FoundationsThe menstrual cycle dictates timing of fertilization and implantation and therefore when life can begin.
Development starts before fertilization with the release of the egg from the ovary (ovulation). This process along with preparation of the uterus for implantation is an endocrine controlled cycle, the menstrual cycle.
This first page will give a brief overview of: menstrual cycle, fertilization, blastocyst and implantation. You are not expected to know everything about these processes, just keep track of the relative "timings" as to when specific processes occur.
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If you would like to know more, you can always click the linked "images", the "More?" or "Notes" links. |
These notes and linked materials have been prepared for Educational purposes only. Please email Dr Mark Hill if you wish to make a comment about this current project.
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Follicle Development |
Ovulation (Play ovulation movie in new window) |
Notes: Human Menstrual Cycle | Week 1 - Oogenesis
Folliculogenesis and Ovulation (986Kb)
Sperm Penetration
(706Kb)
Pronuclear Fusion
(264Kb)
Cell Cleavage (527Kb)
(More? Birth Date)
Notes: Week 1 | Fertilization | Blastocyst | Development Week by Week
If you have some time in the Lab also have a look at the topic of Spermatogenesis and the testis structure.
Links: Week 1 - Spermatogenesis | Blue Histology - Male Reproductive System
Movie: Implantation (451Kb)
Movie: Chorionic Cavity (1.2Mb)
(More? human embryology movies)
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Link to next page in this Practical - Week 3 and 4 This provides information about germ layers and early dynamic processes. |
Use the alphabetical list below to find definitions of terms that are new to you or use the Google search window to search UNSW Embryology site.
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W |X | Y | Z |
antral follicle - (secondary follicle) Term used to describe the developmental stage of ovarian follicle development following preantral (primary) in describing the sequence (primordial, preantral, antral) of follicle development within the ovary. In humans, a number of primordial follicles will begin to develop into primary follicles, some of which will then form antral follicles (secondary), with only a single antral follicle developing into the ovulating follicle (Graffian) each menstrual cycle. (More? Week 1 - Oogenesis)
blastocyst - (Greek, blastos = sprout + cystos = cavity) Term used to describe the hollow cellular mass taht forms in early development. In humans, this stage occurs in the first and second weeks after the zygote forms a solid cellular mass (morula stage) and before implantation. The blastocyst consists of cells forming an outer trophoblast layer, an inner cell mass (embryoblast) and a fluid-filled cavity. The blastocyst inner cell mass is the source of true embryonic stem cells capable of forming all cell types within the embryo. (More? Week 1 - Blastocyst | Week 2 Notes | Stem Cell Notes)
corpus albicans - (Latin, corpus = body, albicans = whitish) The histological structure formed by the degenerating corpus luteum in the ovary if implantation does not occur and the hormone hCG is not released. The structure is white, not yellow, because of the absence of steroid hormone synthesis/accumulation. (More? Week 2 Ovary | Week 1 Notes)
corpus luteum - (Latin, corpus = body, luteum = yellow) The remains of ovarian follicle after ovulation that acts as an endocrine organ (produce progesterone and oestrogens) supporting pregnancy and preventing menstruation (loss of the endometrial lining). Formed by proliferation of both follicular granulosa cells (granulosa lutein cells) and thecal cells (theca lutein cells) after ovulation, which produce progesterone and oestrogens. de Graaf first observed it in the ovary of a cow as a yellow structure, caused by accumulation of steroidal hormones. (More? Week 2 Ovary | Week 1 - Oogenesis)
cytotrophoblast - The "cellular" trophoblast layer surrounding (forming a "shell") the early implanting conceptus. Beginning at uterine adplantation, proliferation and fusion of these cells is thought to form a second outer trophoblast layer, the syncytiotrophoblast. The cytotrophoblast layer contributes to formation of the placental villi, the functional component of the fetal placenta. (More? Week 2 Notes | Placenta Notes | human Chorionic Gonadotrophin)
egg - (oocyte or ovum) An alternative term used to describe the haploid female reproductive cell (germ cell). The term is also used to describe the avian and reptilian shell enclosed structure. (More? Week 1 Notes)
fertilization - (fertilisation) The process of penetration of the oocyte (egg) by the spermatozoa and the combining of their genetic material that initiates development of the embryo. The union of two haploid gametes to form a diploid cell or zygote. (More? Fertilization)
follicle - (Latin, folliculus = little bag, dim. of Latin follis) The functional unit within the ovary that includes the developing oocyte (egg) and the surrounding layers of cells that support that oocyte. Some cells within the follicle are released along with the ooctye at ovulation, while other cells are involved with female sex hormone secretion into the maternal bloodstream. The remnants of the ovulating follicle will form the corpus luteum. (More? Week 1 - Oogenesis | Human Menstrual Cycle | Genital System - Female)
folliculogenesis - The term used to describe the process of follicle development within the ovary. The follicle is the structure developing within the ovary that includes the oocyte (egg) and surrounding support cells. (More? Week 1 - Oogenesis | Human Menstrual Cycle)
gestational age - The clinical term to describe human development timed from the last menstrual period (LMP) and therefore differs by approximately two weeks from research materials timed from fertilization. (More? Development Week by Week)
gonad - (Greek, gonos = seed) A gamete-producing (germ cell) organ. A non-sexual term which is used to describe both the female ovary and male testis. (More? Week 1 Notes)
hCG - An acronym for the hormone human Chorionic Gonadotrophin.
human chorionic gonadotrophin - (hCG) Placental hormone initially secreted by cells (syncitiotrophoblasts) from the implanting conceptus during week two, supporting the ovarian corpus luteum, which in turn supports the endometrial lining and therefore maintains pregnancy. Hormone can be detected in maternal blood and urine and is teh basis of many pregnancy tests. Hormone also stimulates the onset of fetal gonadal steroidogenesis, high levels are teratogenic to fetal gonadal tissues. (More? Placenta Notes | Week 2 Notes)
implantation - The term used to describe process of attachment and invasion of the uterus endometrium by the blastocyst (conceptus). Abnormal implantation is where this process does not occur in the body of the uterus (ectopic) or where the placenta forms incorrectly. (More? Week 2 - Implantation | Week 2 Abnormalities)
infundibulum - The funnel-shaped initial segment of uterine tube (oviduct or Fallopian tube) opening into peritoneal cavity and connected to the ampulla. The peritoneal opening sitting over the ovary. (More? Week 1 - Oogenesis | Genital System - Female)
last menstrual period - (LMP) Clinical term used to describe the menstrual period that occurs before a pregnancy and is used as the date to calculate clinical pregnancy development (gestational age). Note that in humans this is approximately two weeks different from embryonic development, which begins at fertilization around the mid-point of the menstrual cycle.
LMP - Acronym for Last Menstrual Period that occurs before a pregnancy and is used as the date to calculate clinical pregnancy development (gestational age).
menstrual cycle - The human reproductive cycle, an endocrine regulated change in female anatomy and physiology that occur over 28 days (4 weeks, a lunar month) during reproductive life (between puberty and menopause). This cycle ceases during pregnancy and differs from other non-primate vertebrates (eg rats, mice, horses, pig) females that have a reproductive cycle called the estrous cycle (oestrous, British spelling). (More? Human Menstrual Cycle | Estrous Cycle)
oocyte - (Greek, oo = egg, ovum) The term used to describe the haploid egg or ovum formed within the ovary (female gonad) and released to enter the uterine tube and be transported to the uterus. (More? Week 1 - Oogenesis | Genital System - Female)
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. (More? Week 1 - Oogenesis | Week 1 Notes)
primary follicle - (preantral follicle) Term used to describe the developmental stage of ovarian follicle development following primordial in decribing the sequence (primordial, preantral, antral) of follicle development within the ovary. In humans, a number of primordial follicles will begin to develop into primary follicles, some of which will then form secondary (antral follicles), with only a single antral follicle developing into the ovulating follicle (Graffian) each menstrual cycle. (More? Week 1 - Oogenesis)
pronuclear fusion - (Greek, pro = before) The process of the fusion of the two haploid nuclear structures (pronuclei) contributed from the spermatazoa and oocyte to form the first diploid nucleus cell. Can also be called fusion of pronuclei.
pronucleus (Greek, pro = before) The two haploid nuclear structures from spermatazoa and oocyte that will fuse together to form the first diploid nucleus cell. Therefore the nuclear structures that exist "before the nucleus", the plural term is pronuclei. (More? Week 1 Notes)
spermatogenesis - (Greek, genesis = origin, creation, generation) 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 the following cellular changes: meiosis, reoorganization of DNA, reduction in DNA content, reorganization of cellular organelles, morphological changes (cell shape). The final process of change in cell shape is also called spermiogenesis. (More? Week 1 - Spermatogenesis)
syncytiotrophoblast A multinucleated cell currently thought to form by the fusion of cytotrophoblasts (trophoblasts) 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. (More? Week 2 Notes | Placenta Notes | human Chorionic Gonadotrophin)
theca externa - The ovarian follicle stromal cells forming the outer layer of the theca folliculi surrounding the developing follicle within the ovary. Consisting of connective tissue cells, smooth muscle and collagen fibers.
theca interna - The ovarian follicle stromal cells forming the inner layer of the theca folliculi surrounding the developing follicle within the ovary. This vascularized layer of cells respond to leutenizing hormone (LH) synthesizing and secreting androgens which are processed into estrogen. Theca cells do not begin secreting estrogen until puberty.
trophoblast - (Greek, trophe = "nutrition") the trophoblast cells have an important contribution to extraembryonic tissues (fetal placenta and membranes) and processes of early development (adplantation, implantation and endocrine support of pregnancy). Week 1 blastocyst formation the outer layer of cells (adjacent to the zona pellucida) form a flat squamous epithelial layer of cells, the trophoblast layer. Week 2 following blastocyst hatching the trophoblast layer is involved with initial adhesion to the uterine wall and subsequent implantation within the wall. During this period the trophoblast layer differentiates into two distinct layers (syncitiotrophoblast, cytotrophoblast). (More? Week 2 Notes | Week 3 Notes | Placenta Notes)
uterine glands - (endometrial glands) The simple tubular glands formed by invagination of the uterine endometrium (a columnar epithelium of ciliated cells and secretory cells). The glands extend into the underlying thick vascular stromal layer. The glands line the uterus body and change in appearance and secretion during the menstrual cycle. The glands secretions function to provide the initial nutritional support of the conceptus and may have a role in maintaining adhesion. (More? Human Menstrual Cycle | Genital System - Female Uterus | Urogenital Notes)
uterine tube - (uterine horn, oviduct, fallopian tube, salpinx) A pair of tubular structures that transport the oocyte (egg) from the ovary to the uterus body. They are located laterally on the upper uterus and consist medial to lateral of three main parts: isthmus (medial constricted third), ampulla (intermediate dilated portion) and infundibulum (containing the abdominal opening/ostium, surrounded by finger-like fimbriæ). The tube structurally has two main layers: a mucosa (ciliated and secretory epithelium) and a muscularis (inner circular muscle layer and an outer longitudinal layer). (More? Human Menstrual Cycle | Genital System - Female Uterus | Urogenital Notes)
uterus - The female internal genital (reproductive) tract forming a hollow muscular walled organ, embryonically derived from the paramesonephric ducts. The human uterus has two uterine horns (fallopian tubes) where the first week of development occurs and a single hollow body where implantation of the blastocyst normally occurs. Following puberty, the non-pregnant uterus (epithelium and underlying stroma) undergoes cyclic changes under the influence of hormones, the menstrual cycle. This cycle of uterine changes ceases during pregnancy and it contributes the maternal component of the placenta. (More? Genital System - Female Uterus | Human Menstrual Cycle | Genital Notes)
zygote - The first diploid cell that forms following fertilization by fusion of haploid oocyte (egg) and spermatozoa (sperm) resulting in the combination of their separate genomes. (More? Fertilization | Week 1 Notes)
zona pellucida - (Latin, zona pellucida = transparent zone) A specialized extracellular matrix surrounds the developing oocyte (egg, ovum) within the ovary and follwing ovulation. It consists of three types of glycoproteins ZP1, ZP2 and ZP3 which have different roles in fertilization. Following fertilization, the zona pellucida also surrounds the blastocyst during the first week of development, from which it "hatches". The zona pellucida has a role in fertilization, sperm binding, preventing polyspermy, blastocyst development and preventing premature implantation (ectopic pregnancy). (More? Week 1 - Fertilization | Week 1 - Oogenesis | zona pellucida binding protein)
zona pellucida binding protein 1 - (ZPBP1) A spermatozoa protein found located on the acrosome surface which has a role during spermiogenesis (acrosome compaction, Sertoli-spermatid junctions) and also binds the zona pellucida during fertilization. (More? Week 1 - Fertilization | Week 1 - Fertilization)
Movie of Human Embryo Growth (this shows a human embryo growing, all images are to scale)
Movie of Mouse Embryo Growth (this shows a mouse embryo growing)
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