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By the end of this section, you will be able to:
  • Differentiate between the embryonic period and the fetal period
  • Briefly describe the process of sexual differentiation
  • Describe the fetal circulatory system and explain the role of the shunts
  • Trace the development of a fetus from the end of the embryonic period to birth

As you will recall, a developing human is called a fetus from the ninth week of gestation until birth. This 30-week period of development is marked by continued cell growth and differentiation, which fully develop the structures and functions of the immature organ systems formed during the embryonic period. The completion of fetal development results in a newborn who, although still immature in many ways, is capable of survival outside the womb.

Sexual differentiation

Sexual differentiation does not begin until the fetal period, during weeks 9–12. Embryonic males and females, though genetically distinguishable, are morphologically identical ( [link] ). Bipotential gonads, or gonads that can develop into male or female sexual organs, are connected to a central cavity called the cloaca via Müllerian ducts and Wolffian ducts. (The cloaca is an extension of the primitive gut.) Several events lead to sexual differentiation during this period.

During male fetal development, the bipotential gonads become the testes and associated epididymis. The Müllerian ducts degenerate. The Wolffian ducts become the vas deferens, and the cloaca becomes the urethra and rectum.

During female fetal development, the bipotential gonads develop into ovaries. The Wolffian ducts degenerate. The Müllerian ducts become the uterine tubes and uterus, and the cloaca divides and develops into a vagina, a urethra, and a rectum.

Sexual differentiation

This flow chart shows how the sexual organs develop in embryos. The left side of the flow chart shows the development of male organs and the right side of the flow chart shows the development of female organs.
Differentiation of the male and female reproductive systems does not occur until the fetal period of development.

The fetal circulatory system

During prenatal development, the fetal circulatory system is integrated with the placenta via the umbilical cord so that the fetus receives both oxygen and nutrients from the placenta. However, after childbirth, the umbilical cord is severed, and the newborn’s circulatory system must be reconfigured. When the heart first forms in the embryo, it exists as two parallel tubes derived from mesoderm and lined with endothelium, which then fuse together. As the embryo develops into a fetus, the tube-shaped heart folds and further differentiates into the four chambers present in a mature heart. Unlike a mature cardiovascular system, however, the fetal cardiovascular system also includes circulatory shortcuts, or shunts. A shunt    is an anatomical (or sometimes surgical) diversion that allows blood flow to bypass immature organs such as the lungs and liver until childbirth.

The placenta provides the fetus with necessary oxygen and nutrients via the umbilical vein. (Remember that veins carry blood toward the heart. In this case, the blood flowing to the fetal heart is oxygenated because it comes from the placenta. The respiratory system is immature and cannot yet oxygenate blood on its own.) From the umbilical vein, the oxygenated blood flows toward the inferior vena cava, all but bypassing the immature liver, via the ductus venosus    shunt ( [link] ). The liver receives just a trickle of blood, which is all that it needs in its immature, semifunctional state. Blood flows from the inferior vena cava to the right atrium, mixing with fetal venous blood along the way.

Questions & Answers

master gland Kon si h
kajal Reply
Pituitary gland
KUNDAN
pituitary gland because it give harmonies and control other gland
ABDULLAH
glands often secrete hormones which play an important role in maintaining homeostasis.
KUNDAN
pituitary gland
Aftab
pituitary gland is master gland because it present in biran and secrtehormones and play other gland of human body and function its gland so that also called master gland.
ABDULLAH
pituitary glandis the master gland of our body
Nadeem
how do you study for A&P? lab and lecture?
Aubrey Reply
When one is suffering from motion sickness what area of the brain may trigger emesis?
amy Reply
that is the sign of stroke. if the patient have a stroke. the left side of body is weakness, the affected right of cerebrum but if right side of the body is weakness surely in left side!
Larry
thank you sooo much bro
Fatima Reply
helloo
Sentamu
Fatima hw a u
Sentamu
hii
Shubham
any one elaborate fr me foramens of the skull and features which they transmit
Sentamu
icant undrestand plz
zahruuzh Reply
try to read I hop you will understand
state and explain 20 radiology uses
ILYAS Reply
what are chemicals in anatomy and physiology?
Mike Reply
what can I do to find it easy for me in anatomy and physiology course
Mike
study up on the basics of the periodic chart, learn bones and muscles attachments, and learn muscles. Those take the longest to memorize. After that it should be a little easier.
Toni
what are the two types of body cells
Jennifer Reply
what is malnutrition
Claire
malnutrition refers to faulty nutrition resulting from malabsorption,poor diet or overeating. Sometimes too these food do not contain all the six food nutrients in their right proportion.
Yakubu
thank you
Claire
welcome
Yakubu
Will u be malnourished?
Baigwa
gud
Budumari
What's the difference between radiology and radiology
gabriel
Nothing! Radiology it means the study or using of radiation in medical science it can be 1.diagnose or treatment diagnosed radiology! x- ray. ultrasound. ct-scan. mammogram. MRI. 2. treatmen- radiation oncology, like Cobalt 60. and nuclear medicine
Larry
what is X-ray?
Nissar
X-ray is type of light that make it possible to see inside any object. as human body
KUNDAN
How the nervous system develops
ayiesher Reply
From the cells at the back of an embryo
Mma
breifly explain anatomy of thorax
Hadiza Reply
How many region the rib is divided
Konneh
how many bon of human being
Nura
206
John
how to study for the skeletal system
ryaisha
and anatomy
ryaisha
I really need sources immediately
ryaisha
I printed out all the different bones. Put them in the see through protective sheaths and got dry erase markers. I could right on them and erase to help me learn to spell the names of markings and bones.
Toni
Or go to a book store, Barnes and Noble(doesn't have to be this) and they have coloring books for anatomy. $16. Really helpful.
Toni
okay thanks and are what study tools you use to study the materials and get a better understanding
ryaisha
*what are
ryaisha
hiii
Roopa
I prefer diagrams, pictures that lay out each step with the information in each step. For Example: how action potential creates muscles to move. A pictured diagram gives me a better understanding of how each piece plays a role in each step of the process.
Toni
Also for basics, such as memorizing vocab. Flash cards are great. Don't become discouraged if you don't get them all right the first times through. The more you go through them, your brain will remember pieces of information from each and help you to pull out the information 😉
Toni
okay thanks
ryaisha
what is the functions of the lips in human
Momboi Reply
could I say sensation?
Sovilace
kissing
Obrian
for protection
Omar
Lips assist in speech and eating
Cindy
Too many easy questions. Which bones are the axial and appendicular? What are the abbreviations for TEE, TTE, AED, A-Mode, B-Mode, and LTH? What is the difference between hypothalamus and thalamus? Where is the parathyroid located? How many True Ribs do we have?
Sovilace Reply
Transesophageal echocardiography Transthoracic Echocardiography automated external defibrillator brightnees mode Los Hermanos Taverna
Inam
what is anatomy
okello Reply
anatomy is scientific study of body structures and how they relate to each other
Skeater
Are there other functions of the nucleolus apart from synthesis of RNA and formation of ribosomes
Peninah Reply
plays a role in cell response to stress
airiz
what is angle of auscultation
Bryan Reply

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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