Chapter and Physiology Chapter 29

 What is the period of embryonic development?

The first two months after fertilization, during which the developing human is called an embryo.

What is the period of fetal development?

From week 9 until birth, when the developing human is called a fetus.

What is prenatal development?

The time from fertilization until birth, divided into three trimesters.

What is the gestation period?

The time from fertilization to birth, approximately 38 weeks.

What is the prenatal period?

The period before birth, which includes embryological and fetal development.

What is embryological development?

 The first 2 months after fertilization, when all principal adult organs are present.

What is fetal development?

From week 9 until birth, when the placenta is functioning by the end of the 3rd month.

What is the neonatal period?

The first 42 days after birth.

What is developmental anatomy?

The study of the sequence of events from fertilization to the formation of an adult organism.

What is embryology?

 The study of development from fertilization to the fetal period.

: What is obstetrics?

The branch of medicine that deals with pregnancy, labor, and the neonatal period.

What happens during the first week of development?

Fertilization occurs when the genetic material from a sperm and oocyte merge to form a diploid nucleus.

Where does fertilization normally occur?

In the uterine (Fallopian) tube, usually within 12-24 hours after ovulation.

What is capacitation?

The functional changes sperm undergo in the female reproductive tract, allowing them to fertilize an oocyte.

What are the steps sperm take to reach the oocyte?

Sperm penetrate the corona radiata and zona pellucida, triggering the acrosomal reaction, which helps the sperm reach the oocyte.

What is syngamy?

The fusion of a sperm with a secondary oocyte.

What is polyspermy?

The entry of more than one sperm into an oocyte, which is prevented by chemical changes in the oocyte.

 What helps transport the oocyte through the uterine tube?

 Peristalsis and ciliary action.

How do sperm reach the oocyte?

Through the whip-like movements of their flagella and uterine muscular contractions.

What happens during capacitation?

The acrosomal membrane of sperm becomes fragile, allowing them to penetrate the oocyte.

 How does sperm contact the oocyte?

: Sperm penetrates the granulosa cells (corona radiata), then the zona pellucida, before reaching the oocyte membrane.

 What triggers the acrosomal reaction?

A glycoprotein in the zona pellucida binds to sperm receptors, releasing acrosomal enzymes that help sperm penetrate the oocyte.

What happens once a sperm enters the oocyte?

The oocyte completes meiosis, and the male and female pronuclei fuse to form the zygote.

How does the fast block to polyspermy occur?

The oocyte membrane depolarizes within 1-3 seconds after sperm fusion, preventing other sperm from entering.

How does the slow block to polyspermy occur?

Depolarization triggers the release of calcium ions, causing the zona pellucida to harden and prevent additional sperm entry.

: What are fraternal (dizygotic) twins?

Twins resulting from the independent release of two oocytes fertilized by two different sperm, genetically as different as siblings.

What are identical (monozygotic) twins?

Twins from a single fertilized ovum, genetically identical and always the same sex.

What are conjoined twins?

: Identical twins who do not fully separate and share some body structures.

What is cleavage?

The early rapid mitotic cell division of a zygote that produces blastomeres.

What is the morula?

A solid mass of cells formed from successive cleavages.

How does the morula develop?

By day 4, the embryo has formed a solid ball of cells called the morula, starting from two cells and reaching 16 cells by day 3

What happens as the morula moves toward the uterus?

The morula develops into a blastocyst, a hollow ball of cells with a trophoblast, an inner cell mass, and a fluid-filled cavity.

What are the components of a blastocyst?

The trophoblast (future embryonic membranes), inner cell mass (future embryo), and blastocele (fluid-filled cavity).

What are stem cells?

Unspecialized cells with the ability to divide indefinitely and differentiate into specialized cells.

What is the potential use of pluripotent stem cells?

 They can give rise to many different types of cells and may be used to grow tissues for disease treatment.

What is the significance of adult stem cells?

They may have pluripotent potential, as seen in human adult bone marrow, offering clinical significance.

 When does implantation occur?

Implantation, the attachment of the blastocyst to the uterine wall, occurs 7-8 days after fertilization.

What is the role of the trophoblast during implantation?

The trophoblast forms two layers: the syncytiotrophoblast, which secretes enzymes to digest the endometrial cells, and the cytotrophoblast, which maintains the shape of the embryo.

What does the trophoblast secrete?

Human chorionic gonadotropin (hCG), which helps the corpus luteum maintain the uterine lining.

What layers are formed from the trophoblast during implantation on days 8 to 9?

The trophoblast forms the syncytiotrophoblast and cytotrophoblast.

: What are the three regions of the decidua following implantation?

1. Decidua Basalis

2. Decidua Capsularis

3. Decidua Parietalis

Decidua Basalis

Between chorion and stratum basalis; forms the maternal part of the placenta.

Decidua Capsularis

Covers the embryo, between the embryo and uterine cavity.

Decidua Parietalis

Lines noninvolved areas of the uterus.

What is an ectopic pregnancy, and where do most occur?

 An ectopic pregnancy occurs when the embryo develops outside the uterine cavity, most commonly in the uterine tube (ampullar or infundibular portions).

What are the two layers that the trophoblast differentiates into during development?

The trophoblast differentiates into syncytiotrophoblast and cytotrophoblast, which become part of the chorion.

Day 8 of Gastrulation

 Formation of amnion and amnionic cavity. The epiblast and hypoblast form the ectoderm and endoderm.

Day 12 of Gastrulation

The endoderm forms a hollow sphere (yolk sac).

Day 14

The three primary germ layers (endoderm, mesoderm, ectoderm) are formed.

What is the role of the amnion and amniotic fluid?

 The amnion forms from the epiblast and surrounds the embryo, while the amnionic fluid acts as a shock absorber, regulates temperature, and prevents adhesions.

Functions of Yolk Sac

Nutrient transfer and early blood formation.

Amnion

Protects the embryo and creates the amniotic cavity.

Chorion

Forms the embryonic part of the placenta and secretes hCG.

Allantois

Forms the umbilical cord.

What are the functions of the yolk sac during early development?

The yolk sac transfers nutrients to the embryo, forms early blood cells, and produces primitive germ cells (spermatogonia and oogonia).

9th Day of the sinusoids development

Syncytiotrophoblast expands, forming lacunae (small spaces).

12th Day of  the sinusoids development

The lacunae fuse to form lacunar networks, and sinusoids develop to allow maternal blood to enter.

• What is the function of the chorion during development?

The chorion forms from extraembryonic mesoderm and trophoblast layers, becoming the principal part of the placenta and secreting hCG.

What are the different parts of the decidua (endometrial lining) during pregnancy?

Decidua Basalis, Decidua Capsularis, Decidua Parietalis

• What is the function of the placenta and umbilical cord?

 The placenta provides nutrients, produces hormones, and acts as a barrier to some microorganisms. The umbilical cord contains two arteries and one vein, transporting oxygen and nutrients to the fetus.

What is placenta previa, and what complications can it cause?

Placenta previa occurs when the placenta is implanted near or covering the cervix. It can cause spontaneous abortion, premature birth, or maternal mortality.

 How does fetal ultrasonography work, and what is it used for?

 Fetal ultrasonography uses high-frequency sound waves to create images (sonograms). It is used to determine fetal age, growth, position, and detect abnormalities.

What functions does the placenta serve, and what is its role in protecting the fetus?

The placenta exchanges oxygen, nutrients, and waste between mother and fetus, stores nutrients, produces hormones, and acts as a barrier to some microorganisms, but not to drugs like alcohol.

What are the primary germ layers formed during gastrulation

Ectoderm, Mesoderm, Endoderm

What do Ectogerm layers become during gastrulation

Becomes the epidermis and nervous system.

What do mesoderm layers become during gastrulation

Forms muscles, bones, and connective tissues.

What do endoderm layers become during gastrulation

1. Forms the epithelial lining of the gastrointestinal and respiratory systems

What forms all tissues and organs of the developing organism during gastrulation?

The primary germ layers form all tissues and organs of the developing organism.

What develops alongside the primary germ layers during gastrulation, and what role does it play?

A solid cylinder of cells called the notochord develops, which plays an important role in the process of induction.

 What is the oropharyngeal membrane and what will it eventually connect?

 The oropharyngeal membrane will eventually connect the mouth cavity to the pharynx and the remainder of the gastrointestinal tract.

What is the function of the cloacal membrane during development?

: The cloacal membrane will form the openings of the anus and urinary and reproductive tracts.

What is the allantois, and what is its role in human development?

The allantois is a vascularized outpouching of the yolk sac that extends into the connecting body stalk. It is not a prominent structure in humans.

What does neurulation involve, and how does it start?

 Neurulation involves the development of the neural tube. The notochord induces ectodermal cells over it to form the neural plate.

What do the neural folds and neural groove form during neurulation?

The neural folds and neural groove will fuse to form the neural tube.

 What do neural crest cells give rise to?

Neural crest cells give rise to spinal and cranial nerves and their ganglia, autonomic nervous system ganglia, the meninges of the brain and spinal cord, adrenal medullae, and several skeletal and muscular components of the head.

What are the three primary vesicles formed from the head of the neural tube?

The three primary vesicles are the prosencephalon, mesencephalon, and rhombencephalon.

What secondary vesicles develop from the primary vesicles?

The secondary vesicles that develop are the telencephalon, diencephalon, metencephalon, and myelencephalon.

What can cause neural tube defects (NTDs)?

Neural tube defects are caused by the arrest of normal development and closure of the neural tube, leading to conditions like anencephaly and spina bifida.

 What are somites, and how many pairs will develop?

Somites are paired, cube-shaped structures that develop from the mesoderm. Eventually, 42-44 pairs of somites will develop.

What are the three regions of each somite?

Each somite has three regions: the myotome, dermatome, and sclerotome.

 How does the intraembryonic coelom develop?

 Small spaces in the lateral plate mesoderm fuse to form a larger cavity, the intraembryonic coelom.

 What two parts does the lateral plate mesoderm split into after the formation of the intraembryonic coelom?

The lateral plate mesoderm splits into the splanchnic mesoderm and the somatic mesoderm.

What cavities are formed from the intraembryonic mesoderm?

The intraembryonic mesoderm divides into the pericardial, pleural, and peritoneal cavities.

What does the splanchnic mesoderm form?

The splanchnic mesoderm forms portions of the heart, respiratory, and digestive systems.

What does the somatic mesoderm form?

The somatic mesoderm gives rise to bones, ligaments, and the dermis of the limbs, as well as the parietal layer of the serous membranes.

What is angiogenesis, and where does it begin?

Angiogenesis is the formation of blood vessels, beginning in the extraembryonic mesoderm in the yolk sac, connecting stalk, and chorion.

 How does the heart form during development?

The heart forms in the cardiogenic area of the splanchnic mesoderm, where mesodermal cells form a pair of endocardial tubes that fuse to form the primitive heart.

What do chorionic villi contain, and what is their role?

Chorionic villi are projections of the cytotrophoblast that contain blood-filled capillaries, which connect to the embryonic heart via the umbilical arteries and veins.

What is the function of the placenta during pregnancy?

The placenta allows oxygen and nutrients to diffuse from maternal blood to fetal blood, carbon dioxide and wastes to diffuse from fetal blood into maternal blood, serves as a protective barrier, stores nutrients, and secretes important hormones.

What is placenta previa, and how is it treated?

 Placenta previa is a condition where part or all of the placenta is implanted in the lower portion of the uterus near or over the cervix. A cesarean section is the preferred method of delivery if detected

What occurs during the fourth week of embryonic development?

Embryonic folding occurs, converting the embryo from a flat, two-dimensional disc to a three-dimensional cylinder. Somites and the neural tube develop, and pharyngeal arches form.

What signs of development appear in the fourth week?

The otic placode (sign of the developing ear), lens placode (sign of the developing eye), and limb buds (upper limbs appear in the middle of the week, lower limbs appear at the end) develop.

What happens during the fifth week of development?

Rapid brain development and considerable head growth occur during the fifth week.

What developmental changes happen during the sixth week?

The head grows larger in relation to the trunk, there is substantial limb growth, the neck and trunk begin to straighten, and the heart is now four-chambered.

What happens during the seventh and eighth weeks of development?

In the seventh week, the regions of the limbs become distinct, and digits begin to form. By the eighth week, the digits are distinct, the eyelids come together, the tail disappears, and external genitals begin to differentiate.

 What occurs during the fetal period?

During the fetal period, tissues and organs developed during the embryonic period grow and differentiate, with remarkable body growth.

What does the maternal alpha-fetoprotein (AFP) test screen for?

 The AFP test screens for neural tube defects, Down syndrome, trisomy 18, and can also predict the delivery date and reveal the presence of twins.

How is fetal ultrasonography used?

Fetal ultrasonography is used to determine fetal age, evaluate viability and growth, determine position, identify abnormalities, and assist with procedures like amniocentesis.

What is amniocentesis used for, and when is it usually performed?

Amniocentesis is used to detect genetic abnormalities and is typically performed at 14-16 weeks of gestation.

What is chorionic villus sampling (CVS), and when is it done?

CVS involves withdrawal of chorionic villi for chromosomal analysis and can be done earlier than amniocentesis, typically at 8-10 weeks gestation.