Ch. 14 Human Development
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244 Terms
What is the primary function of a sperm cell?
Transfer male genetic material to the egg.
What are the main parts of a sperm cell?
Head, middle section, and tail (flagellum).
What is the function of the sperm tail (flagellum)?
Propels the sperm for movement.
Why does the sperm's middle section contain many mitochondria?
To generate the energy required for movement.
Approximately how many mitochondria are in a sperm cell?
About 75–100 mitochondria.
What structures are located in the sperm head?
Nuclear DNA and the acrosome.
What is the function of the acrosome?
Contains enzymes that digest the zona pellucida during fertilization.
How does the egg cell compare in size to the sperm cell?
The egg is about 10,000 times more massive.
Why is the egg cell not adapted for mobility?
It is specialized for supporting early development rather than movement.
What structures are contained within the egg cell?
Nuclear DNA, mitochondria, and other organelles.
Approximately how many mitochondria are in an egg cell?
About 200,000 mitochondria.
What is the zona pellucida?
A thick glycoprotein layer surrounding the egg.
What structure lies immediately beneath the zona pellucida?
The plasma membrane.
When is fertilization considered complete?
When the sperm fuses with the egg plasma membrane and the genetic material combines.
What are the four major steps of fertilization?
Sperm binding, acrosome reaction, cortical reaction, and genetic transfer.
What occurs during sperm binding?
The sperm binds to the zona pellucida.
What occurs during the acrosome reaction?
Acrosomal enzymes digest the zona pellucida, allowing the sperm to approach the egg plasma membrane.
What occurs during the cortical reaction?
Cortical granules release enzymes that modify the zona pellucida and prevent additional sperm from binding.
What is the purpose of the cortical reaction?
Prevent polyspermy.
What is polyspermy?
Fertilization of one egg by multiple sperm.
What happens if the cortical reaction fails?
Polyspermy occurs and the zygote fails.
What occurs during genetic transfer?
The sperm and egg plasma membranes fuse, and the sperm's genetic material enters the egg.
What genetic material is contributed by the sperm?
Nuclear DNA and a small amount of mitochondrial DNA.
Why does sperm mitochondrial DNA have little effect on the embryo?
The egg contains far more mitochondria than the sperm.
What is a zygote?
The fertilized egg formed after fusion of sperm and egg genetic material.
What happens first during embryogenesis after fertilization?
Cleavage begins while the zygote remains inside the zona pellucida.
What is cleavage?
Rapid cell division without growth in overall size.
How does cleavage progress?
1 cell → 2 cells → 4 cells → 8 cells → 16 cells → 32 cells.
What is a morula?
A 32
What are the two cell populations formed in the morula?
Trophoblast and embryoblast.
What is blastulation?
The process by which the morula develops into a blastocyst.
What is a blastocyst?
An embryo containing an inner cell mass and a blastocoel.
What is the blastocoel?
The hollow cavity within the blastocyst.
What happens to the zona pellucida during blastulation?
It disintegrates.
What structures develop from the inner cell mass?
The amniotic cavity, epiblast, and hypoblast.
What is the bilaminar disk?
The epiblast and hypoblast together.
What forms during the bilaminar disk stage to initiate cell migration?
The primitive streak.
What is gastrulation?
Formation of the trilaminar disk containing the three germ layers.
What are the three germ layers formed during gastrulation?
Ectoderm, mesoderm, and endoderm.
What is neurulation?
Formation of the neural tube from the ectoderm.
What structure forms within the mesoderm during neurulation?
The notochord.
What is the function of the notochord?
Induces the overlying ectoderm to form the neural plate.
What is the neural plate?
Thickened ectoderm that gives rise to the nervous system.
What structure forms when the neural plate folds inward?
The neural tube.
What cells develop along the sides of the neural tube?
Neural crest cells.
What enzyme
containing structure allows sperm to penetrate the egg?
Which reaction prevents polyspermy?
Cortical reaction.
What stage immediately follows the morula?
Blastocyst.
Which embryonic structure contains the inner cell mass and blastocoel?
Blastocyst.
Which embryonic stage forms the ectoderm, mesoderm, and endoderm?
Gastrulation.
Which embryonic structure induces neural plate formation?
Notochord.
Which embryonic structure ultimately develops into the central nervous system?
Neural tube.
During which embryonic stage does implantation occur?
Blastocyst stage.
What happens to the zona pellucida during implantation?
It disintegrates.
What happens to the endometrium during implantation?
It proliferates and forms valleys called crypts.
What are endometrial crypts?
Valleys formed as the endometrium proliferates during implantation.
What is apposition?
The initial attachment of the blastocyst to the endometrium.
What is adhesion during implantation?
The stage when trophoblast cells invade the endometrium.
What happens to the trophoblast during implantation?
It divides and invades the endometrium.
What happens to the endometrium during trophoblast invasion?
It continues proliferating.
Into what two layers does the trophoblast differentiate during implantation?
Syncytiotrophoblast and cytotrophoblast.
What is cytotrophoblast?
The original trophoblast cell layer remaining after differentiation.
What is the syncytiotrophoblast?
Fused trophoblast cells that invade the endometrium.
What happens to the maternal blood vessels during implantation?
They enlarge within the endometrium.
What structures are formed by the syncytiotrophoblast?
Villi.
What is the function of the syncytiotrophoblast villi?
They establish close contact with maternal blood.
What develops within the syncytiotrophoblast villi?
Fetal blood vessels.
How are fetal and maternal blood brought into close proximity during implantation?
Fetal blood vessels within the syncytiotrophoblast villi lie adjacent to enlarged uterine blood vessels.
What structure is formed where fetal villi interface with the uterine lining?
The placenta.
What is the placenta?
The structure formed at the interface between fetal villi and the uterine lining that allows exchange between fetal and maternal blood.
What is the first step of implantation?
Apposition.
Which trophoblast layer actively invades the endometrium?
Syncytiotrophoblast.
Which trophoblast layer consists of the original trophoblast cells?
Cytotrophoblast.
Which trophoblast layer forms villi?
Syncytiotrophoblast.
What embryonic structure ultimately gives rise to the fetal portion of the placenta?
Trophoblast.
What are the three primary germ layers formed during gastrulation?
Endoderm, Mesoderm, and Ectoderm.
What structures are derived from the Endoderm?
The GI tract tube (esophagus, small intestine, and large intestine), lungs, liver, and pancreas.
What part of the digestive system develops from the Endoderm?
The GI tract tube, including the esophagus, small intestine, and large intestine.
Which respiratory organ develops from the Endoderm?
The lungs.
Which accessory digestive organs develop from the Endoderm?
The liver and pancreas.
What structures are derived from the Mesoderm?
The inner layers of the skin, muscles, bones, cardiac muscle, kidneys, bladder, ovaries, and testes.
Which skin layer is derived from the Mesoderm?
The inner layers of the skin.
Which muscular tissues develop from the Mesoderm?
Skeletal muscles and cardiac muscle.
Which skeletal structures develop from the Mesoderm?
Bones.
Which urinary system organs develop from the Mesoderm?
The kidneys and bladder.
Which reproductive organs develop from the Mesoderm?
The ovaries and testes.
What structures are derived from the Ectoderm?
The outer layer of the skin, sweat glands, hair, and the nervous system.
Which skin layer develops from the Ectoderm?
The outer layer of the skin.
Which skin appendages develop from the Ectoderm?
Hair and sweat glands.
Which major body system develops from the Ectoderm?
The nervous system.
Which germ layer gives rise to the GI tract, lungs, liver, and pancreas?
Endoderm.
Which germ layer forms muscles, bones, kidneys, and gonads?
Mesoderm.
Which germ layer forms the nervous system?
Ectoderm.
Which germ layer forms the outer skin?
Ectoderm.
Which germ layer forms the inner layers of the skin?
Mesoderm.
Why is the term Conception discouraged?
It is a poorly defined term and should not be used.
What is gestation?
The period of development from the last menstrual period (LMP) until birth.
How can gestation be divided?
Into months, trimesters, or weeks.
Which method of measuring gestation is the most scientifically accurate and useful?
Weeks.
What marks time 0 of gestation?
The last menstrual period (LMP).