Reproduction in humans

• The testes are responsible for producing sperm and testosterone.
• Scrotum holds the tested outside the abdominal cavity
• The scrotum keeps the testes at a lower temperature optimal for sperm development
• Epididymis stores sperms temporarily
• Vas deferens carries sperms from epididymis to the urethra
• Urethra discharges semen out of the body during ejaculation
• 1. Seminal vesicles, prostate gland and Cowper's glands all secrete seminal fluid that
  2. provides a medium for sperms to swim in
  3. contains sugars that act as an energy source for sperms
  4. contains mucus for lubrication
  5. is alkaline which helps neutralise any acidic urine in the male's urethra and acidic secretions in the female's vagina
• The penis contains erectile tissue and many blood vessels
• The penis transfers semen into the female's vagina during sexual intercourse
• The Ovary produces ova and female sex hormones
• Oviduct is lined with ciliated epithelial cells. The cillia sweep the early embryo towards the uterus and is the site of fertilisation.
• Uterus

  1. Site of implantation of the embryo.
  2. Protects the embryo and provides a stable environment for it to develop in.
  3. its muscular wall contracts to push out the foetus during child birth.
  4. Cervix at the lower end dilates to allow the foetus to pass through during childbirth
• Vagina

  1. Holds the penis and receives the semen during sexual intercourse.
  2. Its environment is acidic to reduce bacterial growth.
  3. Acts as the birth canal for the foetus
• A sperm consists of a head, a midpiece and a tail
• The head of the sperm cell is acrosome which contains enzymes for penetration
• The midpiece contains a nucleus wh contains a 23 haploid number of chromosomes
• The tail is packed with many mitochondria that releases energy for swimming and beats to drive the sperm forward.
• The ova consists of a nucleus, cytoplasm and a cell membrane covered by a jelly coat.
• The cytoplasm contains food to reserve for the early development of the embryo.
• the nucleus of the ova contains a haploid number of chromosome.
• Production of sperms

  • starts at puberty in the life of male
  • takes place in seminiferous tubule inside the testes
  • the increased levels of hormones stimulate the cells near the walls of the tubules to divide mitotically to produce more cells.
  • these cells undergo meiotic cell to become sperms.
  • sperms finally pass to the epididiymis to develop motility and are stored temporaril.
• 1. increased levels of female sex hormones stimulate several follicles to develop further.
  2. The follicles grow in size and move towards the surface of the ovaries. Usually only one mature follicle becomes fully mature at a time
  3. Mature follicles bursts to release ovum into the funnel of the oviduct. Which is called Ovulation.
  4. Ovum is transported along the oviduct by the beating action of the cillia on its inner wall and the peristaltic contraction of its muscular wall.
  5. The ruptured follicle becomes the yellow body.
  6. the yellow body degenerates if fertilisation does not occur.

  
• Development of ova

  • production of ova begins in the ovaries of the foetus before birth.
  • the ovaries contains tens of thousands of immature ova.
  • Each ovum is surrounded by layers of follicle cells, forming a follicle.
• Secondary sexual characters of males

  • Hair grow in armpits and pubic hair
  • larynx enlarges and voice deepens
  • Shoulders broaden
  • Body becomes more muscular
  • Beard grows
• Secondary sexual characteristics of female

  • Hair grows in armpits and pubic hair
  • Breasts develop
  • more fat is deposited under the skin
  • Hips becomes wider
• Preparation for the implantation of the embryo

  • Uterine lining thickens and its blood supply increases before ovulation
  • if fertilisation does not occur, the thickened uterine lining will break down
• Day 1 to 5

  • When no fertilization = yellow body degenerated
  • Thickened uterine lining breaks down alongside with the unfertilised ovum, they are discharged through the vagina. this is called menstruation.
  • Some follicles in the ovary start to develo.

  
• Day 6 to 13

  • Follicles continue to develop
  • Uterine lining thickens and blood supply increases to prepare for the implantation of an embryo.

  
• Day 14

  • ovulation occurs

  Day 15 to 28

  • The ruptured follicle becomes the yellow body, which releases a hormone to increase and maintain the thickness of the uterine lining
  • uterine lining becomes very thick. it is ready to receive an embryo

  
• If fertilisation occurs and the women gets pregnant

  • the degeneration of the yellow body is delayed, uterine lining does not break down and it continues to thicken.
  • menstruation does not occur until the baby is born.
  • Changes in the thickness of the uterine lining in relation to the events occurring in the ovary.
• 1. When a male is sexually excite, the erectile tissue of his penis is filled rapidly with more blood. The penis becomes erect, the male inserts his penis into the vagina of the female
  2. Semen (containing sperm) is finally ejaculated into the vagina.

  
• Journey of sperms towards oviducts

  • After entering the vagina, the sperms swim through the cervix and the uterus into the upper parts of the oviducts, which is the site of fertilization.
• Journey of sperms towards oviducts

  only a small proportion of sperms released in a single ejaculation can reach the upper part of the oviduct because:

  • Some sperms are trapped by the mucus in the vagina
  • Some sperms cannot survive the acidity in the vagina
  • The body temperature of the female is too high for the sperms
  • Some sperms are defective or immobile
• Fusion of sperm and ovum

  1. When sperms meet an ovum in the oviduct, they try to penetrate it
  2. The sperm release enzyme from their acrosomes to digest a path through the jelly coat of the ovum
  3. The head of one of the sperms enters the cytoplasm of the ovum. The jelly coat of the ovum changes to prevent the entry of other sperms.
• Fusion of sperm and ovum

  • The nucleus of the sperm then fuses with the nucleus of the ovum, this is fertilisation and the fertilised ovum is called a zygote
  • The zygote carries the genetic materials of both parents. The diploid number of chromosomes is restored in it.
• Pregnacy

  Implantation

  • After reaching the uterus, the embryo embeds itself into the thickened uterine lining, this is called implantation and marks the beginning of pregnancy.
• 1. Ovulation occurs
  2. Ferilization gives rise to a zygote
  3. The zygote is moved down the oviduct by the beating action of cillia and the peristaltic contraction of the muscular wall of the oviduct. Meanwhile, the zygote divides repeatedly by mitotic cell division to form an embryo
  4. The embryo implants into the uterine lining.