Embryology - general quiz 2

• study of growth and differentiation undergone by an organism from single fertilized cell into highly complex and independent living-being like its parents
• -study of changes which undergo during their development

• prenatal period - 3 periods
• postnatal period

• before birth
• progresses rapidly w/ more drastic morphological changes
• (chicken = egg 21 days)
• 3 periods

• after birth
• changes are gradual and followed by aging

• 1. pre-embryonic period
• 2. embryonic period
• 3. fetal period

• 1st part of prenatal period
• development of gametes(gametogenesis), fusion, cleavage, blastulation, gastrulation and up to implantation

• 2nd part of prenatal period
• implantation to the origin of th primordia of the organs and the formation of the basic body form

• 3rd part of prenatal period
• growth and formation and maturation of the organ system to become competent to assume their specialized functions

developing offsprin during the embryonic period

developing offspring during the fetal period

describe the embryo/fetus and its membranes

branch of embryology concerned with the study of malformations

• development passes through a series of construstive stages like those of in the evolutionanry development of the race to which it belongs
• - we all start off with a tail but loose it
• - all species start with a tail in stage I

complete life from feritization to death

• refers to ancestral history of organism
• -describes evolutionary development

sperm of ovum contained the new individual in miniature form

development occurs through progressive growth and differentiation through a series of causual interaction between various parts

• Prophase, Metaphase, Anaphase, Telophase,
• forms daughters cells
• at no time do members of a chromose unite

• pair of chromatids(diploid), chiasma formation, pulling apart of double structure chromosome
• anaphase (1st division)
• 4 daughters cells that are different from each other (haploid with half the # of chromosomes)

• during chiasma formation
• intimately paired homologous chromosomes interchange chromatid fragments

process which germplasm are converted into highly specialized sex cells (gametes) that are capable of uniting at fertilization and producing a new being

• production of gametes
• spermatozoa - M
• ovum -F
• germ cells give rise to gametes constitute the individual germplasm

• primordial germ cells which are destined to develop into gametes, are originated in the wall of the sac, from where they migrate to get established in the developing gonad
• - wall of yolk sac forms gonads of fetus

• development of sperm
• in testis after puberty
• subdivided into -spermatocytogenesis, spermiogenesis

• primordial germ cells in testis form spermatogonia
• proliferate mitotically to Type A and Type B
• Type B - primary spermatocytes - secondary spermatocyte
• Type A - more Type A and B

proliferate mitotically into Type A and B spermatogonia

proceed in spermatogenesis and replicate ints DNA in interphase of its cells cycle to form primary spermatocytes

• undergo 2 successive meiotic divisions
• 1st division- chromosomes are equally distributed w/ a homologus pair in each daughter cell (division reduction) to produce secondary spermatocytes
• DUPLICATION OF DNA

• produces secondary spermatocytes from primary
• chromosomes are equally distributed and each member of homologous pair goes into one of the daughter cells

• 2nd division form primary spermatocytes
• each member of the homologus pair in now split into 2, 1 going into each of the daughter cells,
• Equational division - spermatids (haploid)

• production of spermatids form secondary spermatocytes
• one member of homologus pair is now split into 2, each going to a daughter cell

• from spermatogoina mitotically dividing
• it divides again and gives Type A and Type B
• it contiues the stem cell line and spermatogenesis are maintained

spermatids undergo some metamorphosis to form differentiated and potentially motlie cells called spermatozoa

• Chromatin content of nucleus becomes concentrated forms bulk head of sperm
• Golgi becomes concentrated and reorganized to form acrosomal cap on head
• Centriole moves away from anterior end talking on the shape of the ring to encircle the flagellum
• Mito becomes concentrated around the proximal part of the flagellum which form the middle piece of the spermatozoa, energy

• sperm + secretions from accessory sex gland = semen
• accessory sex glands- prostate, bulboureathraol gland

50 - 70 days and 2-3 weeks to pass through epididymis

• primordial germ cell form oogonium (active till parturition)
• oogonium replicates DNA in interphase and enters the prophase of first meiotic division - primary oocyte
• first meiotic division is arrested in diplotene stage of prophase 1 and will not resume until puberty
• at birth all primary oocytes are in the dipoltene stage of prophase 1 (resting stage)

• primary oocyte in each ovarian/estrous cycle resume its first meiotic division and lead to the formation of 2 daughter cells.
• - secondary oocyte and first polar body

smaller daughter cell with Secondary oocyte

• genetic material is equally divided but cell cytoplasm is unequal during division
• secondary oocyte - most of cytoplasm
• first polar body - smalle

• completes the second meiotic division only after the stimulus of the penetration of the sperm
• leads to the ovum and second polar body (cytokinesis is unequal again)

• ovulated in horses and dogs only
• in resting prophase is ovulated and both meiotic divisions occur after the stimulation of penetration by sperm

in most species is ovulated and then meiosis later

• most animals the seconday oocyte and first polar body are relesed at ovulation form follicle
• secondary oocyte must be penetrated by spermatozoon before second mitotic division is completed

fusion of sperm and ovum to initiate development of a new individual

mating - insemination is naturally performed

• important for fertilization
• only allows 1 sperm in
• around oocyt even till it is 64 cells

• secondary oocyte - acrosome reaction from sperm
• Penetration of sperm into ovum - zona reaction
• male and female pronuclei inside
• duplication of DNA - swell and duplication of DNA
• Fusion of male and female pronuclei
• Two cell stage - 64 still has zona pellucida

• is spontaneous in most species
• controlled by FSH and LH from adenohypophysis
• ruptured follicles are converted to corpus luteum
• corpus luteum - secretes progesterone
• fimbriated end (abdominal ostium) of oviduct receive ovulated egg w/ peritoneal fluid which enters the uterine tube (ciliary movement and contraction movement)

• from CL
• produces uterine changes facilitaing the implantation and maintenance of the conceptus

• cat and rabbit
• induced by coitus
• Called Induced ovulators

• bitch, sow, cat, small ruminants
• release of more than one oocyte usually from separate follicules

monotocous - one oocyte

transport of sperm is achieved by muscular contration of cervix and uterus and by motility of sperm themselves

• 1-2 days in most species in female repro
• 6-7 days in horse and dog
• sperm host glands in avain vagina - released over time
• 32 days fowl
• 70 days turkey

24 hours

• ampullary region of uterine tube 12-24 hours after ovulation
• spermatozoa first go throught the process of capacitation and acrosomal reaction before can fertilize

removal of glycoprotien coat, and seminal plasma protein from the plasma membrane that overlies the acrosomal region of the spermatozoa

• after capacitation
• release of enzymes (hyaluronidase and trypsin) digest proteins in acrosome
• faciliation the penetration of the oocyte barriers - zona pellucida, oocyte cell membrane

• 2nd miotic division
• fertilized membrane prevents more sperm entry, zona reaction - chemical changes
• F and M germ cells swell - pronuclei
• pronuclei fuse causeing dipoid number of chormosomes
• zygote is formed

• more that one sperm enters the ovum
• common in pigs
• most die early in development

2 cell stage pronuclei fuse causing dipoid chromosomal number

• F and M pronuclei duplicate DNA
• immediately on fusion their chromosose split in the sourse of a normwl mitotic division, forming 2 cell zygote
• restoration of diploid chromosomal number
• determination of the sex XX F XY M - reveresed in avian (F determine sex)
• reptiles - temperature determines sex
• initiation of cleavage

• one ovum is fertilized but divieds at the blastocyst stage inot 2 genetically identical mass
• same sex and bllod group
• 1 - splitting of inner cell mass into 2 completly separate groups, common placenta and chorionic sac, separate amniotic cavities
• 2 - splitting of the inner cell mass at a late stage of development, common placenta, amniotic cavity and chorionic cavity

• 2 separate ova are fertilized
• can have own amnion, chorion and placenta
• placentas can fuse

fertilized ovum lost in peritoneal cavity, implant on peritoneal surface, early embronic death

• dizygous twins in cattle
• common circulation by placental anastomosis usually occurs
• opposite sex - female repro is retarted because of testosterone from Male embryo
• female is infertile - 92% of time
• testosterone inhibits mulerain duct

• impregnation by successive acts of coitus, of two or more ovum that were liberated at approximately the same time, by two or more differnt males
• Cats and dogs

• when pregnant female ovulates, conceive and produce a second younger fetus
• pigs

• Mare - 340 days
• cow - 280
• ewe - 150
• sow - 120
• bitch - 63
• queen - 60

• begining of development of multicellular organism
• mitotic cell divisions - zygote does not increase
• blastomeres - segmentation or fractionation divisions, causes these smaller cells

cleavage, process of segmentation or fractionation divisions, resulting in production of many smaller cells

• first division occur at long axis of cytoplasm
• other divisions at right angles to previous ones
• speed of division is inversely proportional to size of yolk sac

• in mammals
• smaller yolk sac and equally distributed (Isolecithal egg)
• complete division of the zygote = total

• birds
• massive yolk sac (polylecithal cell) prevent complete division of the zygote thus the cleavage is partial

• holoblastic - mammals
• meroblastic - birds

• DNA of mother does not match childs
• dizygous formation of 2 different zygots cause differnt genetic material when take from skin

• 4-6 divisions, solid cluster of cells
• 16 by day four humans
• 16-64 of most domestic animals

• embryonic disc (inner cell mass) becomes rearranged to form 3 separate layers - germ layers
• endoderm
• mesoderm
• ectoderm

• secrteion from blastomeres (blastocoel) loss of zona pellucida (blastocyst)
• change in size of embryo
• embryonic disc - becomes bigger
• periphery cells - trophoblast cells for absortion of nutrients

• periphery of blastocyst
• faciliate absorption of nutrients in early development
• eventually disapears

sercretion from the blastomeres collected within the morula, causing a rupture of the zona pelllcida and formation of fluid filled cavity

• inner cell mass (embryonic disc) detach from inner surface - forms new lining the interior blastocyst
• new enclosed cavity - primitive gut or archenteron
• detachment of cells from inner cell mass is called delamination

formation of endoderm by detachment of cells from the inner cell mass

• cells of upper layer of inner cell mass expand
• trophoblast over the ectoderm disappear

• cells between endo and ectoderm converge towards midline - become elongated
• future longitudinal axis
• cranial end enlarges for form primitive node(hensen's)
• center of cellular proliferation and gives rise to mesodermal cells

• rapid proliferation and invaginate between the ecto and endo layers - forms mesoderm
• primitive node forms head of mesoderm and notochord
• notochord causes ectoderm to form neural ectoderm(neural plate)
• neural plate bounded laterally by neural folds
• median groove develops in neural fold
• forms neural tube
• group of cells detach from neural tube and differenitate inot neural crest cells

• induces ectoderm to form neural ectoderm (neural plate)
• regresses and persists in adult as nucleus pulposus on the intervertebral disc

• primitive streak - mesoderm
• primitive node - head mesoderm and notochord - neural ectoderm(neural plate) - neural folds - neural tube - neural crest

• dorsally proliferating cells from the primitive streak, on sides of notochord form paraxial mesoderm
• laterally forming cells make lateral plate (mesoderm)
• junction between the 2 is intermediate mesoderm

becomes covered by ectoderm

• develop from paraxial mesoderm and primitive streak disapears
• form veterbral column
• used to estimate age of embryo

• 2 layers somatic and splanic
• coelom -space between layers
• somatopleure = somatice + ectoderm
• splanichnopleure = splanic + endoderm

• forms a series of mesodermal thickenings - Somites
• somite differentiates in 3 parts
• Sclerotome - vertebral column
• Myotomes - muscles
• Dermatome - connective tissue

• rapid growth causes elongated disc shape
• intra-embryonic germ layer - underlies the embryonic disc
• extraembryonic germ layer - cells lying peripherally under trophoblast

• surface - epidermis, cutaneous glands, hair, nails, lens of eye
• - epithelium of sense organ, nasal cavity, sinuses, mouth, oral glands enamel, anal canal
• neural - nervous tissue, hypophysis, adrenal medulla, retina of eye

• paraxial - vet column and associated muscles and connective tissue
• intermediate - kidneys, adreal cortex, gonads and genital ducts
• lateral - cardio and lymphatic system, pleura and peritoneum, spleen, muscles, CT

• eipthelium - pharynx, root of tongue, auditory tube, larynx, trachea, and lungs
• digestive tube including glands
• bladder, urethra and associated glands

• grastualtion -ovid embryonic disc is converted into elongated flat disc
• transformation fo flat disc inot roughly curved cylindrical embryo

embryonic disc obtains a cylindrical appearance and lateral and ventral body wall of the embryo is established

• folding of embryo in cephalo-caudal direction
• pronuounced in the cranial and caudal end of embryo
• tail and head are formed

• embryonic disc - curved cylindrical structure
• germ layers - extraembryonic or fetal membranes which surround cylindrical embryo
• lateral and ventral body walls develop - intraembryonic somatopleure
• amnion and chorion - extraembryonic somatopleure
• yolk sac and allantosis - extramembraneous splanchnopleure
• gut - intramembraneous splanchnopleure

• from extramembraneous somatopleure
• keeps growing
• 2nd sac to rupture at parturition

• extraembryonic splanchnopleure
• 1 st sac to rupture w/ cow parturition

• enclosed area on the ventral surface of the embryo at the junction of embryonic and extraembryonic territories constitute the cord
• contains yolk sac with vitellin blood vessels and allantois with its allantois or umbilical blood vessels

• cranial region rapidly grows forming a large head flexed ventrally
• external structures appear
• limb buds appear - somatopleure
• crown-rump length is now used to determine approximate age of the embryo

• vertebral column and is associated muscles and CT
• derivative of mesoderm

• kidneys, adrenal cortex, gonads and genital ducts
• derivative of mesoderm

• cardiovascular and lymphatic system, pleura and peritoneum, spleen, muscles and connective tissues
• derivative of mesoderm

• amnion - extraembryonic somatopleure
• chorion - extraembryonic somatopleure
• yolk sac - extraembryonic splanchnopleure
• allantois - extraembryonic splanchnipleure

protection and nutrition

• from extraembryonic somatopleure, gradually overgrow the embryo and fuse together
• fluid accumulates in cavity - forms fluid filled sac around embryo

excess amount of amniotic fluid (cattle)

• outermost membrane from extramebmbryonic somatopleure
• chorionic villi - finger-like projections develop over surface of chorion to make contact w/ the uterus of the mother (increase surface area)
• chorio-allantoic placenta - chorion fuses with allantosis (main type of placenta)

• from extraembryonic splanchnopleure
• choriovitelline placenta - yolk sac in contact with chorion for 1st quarter of pregnancy(horse and dog)
• birds - viteline vessels absorb nutrition from yold sac

• extraembryonic splanchnopleure
• reservoir for excretory products of fetus
• chorio-allantoic placenta - chorion and allantois fuse
• develops umbilical vessels
• hydroallantois - excessive fluid in allantois
• allantoic calculi: hippomanes in mare

• secretions from endometrial glands are absorbed as grows (histotrophic)
• secretions become insuffiecent source of nutrients so need blood supply from maternal side (hemotrophic)

fetal membranse attach to endometrial epithelium to form fetal and maternal circulations systemfor physiological exchange

• superficial or central implantation
• eccentric implantation
• interstitial implantation

• embryonic sac lies in the uterine lumen or cavity
• Ruminants, equine, procine

• embryonic sac lies in a fold or pocket of uterine wall
• rat, squirrel

• embryonic sac penetrates and embedded into uterine wall
• guinea pig, carnivores, bats, man

nutrition from secretion of uterine glands before implantation

from maternal circulation after implantation

• 2 weeks - sow, bitch, queen, ewe
• 1 month - cow
• >1 month - mare

• nutrition
• respiration through gas exchange
• excretion
• barrier (impermeable to bacteria)
• synthesis of hormones - estrogen, progesterone, gonadotrophins
• (cattle, progesterone 2nd half of pregancy from fetus)

• (endocrine gland)
• structure formed by close contact of fetal membranes and materanl tissue for the purpose of physiological exchange between the fetus and mother
• materal blood(O2 and nutrients) diffuses from uterine artery in to umbilical vein
• excrete - umbilical artery inot uterine vein

• based on - fetal membranes
• shape of placenta
• branching of chorionic villi
• loss of maternal tissues at parturition
• relations in placenta
• histological layers

• choriovitelline (yolk sac) placenta = chorion + yolk sac (horse and dog)
• chorioallantoic Placenta = allantois + chorion (most common, ruminants, pig, carnivores and equine)

• Diffuse - chorionic villi over entire sac (sow, mare)
• cotyledonary - cotyledons (fetal) and caruncles (maternal) form placentomoes (ruminants) 120 in cow
• zonary - band of villi (carnivores)
• discoidal - 2 disc shaped areas (primates, rodents, bats)

• Villous - simple banching of villi (sow, mare and ruminants)
• Labyrinthine - complcated and anastomotic branching of villi (carnivores and primates)

• deciduate - high loss of maternal tissue at parturition B/c of complicated interlocking of tissues( carnivores and primates)
• nondeciduate - little loss of maternal tisse from simple deto-maternal contact (sow, mare, ruminants)

• based on number of layers separating the materanl blood from fetal blood
• 6 layers separating fetal blood from maternal blood
• 3 on fetal side - chorionic epithelium, fetal connective tissue, endothelium of allantoic blood vessels
• 3 maternal side - uterine epithelium, uterine CT, and endothelium of blood vessels of uterus

Epitheliochorial - chorionic epithelium incontact with uterine epithelium, 6 layers (sow and mare)Syndesmochorial - chorionic epi in contact w/ uterine CT, 5 layers (ruminants)Endotheliochorial - chorionic epi in contact w/ ehdothelium of uterine blood vessels, 4 layers (carnivores)Hemochorial - chorionic epi in contact w/ uterine blood, 3 layers (primates)