.
Myotomes
Smooth muscle and cardiac muscle develop from _______.
Splanchnic mesoderm
“Prune Belly”
absence of abdominal muscles, can sometimes see loops of intestines
Thalidomide
a potent teratogen that can acuse severe limb defects
Amerlia
absence of limbs
Meromelia
arrest of disturbance of growth of limbs during development; results in limbs being only partially developed
Syndactyly
Cutaneous: failure of webs to degenerate between two or more digits
Osseous: notches between digital rays do not develop; resulting in lack of separation of the digits
Polydactyly
extra digit(s)
Cleodocranial Dysostosis
autosomal dominant incomplete formation or absence of the clavicle
1st bone in body to ossify
Clavicle
-Initially intramembraneous ossification, then endochondral ossification.
Achondroplasia
autosomal dominant impairment of cartilage development in the epiphyseal plates of bones
- Most common cause of dwarfism
- Fibroblast growth factor receptor 3 (FGFR-3) is invovled
Anomalies of the Integumentary System
Ichthyosis: superficial layer does not slough off
Hemangioma or Angioma: problems with capillary plexi leading to an abnorma buildup of vessels in the skin
-Considered benign tumors
Port-wine stains: birthmarks in which swollen blood vessels create a reddish-purplish discoloration of the skin
Polymastia
extra breast
Polythelia
extra nipple(s)
Macromastia
hypertrophy of the breast
Micromastia
breast hypoplasia (underdevelopment of breast tissue)
Angioblastic Cord canalization
at 22 days
form endocardial heart tubes
________ helps move heart into correct anatomical position.
brain development
Adult Derivative of Embryonic Structure:
Truncus arteriosus
Aorta and Pulmonary Trunk
-separated by aorticopulmonary septum which involes NCC
Adult Derivative of Embryonic Structure:
Bubus cordis
Infundibulum/Cons Arterious = smooth part of right vetricle
Aortic vestibule = smooth part of left ventricle
Adult Derivative of Embryonic Structure:
Primitive Ventricle
Trabeculae carneae of L and R ventricles
Adult Derivative of Embryonic Structure:
Primitive atrium
Trabeculated (pectinate muscles) part of L and R atria
Adult Derivative of Embryonic Structure:
Sinus venosus
Sinus venarum (smooth part of R atrium) Coronary sinus, oblique vein of L atrium
Crista terminalis
junction of muscular and membraneous regions of R atrium
Blood flow input through sinus venous
common cardinal vv.
Umbilical vv.
Vitelline vv.
Atrioventricular canal
endocardinal cushions approach each other and fuse, dividing canal into Right AV canal (becomes tricuspid valve) and left AV canal (becomes mitral valve)
Foramen primum
foramen between free edge of septum primum and the endocardial cushions
R horn of sinus venosus becomes _______.
Sinus Venarum (smooth walled part of right atrium separated by cristae terminalis)
L horn of sinus venosus becomes _______.
Coronary sinus and Olbique vein of L atrium
Fetal Circulation
Placents - Umbilical vein - 1/2 ductus venosus (connects umbilical v. to IVC) - 1/2 Liver sinusoids - hepatic veins - inferior veina cava - right atrium - foramen ovale - left atrium - left ventricle - ascending aorta - superior vena cava - right atrium - right ventricle - pulmonary trunk - Ductus Arteriosus - umbilical arteries (2x) - placenta
Probe patent foramen ovale
more frequent in females
probe can be passed through the superior part of the foramen ovale
Usually small, not clinically significant - physiologic but not anatomic
Results from failure of the valve of the foramen ovale (septum primum) to fuse with the septum secondum at birth
Tetralogy of Fallot
Cynosis is a major symptom
- Pulmonary stenosis
- Ventricular septal defect
- Overriding aorta
- Right ventricular hypertrophy
most common single cause of cyanotic heart disease in newborn infants
transposition of great arteries
Aortic Arch Derivatives:
First Aortic Arch
largely disappears
Maxillary AA
-contributes to external carotid aa
Aortic Arch Derivatives:
Second Aortic Arch
Stapedial aa.
Aortic Arch Derivatives:
Third Aortic Arch
Common Carotid aa.
-from prox. parts of 3rd arch
Aortic Arch Derivatives:
Fourth aortic Arch
Left: pr of Arch of Aorta
Right: Right subclavian a.
Aortic Arch Derivatives:
Fifth Aortic Arch
usually disappears
Aortic Arch Derivatives:
SIxth Aortic Arch
Left: Proximal - Left pulmonary A.
Distal: Ductus Arteriosus
Right: Right Pulmonary Artery
Determining location of recurrent pharyngeal nerves
Right recurrent laryngeal n. - goes around R subclavian
Left recurrent laryngeal n. - wraps around aortic arch passing lateral to the ligamentum arteriosum
Tracheoesophageal septum
formed by tracheoesphageal folds
-divides esophagus and trachea to form laryngotracheal tube (trachea and larynx)
Tracheoesophageal fistula
results from incomplete division of the cranial part of the foregut into respiratory and esophageal part
-causes choking and regurgitation because esophagus goes down into respiratory system
Esophageal atresia
blind sac of esophagus
-baby’s can’t swallow amniotic fluid - Polyhydramnios -> excess amniotic fluid
Four stages of lung development
landular stage (pseudoglandular)
canalicular stage
saccular stage
alveolar stage
Pseudoglanular stage
During 6th-16th weeks there is repeated branching to the level of terminal bronchioles
All major elements of lungs formed BUT not those involve in gas exchange
RESPIRATION NOT POSSIBLE
Fetuses born during this period unable to survive
Canalicular period
Lumina of bronchi and terminal bronchioles become larger
16-26 weeks
Lung tissue highly vascularized
Terminal bronchiles give rise to 2+ respiratory bronchioles –> terminal saccules (primordial alveoli) and 3-6 alveolar ducts
RESPIRATION POSSIBLE
-fetus may survive with intensive care
Terminal sac period
increase # of terminal saccules
26 weeks - birth
terminal sac epithelium becomes very thin
invaded by capillaries
establish blood-air barrier
adequate gas exchange possible is fetus born prematurely
Type I alveolar cells/pneumocytes
gas exchange
Squamous epithelial cells - line terminal sacs
Type II alveolar cells/pneumocytes
pulmonary surfactant secretion
Rounded epithelial cells
Surfactant
monomolecular film in terminal sacs, lowers surface tension
Alveolar period
strucutre analogous to alveoli are present at 32 weeks
Type I alveolar cells are thin enough to form the alveolarcapillary membrane - pulmonary diffusion membrane or respiratory membrane
NO PROBLEMS with survival
Three factors important for normal lung development
Adequate thoracic space for lung growth
Fetal breathing movements
Adequate amniotic fluid volume
Respiratory Distress Syndrome
hyaline membrane disease (HMD) -2% of live born infants -14% of infants weighing less than 2500 grams -white infants > black infants -Male 2x > female Symptoms: -Rapid labored breathing shortly after birth -Expiratory grunting -Nasal flaring -subcostal and intercostal retractions -cyanosis
Treated by:
Intensive respiratory assistance
Surfactant therapy including surfactant lipoprotein and surfactant associated protein A, B & C
SURFACTANT DEFICIENCY IS MAJOR CAUSE OF RDS/HMD
