Fetal Period Flashcards
6 Characteristics of an Embryo at Week 3
(1) A notochord forms in the center of the embryonic disk
(2) Gastrulation commences
(3) A neural groove (future spinal cord) forms over the notochord with a brain bulge at one end
(4) ) Somites, the divisions of the future vertebra, form
(5) Primitive heart tube is forming
(6) The crown-rump length is about 0.2 inches.
9 Characteristics of an Embryo at Week 4
(1) The embryo measures 4 mm (1/8 inch) and begins to curve into a C shape.
(2) The heart bulges; begins to beat
(3) Branchial arches, that will form structures of the face and neck, form.
(4) The neural tube closes.
(5) Arm buds and a tail are visible.
(6) Pulmonary primordium appears.
(7) Hepatic plate, first traits of liver appear.
(8) Oropharyngeal membrane ruptures to form the future mouth.
(9) Anterior and posterior horns differentiate in the spinal cord
8 Characteristics of an Embryo at Week 5
(1) The embryo measures (1/4 inch) in length.
(2) Lens pits and optic cups form the start of the developing eye.
(3) Nasal pits form.
(4) The brain divides into 5 vesicles
(5) Leg buds form and hands form as flat paddles on the arms.
(6) Rudimentary blood moves through primitive umbilical vessels connecting to the umbilical cord.
(7) The metanephros, precursor of the definitive kidney, starts to develop.
(8) The initial stomach differentiation begins.
5 Characteristics of an Embryo at Week 6
(1) The embryo measures (1/2 inch) in length.
(2) Lungs begin to form.
(3) The brain continues to develop.
(4) Arms and legs have lengthened with foot and hand areas distinguishable.
(5) The hands and feet have digits, but may still be webbed.
6 Characteristics of an Embryo at Week 7
(1) The embryo measures (3/4 inch) in length.
(2) Fetal heart tone (the sound of the heart beat) can be heard using Doppler.
(3) Nipples and hair follicles begin to form.
(4) Location of the elbows and toes are visible.
(5) Spontaneous limb movements may be detected by ultrasound.
(6) All essential organs have at least begun.
10 Things that happen in weeks 8-10
(1) Intestines rotate.
(2) Facial features continue to develop.
(3) The eyelids are more developed.
(4) The external features of the ear begin to take their final shape.
(5) The head comprises nearly half of the fetus’ size.
(6) The face is well formed
(7) The limbs are long and thin.
(8) The fetus can make a fist with its fingers.
(9) Genitals appear well differentiated.
(10) Red blood cells are produced in the liver.
When are all major external and internal structures are established? (the embryo has a distinctly human appearance)
During the 4th to 8th weeks
What are teratogens?
are agents such as drugs and viruses that produce or increase the incidence of birth defects
When is the CNS susceptible?
Weeks 3-20
When are the limbs susceptible?
Weeks 4-7
When is the heart susceptible?
Weeks 3-6
When are the eyes and ears susceptible?
Weeks 4-8
What are the 5 methods used to estimate fetal age?
) Crown-rump Length; 2) Head Circumference; 3) Length of Femur; 4) Length of Foot; 5) Abdominal Circumference
What is the size of the embryo at week 4?
1/8 inch
What is the size of the embryo at week 5?
1/4 inch
What is the size of the embryo at week 6?
1/2 inch
What is the size of the embryo at week 7?
3/4 inch (weighs 1 gram)
What is a notable change that occurs during the fetal period?
There is a relative slowdown in the growth of the head compared with the rest of the body
How much do “preterm” infants weigh?
750-1500 grams
When can the genitalia of the fetuses be recognized ?
12-14 weeks
When does the fetal period begin?
8 weeks after fertilization
When does head hair appear?
By the beginning of the 20th week
Around what time is the fetus is usually capable of extrauterine existence?
Approximately 26 weeks
When does fat rapidly develop?
During the 26th to 29th weeks
Describe the two components of the placenta
- A fetal part that develops from the chorionic sac, the outermost fetal membrane
- A maternal part that is derived from the endometrium, the mucous membrane comprising the inner layer of the uterine wall
5 Functions and Activities of the placenta and fetal membranes
1) protection
2) nutrition
3) respiration
4) excretion
5) hormone production
When is development of the maternal blood supply to the placenta complete?
By the end of the 1st trimester (12-13 weeks)
What are the layers in which nutrients and oxygen from the mother must pass through in order to get to the fetus?
Syncytiotrophoblast Cytotrophoblast Mesoderm Capillary endothelium Basement membrane
How many veins and arteries does the umbilical cord have?
2 Umbilical Arteries and 1 Umbilical Vein
Describe Umbilical Arteries
They carry deoxygenated and nutrient poor blood AWAY from the fetus
Describe Umbilical Veins
They carry oxygenated and nutrient rich blood TOWARD the fetal heart
Describe fetal circulation from the placenta to the brain
Placenta –> Umbilical Vein –> Inferior Vena Cava –> Right Atrium –> Foramen Ovale –> Left Atrium –> Left Ventricle –> Head, Neck and Brain
Blood bypasses the liver and lungs by of ______.
ductus arteriosus
In utero what side of the heart is the “high pressure side”?
Right side
How does typical circulation occur at birth?
The baby takes in a breath, which opens the lungs and clears its passages of fluid. Now the left side of the heart is the high pressure side, which closes the foramen ovale.
