Fetal Development Week by Week Overview

Scientist Cindy

9 Feb 202105:33

Summary

TLDRThe script outlines the critical stages of human embryonic development from conception through week 38. It details the formation of vital organs, the establishment of bodily systems, and the physical changes that occur as the embryo evolves into a fetus. Key milestones include the development of the brain and spinal cord, the initiation of a heartbeat, the emergence of limbs, and the maturation of the lungs. By week 12, sexual differentiation is apparent, and by week 20, the fetus shows active movements. The summary covers the progression of fetal growth, highlighting the transition from a tiny embryo to a fully formed, viable human being ready for birth at term.

Takeaways

🚀 The embryonic stage starts at day 15 post-conception and lasts until week 8, marking the initial development of major body structures.
🧠 By week three, the brain, spinal cord, and heart begin to form, with the neural tube emerging as the precursor to the spinal cord.
🔍 In week four, the brain starts to differentiate, and limb buds grow, with the heart beginning to beat rhythmically by week five.
🫁 Week six sees the commencement of lung formation and the establishment of fetal circulation, along with the liver's initiation of red blood cell production.
👶 By week seven, the trunk straightens, and features like nipples, hair follicles, elbows, and toes start to form, with arms and legs showing more movement.
🌀 In week eight, the intestines rotate, and the embryo's facial features further develop, with the heart's development nearing completion.
🦷 From weeks 9 to 12, sexual differentiation continues, and the digestive system shows activity, with the head constituting nearly half the fetus's size.
👶🏻 By week 12, the fetus's limbs are long and thin, digits are well-formed, and fetal gender can be determined via ultrasound.
👀 Between weeks 13 and 16, lanugo hair develops, and the fetus makes active movements, swallowing amniotic fluid, with external genitalia becoming recognizable.
🧠 Weeks 17 to 20 are marked by rapid brain growth, with fetal heart tones audible via stethoscope and the kidneys secreting urine into the amniotic fluid.
👁️‍🗨️ From weeks 21 to 24, the fetus develops a hand grasp and startle reflex, with alveoli beginning to form in the lungs and the production of surfactant commencing.

Q & A

At what stage does the embryonic development begin and how long does it last?
-The embryonic stage of development begins at day 15 after conception and continues through week 8.
What are some of the key developments that occur during the embryonic stage?
-During the embryonic stage, the basic structures of all major body organs and the main external features are completed, including the development of the brain, spinal cord, heart, gastrointestinal tract, and limb buds.
When does the heart begin to beat a regular rhythm during fetal development?
-The heart begins to beat a regular rhythm in week five of fetal development.
What significant developments occur in the fetal brain during week six?
-In week six, the formation of the lungs begins, fetal circulation is established, the liver starts producing red blood cells, and the brain develops further with the central nervous system becoming detectable with brain waves.
What changes are observed in the fetus during week seven of development?
-In week seven, the trunk straightens, nipples and hair follicles form, elbows and toes develop, arms and legs move more frequently, and the diaphragm is formed.
How does the fetus's appearance change by the end of week eight?
-By week eight, the intestines rotate, facial features continue to develop, heart development is complete, and the embryo begins to resemble a human being.
What are some of the developments that occur in the fetus between weeks 13 and 16?
-During weeks 13-16, lanugo develops on the head, the skin becomes almost transparent as bones harden, the fetus makes active movements, and external genitalia become recognizable. Fingernails and toenails are also present as the fetus's weight quadruples.
When can fetal movement, or quickening, be detected by the mother?
-Fetal movement, or quickening, is usually detected by the mother during the phase of weeks 13-16.
What are some of the key milestones in fetal development between weeks 21 and 24?
-Between weeks 21 and 24, eyebrows and eyelashes are well-formed, the fetus has a hand grasp and startle reflex, alveoli begin forming in the lungs, and the lungs start to produce surfactant.
How does the fetus's brain and nervous system develop during weeks 25 to 28?
-During weeks 25-28, there is rapid development of the brain, eyelids are able to open and close, the nervous system can control some of the fetus's functions, and fingerprints are set.
What are the notable developments in the fetus during weeks 29 to 32?
-In weeks 29 to 32, there is a rapid increase in body fat, increased central nervous system control over body functions, rhythmic breathing is established, and the fetus stores iron, calcium, and phosphorus.
What are the final preparations for birth that the fetus undergoes between weeks 33 and 38?
-Between weeks 33 and 38, the fetus's lanugo begins to disappear, body fat increases, earlobes form and become firm, fingernails reach the end of the fingertips, and small breast buds are present on both sexes. The fetus is also supplied with antibodies against disease by the mother.

Outlines

00:00

👶 Embryonic Development Overview

The embryonic stage, commencing at day 15 post-conception and extending to week 8, is a critical period for the formation of the body's major organs and external features. By week three, the brain, spinal cord, heart, and gastrointestinal tract start developing. The neural tube, precursor to the spinal cord, also forms. Limb buds emerge and grow, and by week four, the brain's differentiation advances alongside limb development. Week five marks the onset of the heart's regular rhythm, with initial eye and ear structures becoming apparent. The brain continues to develop in week six, with the lungs beginning to form and fetal circulation being established. The liver starts producing red blood cells, and brain waves become detectable. In week seven, the body straightens, and features like nipples, hair follicles, elbows, and toes form. The fetus begins to move more, and the diaphragm develops. Tooth buds and facial features become visible. Week eight sees the intestines rotating and further facial development, with the heart's completion and the embryo starting to resemble a human. The subsequent weeks through 12 are marked by sexual differentiation, development of teeth buds, and maturation of the digestive and urogenital systems. The fetus's head constitutes nearly half its size, and by week 12, gender determination via ultrasound is possible, revealing long limbs and well-formed digits. From weeks 13-16, lanugo hair develops, and bones harden as the skin remains transparent. The fetus becomes more active, swallowing amniotic fluid, and external genitalia become recognizable. Fingernails and toenails form, and the fetus's weight increases significantly. Fetal movements, or 'quickening,' are typically felt by the mother during this phase. Weeks 17-20 are characterized by rapid brain growth, audible fetal heart tones, and the kidneys' active secretion of urine. The fetus is covered in vernix caseosa, and eyebrows and head hair may appear. Muscles are well developed, and nails are present on fingers and toes. During weeks 21-24, eyebrows and eyelashes are fully formed, and the fetus exhibits a hand grasp and startle reflex. Alveoli start forming in the lungs, and the skin remains translucent. The fetus's eyelids are sealed, but surfactant production begins. By weeks 25-28, the fetus reaches approximately 15 inches in length, with significant brain development and functional nervous system control. Fingerprints are established, and subcutaneous fat becomes visible. Blood formation shifts from the spleen to bone marrow, and the fetus usually adopts a head-down position. From weeks 29 to 32, body fat increases rapidly, and the central nervous system's control over body functions strengthens. Rhythmic breathing is established, though the lungs are not yet fully mature. The fetus stores iron, calcium, and phosphorus. In weeks 33-38, the male fetus's testes descend into the scrotum, and lanugo begins to disappear. The fetus's hand grasp reflex is strong, and body fat continues to increase. Earlobes form and firm up, and fingernails reach the fingertips, with small breast buds present in both sexes. The mother provides the fetus with antibodies for disease protection, and by 38 weeks, the fetus is considered full-term, filling the entire uterine space.

05:02

🤰 Maternal and Fetal Development at Term

The final paragraph discusses the maternal supply of antibodies to the fetus, which is crucial for disease protection. It emphasizes that by 38 weeks, the fetus is considered full-term, having filled all available space within the uterus. This stage signifies the completion of the fetal development process, with the fetus being fully prepared for birth and life outside the womb.

Mindmap

Keywords

💡Embryonic stage

The embryonic stage refers to the period in human development that begins at day 15 after conception and continues through week 8. During this stage, the basic structures of all major body organs and the main external features are completed, including internal organs. This stage is crucial as it lays the foundation for the development of the fetus. The script mentions that by week three, the brain, spinal cord, and heart begin to develop, marking the beginning of the embryonic stage.

💡Neural tube

The neural tube is a critical structure that forms during the embryonic stage and later becomes the spinal cord. It is a hollow structure that arises from the ectoderm and gives rise to the central nervous system. The script highlights that the neural tube forms by week three, which is a significant milestone as it is the precursor to the nervous system's development.

💡Limb buds

Limb buds are the early, undeveloped stages of arms and legs that appear during the embryonic stage. They grow out from the small body and eventually develop into fully formed limbs. The script notes that leg and arm buds begin to appear and grow out from the small body, indicating the start of limb development.

💡Brain differentiation

Brain differentiation is the process by which the brain starts to develop specialized regions and structures during the embryonic stage. In the script, it is mentioned that by week four, the brain begins to differentiate, which is essential for the development of cognitive functions and the overall structure of the brain.

💡Fetal circulation

Fetal circulation refers to the circulation of blood in the developing fetus, which is distinct from the circulation after birth. The script states that fetal circulation is established in week six, which is vital for the oxygenation and nourishment of the developing fetus.

💡Red blood cells

Red blood cells, also known as erythrocytes, are cells that carry oxygen throughout the body. The script mentions that the liver begins producing red blood cells in week six, which is a critical step in the development of the fetal circulatory system.

💡Sexual differentiation

Sexual differentiation is the process by which the biological and morphological differences between males and females develop. The script indicates that sexual differentiation continues through weeks 8 to 12, which is when the physical characteristics that define sex are established.

💡Lanugo

Lanugo is a fine, downy hair that covers the skin of a fetus during pregnancy. The script notes that lanugo develops on the head during weeks 13-16, which is a normal part of fetal development and provides insulation to the fetus.

💡Quickening

Quickening refers to the first noticeable movements of a fetus, which can be felt by the pregnant person. The script mentions that fetal movement, or quickening, is usually detected by the mother during weeks 13-16, marking a significant milestone in pregnancy as it indicates the fetus is active and developing.

💡Vernix caseosa

Vernix caseosa is a white, greasy substance that covers the skin of a fetus, providing a protective layer. The script describes that vernix caseosa covers the fetus during weeks 17-20, which is important for maintaining the skin's integrity and preventing infection.

💡Fetal reflexes

Fetal reflexes are automatic, involuntary responses to stimuli that develop in the fetus. The script mentions the development of reflexes such as the hand grasp and startle reflex during weeks 21-24, which are indicative of the nervous system's maturation and the fetus's ability to respond to its environment.

💡Surfactant

Surfactant is a substance produced in the lungs that helps reduce surface tension, allowing the lungs to expand more easily during breathing. The script states that the lungs begin to produce surfactant during weeks 21-24, which is crucial for the preparation of the fetus for breathing air after birth.

Highlights

The embryonic stage begins at day 15 after conception and lasts through week 8.

By week 3, the brain, spinal cord, heart, and gastrointestinal tract begin to develop.

During week 4, limb buds grow, and the brain starts differentiating.

In week 5, the heart begins a regular rhythm, and early structures of the eyes and ears are noticeable.

Week 6 marks the formation of the lungs, and fetal circulation is established.

Brain waves are detectable, and the primitive skeleton forms in week 6.

By week 7, the embryo shows a straightening of the trunk, and arm and leg movements become more frequent.

In week 8, the embryo starts to resemble a human, and heart development is complete.

By week 12, sexual differentiation continues, and the face and neck are well formed.

In weeks 13-16, the fetus's bones harden, and lanugo (fine hair) develops.

Fetal movement (quickening) is often detected by the mother during weeks 13-16.

During weeks 17-20, the fetus experiences rapid brain growth, and fetal heart tones can be heard with a stethoscope.

Weeks 21-24 see the development of the hand grasp and startle reflex, and alveoli begin forming in the lungs.

In weeks 25-28, the brain undergoes rapid development, and the fetus's nervous system begins controlling some functions.

By week 38, the fetus is considered full-term, filling all available space in the uterus.