Chapter 27 Reproduction and Embryonic Development

reproduction

the creation of new individuals from existing ones

asexual reproduction

the creation of offspring whose genes all come from one parent w/o the fusion of egg and sperm

budding

small outgrowth on animal

offspring=genetic copy of parent

fission

mean of asexual reproduction in which one individual separates into two or more individuals of about equal size,

offspring=genetic copy of parent

fragmentation

splitting of new individals from existing ones,

must be accompanied by regeneration

regeneration

regrowth of lost body parts

advantages of asexual reproduction

-allows animals that do not move or live in isolation to produce offspring

-enables an animal to produce many offspring quickly

disadvantage of asexual reproduction

produces genetically uniform populations

sexual reproduction

creation of offspring by the fusion of two haploid sex cells to form a diploid zygote,

increases genetic variability among offspring by meiosis and random fertilization (greater adaptability to changing environments)

sperm

male gamete that is generally a small cell that moves by means of a flagellum

ovum

female gamete, a relatively large cell, not self-propelled

hermaphroditism

female and male reproductive systems in the same body,

each animal serves as both male and female, so every individual is potential mate and many more offspring produced when both individuals' eggs fertilized

external fertilization

parents discharge gametes into water (where fertilization occurs),

timing is crucial (eggs must be ripe for fertilization when sperm contact them),

by environmental cues, chemical signals, and courtship rituals

environmental cues

temperature and day length cause both males and females to release gametes all at once

chemical signal

emitted by males or females as they release their gametes,

triggers gamete release in members of opp sex

courtship rituals

trigger simultaneous gamete release in same vicinity by the female and male

internal fertilization

occurs when sperm are deposited in or close to the female reproductive tract and gametes unite within the female's body,

requires copulation and complex reproductive systems

copulation

sexual intercourse

ovaries

about one inch long with a bumpy surface (follicles)

produces egg cells and hormones,

ovarian cycle

ovulation

process in which an egg cell is ejected from the follicle (egg mature, migrate to edge of ovary, released),

induced by surge of LH

corpus luteum

solid mass that forms within the ovary after ovulation,

converted from graafian follicle,

secretes progesterone (helps maintain uterine lining during pregnancy) and estrogen

trophoblast

outer layer that allows embryo to implant,

produces HCG to maintain progesterone production of the corpus luteum which maintain endometrium,

forms chorion

gestation

carrying developing young in reproductive tract

fetus

name for embryo after several weeks gestation

prostaglandins

local tissue regulators that stimulate uterine muscle cells,

help oxytocin induce labor

HCG

human chorionic gonadotropin,

hormone secreted by chorion, prevents spontaneous abortion, maintains corpus luteum during first 3 months of pregnancy, produce high levels of progesterone

placenta

structure that taps the mother's blood supply,

trophoblast forms part of this,

organ that provides nourishment and O2 to embryo and helps dispose of its metabolic wastes,

consists of both embryonic and maternal tissues,

composite organ consisting of chorionic villi closely associated with blood vessels of mother's endometrium,

allows protective antibodies to pass from mother to fetus,

viruses and drugs can cross

third trimester

[24 weeks to birth]

period when embryo grows rapidly and prepares for birth,

gains strength it will need to survive outside protective environment of uterus (born prematurely may survive with special medical care after birth),

circulatory system and respiratory system undergo changes to allow switch to air breathing,

gains ability to maintain own temperature,

bones begin to harden and muscles thicken, loses much of fine body hair except on head,

head changes proportions,

becomes less active as fills space in uterus

[at birth, 50 cm long, weighs 2.7-4.5 kg]

extraembryonic membranes

develop as attachments to the embryo and help support it,

amnion, chorion, yolk sac, allantois

chorion

membrane that develops from trophoblast and from mesoderm cells derived from yolk sac,

becomes the embryo's part of the placenta,

secretes HCG

implantation

embedding of the blastocyst in the wall of the uterus

amnion

forms fluid-filled sac around embryo after a month of conception,

breaks just before childbirth + amniotic fluid leaves mother's body through her vagina

first trimester

trimester in which the biggest changes occur,

[a month-old, 7 mm long]

has a notochord and a coelom,

brain and spinal cord begin to take shape from tube of ectoderm,

has 4 stumpy limb buds, a short tail, elements of gill pouches (appear during embryonic development in all chordates, develop into parts of throat and middle ear),

similar to other vertebrates at somite stage of development

[9 weeks, 5.5 cm long]

decidedly human, has all of its organs and major body parts including disproportionately large head,

somites developed into segmental muscles and bones of the back and ribs,

limb buds become arms and legs with fingers and toes (can move),

sex of fetus is evident

blastocyst

blastula stage with trophoblast (outer ring of cells) and embryonic disc (inner mass of cells)

dilation

first stage of labor, time from onset of labor until cervix reaches full dilation of 10 cm,

longest stage of labor (6-12 hours)

allantois

extraembryonic membrane that develops as an extension of yolk sac,

forms part of the umbilical cord (lifeline between embryo and placenta)

in birds and reptiles it is important in waste disposal

inner cell mass

portion of the blastocyst that actually forms the baby

oxytocin

a pituitary hormone that initiates labor,

later with prolactin stimulates milk secretion,

powerful stimulant for smooth muscles in wall of uterus (cause them to contract),

stimulates placenta to make prostaglandins (make muscles contract even more)

yolk sac

contains no yolk,

produces the embryo's first blood cells and germ cells (which give rise to gamete-forming cells in gonads)

fertilization

fusion of sperm and egg,

this process begins gestation

chorionic villi

outgrowths of the chorion that absorb nutrients and oxygen from mother's blood and pass them to embryo via chorionic blood vessels (red), chorionic vessels (blue) carry wastes away from embryo

contain embryonic blood vessels formed from mesoderm,

bathed in tiny pools of maternal blood

labor

strong rhythmic contractions of the uterus that bring about birth,

three stages (dilation of the cervix, expulsion-delivery of infant, delivery of placenta)

similarities between sexes

gonads, tubes and passageways and accessory organs (endocrine and exocrine glands)

sex glands

testes (male)

ovaries (female)

seminiferous tubules

tissue that produces sperm cells

interstitial cells

tissue of male reproductive system that secrete testosterone

scrotum

where testes are located

epididymis

where sperm cells mature.

located within scrotum

vas deferens

sperm duct,

primary sperm carrying tube in male's body

seminal vesicles

muscular pouches that produce thick clear solution that makes up the bulk of the semen

semen

95% glandular secretions, 5% sperm cells

1. transport vehicle for gametes

2. lubricates tubes and passageways

3. nourishes sperm cells

4. protects sperm from vaginal secretons (which are acidic)

ejaculatory ducts

receive semen from vas deferens and seminal vesicles,

secrete milky white secretion.

provide motility

prostate gland

muscular organ that add secretion to semen,

secretes seminal fluid

ejaculation

expulsion of semen from male's body due to muscular contraction of prostate

urethra

connected to ejaculatory duct,

transport semen out of body,

convey urine from bladder

penis

male sex organ that causes an erection during sexual arousal,

highly sensitive to stimulation

glans

head of penis

bulbourethral gland or cowpers gland

located beneath prostate,

mucus-producing gland,

adds mucus to semen before semen enter urethra,

provides ideal condition for sperm,

provides lubrication

ovarian follicles

where eggs mature,

sac-like structure,

produce estrogen

Graafian follicle

ruptured ovarian follicle,

due to hormones of anterior pituitary

fallopian tube or oviduct

primary egg carrying tube,

extends from ovaries to uterus,

lined with cillia,

site of fertilization in humans

tubular pregnancy

egg implants in the fallopian tube,

type of ectopic pregnancy

uterus or womb

large muscular pear-shaped organ,

actual site of pregnancy (human gestation)

capacity to expand for embryo to grow and develop,

menstrual cycle

corpus

large upper region of uterus,

"the body",

where embryo implant

cervix

lower smaller region of uterus,

"neck"

endometrium

uterine lining ,

development promoted by progesterone and estrogen

vagina

female sex organ,

muscular tube that extends from cervix to outside of body,

1. serves as birth canal

2. receives male's penis during intercourse

rugae

folded mucus membrane lining,

ability to stretch/enlarge for passage of fetus

bartholins gland or vulvovaginal gland

pair of mucus-producing glands,

provide lubrication for intercourse,

in female reproductive system

vulva

external structure of female reproductive system,

consist of two pairs of labia,

protect body openings from germs and infection

clitoris

tiny organ of great sensitivity

hormonal regulation

hypothalamus (releasing factors)-->

anterior pituitary (FSH and LH)-->

ovaries (estrogen and progesterone)-->

uterus

neg feedback by levels of estrogen and progesterone to hypothalamus

estrus cycle

female mammals at peak of sexual readiness,

females potentially receptive to males

STD

sexually transmitted diseases,

contagious diseases spread by sexual contact,

problems: pain, scarring, sterility, maybe death,

viral not curable,

bacterial protozoan treated quickly with antibiotics,

contraception

deliberate prevention of pregnancy,

1. prevent release of gamete from gonads

2. prevent fertilization

3. prevent embryo from implanting in uterus,

examples: vasectomy, tubal ligation, rhythm method, natural family planning, withdrawal, condoms, diaphragm, cervical caps (with spermicides), intrauterine devices (IUDs), morning-after pills (MAPs)

cavernous bodies

the structures in the shaft of the penis that engorge with blood during sexual arousal

Acrosome

Tip of sperm head that is used to penetrate the egg

ovarian cycle

the growth of the follicle and ovulation

pre-ovulatory phase: follicle growing and secondary oocyte developing,

post-ovulatory phase: after follicle has become a corpus luteum

menstrual cycle

preparation of the uterine lining for possible implantation of an embryo

Menstruation, Follicle Stage, Ovulation, Corpus Luteum

day 1: 1st day of menstrual cycle

day 3-5: uterine bleeding (menstruation), endometrium breaks down and leaves the body through vagina,

endometrium begins to thicken, reach max at 20-25 days,

menstruation begins again if embryo has not implanted in uterine lining

human sexual response (4 phases)

1. excitement phase: sexual passion builds, penis and clitoris become erect, testes, labia and nipples may swell, vagina secretes lubricating fluid, muscles tighten in arms and legs

2. plateau phase: increases in breathing and heart rates

3. orgasm: rhythmic contractions of reproductive structures, extreme pleasure and ejaculation by male

4. resolution phase: reverses previous responses, structures return to normal size, muscles relax and passion subsides

cleavage

rapid succession of cell divisions that produce a ball of cells from zygote,

embryo does not grow larger

blastocoel

fluid-filled cavity that forms the center of embryo

blastula

hollow ball of cells after cleavage

spermatogenesis

produce sperm in testis,

primary spermatocytes are made continuously in testes, these diploid cells undergo meiosis to form four haploid sperm

oogenesis

begins at embryonic development,

produce ova,

ovaries contain lifetime supply of primary oocytes at birth,

each month one matures to form secondary oocyte which if fertilized, completes meiosis and becomes haploid ovum

embryonic induction

adjacent cells and cell layers influence each other's differentiation via chemical signals

pattern formation

emergence of the parts of a structure in their correct relative positions, involves the response of genes to spatial variations of chemicals in embryo

programmed cell death

cell contain suicide genes that code for proteins that destroy cell

cell migration

cell move to new locations by pseudopodia

changes in cell shape

cells begin to look different because certain genes are producing proteins

notochord

flexible longitudinal rod,

comes from mesoderm,

located between digestive tract and nerve cord,

becomes the spine,

provides support for other tissues

neural tube

develops into brain and spinal cord,

infolding of ectoderm

somites

internal ridges and blocks of mesoderm,

give rise to body segments

coelom

body cavity lined with mesoderm

archenteron

simple digestive cavity

yolk plug

cluster of endodermal cells,

used primarily for hyponutrient storage

ectoderm

continuous with the amnion,

becomes brain, spinal cord, outer skin, nervous system

endoderm

continuous with the yolk sac,

becomes digestive tract and endocrine glands

mesoderm

becomes bulk of most other organs,

muscles, bones, circulatory system, reproductive system and internal organs

morula

ball of cells