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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

so meaning of dissect
Mary Reply
what are lymph nodes
Memory Reply
what is the best book that shows unit 1 about cell unit 2 about tissue unit 3 about embroyology
Abraham Reply
2
Hellen
to understand structure of body able to understand function of system. to understand how to build human body and function
Dereje Reply
hi
Neela
to determine body structures
Petra Reply
to know the use of each and every part of our body
Petra
to understand how our body structures work to support our lives
Petra
Is this a question?
Tammy
So what was the question?
Thamie
All the body work together to make the whole organism life possible
Kwasi
what is carbon dioxide respiratory system why?
Prachi Reply
Carbon dioxide (CO2) is involved with the chemical process of cellular respiration. It is produced as a cellular waste product during the decomposition reactions and serves an important role in maintaining the appropriate acid-base balance in the body.
Tammy
thank you
Prachi
You're welcome!
Tammy
i have not under stood human heart
Simbwa Reply
means?
Dilshan
why a man became wild at the time of sexual intercourse. reason?
Soul
what is anatomy
philemon Reply
what is anatomy in terms of medicine
philemon
it is the study of human and animal form by observing and examined them and sometimes dissecting them and view the tiny thing by the use of microscope
Kwasi
anatomy is simply the scientific study of the body's structures
Petra
study of human body and animal
Crystal
why a man becomes wild at the time of sexual intercourse
Soul
Anatomy is the study of structure of the human body.
Tammy
Physiology is the study of the functions of the human body
Tammy
Describe early studies into the working of human body.
Tonny Reply
please guys help me to answer this question; Define the two divisions of the skeleton ?
Jonathan Reply
two example of appendicular skeleton
Jonathan
upper limb ;eg humerus n lower limb;eg tibia
BRIAN
write notes on the level of organizations of the body .citing examples for each level
Kaddijatou Reply
Jonathan Nyakpaab
Jonathan
what is pathology
Ericka Reply
1 What is Nasogastric Tube 2 what is the difference between Nasogastric Aspiration and Nasogastric Feeling
ONOJA Reply
You measure a patient’s blood pressure at 130/85. Calculate the patient’s pulse pressure and mean arterial pressure. Determine whether each pressure is low, normal, or high.
ONOJA
normal blood pressure 120/80
Mohd
what are nocciceptors
Soul
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Mohd
1 Its a flexible tube of plastic that pass through the nose, down to the eausophagus, and into the stomach, used to add or remove substances in the stomach.
Andile
2 Nasogastric aspiration is process of draining stomach contents via a tube and Nasogastric feeding is a process of giving food liquid through nasogastric tube
Andile
andile sir what is meant by clonoscopy
Soul
colonoscpopy is an exam use to detect abnormalities in the small intestine or the colon
Kwasi
What is the skin
Astony Reply
What is physiology?
Njaleny Reply
it is the study of the structure of the human body and its reationship
Hannah
Physiology is the function of a living organism.
Tammy
It is the study of human body and how it works.
Excellent
if physiology is the function of a living organism.What method is keep for living organism.
Ayoore
what are Nocciceptors
Soul
Nocciceptors are pain receptor
Kwasi
Or is a sensory neutron that responds to damage
Kwasi

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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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