Reproduction in humans

• Sexual reproduction in humans is the process in which organisms give rise to new individuals of their own kind
• Reproduction helps in the continuation of the species
• Some single-celled organisms, like amoeba, reproduce simply by dividing into two
• Multicellular animals, like Hydra, produce side buds which grow in size, separate, and lead an independent life
• Asexual methods of reproduction do not involve eggs or sperms
• In sexual reproduction, males and females produce special types of reproductive cells, known as gametes
• Males produce sperm cells and females produce egg cells (ova)
• When the sperm fuses with the egg, fertilization occurs, forming a zygote
• The zygote grows by cell division and produces an embryo, which grows to become a new individual
• Fission (Binary fission or multiple fission) is the most common method of reproduction in single-celled organisms like Amoeba and Paramecium
• Budding is a process in which buds grow on the outside of the parent body, common in organisms like Hydra
• Regeneration is the ability of animals like Hydra and starfish to regrow missing or lost body parts, including for reproductive purposes
• Most animals reproduce sexually
• The female reproductive system includes ovaries that produce eggs,oviducts, uterus,cervix and vagina
• The male reproductive system includes testis, sperm duct, seminal vesicle, prostate gland, Cowper's gland, epididymis, scrotal sac, and penis
• The uterus in females opens to the outside through the vagina, situated between the rectum and the urethra
• The vagina receives the penis during copulation and also serves as the birth canal
• The urethral opening is seen above the vagina in the region of the vulva
• Sperms are produced in the testes found below the prostate gland
• The testes are outside the abdominal cavity in a sac called the scrotum
• The testes are at a temperature 2-3oC lower than that of the body, which is the most suitable temperature for sperm production and development
• Semen is a mixture of sperm and secretions from seminal vesicles, prostate, and Cowper's glands
• The sperm ducts open into the urethra just below the urinary bladder
• During fertilization, the nucleus of the sperm fuses with the nucleus of the egg
• Implantation is when the fertilized egg (zygote) attaches to the wall of the uterus
• Growth is an irreversible increase in the size and weight of an individual during development
• The zygote divides and redivides to form a cluster of cells, leading to the formation of different parts of the body through differentiation
• The zygote grows into an embryo, which then develops into a fetus with the formation of the heart, circulatory system, and limbs
• At the time of birth, the baby is pushed out with the head first through the vagina due to powerful contractions of the uterus muscles
• Gestation is the full term of development of an embryo in the uterus, lasting about 9 months in humans