Third Trimester: Difference between revisions
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Note the increasing cortex surface area forming visible gyri (folds) and fissures (grooves) on the surface. | Note the increasing cortex surface area forming visible gyri (folds) and fissures (grooves) on the surface. | ||
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==Respiratory== | |||
===Saccular stage=== | |||
[[File:Alveolar-sac-01.jpg|thumb|Alveolar sac structure]] | |||
* week 24 to near term. | |||
* most peripheral airways form widened airspaces, termed saccules. | |||
* saccules widen and lengthen the airspace (by the addition of new generations). | |||
* future gas exchange region expands significantly. | |||
* Fibroblastic cells also undergo differentiation, they produce extracellular matrix, collagen, and elastin. May have a role in epithelial differentiation and control of surfactant secretion | |||
* The vascular tree also grows in length and diameter during this time. | |||
* in late fetal development respiratory motions and amniotic fluid are thought to have a role in lung maturation. | |||
* Development of this system is not completed until late fetal just before birth. | |||
** Therefore premature babies have difficulties associated with insufficient surfactant (end month 6 alveolar cells type 2 appear and begin to secrete surfactant). | |||
==Third Trimester Timeline== | ==Third Trimester Timeline== |
Revision as of 13:51, 19 March 2012
Introduction
The third trimester is a period of development when the fetus slows in growth in length and begins to increase substantially in weight. Some fetal systems, such as the respiratory system, only now begin to mature just prior to birth.
Immune system, IgG to specific maternal antigens transferred passively across the placenta during the last trimester of pregnancy.
Fetal Links: fetal | Week 10 | Week 12 | second trimester | third trimester | fetal neural | Fetal Blood Sampling | fetal growth restriction | birth | birth weight | preterm birth | Developmental Origins of Health and Disease | macrosomia | BGD Practical | Medicine Lecture | Science Lecture | Lecture Movie | Category:Human Fetus | Category:Fetal | |||
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Neural
Comparison of brain growth through the third trimester.
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Respiratory
Saccular stage
- week 24 to near term.
- most peripheral airways form widened airspaces, termed saccules.
- saccules widen and lengthen the airspace (by the addition of new generations).
- future gas exchange region expands significantly.
- Fibroblastic cells also undergo differentiation, they produce extracellular matrix, collagen, and elastin. May have a role in epithelial differentiation and control of surfactant secretion
- The vascular tree also grows in length and diameter during this time.
- in late fetal development respiratory motions and amniotic fluid are thought to have a role in lung maturation.
- Development of this system is not completed until late fetal just before birth.
- Therefore premature babies have difficulties associated with insufficient surfactant (end month 6 alveolar cells type 2 appear and begin to secrete surfactant).
Third Trimester Timeline
(Clinical Week 28-29)
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 | ||
Neural brain cortical sulcation - primary sulci present PMID:11158907 | ||
Neural brain cortical sulcation - insular, cingular, and occipital secondary sulci present PMID:11158907 | ||
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 |
References
Search Pubmed: Third Trimester
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Cite this page: Hill, M.A. (2024, April 26) Embryology Third Trimester. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Third_Trimester
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G