Reproduction system

• Reproductive system


  Collection of internal and external organs in males and females that work together to produce offspring
• Reproductive system


  • Among the most important systems in the entire body due to its vital role in the survival of the species
  • Differs most between sexes and is the only system that does not function until puberty
• Male reproductive system


  Responsible for delivering sperm to the female reproductive system
• Testes


  • Oval-shaped glands responsible for the manufacture of sperm and the sex hormone testosterone
  • Lie outside the body in the scrotum to maintain the optimum temperature for sperm production
• Epididymis


  • Coiled tube where sperm pass for the final stages of maturation

  
• Sperm production


  1. Spermatogonia lining the inner wall of seminiferous tubules

  2. Develop into primary spermatocytes, then secondary spermatocytes, then spermatids, and finally ripe sperm

  3. Thousands of sperm produced every second, each taking about two months to mature

  
• Semen


  Seminal fluid containing 5-10% sperm and the rest fructose, fatty acids, and proteins to nourish the sperm
• A man will produce roughly 525 billion sperm during his whole lifetime and close to 1 billion per month
• There are around 200 to 500 million sperm in an average in a single human ejaculation
• Sperm


  • About 1/500 inch long, with a head containing the nucleus and acrosome, a midpiece with mitochondria, and a tail that propels it forward

  
• Female reproductive system


  Includes external genitalia (vulva) and internal genitalia (uterine tubes, uterus, vagina) connected to the ovaries

  
• Ovaries


  • Produce egg cells and release them for fertilization

  
• Fertilized eggs develop inside the uterus
• Unlike the male, the female reproductive organs are located entirely inside the body
• Menstrual cycle


  Ripen and release an egg at regular intervals

  
• Uterine tubes


  • Connect the ovaries to the uterus, where egg fertilization usually occurs

  
• Vagina


  Carries menstrual flow, receives the male penis during sexual intercourse, and serves as a birth canal during labor
• Ovulation


  1. Follicle-stimulating hormone causes one egg to begin development

  2. Follicle enlarges and increases estrogen production

  3. Luteinizing hormone surge causes the follicle to rupture and release the ripe egg

  
• The ovary contains undeveloped eggs, eggs in follicles at various stages of maturation, and empty follicles forming corpora lutea

  
• Sperm and egg


  • Sperm coagulates in the vagina to form a physical barrier, cervical mucus transports sperm efficiently, sperm undergo biochemical changes to increase speed, sperm must reach the egg within the right time frame and in the correct fallopian tube

  
• Fertilization


  1. Sperm penetrates and fertilizes the egg, forming a zygote with 46 chromosomes

  2. Zygote divides and develops into a blastocyst that implants in the uterine wall

  3. Blastocyst forms an embryonic disc with the primary germ layers (ectoderm, mesoderm, endoderm)

  
• Primordial germ cells are a type of stem cell that are "put aside" early in development to later form oocytes (eggs) and sperm
• Implantation


  Blastocyst burrows into the endometrium
• Inner cell mass


  Becomes the embryo itself
• Embryonic disc formation


  Separates the cell cluster into the amniotic cavity and the yolk sac

  
• Primary germ layers


  • Ectoderm
  • Mesoderm
  • Endoderm
• Primordial germ cells (PGCs)


  Earliest recognizable precursors of gametes, a type of stem cell
• Migration of primordial germ cells

  From yolk sac into the hindgut tissue, then to the sex organs
• Differentiation of primordial germ cells


  Into male testis before puberty and female ovary when the girl is young

  
• Embryonic development


  Cells divide, form groups that become tissues and organs, specialize into different cell types
• Development is head-down, with the brain and head taking shape early, then the body, followed by the arms as small buds, and lastly the legs
• By the end of the embryonic stage, eight weeks after fertilization, all major organs and body parts are formed

  
• Neural tube formation


  Becomes the spinal cord, enlarged at one end as the brain
• The embryo is 4/50– 5/50 inch long at 3 weeks
• Humans must develop male or female gonads and genitalia to be capable of reproduction

  
• Development at 4 weeks

  1. Four-chambered heart beats, sending blood through simple vessels

  2. Intestines, liver, pancreas, lungs, and limb buds can be seen

  3. Embryo is about 1/5 inch long
• Development at 8 weeks


  1. Face and neck take shape, back straightens, fingers and toes can be differentiated

  2. Embryo starts to move

  3. Embryo is 1 to 1-1/5 inch in length
• Fifteen days after conception marks the beginning of the embryonic period
• The embryo contains a flat embryonic disc that now differentiates into three layers: the endoderm, the mesoderm, and the ectoderm
• All organs of the human body derive from these three tissues