Between Week 3 & 4 my rapid growth continues. My body folds over on itself, thus allowing for the formation of the chest and abdominal cavities. A portion of the yolk sac forms the lining of the lungs and intestinal tracts. Arm and leg buds form, and somites in my back begin to form the skin and muscles. Later, these somites will form the skull, spine and ribs. The transparent sac, the amnion, begins forming at 2 weeks, and completely surrounds my tiny body at 4 weeks. The fluid in the sac is sterile, protects my body, provides nutrition, and assists with breathing and swallowing. At 4 1/2 weeks an early cerebellum forms. This portion of the brain controls the muscles, and assists with coordination of my entire body.
The two cerebral hemispheres begin to form and protrusions on each side of the forebrain give rise to the optic vesicles, over which a lens can be seen. The eyes develop from this, and facial features, including an early mouth are formed. The heart’s pacemaker cells in the sinoatrial node appear at 4 weeks. These tissues control my heart rate and rhythm. Watch the video of my heart beating below. At 4 1/2 weeks the two bronchi appear from the lung buds. The bronchial tree rapidly grows at 5 weeks and continues through week 17. At 5 weeks the optic cup forms with pigment cells in the retina. Also my liver starts producing blood cells for the first time within my body. The esophagus, stomach, intestine and pancreas develop now, as do the kidneys. Busy time!
The gonads are forming now and germ cells migrate from the yolk sac into the gonads. My Pituitary Gland forms at week 5 and begins secreting Growth Hormone and ACTH, which stimulates the Adrenal Gland. At week 5 my hand plates form, and my skin is only one layer thick, allowing it to be transparent. Yikes! You can see my Guts and other Innerds! At 5 1/2 weeks my cartilage develops, and at 6 weeks my neurons and their connections, called synapses are beginning. I begin to move now, but my mum won’t be aware of my movement for another 8 to 10 weeks. Float like a Butterfly, Sting like a Bee! Look out Ali! At 6 weeks my external ear is taking shape and my ear canal is opening.
Digital rays form at 5 1/2 weeks, then the fingers and bones of the thumb can be seen. Lymphocytes are formed in my bright red liver, and these help with my immunity. Nipples are present in the arm pit, but later move to the front of the chest. The large muscle of breathing, the diaphragm, forms now, and the intestine protrudes into the umbilicus, allowing room in my tummy for other organs. This is temporary. My hormones continue to be secreted, flowing freely. The Parathyroid Gland secretes a hormone that controls calcium, and the Adrenal Gland secretes stress hormones, as well as hormones that control fluid and electrolytes. The Pancreas begins secreting Glucagon, which controls my sugar. Mum, don’t forget the cake with Panuci Icing!
Brain waves are detected at 6 weeks, 2 days, early taste buds are present at 7 weeks, and hiccups can be observed. Fingers and toes progress at 6 1/2 weeks, and by 7 weeks the heart has 4 chambers, and the pacemaker in the atrium is further developed. The heart rate is at its maximum of 167 to 175 beats per minute at this time. Bone formation on the cartilage occurs in the clavicle and jaw bones between week 6 and 7. I have a startle response and move my legs at 7 weeks. B-lymphocytes are found in my liver, while ovaries are present now in the females, and in my boy-cousins, the Y chromosomes allow for secretion of a substance that stimulates the testes.
At 7 1/2 weeks I bring my hands and feet together, my knees are evident, and I practice kicking. Nephrons, the filtering organ of the kidneys, are present, as are tendons that connect my muscles to my bones. At the end of my embryonic period my eyelids grow and begin to fuse shut. I have over 90% of the adult structures at 8 weeks, the end of my embryonic period.
"The poor have much to teach you. You have much to learn from them."
— St. Vincent de Paul
My fellow embryos and fetuses are some of the poorest people I know.
For more information, visit: www.ehd.org.
With love,
Rose M. Bryo
At 4 1/2 weeks gestation, my heart beats for you, Mum.
Rose M. Bryo, 2 months gestation, Self Portrait, Graphite on Drawing Paper