Biology Ch. 13 Reproduction in Humans PDF

Ch. 13 Reproduction in Humans Human Reproductive System Male reproductive system 1. Gamete-producing organs: testes produces sperms and male sex hormones located in the scrotum (a sac which hangs outside the abdominal...

Ch. 13 Reproduction in Humans Human Reproductive System Male reproductive system 1. Gamete-producing organs: testes produces sperms and male sex hormones located in the scrotum (a sac which hangs outside the abdominal cavity) —> keeps the testes 2-3 degrees Celsius under our body temperature (optimal temperature for sperm production) 2. System of ducts Epididymis: Long coiled tube that lies on each testis stores sperms temporarily Vas Deferens (sperm duct) carries sperms from epididymis to urethra urethra discharges semen out of the body during ejaculation discharges urine 3. Glands: seminal vesicles, prostate gland, Cowper’s glands secrete seminal fluid provides medium for sperms to swim in contains sugars: energy source for sperms contains mucus: lubrication alkaline: neutralize acidic urine in male’s urethra and secretions in female’s vagina semen: seminal fluid+sperms 4. A copulatory organ: penis contains erectile tissue and many blood vessels transfers semen into female’s vagina during sexual intercourse Ch. 13 Reproduction in Humans 1  Female Reproductive system 1. Gamete-producing organs: ovaries produce ova and female sex hormones 2. Oviducts each contains a funnel-shaped opening near an ovary lined with ciliated epithelial cells: beat to sweep the ovum or the early embryo towards the uterus site of fertilization 3. uterus has a thick muscular wall with a lining rich in blood supply pear-shaped organ site of implantation protects embryo or foetus and provides a stable environment for it to develop in its muscular wall contracts to push out the foetus during childbirth has a ring of muscle (cervix) at the lower end dilates during childbirth to allow the foetus to pass through 4. vagina holds the penis and receives semen during sexual intercourse acidic environment—>reduce bacterial growth the birth canal for foetus Human Gametes Structure 1. Sperms looks like a tadpole has 3 main parts: head: contains nucleus (contains 23 chromosomes) and acrosome (contains enzymes) Ch. 13 Reproduction in Humans 2  middle piece: contains many mitochondria for energy production tail: beats to drive the sperm forward 2. ova spherical in shape relatively large (comparing to sperms) contains: nucleus with 23 chromosomes cytoplasm with food reserves cell membrane jelly coat Production 1. Sperm production Starts at puberty Takes place in seminiferous tubules in testes Continuous process throughout adult life At puberty, seminiferous tubules begin to produce more male sex hormones, this stimulates cells near the walls of the tubules to divide mitotically. The cells then undergo meiotic cell division to become sperms. The sperms then pass into the epididymis, where they develop motility and stored temporarily a man can produce millions of sperms every day 2. Ova development Starts before birth At birth, ovaries contain tens of thousands of immature ova each ovum is surrounded of follicle cells, forming follicles at puberty, body begins to produce more female sex hormones, this stimulates several follicles to develop further, they grow in size and move towards the surface of the ovaries. Usually only one follicle will become fully mature at a time. The mature follicle will then burst to release the ovum into the funnel of the oviduct, this process is called Ch. 13 Reproduction in Humans 3  ovulation. After ovulation, the ruptured follicle becomes the yellow body and it degenerates if no fertilization occurs Menstrual cycle Refers to the cycle of building up and breaking down of the uterine lining Day 1-5 the yellow body degenerates if fertilization does not occur the thickened uterine lining breaks down and then discharged through vagina (menstruation) some follicles start to develop Day 6-13 Follicles continue to develop uterine lining thickens and blood supply increases (prepare for implantation of embryo) Day 14 Ovulation occurs Day 15-28 ruptured follicle becomes the yellow body releases hormone to increase and maintain thickness of uterine lining uterine lining becomes very thick and ready to receive an embryo If fertilization occurs, the degeneration of the yellow body is delayed. The uterine lining does not break down and continues to thicken. Menstruation does not occur until childbirth Menopause occurs at around the age of 50 Fertile period Around Day 9-16 sperms can live in the female body for up to 5 days and an ovum can be fertilized for 1 to 2 days only Ch. 13 Reproduction in Humans 4  Fertilization transfer of sperms into female body sperms are brought into a female body during sexual intercourse erectile tissue of penis is filled with more blood and becomes erect when male is sexually excited, the male then inserts penis into vagina of female semen is ejaculated into vagina journey of sperms towards oviducts sperms swim through the cervix and uterus to the upper part of the oviducts after entering vagina Limitations: trapped by mucus cannot survive the acidity high temperature of the female defective or immotile sperms Fusion of sperms and ovum 1. sperms meet ovum in oviduct 2. sperms release enzymes from acrosomes to digest through the jelly coat 3. head of one of the sperms passes through the cell membrane of the ovum and enters the cytoplasm, the jelly coat of the ovum then becomes impermeable to prevent entry of other sperms 4. chromosomes of zygote is restored to diploid (46 chromosomes) Pregnancy Implantation After fertilization, the zygote is moved down the oviduct by the beating action of cilia and the peristaltic contraction of the oviduct wall, while the zygote divides repeatedly by mitotic cell division to from an embryo The embryo then embeds itself into the thickened uterine lining Ch. 13 Reproduction in Humans 5  Development of embryo 1. formation of amnion cells from embryo form a membrane called the amnion about five days after implantation —> encloses the embryo between amnion and embryo is filled with amnion fluid acts as a cushion to protect embryo from mechanical injury provides stable environment for development of embryo prevents embryo from desiccation allows embryo to move around easily lubricated vagina during childbirth 2. formation of placenta formed by finger-like villi developed by the embryo and some maternal uterine tissue connected to the embryo by the umbilical cord the umbilical cord contains two umbilical arteries and one umbilical vein which carries deoxygenated and oxygenated blood away from and towards the embryo respectively the maternal blood and embryo’s blood are separated avoids breakage of embryo’s blood vessels due to the maternal higher blood pressure avoids clumping of blood due to incompatible maternal and embryo’s blood types prevents entry of pathogens and toxins placenta allows the exchange of materials such as nutrients, oxygen and antibodies to the embryo’s blood carbon dioxide and metabolic wastes away from the embryo’s blood the embryonic villi greatly increases the surface area for the exchange of materials the walls of the embryo’s capillaries and embryonic villi are very thin, this provides a short distance for diffusion of materials Ch. 13 Reproduction in Humans 6  there are a lot of blood vessels which can carry materials away rapidly, so a steep concentration gradient of materials between embryo’s blood and maternal blood is maintained Formation of twins 1. Identical twins same genetic make-up one ovum is fertilized and one zygote is formed. The zygote divides into two separate cells, each of the two cells undergoes mitotic cell division repeatedly to form a ball of cells. The two embryos develop into two genetically identical individuals 2. fraternal twins different genetic make-up two ova are fertilized by different sperms, two zygotes are formed. Each of the zygotes divides into two cells. The cells then undergo mitotic cell division repeatedly to from a ball of cells. The two embryos develop into two genetically different individuals Birth process Stage 1 - Dilation 1. cervix dilates 2. muscles of uterine wall contract strongly and tear the amnion 3. amnion breaks 4. amniotic fluid flows out (lubricant) Stage 2 - Delivery of foetus 1. muscles of uterine wall contract more strongly and frequently to push the foetus out 2. delivery of foetus is aided by mother’s active pushing (contraction of abdominal muscles) 3. foetus pushed out Stage 3 - Delivery of placenta Ch. 13 Reproduction in Humans 7  1. placenta detaches from uterine wall and pushed out by further muscular contractions Birth control Preventing ovulation 1. Hormonal method Contraceptive pills Preventing sperms from meeting the ovum 1. Rhythm method (unreliable) calendar method temperature method 2. Barrier methods condoms diaphragms 3. Hormonal method mini pills 4. surgical methods vasectomy (male) tubal ligation (female) Preventing implantation of embryos 1. IUD (intrauterine device) Ch. 13 Reproduction in Humans 8