reproduction Flashcards
Reproduction
Reproduction is a process through which organisms produce young ones of their own kind to maintain their species.
Asexual reproduction
It is a kind of reproduction in which a single organism gives rise to offspring by mitotic cell division, during which the total number of chromosomes is exactly replicated and passed on to the daughter cells, so that the offspring are genetically identical to the parent.
Asexual reproduction
(Advantages and Disadvantages)
Advantages:
(i) The offspring are genetically identical to the parent.
(ii) Increase in number is very rapid.
(iii) Tissue culturing in plants and cloning in animals are very easy.
Disadvantages:
(i) It is not good for survival of a species.
(ii) In the cloning there is rapid aging and low resistance to environmental stress and diseases. Similarly cloning is still not being accepted socially and morally in general.
Sexual Reproduction
It is a kind of reproduction in which usually two parents are involved and a fertilized egg is produced through the union of meiotically produced specialized sex cells (egg and sperm) from each parents
Sexual Reproduction (Advantages and Disadvantages)
Advantage:
Meiosis or reduction division gives rise to spores (sporogenesis) or gametes (gametogenesis). As a result, the chromosome number is halved (haploid). Similarly reshuffling of genes also occur which lead to new recombination of genes.
This not only maintains the chromosome number in a species but also produce genetic variations. It is an important factor in the survival of a species or a population
Methods of asexual reproduction are
fission, sporulation, budding, vegetative propagation, artificial propagation, parthenogenesis and apomixes etc. The layering, grafting, budding etcare the artificial asexual methods of reproduction in plants
Oviparous
Lay shelled eggs and fertilization is external
Viviparous
Give birth to young ones and fertilization is internal
Ovoviviparous
Lay shelled eggs but filertilization is internal
Sperm Storage
-Fluid secreted by sertoli cells provides liquid medium, protection and nourishment to sperms while they are in the tubules
-The sperms are then transferred to the main duct of the male reproductive tract, the vas deferens which forms highly convoluted epididymis
-The sperms then pass through the urinogenital duct and are discharged out.
Spermatozoa
Spermatozoa (sperm) are the male sex cells that carry a man’s genetic material. They are so tiny that they can’t be seen without a microscope. In a healthy man, one ejaculation usually contains between 40 million and 600 million sperm. Sperm have an oval head, a short middle, and a long tail
spermatid
A spermatid is the haploid male sexual cell formed after meiosis from spermatocytes that eventually matures into a spermatozoon. Spermatogenesis is the formation of male sexual cells or sperms in the testis, the male reproductive organ.
spermatogenesis
formation of sperm
spermiation
release of sperm from sertoli cells
spermiogenesis
formation of sperm by spermatids
spermatocyte
a cell giving rise to sperm especially : a cell that is derived from a spermatogonium and ultimately gives rise to four haploid spermatids.
Birth:
Gestation Period:
The total gestation period (pregnancy) is usually about 280 days
Birth:
Secretion of Progesterone
Once the placenta is established, it starts secreting the progesterone hormone which maintains the pregnancy.
Any disturbance in the secretion of progesterone may lead to premature births or miscarriage. Human embryo is enclosed in amniotic sac filled with amniotic fluid (protective and shock absorptive).
Birth:
Placenta
It is a structure which develops between the developing child and the uterus. It develops partly from tissue of the uterus and partly from the extra embryonic membrane of the developing child. The embryonic blood vessels that supply nutrients to the developing child and remove metabolic wastes are separated from the blood vessels of the mother. Because of this separation, the placenta can selectively filter different materials and micro-organisms.
Birth:
Secretion of LTH and Placental Lactogen
During this period pituitary gland produce luteotropic hormone (LTH). Placenta also secretes human placental lactogen .Both these hormones stimulate mammary development in preparation for lactation.
Birth:
Fetus Formation
From beginning of the 3rd month of pregnancy the human embryo is referred to as the fetus. Most of the major organs are formed by the 12thweek of pregnancy and the remainder of the gestation period is taken up by growth.
Birth:
Onset of Birth
It was thought that hormonal activities within the mother i.e., decrease in progesterone level onset the birth. But recent evidence suggests that there is a high degree of fetal involvement in the timing of birth.
The initial stage of birth is the result of the stimuli from the fetal pituitary. The ACTH released from fetal pituitary stimulates the fetal adrenal gland to release corticosteroids which cross the placental barrier and enter the maternal blood circulation causing a decrease in progesterone production.The embryonic blood vessels that supply the developing child with nutrients and remove the metabolic wastes are separated from the blood vessels of the mother. Because of this separation, the placenta can selectively filter many types of incoming materials and micro-organisms.
{fetus to mother = CO2, urea and hormone}
{mother to fetus = nutrients, O2, antibodies, vitamins, H2O}
Birth:
Oxytocin and Labour
The reduction of progesterone level stimulates the pituitary gland to produce oxytocin hormone. This induces labour pains i.e. contraction of the uterus walls.
The release of oxytocin occurs in “waves” during labour and provides the force to expel the fetus from the uterus.
Birth:
Delivery
The cervix dilates and the uterine contractions spread down over the uterus and arc strongest from top to bottom, thus, pushing the baby downward leading to the delivery of the baby. The umbilical cord is ligated and baby is released from the mother.
Birth:
Release of After Birth
Within 10-45 minutes after birth the uterus contracts and separate the placenta form the wall of the uterus and placenta then passes out through the vagina. This is called after birth.
Bleeding During Delivery:
Bleeding, throughout this period, is controlled by the contraction of smooth muscle fibers which completely surround all uterine blood vessels supplying the placenta. Average loss of blood is about 350 cm.
Test Tube Babies:
If some physiological and physical abnormalities, in reproductive system in any of the two parents then test tube baby is possible.
Parental sperm and ovum is fertilized in vitro outside the female body and then the zygote is implanted back into the mother uterus, placenta establishes and remaining development takes place in the body of the mother leading to normal birth.
