Growing Fetus Ppt

8/6/2019 Growing Fetus Ppt

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(8th edition)



Development - the gradual modification of anatomical structures during theperiod from fertilization to maturity

y Major Phases of Development

fertilization - fusion of the male and femalegametes

embryological development - first two monthsafter fertilization

fetal development - from the beginning of the9th week until birth

postnatal development - commences at birth

(8th edition)



Terms to denote Fetal Growth

OVUM

- From ovulation to fertilization

ZYGOTE

- From fertilization to implantation

EMBR Y O

- From implantation to 5-8 weeks

FETUS

- From 5-8 weeks until term(8th edition)



Gestation - the time spent in prenatal

development

y Can be divided into 3 three month trimesters:

first trimester - embryological development

and early fetal development; this trimesterbegins with fertilization; the basic structure of all the major organ systems appear

second trimester - development of organs andorgan systems; by the end of this trimester thefetus looks human

(8th edition)



third trimester - characterized by rapid fetalgrowth; by early in this trimester most of the

organ systems become fully functional; thistrimester ends in birth.

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Fertilization

y A lso referred as conception, impregnation, orfecundation

y Is the union of an ovum and a spermatozoon.

y

Involves the fusion of two haploid gametes with 23 chromosomes each to produce a zygotethat contains 46 chromosomes.

y fertilization generally occurs in the outer thirdof fallopian tube, ampullar portion.

y oocyte - it is surrounded by corona radiata which is a protective layer of cells, and a ring of polysaccharide fluid the zona pellucida thenthe oocyte will travel through the uterine tubetoward the uterus.

(8th edition)



y sperm (fig. 28.2) - are introduced into the femalereproductive tract; of the 200 million spermatozoaejaculated into the vagina, about 10,000 enter theuterine tube, and fewer than 100 sperm reach theegg.

y

Reaches the cervix within eighty seconds.y Reaches the fallopian tube within 5 minutes after

deposition.

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y the acrosomal cap of sperm contains the enzyme

hyaluronidase which breaks down the bondsbetween the cells of the corona radiata

y dozens of sperm are needed to penetrate thecorona radiata

y a single sperm makes contact with the oocytemembrane through CA P ACIT A TION- a finalprocess that sperm must undergo to be redy for

fertilization.y Consist of changes in the plasma-membrane of the

sperm head, which reveal the sperm- bindingreceptor sites.

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(8th edition)

Cleavage (fig. 28.4) - is a series of cell divisions that subdivide the

cytoplasm of the zygote



y

Then the zygote migrates over the next 3- 4days towards the uterus.

yThe first division is completed roughly 24hours after fertilization

yThe following divisions occur at 10-12 hourintervals:

morula - solid ball of cells that results after3 days of cleavage; all of the cells areidentical; the morula reaches the uterus onday 4

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blastocyst - hollow ball of cells after 3

more days of cleavage (6th day)the cells are no longer identical

the inner cavity is called the blastocele

(=b

lastocyst cavity); the outer layer of cells is called the trophoblast

the inner cell mass is a group of cells that will become the embryo; the trophoblastprotects the inner cell mass from theoutside environment

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Implantation (fig. 28.5)- seven days after fertilization, implantation begins as

the blastocyst connects to the endometrium of the uterus

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(8th edition)

y The trophoblast erodes a path through theendometrium by secreting hyaluronidase

y The trophoblast continues to enlarge and spreadinto the surrounding endometrium

y The erosion of uterine glands releases nutrients

that are absorbed by the trophoblast anddistributed by diffusion to the inner cell mass.

y Trophoblastic extensions encircle endometrialcapillaries

y Capillary walls are destroyed and maternal blood



y percolates through trophoblastic channels called

lacunaey V illi - extend from the trophoblast into the

endometrium and larger endometrial blood vessels are surrounded and broken down resulting

in greater blood flow through the lacunaey Implantation most often occurs in the fundus or

body of the uterus;

y Ectopic pregnancy - when implantation occursanywhere but the uterus; if implantation takesplace in the uterine tubes it can be life-threatening

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Embryonic Development: Gastrula to Fetus

y A mniotic cavity - formed by the time of implantation inthe blastocyst; this cavity is formed when the inner massseparates from the trophoblast

y There are two layers of cells that comprise the inner mass.

(AMNIOTIC cavity and the yolk sac)

y The 3 Germ Layers - these three layers of cells willdifferentiate into all of the structures of the body:

ectoderm - will form the skin, hair, nails, brain, spinalcord, epithelium of nasal passages, and mouth

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mesoderm - will form the bones, muscles, heart, blood vessels, kidneys

endoderm - will form the pancreas, thyroid gland, liver,

urinary bladder, respiratory epithelium, digestiveepithelium

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y Four extraembryonic membranes:

yolk sac - important site of blood cell formation

amnion - surrounds the fluid-filled amniotic cavity which protects the embryo

allantois - will give rise to the urinary bladder

chorion - combination of mesoderm and trophoblastthat will form the placenta

y Chorionic villi - branch and enlarge within theendometrium; embryonic blood vessels develop within each

villus and blood blood f low begins in them by thebeginning of the 3rd week; they provide the surface area foractive and passive exchange of gases, nutrients, and wasteproducts between fetal and maternal blood streams

(8th edition)



y Placentation - the enlarging chorion becomes

the placenta

by the end of the 4th week a body stalk hasformed that connects the embryo and chorion;

the body stalk contains blood vessels that carry blood to and from the placenta

the placenta becomes concentrated in a disc-shaped area in the endometrium

near the end of the first trimester the fetusmoves farther from the placenta

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the fetus and placenta remain connected by the

umbilical cord which now contains the placentalblood vessels

the placenta provides nutrients to the embryo-fetus, a site for gas exchange between the

mother and the embryo-fetus, and a place wherethe embryo-fetus can get rid of its wastes

Latin word for pancake

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y Umbilical arteries - these paired arteries carry bloodfrom the embryo-fetus to the placenta (fig. 28.14)

y Umbilical vein - this vein carries nutrient and oxygen richblood from the placenta to the embryo-fetus (fig. 28.14)

*Mother and baby's blood do not mix!

(8th edition)



The Endocrine Placenta - the placenta produces and

releases hormones

(8th edition)



y hCG - human chorionic gonadotropin appears in the

bloodstream soon after implantation the presence of hCG in the urine is a reliable indication

of pregnancy; pregnancy kits test for the presence of thishormone

hCG maintains the integrity of the corpus luteum andpromotes the secretion of progesterone

in the absence of hCG the pregnancy would end as theendometrium is sloughed off; in the presence of hCG,

the corpus luteum persists for 3-4 monthsby the end of the 1st trimester the placenta is secreting

estrogens and progesterone and the corpus luteum is nolonger needed

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y hPL - human placental lactogen; helps prepare the

mammary glands for milk productiony Relaxin - peptide hormone that has several functions:

relaxin increases the flexibility of the pubic symphysis which permits the pelvis to expand during delivery

it triggers the dilation of the cervix which allows thefetus to move out of the uterus and into the vaginalcanal

it suppresses the release of oxytocin by the

hypothalamus and delays the onset of labor contractionsy Progesterone and Estrogens - maintain the endometrial

lining which allows the pregnancy to continue; at the endof the third trimester, estrogen production accelerates,

which stimulates labor(8th edition)



(8th edition)

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Growing Fetus Ppt