The Reproductive System - The term Embryology will be used to study the ontogenetic development in human, which is the life history of one organism from a single-celled zygote to the birth, including all phases of differentiation and growth, which includes the following phases: 1. Gametogenesis: It is the process of production of gametes in both sexes including spermatogenesis and oogenesis. 2. Fertilization: This includes a number of independent biological and physiological processes that end in fusion of mature germ cells to form a zygote. Zygote = fertilized ovum, it is the beginning of a new human being. It is called zygote during a period of first 2 weeks. The zygote undergoes the following changes: Cleavage is a rapid and successive mitotic division of the zygote ends in implantation in which plastola is embedded in the endometrium. 3. Embryo: Its period from the beginning of 3rd week to the end of 8th week of gestation. The stage of embryogenesis includes the following changes: a. Gastrulation: the process by which the inner cell mass (embryoblast) is differentiated into a trilaminar disc (ectoderm, mesoderm and endoderm). b. Organogenesis (organ formation): in which the three germinal layers continue to divide forming groups of cells, each will produce a certain organ or a part of the fetus. 4. Stage of fetal development (period of growth and histological differentiation): Fetus: is the period from the beginning of 9th week till time of birth (duration of pregnancy in human is 40 weeks), where the organs begin to grow and increase in volume. In this way, the fetus reaches gradually its size at birth. The cells become histologically differentiated; this means that the cells will be able to perform their activities and the young baby will be capable to has his independent life outside his mother.
Gametogenesis: It is the process of production of gametes in both sexes and to have a better understanding of this process, we must have an overlook of structure and function of reproductive systems in both sexes.
1 سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة. جامعة طرابلس/ كلية العلوم/ حقوق الطبع و النسخ خاصة لقسم علم الحيوان
Male reproductive system
It consists of: - Primary sex organs (gonads) = 2 testes - Secondary sex organs include: 1. Excretory tubules of the testes that transmit sperms from seminiferous tubules of the testes to the ejaculatory duct (through tubuli recti --- rete testis --- vasa efferenta --- epididymus ---vas deferens --- ejaculatory duct that opens into the urethra). 2. Glands: seminal vesicles, prostate and bulbourethral (Cowper’s) glands.
Testes Testes are descended from abdominal cavity, during intra-uterine development, to reach the scrotum at the time of birth. Each testis is oval surrounded by a fibrous capsule called tunica albuginea and is formed of about 250 testicular lobules separated by connective tissue stroma. Each lobule consists of 1-4 seminiferous tubules embedded in a loose connective tissue rich in blood vessels, lymph vessels, nerves and interstitial (leydig’s cells).
2 سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة. جامعة طرابلس/ كلية العلوم/ حقوق الطبع و النسخ خاصة لقسم علم الحيوان
Seminiferous tubule (30-70 cm long) begins tortuous and ends by narrow straight tubule (tubuli recti) that opens in a network of tubules (rete testis). Seminiferous tubules are lined by a thick germinal epithelium that consists of: 1. Spermatogenic cells: 4-8 layers of germ cells that undergo the process of spermatogenesis. 2. A much less number of tall subtentacular (Sertoli) cells. Function of testes: 1. They are the primary sex organs in male where spermatozoa are formed in the seminiferous tubules. 2. Interstitial (Ledig) cells secrete the male hormone (testosterone), which is essential for the development of secondary sex characters and proper spermatogenesis. 3. Sertoli cells have many functions, which are important for supporting, protecting and nourishing the developing spermatogonia and act as blood-testis barrier that maintain the proper spermatogenesis. Testes start to function at the time of puberty and their functions are regulated by hormones of hypothalamus-pituitary-testicular axis.
3 سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة. جامعة طرابلس/ كلية العلوم/ حقوق الطبع و النسخ خاصة لقسم علم الحيوان
Female reproductive system
The female reproductive system is more complex than male one because it serves more purposes. Its physiology is cyclic and hormones are secreted in a more complicated sequence sequence, it is consists of: - Primary sex organs (gonads) = 2 ovaries - Secondary sex organs; include: 1. The internal nternal genitalia (duct system): uterine (Fallopian tubes, uterus and vagina). 2. The external genitalia. 3. Two mammary gland. Menarche is the time of 1st menstruation (puberty) Menopause is the time of stopping menses
4 سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة. جامعة طرابلس/ كلية العلوم/ حقوق الطبع و النسخ خاصة لقسم علم الحيوان
The ovary: It is an almond-shaped organ found in the pelvic cavity. It is covered by a capsule called tunica albugenia. It consists of cortical region containing ovarian follicle, interstitial glands and medullary region of loose connective tissue. Function of the ovary 1. Production of female gametes (ova) 2. Production of female sex hormones: estrogen and progesterone. The uterine (fallopian) tube: it is a canal about 10 cm long, consists of 4 parts: 1. Interstitial part. 2. Isthmus. 3. Ampulla. 4. Infundibulum with fimbrial processes. It provides a passage for the ovum into the uterus.
5 سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة. جامعة طرابلس/ كلية العلوم/ حقوق الطبع و النسخ خاصة لقسم علم الحيوان
The uterus: It is a thick muscular hollow viscus, consists of: Body: upper two third Cervix: lower third. It provides a mucous membrane suitable for implantation and carry the growing embryo till birth.
The female sexual cycle
The female sexual cycle is a monthly sequence of changes caused by shifting patterns of hormone secretion. Its normal duration is 28 ± 3 days and the major events occur are summarized in the following table:
Days 1-14
Phase
Major events
Follicular Phase:
1-5
Menstrual phase
Menstruation occurring; FSH level is high. Primordial follicle developing into primary and then secondary follicle.
6-13
Pre-ovulatory phase
Rapid growth of one follicle and atresia of the others; drop in FSH level; proliferation of endometrium; development of mature follicle; sharp rise in LH level.
14
Ovulation
Rupture of follicle and release of oocyte.
15-28
Post-ovulatory phase
Formation of corpus luteum; secretion of progesterone, proliferation of endometrial glands; if fertilization does not occur, corpus luteum will be atrophied with falling of progesterone level and endometrial ischemia.
6 سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة. جامعة طرابلس/ كلية العلوم/ حقوق الطبع و النسخ خاصة لقسم علم الحيوان
The female sexual (menstrual) cycle
7 حقوق الطبع و النسخ خاصة لقسم علم الحيوان /كلية العلوم /جامعة طرابلس .سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة
Fertilization It is the fusion of 2 mature cells (mature ovum + mature sperm) to form a zygote. Its normal site is the ampulla (internal third of the uterine tube). It should be noted that the spermatozoon is not capable to fertilize the ovum except after about 10 hours after ejaculation during which a series of changes occur in the sperm called capacitation by which the sperm can undergo an acrosomal reaction that release the enzymes necessary for penetration of the ovum. When one sperm success to enter the ovum, it undergoes a series of changes that prevent fertilization by more spermatozoa (polyspermy). Fertilization results in determination of sex (44, XY = male or 44, XX = female), restoration of diploid number of chromosomes (46), and initiation of cleavage.
Cleavage It is a rapid successive mitotic division of zygote. Its site is at uterine tube medial to ampulla. Zygote ---- 2cells (blstomere) stage ---- 4 cells stage ---- 8 cells stage ---- 16 cells stage ---morula ---- blastocyst.
Implantation It is the embedding of the blastocyst into the compact layer of the endometrium. Its normal site is at the upper part of the posterior wall of the uterus near midline and it takes place in 5 days. Trophoblast undergoes mitotic division and differentiated into inner cyto-trophoblast and outer synsytotrophoblast. The later secretes histolytic enzymes that pore in the compact layer of endometrium through which the blastocyst will invade and implant, and then the pore in the endometrium is closed by fibrin plug after the end of implantation. During implantation there are changes in both outer cell mass (Trophoblast) and inner cell mass (Embryoblast). -
Trophoblast form chorionic villi
-
Embryoblast undergoes embryogenesis to develop embryo.
8 سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة. جامعة طرابلس/ كلية العلوم/ حقوق الطبع و النسخ خاصة لقسم علم الحيوان
Cleavage and implantation
Embryogenesis It is the changes in the Embryoblast to become organized into the three primary layers: ectoderm, mesoderm and endoderm. Two weeks after fertilization, the germ cell layers are present and the embryonic stage of development begins, which extends over the next 6 weeks. A set of membranes are formed external to the embryo. The embryo begins receiving its nutrition primarily from the placenta and the germ layers differentiate into primitive organs as their presence at 8 weeks marks the transition from embryonic stage to fetal stage. Parental Nutrition: The nutrition of conceptus is divided into 2 phases: a. Trophoblastic phase, which is predominant for the first 8 weeks of pregnancy (Trophoblast digests the maternal decidual cells that are rich in glycogen, proteins and lipids), then starts to decline and ends by 12 weeks. 9 سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة. جامعة طرابلس/ كلية العلوم/ حقوق الطبع و النسخ خاصة لقسم علم الحيوان
b. Placental phase: starts by the beginning of the 9th week and become the only mode of nutrition starting from 12 weeks until birth. Placenta starts to develop from 11th day of pregnancy till the end of the 12th week and most development occurs in the embryonic stage. Placenta is formed of 2 parts: a. Maternal part: decidua basalis. b. Fetal part: chorionic villi facing decidua basalis. Placental functions include nutrition, excretion, respiration and endocrine functions. Embryonic Membranes: They include 4 membranes: Amnion, Yolk sac, Allantois and Chorion. The amnion is a transparent sac that develops from ectodermal cells of embryonic disc. It grows to completely encloses the embryo and become filled with amniotic fluid, which has the following functions: -
Protection of the embryo.
-
Allow growth and movement of embryo.
-
Controls body temperature of embryo.
-
Prevents adhesions in embryo.
The yolk sac is formed partly from endometrial cells of embryonic disc opposite the amnion. Its functions are: -
Form part of the digestive system.
-
Produce the first blood cells and germ cells.
The allantois is an out pocketing of the posterior end of the yolk sac and becomes part of the urinary bladder. The chorion is the outer most membrane and forms chorionic villi and fetal portion of placenta.
10 سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة. جامعة طرابلس/ كلية العلوم/ حقوق الطبع و النسخ خاصة لقسم علم الحيوان
