Introduction to Developmental Anatomy

Week 1 Material

What is cell division

proliferation of a given cell type

Somatic cells are

non-sex cells

gametes are

sex cells

what process do somatic cells use

mitosiswh

what process do gametes use

meiosis

what is the result of meiosis

four genetically unique haploid cells

what is the result of mitosis

two genetically identical diploid cells

what is cell differentiation?

expression of differing genetic products to alter cell morphology (structure) and function

T or F - structure is much different than function

false - structure = function

an embryo is an individual developing from a _______ through the formation of the ______ ______.

zygote

organ systems

A fetus continues to develop from the embryo through growth and maturation with

support from the dam

What is the average gestation length of a horse

340

What is the average gestation length of a cow

283

What is the average gestation length of a sheep

147

What is the average gestation length of a pig

114

What is the average gestation length of a dog

63

how many days does a horse exist as an embryo

60 (h)

how many days does a cow exist as an embryo

60 (c

how many days does a sheep exist as an embryo

45

how many days does a pig exist as an embryo

37

how many days does a dog exist as an embryo

35

what is the percentage of pregnancy spent as a fetus in horses?

82

what is the percentage of pregnancy spent as a fetus in cows?

79

what is the percentage of pregnancy spent as a fetus in sheep?

69

what is the percentage of pregnancy spent as a fetus in pigs?

68

what is the percentage of pregnancy spent as a fetus in dogs?

44

what is fertilization

the union of the DNA from a HAPLOID oocyte with that of a HAPLOID spermatozoon

what does fertilization produce?

a zygote (fertilized egg)

the zygote is considered the first

diploid cell for the new individual

the cleavage creates equal mitotic divisions to increase

cell numbers

during the cleavage activity, cells stay within the

overall size of the zygote

during cleavage, the zygote routinely get smaller and smaller as they divide as enclosed by the

zona pellucida

what are new cells after cleavage called

blastomeres

what is the morula

a globular solid mass of blastomeres formed by cleavage of a zygote

when is the embryo considered a morula

between 4-6 cell divisions

the cells of the morula differentiate to form the

blastocyst

the blastocyst is a hollow sphere containing ______ ______ _____, which will go on to form the ________

inner cell mass

embryo

a blastocyst is lined with _______

trophoblasts

the trophoblasts will go on to form some of the

fetal membranes

late in the stage of a blastocyst, what two things develop?

yolk sac and amniotic sac

the blastocyst is then followed by the

gastrula

what is gastrulation

the formation of the three germ cell layers from the blastocyst

what are the three layers of the gastrula

endoderm, mesoderm, ectoderm

the beginning of gastrulation is marked by the appearance of the

primitive streak

the primitive streak establishes these three things

1. body’s cranial and caudal axes

2. midline of embryo

3. where cells migrate to form 3 germ layers

what is the ectoderm and what hings can it become

the outside

tooth enamel, epithelial lining of mouth and rectum, nervous system, cornea and lens of eye

what is the mesoderm and what things can it become

the middle layer

notochord, excretory system, adrenal cortex, dermix of skin, muscular layer of intestines

what is the endotherm and what things can it become

inside layer

thymus, liver, pancreas, epithelial lining of respiratory and digestive tract, lining of bladder and reproductive systems, thyroid+parathyroid glands

the notochord is a grouping of cells at the

cranial end of the primitive streak

the notochord goes on to help form the

head

nervous system

somites

the notochord precedes

neurulation

what is neurulation

development of the nervous system with neural tube

shortly after _______ is complete, a block of _______ tissue begins to differentiate into the notochord

gastrulation; mesoderm

somites are made up of

blocks of mesoderm

where are somites located

lateral to the notochord

what do somites go on to form

bone

skin(dermis)

skeletal muscle

organogenesis

organization of differentiated cells into specific tissues → then organs

when does organogenesis occur

starts at the end of gastrulation and continues to birth

does organogenesis inlcude neurulation?

yes

what is the process of organogenesis

molecules → cells → tissues → organs → organ systems → organism

the neural tube leads to the eventual formation of the

central nervous system

The C-shaped embryo is considered a

uniform stage amongst almost all species of animals

what features define the c-shaped embryo (4)

cylindrical

obvious head and early eye

rudimentary nervous system

tubular beating heart

what is implantation

the developing embryo attaches to the uterine lining and adheres to it

when does implantation occur

after fertilization, typically still in the blastocyst stage

T or F, the uterine lining is formed during implantation

F - the uterine lining has been prepared

what occurs after implantation

placentation

the placenta is the site of exchange of

gases, nutrients, and waste products for the embryo

what creates the placenta

four fetal membranes

the placenta is attached to the embryo by the _______ ______

umbilical cord

the placenta is attached to the mother by implanting inot the

uterus to varying degrees

what are the four fetal membrane

1 yolk sac

2. allantois

3. amnion

4. chorion

what is the yolk sac

acts as early benefit

what is the allantois

site of waste storage

what is the amnion

a fluid space the surrounds the developing embryo/fetus

what is the chorion

outermost fetal membrane layer

the yolk sac serves as a potential source of ______, _______, _______- in early development

nutrients, blood cells, and waste exchange

the yolk sac is large and persistent in

birds and other egg-borne species

in mammals, the yolk sac

regresses

what are the two fates of the allantois

may remain as separate sac or

may fuse with the other fetal membranes

the amnion forms as

folds fuse above the embryo, creating a fluid-filled space within which the embryo floats

is the embryo tethered to anything in the amnion?

yes, to the placenta by the umbilical cord

amniotic fluid is similar to

fetal and maternal plasma

the amnion also contains

secretions from the fetus

As the GI tract and urinary tract develop, the fetus

swallows and excretes amniotic fluid

the chorion arises from ________ and forms the outer boundary of the _______

trophoblasts

conceptus

the chorion attachment to the uterus occurs through the

chorionic villi

placentation is the formation and fusion of the fetal placenta to the

endometrium of the uterine wall

what gases does placentation exchange

oxygen and carbon dioxide

what does the umbilical cord do

transports between placenta and fetus

why is actual blood not shared between the mother and fetus?

it serves as a safety mechanism for the fetus (may be seen as “foreign” and can be rejected)

the umbilical cord passes into the embryo/fetus through

an opening in the ventral body wall

the umbilical cord contains these 3 things:

two umbilical veins and arteries

urachus

vestiges of yolk sac

T or F, the umbilical veins may fuse into one

T

what is the urachus

connects the urinary tract to the allantois

umbilical arteries carry blood _____ from the fetus, and so carry ____________ blood

away, non-oxygenated

what is the difference between reptile + bird placentas vs mammals?

reptiles and birds have a much larger allantois and yolk sac, and rely less on the amnion

What are the three classification of placentas

1. number of tissue layers between maternal and fetal circulation

2. shape/attachment to uterus

3. amount of tissue lost at parturition

6 layers is what type of placenta

epitheliochorial

4 layers is what type of placenta

endotheliochoral