Biology 10.1- 10.2 Chapter: Pre-Implantation Development

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Questions and Answers

What is the initial step required for fertilization to occur after ovulation?

Formation of the placenta

Travel of the sperm through the uterine cavity

Modification of the sperm's genetic material

Release of the secondary oocyte from the ovary (correct)

Which structure helps transport the oocyte from the ovary to the uterine cavity?

Endometrium

Cervical canal

Follicular cells

Fimbriae (correct)

During capacitation, which change occurs in the sperm?

Decrease in motility

Formation of a zona pellucida

Alteration of sperm head permeability (correct)

Release of glycoproteins

The zona pellucida is located between which two structures?

Corona radiata and plasma membrane Signup and view all the answers

What triggers the acrosome reaction in sperm during fertilization?

Binding to glycoproteins in the zona pellucida Signup and view all the answers

What occurs immediately after the fusion of sperm and oocyte plasma membranes?

Depolarization of the oocyte's membrane Signup and view all the answers

How long after ovulation does the initial pre-implantation development phase typically occur?

10-12 days Signup and view all the answers

What is the primary function of the placenta during pregnancy?

To mediate fetal-maternal gas and nutrient exchange Signup and view all the answers

What happens to most sperm mitochondria after entering the oocyte?

They are destroyed. Signup and view all the answers

What triggers the cortical reaction after sperm fusion with the oocyte?

Increase in intracellular calcium levels. Signup and view all the answers

What is the function of the cortical granules during fertilization?

They block additional sperm from entering the oocyte. Signup and view all the answers

What occurs immediately after the formation of the zygote?

Epigenetic modifications begin. Signup and view all the answers

What is formed when the haploid male and female pronuclei fuse?

Diploid zygote. Signup and view all the answers

What is the primary outcome of cleavage during early embryonic development?

Division of cells without growth, resulting in blastomeres Signup and view all the answers

Which of the following describes totipotency?

The ability to give rise to all embryonic cell types. Signup and view all the answers

What happens during the period of embryonic cleavage?

The zygote begins rapid mitotic cell divisions. Signup and view all the answers

What stage follows the morula in early embryonic development?

Blastocyst Signup and view all the answers

Which component of the sperm enters the oocyte along with the sperm nucleus?

A pair of centrioles. Signup and view all the answers

Which part of the blastocyst develops into the embryo?

Inner cell mass Signup and view all the answers

What must happen for the blastocyst to develop further after fertilization?

It must implant into the uterine lining Signup and view all the answers

During which phase of the uterine cycle does the endometrium become primed for implantation?

Secretory phase Signup and view all the answers

What is the function of trophoblastic cells in the blastocyst?

They form the outer cell layer and develop into extraembryonic tissues Signup and view all the answers

What is the fluid-filled cavity within the blastocyst called?

Blastocoel Signup and view all the answers

Which step must occur before successful fertilization can take place?

The acrosome reaction Signup and view all the answers

What is the role of the blastopore during gastrulation?

It becomes the anal opening in mammals Signup and view all the answers

Which germ layer is responsible for forming the nervous system?

Ectoderm Signup and view all the answers

What does the archenteron eventually become during development?

The digestive tract Signup and view all the answers

During organogenesis, which germ layer is influenced by signaling molecules from the notochord?

Ectoderm Signup and view all the answers

Which type of cells are primarily located on the exterior of the embryo after gastrulation?

Ectodermal cells Signup and view all the answers

What is the outcome of gastrulation in embryonic development?

Development of a three-layered embryo Signup and view all the answers

Which germ layer gives rise to muscle and bone?

Mesoderm Signup and view all the answers

What process involves the differentiation of primary germ layers into functional organs?

Organogenesis Signup and view all the answers

What type of cell arises from the ectoderm during neurulation that contributes to the peripheral nervous system?

Neural crest cells Signup and view all the answers

During neurulation, what structure forms from the upward movement of the edges of the neural plate?

Neural folds Signup and view all the answers

What is the embryonic stage called after the ectodermal cell types are specified?

Neurula Signup and view all the answers

What is the primary outcome of the fusion of the lateral edges of the neural folds?

Creation of the neural tube Signup and view all the answers

What type of cells do neural crest cells differentiate into during development?

Neurons and glia of the peripheral nervous system Signup and view all the answers

Which structures are formed from the segmentation of mesodermal tissues adjacent to the neural tube?

Somites Signup and view all the answers

The neural groove is primarily located where in relation to the neural folds?

Below Signup and view all the answers

What type of precursor cells do somites develop into?

Muscle and connective tissue precursor cells Signup and view all the answers

Study Notes

Pre-Implantation Development

Fertilization is the union of male and female gametes to form a zygote, typically occurring in the uterine tube within 12-24 hours after ovulation
The developing embryo travels to the uterine cavity and must implant to allow for pregnancy
The time between fertilization and implantation takes place within 12 days after ovulation.

Fertilization

Capacitation prepares sperm to penetrate the oocyte through changes in the sperm's plasma membrane and flagellar motility.
Contact with the oocyte involves sperm moving past the corona radiata and reaching the zona pellucida via binding to zona pellucida glycoproteins using receptors located in the sperm head.
Acrosome reaction involves the release of hydrolytic enzymes from the acrosome, causing zona pellucida degradation.
Fusion of the sperm and oocyte plasma membranes triggers oocyte plasma membrane depolarization.
Sperm contents enter oocyte including the nucleus, mitochondria, and centrioles.
Cortical reaction occurs after sperm fusion, boosting intracellular calcium levels. This triggers cortical granules to fuse with the oocyte plasma membrane, preventing polyspermy.
Following fusion, the secondary oocyte completes meiosis II, with its nucleus becoming the female pronucleus
The male pronucleus forms from the sperm nucleus, and the two pronuclei fuse to form a diploid (2n) zygote.

Cleavage

After zygote formation, epigenetic modifications occur, leading to totipotency, the ability to develop into all embryonic cell types. Some parental epigenetic modifications remain, such as imprinted genes.
The zygote undergoes rapid mitotic cell division, known as embryonic cleavage, without cell growth, resulting in smaller daughter cells known as blastomeres.
The 3-4 day old morula stage consists of 16-32 blastomeres.
The morula travels from the uterine tube to the uterine cavity
By days 4-5, the developing embryo reorganizes into a blastocyst, containing a fluid-filled cavity known as the blastocoel, and consists of two cell populations: the inner cell mass and the trophoblast.

Implantation

For development to continue beyond the blastocyst stage, the blastocyst must implant into the uterine lining.
Surge in progesterone and estrogen during the secretory phase of the uterine cycle promotes implantation.
The developing trophoblastic cells attach to the endometrial surface causing the blastocyst to burrow into the endometrial lining.
The endometrial cells proliferate and surround the blastocyst, now referred to as an embryo, sealing it off from the uterine cavity.
The endometrium supports and nourishes the embryo until the placenta is fully formed.

Placenta

The placenta is a transient organ that mediates fetal-maternal gas and nutrient exchange.
Placental development starts when the trophoblast cells differentiate into two layers: cytotrophoblast and syncytiotrophoblast.
The cytotrophoblast proliferates and migrates into the underlying endometrium
The syncytiotrophoblast produces enzymes that invade the maternal tissues.
The placenta is comprised of a maternal portion, the decidua basalis, and a fetal portion, the chorionic villi
Maternal blood flows through the maternal side of the placenta, while the fetal side houses capillaries that carry fetal blood.
The placenta allows for the exchange of oxygen, nutrients, and waste products between the maternal and fetal circulations without direct contact between the maternal and fetal blood.

Concept Check

Capacitation is essential for sperm to reach the oocyte; its failure leads to a failed fertilization sequence.
The acrosome reaction allows the sperm to penetrate the zona pellucida, its failure means the sperm cannot reach the oocyte.
The cortical reaction prevents polyspermy, its failure leads to multiple sperm entering the oocyte, usually leading to a non-viable embryo.

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Description

This quiz covers the crucial processes of fertilization and pre-implantation development in human embryology. Explore the stages from sperm capacitation to the implantation of the embryo in the uterine cavity. Test your understanding of these fundamental biological concepts.