| Obstetrics | Field of study concentrated on pregnancy, childbirth and the postpartum period |
| 3 Phases of Embryology | 1. Pre-Embryonic Period
2. Embryonic Phase
3. Fetal Phase |
| 4 Stages of the Embryonic Phase | 1. Fertilization
2. Cleavage
3. Gastrulation
4. Development of body form |
| Average length of the Embryonic Phase | 2-8 weeks
(Depending on specie) |
| Fertilization | Sperm and ovum fuse to form a Zygote.
(haploid + haploid = diploid) |
| Where does fertilization occur? | Uterine Tube |
| Name the glycoprotein layer that prevents additional sperm from entering the ovum after fertilization | Zona pellucida |
| Corona Radiata | Layer of follicular cells that surround the Zona Pellucida; does not impede fertilization; gradually desquamates to uncover nutrient pores in ZP |
| Zona pellucida | Glycoprotein layer that surrounds the ovum; becomes impermeable to sperm after fertilization |
| What type of division does the zygote undergo | Mitosis |
| Factors that affect the rate at which cleavage occurs | 1) Quantity
2) Distribution of yolk in the ovum
The presence of a large amount of yolk mechanically retards cleavage because yolk cannot divide as rapidly as cytoplasm can |
| Oligolecithal | Type of ova with a small amount of yolk
(Mammalian Ova) |
| Isolecithal | Type of ova with yolk that is evenly distributed and nucleus is positioned centrally
(Mammalian ova; resultant blastomeres are all the same size = cleavage is equal) |
| Where does cleavage begin and end? | Uterine tube; Uterus |
| Holoblastic | Complete cleavage that divides the whole egg into distinct and separate blastomeres
(e.g. mammals) |
| Meroblastic | Incomplete cleavage as a result of the presence of an impeding mass of yolk material
(e.g. eggs of birds) |
| At what cell stage does the embryo have a mulberry-like appearance? | 16-64 cell stage
(known as a Merula) |
| Blastocyst cavity | Fluid filled cavity within the blastomere
(Fluid filled spaced develop between the cells in the centre of the morula, they coalesce to form the blastocyst) |
| Trophoblast | 1. The membrane that forms the wall of the blastocyst in early development; aids implantation in the uterine wall
Gives rise the the placenta |
| Embryoblast | Central cells (mainly from the animal pole) group together against the trophoblast to form the inner cell mass known as the Embryoblast
Subsequently forms the embryo |
| Blastocyst | A structure formed in the early development of mammals. It possesses an inner cell mass (embryoblast) which subsequently forms the embryo. The outer layer of the blastocyst consists of cells collectively called the trophoblast. This layer surrounds the inner cell mass and a fluid-filled cavity known as the blastocyst cavity. |
| When is the Zona Pellucida lost in Ungulates? | After the Morula has been transformed into a blastocyst
(Blastocyst looses is spherical shape after the loss of the ZP) |
| When is the Zona Pellucida lost in Carnivores? | After the commencement of gastrulation - at the stage when the somites start to form
(Blastocyst looses is spherical shape after the loss of the ZP) |
| What is the shape of the Carnivore blastocyst after the loss of the Zona Pellucida? | Lemon-shaped |
| What is the shape of the Horse blastocyst after the loss of the Zona Pellucida? | Ovoid |
| What is the shape and lenght of the ruminant blastocyst after the loss of the Zona Pellucida? | Narrow, tube like structure
50 cm + |
| What is the shape and lenght of the Pig blastocyst after the loss of the Zona Pellucida? | Narrow, tube like structure
1.5m |
| From what structure does the Embryonal Disc develop? | Embryoblast
(The embryonal disc will later develop into the Embryo Proper) |
| What structure is responsible for absorbing nutrients from the the lumen of the uterus and for secreting fluid into the blastocyst cavity? | Trophoblast |
| After the loss of the _______ rapid enlargement of the blastocyst occurs. | Zona Pellucida |
| Covering layer of Rauber | The part of the trophoblast that lies over the embryoblast.
(Develops slower than the rest of the trophoblast) |
| Eutheria | Placental Mammals |
| Gastrulation | Differentiation of the 3 germ layers
Transforms the unilaminar blastocyst into a trilaminar gastrula |
| What stage of the embryonal development sees the effects of the genes of the new individual's nuclei being expressed? | Gastrulation |
| Cleavage is controlled by... | Properties transferred by the maternal nucleus to the cytoplasm of the the zygote. |
| What does the Ectoderm layer differentiate into? | Reception of stimuli and protection of the organism |
| What does the Mesoderm layer differentiate into? | Support, movement, excretion and reproduction |
| What does the Endoderm layer differentiate into? | Digestion and respiration |
| Name the 4 stages of Gastrulation | 1. Formation of the Hypoblast and Embryonal disc
2. Primitive Streak Formation
3. Cell involution and Notochord Formation
4. Neurulation and Initial differentiation of the Mesoderm |
| When does Gastrulation commence? | After formation of the embryoblast |
| Hypoblast Formation | The hypoblast is a tissue type that forms from the inner surface of the embryoblast. It lies beneath the epiblast and consists of extended squamous epithelium. The hypoblast gives rise to the yolk sac, which in turn gives rise to the chorion. |
| Embryonal Disc Formation | After the loss of the Covering Layer of Rauber the exposed Embryoblast is transformed into a slightly convex layer of cells known as the Embryonal Disc.
The Embryonal Disc is continues with the Trophoblast |
| Name the 2 layers of the Embryonal Disc | Hypoblast; Epiblast |
| What are the first 2 processes that occurs more or less simultaneously in the first stage of gastrulation? | Hypoblast Formation
Embryonal Disc Formation |
| Name the 2 structures that are responsible for moving the cells destined to form the endoderm, mesoderm and ectoderm into their predefined areas within the epiblast | Primitive Streak
Primitive Node |
| What phase of Gastrulation is the first step in the development of body cavities? | Primitive Streak Formation |
| Primitive streak formation is the ____ stage in gastrulation | 2nd |
| Primitive streak formation | A dull, thickened stripe develops in the middle of the epiblast in the caudal half of the embryonal disc. It is formed by the medial and caudal migration of proliferating epiblast cells
Continued cell migration causes cranial elongation of the primitive streak until it extends over all but the cranial third of the embryonal disc. |
| Primitive node | The caudal migration of proliferating epiblast cells from the cranial part of the embryonal disc causes a discrete aggregation of cells at the cranial end of the primitive streak; this thickening is known as the primitive node |
| What process changes the primitive streak to a primitive groove? | Cell Involution |
| Cell Involution | Proliferating cells immediately adjacent to the primitive streak are involuted into the area between the epi- and hypoblast
The process of involution physically alters the primitive streak and it changes into a primitive groove, flanked on either side by a primitive fold. |
| Endoderm Formation | Some of the involuted cells invade the hypoblast and, multiply and form a layer on the deep surface of the embryonal disc known as the Embryonic Endoderm. |
| Extraembryonic Endoderm | Development if the endoderm displaces the hypoblast to the periphery of the Embryonic Disc. The Hypoblast now only lines the yolk sac and is now referred to as the EEE. |
| Involution gives rise to the formation of what 2 germ layers? | Endoderm; Mesoderm |
| Mesoderm Formation | The remaining involuted cells (i.e. those that did not invade the hypoblast to form the endoderm) now constitute the mesoderm. |
| In what anatomical directions does the mesoderm expand with continued cell involution and proliferation? | Cranially, caudally and laterally (excluding the area immediately cranial to the primitive node, the prechordal plate and the cloacal membrane.
It expands beyond the periphery of the embryonal disc and between the trophoblast and extraembryonic endoderm of the entire yolk sac. |
| Embryonic Mesoderm | Mesoderm within the embryonal disc |
| Extra-embryonic mesoderm | Mesoderm beyond the periphery of the Embryonic Disc |
| Only the ______ mesoderm will contribute to the formation of the embryo proper | Embryonic |
| The prechordal plate (circular area) is situated at the _____ edge of the embryonal disc and later forms the _______ membrane. | Cranial; Oropharyngeal |
| The cloacal membrane (circular area) is situated just _____ to the primitive streak | Caudal |
| The mesoderm is prevented from invading the prechordal plate and the cloacal membrane by firm adhesion between the ________ and _______ | Epiblast and Endoderm
(The area in front of the prechordal plate is, however, eventually invaded by the expanding mesoderm) |
| Where does the pleuropericardial coelom develop? | The area in front of the prechordal plate |
| What process sees the zygote transform into a blastocyst? | Cleavage |
| Notochordal Process develops from the _____ | Primitive node |
| Notochordal canal | Lumen of the Notochordal Process |
| Primitive Pit is a indentation of the _______ _______ | Primitive Node |
| The ______ forms the entrance to the Notochordal Canal | Blastopore |
| Neurulation | Notochord-induced transformation of ectoderm into nervous tissue |
| Notochord Formation | The notochord develops from the primitive node located at the cranial end of the primitive streak. From the node, cells proliferate and migrate forward into the future head region where they become the rod-shaped notochord. |
| The notochordal process extends between the ___ . | Epiblast and endoderm |
| Neurenteric canal | Temporarily connects the future amniotic cavity and yolk sac
(Previously Notochordal canal) |
| What structure induces the development of the brain and spinal chord and plays a role in the formation of the vertebral column and the basal portion of the skull? | Notochord |
| What structure serves as the primary inducer for development if the Embryo Proper? | Primitive Node |
| Ectoderm Formation | All the epiblast cells that did not involute constitute the ectoderm |
| Neuro-ectoderm | The ectodermal cells on the dorsal midline
Destined to form the future brain and spinal cord. |
| Neural Plate | Thickening of the Neuro-ectoderm cranial to the Primitive Node
Wide, flat cranially = Future Brain
Narrower in the middle, caudally = future spinal chord |
| Neural Groove | Dorsal surface of the neural plate invaginates forming the NG |
| Neural Folds | Borders the Neural Groove on either side |
| Neural Tube | Neural folds fuse along the dorsal midline to form the NT
The lumen of the NT is the Neural Canal |
| Neural Canal | Lumen of the Neural Tube
Temporarily communicates with the amnotic cavity via the rostral and caudal neuropores. The rostral neuropore closes last. |
| Neuropore | Rostral or Caudal opening of the Neural Tube
Temporarily communicates with the amniotic cavity.
(Rostral opening closes last.) |
| During neural tube formation, two cell cords, the neural crests, develop in the angles of junction between the _____ and _____
The neural crests separate from both the _____ and _____ and come to lie dorsolaterally on either side of the neural tube, extending over its whole length. | Ectoderm and Neuro-ectoderm |
| That part of the neural tube destined to form the brain bends ________, enlarges and forms three vesicles; these vesicles are the primordia of the ______, _____ and _____ | Ventrally
Prosencephalon, Mesencephalon and Rhombencephalon |
| Name the structure that causes ventral bending of the Neural Tube at the level of the Mesencephalon. | Cephalic Flexure |
| Name the structure that causes ventral bending of the Neural Tube at the junxtion between the Rhombencephalon and the Spinal Chord. | Cervical Flexure |
| After the formation of the future brain from the Neural Tube, the remaining NT forms the ______ | Spinal Chord |
| What structure remains as the central canal of the spinal chord and continues rostrally with the _____ ventricle. | Neural Canal; Fourth (in the Rhombencephalon) |
| Sulcus Limitans | From the level of the mesencephalon, a longitudinal groove develops bilaterally in the walls of the neural canal. |
| What groove divides the neural tube in dorsal and ventral parts? | Sulcus Limitans |
| Paraxial Mesoderm | Distinct longitudinal columns adjacent to the Notochord
(Originates from mesoderm) |
| Lateral Mesoderm | Mesoderm peripheral to Paraxial Mesoderm |
| Numerous _____ _____ that divide the paraxial mesoderm into blocks known as somites. | Transverse Fissures |
| Somite development progresses in a _____ direction, with the first somite forming just ___ to the ___ end of the notochord. | Cranio-caudal; caudal; rostral |
| What structure is used to estimate embryonal age? | Number of Somites |
| The number of somites is constant for each species: there are _-_ pairs of somites
for the head and ___ pair(s) for each vertebral segment | 4-6;1 |
| Tissues that somites give rise to include ... | Bone
Muscle
Dermis |
| From what germ layer does Somites originate? | Mesoderm |
| While the somites are forming, small cavities start developing in the lateral mesoderm. These cavities coalesce to form a single cavity known as the _____. | Splanchnocoele |
| The coelom splits the lateral mesoderm into two layers, namely... | Somatic and Splanchnic Mesoderm |
| Endocoelom | Portion of the coelom within the embryonic mesoderm |
| Exocoelom | Portion of the coelom in the extra-embryonic mesoderm |
| The splitting of the lateral mesoderm extends into the _____ mesoderm and the coelom eventually completely surrounds the yolk sac. | extra-embryonic |
| When does the endo- and exocoelom become clearly defined? | Only when the body starts developing its cylindrical shape |
| Small cavities develop in the mesoderm in front and on either side of the prechordal plate. These cavities coalesce and form a _____ tube (seen from above) peripheral to the developing _____ region. | ∩-shaped tube; head |
| The 1-shaped tube is known as the _____ _____ and it communicates caudally with the _____. | pleuropericardial coelom; endocoelom |
| Septum transversum | The thickish plate of unsplit mesoderm separating the pleuropericardial coelom from the exocoelom |
| Septum transversum will later form part of the _____ | Diaphragm |
| _____ plate will develop in the ventral wall of the pleuropericardial coelom. | Cardiogenic |
| Somatic mesoderm becomes associated with the ectoderm (trophoblast) to form a membrane known as the _____ | Somatopleure |
| Splanchnic mesoderm and endoderm form a membrane known as the _____ | Splanchnopleure |
| The lateral mesoderm remains connected to the somites of the paraxial mesoderm by a narrow mesodermal bridge known as the _____ | Nephrotome |
| The nephrotome will later form parts of the _____ _____. | Urogenital tract |
