BGDA Practical 12 - Embryo to Fetus

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


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

Stage22 bf1c.jpg
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

Embryo Anatomy

Now examine selected regions of the Stage 22 embryo and their overall development in the 3D animations.

Stage22 ALL3d.jpg
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 ‎‎GIT Stage 22
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 ‎‎Stage 22 Neural
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Virtual Slides

Stage 22 - Eye and Nose

Stage 22 image 008.jpg

 ‎‎Mobile | Desktop | Original

Stage 22 | Embryo Slides
Stage 22 - Eye

Stage 22 image 008-eye.jpg

 ‎‎Mobile | Desktop | Original

Stage 22 | Embryo Slides
Stage 22 - Oral Cavity and Inner Ear

Stage 22 image 011.jpg

 ‎‎Mobile | Desktop | Original

Stage 22 | Embryo Slides
Stage 22 - Larynx and Medulla

Stage 22 image 015.jpg

 ‎‎Mobile | Original

Stage 22 | Embryo Slides
Stage 22 - Neck

Stage 22 image 017.jpg

 ‎‎Mobile | Desktop | Original

Stage 22 | Embryo Slides
Stage 22 - Atria and Lungs

Stage 22 image 025.jpg

 ‎‎Mobile | Desktop | Original

Stage 22 | Embryo Slides
Stage 22 - Liver and Ductus Venosus

Stage 22 image 034.jpg

 ‎‎Mobile | Desktop | Original

Stage 22 | Embryo Slides
Stage 22 - Pelvis

Stage 22 image 048.jpg

 ‎‎Mobile | Desktop | Original

Stage 22 | Embryo Slides
Stage 22 - Spinal Cord

Stage 22 image 033-spinal-cord.jpg

 ‎‎Mobile | Desktop | Original

Stage 22 | Embryo Slides
Stage 22 - Spinal Cord (rotated)

Human Stage22 spinal cord03.jpg

 ‎‎Mobile | Desktop | Original

Stage 22 | Embryo Slides

Week 8 - Stage 23

Stage23 bf1c.jpg
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

Carnegie Stage 23 MRI movies
Stage23 MRI 3D01 icon.jpg
 ‎‎Embryo Surface
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Stage23 MRI 3D02 icon.jpg
 ‎‎Embryo CNS
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Stage23 MRI S02 icon.jpg
 ‎‎Sagittal Embryo
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Stage23 MRI T01 icon.jpg
 ‎‎Trans. Embryo
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Stage23 MRI C01 icon.jpg
 ‎‎Coronal Embryo
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Stage23 MRI S01 icon.jpg
 ‎‎Sagittal Head
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Stage23 MRI S04 icon.jpg
 ‎‎Sagittal GIT
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Stage 23 MRI Movies: Surface | Central Nervous System | CNS (labeled) | Sagittal | Sagittal (labeled) | Transverse | Transverse (labeled) | Coronal | Sagittal Head (labeled) | Sagittal GIT (labeled) | Carnegie stage 23

Week: 1 2 3 4 5 6 7 8
Carnegie stage: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Stage 23 Links: Week 8 | System Development | Lecture - Limb | Lecture - Head Development | Lecture - Sensory | Science Practical - Head | Science Practical - Sensory | Science Practical - Urogenital | Historic - Skull Development | Carnegie Embryos | Madrid Embryos | Category:Carnegie Stage 23 | Next Fetal Development
  Historic Papers: 1954 Stage 19-23


Stage 22 image 217.jpg

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)[1]

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.

Spinal Cord

Human Stage22 spinal cord02.jpg

Week 8 Developing Spinal Cord (virtual slide) 
Stage 22 - Spinal Cord (rotated)

Human Stage22 spinal cord03.jpg

 ‎‎Mobile | Desktop | Original

Stage 22 | Embryo Slides
These listed features link to zoomed views of the virtual slide with the named feature generally in the centre of the view.

Use the (-) at the top left of the screen to see where this feature is located.

Spinal Cord Features Other Features

Oral Cavity

Renal and Genital

Stage 22 image 302.jpg 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.

Stage 22 image 301.jpg

Week 10 - Fetus (40mm)

Human week 10 fetus 01.jpg

Size comparison embryo-fetus actual.jpg 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.
Size comparison embryo-fetus.jpg 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.

Related Images

Human- fetal week 10 planes icon.jpg

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.


  • adrenal cortex (intermediate mesoderm)
  • adrenal medulla (neural crest)
<html5media height="500" width="560">File:Adrenal medulla.mp4</html5media> 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

Adrenal medulla.jpg
 ‎‎Adrenal Medulla
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Human-adrenal gland 01.jpg Week10 adrenal.jpg
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.)

Embryo to Fetus Interactive Component

Attempt the Quiz - Embryo to Fetus  

Here are a few simple Quiz questions that relate to Embryo to Fetus transition from the lecture and practical.

1 Which of the following answers describes the human embryonic period:

  the period before replacement of cartilage within the humerus by bone marrow begins
  a discrete entity that has not yet reached 8 weeks of development since the first mitotic division
  the developmental period up to 8 post-ovulatory weeks
  the period when more than 90% of the more than 4,500 named structures of the adult body have appeared
  all of the above are correct

2 In human development, the first trimester is best described as:

  the period when organs begin to function
  the embryonic period and the beginning of the fetal period
  the least critical time of human development
  the beginning of fetal sensory function
  all of the above are correct

3 Which of the following limb development processes has not completed by the end of the first trimester:

  ossification of the limb long bones
  rotation of the upper limb
  rotation of the lower limb
  apoptosis between the digital rays
  molecular patterning of the limb bud

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

Additional Information: first trimester timeline | Embryonic Development | Week 9 | Week 10

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: Fetal Development - 10 Weeks Fetal Development - 12 Weeks

Human Fetal Adrenal Cortex

Ishimoto H & Jaffe RB. (2011). Development and function of the human fetal adrenal cortex: a key component in the feto-placental unit. Endocr. Rev. , 32, 317-55. PMID: 21051591 DOI.

"Continuous efforts have been devoted to unraveling the biophysiology and development of the human fetal adrenal cortex, which is structurally and functionally unique from other species. It plays a pivotal role, mainly through steroidogenesis, in the regulation of intrauterine homeostasis and in fetal development and maturation. The steroidogenic activity is characterized by early transient cortisol biosynthesis, followed by its suppressed synthesis until late gestation, and extensive production of dehydroepiandrosterone (DHEA) and its sulfate (DHEA-S), precursors of placental estrogen, during most of gestation. The gland rapidly grows through processes including cell proliferation and angiogenesis at the gland periphery, cellular migration, hypertrophy, and apoptosis."

Trunk Muscle Development

This recent study shows an example of trunk muscle development at the end of the embryonic period.

Carnegie stage 22 - pectoralis major muscle.jpg Pectoralis Major Muscle Development[2]

(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

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.[3]

Anti-Müllerian Hormone Levels
Lower AMH Higher AMH
recurrent miscarriage[4] - Serum AMH levels may reflect quality, and quantity of the remaining oocytes in these patients, and RM patients may have a low ovarian reserve, and a potentially poor oocyte quality.

polycystic ovarian syndrome[3] - salivary and serum can be used for the diagnosis


Predictive Utility in Assisted Reproductive Technologies Outcomes "Anti-Müllerian hormone (AMH) has become one of the most informative biochemical markers of the ovary and is considered the earliest and most sensitive marker of reproductive aging. The accuracy of AMH in predicting ovarian response to controlled ovarian stimulation has led to AMH-based prognostication counseling and individualization of assisted reproductive technology (ART) stimulation protocols to optimize ovarian response and minimize hyperstimulation risks. Although AMH is considered a good predictor of quantitative ART outcomes, its correlation with qualitative ART outcomes is still controversial. The aim of this review is to provide an updated overview of the clinical utility of AMH in predicting ART outcomes.[5]


  1. . (1970). Embryonic vertebrate central nervous system: revised terminology. The Boulder Committee. Anat. Rec. , 166, 257-61. PMID: 5414696 DOI.
  2. 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.
  3. 3.0 3.1 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.
  4. McCormack CD, Leemaqz SY, Furness DL, Dekker GA & Roberts CT. (2019). Anti-Müllerian hormone levels in recurrent embryonic miscarriage patients are frequently abnormal, and may affect pregnancy outcomes. J Obstet Gynaecol , 39, 623-627. PMID: 30917731 DOI.
  5. Granger E & Tal R. (2019). Anti-Müllerian Hormone and Its Predictive Utility in Assisted Reproductive Technologies Outcomes. Clin Obstet Gynecol , 62, 238-256. PMID: 30994481 DOI.


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Cite this page: Hill, M.A. (2024, April 13) Embryology BGDA Practical 12 - Embryo to Fetus. Retrieved from

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G