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Charlotte Lozier Institute

Phone: 202-223-8073
Fax: 571-312-0544

2776 S. Arlington Mill Dr.
#803
Arlington, VA 22206

The
Voyage of Life
Weeks 1 and 2
Week 3
Week 4
Week 5
Week 6
Week 7
Week 8
Week 9
Week 10
Week 11
Week 12
Week 13
Week 14
Weeks 15 & 16
Weeks 17 & 18
Weeks 19 & 20
Weeks 21 & 22
Month 6
Month 7
Month 8
Month 9 and Birth

Week 7

Limbs and major organs form

Human Prenatal Age
  • Post-conception week 5
  • Days 28-34
  • Gestational Week 7
Highlights

  • Almost all major organs have started to form, including the lungs, liver, kidneys, stomach, and pancreas.

  • The preborn baby has arm and leg buds.

  • The embryo starts receiving nutrients and oxygen and expelling waste using the umbilical cord and placenta.1 

This week, the preborn baby is about 10,000 times bigger than he was at conception. For perspective, that makes him the size of a blueberry, or a little under a quarter inch from rump to head. At this point, his head is one-third of his overall size2 because the head grows faster than the rest of the body. In fact, since most newborn babies are born with about 100 billion brain cells, called neurons, the brain must grow at an average rate of 250,000 neurons per minute throughout the pregnancy.3

Brain development

In the first few weeks of the embryo’s life, brain growth is astonishing!

7
Weeks
By the end of week 7, the brain has separate right and left cerebral hemispheres,4 and a cerebellum. The cerebral hemispheres will direct speech, decision making, movement, balance, vision, memory, and many other functions. The cerebellum will control muscle coordination.
Face and body development

The face becomes more recognizable in week seven. Outgrowths from the forebrain become the optic nerve and the back of the eye. These cells interact with the outer surface of the embryo and form the eye’s lens.5 The nose gets a pair of little depressions that will become the baby’s nostrils. The early mouth and tongue start taking shape.6

At this stage, the embryo’s skin is just one cell thick. That makes the skin transparent and capable of excreting water and salts into the amniotic fluid.7 The limb buds keep growing, with the arm buds growing before the leg buds.

At this stage, the embryo’s skin is just one cell thick.
Heart development

The heart’s pacemaker cells also develop in week seven. These cells integrate into the right atrium of the heart.8 From this position, these pacemaker cells work in cooperation with nerve impulses to control a person’s heart rate for the rest of her life.

Lung development

The respiratory system begins forming at the very end of the sixth week gestation, around 26 days after conception. First, the 2 primary lung buds grow. These lung buds become the left and right lung. By 6 ½ weeks, the major airways to the left and right lungs, called bronchi, have grown. These bronchi divide into three major lobes on the right and two major lobes on the left.9  In week 7, the airways start branching repeatedly. This continues over the next ten to twelve weeks, until the airways have branched at least 17 times. After birth, these airways connect the alveoli, where air is exchanged in the lungs, to the windpipe and the external air.10

After the lung forms airways, it increases the surface area for gas exchange by creating new alveoli. Ninety percent of the gas exchange area is formed by subdividing existing airspaces by forming new walls to create new alveoli in a process called alveolarization. This process continues from 36 weeks gestation until the person is about 21 years old.11

Illustration of the stages of lung development. The lungs start developing around six weeks gestation. The lungs become progressively more branched and more able to exchange gases with the blood, so that the full-term newborn baby can breathe unaided. At birth, the baby will have developed 300 to 600 million alveoli, or about 1000 per alveolar sac. (Image Credit: Science Source)
Eggs and Sperm

This week, between 1000 and 2000 primary germ cells migrate to the developing ovaries or testes. Interestingly, a woman’s body creates all of her eggs starting at seven weeks gestation and finishing around five months. Similarly, in a man’s body, the primary germ cells that migrate in week 7 become spermatagonia, which will create all of the man’s sperm.12

Dive Deeper
Future Eggs and Sperm
Did you know that all of a woman’s eggs formed before she was born?
Read More
Back to The Voyage of Life
Sources
  1. Moore, Keith L, TVN Persaud, and Mark G. Torchia. The Developing Human, Clinically Oriented Embryology. 10th ed. Philadelphia: Elsevier, 2016.
  2. J. Laffont, “Embryology of the Brain,” Journal of Neuroradiology = Journal De Neuroradiologie 9, no. 1 (March 1982): 5–14.
  3. Sandra Ackerman, The Development and Shaping of the Brain, Discovering the Brain (National Academies Press (US), 1992), https://www.ncbi.nlm.nih.gov/books/NBK234146/.
  4. Ronan O’Rahilly and Fabiola Müller, “Significant Features in the Early Prenatal Development of the Human Brain,” Annals of Anatomy = Anatomischer Anzeiger: Official Organ of the Anatomische Gesellschaft 190, no. 2 (2008): 105–18, https://doi.org/10.1016/j.aanat.2008.01.001.
  5. Sadler, Thomas W. Medical Embyrology. 14th ed., 2019.
  6. Sadler, Thomas W. Medical Embyrology. 14th ed., 2019.
  7. Moore, Keith L, TVN Persaud, and Mark G. Torchia. The Developing Human, Clinically Oriented Embryology. 10th ed. Philadelphia: Elsevier, 2016.
  8. Moore, Keith L, TVN Persaud, and Mark G. Torchia. The Developing Human, Clinically Oriented Embryology. 10th ed. Philadelphia: Elsevier, 2016.
  9. Moore, Keith L, TVN Persaud, and Mark G. Torchia. The Developing Human, Clinically Oriented Embryology. 10th ed. Philadelphia: Elsevier, 2016.
  10. Moore, Keith L, TVN Persaud, and Mark G. Torchia. The Developing Human, Clinically Oriented Embryology. 10th ed. Philadelphia: Elsevier, 2016.
  11. Schittny JC. Development of the lung. Cell Tissue Res. 2017 Mar;367(3):427-444. doi: 10.1007/s00441-016-2545-0
  12. Moore, Keith L, TVN Persaud, and Mark G. Torchia. The Developing Human, Clinically Oriented Embryology. 10th ed. Philadelphia: Elsevier, 2016.
See Full Bibliography

All images and illustrations on The Voyage of Life were reviewed by credentialed scientists for accuracy.

Medical art animation was used to provide a schematic representation of fetal development, with some features, including timing, not to scale. The animation was chosen as an ethically uncompromised guide to fetal development. There are many real human images at each developmental age showing the most accurate fetal forms throughout development. A concerted effort was made to use images and material in which the human embryo or fetus did not undergo any known harm.

Page last updated on August 22, 2023
Sperm-egg fusion
Sperm-egg fusion