Glossary: Human Reproduction | Biology for JAMB PDF Download

The Male Reproductive System

• Scrotum: The testes are situated outside the abdominal cavity within a pouch called scrotum. The scrotum helps in maintaining the low temperature of the testes (2–2.5 degree celcius lower than the normal internal body temperature) necessary for spermatogenesis.
• Testicular lobules: The testis is covered by a dense covering. Each testis has about 250 compartments called testicular lobules.
• Seminiferous tubules: Each testicular lobule contains one to three highly coiled seminiferous tubules in which sperms are produced. 
• Male germ cells: Each seminiferous tubule is lined on its inside by two types of cells called male germ cells (spermatogonia) and Sertoli cells. The male germ cells undergo meiotic divisions finally leading to sperm formation.
• Sertoli Cells: Sertoli cells provide nutrition to the germ cells.
• Interstitial cells or Leydig cells: Leydig cells synthesise and secrete testicular hormones called androgens.
• Urethral meatus: The urethra originates from the urinary bladder and extends through the penis to its external opening called urethral meatus.
• Foreskin: The enlarged end of penis called the glans penis is covered by a loose fold of skin called foreskin.

 The Female Reproductive System

• Accessory ducts: The oviducts (fallopian tubes), uterus and vagina constitute the female accessory ducts.
• Womb: Uterus is also called as womb.
• Cervical canal: The uterus opens into vagina through a narrow cervix. The cavity of the cervix is called cervical canal.
• Mons pubis: Mons pubis is a cushion of fatty tissue covered by skin and pubic hair in females.
• Labia majora: The labia majora are fleshy folds of tissue, which extend down from the mons pubis and surround the vaginal opening. 
• Labia Minora: The labia minora are paired folds of tissue under the labia majora.
• Hymen: The opening of the vagina is often covered partially by a membrane called hymen.
• Clitoris: The clitoris is a tiny finger-like structure which lies at the upper junction of the two labia minora above the urethral opening.

Gametogenesis

• Spermatogenesis: In testis, the immature male germ cells (spermatogonia) produce sperms by spermatogenesis that begins at puberty.
• Spermatids: The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids.
• Spermiogenesis: The spermatids are transformed into spermatozoa (sperms) by the process called spermiogenesis.
• Spermiation: After spermiogenesis, sperm heads become embedded in the Sertoli cells, and are finally released from the seminiferous tubules by the process called spermiation.
• Acrosome: The sperm head contains an elongated haploid nucleus, the anterior portion of which is covered by a cap-like structure, acrosome. The acrosome is filled with enzymes that help fertilisation of the ovum.
• Oogenesis: The process of formation of a mature female gamete is called oogenesis.
• Primary Follicle: Each primary oocyte then gets surrounded by a layer of granulosa cells and is called the primary follicle.  
• Secondary follicle: The primary follicles get surrounded by more layers of granulosa cells and a new theca and are called secondary follicles.
• Antrum: The secondary follicle soon transforms into a tertiary follicle which is characterised by a fluid filled cavity called antrum.
• Ovulation: The Graafian follicle ruptures to release the secondary oocyte (ovum) from the ovary by the process called ovulation. 

Menstrual Cycle

• Menstrual Cycle: The reproductive cycle in the female primates (e.g. monkeys, apes and human beings) is called menstrual cycle.  In human females, menstruation is repeated at an average interval of about 28/29 days, and the cycle of events starting from one menstruation till the next one is called the menstrual cycle.
• Menarche: The first menstruation begins at puberty and is called menarche.  In human beings, menstrual cycles ceases around 50 years of age; that is termed as menopause.

Fertilisation and Implantation

• Fertilisation: The process of fusion of a sperm with an ovum is called fertilisation.
• Cleavage & Blastomeres: The mitotic division starts as the zygote moves through the isthmus of the oviduct called cleavage towards the uterus and forms 2, 4, 8, 16 daughter cells called blastomeres.
• Morula: The embryo with 8 to 16 blastomeres is called a morula
• Implantation: When the blastocyst becomes embedded in the endometrium of the uterus. This is called implantation and it leads to pregnancy.

Pregnancy and Embryonic Development

• Chorionic villi: After implantation, finger-like projections appear on the trophoblast called chorionic villi.
• Placenta: The chorionic villi and uterine tissue become interdigitated with each other and jointly form a structural and functional unit between developing embryo (foetus) and maternal body called placenta.
• Stem cells: Inner cell mass of embryo contains certain cells called stem cells which have the potency to give rise to all the tissues and organs. 

Parturition and Lactation

• Gestation Period: The average duration of human pregnancy is about 9 months which is called the gestation period.
• Parturition: Vigorous contraction of the uterus at the end of pregnancy causes expulsion/delivery of the foetus. This process of delivery of the foetus (childbirth) is called parturition.
• Foetal ejection reflex: The signals for parturition originate from the fully developed foetus and the placenta which induce mild uterine contractions called foetal ejection reflex.
• Colostrum: The milk produced during the initial few days of lactation is called colostrum which contains several antibodies absolutely essential to develop resistance for the new-born babies.

Abbreviations

• GnRH: Gonadotropin releasing hormone 
• LH: Luteinising hormone
• FSH: Follicle stimulating hormone