Chapter 5 - Embryology Flashcards
Define zygote
A fertilized egg
What are the four early phases of embryonic development? provide a brief synopsis of each.
The four early phases of embryonic development are
- Cleavage - rapid mitotic division and movement to the uterus
- Implantation - implantation of the blastula in the endometrium
- Gastrulation - invagination and differentiation of three primary germ layers
- Neurulation - development of the nervous system
What important characteristics of the embryo change and remain the same during the cell divisions of cleavage?
- the embryo is no longer a unicellular organism
- the total size of the embryo remains the same
- the nuclear to cytoplasm ratio increases
- the surface area to volume ratio increases
What is an important result of the change in surface area to volume that occurs during the cleavage phase?
The cells achieve increased area for gas and nutrient diffusion relative to overall volume.
What are the two types of cleavage and how do they differ?
The two types of cleavage are
- Indeterminate cleavage – a cleavage that results in cells maintaining their totipotency or ability to develop into a complete organism
- a cleavage whose future differentiation pathways are defined, i.e. the resulting cells are committed to differentiating into certain cell types
When do the first, second, and third cleavages occur? Why is this important?
the first, second, and third cleavages occur at 36, 60, and 72 hours postfertilization, respectively. At this point the eight-celled embryo has completed its journey to the uterus.
What is a morula?
A morula is the form the embryo takes after several cell division. It is a solid mass of of cells and resembles a mulberry (or blackberry).
Define Blastulation
Blastulation is the process by which a morula develops into a blastula, a hollow cell mass with a fluid-filled cavity known as a blastocoel. The mammalian blastula is known as a blastocyst.
Mnemonic: an embryo with a “blasted-out” cavity is a blastula
What are the two cell groups that comprise a blastocyst? What do these develop into?
- Trophoblast – cells that surround the blastocoel and develop into the chorion and later the placenta
- Inner cell mass – cells that protrude into the blastocoel and develop into the organism itself
Define endometrium
The mucosal lining of the uterus where the embryo implants. Progesterone is necessary for the maintenance of the endometrium during pregnancy.
What occurs during implantation?
During implantation the blastocyst implants itself into the endometrium, forming a connection to maternal circulation for nutrient and gas exchange.
What hormones and enzymes are important during the implantation phase and what do they do?
Progesterone secreted by the mother promotes proliferation of the endometrial mucosal layer to help the embryo implant, while proteolytic enzymes secreted by embryonic cells burrow into the endometrial lining to allow for implantation.
Define gastrulation
The process by which a blastula differentiates into a gastrula with three distinct primary cell layers. This process begins with a small invagination in the blastula and proceeds until the formation of a deep cavity and the elimination of the blastocoel.
What are the three cell layers, and from what part of the gastrula do they develop?
The three primary cell layers are
- ectoderm – the cell layer on the outside of the cavity
- mesoderm – from cells that migrate into the area between the inner and outer cell layers
- endoderm – the cell layer inside the cavity
What is the ectoderm and what structures does it give rise to?
The ectoderm is the outermost cell layer and gives rise to the outermost layer (including the epidermis, hair, nails, epithelium of the nose, mouth and anal canal) and the nervous system.
Mnemonic: “attracto”-derm, these are the systems that attract us to other people: their looks, their eyes, and their smarts.
What is the mesoderm and what structures does it give rise to?
The mesoderm is the primary germ layer that lies between the ectoderm and endoderm. It gives rise to the musculoskeletal system, circulatory system, kidneys, excretory system, gonads, and muscular and connective tissue coats of the digestive and respiratory systems.
Mnemonic: “means”-o-derm, this is how we get from place to place in the world, and how constituents get from place to place in the body.
What is the endoderm and what structures does it give rise to?
The innermost of the three primary germ layers, the endoderm gives rise to epithelial linings of the digestive and respiratory tracts and parts of the liver, pancreas, thyroid, bladder, and distal urinary and reproductive tracts.
Mnemonic: The endoderm gives rise to the two “inner tubes” of the body, the respiratory tube, which includes the lungs, and the digestive tube, which includes the entire digestive tract from the mouth to the anus and the organs attached to it (accessory organs of digestion).
What is the name of the cavity created by the invagination during gastrulation? What is the name of the opening?
The cavity created by the deep invagination is known as the archenteron, and the opening is called the blastopore.
What is the blastopores fate in protostomes? in deuterostomes?
In protostomes the blastopore develops into the mouth
In deuterostomes, such as humans, the blastopore develops into the anus
Mnemonic: *proto *means before, and the mouth comes before the anus in the digestive tract. deu is the number two, which should remind us of going “number two”
