lecture 5 - embryology, growth & development pt.3

around what day does embryonic folding begin?

20

explain the entire process of folding

Longitudinal: 

• amniotic cavity + ectoderm layer + mesoderm layer used to create folds on either side of neural tube (lateral folds)

• a pocket forms on either side of the neural tube (coelom)

Day 25:

• some of the yolk sac begins to get pinched off in the midgut area (yolk stalk)

• coelom get larger

Median: 

• at head and tail region, amniotic cavity is folding around 3 germ layers

• begins to form the ends of the gut tube from the endoderm layer (hindgut + foregut)

• there is a pinching off of the yolk sac near the connecting stalk called the allantois

Day 25:

• foregut and hindgut have gotten close to each other → forms the midgut region

• oropharyngeal + cloacal membrane comes in contact w/ endoderm

Overall: 

• evaginations (out-pockets) begin to form (ie lung buds, liver and pancreas, branchial arches)

• evaginations of gut tube start to move and eventually form structures that are part of the head + neck region (ie pharynx)

in order for us to go from a two-dimensional three layers of cells into a three-dimensional structure, we have to fold the ______ cavity around the _____ germ layers.

amniotic, three

2 ways the amniotic cavity folds around the 3 germ layers

1. folds longitudinally (lateral folds) to form the gut tube

2. folds in the median plane to make a head and tail fold

explain the longitudinal folding (day 20)

• amniotic cavity + ectoderm layer + mesoderm layer used to create folds on either side of neural tube (lateral folds)

• a pocket forms on either side of the neural tube (coelom)

coelom

formed during longitudinal folding

• a space on either side of the neural tube (in the mesoderm)

• eventually becomes the body cavities

lateral folds

folds on either side of the neural tube using the amniotic sac, ectoderm + mesoderm layer when folding longitudinally

explain the folding in the median plane (day 20)

• at head and tail region, amniotic cavity is folding around 3 germ layers

• begins to form the ends of the gut tube from the endoderm layer (hindgut + foregut)

• there is a pinching off of the yolk sac near the connecting stalk called the allantois

allantois

pinching off of the yolk sac near the connecting stalk during folding along the median plane

• eventually becomes part of the bladder

folding in the median plane (day 25)

• foregut and hindgut have gotten close to each other → forms the midgut region

• oropharyngeal + cloacal membrane comes in contact w/ endoderm

eventually, the oropharyngeal membrane will ________, giving us an opening for the ____ in the _____ region.

disintegrate, mouth, foregut

eventually, the cloacal membrane will ________, giving us an opening for the ____ in the _____ region.

disintegrate, anus, hindgut

explain folding longitudinally (day 25)

• some of the yolk sac begins to get pinched off in the midgut area (yolk stalk)

• coelom get larger

yolk stalk

occurs when folding longitudinally

• narrowed region of the yolk sac that is beginning to get pinched off

by day __, the amniotic cavity has made it fully around the 3 germ layers

30

explain day 30 of folding

• evaginations (out-pockets) begin to form (ie lung buds, liver and pancreas, branchial arches)

• evaginations of gut tube start to move and eventually form structures that are part of the head + neck region (ie pharynx)

pharyngeal pouches

evaginations of the gut tube that will eventually form our tonsils and auditory tubes

auditory tubes

passageway from our throat to our ears

• formed by evaginations of the gut tube

branchial arches

• evaginations in the region of the head

• form in the ectoderm layer

evaginations

pockets/pouches attached to a region that go on to form other regions of the body

lung buds

an evagination from the gut tube that will eventually become the lungs

what causes the embryo to curve around the spinal area on day 30?

the development of the neural tube, somites and vertebral column is faster than the rest, causing the embryo to curve

evaginations from the gut tube form

• anterior pituitary

• thyroid gland

• lungs

• liver

• pancreas

• auditory tubes

branchial arches form

• pharynx

• auditory tubes

• tonsils

• thymus

• parathyroid glands

what does the coelom form (in order)

• fuses first around the heart as the pericardial cavity

• expands to become the pleural and peritoneal cavities

• cavities eventually become separated by serous membranes

the limbs begin as ____ ____

limb buds

limb bud development for the upper limbs starts around day __, and for the lower limbs __

24, 28

limb bud

ectoderm cells thicken in area of limb → form the apical ectodermal ridge

• job is to stimulate outward growth of tissues

explain the development of limb buds

• ectoderm cells thicken in area of limb → form the apical ectodermal ridge (stimulates outward growth of tissues)

• mesoderm cells underneath proliferate

• bones form

what is the order of systems that are built?

1. cardiovascular

2. skeletal

3. muscular

4. nervous

the way our limbs are built is from ______ to ______

proximal, distal

it takes about _ weeks to get to the stage where we have all our digits (fingers)

7

what is the very last thing to happen in the development of our limbs?

removing of the webbing b/w the fingers via apoptosis

apoptosis

also known as pre-programmed cell death

• method to which the webbing b/w the fingers is removed

removal of the webbing b/w the fingers via apoptosis happens around week _

8

the development of organs and structures in the body is being stimulated by _____ signals from one cell to another

chemical

what is the name of one of the proteins that help stimulate limb bud development in humans?

sonic hedgehog protein

thalidomide was originally a drug developed in the 1950s as a ______. It was later prescribed to women who were pregnant to help reduce ______ _______.

sedative, morning sickness

what happened to children born to mothers who took thalidomide?

often born w/o limbs, many mothers also had miscarriages or children were underdeveloped in organ systems

what does thalidomide do?

inhibits the formation of blood vessels

depending on when women take _______ during their pregnancy, it can affect the development of very specific _____ _______.

thalidomide, organ systems

what happens if a limb bud doesn’t have a blood supply?

• apical ectodermal ridge forms + starts to grow outwards

• becomes stunted w/o blood supply

• mothers stopped taking thalidomide (bc morning sickness had gone away) and so the limb buds resume growing

• at this stage the middle portions of the arms have been skipped, so children end up with formed hands/feet very close to the body

the skeleton develops from what

mesoderm + neural crest cells

the skeleton forms as a ________ skeleton first before the bone

cartilage

muscle develops from what

myoblasts

myoblasts

differentiated from somites

• early embryonic cells that develop into skeletal muscle fibers

• migrate to wherever muscle needs to be built

once myoblasts reach their destination, they ____ together to form ____________ cells.

fuse, multi-nuclear

the nervous system develops from what

neural tube + neural crest cells

know this diagram

mnemonic to remember what the branchial arches form

Farmer Audie Tongs Threw Parsnips

Pharynx

Auditory tubes

Tonsils

Thymus

Parathyroid glands

mnemonic to remember what the gut tube forms

Ants Tire, Lungs Live, Pancakes Audibly

Anterior pituitary

Thyroid gland

Lungs

Liver

Pancreas

Auditory tubes