BGDA Practical 12 - Third Trimester: Difference between revisions
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===Neural Development=== | ===Neural Development=== | ||
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=== Third Trimester === | === Third Trimester === |
Revision as of 08:16, 1 June 2016
Practical 12: Embryo to Fetus | Second Trimester | Third Trimester | Birth | Neonatal | Abnormalities |
Introduction
- Survival issues for early delivery
- Fetal Respiratory
- Fetal Genital
- Fetal weight
- Fetal Neural
- Fetal Cardiovascular
- Fetal Renal
- Fetal Growth - Fetal Growth Restriction, Developmental Origins of Health and Disease
Week 24+
- Earliest potential survival expected if born.
- Most of the serious illness and mortality is concentrated in the 1 to 2 percent of infants who are born at less than GA 32 weeks (week 30) and who weigh less than 1500 g.
Class Models
Observe the differences between the fetus and uterus at the end of the second trimester and at term.
- size and weight
Fetal Weight
Endocrine
During the third trimester fetal endocrine organs are differentiated and secreting fetal hormones.
Endocrine - Fetal thymus weight growth
Respiratory
Week 24 to 40 lung histology - terminal sac, end month 6 alveolar cells type 2 appear and begin to secrete surfactant
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Genital
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Testes DescentThe linked animation shows the descent of the testes (between week 7 to 38, birth). Descent of the testes into the scrotal sac begins generally during week 26 and may take several days.
Incomplete or failed descent can occur unilaterally or bilaterally, is more common in premature births, and can be completed postnatally. (see also cryptorchidism). |
Start of testis descent | End of testis descent |
Neural
Comparison of brain growth through the third trimester.
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Renal
The functional unit of the kidney is the nephron and the process of their initial formation is called nephrogenesis. During development nephron number increases from about 15,000 at 15 weeks (GA 17 weeks) increasing to about the adult number by 36 weeks. Each adult kidney typically contains about 750,000 nephrons, though the total number can vary significantly from as few as 250,000 to as many as 2,000,000.
MRI appearance of normal fetal kidneys.(GA 25)
In humans, nephrogenesis only occurs before birth, though nephron maturation continues postnatally.
Infant Drug Clearance
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Teratogen (Greek, teraton = monster) Any agent that causes a structural abnormality following exposure during pregnancy. The overall effect depends on dosage and time of exposure.
Fetal Growth
Fetal Growth Restriction
The term "Fetal Growth Restriction" (FGR) or intrauterine growth restriction (IUGR) are used to describe when the fetus does not reach full growth potential. This is usually determined by clinical sonography calculations of fetal weight, fetal size, or symmetry.
Developmental Origins of Health and Disease (DOHaD)
Environmental derived abnormalities relate to maternal lifestyle, environment and nutrition and while some of these directly effect embryonic development, there is also growing evidence that some effects are more subtle and relate to later life health events. This theory, now called "developmental origins of health and disease" (DOHAD or DOHaD) and also previously Fetal Origins Hypothesis, is based on the early statistical analysis carried out by David Barker (1938 - 2013) of low birth weight data collected in the early 1900's in the south east of England which he then compared with these same babies later health outcomes. The theory was therefore originally called the "Barker Hypothesis" and has recently been renamed as "fetal origins" or "programming". Several origins have been suggested including: fetal undernutrition, endocrine (increased cortisol exposure), genetic susceptibility and accelerated postnatal growth.
Practical 12: Embryo to Fetus | Second Trimester | Third Trimester | Birth | Neonatal | Abnormalities |
Additional Information
Additional Information - Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page. |
- Links: Third Trimester
Neural Development
Third Trimester
(Clinical Week 28) Third Trimester
Event | ||
Clinical third trimester | Hearing 3rd Trimester - vibration acoustically of maternal abdominal wall induces startle respone in fetus. | |
Respire Month 7 - respiratory bronchioles proliferate and end in alveolar ducts and sacs | ||
Genital male gonad (testes) descending | ||
Nail Development fingernails reach digit tip | ||
Neural brain cortical sulcation - primary sulci present[1] | ||
Neural brain cortical sulcation - insular, cingular, and occipital secondary sulci present[1] | ||
Nail Development toenails reach digit tip
Lens Development - lens growth and interocular distance plateaus after 36 weeks of gestation[2] | ||
Birth | Clinical Week 40
Heart pressure difference closes foramen ovale leaving a fossa ovalis Thyroid TSH levels increase, thyroxine (T3) and T4 levels increase to 24 h, then 5-7 days postnatal decline to normal levels Adrenal - zona glomerulosa, zona fasiculata present
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References
BGDA: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12 | Lecture Neural | Practical 14 | Histology Support - Female | Male | Tutorial
Glossary Links
- 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
Cite this page: Hill, M.A. (2024, June 8) Embryology BGDA Practical 12 - Third Trimester. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDA_Practical_12_-_Third_Trimester
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G