Human Development Outline

Human Development Outline

I. Fertilization

            A. Ovulation

                        1. One ovum is released from one of the ovaries

                        2. Swept into the funnel-shaped end of one of the fallopian tubes

                        3. The mucus in the cervix becomes more fluid and more elastic allowing sperm                             to enter the uterus rapidly

                        4. Egg is haploid containing 23 chromosomes

            B. At height of sexual arousement:

                        1. Sperm (mixed with seminal fluid, prostate fluid, etc.) is ejaculated inside                                    vagina

                        2.  Travels through cervix and down one of fallopian tubes towards uterus

                        3. Sperm is haploid containing 23 chromosomes of which one is an X while the                              other is either X or Y predicting sex

            C. Union of Sperm and Egg

                        1. Of millions of sperm ejaculated, only one may penetrate ovum

                        2. Once one sperm penetrates, ovum changes electrical characteristics preventing                            additional sperm from penetrating 

                        3. Newly "Fertilized Ovum" is called a Zygote

                        4. Zygote is Diploid containing a normal 46 chromosomes (23 from ovum, 23                                 from sperm)

II. First Trimester

            A. Day 1

                        1. Zygote is formed by the union of sperm and ovum

            B. Day 2

                        1. The Zygote divides into two identical cells through a process called cleavage

                        2. The two daughter cells are called Blastomeres

            C. Day 3

                        1.  These daughter cells divide again forming 4 identical blastomeres

                        2. Embryo is not increasing in size because blastomeres become smaller each time               they divide

            D. Day 4

                        1. Still in uterine tube

                        2. Contains 12-16 cell configured as a solid ball of cells called a Morula

            E. Day 5

                        1.  Has completed journey from uterine tube and enters uterus

                        2. Embryo begins to develop a fluid filled cavity

                        3. Collection of cells on one end

                        4. Called a Blastocyst

            F. Day 6

                        1. Implantation begins

                        2. The blastocyst having specialized adhesion molecules bind to epithelial cells of             endometrium

                        3. Cells of wall full of nutrients and water

                        4. Zona Pellucida is now shed

            G. Day 7

                        1. Inner cell mass has rearranged to form central layer of columnar ectoderm cells   

            H. Day 8

                        1. Cells become lined on the blastocoel side by loosely arranged endoderm cells

                        2. Double layer of cells, called Embryonic Disk, forms (from what embryo                                    develops

                        3. Amniotic cavity appears, enclosed by the amnion

            I. Day 9

                        1. Lacunae appear

                        2. Primitive Yolk Sac is present

            J. Day 10

                        1. Implantation is completed

                        2. Trophoblast cells have released enzymes that have digested, liquefied, and                                 separated maternal cells forming entry way inside uterine wall 

                        3. Inner cell mass is united with nutrients

            K. Day 11

                        1. Slight bulge on the inner surface of the uterine wall

                        2. Ectodermal cells of trophoblast have developed into a continuous layer called                            the Cytotrophoblast

                        3. Enclose embryo

            L. Day 12

                        1. Blastocyst has started to produce hormones

                        2. Physicians define to be the "start of pregnancy"

                        3. Vesicle called the yolk sac is fully formed (no known function)

                        4. Mesoderm cells are formed- begin to line the inside of cytotrophoblast and                                 outside of yolk sac

            M. Day 13

                        1. A "primitive streak" appears (later develop into fetus' central nervous system)\

                        2. Outpocketing of posterior end of embryo

                        3. Allantois arises

                        4. Blood Vessels in Embryonic Stock

            N . Day 14

                        1. Prochordal Plate and Embryonic Disk are noticable

            O. Week 3

                        1. Now 1/12th inch long

                        2. Heart begins to beat

                        3. Development of brain, spinal cord, heart, and gastrointestinal tract begins

            P. Week 4

                        1. Arm, leg, and  tail buds visible

                        2. Heart is now beating at a constant rhythm

                        3. Placenta beginning to form and producing some important hormones (hCG)

                        4. Movement of rudimentary blood through main vessels

                        5. Early eye and ear structures forming

                        6. 1/4 inch long

            Q.  Month 2

                        1. 1.25 inches long

                        2. Gonads have differentiated (sex cannot be determined)

                        3. Limbs now evident  (fingers and toes not yet separated)

                        4. Amniotic fluid is continually secreted

                        5. Now referred to as a Fetus

            R. Month 3

                        1. 3 inches

                        2. All major organ systems are present

                        3. Bones rapidly begin to undergo ossification

                        4. Facial hair

III. Second Trimester

            A. Month 4

                        1. 7-8 inches long

                        2. Heart beats regularly (fluid it pumps is only partially blood)

                        3. Brain convolutions have begun to form

                        4. Eyes sensitive to light shined on eyelids

            B. Month 5

                        1. 9-11 inches

                        2. Fingers and toes are well formed

                        3. Nails develop

                        4. Gastrointestinal tract and lungs are well formed (neither functional)

            C. Month 6

                        1. 12-14 inches

                        2. Skeletal formation

                        3. Sweat glands and hair follicles are numerous in skin

IV. Third Trimester

            A. Month 7

                        1. Lanugo is starting to disappear from baby's face

                        2. Is able to hear

                        3. Building up a layer of fat

                        4. 16 inches

                        5. Beginnings of all essential external and internal structures are present

            B. Month 8

                        1. Turned face down preparing for birth

                        2. 18 inches    

                        3. Small breast buds

            C. Month 9

                        1. Baby is fully formed

                        2. Lungs mature

                        3. 20 inches

                        4. Genitalia show fusion of urethral folds

 

V. Parturition

            A. Dilation (the opening of the cervix)

                        1. Caused by baby pushing out-- marks beginning of uterine contractions

                        2. Normally lasts 2-16 hours

            B. Expulsion (begins when entire head has emerged)

                        1. Contractions last 50-90 seconds (1-2 minute intervals in between)

                        2. Usually, as soon as head appears, the shoulders and rest of body quickly follow

                        3. Umbilical cord tied and cut off

                        4. First breath

                        5. Cleaned and examined

            C. Placental

                        1. Uterus continues to undergo contractions

                                    - Shrinks in size

                                    - expels blood, fluid, and the placenta

Sources:

http://www.americanpregnancy.org/duringpregnancy/fetaldevelopment3.htm

http://www.baby2see.com/development/first_trimester.html

http:/ http://www.religioustolerance.org/abo_fetu.htm/www.ehd.org/dev_article_unit1.php

Human Development Packet