2010 BGD Practical 12 - Second Trimester
- 1 Introduction
- 2 Week 12
- 3 Week 16+ (4 months)
- 4 Ultrasound
- 5 Additional Information
- 6 Glossary Links
- Early fetal - week 12
- placental changes and fetal membrane changes
- length changes
- clinical diagnosis (ultrasound)
- Fetal Endocrine
BGD Cycle A 2010 Audio - Dr Mark Hill Monday 17th May 2010 3-5pm G2G4.
<wikiflv height="372" width="500" autoplay="true">Ultrasound_12_week.flv|Ultrasound_12_week_icon.jpg</wikiflv>
|Fetal head lateral||Fetal head medial|
- Genital male and female external genital differences observable
- Respiratory Month 3-6 - lungs appear glandular, end month 6 alveolar cells type 2 appear and begin to secrete surfactant
- Tongue Week 12 - first differentiated epithelial cells
Week 16+ (4 months)
Respiratory Development Overview
- week 4 - 5 embryonic
- week 5 - 17 pseudoglandular
- week 16 - 25 canalicular
- week 24 - 40 terminal sac
- late fetal - 8 years alveolar
Skin Development Overview
- 4 weeks
- simple ectoderm epithelium over mesenchyme.
- 1 - 3 months
- ectoderm - germinative (basal) cell repeated division of generates stratified epithelium.
- mesoderm - somite dermatome spreads out under the epithelium, differentiates into connective tissue and blood vessels.
- 4 months
- basal cell - proliferation generates folds in basement membrane.
- neural crest cells - (melanocytes) migrate into epithelium. These are the pigment cell of the skin.
- embryonic connective tissue - differentiates into dermis, a loose ct layer over a dense ct layer. Beneath the dense ct layer is another loose ct layer that will form the subcutaneous layer.
- Ectoderm contributes to nails, hair follictles and glands.
- Nails form as thickening of ectoderm epidermis at the tips of fingers and toes. These form germinative cells of nail field.
- Cords of these cells extend into mesoderm forming epithelial columns. These form hair follicles, sebaceous and sweat glands.
- 5 months
- Hair growth initiated at base of cord, lateral outgrowths form associated sebaceous glands.
- Other cords elongate and coil to form sweat glands.
- Cords in mammary region branch as they elongate to form mammary glands. These glands will complete development in females at puberty. Functional maturity only occurs in late pregnancy.
- primary follicles begin to form in the ovary and are characterized by an oocyte.
|Female External||Male External|
Different body tissues reflect sound waves differently. In ultrasound, a beam of sound waves (frequency 3 to 10 MHz) are passed through the body, the reflected waves are analysed by a computer, and an image is then generated on a display screen. The sound source is usually a transducer placed on the surface of the abdomen.
There can be number of different parameters, depending on gestational age, that are commonly recorded during an ultrasound procedure. These measurements (and ratios) include embryonic/fetal size and key lengths and sizes of specific structures, fetal membrane sizes/volumes, placental location/size. In addition, general body movements, including heartbeat, can be observed.
|Ultrasound Fetal (GA 19 weeks)
Ultrasound scan through the fetal trunk to measure abdominal circumference (AC).
Embryonic/Fetal Size: crown-rump length (CRL), biparietal diameter (BPD), abdominal circumference (AC)
Embryonic/Fetal Structures: femur length (FL), head circumference, nuchal translucency, heart size/rate
Fetal Membrane: gestational sac diameter (GS), yolk sac diameter (YS), meconium peritonitis, umbilical cord stricture
Placenta: location, size, umbilical cord stricture
Ultrasound - Abnormalities
See Ultrasound movie for Cleft lip 1
BGD Cycle A 2010 Audio - Dr Mark Hill Monday 17th May 2010 3-5pm G2G4.
The following information is a detailed timeline of second trimester development and content does not form part of the current practical class.
(Clinical Week 14)
|Clinical second trimester|| Week 12 - CRL 85 mm, femur length 15 mm, biparietal diameter 25 mm
Sense - Hearing Week 12-16 - Capsule adjacent to membranous labrynth undegoes vacuolization to form a cavity (perilymphatic space) around membranous labrynth and fills with perilymph
Genital male and female external genital differences observable
Respiratory Month 3-6 - lungs appear glandular, end month 6 alveolar cells type 2 appear and begin to secrete surfactant
Tongue Week 12 - first differentiated epithelial cells (Type II and III)
female genital canal (80 days) formed with absorption of the median septum
|Tongue Week 12 to 13 - maximum synapses between cells and afferent nerve fibers
|Tongue Week 14 to 15 - taste pores develop, mucous
Ovary Development 100 days - primary follicles present
|Pancreas glucagon detectable in fetal plasma|
|14 cm|| Sense - Hearing Week 16-24 - Centres of ossification appear in remaining cartilage of otic capsule form petrous portion of temporal bone. Continues to ossify to form mastoid process of temporal bone.
Pituitary adenohypophysis fully differentiated
Respiratory Week 16 to 25 lung histology - canalicular
Skin 4 months - basal cell- proliferation generates folds in basement membrane; neural crest cells- (melanocytes) migrate into epithelium; embryonic connective tissue- differentiates into dermis, a loose ct layer over a dense ct layer. Beneath the dense ct layer is another loose ct layer that will form the subcutaneous layer. Ectoderm contributes to nails, hair follictles and glands. Nails form as thickening of ectoderm epidermis at the tips of fingers and toes. These form germinative cells of nail field. Cords of these cells extend into mesoderm forming epithelial columns. These form hair follocles, sebaceous and sweat glands.
primary follicles begin to form in the ovary and are characterized by an oocyte
glandular urethra forms and skin folds present
|Tongue Week 18 - substance P detected in dermal papillae, not in taste bud primordia
Skin vernix caseosa covers skin
|Pituitary week 20 to 24 growth hormone levels peak, then decline
Skin lanugo, skin hair
Skin 5 months - Hair growth initiated at base of cord, lateral outgrowths form associated sebaceous glands; Other cords elongate and coil to form sweat glands; Cords in mammary region branch as they elongate to form mammary glands.
|Neural brain cortical sulcation - sylvian fissure, interhemispheric fissure, callosal sulcus, parietooccipital fissure, and hippocampic fissures present(PMID:11158907|
|Respiratory Week 24 to 40 lung histology - terminal sac
Earliest potential survival expected if born
ovarian follicles can consist of growing oocytes surrounded by several layers of granulosa cells
|Respiratory end month 6 alveolar cells type 2 appear and begin to secrete surfactant|
- Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link
- 2010 BGD: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12
Cite this page: Hill, M.A. (2020, January 21) Embryology 2010 BGD Practical 12 - Second Trimester. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2010_BGD_Practical_12_-_Second_Trimester
- © Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G