12_13 Test.pdf

Chapter 12/13 Test Human Bio Fertilisation, Blastocyst Formation, and Implantation: Describe the sperm's journey from ejaculation to fertilisation. 1. Ejaculation and Entry into the Vagina: During ejaculation, sperm is released in semen, which contains millions of sperm cells. This semen i...

Chapter 12/13 Test Human Bio Fertilisation, Blastocyst Formation, and Implantation: Describe the sperm's journey from ejaculation to fertilisation. 1. Ejaculation and Entry into the Vagina: During ejaculation, sperm is released in semen, which contains millions of sperm cells. This semen is deposited into the vagina near the cervix. The vaginal environment is acidic, which is hostile to sperm, but the semen has alkaline properties to help protect the sperm for a short time. 2. Passage Through the Cervix: After entering the vagina, sperm must travel through the cervix. During ovulation, cervical mucus becomes thinner and more fluid, making it easier for sperm to pass through. Only a small percentage of sperm make it through the cervix, as it acts as a filter for less healthy sperm. 3. Travel Through the Uterus: Once through the cervix, the sperm enters the uterus. The uterus has muscle contractions that help propel sperm towards the fallopian tubes. The sperm must also avoid being attacked by the immune system, which may recognise them as foreign. 4. Reaching the Fallopian Tube: The sperm continues its journey toward the fallopian tubes. If ovulation has occurred recently, the egg will be present in the fallopian tube. 5. Encountering the Egg: Only a few sperm (out of the millions ejaculated) reach the egg. Once they do, they must penetrate the protective outer layers of the egg: the corona radiata (a layer of cells surrounding the egg) and the zona pellucida (a glycoprotein layer). The many sperm release enzymes from the acrosomes (a cap-like structure) to help one sperm break through the corona radiata in order to encounter the zona pellucida. This initiates the acrosomal reaction, causing digestive enzymes from the acrosome to be released, to break down zona pellucida. They break down the glycoprotein matrix of zona pellucida, giving sperm access to plasmma memebrane. 6. Fusion of Sperm and Egg (Fertilisation): Once a sperm successfully penetrates the zona pellucida, its plasma membrane fuses with the egg’s membrane. This triggers a reaction in the egg that prevents other sperm from entering by forming a fertilisation membrane around the oocyte. Chapter 12/13 Test Human Bio The nucleus of the sperm enters the egg and fuses with the egg’s nucleus, forming a zygote with 46 chromosomes (23 from each parent). Once sperm enters, the tail is absorbed and head begins to move through the cytoplasm as male pronucleus which is the haploid nucleus of sperm. Entrance of sperm stimulates secondary oocyte to compete meiosis II The Oocyte nucleus develops into a female pronucleus Fertilisation is now complete and the fertilised oocyte is a zygote. How is the time taken for the sperm to travel to uterine tubes so fast? The travel of the sperm is helped by the muscular contraction of the uterus and uterine tubes to push sperm forward, as well as uterine contraction and beating cilia to transport ova towards the uterus after ovulation. Sperm also have a flagellum tail which provides them motility. How does the zygote develop into a blastocyst, and what is the significance of this stage? Once the secondary oocyte has been fertilised, it becomes a diploid zygote. This zygote travels down the fallopian tubes towards the uterus. It begins to divide by mitosis, creating identical cells. This means it goes from 1 cell to two cells, to 4 cells, to 8 cells, then 16 and so on. The zygote is also totipotnet. After 6 days the original zygote has reached the uterus and is now a blastocyst. The blastocyst is a hollow ball of cells that surround a cavity filled with fluid, with a group of about 30 cells called inner cell mass in the side. These stem cells in the inner cell mass are pluripotent and develop into different body cells. Describe the process of implantation and explain why it is crucial for pregnancy. Implantation is when the blastocyst sinks into the lining of the endometrium and firmly attaches to the wall of uterus, after floating free for 3 days in the uterus. This enables the blastocyst to get nourishment for growth and development by absorbing nutrients from the glands and blood vessel of the uterine lining. The uterine lining is kept thick and rich by hormones such as progesterone and estrogen. Implantation is crucial for pregnancy as it connects the blastocyst to the mother's blood supply, ensuring the embryo receives essential oxygen, nutrients, and hormones for growth. It also triggers the secretion of hCG, which sustains progesterone production to maintain the uterine lining and prevent menstruation. Implantation is necessary for the formation of the placenta, which facilitates nutrient and waste exchange between mother and fetus. Additionally, the endometrium provides a protective and stable environment for the embryo’s continued development. Without implantation, pregnancy cannot proceed. How is the blastocyst dependent on hormones when implanted? The blastocyst relies on hormones, primarily hCG, progesterone, and estrogen, for successful implantation and continued development. These hormones ensure the uterine lining is properly maintained and a Chapter 12/13 Test Human Bio menstrual cycle does not start again, suppress uterine contractions, and support the growth of the embryo and placenta, ultimately enabling a successful pregnancy. The corpus luteum produces estrogen and progesterone until the placenta is formed and can produce hCG after about 8 weeks. Without these hormonal signals, the blastocyst would not be able to survive or develop properly in the uterus. Cell Differentiation Process after Fertilisation: How does the zygote transition from totipotent to pluripotent cells, and what are the main events in this process? Once the secondary oocyte has been fertilised, it becomes a diploid zygote. This zygote travels down the fallopian tubes towards the uterus. It begins to divide by mitosis, creating identical cells. This means it goes from 1 cell to two cells, to 4 cells, to 8 cells, then 16 and so on. The zygote is also totipotnet. After 6 days the original zygote has reached the uterus and is now a blastocyst. The blastocyst is a hollow ball of cells that surround a cavity filled with fluid, with a group of about 30 cells called inner cell mass in the side. These stem cells in the inner cell mass are pluripotent and develop into different body cells. Primary Germ Layers: What are the three primary germ layers formed after fertilisation, and what tissues and organs develop from each? While the blastocyst is implanted in lining of uterus, during the third week, inner cell mass undergoes changes as cells change to multipotent. This results in the formation of three layers of cells called the primary germ layer. These layers are embryonic tissues that differentiate into all tissues and organs of the body. 1. Ectoderm: ○ Nervous System: Brain, spinal cord, peripheral nerves. ○ Skin: Epidermis (outer skin layer), hair, nails, and glands. ○ Sensory Organs: Eyes, ears, and olfactory structures. ○ Other Structures: Mammary glands and enamel of teeth. 2. Mesoderm: ○ Musculoskeletal System: Skeletal muscles, bones, and cartilage. ○ Circulatory System: Heart, blood vessels, and blood cells. ○ Reproductive System: Gonads (ovaries and testes) and reproductive ducts. ○ Urinary System: Kidneys and ureters. ○ Connective Tissues: Dermis of the skin and various internal organs. 3. Endoderm: ○ Gastrointestinal Tract: Lining of the digestive tract from the esophagus to the anus. ○ Respiratory System: Lining of the trachea, bronchi, and lungs. Chapter 12/13 Test Human Bio ○ Liver and Pancreas: Hepatic and pancreatic tissues. ○ Urinary Bladder: Urethra and urinary bladder lining. ○ Thyroid and Parathyroid Glands: Thyroid gland and parathyroid glands. Use the position of the primary germ layers to justify the structures that they eventually form. ○ The ectoderm, being the outermost layer, forms structures that interact with the external environment (e.g., skin, nervous system). ○ The mesoderm, as the middle layer, forms connective tissues, muscles, and systems that integrate and support the body internally. ○ The endoderm, being the innermost layer, forms the internal linings of organs, particularly those involved in digestion, respiration, and glandular function. Embryonic Membranes: (Do diagram practices) Name the embryonic membranes and describe their roles during development. Amnion The thin, transparent membrane surrounds the embryo. Filled with amniotic fluid. Functions: ○ Cushions the embryo against mechanical shocks. ○ Maintains a stable temperature. ○ Provides a buoyant environment for free movement. ○ Facilitates the exchange of nutrients and waste. Chorion Outermost membrane around the embryo. Contributes to the formation of the placenta. Functions: ○ Facilitates nutrient and gas exchange with the mother. ○ Produces hormones like hCG to support pregnancy. ○ Acts as a protective barrier against pathogens. Allantois Sac-like structures develop from the posterior part of the embryo. Functions: ○ Stores metabolic waste produced by the embryo. Chapter 12/13 Test Human Bio ○ Contributes to the development of blood vessels for the umbilical cord and placenta. ○ Plays a role in gas exchange (less prominent in humans). Yolk Sac The membrane surrounding the yolk is associated with early embryonic development. Functions: ○ Provides nutrients to the embryo before the placenta forms. ○ Produces the first blood cells (hematopoiesis). ○ Contributes to the development of the circulatory system. ○ Aids in the formation of primordial germ cells (sperm and eggs). How does the amnion contribute to protecting the embryo? Cushioning Effect: Filled with amniotic fluid that absorbs shocks. Reduces the risk of injury from external impacts. Thermal Regulation: Maintains a stable temperature around the embryo. Protects against temperature fluctuations. Buoyant Environment: Allows the embryo to float and move freely. Supports the development of the musculoskeletal system. Protection from Infection: Provides a sterile environment to shield the embryo from pathogens. Facilitating Development: Enables organ formation and other developmental processes without interference from surrounding tissues. Placenta Structure, Function, and Chorionic Villi: What is the structure of the placenta, and how is it formed? The placenta develops in the first 3 months of gestation from both maternal and foetal tissues. It is an organ that supplies nutrients and removes wastes from the developing baby or foetus. It also serves as an endocrine organ, producing hormones to support pregnancy. Chapter 12/13 Test Human Bio The foetal part of the placenta starts developing when the blastocyst is implanted. Chorionic villi projections develop from the chorion, an extraembryonic membrane, and grow into the endometrium. They contain blood vessels and act like tree roots. They become bathed in pools of the mother's blood and allow for the transport of substances between the foetus and maternal blood via diffusion or active transport. How do the chorionic villi aid in material exchange between the mother and fetus? Explain how nutrients, gases, and wastes are exchanged between the fetus and mother via the placenta. Nutrient Exchange Structure: The placenta has finger-like projections (villi) that increase surface area for exchange. Nutrients from Mother: Essential nutrients (like glucose and amino acids) flow from the mother’s blood to the fetus’s blood. On the mother's side, uterine arteries carry blood from the mother to the placenta where blood allows diffusion and active transport, then uterine veins carry this now depleted and deoxygenated blood back to the mother's body. Transport Methods: ○ Diffusion: Small molecules passively move from high to low concentration. ○ Active Transport: Larger molecules are moved against the concentration gradient using energy. Gas Exchange Oxygen: Diffuses from the mother’s blood into the fetus’s blood, where fetal hemoglobin efficiently binds it. Carbon Dioxide: Moves from the fetus’s blood to the mother’s blood to be exhaled. Waste Removal Fetal Waste: Metabolic waste (like urea) produced by the fetus is transferred to the mother’s blood. Excretion: The mother’s kidneys process and excrete these wastes. Blood Flow Dynamics Separate Circulation: Maternal and fetal blood do not mix; they exchange substances through the placenta. Umbilical Cord: Nutrient-rich blood returns to the fetus via the umbilical vein; waste-laden blood exits through umbilical arteries. Chapter 12/13 Test Human Bio Hormonal Signaling The placenta produces hormones that support pregnancy and fetal development. Umbilical Cord and Exchange of Materials: What is the role of the umbilical cord in fetal development? Umbilical Cord and Blood Flow: The umbilical cord connects the fetus to the placenta and contains: ○ Two umbilical arteries: These carry deoxygenated blood and waste products from the fetus to the placenta. ○ One umbilical vein: This carries oxygenated, nutrient-rich blood from the placenta back to the fetus. Pregnancy Stages and Important Characteristics: Outline the key developmental milestones for each month of pregnancy. What are the most critical changes that occur in the fetus during the first, second, and third trimesters? Changes in the Pregnant Mother: What physiological changes occur in the mother's body to support pregnancy? Increased blood volume to cater for extra blood flowing through placenta Increased urine production Increased breast size due to the development of milk-secreting tissues Increased abdomen due to growing uterus Emotional state affected due to fears around pregnancy and change in hormones How do hormonal levels change during pregnancy, and what effects do these hormones have? Explain why heavily pregnant women often prefer to eat smaller meals than normal. 1. Reduced Stomach Capacity As the uterus grows, especially in the later stages of pregnancy, it expands upwards and pushes against the stomach. This reduces the stomach's physical capacity to hold large amounts of food, making women feel full more quickly after eating. 2. Increased Pressure on the Digestive System The growing baby and uterus put pressure on other abdominal organs, including the intestines and stomach. This compression slows down digestion and can make large meals uncomfortable or difficult to digest. 3. Heartburn and Acid Reflux Chapter 12/13 Test Human Bio The pressure on the stomach can force stomach acid up into the esophagus, leading to heartburn or acid reflux. This discomfort often worsens after large meals, making smaller, more frequent meals a more comfortable option for heavily pregnant women. 4. Slower Digestive Transit Hormonal changes, particularly an increase in progesterone, relax the smooth muscles of the digestive tract, leading to slower digestion. This can cause bloating, indigestion, and constipation, all of which can be exacerbated by larger meals. Birth Process: What are the main stages of labour and delivery? The are 3 stages of partruition. In preparation for labour, several hormonal changes occur: ○ The ligaments of the pelvis soften. ○ The uterus is more resistant to stimuli as well as strengthened ○ Cervix softened, shortened and beginning to open up The foetus has settled with its head in the mother's pelvis, with its head facing mother's hip bone with knees drawn up and legs crossed with the sides of the head against the bladder and bowel. This takes up as little space as possible. The first stage is often called dilation, and it is where the cervix gradually opens up. ○ During the last 3 months of gestation weak contraction occur, which become stronger until they are strong and every 30 minutes, which marks the start of the birth process. ○ Waves of contraction travel from the uterus to cervix, shortening muscle fibres in the uterus which then pulls on the cervix, pulling it open. ○ This allows the foetus to move deeper into the pelvis. As contraction gets stronger, the head of the foetus is pushed forcefully on the cervix. ○ When the cervix is fully dilated at around 10cm, the birth canal between the uterus, cervix and vagina is formed. ○ The foetus then passes through the birth canal, aided by uterus contraction and voluntary contractions of abdominal muscle by the mother pushing. Complete dilation marks end of the first stage. The second stage is the delivery of the foetus, called expulsion. Often begins with the breaking of the waters, which is the bursting of the amniotic sac which releases a gush of water from the vagina. From full dilation to birth takes 20 min up to 2 hours. As foetus moves through the cervix, it stretches the vagina. This stimulates the mothers abdominal muscles to contract, pushing foetus through the vagina. Chapter 12/13 Test Human Bio The baby's head begins to turn towards the mother back. With each contraction the head advances, then pulls back in between, but overall gradually moves out. The head becomes visible. The mother is working very hard and her pulse rate is elevated and she is sweating, trying to take rest between contractions. Eventually, the abys head stretches over the vaginal entrance and all tissue becomes tightly stretched as forced into the world. Once head emerges, foetus turns sideways, allowing the shoulders to move through. The pressure on its head may push it out of shape, however, the bones of the skull are pliable and will move back into place with time. The third stage is the afterbirth, where the placenta and other tissues are expelled. Once the baby is born and begins breathing with its own lungs, it is still connected to the placenta via the umbilical cord. The amnion, chorion and placenta are still inside the uterus. The umbilical is tied, clamped then cut, contracting the arteries and veins within the umbilical cord. The stump falls away just leaving the navel behind. The uterus continues contracting, and about 5 minutes after the birth, the afterbirth of the placenta, membranes and umbilical cord takes place and are expelled. There is little blood lost in this as placental blood vessels constrict and uterus contractions squeeze shut the vessels that supply blood to the placenta Blood clots stop leakage Changes in the Baby at Birth: What major changes occur in a newborn's circulatory system immediately after birth? 1. Foramen Ovale Closes Before birth: There’s a small hole (foramen ovale) between the two top chambers of the baby’s heart, allowing blood to skip going to the lungs since the baby gets oxygen from the placenta. After birth: When the baby takes its first breath, blood starts going to the lungs to get oxygen. This causes the hole to close, so blood flows the right way through the heart and lungs. 2. Ductus Arteriosus Closes Before birth: There’s a vessel (ductus arteriosus) that connects two big arteries in the baby’s heart, letting most of the blood bypass the lungs. After birth: As the baby breathes, the lungs need more blood for oxygen. The ductus arteriosus closes, so blood can now flow properly into the lungs. Chapter 12/13 Test Human Bio 3. Ductus Venosus Closes Before birth: There’s another shortcut (ductus venosus) that sends blood from the umbilical cord directly to the heart, bypassing the liver. After birth: Once the umbilical cord is cut, this shortcut isn’t needed anymore, so it closes. Blood now flows through the baby’s liver like normal. 4. Lungs Start Working Before birth: The baby’s lungs are filled with fluid, and only a little blood goes through them because the placenta does the job of providing oxygen. After birth: When the baby takes its first breath, the lungs fill with air, and blood starts flowing into them to get oxygen. 5. Blood Pressure Increases Before birth: Blood flows easily through the placenta, which has low pressure. After birth: Once the umbilical cord is cut, the placenta is no longer part of the baby’s circulation. The baby’s blood pressure increases to ensure enough blood flows through the body. 6. Oxygen Levels Increase Before birth: The baby gets oxygen from the placenta, and oxygen levels are lower. After birth: The baby starts breathing, and the lungs take over, increasing the oxygen levels in the blood, which helps the baby grow and stay healthy. Maintaining a Healthy Pregnancy: What are the key factors in maintaining a healthy pregnancy? How can nutrition and lifestyle choices impact fetal development and pregnancy outcomes? Teratogens? Chapter 12/13 Test Human Bio Contraception Overview 1. Define contraception and its purpose in reproductive health. 2. Explain why contraception is important for both individual health and public health. Detection of Ovulation 3. Describe two methods used to detect ovulation in women. Rhythm method: An egg can only survive for two days, and sperm for 4 days, so intercourse should not occur between 4 days before and 4 days after ovulation if pregnancy is to be avoided. Extra days in case ovulation is early or late should be incorporated as well. However, womens cycles can be irregular, and there is no sure way of knowing when ovulation occurs. Mucus method: The time of ovulation is predicted by observing the change in mucus of the cervix. After menstruation, there is less, and then approaching ovulation there is an increase. At ovulation, the mucus is clear, then becomes cloudy after. Intercourse is considered ‘safe’ when there is no mucus and more than three days after the last day of clear mucus. Temperature method: Refinement of rhythm method. A female takes her body temperature every morning to determine the time of ovulation more accurately. Ovulation is accompanied by a sharp drop of body temperature and then a rise. Using this, she can predict ovulation and then use the rhythm method. Safely have intercourse 3 days after temperature rises again. Symptothermal method: 4. How can ovulation detection be helpful for both conception and contraception? 5. What hormonal changes are tracked to determine the fertile window in the menstrual cycle? Mechanical Barriers 6. What are mechanical barrier methods of contraception? Give examples. 7. Explain how condoms reduce the risk of pregnancy and sexually transmitted infections (STIs). 8. Compare the effectiveness of male and female condoms as mechanical barrier methods. Spermicides Chapter 12/13 Test Human Bio 9. How do spermicides work to prevent pregnancy? 10. Discuss the effectiveness of spermicides when used alone versus with other contraceptive methods. Hormonal Contraception for Women 11. How do hormonal contraceptives for women prevent pregnancy? 12. Explain the role of estrogen and progesterone in combined oral contraceptive pills. 13. Compare the benefits and potential risks of hormonal contraceptives for women. Hormonal Contraception for Men 14. What are the current developments in hormonal contraception for men? 15. Discuss the challenges and potential side effects associated with male hormonal contraceptive methods. Contraceptive Pills 16. What is the difference between the combined oral contraceptive pill and the progestogen-only pill? 17. How do oral contraceptives regulate the menstrual cycle? Hormone Implants 18. Describe how hormonal implants work as a long-term contraceptive option. 19. What are the advantages and disadvantages of using hormone implants? Intrauterine Devices (IUDs) 20. What is the difference between a copper IUD and a hormonal IUD? 21. Explain how an IUD prevents pregnancy and its duration of effectiveness. 22. What are some potential side effects of IUDs? Emergency Contraception for Women 23. What options are available for emergency contraception, and how do they work? 24. When is emergency contraception most effective, and what factors influence its efficacy? Sterilisation 25. Differentiate between male and female sterilisation procedures. 26. Explain the permanence and risks associated with sterilisation as a contraceptive method. Choice of Contraceptive Methods Chapter 12/13 Test Human Bio 27. What factors should individuals consider when choosing a contraceptive method? 28. How do cultural, religious, and personal beliefs influence the choice of contraception? Reliability and Ethical Issues Around Contraception 29. Rank contraceptive methods from most to least reliable. Discuss the reasons for this ranking. 30. What are some ethical issues surrounding the use and access to contraception? Sexually Transmitted Infections (STIs) 31. Name three common sexually transmitted infections (STIs) and describe their symptoms. 32. How can the use of contraceptives help prevent the transmission of STIs? 33. Characterise between viral and bacterial. Human Immunodeficiency Virus (HIV) 33. How is HIV transmitted, and what are the long-term effects of an HIV infection? 34. Discuss the role of contraception in preventing the spread of HIV. Control of STIs 35. What public health strategies are used to control the spread of STIs? 36. How do education and access to contraception impact STI prevention? Define fertilisation