Template talk:Second Trimester Timeline

Second Trimester Timeline 

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Week	Stage	Event
12	Clinical second trimester (GA Clinical Week 14) Second Trimester	Week 12 - CRL 85 mm, femur length 15 mm, biparietal diameter 25 mm 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) Genital 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 Hearing - Outer Ear Development Week 13 - Meatal plug disc-like, innermost surface in contact with the primordial malleus, contributes to the formation of the tympanic membrane.
14		Tongue Week 14 to 15 - taste pores develop, mucous Ovary Development 100 days - primary follicles present Nail Development toenails appear Head Development facial skeleton remodelling begins Hearing - Inner Ear Development Week 14 GA 16 - neural-crest-derived melanocytes, now intermediate cells of the stria vascularis, tightly integrate with Na+ /K+ -ATPase-positive marginal cells, which started to express KCNQ1 in their apical membrane.
15		Pancreas glucagon detectable in fetal plasma. Spleen Week 15 -alpha-smooth muscle actin (alpha-SMA)-positive reticulum cells scattered around the arterioles.
16	14 cm	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 Hearing - Outer Ear Development Week 16.5 - External auditory meatus is fully patent throughout its length, lumen is still narrow and curved. Hearing - Inner Ear Development Week 16 GA 18 - cells in the outer sulcus express KCNJ10 and gap junction proteins GJB2/CX26 and GJB6/CX30, but these are not expressed in the spiral ligament. gap junction cartoon Neural - Cerebrum development of the periinsular sulci (week 16-17, GA 18-19 weeks) 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		Neural - Brain development histology week 17 Tooth Development Week 17 - First papilla of the permanent dentition appear (first molar) immediately behind the second milk molar, milk teeth are well advanced (Fetus 180 mm).
18		Tongue Week 18 - substance P detected in dermal papillae, not in taste bud primordia Skin vernix caseosa covers skin Spleen Week 18 - alpha-SMA-positive reticulum cells increase in number and began to form a reticular framework. An accumulation of T and B lymphocytes occurred within the framework, and a primitive white pulp was observed around the arterioles. Hearing - Outer Ear Development week 18 - External auditory meatus is already fully expanded to its complete form. Neural - Cerebrum central sulci and opercularization of the insula (week 18-20, GA 20-22 weeks)
19		Neural week 19 neuronal migration ends and the radial glial cells that aided the migration now become transformed into astrocytes and astrocytic precursors.
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.
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22		Neural brain cortical sulcation - sylvian fissure, interhemispheric fissure, callosal sulcus, parietooccipital fissure, and hippocampic fissures present Spleen - Week 22 - antigenic diversity of the reticular framework was observed, and T and B lymphocytes were segregated in the framework. T lymphocytes were sorted into the alpha-smooth muscle actin-positive reticular framework, and the periarteriolar lymphoid sheath (PALS) was formed around the arteriole. B lymphocytes aggregated in eccentric portions to the PALS and formed the lymph follicle (LF). The reticular framework of the LF was alpha-SMA-negative. Neural - Cerebrum covering of the posterior insula (week 22-24, GA 24-26 weeks)
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24		Respiratory Week 24 to 40 lung histology - terminal sac Spleen Week 24 - marginal zone appeared in the alpha-smooth muscle actin-positive reticular framework around the white pulp. Tooth Development Week 24 - Permanent incisors and canines appear. 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 Neural - Cerebrum closure of the laeteral sulcus (Sylvian fissure or lateral fissure) (week 25-26, GA 27-28 weeks)