Fertilization early embryo dev't

General Anatomy Lecture # 24

Fertilization

Fertilization

At the time of coitus 200-600 million sperms are deposited into the female vagina in the vicinity of cervix.

Following ejaculation, semen undergoes clotting by the action of enzymes present in the prostatic secretion.

After about 5 minutes clot liquefies and spermatozoa become actively motile: the tails perform undulating movements which propels them forwards. The speed varies with the environment but on the average it is 2 -3 mm/min.

Prostaglandinds reverse the peristaltic contractions of the uterus and uterine tubes thus helping the ascent of spermatozoa to the site of fertilization.

Out of millions of spermatozoa only 300-500 reach the site of fertilization and it is only one which is able to fertilize.

A freshly deposited sperm is not able to fertilize the secondary oocyte until it is conditioned in the female genital tract for sometimes lasting about 7 hours.

During this time glycoprotein coat and seminal plasma proteins are removed from the plasma membrane that overlies the acrosomal region of the spermatozoa.

This process whereby freshly ejaculated sperms develop the capacity to fertilize a secondary oocyte is called capacitation of sperm.

Fertilization:

the fusion of the sperm cell nucleus with the egg cell nucleus to produce a zygote (fertilized egg)

Fertilization:

External Occurs outside of the body of the

female Increased number of eggs

produced to insure the survival of the species

Fertilization:

Internal Occurs inside the body of the

female Fewer number of eggs are

produced

Fertilization:

fertilization in mammals occurs in the oviduct

The ova is viable for approximately 24 hours after ovulation

REPRODUCTION AND EMBRYONIC DEVELOPMENT THE PROCESS OF FERTILIZATION

THE SPERM APPROACHES THE EGG THE SPERM’S ACROSOMAL ENZYMES DIGEST

THE EGG’S JELLY COAT PROTEINS ON THE SPERM HEAD BIND TO EGG

RECEPTORS THE PLASMA MEMBRANES OF SPERM AND EGG

FUSE THE SPERM NUCLEUS ENTERS THE EGG

CYTOPLASM A FERTILIZATION ENVELOPE FORMS

Implantation After approximately

a week, the developing embryo is implanted into the uterus

Embryo: conception to 8 weeks

Embryonic Development

Embryo:

a multicellular organism in the early stages of development

2 four cell stage embryos

Eight cell stage embryo

Embryo:

The beginning developmental processes are always the same in all animals:1) cleavage2) growth3) differentiation

Embryo:

after fertilization the diploid ZYGOTE undergoes cleavage divisions in the oviduct

Cleavage

the first series of cell divisions by mitosis after fertilization

Cell division is rapid, new cells do not take time for the growth phase G1

cell growth does not occur so cells decrease in size with each cleavage division

REPRODUCTION AND EMBRYONIC DEVELOPMENT

CLEAVAGE PRODUCES A BALL OF CELLS FROM THE ZYGOTE

CLEAVAGE RAPID SUCCESSION OF CELL DIVISIONS THAT

PRODUCES A BALL OF CELLS – A MULTICELLULAR EMBRYO – FROM THE ZYGOTE


CLEAVAGE PRODUCES A BALL OF CELLS FROM THE ZYGOTE

BLASTOCOEL FLUID-FILLED CAVITY IN THE

CENTER OF THE EMBRYO BLASTULA

HOLLOW BALL OF CELLS THAT RESULTS WHEN CLEAVAGE IS FINISHED

Cleavage divisions

Morula forms (solid ball of cells) Blastula forms (hollow ball of cells) Cells begin to grow before dividing

Differentation Gastrulation: one side of

the blastula invaginates (indents) forming a gastrula

Three cell layers form. SECOND MAJOR

PHASE OF EMBRYONIC DEVELOPMENT; ADDS MORE CELLS TO THE EMBRYO; SORTS THE CELLS INTO DISTINCT CELL LAYERS

Differentation

Differentiation

The changing of unspecialized embryonic cells into the specialized cells, tissues and organs of a multicellular animal


GASTRULATION PRODUCES A THREE-LAYERED EMBRYO GASTRULA

THREE-LAYERED STAGE OF THE EMBRYO THREE LAYERS ARE LABELED

ECTODERM ENDODERM MESODERM


GASTRULA LAYERS DEVELOP INTO…


ORGANS START TO FORM AFTER GASTRULATION NOTOCHORD NEURAL TUBE SOMITES COELOM


CHANGES IN CELL SHAPE, CELL MIGRATION, AND PROGRAMMED CELL DEATH GIVE FORM TO THE DEVELOPING ANIMAL PROGRAMMED CELL DEATH =

APOPTOSIS TIMELY, TIDY SUICIDE OF CELLS NECESSARY TO CREATE SPACE

BETWEEN FINGERS AND TOES

REPRODUCTION AND EMBRYONIC DEVELOPMENT THE EMBRYO AND PLACENTA TAKE SHAPE DURING THE

FIRST MONTH OF PREGNANCY GESTATION

PREGNANCY; THE CARRYING OF DEVELOPING YOUNG WITHIN THE FEMALE REPRODUCTIVE TRACT

AN OVERVIEW OF DEVELOPMENT EVENTS BLASTOCYST MAMMALIAN EQUIVALENT OF A

BLASTULA TROPHOBLAST OUTER LAYER THAT ALLOWS

UTERINE IMPLANTATION PLACENTA COMBINATION OF TROPHOBLAST AND

MATERNAL CELLS

REPRODUCTION AND EMBRYONIC DEVELOPMENT AN OVERVIEW OF DEVELOPMENT EVENTS

REPRODUCTION AND EMBRYONIC DEVELOPMENT EXTRAEMBRYONIC MEMBRANES

AMNION PROTECTIVE FLUID YOLK SAC NO YOLK IN HUMANS, BUT SAME NAME;

NOURISHMENT FOR NON-PLACENTALS CHORION BECOME EMBRYOS PART OF PLACENTA

RELEASES HUMAN CHORIONIC GONADOTROPIN (HCG)

CAUSES CORPUS LUTERUM TO STAY; PREVENTS MENSTRUATION

ALLANTOIS FUNCTIONS IN WASTE DISPOSAL; WILL BECOME THE UMBILICAL CORD


EXTRAEMBRYONIC MEMBRANES

REPRODUCTION AND EMBRYONIC DEVELOPMENT THE PLACENTA

CHORIONIC VILLI CONTAIN EMBRYONIC BLOOD VESSELS

NEAR MATERNAL BLOOD; NO DIRECT MIXTURE OF BLOOD

NUTRIENTS, GASES, WASTE PRODUCES ARE PASSED THROUGH THE PLACENTA

DRUGS, ALCOHOL, VIRUSES CAN PASS THROUGH

ANTIBODIES CAN PASS THROUGH

Placenta organ that

forms from the embryo and the uterus

Placenta

contains blood vessels from the mother and the developing baby

Placenta Oxygen & nutrients diffuse from

the mother’s blood vessels into the baby’s blood vessels

Wastes diffuse from the baby’s blood vessels into the mother’s blood vessels

Umbilical Cord

two arteries and a vein Connects the fetus to the placenta

Amniotic Sac Contains fluid

(amniotic fluid) that protects fetus by giving it a stable environment and absorbing shock

Fetus

By the end of the 8th week of pregnancy the embryo is called a fetus and all of the major structures are present

Later Stages of Fetal Development

Human gestation

the period between fertilization and birth

approximately 38-40 weeks

Teratogens

Substances that may harm the developing fetus and result in the formation of birth defects

Teratogens include:

Alcohol, certain drugs/medications, infections, and certain chemicals

How do twins form???

Monozygotic Twins(Identical Twins)

One egg is fertilized by one sperm Embryo splits into two during the early

stages of development Have identical genes and must be of

the same sex (Incidence: about 3 in every 1000

births)

Dizygotic Twins(Fraternal Twins)

Two eggs are ovulated and each is fertilized by a sperm cell

No more genetically similar than any other sibling in the family (can be same/different sexes)

Maternal age, use of assisted reproductive technologies are factors

Incidence (6.7/1000 births in Japan to 40/1000 births in Nigeria)


NO TIME FOR FUNNY JOKES…WE HAVE TO RACE TO THE FINISH!!!! NERVOUS SYSTEM NEXT!!!

Technology

Fertilization early embryo dev't