Chapter 3 Embryogenesis And Develoment Flashcards
Fertilization
Usually occurs in the widest part of the fallopian tube (the AMPULLA). When sperm meets the secondary oocytes, It releases acromial enzymes that allow the head of the sperm to penetrate the Corona radiata and zona pellucida.
Acrosome
Sperm organelle that covers the sperm nuclei and contains acrosomal enzymes that help penetrate the egg. After the first sperm comes in contact with the secondary oocyte, it forms a tube like structure known as the acrosomal apparatus.
Cortical reaction
Release of calcium ions after penetration of the sperm through the cell membrane. These calcium ions depolarize the membrane of the ovum which prevents fertilization of the ovum by multiple sperm cells, and increases the metabolic rate of the newly formed diploid zygote.
Fertilization membrane
Depolarized impenetrable membrane that form as a result of the cortical reaction, prevent fertilization of the ovum by multiple sperm cells.
Two different mechanisms of twinning.
Dizygotic (fraternal) twins
Monozygotic (identical) twins
Dizygotic (fraternal) twins
Forms from the fertilization of two different eggs released during one ovulatory cycle by two different sperm. No more genetically similar than any other pair of siblings.
Monozygotic (identical) twins
Form when a single zygote splits into two. Because the genetic material is identical, the genome of the offspring will be too. If division is incomplete, conjoined twins may result where the two offspring are physically attached.
Three types of monozygotic twins
Monochorionic/monoamniotic: share the same amnion and chorion
Monochorionic/diamniotic: have their own amnion, but share the same chorion
Dichorionic/diamniotic: each have their own amnions and chorions
The type of twinning that occurs is a result of when the separation of the zygote occurred.
Cleavage
Rapid mitotic cell division as the zygote moves to the uterus for implantation. The first cleavage officially creates an embryo, as it nullifies one of the zygotes defining characteristics: unicellularity.
Two types of cleavage
Indeterminate cleavage and determinate cleavage.
Indeterminate cleavage
Results in cells that can still develop into a complete organism.
Fun fact, monozygotic twins have a identical genome because they both originate from indeterminately cleaved cells of the same embryo.
Determinate cleavage
Results in cells with fates that are already DETERMINED, as the name implies. In other words, these cells are committed to differentiating into a certain type of cell.
Morula
Solid ball of cells, several divisions after fertilization. Comes from the Latin word for mulberry, which might help us grasp what an embryo at the stage looks like.
Blastula
Once the morula is formed, it undergoes blastulation which forms a blastula: hollow ball of cells with the fluid filled inner cavity known as a blastocoel. The mammalian blastula is known as a blastocyst.
Blastocyst
The mammalian blastocoel is known as a blastocyst, consisting of two noteworthy cell groups: the trophoblast and the inner cell mass.
Trophoblast cells
Surround the blastocoel and give rise to the chorion and later the placenta.
Inner cell mass
Protrudes into the blastocoel and gives rise to the organism itself.
The trophoblast gives rise to the placenta. The inner cell mass gives rise to the organism.
Chorion
Trophoblastic cells give rise to the chorion, an extraembryonic membrane that develops into the placenta.
Chorionic villi
The trophoblasts form the chorionic villi, which are microscopic fingerlike projections that penetrate the endometrium and develop into the placenta that support maternal-fetal gas exchange.
Umbilical cord
Connection between the embryo and the placenta. Consists of two arteries and one vein encased in a gelatinous substance. The vein carries freshly oxygenated blood rich with nutrients from the placenta to the embryo, the umbilical arteries carry de oxygenated blood, and waste to the placenta for exchange.
Anatomy of pregnancy
Ectopic pregnancy
Occurs when the blastula implants itself outside the uterus. Over 95% of ectopic pregnancies occur in the fallopian tubes. Generally not viable because the fallopian tube is not an environment in which an embryo can properly grow. A suspected ectopic pregnancy is often a surgical emergency.
Yolk sac
Site of early blood cell development, support the embryo until the placenta is functional.
Two noteworthy extra embryonic membranes
Allantois (Alan-tow-iss) and amnion.
Allantois
Involved in early fluid and gas exchange between the embryo and the yolk sack. The UMBILICAL CORD is formed from remnants of the yolk sac and the allantois.
Amnion
Surrounds the allantois. The amnion is thin, tough membrane filled with amniotic fluid. Serves as a shock absorber during pregnancy.
The allantois is a hollow sac-like structure filled with clear fluid that forms part of a developing amniote’s conceptus (which consists of all embryonic and extraembryonic tissues). It helps the embryo exchange gases and handle liquid waste.
Amniocentesis
Process of aspirating amniotic fluid by inserting a thin needle into the amniotic sac. the amniotic fluid contains fetal cells that can be examined for chromosomal abnormalities as well as sex determination. Opportunity for early screening tests.
Gastrulation
The generation of three distinct cell layers once the cell mass implants known as the primary germ layers: endoderm, mesoderm, ectoderm.
Early stages of Embryonic development (zygote to gastrula)
Gastrula
Invaginated blastula
Archenteron
Name for the invaginated membrane into the blastocoel, later develops into the gut.
Blastopore
The opening of the archenteron.
In deuterostomes, the blastopore develops into the anus.
In protostomes, the blastopore develops into the mouth.
Dueterostomes and protostomes
Dueterostomes, such as humans, the blastopore develops into the anus.
In protostomes, such as anthropods and mollusks, the blastopore develops into the mouth.
Primary germ layers
Ectoderm, mesoderm, endoderm
Ectoderm
Outermost layer of the three primary germ layers. Gives rise to the integument (skin), including the epidermis, hair, nails, and the epithelia of the nose, mouth, and lower anal canal. Also gives rise to the lens of the eye, THE NERVOUS SYSTEM, and inner ear.
Mesoderm
The middle layer of the three primary germ layers. Gives rise to the muscular skeletal, circulatory, and most of the excretory systems. Also gives rise to the gonads as well as the muscular and connective tissue layers of the digestive and respiratory systems and the adrenal cortex.
Mnemonic for the primary germ layers
Formation of the neural tube
The notochord induces a group of overlying ectodermal cells to slide inward to form neural folds, which surrounding neural groove. the neural folds grow toward one another until they fuse into a neural tube, and give rise to the central nervous system. At the tip of each general fold are neural crest cells that migrate outward to form the peripheral nervous system. Ectodermal cells will then migrate over the neural tube and crest to cover the rudimentary nervous system.
Embryonic stem cells image
Apoptosis
Programed cell death. The cell undergoes changes in morphology and divides into many self-contained protrusions called apoptotic blebs which can then be broken apart into apoptotic bodies.
Placenta
ORGAN where nutrients, gas, and waste exchange occurs. Facilitated by diffusion, which requires a gradient, which implies there is a higher partial pressure of oxygen in maternal blood than in fetal blood.
Note: the placenta also qualifies as an endocrine organ because it produces progesterone, estrogen, and human chorionic gonadotropin (hCG), all which are essential for maintaining pregnancy.
