EGG AND SPERM: FERTILIZATION

Gamete viability

1. Oocyte viability -12 to 24 hours after ovulation

2. Sperm viability – 1 to 3 days; up to 5

Sperm transport

1. Sperm transport – millions are deposited with force in vagina

2. Leakage – millions leak from vagina

3. Acidic environment – of the vagina; millions more lost

4. Cervical mucus – if not liquefied, millions more will not get through

5. Uterine contractions – distributes through out uterus; phagocytes get them

Sperm capacitation

1. Capacitation – weakening sperm cell membrane to release hydrolytic enzymes

2. Purpose – why not before; wouldn’t want this to happen in male repro system

4. Cholesterol – is depleted as sperm swims through cervical mucus, uterus, u. tube

5. Mechanism – still unknown

Fertilization

1. Acrosomal reaction – from hundreds of ruptured acrosomes

-a. Acrosomal enzymes – digest surrounding cells and material

2. Corona radiata – intercellular cemnent between granulosa cells digested

3. Zona pellucida – holes must be digested in this

4. Fusion – of two gametes; sperm nucleus enters egg

5. Polyspermy – would result if more than one sperm entered; 3n or more

6. Fast block – prevents polysspermy; Na ions enter; depolarizes; sperm can’t bind

7. Slow block – detaches sperm and destroys receptors that can attach to egg

-a. Cortical reaction – also called; cortical granules under membrane; stuff does this

8. Meiosis II – is completed

-a. Second polar body – is produced; disintegrates with first polar body

9. Pronuclei – male and female nuclei swell

-a. Mitotic spindle – forms between them

-b. Rupture – pronuclei spill their chromosomes

-c. Diploid number – is restored

10. Zygote – what the resulting cell is called

EMBRYONIC DEVELOPMENT

Cleavage

1. Cleavage – period of rapid mitotic division of the zygote

2. Morula – at about 3 days; ball consisting of 16 or more cells; still in tube

3. Blastocyst – fluid filled hollow sphere

-a. Trophoblasts cells – single layer flattened cells; becomes placenta

-b. Inner cell mass – cluster rounded one side blastocyst; embryo

Implantation

1. Trophoblast cells – those covering inner cell mass adhere to endometrium

-a. Digestive enzymes – are secreted

-b. Endometrium - thickens at the point of contact inflammatory-like reaction

2. Trophoblast layers - two distinct

-a. Cytotrophoblast - cells of the inner layer retain cell boundaries

-b. Syncytiotrophoblast - multinucleated cytoplasm that invades the endometrium

3. Endometrial cell proliferation - covers over, seals blastocyst from uterine cavity

4. Human chorionic gonadotropin (hCG) - LH like, trophoblast, corpus lureum

-a. Chorion - develops from the trophoblast cells continues hormonal stimulation

5. Placenta – 2 to 3 month; placenta major producer of estrogen and progesterone

6. Corpus luteum - degenerates after 2 months

7. Pregnancy test - use antibodies against hCG

8. Nutrition - of the embryo changes

-a. Endometrial cells - digested initially

-b. Placenta - nutrients and oxygen, carrying away waste by the 2nd month

Placentation

1. Placenta - a temporary organ; originates from embryonic and maternal tissue

2. Chorion - the trophoblast give rise to

-a. Extraembryonic mesoderm – develops on inner side of trophoblast; now chorion

3. Chorionic villi - extensions of chorion, into the stratum functionalis

4. Lucanae (intervillus spaces) - erosion of stratum functionalis, blood filled spaces

5. Decidua basalis - endometrium between chorionic villi and stratum basalis

6. Decidua capsularis - endometrium between embryo, uterine cavity, degenerates

7. Placental layers - chorionic villi and the decidua basalis

8. Exchange function - fully functioning by 3rd month, exchanges well before

9. Hormone function - role of the chorion

-a. hCG - produced from the very beginning

-b. Steroidal hormones - estrogen and progesterone production increase through out

Embryonic membrane

1. Amnion - surrounds embryo, physical protection, transparent membranous sac

-a. Amniotic fluid - cushioned from trauma, from maternal blood, fetal urine

2. Yolks sac - hangs from the ventral surface of the embryo

-a. Nutritive function - contains little yolk because placenta provides most nutrients

-b. Gut - forms part of the digestive tube

-c. Blood cells - first producer of these

3. Allantosis - from out cropping from the caudal end of the yolk sac

-a. Shelled eggs - animals develop in these use this to store excreta

-b. Placental mammals - is used to construct the umbilical cord

5. Chorion – forms placenta encloses embryo, all other membranes

Gastrulation: germ layer formation

1. Embryonic disc - 3rd week after fertilization cellular; 2 layered disk

2. Primitive streak - after amnion forms; raised grove, longitudinal axis

3. Cell migration - migrate to primitive streak; laterally between upper and lower

4. Ectoderm - dorsal boundary of the embryonic disc; skin and nervous system

5. Endoderm - ventral surface; epithelial lining of digestive, respiratory, urogenital

6. Mesoderm - between endoderm and ectoderm; forms almost everything else

-a. Notochord - a rod of mesoderm; forms beneath the primitive streak

-b. Mesenchyme - unlike endoderm, ectoderm (epithelial, adhere), star shaped

Organogenesis: differentiation of ectoderm

1. Neuralation - the differentiation of the ectoderm into the brain and spinal cord

-a. Notochord - releases chemical messages to induce neuralation

-b. Neural plate - 17 day old; thickening in the ectoderm above the notochord

-c. Neural grove - 18 day old; beginning of the folding in of the neural plate

-d. Neural fold - by day 21 the neural grove deepens

-e. Neural tube - by day 23 superior margins fuse; detaches from surface ectoderm

-f. Neural crest cells – become cranial, spinal, sympathetic ganglia; adrenal medulla

-g. Brain - anterior end neural tube

2. Skin - most remaining ectoderm becomes the epidermal layer of the skin

3. Other structures - cornea, mucosa (oral, nasal cavities, sinuses) endocrine (some)

Organogenesis: differentiation of endoderm

1. Cylindrical body –from folding of the 3 layered embryonic disc

2. Primitive gut - the tube of endoderm becomes the epithelial lining

-a. Yolk sac – part of it enclosed as part of the gut

3. Respiratory mucosa - forms as out pocketing of the foregut

4. Hindgut - reproductive and urinary epithelial lining associated glands

5. Midgut endoderm - gives rise to liver and pancreas

6. Mesoderm - forms the walls of these organs

Organogenesis: differentiation of mesoderm

1. Notochord - first mesoderm differentiation; remnant, part intervertebral disc

-a. Nucleus pulposus – remnant; springy part of intervertebral disc

2. Mesodermal aggregates - on sides of notochord; somites, intermediate, lateral

3. Somites - series paired mesodermal aggregates; flank the notochord laterally

-a. Sclerotome - form the vertebrae and ribs

-b. Dermatome - dermis of the dorsal part of the body

-c. Myotome - muscles of the trunk, neck, and most of the limbs

4. Intermediate mesoderm - forms gonads, skin, and adrenal cortex

5. Lateral mesoderm - consist of paired mesodermal sheets

-a. Somatic mesoderm - dermis (ventral body), parietal serosa, limb buds

-b. Splanchnic mesoderm - forms heart, blood vessels; contributes to viscera

6. Coelom - ventral body cavity resulting from the folding of the

7. Mesodermal tissue – others include

-a. Muscle - skeletal, cardiac, and smooth

-b. Connective tissue - bone, cartilage, and other connective tissues

-c. Endothelium - of blood vessels and lymphatics

8. Cardiovascular system – from splanchnic mesoderm (already stated)

FETAL DEVELOPMENT

Fetal development

1. Fetus – from weeks 9 to 40

2. Differentiation – still occurring; not just getting bigger

3. Ossification – begins at about week 8

4. Notochord – begins degenerating around week 9

5. Myelination – of spinal cord; week 21

Fetal circulation

1. Umbilical vein - oxygenated blood from the placenta to the fetus

2. Liver - some blood through, out the hepatic veins; nutrients to liver cells

3. Ductus venosus - venous shunt bypasses liver into the inferior vena cava

4. Foramen ovale – blood from right to left atrium; bypasses pulmonary circuit

5. Ductus arteriosus - from pulmonary trunk to the aorta

6. Umbilical arteries - branches internal iliac; poorly oxygenated; metabolic waste

7. Newborn circulation - umbilical vein, arteries and shunts are occluded

-a. Ligamentum teres - remnant of the umbilical vein

-b. Ligamentum venosum - remnant of the ductus venosus

-c. Fossa ovalis - remnant of the foramen ovale

-d. Ligamentum arteriosum - remnant of the ductus arteriosus

-e. Medial umbilical ligaments - remnants of the umbilical arteries

Fetal testing

1. Amniocentesis - after the 14th week; amniotic fluid, several weeks, karyotype

2. Chorionic villi sampling – tube suctions piece of chorionic villi; 8 wks. karyotype

3. Risk - both procedures so they are usually not done unless the risk is worth it

PREGNANCY

Hormonal changes

1. Human chorionic gonadotropin – LH like; keeps corpus luteum secreting hormones

2. Chorion – produces estrogen and progesterone at about 3 months

3. Relaxin – corpus luteum, then chorion; relaxaton of pubic symphysis, pelvic ligaments

Anatomical changes

1. Chadwick’s sign - purplish hue of vagina, increased vascularity engorgement

2. Breast - engorge with blood, enlarge, and areolar darkens; estrogen, progesterone

4. Uterine enlargement – from fist size to occupying most of abdominopelvic

5. Lordosis - increased lumbar curvature may result in back aches

6. Waddling gait - pubic symphysis and pelvic ligaments relax

7. Weight gain -29 pounds; fetus, placenta, organs and breast, blood volume

Metabolic changes

1. Nutrition - especially protein, calcium, and iron

-a. Folic acid - may prevent spina bifida an anencephaly

-b. Caloric increases - no more than 300 extra calories per day

2. Basal metabolic rate – increases by 15% second trimester

3. Blood calcium – kept high; Parathyroid hormone; fetal bone growth

Physiological changes

1. Gastrointestinal system – hormones; squeeze

-a. Morning sickness – nausea; first few months levels of steroid hormones

-b. Heartburn - reflux stomach acid; stomach is crowded by the uterus

-c. Constipation - mobility of the digestive system is reduced

2. Urinary system – several changes

-a. Urine production - increase urine; also disposing fetal metabolic waste

-b. Stress incontinence - compress bladder; urination increase in frequency, urgency

3. Respiratory system - includes

-a. Nasal mucosa – estrogen, nasal mucosa edematous, stuffiness, nose bleeds

-b. Vital capacity - increases

-c. Respiratory rate - increases

4. Cardiovascular system - include

-a. Blood volume - increases 25 to 40%; including cells; fetal needs

-b. Cardiac output - ↑ blood pressure, pulse, pump greater circulatory volume

-c. Varicose veins – compression, uterus, impair blood return from the lower limbs

PARTURITION

Initiation of labor

1. Estrogen - levels rise to their highest levels the last couple weeks

-a. Oxytocin receptors - on myometrial cells become numerous

-b. Progesterone quieting - of uterine smooth muscle is antagonized

2. Braxton Hicks contractions - weak, irregular contractions (false labor)

3. True labor false labor converted; two important chemical signals

-a. Oxytocin -by fetus; uterine stimulant; causes placenta release prostaglandin

-b. Prostaglandin - also a powerful uterine muscle contractor

4. Hypothalamus – emotion, physical stress posterior pituitary release oxytocin

5. Positive feedback - ↑oxytocin, ↑uterine contraction, ↑cervical pressure, ↑oxytocin

Stages of labor

1. Dilation stage (stage 1) - onset of labor to fully dilated by the infants head; 10 cm

-a. Infants head - forces against the cervix making it thinner and dilating it

-b. Duration - longest lasting 6 to 12 hours, or even longer

-c. Engagement - head in pelvis; rotates, greatest dimension anteroposterior line

2. Expulsion stage (stage 2) - from full dilation to delivery

-a. Contractions – stronger and more frequent

-b. Duration - 50 minutes first birth and 20 for others

-c. Crowning - largest diameter of baby’s head distending the vulva

-d. Episiotomy - incision made to widen the vagina to reduce tissue tearing

-e. Vertex presentation - head first acts as a wedge to dilate; normal

-f. Breach presentation- buttocks first, other nonvertex presentation; complications

3. Placental stage (stage 3) - delivery of the placenta; within 30 minutes after birth

-a. Uterine contractions - compress vessels, prevent bleeding, detaches placenta

-b. Afterbirth - placenta and fetal membranes

-c. Umbilical cord - is tugged to remove placenta; must remove all; prevent bleeding

NEONATAL ADJUSTMENTS

Neonatal adjustments

1. Neonatal period - four week period immediately after birth

2. Respiratory control centers – detached; CO2; central acidosis; first inspiration

3. Vascular adjustments - several

-a. Umbilical arteries - constricts and becomes fibrosed

-b. Umbilical vein - becomes the ligamentum teres (round ligament of the liver)

-c. Ductus venosum – collapses; blood stops flowing through umbilical vein

-d. Foramen ovale - left heart pressure ↑; right heart pressure ↓ closes a flap

-e. Ductus arteriosus - constricts and is converted to the ligamentum arteriosum

4. Transitional period - 6 to 8 hours after birth; sleep wake cycle develops

LACTATION

Lactation

1. Prolactin - released by anterior pituitary stimulates milk production

2. Colostrum – few days before milk less lactose fat, more protein, Ig A

3. Mechanical stimulation - mechanoreceptors impulse; hypothalamus, prolactin

4. Let-down reflex - the ejection of the milk from the alveoli

-a. Nipple pressoreceptors - activated due to suckling of infant

-b. Hypothalamus – posterior pituitary; oxytocin

-c. Oxytocin – myoepithelial cells contract

5. Maternal advantages - oxytocin helps shrink uterus

6. Neonate advantages - several

-a. Nutrition – fats, iron is better absorbed amino acids are metabolized better

-b. Protection - along with Ig A, there is lysozyme, complement, and more

7. Nursing stops - stimulus for prolactin stops and so does milk production

VOCABULARTY OF GENETICS

General

1. Genetics - the study of the mechanisms of heredity

2. Gregory Mendel - first proposed the rules of gene transmission in the mid 1800’s

3. Sex chromosomes - a pair of chromosomes, X and Y, which determine genetic sex

4. Autosomes - the other 22 pairs; determine the expression of most traits

5. Karyotype - diploid chromosomal complement

6. Genome - the diploid genetic (DNA) make up

Gene pairs (alleles)

1. Locus - the location of a gene on chromosomes

2. Allele - same location on homologous chromosomes; code for forms of the gene

3. Homozygous - when both alleles code for the same form of the trait

4. Heterozygous - when both alleles code for different forms of the trait

5. Dominant - when one allele mask the expression of the other, capital letter (J)

6. Recessive - the allele which is being masked, small letter (j)

7. Homozygous dominant - both alleles code for the dominant trait (JJ

8. Heterozygous dominant - 1 dominant; 1 recessive (Jj)

9. Homozygous recessive - both code for the recessive trait ( jj)

10. Allele frequency - the dominant is not always the most frequently expressed

Genotype and phenotype

1. Genotype - genetic make up includes jj, Jj, and JJ1. Genotype - genetic make up includes jj, Jj, and JJ

2. Phenotype - the outward expression of the genotype

SEX AND GENETIC VARIABLITY

Segregation and independent assortment of chromosomes

1. Metaphase I - the pairs of homologous chromosomes pair up

2. Segregation - members of allele pair go to different gametes during meiosis

3. Independent assortment - allele pairs randomly distributed

4. 2ⁿ- calculate the number of possible gametes; n = 23 leads to 8.5 million

Crossover of homologues and gene recombination

1. Linked genes - genes which are on the same chromosome; inherited as a block;

2. Recombinant chromosomes - can result during meiosis as

3. Crossover - breaks occur between linked genes

-a. Chiasma - name for the crossover

-b. Number - many crossovers can occur during synapsis

-c. Chromosome length - the longer the greater the number of crossing over

Random fertilization

1. Random fertilization – incredible amount of variability

2. Possible number - 72 trillion different combinations (8.5 million • 8.5 million)

TYPES OF INHERITANCE

Dominant-recessive inheritance

1. Human inheritance - few visible phenotypes are result of this type of inheritance

2. Punnett square - combinations of genes in offspring; parents of known genotype

-a. Percentages - possible percentages genotype and phenotype

3. Phenylketouria – phenylalanine metabolism disorder; mental retardation; recessive

4. Dominant traits - listed

-a. Normal traits - widows peak, dimples, freckles, and detached earlobe

-b. Dominant disorders – rare; death of the fetus or child; Huntington’s

5. Recessive traits - listed

-a. Positive traits - such as normal vision and not having astigmatism

-b. Recessive disorders - most disorders; Tay-Sachs, cystic fibrosis

-c. Carriers - people who are heterozygous dominant for a

Incomplete dominance (intermediate inheritance)

1. Heterozygous - between homozygous dominant and homozygous recessive

2. Sickle cell anemia - both alleles for sickle cell anemia suffer all the symptoms;

3. Sickle cell trait – heterozygous; healthy but may suffer when oxygen level low

Multiple-allele inheritance: Codominance

1. Multiple-allele inheritance - more than two forms of gene which can be present

2. ABO blood groups - three possible alleles: I^A, I^B, and i with the

3. Codominant – in ABO blood group; I^A and I^B are codominant

4. Type A – phenotype: genotypes I^AI^A or I^Ai

5. Type B – phenotype: genotype I^BI^B or I^Bi

6. Type AB – phenotype: genotype I^AI^B

7. Type O – phenotype: genotype ii

Sex determination

1. Sex chromosomes – 23 pair, not homologous like the autosomal

2. Females – have X and X

3. Males – have X and Y

Sex-linked inheritance

1. Sex linked - genes carried on sex chromosomes

2. Sex chromosomes - are not true homologous chromosomes

3. X-linked – only on the X chromosome; usually case as it has 2500 genes

-a. Recessive - expressed if on X chromosome in the male; hemophilia, color blind

4. Y-linked - only on the Y chromosome which is; 15; hairy pinna

Polygene inheritance

1. Polygene inheritance - phenotypes depend on different gene pairs acting together

2. Skin color - controlled by three sets of alleles

3. Continuous variation - or qualitative variation in the phenotype considered

4. Bell shaped curve - when the phenotypes are plotted on a graph

5. Other examples - height and eye color