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Pre-embryonic cleavages

This figure shows the different stages of cell divisions taking place before the embryo is formed. The top panel shows the cell divisions occurring in the uterine tube and the bottom panel shows the cell divisions occurring in the uterus.
Pre-embryonic cleavages make use of the abundant cytoplasm of the conceptus as the cells rapidly divide without changing the total volume.

As the blastocyst forms, the trophoblast excretes enzymes that begin to degrade the zona pellucida. In a process called “hatching,” the conceptus breaks free of the zona pellucida in preparation for implantation.

View this time-lapse movie of a conceptus starting at day 3. What is the first structure you see? At what point in the movie does the blastocoel first appear? What event occurs at the end of the movie?

Implantation

At the end of the first week, the blastocyst comes in contact with the uterine wall and adheres to it, embedding itself in the uterine lining via the trophoblast cells. Thus begins the process of implantation    , which signals the end of the pre-embryonic stage of development ( [link] ). Implantation can be accompanied by minor bleeding. The blastocyst typically implants in the fundus of the uterus or on the posterior wall. However, if the endometrium is not fully developed and ready to receive the blastocyst, the blastocyst will detach and find a better spot. A significant percentage (50–75 percent) of blastocysts fail to implant; when this occurs, the blastocyst is shed with the endometrium during menses. The high rate of implantation failure is one reason why pregnancy typically requires several ovulation cycles to achieve.

Pre-embryonic development

This figure shows the different stages in pre-embryonic development. A diagram of the uterus is shown and from this image, eight callouts show the different stages of development.
Ovulation, fertilization, pre-embryonic development, and implantation occur at specific locations within the female reproductive system in a time span of approximately 1 week.

When implantation succeeds and the blastocyst adheres to the endometrium, the superficial cells of the trophoblast fuse with each other, forming the syncytiotrophoblast    , a multinucleated body that digests endometrial cells to firmly secure the blastocyst to the uterine wall. In response, the uterine mucosa rebuilds itself and envelops the blastocyst ( [link] ). The trophoblast secretes human chorionic gonadotropin (hCG)    , a hormone that directs the corpus luteum to survive, enlarge, and continue producing progesterone and estrogen to suppress menses. These functions of hCG are necessary for creating an environment suitable for the developing embryo. As a result of this increased production, hCG accumulates in the maternal bloodstream and is excreted in the urine. Implantation is complete by the middle of the second week. Just a few days after implantation, the trophoblast has secreted enough hCG for an at-home urine pregnancy test to give a positive result.

Implantation

This figure shows the different steps during implantation. The top panel shows how the blastocyst burrows into the endometrium. The middle panel shows the blastocyst completely surrounded by the endometrium. The bottom panel shows the implanted embryo growing in the uterus.
During implantation, the trophoblast cells of the blastocyst adhere to the endometrium and digest endometrial cells until it is attached securely.

Most of the time an embryo implants within the body of the uterus in a location that can support growth and development. However, in one to two percent of cases, the embryo implants either outside the uterus (an ectopic pregnancy    ) or in a region of uterus that can create complications for the pregnancy. If the embryo implants in the inferior portion of the uterus, the placenta can potentially grow over the opening of the cervix, a condition call placenta previa    .

Questions & Answers

Capillary permeability
what do you want to know about it?
Ramsin
Hello, I want to search about the topic, information and pictures
syncitium is the property of which of the following muscle
Shahab Reply
can I get the questions of human physiology that is present in HSC 2nd semester
Sai Reply
i now madam
irpa
ha can u please send me the PDF of questions
Sai
it's important to me to have that information please send as fast as u can
Sai
me too if possible?
Ramsin
If a molecule can only pass through a membrane with the assistance of a membrane protein, but the direction of its travel is controlled only by its concentration, the process is called?
osmosis
chozen
A 52 year old woman turned her head quickly, during a tennis game and suddenly felt a sharp pain in her neck along her upper limb. Physical examination and medical imaging revealed a herniated degenerated IV disc in the cervical region of her vertebral column.
Isaac
a. What probably caused the IV disc herniation? b. What cause IV disc degeneration? c. What are the result of disc degeneration?
Isaac
b
Mirasol
Describe the neural control of erection and ejaculation.
Nana Reply
A 52 year old woman turned her head quickly, during a tennis game and suddenly felt a sharp pain in her neck along her upper limb. Physical examination and medical imaging revealed a herniated degenerated IV disc in the cervical region of her vertebral column. a)What probably caused the IV di
Isaac
a) What probably caused the IV disc herniation? b) What cause IV disc degeneration? c) What are the result of disc degeneration?
Isaac
iv disc herniation compress the nerve cause numbness tingling sensation even paralysis in severe cases...
Khawaja
explain more
DANIELLA Reply
yes
Ramzan
function of skeleton
Josiah Reply
- for movement - blood production by the bone marrow
Daniel
production of calsium and phosphorus
Juma
Shortly after childbirth, a woman consulted her physician about a tender swelling in her perineal region. 8. What fossa related the perineal swelling? 9. Describe what vessel may cause the collection of blood in the fossa after childbirth?
Isaac
what is heart
Subhajit Reply
it is the tissue..which pump blood to the all parts of body
GRAY
the heart is a conical , hollow, muscular organ which works continuously through out the life of a person ,it is about the size of a clenched fist and weighs about 300 grams and also the heart is in the chest just behind the breast bone and between the two lungs
Mary
a hollow muscular organ that pumps blood through the circulatory system by regular contractions
Johnny
is a muscular organ that pumps blood lungs and other body tissues through vessels
Nolosha
Shortly after childbirth, a woman consulted her physician about a tender swelling in her perineal region. 8. What fossa related the perineal swelling? 9. Describe what vessel may cause the collection of blood in the fossa after childbirth?
Isaac
Shortly after childbirth, a woman consulted her physician about a tender swelling in her perineal region. 8. What fossa related the perineal swelling? 9. Describe what vessel may cause the collection of blood in the fossa after childbirth?
Isaac Reply
inguinal fossa femoral vein?
Jeen
if you dont the answer by now you should seek another line of work. as a professor it is my duty to let you know about your lacking.
Arif
branches of brachial plexus
Arooj Reply
musculocutaneous, median, ulnar, axillary, and radial nerves.
Shakerah
Shortly after childbirth, a woman consulted her physician about a tender swelling in her perineal region. a.What fossa related the perineal swelling? b.Describe what vessel may cause the collection of blood in the fossa after childbirth?
Isaac
What is great Auricular nerve?
ZUBAIR Reply
it originates from the cervical plexus that provides sensory innervation to the skin.
Daniel
why it is called Auricular nerve
Amber
is any payment is needed to use this app
Suprith Reply
is it a question?
Samenjo
doubt about this app
Suprith
which lines divide the body into nine quadrant
Julius Reply
nine regions of abdomen can b marked using two horizontal & two vertical lines...the vertical lines are the mid clavicular lines taken from the mid point of each clavicle. the upper horizontal lines is the subcostal line taken from the inferior parts of the lowest costal cartilage...
Khawaja
to get a better understanding for the function
Rashana Reply
anatomy and physiology work closely together
Rashana
anatomy to you about the structure of the while physiology is the the study of the body function
Rashana
what is the difference between negative and positive feedback
Rashana
The key difference bewteen positive and negative feedback is their response to change. Positive feedback amplifies change while negative reduces change.
ladychen
negative feed back produces a response that brings back to normal while positive feed back produces a response that stimulates
Julius
examples of the body structure
Naki Reply
body's structure
Naki

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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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