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Development in frog
(i) Breeding
An aquatic embryo is surrounded by water, which protects the embryo, keep it moist, removes wastes and permits gas exchange. In land vertebrate (reptiles, birds and mammals), these functions are taken over by the extra embryonic membranes. These membranes are formed outside the embryo from the trophoblastic only in amniotes and perform specific function. Some of these membranes take part in the formation of placenta in mammals.
(1) Yolk sac : It is formed below the embryo. It contains fluid, not yolk. The yolk sac is a vestigeal organ inherited from the oviparous reptilian ancestors. Yolk sac encloses by outer mesoderm and inner endodermal layer.
Function : In human beings, it is vestigial. In human embryo it act as the site of blood cell formation until about the 6th week, when the liver takes over this role.
(2) Amnion : It is formed above the embryo. It consist of outer more...
The female reproductive system consists of a pair of ovaries, a pair of fallopian tubes, uterus, vagina, external genitalia or vulva and breasts.
Reproductive organ
(1) Ovaries : Ovaries are the primary sex organs of female.
The ovaries are almond shaped bodies, about 3 cm long, 1.5 cm wide and 1 cm thick. The ovaries, like the testes, have both an exocrine function (production of ova) and an endocrine role (secretion of female sex hormones : estrogen and progesterone). After menopause, the ovaries become small and lose follicles.
Each ovary is located close to the lateral walls of the pelvic cavity, being suspended from the dorsal body wall just behind the kidney, by a section of peritonium, the mesovarium.
Each ovary is a compact or solid organ, consisting of an outer cortex and inner medulla. The stroma of the cortical region is composed of spindle shaped fibroblasts. A poorly delineated more...
Definition : Fusion of a haploid male gamete (spermatozoan) and a haploid female gamete (ovum) to form a diploid cell, the zygote, is called fertilization or syngamy.
Site of fertilization : Fertilization in human female is internal as in other mammals. It takes place usually in the ampulla of the fallopian tube.
Steps of fertilization
(1) Approach of sperm to ovum : Male discharge semen (3.5 ml) high up in the female’s vagina, close to the cervix during coitus. This is called ejaculation or insemination. This ejaculation contains as many as 400 million sperms but only about 100 sperms reach the fallopian tube because many sperms are either killed by the acidity of female genital tract or engulfed by the phagocytes of the vaginal epithelium. The sperm swim in the seminal fluid at the rate of 1-4 mm per minute by the aspiratory action of the uterus and peristaltic movement more...
The process of the formation of haploid gametes from the undifferentiated, diploid germ cells in the gonads for sexual reproduction is called gametogenesis.
The process of Gametogenesis is stimulated by the FSH or Follicle Stimulating Hormone and for this process Vitamin "A" and "E" are also necessary.
As a result of this process, male gamete sperm and female gamete egg is formed.
Types of gametogenesis
(1) Spermatogenesis
The process of formation of sperms in seminiferous tubules of the testis of the male animal is termed as spermatogenesis.
In mammals, testis have several coiled tubules in it called the seminiferous tubules. Sperms are formed in these tubules. The inner wall of seminiferous tubules is made up of germinal epithelium whose cells are cuboidal.
The endodermal cells of yolk sac migrate in testes and become primordial germ cells. Due to the division of these cells sperms are formed.
Definition : Gastrulation is a dynamic process involving critical changes in the embryo such as differentiation of cells, establishment of the three primary germ layers and transformation of the single walled blastula into a double walled gastrula.
Types of gastrular movement or morphogenetic movement : The movements of cells during gastrulation is called formative or morphogenetic movements. Following types of gastrular movements are found in different animals
(1) Epiboly : It involves the morphogenetic movement of prospective ectodermal (micromeres) blastomeres antero-posteriorly to envelop the presumptive endodermal and mesodermal blastomeres. It is found in telolecithal egg of frog.
(2) Emboly : It involves inward movement of prospective endodermal and chorda-mesodermal blastomeres from the surface of blastula. Emboly includes following methods :
(i) Invagination : It involves insinking of endodermal cells in the blastocoel to form archenteron. It is found in amphioxus. more...
Gestation period : Gestation period is the duration between fertilization and parturition.
Gestation period
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