Embryology: The First Week of Human Development Lecture 2 Syed

Question 1

How many chromosomes to human somatic cells contain?

Answer 1

They contain 23 pairs of chromosomes for a total of 46

Question 2

What is a chromatid?

Answer 2

One of the two strands of a chromosome joined together by a centromere

Question 3

During which phase does crossing over occur?

Answer 3

They only cross over during meiosis I

Question 4

What do you call the parent cells that produce sperm?

Answer 4

Spermatogonia - diploid cells

Question 5

What do spermatogonium cells do at the very beginning of the cycle?

Answer 5

Each one divers by mitosis to an exact copy of itself called a primary spermatocyte.

Question 6

Understand overall process of gametogenesis

Answer 6

Sir, yes sir (add pic)

Question 7

What do primary spermatocytes ultimately produce?

Answer 7

They undergo meiosis and ultimately make haploid cells called spermatids, which have 23 chromosomes

Question 8

How are initial spermatids different than sperm cells?

Answer 8

The spermatids must undergo further changes to form a sperm cell - they lose their cytoplasm and grow a flagellum

Question 9

How many sperm are formed per spermatocyte?

Answer 9

Four new sperm are formed - each have 22 autosomes and either an X or Y chromosome

Question 10

R-selection vs. K-selection

Answer 10

R-selection makes a species prone to numerous reproduction at low cost per individual offspring, while K-selected species expend high cost in reproduction for a low number of more difficult-to-produce offspring

Question 11

Explain the process of oogenesis up till puberty

Answer 11

The parent cells (oogonia) are diploid. They start the process of meiosis and form primary oocytes prior to birth. They are arrested in Prophase I (month 5 in utero) and stay here until puberty

Question 12

What happens in oogenesis after puberty?

Answer 12

Only one secondary oocyte usually develops. It is expelled (ovulated) from one of the two ovaries each month (they may not switch from side to side though)

Question 13

What happens to the secondary oocyte after Meisosis I?

Answer 13

The secondary oocyte receives the bulk of the cytoplasm and is the cell that is arrested in metaphase II. The second cell becomes a polar body because it doesn’t get much cytoplasm

Question 14

What happens if the secondary oocyte is not fertilized?

Answer 14

The secondary oocyte is degenerated, still arrested in metaphase II

Question 15

What happens if the secondary oocyte is fertilized?

Answer 15

The secondary oocyte finishes meiosis. Two new cells are produced, with unequal cytoplasm. The lesser one becomes another polar body and degrease. The other one becomes an ovum which can support a fertilized zygote.

Question 16

What is aneuploidy?

Answer 16

When there are numerical errors in # of chromosomes and there not exactly 46 chromosomes

Question 17

What is nondisjunction?

Answer 17

When the process of separation of homologous chromosome pairs fails. Can happen in either meiosis I or II. It’s worse if it happens in the firs division because then non of them will have there irate number of chromosomes. (pic)

Question 18

What are some common Trisomies/monosomies?

Answer 18

• Down syndrome, trisomy 21
• Klinefelter syndrome, 47 XXY = There’s a Y, so you’re a male, but because of the two X’s, it affects physical appearance
• Turner’s Syndrome, 45 X0, Have morphological issues. Can have more cardiovascular issues

Question 19

Why do problems arise in offspring of older women?

Answer 19

• Prolonged dormancy of oocytes, put to 40 yrs
• Incidence of trisomy 21 increases with maternal age. Main cause is maternal meiotic nondisjunction
• Men don’t have nearly as many problems

Question 20

What are teratogens and what are some examples?

Answer 20

They’re external agents that produce developmental malformations. Literally anything that can cause a birth defect.
Ex: radiation, infections, temp, drugs, toxins, malnutrition, mechanical forces

Question 21

What are the four reasons for the variations in teratogen responses?

Answer 21

1. Concentration and method of teratogen delivery
2. Timing of exposure during development (When were you exposed? Week 8, 20?
3. Variation in susceptibility due to genetic variation (Can you metabolize alcohol better than others?)
4. Synergistic interactions between the teratogen and other compounds (It could be a minor problem, but can lead to other bad things when combined with other factors)

Question 22

What are the two protective layers that form around the secondary oocyte?

Answer 22

The corona radiata and the zona pellucida form protective layers around the secondary oocyte

Question 23

Where in the uterine tube does fertilization occur?

Answer 23

Occurs in the widest part of the uterine tube - the ampulla

Question 24

How does the egg stop multiple sperm from entering?

Answer 24

Once one sperm enters, the egg changes the resting potential of the membrane, which zaps the rest of the sperm. Then the receptors are destroyed to stop anything else form coming in.

Question 25

What is the pre-embryonic period?

Answer 25

It is the first 2 weeks of development when the zygote becomes a spherical, multicellular structure

Question 26

What is the embryonic period?

Answer 26

It is the third through the eighth week of development during which all major organs systems appear.

Question 27

What is the critical period of development?

Answer 27

The first 3 to 8 weeks are the most important. All the organs are developing, etc??

Question 28

What are the three major events in embryogenesis?

Answer 28

Cleavage: Division of zygote and formation of blastocyst
Gastrulation: Formation of germ layers. Everything in the body comes from some form of this
Organogenesis: Germ layers differentiate so as to give rise to all organs in the body

Question 29

What happens to the cells during cleavage?

Answer 29

Divisions increase the number of cells, but it remains the same size. Cells get smaller and smaller

Question 30

What is a morula?

Answer 30

It is the 8-cell stage where the cells become tightly compacted into a ball

Question 31

Inner cell mass vs. Outer cell mass of blastocyst

Answer 31

The inner cell mass is called the embryoblast. It is the part that actually becomes the embryo. The outer cell mass is called the trophoblast cells. These are the ones that help with the placenta
- When this forms, the zona pellucida also begins to dissipate

Question 32

What are the three types of Twinning and what do they consist of?

Answer 32

A. Cleavage of early embryo - They can start as one embryonic egg, but can split into two separate ones
B. Splitting of ICM (inner cell mass) - This happens later in cycle. Can be problematic if one twin becomes dominant and gets all the resources
C. Incomplete division of ICM - When it tries to split but doesn’t happen all the way. Can lead to conjoined twins.

Question 33

What is implantation?

Answer 33

It is the process by which the blastocyst brows into and embeds within the endometrium. Two cavities are present (trophoblast cells and embryoblast cells)

Question 34

What is an ectopic pregnancy?

Answer 34

It is when the implantation of the blastocyst occurs outside the uterine cavity.

Question 35

What two cavities form from each, the embryo and trophoblast?

Answer 35

From the embryo, the epiblast and hypoblast are formed

From the trophoblast, the syncytiotrophoblast and cytotrophoblast are formed.

Question 36

What is hCG?

Answer 36

Human chorionic gonadotrophin. It signals the ovary to continue to secrete hormones to maintain the pregnancy. Ex: Telling it to continue sending estrogen