Embryology Flashcards
Zona pellucida
Specialized extracellular matrix surrounding the developing oocyte, consists of glycoproteins, works in oocyte development, protection, fertilization, spermatozoa binding, preventing polyspermy, blastocyst development and preventing premature implantation
Cleavage
Period of rapid division in early embryogenesis when the total size of the developing embryo does not change but the amount of cell rapidly increases
Morula
Early stage in post-fertilization development when cells have rapidly divided mitotically to produce solid mass of cell that looks like a mulberry
Compaction
Event prior to morula formation where 8 cell embryo undergoes changes in cell morphology and cell-cell adhesion that initiates formation of a solid ball of cells (morula)
Trophoblast
Outer layer of cells of blastocyst, involved with implantation an formation of placenta, further differentiates into syncitiotrophoblast an cytotrophoblast
Embryoblast
Cellular mass component of blastocyst that will give rise to the embryo, also called inner cell mass
Blastocoel
Cavity of the blastocyst filled with fluid
Blastocyst
Stage following morula when a fluid-filled cavity has formed with trophoblast layer forming an outer “shell” and inner cell mass concentrated on one wall of the blastocoel
Blastulation
The process leading to the formation of a blastocyst
Amniotic cavity
Fluid-filled extraembryonic coelem formed initially by epiblast, forms the innermost fetal membrane
Acrosome
Spermatozoa cap-shaped cellular structure that contains a packet of enzymes that allows it to dissolve a hole in zona pellucida allowing fertiliation
Ampulla
Anatomical description of the opening end of the uterine tube lying above the ovary
Bilaminer disc
Term used in early embryonic development to describe the inner cell mass differentiating to form an initial two layered structure (epiblast and hypoblast), in human development occurs during week 2
Caudal
Anatomical term referring to structure that are more towards the tail
Corona radiata
The granulosa cells that directly surround the oocyte, within the antral follicle of the ovary, these cells are released along with the oocyte at ovulation and provide physical protection and the initial structural barrier that spermatazoa must penetrate during fertilization
Cortical granule
Specialized secretory vesicles (granules) just beneath the plasma membrane in oocyte, after fertilization, these vesicles fuse with the plasma membrane, releasing their contents, which block polyspermy
Cytotrophoblast
The cellular trophoblast layer surrounding the early implanting conceptus, proliferation and fusion of these cells is thought to form a second outer trophoblast layer, the syncytiotrophoblast, contributes to formation of the placental villi, the functional component of the fetal placenta
Differentiation
Process of development of specific cell types from stem or precursor cells by gene activation and repression
Ectoderm
One of the initial 3 germ cell layers formed during gastrulation,
will form the nervous system, sensory placodes and also generates the entire epithelial layer of the skin covering the embryo, formed from the epiblast following gastrulation, with a central columnar epithelium (neural plate) and lateral cuboidal epithelium and is continuous with and forms the epithelium that lines the amniotic cavity, in humans forms during week 3 and 4 of development
Egg
An alternative term used to describe the haploid female reproductive cell, also called oocyte or ovum
Endoderm
One of the initial 3 germ cell layers formed by the process of gastrulation, forms as a cuboidal epithelium and contributes not only to the trilaminar embryo, but also lines the yolk sac, forms the entire epithelial lining of the gastrointestinal tract (GIT), contribute to the accessory organs of GIT and also forms the epithelial lining of the respiratory tract, in humans forms during week 3 of development.
Endometrium
The epithelium lining of the non-pregnant uterus, during pregnancy this epithelium undergoes changes described as the decidual reaction and is renamed the “decidua”.
Epiblast
Layer of the bilaminar embryo that generates all three germ cell layers: ectoderm, endoderm and mesoderm, both the endoderm and mesoderm are formed by epiblast cell migration through the primitive streak during gastrulation in week 3, remaining cells then form ectoderm and line the amniotic cavity, in human development forms in week 2 within the implanting blastocyst at the bilaminar embryo stage of development.
Estrogen
Sex hormone found in both male and female, in female produced by the ovaries and is responsible for development of secondary feminine sex characteristics, together with progesterone regulate changes that occur each menstrual cycle, during male embryonic development exposure to high levels of estrogen can lead to genital abnormalities
Fallopian tube
A pair of tubular structures designed to transport the oocyte (egg) from the ovary to the uterus body
Fertilization
The process of penetration of the oocyte (egg) by the spermatozoa and the combining of their genetic material that initiates development of the embryo, union of two haploid gametes to form the first diploid cell, the zygote
Gastrulation
The process of differentiation forming a gastrula, converts the bilaminar embryo into the trilaminar embryo establishing the 3 germ layers that will form all the future tissues of the entire embryo, also establishes the initial body axes
Germ layers
The first three cellular layers (ectoderm, mesoderm, and endoderm) that will form all tissues of the embryo, in human begin to form during week 3 of development
Gestation
The period of time from conception to birth
Hypoblast
The transient epithelium that forms during week 2 of human development and lines beneath the epiblast layer, during trilaminar embryo development, beginning in humans in week 3, the process of gastrulation replaces the layer within the embryo with endoderm germ layer
Implantation
The term used to describe the process of conceptus invasion of the uterus endometrium by the blastocyst, this process follows conceptus adplantation (attachment) to the endometrium, in humans occurs during the second week of development
Lutenizing hormone (LH)
Glycoprotein hormone releasd from anterior pituitary, hormone that acts on the gonad and has a role in male and female reproduction, in female increase in concentration during the menstrual cycle triggers ovulation, in male stimulates testis interstital cell (Leydig cell) production of testosterone
Meiosis
The cell division that occurs only in production of germ cells where there is a reduction in the number of chromosomes (diploid to haploid) which is the basis of sexual reproduction
Mesenchyme
Term used to describe the cellular organisation of undifferentiated embryonic connective tissue, mainly derived from mesoderm and neural crest, which will form most of the adult connective tissues
Mesoderm
The middle layer of the 3 germ cell layers of the trilaminar embryo, each region of this early layer will later form different structures, this middle layer contributes all connective tissues of the body, except in the head region where neural crest also will contribute
Axial mesoderm
Alternative name for the notochord, an early embryonic structure lying in the midline of mesoderm within the early trilaminar embryo
Paraxial mesoderm
In early development, the two lateral strips of mesoderm lying beside the axial mesoderm (notochord), at body level will segment into somites, at the head level it remains unsegmented.
Mitosis
The normal division of all cells where chromosome number is maintained (diploid)
Menstrual cycle
The human reproductive cycle, an endocrine regulated change in female anatomy and physiology that occur over 28 days during reproductive life (between puberty and menopause), this cycle ceases during pregnancy
Neuralation
The general term used to describe the early formation of the nervous system, often used to describe the early events of differentiation of the central ectoderm region to form the neural plate, then neural groove, then neural tube, in humans, begins in week 3 and continues through week 4.
Neural crest
A cell region at edge of neural plate, then atop the neural folds, that remains outside and initially dorsal to the neural tube when it forms, these paired dorsal lateral streaks of cells migrate throughout the embryo and can differentiate into many different cell types, those that remain on the dorsal neural tube form the sensory spinal ganglia (DRG), those that migrate ventrally form the sympatheitic ganglia, also migrate into the somites and regions throught the entire embryo
Neural plate
The first stage in early development of the central nervous system, in the trilaminar embryo the central region of the ectoderm (in the midline above the mesodermal notochord) initially forms a columnar epithelium described as the neural plate
Neural tube
The third stage in early development of the central nervous system, neural plate will fold dorsally to form the neural groove, which then fuses to form initially a hollow tube open at either end, forms the central nervous system (brain and spinal cord)
Notochord
The rod of cells lying in the midline of the trilaminar embryo mesoderm layer ventral to the neural tube, thought to have at least 2 early roles in development and later roles in patterning surrounding tissues, 1. Mechanical, influencing the folding of the early embryo; 2. Morphogenic, secreting sonic hedgehog a protein which regulates the development of surrounding tissues (neural plate, somites, endoderm and other organs), in humans forms in week 3 and is eventually lost during the formation of the vertebral column, also known as axial mesoderm
Oogenesis
Process of diploid oogonia division and differentiation into an haploid oocyte (egg) within the ovary (female gonad), mammalian meiosis will only be completed within the oocyte if fertilization occurs
Ovulation
The term used to describe the process of the mature follicle releasing the oocyte or ovum (and support cells) from the ovary surface into the peritoneal cavity, in humans, generally a single oocyte is released from a cohort of several maturing follicles, more than one follicle may be released (superovulation) following reproductive therapeutic treatment
Placenta
The developmental organ formed from maternal and fetal contributions in animals with placental development, the functional exchange region are the placental villi or chorionic villi, has many different functions including metabolism, transport and endocrine, forms from trophoblast
Pluripotent
A stem cell term describing the ability of a stem cell to form (differentiate) into many different cell types
Polyspermy
Abnormality associated with more than a single spermatozoa fertilising the oocyte, can result in parthenogenesis and hydatidiform mole formation
Primitive streak
Visible region on the surface of the early epiblast embryonic bilaminar disc, representing the site of cell migration during gastrulation (cell migration to form endoderm then mesoderm), extends centrally from the primitive node (Hensen’s node) to the disc periphery near the connecting stalk, the orientation of the streak establishes the early body axis (rostro-caudal, head-tail), in the human embryo, gastrulation occurs from week 3 through to week 4.
Primitive node
The small circular region located at the cranial end of the primitive streak, where gastrulation occurs, and is a controller of this process, the second role is to act as an initial generator of the left-right (L-R) body axis, centered around the primitive pit, the site of epiblast extension cranially to form the initial axial process
Rostral
Anatomical term referring to head
Somatic mesoderm
Mesoderm derived from lateral plate mesoderm, and found closest to the ectoderm and separated from other component of lateral mesoderm by the intraembryonic coelom, forms connective tissue of the body wall and the skeletal elements of the appendicular skeleton and sternum
Somite
Segmental block of mesoderm formed from paraxial mesoderm adjacent to notochord in the body of the embryo, form in lateral pairs in a rostro-caudal sequence, the number of pairs formed is used to stage many embryos, somite structure is developmentally transient, dispersing and differentiating to muscle, bone and connective tissues of the body
Spermatogenesis
The term used to describe the process of diploid spermatagonia division and differentiation to form haploid spermatazoa within the testis (male gonad), the process includes meiosis, reorganization of DNA, reduction in DNA content, reorganization of cellular organelles, morphological changes (cell shape), the process following meiosis is the change in cell shape and organization, called spermiogenesis.
Spina bifida
A neural tube defect (NTD) caused by failure of the early neural tube to close correctly, this defect can occur anywhere along the length of the neural tube at the level of the spinal cord, because the neural tube remains open in adddition to the neural effects, the surrounding spinal column/vertebra, connective tissue and skin may also be affected, the two main forms are open (neural elements are exposed to the external environment) or closed (occult, covered with skin)
Splachnic mesoderm
Gastrointestinal tract (endoderm) associated mesoderm formed by the separation of the lateral plate mesoderm into two separate components by a cavity, the intraembryonic coelom, embryonic origin of the gastrointestinal tract connective tissue, smooth muscle, blood vessels and contribute to organ development (pancreas, spleen, liver)
Spinal ganglia
A peripheral nervous system sensory ganglia derived from the neural crest, lying laterally paired and embryonically dorsal to the spinal cord, in the adult found anatomically ventral to the spinal cord, connects centrally with the dorsal horn of the spinal cord
Syncitiotrophoblast
Multinucleated cell currently thought to form by the fusion of another trophoblast cell the cytotrophoblasts, within the trophoblast layer (shell) of the implanting conceptus, in early development, these cells mediate implantation of the conceptus into the uterine wall and secrete the hormone (human Chorionic Gonadotrophin, hCG) responsible for feedback maintainance of the corpus luteum (in maternal ovary) and therefore maintaining early pregnancy
Syncitium
Cellular term describing a single cell cytoplasm containing a number of nuclei that can be formed during development in two ways, 1. by incomplete cell division, as occurs in spermatogenesis when maturing spermatozoa do not complete cytokinesis and remain joined by cytoplasmic bridges, 2. by fusion of initially separate cells together, as occurs in placentation with syncytiotrophoblast formation and during skeletal muscle development when myoblasts fuse to form myotubes
Zygote
First diploid cell that forms following fertilization by fusion of oocyte and sperm