Reproduction

• Reproduction is a process through which organisms produce young ones of their own kind to maintain their species
• Reproduction is of two types: asexual reproduction and sexual reproduction
• Asexual reproduction:

  • Single organism gives rise to offspring by mitotic cell division
  • Offspring are genetically identical to the parent
  • Advantages: offspring are genetically identical, rapid increase in number, easy tissue culturing in plants and cloning in animals
  • Disadvantages: not good for species survival, rapid aging and low resistance to environmental stress and diseases in cloning
• Sexual reproduction:

  • Involves two parents and a fertilized egg is produced through the union of specialized sex cells (egg and sperm) from each parent
  • Advantage: chromosome number is halved, reshuffling of genes leads to genetic variations important for species survival
  • Evolution of sexual reproduction leads to differentiation of sexes and fertilization process
• Male reproductive system:

  • Consists of external genitalia including testes, male reproductive organ, and various accessory glands
  • Testes located outside the body in the scrotum
  • Seminiferous tubules in testes produce sperms through cell division
  • Hormone production by interstitial cells includes testosterone essential for sperm production and male secondary sexual characteristics
  • Sperm storage and transfer through male reproductive tract
• Female reproductive system:

  • Consists of ovaries, oviducts, uterus, and external genitalia
  • Ovaries produce eggs through division of oogonia and meiotic division
  • Ovulation is the discharge of ovum from the ovary
  • Ovum transferred to oviduct for fertilization, then to the uterus for further development
  • Uterus opens into the vagina through the cervix
• Female Reproductive Cycle:

  • Production of egg is a cyclic activity
  • Menstrual cycle is a 28-day periodic reproductive cycle involving structural and physiological changes in the female reproductive system
  • Regulated by pituitary gonadotropin hormone
  • Involves ovaries cycle and uterine cycle, divided into four phases
• Role of FSH:

  • Pituitary gland releases follicle stimulating hormone (FSH) at the start of puberty
  • FSH stimulates the development of several primary follicles
  • Only one follicle continues to grow with its primary oocytes, while the rest break down by follicle atresia
• Role of Estrogen:

  • Ovary produces estrogen hormone under the stimulus of FSH
  • Functions of estrogen:
  • Stimulates the endometrium and vascularizes it
  • Inhibits the secretion of FSH from the pituitary gland
• Role of LH:

  • Decrease of FSH and increase of estrogen cause the pituitary gland to secrete luteinizing hormone (LH)
  • LH induces ovulation, releasing the ovum from the follicle
  • Ovulation coincides with the thickening of the uterus
• Role of Progesterone:

  • After the release of the egg, cells are modified to form corpus luteum
  • Corpus luteum secretes progesterone
  • Functions of progesterone:
  • Develops the endometrium and makes it receptive for implantation of the zygote
  • Leads to placenta formation
• Menstrual Cycle:

  • If fertilization does not occur, corpus luteum degenerates
  • Progesterone secretion reduces, leading to breakdown of the endometrium and menstruation
  • Menstruation usually lasts for 3-7 days
  • Uterus is ready to enter the next cycle after menstruation
• Period of Menstrual Cycle:

  • Human menstrual cycle generally repeats every 28 days
  • Menopause is the end or complete stop of the menstrual cycle, after which the female stops producing ova
  • Malnourishment and emotional stresses can affect the female reproductive cycle
• Oestrous Cycle:

  • Reproductive cycle found in all female mammals except humans
  • Oestrous cycle involves cyclic structural and physiological changes in the female reproductive tract
  • Estrogen production prepares the uterus for conception and follicle develops ova
  • Physical stimulus of mating is needed for ovulation
• Gestation Period:

  • Total gestation period is usually about 280 days
  • Placenta secretes progesterone to maintain pregnancy
  • Disturbance in progesterone secretion may lead to premature births or miscarriage
• Placenta:

  • Develops between the developing child and the uterus
  • Selectively filters different materials and micro-organisms
  • Secretes LTH luteotropic hormone and placental lactogen to stimulate mammary development for lactation
• Fetus Formation:

  • Human embryo is referred to as fetus from the beginning of the 3rd month of pregnancy
  • Major organs are formed by the 12th week of pregnancy
• Onset of Birth:

  • Fetal involvement in the timing of birth
  • ACTH released from fetal pituitary stimulates fetal adrenal gland to release corticosteroids, leading to decreased progesterone production
• Labour:

  • Reduction of progesterone level stimulates pituitary gland to produce oxytocin hormone
  • Oxytocin induces labor pains by contracting the uterus walls
  • Delivery involves cervix dilation and uterine contractions pushing the baby downward for delivery
• After Birth:

  • Uterus contracts to separate placenta from the wall and passes out through the vagina
  • Average blood loss during delivery is about 350 cm
• Test Tube Babies:

  • Possible in cases of physiological and physical abnormalities in the reproductive system of parents
  • Fertilization of parental sperm and ovum in vitro, followed by implantation of zygote back into the mother's uterus for normal birth
• Sexually Transmitted Diseases (STD):

  • Unhealthy attitudes and low moral values can lead to serious complications
  • Gonorrhoea:
  • Caused by Neisseria gonorrhoeae
  • Affects mucous membrane of urinogenital tract
  • Highly contagious through sexual contacts
• Syphilis:

  • Caused by Treponema pallidum
  • Damages reproductive organs, eyes, bones, joints, central nervous system, heart, and skin
  • Spread through sexual contact
• Genital Herpes:

  • Caused by herpes simplex type 2 virus (HSV-2)
  • Produces genital soreness and ulcers in infected areas
  • Most frequently transmitted by sexual contact, can be transmitted to infants during birth
• AIDS (Acquired Immune Deficiency Syndrome):

  • Caused by HIV (Human Immunodeficiency Virus)
  • Patient loses immunity power
  • Majorly spread through sexual contact
• Control of Sexually Transmitted Diseases (STD):

  • Can be controlled by avoiding sexual contacts with carriers or diseased persons and adopting hygienic conditions
  • Treatment involves medication for a long period, except for AIDS
• Reproduction is the mechanism of producing new generations and maintaining species
• Reproduction differs from all other functions of animals because it is not concerned with the survival of an individual
• Reproduction is very important for the survival of a species or population
• There are 2 types of reproduction:

  • Sexual reproduction
  • Asexual reproduction
• In sexual reproduction, both parents are involved and gametes from both parents are involved
• In asexual reproduction, only 1 parent is involved and no gamete is required
• Asexual reproduction is primitive and more likely to occur in organisms like bacteria
• Human Reproductive System:

  • Unique in two ways:
  • It is not functional until a person reaches the stage of puberty and becomes functional on activation of sex hormones
  • In males and females, all systems are similar but their reproductive systems are quite different from each other