Week 7 to 8

Fingers, toes, and a working digestive system

Human Prenatal Age
  • PCW 8
    i
  • Days 49-55
  • Gestational Week 10
Highlights
  • Toes and fingers are free to wiggle.

  • The embryo shows a preference for the right or left hand.1

  • The electrical activity recorded from the heart of an unborn child resembles that of a newborn.2

  • The brain is still extremely large and makes up ~43% of the embryo’s total weight.3 For comparison, the brain is only 10% of the newborn’s body weight and 2% of an adult’s body weight.

  • The eye finishes forming, complete with a lens, cornea, iris, and retina.4

This week marks the end of the embryonic period.  During the last eight weeks, the embryo has grown from a single cell into nearly one billion cells that form over 4,000 distinct anatomic structures.5 The adult has about 4,500 named body parts, so this means that over 90% of these structures first appear during the embryonic period.6

This image shows a real living embryo in the womb, recorded using fetoscopy. Note how the fingers are separate and the toes are all free to wiggle. (Image Credit: The Center for Bio-Ethical Reform)

The embryo can now bend his elbows and bring his hands together. The embryo can also roll over within the amniotic sac, squint, grasp and point his toes.7 When the embryo touches his face, he will frequently move his head away.8 The embryo even makes intermittent breathing motions.9

In the eighth week after conception, the digestive system and kidneys start working. The stomach and pancreas start making most of the digestive enzymes.10 Interestingly, there is not enough space in the fetal abdomen for the entire intestine, so a few of the loops of intestine remain just under the umbilical cord until 10 weeks after conception.11  The kidneys start to filter toxins out of the blood stream. The embryo starts to produce urine and pee into the amniotic fluid.12  After an adult swallows food, contractions in his esophagus and intestines help propel the food forward in a process called peristalsis. Peristalsis begins in the embryo’s large intestine in the eighth week and continues for the rest of his life.13

This week, males develop testes. The testes start producing testosterone, and another hormone called anti- Mullerian hormone. These hormones help develop the rest of the male genitalia. Without these two hormones, the embryo would develop female genitalia, even if the embryo had a Y-chromosome and was genetically male.14

Up until this point, the embryo’s internal organs were easily viewed through the thin skin. Around eight weeks after conception, the skin develops a second layer of cells, hiding the internal organs but leaving most blood vessels visible.15

Note how the skin is opaque on these fingers and toes. Just a few days ago, it was easy to see the developing tissues underneath. (Image Credit: Priests for Life)
The eye continues developing rapidly.
Dive Deeper
Eight weeks after conception, it is possible to determine left-handedness or right-handedness...
The eyes begin forming 22 days after conception...