CH 26 - Reproduction and Development part 1

reproductive systems contribute to

homeostasis of other body systems

conceptus -

zygotę to birth

during the first week, the cells of the embryo cleave as it travels through

the oviduct to the uterus; by the end of the week, a blastocyst has formed

during week two, the embryo implants into the

uterus

iiumostaining - the large cells are the cells of the

trophoblast, the blue color is GATA3 (a TF that helps specify its fate)

iiumostaining - yellow-green nuclei are the cells of the

inner cell mass (ICM) (from the amnion and the body of the fetus)

iiumostaining - the green-yellow staining is from the

antibodies to OCT4 (protein that allows these cells to retain their pluripotent)

iiumostaining - the red nuelci are expressing

GATA6 (a TF that promotes their becoming amnion cells)

iiumostaining - the area around the cell membranes ar stained pink by

phalloidin (actin microfilament)

embryology

study of the origin and development of a single individual

prenatal period - embryonic period

first 8 weeks

prenatal period - fetal period -

remaining 30 weeks

embryonic period major events

organs form from 3 primary germ layers; the basic body plan emerges

detal period major events

organ in size and complexity

primary germ layers

endoderm, mesoderm, ectoderm

endoderm

internal layer; lung cells (alveolar cell), thyroid cells, digestive cells (pancreatic cell)

mesoderm

middle layer; cardiac muscle cells, skeletal muscle cells, tubule cells of the kidney, RBC, smooth muscle cell (in gut)

ectoderm

external layer; skin cells of epidermis, neuron on brain, pigment cells

3% of all newborns exhibit

a significane birth defect

congenital defects increased to 6% by age 1 initally

unrecognizable conditions become evident

• multiple causes (genetic, chemical, environment)

critical or danger period

weeks 3-8

prior to week 3 development terminates

naturally (destruction of critical cell lines)

after week 8, deformities are

less severe

teratology

study of birth defects and fetuses with congenital deformities

teratogen

an agent or factor which causes malformation of an embryo '

• heavy metals, drugs, alcohol, pesticides, perscription drugs

fetal alcohol syndrome (FAS)

result of alcohol consumption during pregnancy

• microcephaly (small head and jaw), growth deficiencies

fetal alcohol spectrum disorders (FASD)

occur in 1% of births

• mental retardation, unusually shaped eyes and lips, heart defcects, learning problems

thalidomide

1958-1962 used a sedative and to relieve morning sickness

thalidomide - when take during days 24-36 of pregnancy results in

severe limb defects “flipper like limbs”

basic body plan - skin

dermis and epidermis

basic body plan - outer body wall

trunk muscles, ribs, vertebrae

basic body plan - body cavity and digestive tube

inner tube

basic body plan - other

• kidneys and gonads - deep to body wall

• limbs

week 1 =

from zygote to blastocyst

fertilization - lateral third of uterine tube

zygotę (fertilized oocyte) moves towards the uterus, cleavage occurs and daughter cells from from zygote

morula -

solid cluster of 12-16 cells

blastocyst -

fluid-filled structures of 60 cells

• inner cell mass (ICM) - forms embryo

• trophoblast - helps form placenta

stages of first week

1. zygote

2. four-cell

3. morula

4. early blastocyst

5. late blastocyst (implants at this stage)

week 2 -

two0layered embryo

week 2 - bilaminar embryonic disc -

ICM divided into 2 sheets - epiblast and hypoblast

amniotic sac -

formed by an extension of epiblast

amniotic sac membranes

• outer membrane forms the amnion

• inner membrane forms the amniotic sac cavity (filled with amniotic fluid)

yolk sac - formed by

an extension fo hypoblast

digestive tube forms from

yolk sac

tissues around yolk sac give rise to

earliest blood cells and blood vessels

embryo at 5-6 weeks is

sexually indifferent

mesonephric ducts →

future male ducts

paramesonepshric ducts →

future female ducts

gondal ridge -

glands of both male/female being to develop at week 5 as masses of intermediate mesoderm

sexual indifferent because

gonadal ridge and ducts are structurally identical

gondala ridges are “seeded” by

migrating primodrial germ cells (yolk sac)

germ cells become

male spermatogonia or female oogonia

once “seeding” occurs, gonadal ridges differentiate into

testes or ovaries

differentiation based on presence/absence of

male-inducing single called SRY protein

male embryos - sexual differentiation begins in

week 7

male embryos - mesonephric duct becomes

male sex ducts

• epididymis, ductus deferens, ejaculaatory duct

male embryos - paramesonephric duct

degenerate

female embryos - sexual differentiation begins in

week 8

female embryos - outer portion os immature ovaries form

ovarian follicles

female embryos - paramesophric ducts

differentiated into female duct system (uterus, uterine tubes, vagina)

female embryos - mesoenphric ducts

degenerate

external genitals develop from

identical structures in week 8

development of external genitalia - males →

genital tubercle enlarges, forming the corpora canvernosa and glans of the penis

development of external genitalia - males → urethral folds fuse to from

ventral aspect of the penis and spongy urethra

development of external genitalia - males → the two labioscrotal swellings join to form

the scrotum

hypospadias

common congenital abnormality of the male urethra

hypospadias is the failure of

the two urethral folds to fuse completely

• producing urethral opening on the undersurface of the penis

• more urine exits the underside of the of the penis than the tip; surgical correction required

development of external genitalia -females →

genital tubercle becomes the clitoris

development of external genitalia - females → unfused urethral folds become the

labia minora

development of external genitalia, females - unfused labioscrotal swellings become

the labia major

development of external genitalia - urethral groove persists

as the vestibule

both sexes, the gonads originate in

the dorsal body wall of the lumbar region

glands descend caudally during the

fetal period

male fetuses →

testes descend toward the scrotum followed by their blood vessels and nerves

descent of the testes - vaginal process pushes through

muscle wall to make he inguinal canal

testes suddenly enter the scrotum (7 months)

• proximal part of the vaginal process closes and the caudal part becomes the “sac-like” tunica vaginalis

• failure to close the tunica vaginalis can result in a congenital inguinal hernia

gubernaculum (“governor”) -

fibrous cord, extends from testis to flood of the scrotal sac; thought to be involved in descent

crytorchidism

congenital condition so newborn makes in which one or both testes fail to descend into the scrotum

• undescended testis may be located in either the inguinal canal or the pelvis cavity is sterile due to the higher temperature

ovarian descend during

teal development; only into the pelvis

ovarian descent - broad ligament blocks

further descent

ovarian descent - each ovary is guided in its descent by

a gubernaculum, that is anchored in the labium majus

ovarian descent - inferior part of the gubernaculum becomes the

round ligament of the uterus, and its superior part becomes the ovarian ligament