Topic 8 Growth and Development in Human and Plants PDF

Prepared by : Norlaila Najwa bt Rahman Learning Outcome On completion of this chapter, students should be able to: Outline the process of fertilisation in human Describe the human menstrual cycle Describe the stages of embryonic development Describe the fetal development from embryo t...

Prepared by : Norlaila Najwa bt Rahman Learning Outcome On completion of this chapter, students should be able to: Outline the process of fertilisation in human Describe the human menstrual cycle Describe the stages of embryonic development Describe the fetal development from embryo to fetus. Explain the identical, non-identical and conjoined twins  Human menstrual cycle After puberty in women, the ovaries and the uterus go through a series of changes that recur approximately every 28 days – the menstrual cycle. Ovarian Cycle Uterine Cycle 1 2  Uterine Cycle 3 4 Hormonal Control of Menstrual Cycle The menstrual cycle is coordinated by the anterior pituitary gland and ovaries The anterior pituitary gland secretes follicle stimulating hormone (FSH) and luteinising hormone (LH) FSH & LH control the activity of the ovaries. The corpus luteum secretes both oestrogen (stimulate endometrium to grow, thicken and develop numerous blood capillaries) and progesterone (to maintain the uterus lining) Hormonal Control of Menstrual Cycle FSH and LH are in relatively high concentrations during menstruation and so cause one follicle to mature The presence of FSH and LH stimulates oestrogen to be produced by the cells surrounding the follicle Oestrogen however, has a negative feedback on FSH and LH so their concentrations decrease  Hormonal Control of Menstrual Cycle When oestrogen reaches a level two to four times initial value, it stimulates a serge of LH and FSH causing the graffian follicle to burst and ovulation occurs The corpus luteum is now formed and so oestrogen and progesterone are released, Oestrogen progesterone also inhibits secretion of FSH and LH so that no more follicles develop Corpus luteum begins to degenerate and so decrease in progesterone causing menstruation Conception A female egg - ovum is released If not fertilized, it disintegrates and is flushed away with menstruation If it fertilized in the fallopian tube by a sperm - conception occurs This union is what we called as zygote Fertilization has three important genetic consequences : 1) restoration of the diploid chromosome number 2) determination of the sex of the offspring 3) allows genetic variation Fertilization The egg is viable for 12 to 24 hours after ovulation Sperm are viable for 12 to 48 hours after ejaculation Sperm cells must make their way to the uterine tube for fertilization to be possible Fertilization occurs in fallopian tube 12 to 24 h after ovulation Penetration of Sperm 1) Capacitation - Occurs while migrating through female reproductive tract - Removal of a layer of glycoprotein and plasma protein from the outer surface of the sperm by enzymes in uterus - Cholestrol is also lost from the surface membrane around the sperm head, weakening the membrane - Sperm able to swim more actively - Capacitated sperm penetrate the corona radiata, contact the zona pellucida and undergo acrosomal reaction Penetration of Sperm 2) Acrosomal Reaction - sperm binds to the zona pellucida and undergoes acrosomal reaction - enzymes hyaluronidase are released near the oocyte - hundreds of acrosomes release their enzyme to digest the zona pellucida -once sperm penetrates the zona pellucida, the plasma membrane of the head of the sperm fuses with the plasma membrane of the oocyte Penetration of Sperm 3) Cortical reaction - Sperm reaches the zona pellucida and penetrates it - The cortical granules released their contents to cause zona pellucida to thicken and harden forming the “fertlization membrane” to prevent the entry of other spermatozoan. Development of zygote As early as 12 hours after fertilization, you can see the two bundles of genetic material( two pronuclei) one from each parent. By 18-20 hours after fertilization, these pronuclei fuse and starts out as two cells become one ( called a zygote ) Prenatal Baby Development Development of the baby during the period before birth Develops in three stages Zygote Embryo Fetus  Stages in Embryonic Development Upon fertilization, several mitotic divisions occur (cleavage) while the zygote continues its journey to the uterus. The cytoplasm of one large cell, the zygote, is being partitioned into smaller cells called blastomeres. The blastomeres forming the outer layer of the blastula is called a trophoblast and this layer differentiates and forms a thickened mass of cells called the inner mass cells. At this stage, it is called blastocyst. The zygote is now about a week old. Stages in Embryonic Development The outer wall of the blastocyst is sticky and adheres to the uterine wall and burrows itself into the endometrium, a process called implantation. The trophoblast will form the foetal portion of the placenta The inner cell mass grows and will become the embryo. Organogenesis After that, gastrulation begins. Gastrulation involves a series of cell migrations to positions where they will form three primary germ layers. Gastrulation leads to organogenesis or organ formation. The three layers formed are the ectoderm, endoderm and mesoderm. The three germ layers give rise to specific organs and organ system. Germ layers Organs Ectoderm Forms the epidermis, nervous system and sensory system Mesoderm Forms the innermost lining of the digestive tract, as well as associated digestive organs such as the pancreas and liver, also found in parts of the reproductive system Endoderm Forms most other organs and tissues including the kidneys, heart, muscles, dermis and the notochord Embryonic Development ØThe 3 germ layers give rise to 4 extraembryonic membranes : chorion, amnion, allantois and yolk sac ØThey protect the embryo, prevent it from drying out, help in obtaining food and oxygen and eliminating wastes The outermost membrane, the chorion, encloses the entire embryo Like the chorion, the amnion encloses the entire embryo. The amniotic cavity, the space between the embryo and the amnion becomes filled with amniotic fluid Embryonic Development The allantois is an outgrowth of the developing digestive tract. Allantois is small and nonfunctional, except that its blood vessels contribute to the formation of umbilical vessels joining the embryo to the placenta A yolk sac connected to the embryo, it walls serve as temporary centers for the formation of blood cells. The developing fetus connected to the placenta by the umbilical cord. The umbilical cord carries blood vessels to and from the placenta Roles of Chorion Chorion is the outer trophoblastic layer Chorion helps in the process implantation Chorion forms the placenta Chorion absorbs nutrients from the endometrium Later many chorionic villi are formed to increase the surface area for absorption of nutrients Chorion fuses with amnion to form protective layer for developing fetus Roles of Amniotic fluid Fluid found in the cavity first formed in the inner cell mass. § enables the fetus to grow and move freely § prevent the embryo from drying out § protects the fetus from abrupt temperature changes § the fluid can cushion any impact on the fetus from outside the body § serves as lubricant so that the wall of the uterus does not rub against the fetus during birth Roles of Placenta Mutual exchange of substances between mother and fetus Oxygen, water, amino acids,glucose, mineral ions and vitamins diffuse from mother's blood to fetus CO2 , urea, uric acid and other wastes dffuse from fetus blood to the mother Placenta disallows pathogens and toxins to cross into the fetus blood excepts HIV and Rubella viruses Placenta prevents sex hormone from mother diffusing to fetus blood Placenta produces progesterone and oestrogen which control the development of the uterus wall, mammary glands and prevent ovulation and menstruation Embryonic Development Fetal Development Human gestation period or the duration of pregnancy, averages 266 days (38 weeks or about 9 months) Development from conception to birth is divided into 3 stages called trimesters. Each trimester is 3 months First trimester- fetus forms most of its organ Second and third trimesters - growth and enlargement of the fetus Fetal Development At 1 months : Development of all organ system Beginning of the eye can be seen, as well the bulging heart& the umbilical cord Fetal Development At 2 months : The embryo becomes easily recognizable as human After the 8th week, the developing human is called a fetus About the size of the kidney bean Fetal organ system start to function & the bones start to harden Has slightly webbed fingers Fetal Development Months 3 & 4 : During the third month, the kidneys develop sufficiently for the fetus to begin elimination some wastes as urine into the amniotic fluid The limbs are well develop, bone starts to harden, teeth form Eyelashes, eyebrows, fingernails begin to appear Becomes possible to distinguish the sex of the baby Heartbeat able to be heard with a stethoscope Fetal Development At 5-7 months: The fetus seems to respond to external sound (if you talk/sing, the fetus can hear you) Mother begins to feel movement Doing various flip-turns & kicks inside amniotic fluid Lanugo (fine hairs) covers the fetus The fetus is also covered by a substance called vernix to help protect the delicate skin Cerebrum grows rapidly At 7 months, can survive if born early Fetal Development At 8 - 9 months : The fetus sleeps 90 - 95 % of the day & sometimes experiences REM sleep, an indication of dreaming Fetus show grasping and sucking reflexes, may suck its thumb Get antibodies from mother before birth Probably turned head down in preparation for birth At birth, the average full-term baby weights about 3kg ad 52 cm in total length Fetal Development Premature baby : Any infant born before 37 weeks is considered premature Babies born at 28 weeks or less are at greatest risk of death and severe defects Babies born closer to 37 weeks have a greater chance of survival with competent medical care A baby that weights less than 2.5 kg is considered low birth weight and is at risk even if not premature Identical twins/ Monozygotic/ Maternal twins Occur when a single egg is fertilized to form one zygote which then divides into two separate embryos The two embryos develop into fetus sharing the same womb and two identical cells will result have identical genes Conjoined twins Very rarely, the two inner cell masses do not completely separate and give rise to conjoined twins Conjoined twins who are physically attached and usually share one or more body parts. Fraternal Twins / Dizygotic twins Usually occur when two fertilized eggs are implanted in the uterine wall at the same time Two eggs are independently fertlized by two different sperm cells The two eggs form two zygotes Each zygote has its own distinctive genetic endowment, so the individuals produced are not identical They have separate placenta They have same or opposite sex and they don't have to look at all alike Learning Outcome On completion of this chapter, students should be able to: Explain the roles of hormones during pregnancy, labour and lactation Explain the birth control method Describe the process of formation of seed in plants Explain the types of germination Pregnancy Test Doing a pregnancy test If you have missed a period and recently had unprotected sex, you may be pregnant. When you can do a pregnancy test You can carry out most pregnancy tests from the first day of a missed period. If you don't know when your next period is due, do the test at least 21 days after you last had unprotected sex. You can do a pregnancy test on a sample of urine collected at any time of the day. Where you can get a pregnancy test You can buy pregnancy testing kits from pharmacists and some supermarkets. They can give a quick result and you can do the test in private. Pregnancy - Hormone If pregnancy occurs, the blastocyst formed will secrete human chorionic gonadotrophin (HCG) to stimulate the continual release of progesterone and oestrogen from corpus luteum The level of progesterone increases to maximum around eighth month and decreases to minimum at the end of pregnancy. The level of oestrogen increases to maximum at the end of pregnancy Pregnancy - Hormone Roles of progesterone Roles of oestrogen a) maintains the lining of the uterus a) it controls the growth of the uterus and control the growth of the uterus especially myometrium muscles b) stimulate the development of milk b) stimulates development of milk glands duct system c) inhibits release of FSH and prevents c) inhibits release of FSH and prevents menstruation menstruation d) increases the sensivity of uterus d) inhibits contraction of myometrium myometrium to oxytocin so the muscle relaxes and helps to prevent miscarriage The secretion of progesterone and oestrogen from corpus luteum is slowly replaced from the placenta as it develops The Process of Parturition Parturition is the process of birth occurs after full term of gestation about 40 weeks in normal birth There are many factors causing the start of birth process : a ) During the final month of pregnancy, the uterus becomes more and more sensitive to oxytocin. b) oxytocin causes contraction of the smooth muscle of the myometrium c) prostaglandins increase the power of contractions d)The release of oxytocin occurs in 'waves' that start the labour. e) The onset of contractions of the myometrium marks the beginning of 'labour pains'. The Process of Parturition Three stages of labour : - Dilation stage - Expulsion stage - Placental stage The Process of Parturition - First Stage The first stage is when the cervix dilates. a) Labour starts with very mild contraction. Contractions gradually get stronger and more frequent. The more uterus contracts, the greater the stimulation of stretch receptors in the uterus and cervix b) More prostaglandins are secreted by the uterus and result in more powerful contractions c) Contractions spread down the uterus and are strongest from top to bottom, so pushing the baby downwards d) The amniotic 'bag' bursts (the water break) at around this stage releasing the amniotic fluid e) The cervix will gradually dilate during the contractions. When the cervix is fully dilated to about 10 cm, it is wide enough for the baby head to pass through f) the dilation stage is the longest part of labour, lasting 6-12 hours or more The Process of Parturition - Second stage Expulsion stage a) Contraction reaches maximum intensity, occuring at 2 to 3 minutes intervals and lasting a full minute b)Expulsion continues until the fetus has emerged from the vagina usually head first c) Once the head of the baby comes out, the rest of the body can easily slipped out with the amiotic fluid as lubricant d) The baby take in the first breath of air usually aided by crying to make use of the lungs for the first time e) the umbilical cord is clamped and cut. f) In most cases, the expulsion stage lasts less than 2 hours g) The arrival of newborn infant into the outside world is delivery or birth The Process of Parturition - Third stage a) The placenta is delivered within 15 minutes after the delivery of the baby b) the release of the placenta, umbilical cord and the embryonic sac are called 'afterbirth' c) the last few powerful contractions of the uterus cause the placenta to detach from the uterus wall and to come out through the vagina Lactation The production and secretion of milk from the mammary gland Lactation is an aspect of postnatal care unique to mammals In response suckling by the newborn, the hypothalamus signals the anterior pituitary to secrete prolactin, which stimulates the mammary glands to produce milk. Suckling stimulates the secretion of a posterior pituitary hormone, oxytocin which triggers release of milk from the mammary glands. During the first day or so after birth, the breasts produce creamy milk called colostrum, that is rich in antibodies but low in fat and lactose - help protect the newborn baby until its own immune system matures Later, high fat and lactose content of milk help the baby to grow rapidly Contraception There are many types of contraception widely used now days for family planning purposes. Each method has its advantages and suits special cases and not necessarily suits others the choice of contraception depends on different needs of the patients like the period of contraception and also doctor should decide which method suits needs more. No method of contraception is completely effective. Types:- 1. Natural contraception (calendar) 2. Mechanical contraception (devices provide barrier) 3. Hormonal contraception (pill, injection) 4. Surgical contraception (tubal ligation, vasectomy) Birth Control Pills Pills are safe and effective when taken properly Pills are over 99% effective How does the pills work? Stops ovulation Thins uterine lining Thickens cervical mucus Depo-Provera Birth control shot given once every three months to prevent pregnancy 99.7% effective preventing pregnancy No daily pills to remember The shot works the same way as the pill IMPLANTS Implants are placed in the body filled with hormone that prevents pregnancy Physically inserted in simple 15 minute outpatient procedure Plastic capsules the size of paper matchsticks inserted under the skin in the arm 99.95% effectiveness rate  SPERMICIDES Chemicals kill sperm in the vagina Different forms: -Jelly -Foam Some work instantly, others require pre-insertion Only 76% effective (used alone), should be used in combination with another method i.e., condoms MALE CONDOM üMost common and effective barrier method üLatex should only be used in the prevention of pregnancy and spread of STI’s (including HIV) Typical effectiveness rate = 88% available Combining condoms with spermicides raises effectiveness levels to 99%  FEMALE CONDOM Made as an alternative to male condoms Polyurethane Physically inserted in the vagina Typical rate = 79% Woman can use female condom if partner refuses It is inserted into the vagina. The closed end covers the cervix. Intended for one-time use and then discarded. blocking sperm from entering the cervix. The sponge also contains a spermicide that kills sperm. It is available without a prescription. CERVICAL CAP Latex barrier inserted in vagina before intercourse “Caps” around cervix with suction Fill with spermicidal jelly prior to use Can be left in body for up to a total of 48 hours Must be left in place six hours after sexual intercourse Perfect effectiveness rate = 91% Typical effectiveness rate = 80% INTRAUTERINE DEVICES (IUD) T-shaped object placed in the uterus to prevent pregnancy A Natural childbirth required to use IUD Extremely effective without using hormones > 97 %  TUBAL LIGATION Surgical procedure performed on a woman Fallopian tubes are cut, tied, prevents eggs from reaching sperm Failure rates vary by procedure, from 0.8%-3.7% May experience heavier periods VASECTOMY Male sterilization procedure Ligation of Vas Deferens tube Faster and easier recovery than a tubal ligation Failure rate = 0.1%, more effective than female sterilization Seed Development Seed are produced by flowering plants, the angiosperms and a group of plants often called evergreens, the gymnosperms, such as pines and firs. The inner part of each seeds is an embryo, which is a young plant The embryo and its food supply are enclosed by a seed coat or testa formed from the integuments of the ovule. The seed coat is often thin and papery, like that covering each peanut seed. Seed development Monocot are flowering plant that produce seeds each with only one cotyledon, example corn. Dicots are flowering plants that produce seeds each having two cotyledons, example bean. The radicle is the embryonic root. The plumule is the embryonic shoot. The region of the embryo above the attachment of cotyledons is the epicotyl, which give rise to the shoot, made up of stem and leaves Seed development The region below the attachment point is the hypocotyl, radicle is often at the tip of the hypocotyls. The embryo of monocot seed is enclosed by two sheaths, a coleoptile, which cover the young shoot(plumule) and the coleorhiza, which cover the young root(radicle) The cotyledons will absorb nutrient from the endosperm and transfer them to the embryo when the seed germinates. Seed germination In order for germination to occur, certain requirement must be met which will vary from species to species. First and foremost, seed must be viable, meaning it must be capable of germination Proper storage of seed also factors in seed germination. Seed must be placed in proper environmental conditions; optimal moisture, proper temperature and oxygen must all be considered. Light also may or may not be needed for seed germination Seed germination - cont.. Imbibition (absorption) of water is the first process that occurs during germination. Once imbibition of water has occurred, activation of enzymes is initiated. These enzymes function in the breaking down of storage material within the seed into simpler compounds such as sugars, which are utilized by the embryo for germination The first organ emerge from seed is the radicle then plumule. The radicle grow downward into the soil whereas plumule grow upward to the soil surface. Seed germination - cont.. Seedling growth can be of two types: ØEpigeal germination and ØHypogeal germination Both refer to the position of the cotyledons during germination Epigeal Germination Epigeal (epi = above) germination occur when the hypocotyl elongate and pulling the cotyledon above the surface of the soil. The cotyledons function as leaves until a true leave emerge. Example bean Stimulate by light, the hypocotyls straightens, rising the cotyledons and epicotyl The epicotyl spread its first leaves, expand become green and begin making food by photosynthesis Hypogeal Germination Hypogeal (hypo = under) germination occur when the cotyledons remains underground with only the shoot (plumule) emerging from the soil surface. The radicle grows downward through a coleorhiza, from which primary root develops Coleoptile pushes upward through the soil and into the air. Once above the soil, the first leaves burst out of the coleoptile and begin making food by photosynthesis Factors affecting seed germination 1. Water 2. Oxygen 3. Temperature 4. Light 1) WATER Germination starts with the absorption of water (imbibition). The absorbed water cause the seed to expand and the testa ruptured. 2) OXYGEN Another factor affecting germination is concentration of oxygen available to the seed. Germinating seed are very metabolically active - respiration converts the stored food in the seed into energy for germination Oxygen deficiency occurs if seeds are planted in flooded or compacted soil 3) Temperature The optimum temperature is different by plant species The optimum temperature for most crop plants is around 25oC to 30 oC. Germination rate is low at lower temperature 4) Light needed for photosynthesis process 5) pH Soil pH also affects the availability of nutrients and minerals needed for plant growth and metabolism Seed dormancy ‘Dormant’ means ‘sleeping’ or ‘resting’ Seed dormancy in nature usually exists to delay germination until favorable environmental conditions are present for seed germination, growth and development. Two types of seed dormancy have been recognized; seed coat dormancy and embryo dormancy Basically, seed coat dormancy prevents the embryo inside from imbibing water. Embryo dormancy is due to the presence of growth inhibitors, especially ABA (abscisic acid), as well as the absence of growth promoters, such as GA (gibberellic acid). The End