Identify the development and form of the week 8 embryo (Stage 22 and 23). This 3D reconstruction animations showing specific systems and the histological sections from which these were prepared. There are also virtual slides and selected cross-sections showing specific features.
Then look at the week 10 early fetus and observe developmental changes. The selected mid-sagittal section shows the overall fetal anatomy and the gallery of excerpts have further detailed descriptions of these regions.
Week 8 - Stage 22
|| stage 22, Week 8, 54 - 56 days, 23 - 28 mm
Mesoderm: heart prominence, ossification continues
Head: nose, eye, external acoustic meatus
Body:straightening of trunk, heart, liver, umbilicus: placental cord, midgut herniation, allantois, vitelline duct
Limb: upper limbs longer and bent at elbow, foot plate with webbed digits, wrist, hand plate with separated digits
Straightening of trunk, pigmented eye, eyelid, nose, external acoustic meatus, ear auricle, scalp vascular plexus, separated digits (fingers), thigh, ankle, umbilical cord
Now examine selected regions of the Stage 22 embryo and their overall development in the 3D animations.
Week 8 - Stage 23
|| Week 8, 56 - 60 days, 27 - 31 mm
scalp vascular plexus, eylid, eye, nose, auricle of external ear, mouth, sholder, arm, elbow, wrist, toes separated, sole of foot, umbilical cord
Mesoderm: ossification continues
Head: eyelids, external ears, rounded head
Body: straightening of trunk, intestines herniated at umbilicus
Limbs: hands and feet turned inward
| Week 8 Developing Cortex
| Human embryo, Week 8, (GA week 10) Carnegie stage 22 section from the neural tube at the level of the developing cortex. Inset (upper right) shows whole section overview and approximate level of section (red line). Grey box shows detailed image region of developing cerebrum layer thicknesses are shown in microns.
Developing Cortex will form from the thin outer layer called the cortical plate. The underlying layers transient structures that continue to supply cells to the cortex through fetal period, most of these layers will eventually be lost, except for a thin ventricular layer. Cells migrate out along radial glia that establish the initial columnar and layered structure of the cortex. Layers are named according to the nervous system revised terminology (1970)
Developing Vascular blood vessels can also be seen spanning the developing layers. In the adult, these vessels will be lined with non-fenestrated endothelial cells that together with other vascular cells (pericytes and vascular smooth muscle cells), glial cells (astrocytes and microglia) and neurons will form the "blood-brain barrier".
Developing Ventricular Space is cerebrospinal fluid (CSF) filled and the lateral ventricles form within the cortical region. The inset image shows lying within the lateral ventricles, the choroid plexus the modified vascular structure that forms and secretes the CSF.
Developing Meninges layers lie outside the neural tube. The thin pia mater that closely covers the entire brain. The mesh-like arachnoid mater and the sub-arachnoid space that will also be CSF filled. The dense dura mater lies outside these 2 layers and under the skull, it cannot be seen in the enlarged image.
- Oral Cavity (stage 23)
Renal and Genital
|| Note the development, relative position and size of organs within the lower peritoneal cavity. The intra-abdominal portion of the placental cord can be seen on the right.
- Mesonephros - renal middle transient stage of kidney has commenced degeneration.
- Male gonad - testis sex cords developing as a precursor to seminiferous tubule differentiation.
- developing mesonephric duct (Wolffian duct) will form the ductus deferens.
- degenerating paramesonephric duct (Mullerian duct) due to AMH secretion. In female this would develop to form the uterus.
Week 10 - Fetus (40mm)
- Human Female Fetus (week 10)
Sagittal Section (plane D)
Pituitary and Lamina Terminalis
Midgut Herniation (label)
|| This is an image of the actual size comparison shown in the introduction of the Embryonic stage 13, 23 and Fetal stage 10 week 40mm. This stage of development is after the embryonic period (up to week 8), but only 2 weeks into early fetal development.
|| The fetal period is a time of extensive growth in size and mass as well as differentiation of organ systems established in the embryonic period. In particular, the brain continues to grow and develop, the respiratory system differentiates, the urogenital system further differentiates between male/female, endocrine and gastrointestinal tract begins to function.
Compare this 10 week fetus with the earlier Carnegie stage embryos: size, head/body proportions, brain, head, skeletal development.
Note that in the early fetus the midgut remains herniated and will only be taken into the peritoneal cavity on further body wall growth.
There are 4 sections taken in the sagittal plane (moving from the right at Plane A towards the midline at Plane D). Click on the small images (or the text below) to open the linked large image pages.
Fetus (week 10) Planes A (most lateral), B (lateral), C (medial) and D (midline) from lateral towards the midline.
- Image Source: UNSW Embryology, no reproduction without permission.
|| Cartoon shows example of some neural crest medial migration during week 4 and 5 and the structures formed at the level of the body.
- Cells staying dorsal to neural tube - dorsal root ganglia (DRG)
- Cells migrating ventral to neural tube - sympathetic ganglia
- Cells migrating peritoneal cavity wall - adrenal medulla
- Cells migrate into GIT wall - enteric nervous system
| Human Embryo (8 weeks, stage 22) adrenal gland showing the fetal and permanent adrenal cortex. Note that the medulla of the adrenal gland is not yet encapsulated by the cortex. 8-9 weeks post conception (wpc) adrenal cortex synthesizes cortisol under the regulation of ACTH (also stimulates androstenedione and testosterone secretion).
|| Human Fetus (10 week, 40mm, parasagittal section) shows location of the developing adrenal gland. The spongy appearance at the centre of the adrenal is the degenerating fetal cortex. The dense region around the outside of the adrenal is the developing adult cortex.)
| 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: Fetal Development - 10 Weeks Fetal Development - 12 Weeks
Trunk Muscle Development
This recent study shows an example of trunk muscle development at the end of the embryonic period.
|| Pectoralis Major Muscle Development
(A) Frontal view of the reconstructed pectoralis major portions of a stage 23 human embryo (56–60 days of development), specimen number 950. All other muscles are hidden. Depicted are three heads of the pectoralis major: clavicular head (light blue), sternocostal head (red) and abdominal head (yellow) and bones (white).
(B) Transverse section of the left shoulder region. The pectoralis major muscle is divided into three heads at this stage and is therefore even more partitioned than in adults (Gilroy et al. 2009). The tree heads of the left pectoralis muscle and the second rib and humerus of the same specimen as in (A) are tagged.
Legend: AH, abdominal head; CH, clavicular head; PM, pectoralis major muscle; SCH, sternocostal head. Scale bar: ~5 mm.
Anti-Müllerian Hormone (AMH) has several adult diagnostic uses. For example, a recent study has shown that salivary and serum androgens with anti-Müllerian hormone measurement can be used for the diagnosis of polycystic ovary syndrome.
- ↑ . (1970). Embryonic vertebrate central nervous system: revised terminology. The Boulder Committee. Anat. Rec. , 166, 257-61. PMID: 5414696 DOI.
- ↑ Warmbrunn MV, de Bakker BS, Hagoort J, Alefs-de Bakker PB & Oostra RJ. (2018). Hitherto unknown detailed muscle anatomy in an 8-week-old embryo. J. Anat. , , . PMID: 29726018 DOI.
- ↑ Sathyapalan T, Al-Qaissi A, Kilpatrick ES, Dargham SR, Keevil B & Atkin SL. (2018). Salivary and serum androgens with anti-Müllerian hormone measurement for the diagnosis of polycystic ovary syndrome. Sci Rep , 8, 3795. PMID: 29491484 DOI.
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Cite this page: Hill, M.A. (2018, June 18) Embryology BGDA Practical 12 - Embryo to Fetus. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDA_Practical_12_-_Embryo_to_Fetus
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