Development and Inheritance

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Development and InheritanceChapter 19

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INTRO:Development

DEVELOPMENT

Involves:1. The division and differentiation of cells2. The changes that produce and modify

anatomical structures.Begins at fertilization (conception)Occurs among several periods:

EmbryologicalFetalPrenatalPostnatal

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INTRO:Development

DEVELOPMENT

QUESTION: Why might the science of development important to us as Christians?

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INTRO:Inheritance

INHERITANCE

The transfer of genetically determined characteristics from generation to generation.

Taken to the extreme, this would reference evolutionary biology.

At minimum, we can account for adaptation (aka microevolution).

Genetics is the study of the mechanisms responsible for inheritance.

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Fertilization

Fusion of 2 haploid gametes:Spermatazoon

Paternal genetic information Takes ½-2 hours to go from vagina to upper uterine tube

10,000 of 200,000,000 get to upper uterine tube <100 reach the ovum. Multiple spermatozoa required to breach corona radiata

Ovum Nourishment Genetic programming 2x diameter of spermatozoon 2000x volume of spermatozoon

Produce a zygote of 46 chromosomes Pop culture references:

Tool – 46 & 2

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Fertilization

Activation of the oocyteOvulation happens before the oocyte is completely mature.

It’s development is on pause: fertilization or death

The corona radiata must be affected by multiple sperm.

The collective pool of the enzume hyaluronidase from the acrosomal body of the spermatozoa breaks the bonds between adjacent follicle cells of the corona radiata.

Activation occurs when a spermatozoon contacts the zona pellucida. This membrane is broken by additional acrosomal enzymes to breach the oocyte membrane. This is fertilization.

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Fertilization

An overview of prenatal developmentPrenatal development (before birth)Aka, gestation, pregnancy3 trimesters

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The First Trimester

1st TRIMESTERPeriod of embryological and early fetal development, also the most dangerous.

The basic components of each major organ systems appear.

Only about 40% of embryos survive this trimester.

4 general processes occur:1. Cleavage & blastocyst formation2. Implantation3. Placentation4. Embryogenesis

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The First Trimester

CLEAVAGE & BLASTOCYST FORMATIONCleavage: a series of cell divisions that begins immediately after fertilization.

1st cleavage is 30 hours after fertilization.

Every other cleavage is 10-12 hours after the previous.

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The First Trimester

CLEAVAGE & BLASTOCYST FORMATIONBlasto-meres: (blast – precursor; meros – part): the products of cleavage; genetically identical daughter cells.

The blastomeres form a blastocyst.Blasto-cyst: (precursor cell) a hollow ball with an inner cavity called a blastocoele.

Blasto-coele: (koiloma – cavity).Tropho-blast: (tropho – food): food for embryo.

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The First Trimester

IMPLANTATIONWhen it’s fully formed, the blastocyst contacts the endometrium. At that point, cleavage ends and implantation begins. These structures form:

1. Amniotic cavity2. Gastrulation and germ layer3. Extraembryonic membranes

1. Yolk sac2. Amnion3. Allantois4. Chorion

hCG – human chorionic gonadotropin appears in bloodstream after implantation.

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The First Trimester

PLACENTATION Placenta formationPlacenta – temporary structure in uterine wall.Provides a site for diffusion between the fetal and maternal circulatory systems.

Functions as a temporary endocrine organ for the mother.

EMBRYOGENESIS Making an embryo

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The Second and Third Trimester

End of week 12 is the end of the first trimester

At this point the basic elements of all the major organ systems have formed.

2ND TRIMESTER: Mostly development of organs and completing organ systems. Body proportions change and at the end of the 2nd trimester, the baby looks more familiar as a human.

Amnion:baby’s growth is faster than the amnion’s

Once it touches the chorion, they fuse.

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The Second and Third Trimester

3rd TRIMESTER:Very rapid fetal growth. The baby is fully functional at the beginning of this trimester.

A baby born 1-2 months premature has a decent chance of survival.

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Effects of pregnancy on Maternal Systems

INCREASES IN THE MOTHER’S SYSTEMS:

Respiratory rateTidal volumeBlood volumeNutritional requirements climb 10-30%

GFR increases by 50%Mammary gland size (and secretory activity starts)

Uterus size

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Effects of pregnancy on Maternal Systems

THE UTERUS Increase occurs mostly from enlargement of existing smooth muscle cells rather than by the increase in the total number of cells.

EstrogenStimulating hormoneContraction increaser

Progesterone Inhibiting hormoneContraction decreaser

Also present: prostaglandins and relaxin

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Labor and Delivery

The goal of labor is parturition: forcibly expelling the baby from the uterus.

3 Stages of Labor1. Dilation2. Expulsion3. Placental

Dilation: references the opening of the cervix.

Beginning of labor. Baby slides down cervical canal. Varies greatly, but typically lasts 8+ hours. Contractions sweep from top of uterus toward cervix.

Occur every 10-30 minutes and steadily increase in frequency and strength

Amnion rupture: “water breaks”

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Labor and Delivery

Expulsion: occurs until baby is out of vagina. Complete dilation of cervix, pushed open by baby. Normally takes less than 2 hours.

Newborn arrival is delivery, or birth.

Procedures for complications in first 2 stages:

Episiotomy If vaginal canal is too small, it poses a danger to perineal tearing.

Perineum sometimes intentionally cut (episiotomy) to ensure a clean break in the skin versus jagged edges.

C-section (cesarean section) Incision made through abdominal wall Uterus opened just enough to allow delivery.

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Labor and Delivery

Placental StageOnce baby is delivered, placenta still in uterus

Contraction of uterus tears the connection between the endometrium and the placenta.

Ejection of placenta (afterbirth) normally occurs within 1 hour of delivery

Ejection accompanied by blood loss.

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Labor and Delivery

Premature LaborContractions occur prior to full development.

Survivability dependent largely on birth weight

<14 oz. will not survive – organs cannot support life.

17.6 oz. is the threshold.25-27 weeks increases developmental abnormality risk.

28-36 weeks is called premature delivery

High rate of survivability and low chance of developmental abnormalities.

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Labor and Delivery

Multiple Births1:89 births are twins1:892 births are triplets

Fraternal – dizygotic; “2-zygotes” 2 eggs fertilized simultaneously Can be of the same or different sex 70% of all twin births

Identical – monozygotic; “1 zygote” Happens 2 ways:

1. Blastomeres split early in cleavage 2. Inner cell mass splits before gastrulation If the split is not complete, conjoined twins

develop Same sex 30% of all twin births

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Postnatal Development

Life stages:Neonatal InfancyChildhoodAdolescenceMaturity

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Postnatal development

Neonatal period0-1 month after birthBlood flow changesHeart rate decreasesBody temperature control limitedUrine can’t really be concentrated yet

From the mom, mammary glands first produce colostrum for a few days, then milk.

Colostrum High protein concentration (many are antibodies) Low fat

Milk Water, proteins, amino acids, lipids, sugars, salts, lysozymes (enzymes with antibiotic properties.

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Genetics, Development, and Inheritance

Phenotype: physical displayGenotype: genetic information

Allele: all the forms of a particular gene: A/a i.e. the letter of the alphabet.

Upper-case letter (A): dominant Lower-case letter (a): recessive

Homozygous: same caseHeterozygous: different case

2 members of a pair are homologous22 autosomal chromosomes1 sex chromosome pair

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Genetics, Development, and Inheritance

Types of inheritance:Simple – single pair of allelesPolygenetic – interactions among >1 pair of alleles

Males: XYFemales: XX