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HUMAN REPRODUCTION

IMPORTANT TERMS:

 v  Accessory/External Sex Characters: The characters which distinguish the male from the female of a species in appearance, but do not directly play any role in reproduction.

v  Acrosin (Zona lysine): That helps to digest Zona pellucida.

v  Archenteron: A cavity formed in gastrula, also called primitive gut.

v  Blastocyst (Blastula): A stage after morula with a fluid filled cavity called blastocoels.

v  Capacitation: Activation of sperm by the secretion of the epithelial lining of oviductal mucosa.

v  Corona Radiata: The radiating rows of follicle cells surrounding the ovum at the time of ovulation.

v  Corpus Luteum: A large mass of big conical yellow cells formed from ruptured Graafian follicle in the ovary after ovulation. It secretes hormone progesterone.

v  Endometrium: The inner lining of uterus.

v  Gametogenesis: The process of formation of gametes/sex cells for sexual reproduction.

v  Gastrulation: The phase of embryonic development involving movement and transport of cells in the blastula to specific locations to form a three layered gastrula.

v  Graafian Follicles: Sac like masses of cells containing ova present in the ovary. Only one Graafian follicle mature in a mouth. It secretes hormone estrogen.

v  Hyaluronidase (Corona penetrating enzyme):An active enzyme present in sperm lysins, that dissolves ground substances of follicle cell or corona radiata.

v  Implantation: Embedding of blastocyst in the uterus.

v  Menopause: Refer to permanent stoppage of menstrual cycle and ovulation at the age around 50 years.

v  Menstrual Cycle (Ovarian cycle): Refer to cyclic changes in the reproductive tracts of human females, culminating into a menstrual flow of blood from the vagina.

v  Neurolation: The phase of embryonic development during which primordium of nervous system i.e., the neural plate, is laid down.

v  Oogenesis: The process of formation of ova (female gametes) in the Graafian follicles of ovary.

v  Organogenesis: The process of differentiation of cells at specific locations of the germ layers of gastrula to form the organ rudiments.

v  Ovulation: The process of rupture of a mature Graafian follicle and liberation of the ovum (secondary oocyte from it).

v  Ovulation: Release of ova (secondary oocyte) from Graafian follicle around 14th day of the menstrual cycle.

v  Parthenogenesis: Development of a complete animal from an ovum without its union with the sperm.(or) Phenomenon of the development of a fully formed individual directly from an unfertilized ovum.

v  Primary Sex Organs: Refers to gonads which produce gametes as well as sex hormones.

v  Reproduction: The process by which an organism produces young individuals of its own species.

v  Secondary Sex Organs: Refers to accessory organs like prostate and seminal vesicles in males and fallopian tubes and uterus in females. These do not produce gametes or hormones.

v Semen: The fluid mixture of spermatozoa and the secretions of accessory glands.

v  Spermatogenesis: The process of formation of spermatozoa in testes.

v  Taratogens (Monster Forming): Chemical substances that cause malformations in the developing embryo.

v  Trophoblast: Outer layer of cells in a blastocyst, which draws food for the embryo from the uterine circulation of the mother.

v  Zona Pellucida: A transparent non-cellular layer around the ovum present between vitelline membrane and corona radiata.

                           ADDITIONAL INFORMATION:

v  Aristotle (384-322 BC): Studied the embryonic development of the chick and of many other animals. He is regarded as the ‘Father (Founder) of Embryology’.

v  Amniocentesis: A technique of drawing amniotic fluid and testing it to find out the disorders and sex of the foetus.

v  Circumcision: A religious rite in Muslims and Jews, in which a part or all of the prepuce is cut-off.

v  Crytorchidism: A condition in which testes are unable to descend in scrotal sacs.

v  Ecotopic Pregnancy: Impregnation of ovum outside the uterus (in fallopian tube, cervix, ovary).

v  Leeuwenhoek (1632-1723): Discovered human spermatozoa in 1675 in the semen with self designed microscope.

v  The cavity of uterus can expand 500 times during pregnancy, from 10cm3 to 5000cm3.

v  Twins: (i) Fraternal Twins (Dizygotic or Non identical Twins): Two offspring that have developed in the uterus at the same time but are the result of independent fertilization of two ova.(ii) Monozygotic Twins (Identical Twins): Two offspring developed from a single fertilized ovum. At an early stage the zygote (fertilized ovum) separates into two independent cells that develop into offspring of the same sex with identical characteristics. (iii) Siamese Twins (united Twins): Named after Chang and Eng born in Siam (Thialand). Their parents were Chinese. Siamese twins were joined in a small area. Now modern surgical techniques have made it possible to separate infants.

v  Free Martin: A sexually undeveloped female calf twined with a male.

v  Foetus: It is the unborn young one of a viviparous animal after it has taken from in the uterus. In human beings, it represents the product of conception from the end of the eighth week to the moment of birth.

v  Types of Placenta:

1. On the basis of foetal membranes involved

(i) Yolk sac placenta: Develops from yolk sac and chorion, e.g., metatherian mammals (Kangaroo, Opassum).

(ii) Chorio-allantonic placenta: Derived from allantois and chorion, e.g., most eutherian mammals.

(iii) Chorionic placenta: Formed from chorion, e.g., human beings.

2. On the basis of Histology: Six tissue barriers in placenta are (a) Endothelium of foetal blood vessels (b) Foetal connective tissue (c) Trophoblast (d) Uterine epithelium (e) Uterine connective tissue and (f) Endothelium of maternal blood vessels. There are five histological type of placenta found in animals:

(i) Epitheliochorial placenta: All the six tissue barriers (layers) of the placenta are present.

(ii) Syndesmochorial placenta: Uterine epithelium is absent; with five placental barriers, e.g., cow, goat, buffalo, camel and giraffe.

(iii) Endotheliochorial placenta: Uterine epithelium and uterine connective tissue are absent; with four placental barriers e.g., dog, cat, lion, tiger, bear and mangoos.

(iv) Haemochorial placenta: All the three uterine tissue barriers (uterine epithelium, uterine connective tissue and endothelium of maternal blood vessels are absent: with three placental barriers, e.g., lemur, apes and men.

(v) Haemoendothelial placenta: All the three uterine tissue barriers and two foetal tissue barriers (foetal connective tissue and trophoblast) are absent; only one placental barrier, e.g., rat, rabbit and guinea pig

Mr. A. KINGSLIN M.Sc, BEd, Phd,(doing)
Post Graduate Teacher in Botany
St. Mary Goretty Hr. Sec School, Manalikarai 
Kanyakumari district





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