Origins of Body Form

Date : xx / xx / xxxx

The First Month of Human Life (2.19)Lecture 1

Dr. Shahira SamirProfessor of Anatomy & Embryology

Objectives

By the end of this session ( the 3 lectures) you should be able to describe the:

• Production of the gametes (eggs and sperm)

• Fertilization, implantation and some causes of infertility

• Methods of contraception

• Formation of the germ layers

• Formation of the body plan

• Origin of organs and tissues

Gametogenesis

What is spermatogenesis?Process of formation of complete

motile spermatozoa from primordial germ cells (spermatogonia).

When?Puberty→ Old age

Where?

Seminiferous tubules of testis

How (STEPS)?

1. Proliferation: → Daughter spermatogonia (46-diploid)

2. Growth:→ Large 1ary spermatocytes (46-diploid)

How? STEPS of Spermatogenesis

3. Maturation:→ Meiosis I; 2 2ary spermatocytes (23-haploid)---Meiosis II (mitosis); each→ 2 spermatids (23-haploid)

4. Transformation

(Spermiogenesis)

How? STEPS of Spermatogenesis

4. Transformation (Spermiogenesis)

1.Head: Acrosome + Nucleus

2.Neck: Follows the head &

contains the centriole.

3.Body: Middle piece containing

mitochondria

4.Tail: end piece containing the

axial filament

Structure of a sperm:

• Depends on the number, shape and motility of sperm.

- Sterile males produce less than 10 millionsperm/ml of semen (normal is 100 million/ml or 300-500 million/ ejaculate). - Abnormal forms should not exceed 10%. - Normally 70% are motile.

Male fertility

What is oogenesis?Process of differentiation of mature oocyte (ready for

fertilization) from primordial germ cells (oogonia).

When? Begins:

3rd month of intrauterine life → birth;

then after puberty (during each ovarian cycle) and after fertilization

Ends: at menopause

Where?Ovary

How (STEPS)?

How? STEPS of oogenesis

During fetal life (prenatal maturation)1. Proliferation: in early fetal life→ Daughter

oogonia (46-diploid)2. Growth:→ Large 1ary oocytes (46)→ begin

1st meiotic division (before 5th month, all are 1ry oocyte, no oogonia)

oogonia

How? STEPS of oogenesis

Postnatal maturation1. Completion of 1st meiotic division:→ 2ary

oocyte (23-haploid) + 1st polar body (haploid) (occurs at puberty, ovarian cycle)

2. Second meiotic division: occurs after ovulation, only if fertilization occurs: → mature ovum (23-haploid) + 2nd polar body

oogonia

• No of 1ary oocytes:at puberty: 40 000

• No of ovulated 2ry oocyte in the fertile period of a woman around 480 (12x40); this is reduced by contraceptive pills, pregnancy & unovulatory cycles

• the rest atretic• The 1st meiotic division: long (up to 45 yrs)→ high

frequency of meiotic error in increasing maternal age

The 1st meiotic division: long (up to 45 yrs)→ high frequency of meiotic error in increasing maternal age→ The primarycause of Down syndrome (Trisomy 21) is maternal meiotic nondisjunction

Primordial follicles (Primary oocyte + surrounding flat epithelial cells) -----

---- Primary follicles---------Graafian follicle

Ovulation:

Definition: Rupture of Graafianfollicle & discharge of 2ary oocyteOnset: 14th day of menstrual cycleSigns: - Body temperature

- Sometimes pain: mittelschmerz (German for “middle pain”)

Steps of ovulation

1. 2ary oocyte rupture of Graffian follicle to enter uterine tube

2. If fertilization occurs, 2nd meiotic division occurs to give mature ovum & 2nd

polar bodyIf no fertilization→ dies

Steps of ovulation

3. The follicle under the effect of LH hormone→ Luteinization= lipid deposition (yellow in colour) so named: Corpus Luteum which secrete progesterone

Fate of Corpus Luteum:

1. If fertilization---------

Corpus luteum of

pregnancy (secretes

progesterone for 3-4

months till formation

of placenta).

2. If no fertilization------

Corpus luteum of

menstruation--------

Corpus albicans

Which of the following has a haploid number of chromosomes?A. SpermatogoniaB. OogoniaC. Primary spermatocyteD.Primary oocyteE. Spermatid

Corpus luteum is:A. Part of the uterusB. A stage of oogenesisC. Follicular cells remaining after ovulationD.A stage of spermatogenesisE. Part of the sperm

The source of energy for the sperm lies in its:A. HeadB. NeckC. Middle pieceD.TailE. Acrosome