Human development

Question 1

What happens during an orgasm?

Question 2

What happens during an orgasm?

Question 3

Two ways the journey of the sperm assisted?

Question 4

Mechanical ways the sperm is assisted

Answer 4

> uterus and uterine tube contracts occurring in orgasmic phase (female) >Flagellum (male) >Uterine and uterine tube cillia(female)

Question 5

Chemical ways the sperm is assisted

Answer 5

>Oxytocin from posterior pituitary (female) >Prostaglandins from semen

Question 6

How long does the spermatozoa arrive in the uterine tube?

Answer 6

2-7 hours post coitus

Question 7

Two ways the journey of the sperm assisted?

Question 8

Mechanical ways the sperm is assisted

Answer 8

> uterus and uterine tube contracts occurring in orgasmic phase (female) >Flagellum (male)

>Uterine and uterine tube cillia(female)

Question 9

Chemical ways the sperm is assisted

Answer 9

>Oxytocin from posterior pituitary (female) >Prostaglandins from semen

Question 10

How long does the spermatozoa arrive in the uterine tube?

Answer 10

2-7 hours post coitus

Question 11

What is fertilisation?

Answer 11

• fertilisation involves the fusion of two haploid gametes

Question 12

How many chromosomes are in each hapoid gamete?

Answer 12

23 chromosomes

Question 13

Where does fertilisation ussueally occur?

Answer 13

• near the junction between the ampulla and isthmus of the uterine tube

Question 14

Step 1 of fertilisation

Answer 14

• Ovulation releases a seconary oocyte and the first polar body
• Both are surrounded by the corona radiata
• The oocyte is suspended in metaphase of meiosis II

Question 15

Step 2 of fertilisation

Answer 15

Fertilisation and oocyte activation

• Acrosomal enzymes from multiple spermatozoa create gaps between the cells of corona radiata
• A single sperm then makes contact with the oocyte membrane and membrane fussion occurs, triggering oocyte activation
• The secondary oocyte is now an ovum

Question 16

Step 3 of fertilisation

Answer 16

Pronucleus formation begins

• The sperm is absorbed into the cytoplasmm and the female nuclear material within the ovum reorganises as the female pronucleus

Question 17

Step 4 of fertilisation

Answer 17

Spindle formation and cleavage preparation

• The male pronucleus develops, and spindle fibers appear in preparation for cell division
• This is the strat of the process of cleavage, a series of cell divisions that produces an increasing number of smaller and smaller daughter cells.

Question 18

Step 5 of fertilisation

Answer 18

Amphimixis occurs and cleavage begins

• The pronucleus migrates toward the center of the ovum, where the spindle fibers are forming
• The two pronuclei then fuse in a process called amphimixis
• The cell is now a zygote containinfg 46 chromosomes
• Fertilisation is now complete

Question 19

Step 6 of fertilisation

Answer 19

Cytokinesis begins

• The first cleavage division nears completion about 30 hours after fertilisation
• This produces two daughter cells, each one-half the size of the original zygote.
• These cells are called blastomeres.

Question 20

Explain oocyte activation

Answer 20

• is a series of changes in the metabolic activity of the oocyte leading to Ca⁺ release from the smooth ER.
• The rise in Ca⁺ has three effects
  
  1. Enzymes are released that prevent fertilisation by more than one sperm
  2. completion of meiosis II and formation of the second polar body
  3. Activation of enzymes that cause a rapid increase in the cells metabolic rate

Question 21

What happens during cleavage?

Answer 21

The cytoplasm of the zygote becomes subdivided among an increasing number of progressively smaller blastomeres,

Question 23

How long does cleavage last?

Answer 23

About 7 days

Question 24

Day 0

Answer 24

Fertilisation

Question 25

Day 1

Answer 25

Two cell stage

Question 26

Day 2

Answer 26

Four-cell stage

Question 27

Day 3

Answer 27

early morula

Question 28

Day 4

Answer 28

Advanced morula

Question 29

Day 5

Answer 29

Loss of zona pellucida and transport to uterus

Question 30

Day 6: Blastocyst

Answer 30

* The blastocyst is freely exposed to the fluid contents of the uterine cavity with the loss of zona pellucida * The uterine cavity contains the glycogen- rich secretions of the uterine glands * The rate of growth and cell diviosion now accelerates, and the blastocyst enlarges rapidly.

Question 31

Day 7: implatation

Answer 31

* When fully formed, the blastocyst contacts the endometrium * Implantation begins with he attachment of the blastocyst to the endometrium of the uterus * Implantation proceeds as the blastocyst erodes the endometrial lning and becomes enclosed within the endometrium by day 10

Question 32

Day 8: Trophoblast development

Answer 32

* At the point of contact , the trophobast cells divide rapidly,making the trophobast several layers thick. * The cells closest to the blastocoele remain intact, forming a layer of cellular trophoblast. * Near the endometrial wall, the plasma membranes separating the trhophoblast cells disappear, creating a layer of cytoplasm containing multiple nuclei * This layer is called syncytial trophoblast

Question 33

Day 9: Formation of amniotic cavity

Answer 33

* As implantation proceeds, the syncyntial trophoblast continues to enlarge and erode the surrrounding endometrium * Nutrients released by the eroding uterine glands are absorbed by the syncyntial trophoblast