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Histo Repro
Histology Final
103
Veterinary Medicine
Professional
11/26/2009

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Cards

Term
Give a general overview of ovulation.
Definition

Involves:

  • Rupture of one or more mature ovarian follicles
  • Shedding of some of its contents from the surface of the ovary
  • Remainder of the follicle is converted under hormonal influence into the corpus luteum
Term
What is the corpus luteum?
Definition
  • Important endocrine structure
  • Secretes progesterone & estrogens
    • These produce uterine changes that facilitate implantation & maintenance of the conceptus
Term
What controls ovulation?
Definition
Luteinising Hormone (LH) produced in the glandular pituitary
Term
What is the mechanism of action for ovulation?
Definition
Increased pressure within the follicle
Term
What structures are shed from the ovary during ovulation?
Definition
  1. Germ cell
  2. 1st polar body
  3. Zona pellucida
  4. Corona radiate
Term
What kind of germ cell is shed during ovulation?
Definition
  • Usually a secondary oocyte, arrested in metaphase
  • In horses and dogs, its a primary oocyte that has not completed division
Term
When is a 1st polar body formed?
Definition
Formed in the 1st meiotic division just prior to ovulation
Term
What is the zona pellucida?
Definition
Membranous envelope of mucopolysaccharide surrounding the germ cell & 1st polar body
Term
What is the corona radiate?
Definition
Surrounding layer of follicular epithelial cells
Term
What happens during ovum capture/transport?
Definition
  1. Ovulated structures shed from the ovary surface to the peritoneal cavity
  2. Pass into the oviduct
    • Assisted by the action of the cilia of the infundibulum
    • Second factor is the constant stream of peritoneal fluid entering the oviduct
  3. Germ cell & related structures are assisted in passage to the uterus by muscular contractions of the oviduct & its cilia
Term
What structures make up the oviduct?
Definition
  1. Infundibulum
  2. Ampulla
  3. Isthmus
Term
What is capacitation?
Definition
  • The ability of sperm to fertilize the female germ cell
  • Occurs within the female tract
  • Involves biochemical changes within the sperm
Term
How is transport of sperm acheived?
Definition
  • Partly by muscluar contraction of the female tract
  • Partly by the motility of the sperm
  • Cilia of the uterine tube do not assist because they beat towards the uterus
Term
How long can sperm remain viable in the female tract?
Definition
  • Most species 1-2 days
  • Horse & dog 6-7 days
  • Birds 32 days in fowl; 70 days in turkey
Term
Where does fertilization occur?
Definition
In the ampulla region of the oviduct
Term
When does fertilization occur?
Definition
12-24 hours after ovulation
Term
What barriers do spermatozoon have to cross to penetrate the female germ cell?
Definition
  1. Corona radiata
  2. Zona pellucida
  3. Cell membrane of oocyte
Term
Why is the corona radiata not a significant barrier to the spermatozoon.
Definition

By the time fertilization is occuring, the corona radiate cells are already fragmenting

(in ox they have already disappeared completely)

Term
How do spermatozoon overcome the zona pellucida barrier?
Definition
By the actino of enzymes produced in the acrosome of the sperm
Term
How do spermatozoon get past the cell membrane of the oocyte?
Definition
  • Tail of the sperm is shed
  • Cell membranes of the female & male germs cells rupture & then unite together
  • Thus, enclosure of sperm within the cytoplasm of the female cell
Term
What happens immediately after spem penetration?
Definition
  1. Completion of 2nd meiotic division of the oocyte
  2. Block to polysperray through cortical reaction
  3. Haploid female & male germ cells swell &  occupy a central position w/n cytoplasm to become pronuclei
  4. Pronuclei fuse together to create a diploid zygote
Term
The 2nd meiotic division of the oocyte produces what?
Definition
The ovum & 2nd polar body
Term
The presence of what is sure evidence of fertilization?
Definition
2nd polar body
Term
What is a block to polysperray, and how does it occur?
Definition
  • Prevents further sperm from penetrating the female germ cell
  • Cortical granules in the oocyte cytoplasm align at the periphery of the ooctye, adjacent to the plasma membrane (cortical recation)
Term
What is the significance of a diploid zygote?
Definition
It is genetically different from either parent
Term
Where does teh zygote with the polar bodies lie?
Definition
Inside the zona pellucida
Term
How is the 2-cell zygote formed?
Definition
  1. Prior to fusion, male & female pronuclei duplicate their DNA
  2. Immediately on fusion, their chromosomes split in the course of normale mitotic division
  3. This results in a 2-cell zygote
Term
Which gender determines the offspring's sex?
Definition
  • Mammals: males
  • Birds: females
Term
What is polyspermy?
Definition
  • When more than one sperm penetrates the female germ cell
  • 3 or more pronuclei may occur & fuse to make a triploid embryo
  • Common in pigs
  • Most die in early development, but rare viability in humans & cats
Term
How is a morula formed?
Definition
  • After 2-cell stage, cell division occurs without increasing the conceptus size (still enveloped in the zona  pellucida)
  • Through this cleavage or segmentation, the resulting daughter cells (called blastomeres) are progressively smaller and smaller
  • Once the concetus is a solid ball of blastomeres, its called a morula ("little mulberry")
Term
What provides nutrition for the morula?
Definition
Deutoplasm- yolk droplets contained within the cytoplasm of the cells
Term
Up to what stage does the conceptus lie free within the lumen of the oviduct or uterus?
Definition
Morula stage
Term
What disappears in the blastocyst (blastula) stage?
Definition
  • Zona pellucida
  • Frees the conceptus to enlarge & rapidly grow to fill the uterine lumen
Term
How is the blastocoele formed?
Definition
  • In the blastocyst, intercellular fluid-filled spaces start to appear
  • These combine into 1 single, enclosed cavity called the blastocoele
Term
What two cellular groups can be recognized in the blastocyst?
Definition
  1. Embryoblast
    • inner cell mass
  2. Trophoblast
    • outter cell mass
Term
What does the embryoblast give rise to?
Definition
The embryo proper
Term
What does the trophoblast form?
Definition
Various extra-embryonic membranes associated with embryo nutrition
Term
What provides nutrition for the blastocyst?
Definition
Selective diffusion through the torphoblast of various nutrients derived from the secretions of the endometrial glands
Term
When is the blastocyst stage reached?
Definition
  • Most species: At end of th 1st week of development
  • Dogs: At end of the 2nd week
Term
What is implantation?
Definition
  • When the conceptus becomes attached to or embedded in position in the uterus
  • Establishes the close link between foetal & maternal tissue necessary for development of the placenta
Term
What is the definitive organ for nutrition of the foetus?
Definition
Placenta
Term
What is central implantation?
Definition
  • Occurs in domestic species
  • Embryo remains located in the uterine lumen
Term
What is interstitial implantation?
Definition
  • In humans & guinea pigs
  • Conceptus migrates through the uterine epithelium into the substance of the endometrium
Term
What structural changes occur during implantation?
Definition
  • Changes in the endometrium from the action of progesterone (from the corpus luteum)
  • Changes in the conceptus
    • Elongation of the blastocyst occurs (particuarly in the pig) to greatly increase the surface area of contact b/w the trophoblast & uterine epithelium
    • Simple adhesions develop
    • Junctional complexes form
Term
When does implantation occur?
Definition
  • Pig: 12 days
  • Dog: 18 days
  • Sheep: 10 days & cmopleted 4-5 weeks later
  • Horse: 2 months & completed ~ the 14th week
Term
What is a polytocous species?
Definition
Bear many young
Term
Where do the ceonceptus implant in polytocous species?
Definition
  • Evenly along both horns
  • Some transuterine migration may occur
Term
What are the two types of twinning?
Definition
  • Dizygous
  • Monozygous
Term
What is dizygous twinning?
Definition
  • 2 separate ova are fertilized
  • Genetically similar like normal brother/sister relationships
Term
What is monozygous twinning?
Definition
  • 1 ovum is fertilized but divides at the blastocyst stage into 2 individuals
  • Genetically identical
  • Same sex & blood groups
  • Notable in huamsn & cattle
Term
What is ectopic implantation?
Definition
  • A fertilized ovum may be lost into the peritoneal cavity & become implanted into a peritoneal surface
  • Usually results in early embryonic death
Term
What helps to prevent ectopic pregnancies?
Definition
  • Zona pellucida
  • Avoids direct contact b/w trophoblast & maternal epithelium
  • Delays expansion of the conceptus while still in the oviduct
Term
What is freemartinism?
Definition
  • In dizygous twinning in cattle, the development of a common circulation by placental anastomosis usually occurs
  • If the twins are opposite sex, the female develops a type of intersex known as freemartin
Term
What is gastrulation?
Definition
Process where the blastula (single-layered structure) becomes a gastrula (trilaminar structure)
Term
What are the three layers of the gastrula (germ layers)?
Definition
  1. Ectoderm
  2. Mesoderm
  3. Endoderm
Term
How is the embryonic endoderm formed?
Definition
  • Delamination
  • The embryoblast mass cells give rise to a second inner layer or smaller, darker cells (the embryonic endoderm)
Term
How is the epiblast formed?
Definition
  • Covering of trophoblast cells over the embryoblast disappears
  • Exposed cells of the embryoblast proliferate to form the epiblast
Term
What does the epiblast produce?
Definition
  • Produces the bilaminar germ disc/embryonic disc that is continuous with the trophoblast
Term
How are the trophectoderm (extraembryonic ectoderm), hypoblast, and bilaminar omphalopleure created?
Definition
  • Endoderm spreads outwards from the germ disc to line the internal aspect of the trophoblast that is now called the trophectoderm
  • The endoderm so formed is called the hypoblast and encloses the yolk sac or primitive gut
  • 2 layered wall is called the bilaminar omphalopleure
Term
How is the primitive streak formed?
Definition
  • Rapid growth of the embryonic disc occurs in an uneven manner, converting the ovoid disc into a pear-shaped structure
  • A whitish line, called the primitive streak, appears on the embryonic ectodermal layer
  • This establishes the polarity of the embryo, developing as it does near its caudal end
  • Primitive streak is produced as a result of the proliferation & convergence of ectodermal cells & forms a linear thickening along the ectoderm
Term
How is the mesoderm formed?
Definition
  • From the primitive streak, cells invaginate between the ectodermal & endodermal layers of the embryonic germ disc
  • These progressively form a 3rd germ layer in this intermediate position, which is called the mesoderm
Term
How is the intraembryonic mesoderm formed?
Definition
  • The mesoderm spreads throughout most of the embryonic disc as the intraembryonic mesoderm, thus converting it into a trilaminar germ disc
Term
How is the extraembryonic mesoderm formed?
Definition
  • The mesoderm continues to spread peripherally beyond the limits of the embryonic disc proper to give rise to the extraembryonic mesoderm
  • This spreads progressively between the extraembryonic ectoderm & the extraembryonic endoderm to form a trilaminar ophalopleure
Term
How is the notochord formed?
Definition
  • Cranial extremity of the primitive streak presents a rounded expansion termed the node of Hensen (primitive node)
  • From here, cells invaginate & migrate forming a rode of mesdermal cells called the notochord
  • Extends as far cranial as the buccopharyngeal membrane
Term
What is the first indication of the future mouth?
Definition
The buccopharyngeal membrane
Term
What are the 3 subdivisions of the intraembryonic mesoderm?
Definition
  1. Paraxial mesoderm
  2. Intermediate mesoderm
  3. Lateral plate mesoderm
Term
What are the 2 circular zones of the disc that are not invaded by the mesoderm and remain bilaminar?
Definition
  1. Buccopharyngeal membrane
  2. Cloacal membrane
Term
How are somites formed?
Definition
  • Beginning cranially, transverse fissures appear in the paraxial region of the membrane to produce paired blocks of mesodermal cells, called somite
  • Soon after formation, they disaggregate & move to respective areas of the embryo
Term
How many somites are there?
Definition
One pair per vertebral segment & 4-6 pairs in the head
Term
What do somites form?
Definition
Skeletal, muscular, & dermal elements
Term
What are the differentiating elements of somites?
Definition
  1. Sclerotome
  2. Myotome
  3. Dermatome
Term
What is intermediate mesoderm sometimes called nephrogenic mesoderm?
Definition
Intermediate mesoderm forms the precursors for the kidneys & some parts of the genital system
Term
What does embryonic somatopleure form?
Definition
Parts of the body wall, except musculature & ribs
Term
What does splanchnopleure form?
Definition
GI tract located in the thorax & abdomen
Term
How is the intraembryonic coelom formed?
Definition
  • Extraembryonic mesoderm splits into 2 layers separated by a cavity- the extraembryonic coelom (exocoelom)
  • This cavity spreads gradually to involve the lateral plate mesoderm to form the intraembryonic coelom
Term
What is the somatopleure?
Definition
The outer layer of mesoderm that is adjacent to the ectoderm of the coelom
Term
What is the splanchnopleure?
Definition
The inner layer of mesoderm that is adjacent to the ectoderm of the coelom
Term
What is the future peritoneal cavity?
Definition
The intraembryonic coelom formed w/n the lateral plate mesoderm
Term
What makes the future pericardial cavity and primitive pleural cavity?
Definition
  • The introembryonic coelom on either side spreads cranial to untie the midline, cranial to the buccopharyngeal membrane
  • The entire intraembryonic coelom is horseshoe shaped
  • The midline region is the future pericardial cavity
  • The narrow intermediate region is the primitive pleural cavity
Term
What are the 3 basic germ layers of the embryonic part of the gastrula?
Definition
  1. Ectoderm
  2. Mesoderm
  3. Endoderm
Term
Describe the embryonic part of the gastrula and its development.
Definition
  • Flat structure
  • Undergoes development that transforms the flat structure into a tubular structure
    • This begins shortly after the first somites appear, initially in the head region
Term
What is the basic pattern is adult vertebrae?
Definition
  • One tube inside the other
  • Outer tube: body wall (ecto & mesoderm)
  • Inner tube: digestive tube (meso & endoderm)
  • Space in b/w is the coelomic cavity
Term
How are the neural plate and neural tubes formed in the head region?
Definition
  1. Notochord serves as the inductor for the formation of the head
  2. Thickening of the ectoderm over the cranial end of the notochord to form the nueral plate (precursor of the brain)
  3. Neural plate folds & forms the neural tube (later differentiates into majore parts of the brain)
  4. Appearance of neural crest cells on dorsolateral sides of the neural tube
Term
What do neural crest cells give rise to?
Definition
  • Pigmented cells (melanocytes) of the skin
  • Glial cells of the CNS
  • Chromaffin cells of the adrenal medulla
  • Neurolemocytes (Schwann cells) of peripheral nerves
Term
What are the early features of the head?
Definition
  • Head region forms first
  • Most advanced part of body
  • Specific modifications of the basic cylindrical pattern are 1st seen here
Term
How is the cylindrical shape of the head region formed?
Definition
  1. Cranial end of embryo grows up & forward
  2. It folds back to form head fold
  3. At same time, lateral folding of ectoderm on each side of embryo
  4. At cranial end of embryo, ectoderm encompasses the underlying mesoderm
  5. 2 lateral folds fuse together ventrally to create cylindrical outgrowth that is the head
    • Rostral end is closed because of forward growth
  6. Inner tube is the foregut
  7. Ectoderm covering the head is continuous with the rest of the ectoderm
  8. Head is elongated by continued growth & folding
  9. Caudal part of head incorporates the 1st several pairs of somites to form the musculo-skeletal strucutres of the head
Term
What are the results of body folding?
Definition
  • Embryo converted from flat disc to curved cylindrical structure
  • Lateral & ventral body walls develop by folding of somatopleure
  • Gut is formed by being nipped off the yolk sac & trapped w/in the developing body of the embryo
  • Embryo is completely surround by the fluid filled amnion
  • A group of structures are bunched together at mid-abdominal level (future umbilical cord)
Term
How dos the gut communicate with the yolk sac?
Definition
At first widely & later by the narrow vitello-intestinal duct
Term
What do the fetal membranes do?
Definition
  • Several membranes which develop 'outside' the developing embryo (extraembryonic membranes)
  • Serve protective & nutritive functions for the embryo
Term
How is the yolk sac formed?
Definition
  • Endoderm spreads around the inner surface of the trophoblast
  • 2 layered wall is the bilaminar omphalopleure
  • In domestic species, the yolk sac greatly enlarges as the whole blastocyst elongate
Term
How is the yolk sac wall converted into a trilaminar omphalopleure, and how are vitelline vessels formed?
Definition
  • Extraembryonic mesoderm spreads outwards from the trilaminar germ disc
  • Progressively converts the yolk sac wall into a trimlaminar omphalopleure
  • Blood vessels develop in this mesoderm & coalesce to form vitelline vessels
Term
What is the choriovitelline placenta?
Definition
  • The apposition of part of the yolk sac to the trophoblast (developing chorion) causes a temporary, localized placenta (the choriovitelline placenta)
  • Remains functional longest in carnivores & horses
  • Replaced later by the definitive placenta
Term
How does the chorion develop?
Definition
  • Develops from the trophoblast & outer layer of the extraembryonic mesoderm
  • After this splits, its part of the extraembryonic portion of the somatopleure
Term
Why is the chorion important?
Definition
  • A very large sac in domestic species
  • When fused with the allantois, its particuarly important in the development of the definitive chorioallantoic placenta
Term
How is the amnion formed?
Definition
  • Folds of the somatopleure develop, gradually overgrow the embryo, & fuse together
  • The fusion completes the amnion & the chorion
  • Concurrent folding of the embryo leads to teh union being carried ventrally to surround the embryo & form the outer lining of the umbilical cord
  • Great accumulation of fluid causes the amnion to become a very large, fluid-filled sac
Term
How is the allantois formed?
Definition
  • Forms as a diverticulum of the hindgut
  • Consists of an endodermal lining with a convering mesoderm
  • Continues to grow into the extraembryonic coelom
  • Enlarges greatly in size due to fetal urine (in domestic species)
Term
How are the allantochorion and allantoamnion formed?
Definition
  • The allantois fuses with the chorion & the amnion
  • The joint membranes are the allantochorion & allantoamnion
Term
What are the umbilical vessels?
Definition
  • Vessels associated with the allantois
  • Umbilical arteries are large vessels arising from the caudal aorta
    • They ramify in the allantochorion
    • Provide the fetal vascular component of the chorioallantoic placenta
Term
What is the placenta?
Definition
  • The organ of fetal nutrition, respiration, & excretion
  • Has fetal & maternal structural components
  • Maternal components are specializations of the endometrium
Term
What is the umbilical cord?
Definition
  • A combined group of structures which enter & leave the embryo at the ventral body wall
Term
What lines the outer surface of the umbilical cord?
Definition
  • Amnion
Term
What does the umbilical cord contain?
Definition
  • Vitello-intestinal duct
  • Stem of the allantois
  • Umbilical vessels
  • These all lie in loose embryonic connective tissue called Wharton's jelly
Term
What is the urachus?
Definition
  • A tubular structure connecting the future urinary bladder with the allantoic cavity
  • Proximal part of the allantois
  • Its connection to the future bladder marks the site of origin of the allantois from the early hind gut
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