2010 BGD Practical 12 - Second Trimester

From Embryology
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Practical 12: Embryo to Fetus | Second Trimester | Third Trimester | Birth | Neonatal | Abnormalities


Introduction

3D ultrasound static image of the 12 week fetus
  • Early fetal - week 12
  • placental changes and fetal membrane changes
  • length changes
  • clinical diagnosis (ultrasound)
  • Fetal Endocrine

Practical Audio

Mark Hill.jpg

BGD Cycle A 2010 Audio - Dr Mark Hill Monday 17th May 2010 3-5pm G2G4.

Note - this is a live unedited recording from the practical and may contain errors in either descriptions or content.

listen Part 3 | download (1.74 Mb MP3 15:14)

Week 12

<wikiflv height="372" width="500" autoplay="true">Ultrasound_12_week.flv‎|Ultrasound_12_week_icon.jpg</wikiflv>


Size

Fetal length change

Systems

Fetal head lateral.jpg Fetal head medial.jpg
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

Lung alveoli development cartoon

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.

Gonad Development

  • primary follicles begin to form in the ovary and are characterized by an oocyte.
Female external 001 icon.jpg Male external 001 icon.jpg
Female External Male External

Ultrasound

About Ultrasound

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.

Ultrasound Measurements

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).
Ultrasound Fetal (GA 19 weeks)

Ultrasound scan through the fetal trunk to measure abdominal circumference (AC).

placental cord knot

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

Practical Audio

Mark Hill.jpg

BGD Cycle A 2010 Audio - Dr Mark Hill Monday 17th May 2010 3-5pm G2G4.

Note - this is a live unedited recording from the practical and may contain errors in either descriptions or content.

listen Part 4 | download (316 Kb MP3 2:41)

BGDsmall.jpg

Practical 12: Embryo to Fetus | Second Trimester | Third Trimester | Birth | Neonatal | Abnormalities


Additional Information

The following information is a detailed timeline of second trimester development and content does not form part of the current practical class.

Second Trimester

(Clinical Week 14)

Week
Stage
Event
12
Clinical second trimester Fetal head lateral.jpg 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

13
  Tongue Week 12 to 13 - maximum synapses between cells and afferent nerve fibers

 

14
Tongue Week 14 to 15 - taste pores develop, mucous

Ovary Development 100 days - primary follicles present

15
  Pancreas glucagon detectable in fetal plasma
16
14 cm Fetal size change.jpg 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

17
 
18
Tongue Week 18 - substance P detected in dermal papillae, not in taste bud primordia

Skin vernix caseosa covers skin

Spleen -SMA-positive reticulum cells increase in number and begin to form a reticular framework. PMID: 1925578

19
   
20
  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.

21
   
22
  Gray0038.jpg Neural brain cortical sulcation - sylvian fissure, interhemispheric fissure, callosal sulcus, parietooccipital fissure, and hippocampic fissures present(PMID:11158907

Spleen - antigenic reticular framework diversity, T and B lymphocytes segregated in the framework PMID: 1925578

23
   
24
  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

25
  Respiratory end month 6 alveolar cells type 2 appear and begin to secrete surfactant


Glossary Links

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2010 BGD: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12

Cite this page: Hill, M.A. (2019, December 14) Embryology 2010 BGD Practical 12 - Second Trimester. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2010_BGD_Practical_12_-_Second_Trimester

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G