FHMP 027 CAL: the origins of body form and cell differentiation

Question 1

In humans how many chromosomes are found in the second polar body from oogenesis?

Answer 1

• 23
• haploid

Question 2

what is a Graafian follicle?

Answer 2

• a mature ovarian follicle composed of somatic cells surrounding a single oocyte
• also known as tertiary, preovulatory and antral follicles

Question 3

what are granulosa cells of the ovary and what do they form during pregancy?

Answer 3

• cells in your ovary which produce oestrogen progesterone
• they form the corpus luteum (luteal body)

Question 4

what do granulosa cells become if there is no implantation?

Answer 4

• corpus albicans (white body)
• a connective tissue scar on the ovary that stays for a few months after the corpus leuteum degenerates

Question 5

how long after ovulation is the human egg capable of being fertilised?

Answer 5

• 24 hours

Question 6

• how long can sperm remain active in the female reproductive tract

Answer 6

• up to 5 days

Question 7

what is a zygote?

Answer 7

• once the sperm has fertilised an egg
• earliest stages of embryogenesis

Question 8

what prevents the fertilised egg from implanting in the fallopian tubes?

Answer 8

• zona pellucida

Question 9

how many cells are present when the embryo undergoes compaction?

Answer 9

• 12-16 cells

Question 10

what proportion of human blastocyts fail to implant causing a spontaneous abortion?

Answer 10

• 1/3

Question 11

what tissue layers are found in the bilaminar disc?

Answer 11

• epiblast and hypoblast

Question 12

what tissue layers are found in the trilaminar disc?

Answer 12

• ectoderm, mesoderm, endoderm

Question 13

what structure does the prechordal plate become?

Answer 13

• buccopharyngeal membrane

Question 14

what process gives rise to the first blood vessels to form in the embryo?

Answer 14

• vasculogenesis

Question 15

where do the first blood cells form in the embryo?

Answer 15

• formed by the extraembryonic mesoderm lining the yolk sac

Question 16

in the embryo, where do you find the vitelline blood vessels?

Answer 16

• yolk sac
• vitelline arteries branch from the dorsal aorta

Question 17

what happens to change primary stem villi into secondary stem villi?

Answer 17

• primary villi are composed only of trophoblast
• mesoderm grows into the core forming secondary villi and branches of the umbilical artery and umbilical vein grows into the mesoderm to form tertiary villi

Question 18

what endodermal structure is formed by the head fold?

Answer 18

• endoderm is initially a flat simple epithelium forming the embryonic surface of the yolk sac
• it is turned into a tube by the process of ventral folding
• first embryonic tissue pushes in from the rostral end to form the head fold and then the foregut

Question 19

what is the vitelline duct?

Answer 19

• tube joining the midgut to the yolk sac formed during embryonic folding

Question 20

what are the first segmented structures to appear in the human embryo?

Answer 20

• somites
• during 4th week of development

Question 21

how many somites are present on the 28th day of development

Answer 21

• 30-32 pairs

Question 22

why are somites useful in staging an embryo?

Answer 22

• because they form at a steady rate and are clearly visible through thr surface of the embryo

Question 23

what is preformation?

Answer 23

• in the 17th and 18th century people believed humans were fully formed already in the head of the sperm

Question 24

what is epigenesis?

Answer 24

• where tissues and organs form gradually and the complexity of the embryo increases with time

Question 25

what does totipotent mean?

Answer 25

- forms all embryonic and extraembryonic cell types

Question 26

what does pluripotent mean?

Answer 26

- forms all embryonic cell types

Question 27

what does multipotent mean?

Answer 27

- forms multiple cell types

Question 28

what does tri or bi potent mean?

Answer 28

- form 3 or 2 different cell types

Question 29

what does unipotent mean?

Answer 29

- forms only 1 cell type

Question 30

what are the 3 states of cell commitment?

Answer 30

- specification - determination - differentiation

Question 31

what is specification?

Answer 31

- cells receive instructions on what they are to become but they do not become fully committed - their fate can be changed if move to a new environment

Question 32

what is determination?

Answer 32

- cells become committed to their cell type fate - cannot be changed

Question 33

what is differentiation?

Answer 33

- cells acquire those characteristics that distinguish them for their cell type

Question 34

what are the 3 mechanisms of cell commitment?

Answer 34

- localised determinants - embryonic induction - morphogen gradients

Question 35

what is localised determinants?

Answer 35

- in the 1800s it was suggested that cell fates may be specified by localised determinants, laid down in the cytoplasm of the egg during oogenesis - each major cell type has its own determinant - so only cells with a muscle determinant will become muscle - however, this was found not to be true using sea urchin embryos which showed if you split the embryo early, all larvae will grow normally and contain all cell types - called regulative development

Question 36

what is embryonic induction?

Answer 36

- the process whereby a cell's fate is changed by signals from an adjacent group of cells - it requires 2 types of cells: a signaling cell and a responding cell - competence = the ability of a cell to respond to a signal

Question 37

what are morphogen gradients?

Answer 37

- a mechanism by which the emission of a signal from one part of an embryo can determine the location, differentiation and fate of many surrounding cells - e.g. hedgehog genes

Question 38

what are induced pluripotent cells?

Answer 38

- adult cells that are reprogrammed to take on a different cell types

Question 39

what are epigenetic control mechanisms?

Answer 39

- gene transcription is regulated through epigenetic mechanism which affect chromatic structure , including modifications of both DNA and associated core histones, methylation of DNA in gene promoters is associated with gene silencing while methylation of core histones is associated with both gene activation and silencing

Question 40

whats the difference between transcribe genes and non-transcribed genes?

Answer 40

- transcribed genes = contain histone modifications that create loose chromatin that is accessible to transcription factors -non-transcribed genes = may have highly methylated DNA and alternative histone modification to create compact chromatin which in inaccessible to transcription factors