Transcript Chapter 24
Chapter 24 Development & Inheritance Copyright 2010, John Wiley & Sons, Inc. Fertilization Genetic material from haploid sperm & ovum merge into single diploid nucleus Occurs in Uterine tube= 12-24 hours after ovulation Sperm last ~48 hours Contraction of uterus & uterine tube walls help move sperm Prostaglandins in semen help stimulate Fertilization Sperm Capacitation- ready for penetration Acrosomal enzymes penetrate outer cell layers and one sperm fuses with ovum meiosis II is completed- polar body discarded Fusion of DNA’s diploid = zygote Rapid cell division = cleavage Fertilization Fertilization Early Development Continual division ball of small cells =Morula- enters uterine cavity ~ day 4-5 Reorganizes around fluid filled cavity =blastocyst- about same size as zygote Rearrangement Inner cell mass embryo + Trophoblast fetal part of Placenta Implants after ~2 days ~6 days after fertilization Early Development Early Development nd 2 Week of Development Trophoblast synctiotrophoblast + cytotrophoblast chorion Aids in implantation & secretes hCH Inner cell mass hypoblast & epiblast Cavity in epiblast amniotic cavity Thin membrane develops to surround embryo = amnion filled with amniotic fluid Hypoblast ceils –cover inner surface= wall of yolk sac (from blastocyst cavity) 2nd Week of Development Yolk sac –nutrients for weeks 2 & 3 + source of blood cells (week 3-6) Day 9 – blastocyst embedded in endometrium Lacunae develop in trophoblast Maternal blood and secretions fill Serve as exchange point for embryonic nutrient and waste removal Day 12 - cells from yolk sac + two layers of trophoblast chorion surrounds embryo & becomes fetal part of placenta 2nd Week of Development 2nd Week of Development rd 3 Week Gastrulation= transformation of disc from 2 -> 3 layers= Primary ectoderm, mesoderm & endoderm Cells of epiblast move inward & detach Push out cells of hypoblast endoderm Become mesoderm Rest of epiblast ectoderm Mesoderm notocord vertebrae Ectoderm neural plate neural tube neurulation rd 3 Week rd 3 Week Allantois, Chorionic Villi & Placenta Outpouch of yolk sac allantois Chorionic villi develop with capillaries end 3rd week - capillaries connect to embyronic heart via umbilical arteries & veins Placenta: chorionic villi & maternal endometrium Exchange organ. Some viruses can get through Allantois, Chorionic Villi & Placenta Allantois, Chorionic Villi & Placenta Allantois, Chorionic Villi & Placenta th 4 th 8 Weeks All major organs appear at this time Converted from disc to cylinder 22 days Ear- otic placode & eyes- lens placode 4th week- upper & lower limb buds & heart prominence on surface 5th week- rapid growth of brain & head Neck & trunk straighten, 4 chambered heart, digits appear End of 8th week looks human fetus Fetal Birth Continual growth & differentiation Few new structures added Last 2 1/2 months – half of weight added Fetal Birth Fetal Birth Fetal Birth Fetal Birth Fetal Birth Fetal Birth Fetal Birth Fetal Birth Hormones hCG- maintains corpus lutem progesterone & estrogen Chorion secretes several hormones: estrogens after 3-4 wks & progesterone by wk 6 Peaks at week 9 Rise through pregnancy Progesterone helps keep myometrium relaxes & cervix closed Hormones (cont.) Relaxin- increases flexibility of pubic symphysis & ligaments & relaxes cervix for birth Human placental lactogen (hPL) Rises with fetal mass Prepare mammary glands Support metabolic capacity Corticotrophin-Releasing Hormone (CRH) Helps support birth timing & cortisol production for lung maturation Endocrine Support Trophoblast cells secrete hCG hCG maintains corpus luteum corpus luteum continues to secrete relaxin, progesterone and estrogen & Chorion adds hPL, progesterone + estrogen & CRH Estrogen & progesterone promote growth, development and maintenance of the uterine wall hPl supports maternal growth and changes CRH corticoids lung maturation Changes During Pregnancy Uterus fills up pelvic cavity-3rd month Further growth into abdominal cavity Pushes on intestines, stomach, liver Skin changes: areola, pigmentation around eyes, stretch marks Increased: maternal C.O., blood volume, nutrient consumption appetite , O2 needs ventilation , renal activity Pressure: diaphragm dyspnea Stomach acid reflux & nausea Bladder frequent urination Exercise During Pregnancy Major issues: postural changes with weight gain extra Heat production may affect development early on Care to avoid dehydration Moderate exercise doesn’t hurt May be beneficial Labor & Delivery Labor = expelling fetus from uterus through vagina= parturition Progesterone inhibits contractions Estrogen rises toward end overcome inhibition + prostaglandin production + oxytocin receptors on myometrium Oxytocin contractions Stages of Labor Dilation: onset to complete dilation of cervix Expulsion- dilation to complete delivery Placental- powerful uterine contractions expel placenta Positive Feedback Contractions baby’s head against cervix Neural signals hypothalamus more oxytocin more pushing Stops after birth when cervix is not stretched True labor shows rhythmic pulses of contraction Negative Feedback Systems Interactions Animation Positive Feedback Control of Labor You must be connected to the internet to run this animation. Lactation Prolactin(PRL) milk production PRL increases as pregnancy proceeds Progesterone inhibits milk production Progesterone decreases after delivery Oxytocin milk letdown feedback loop for maintenance Suckling nerve input to hypothalamus maintain PRL & release oxytocin Colostrum Formed during first few days after birth Less lactose & no fat + antibodies Protect infant during first few months of life Good nutrition for infant Oxytocin also speeds maternal recovery Inheritance Passage of hereditary traits- genetics 23 pairs of chromosomes 1 maternal and 1 paternal Each homolog (one of pair) has gene for same traits variant genes for a trait = alleles Genotype= genetic makeup Homozygous = have 2 of same allele Heterozygous= 2 different alleles Phenotype= trait that is visible (brown eyes) Inheritance Dominant allele shows product no matter what the other allele is Recessive allele masked by other allele Can have incomplete dominance phenotype mixture of allele products Inheritance can be simple (one gene) or multiple allele. Inheritance Autosomes & Sex Chromosomes Autosomes: chromosomes where members of pair look alike - 22 pairs Sex chromosomes - look different Females have 2 X chromosomes Males have X and Y chromosomes Maleness from SRY of Y chromosome Traits on X but not Y sex linked inheritance Autosomes & Sex Chromosomes Autosomes & Sex Chromosomes End of Chapter 24 Copyright 2010 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information herein.