Animal Reproduction

Two Modes Asexual – Invertebrates

Fission Splitting into two

Budding Splitting off parent

Sponges produce gemmules Fragmentation

Parent breaks into pieces Mature individuals are created through regeneration.

Arm of a star fish create an adult. Sexual

Involve a large non-motile cell Ovum

Small Mobile Cell Spermatazoan

Advantages and Disadvantages of Asexual Reproduction Advantages

Enables the animal to reproduce in an isolated environment.

Many offspring can produced very quickly and thus colonize a new habitat rapidly

Ideal for stable environments Disadvantages

No genetic variability in case the environment changes

One disease can kill the entire population

Reproductive Patterns Vary

Some animals will switch to sexual reproduction under environmental stress and reproduce asexually under favorable conditions.

Some animals only reproduce through parthenogenesis. Adult develops from an unfertilized egg Adults that develop in this manner are usually haploid

Whip tail lizards create a diploid zygote by doubling their chromosomes after meiosis

There are no males Mating females switch roles and act male or female depending on

the level of estrogen or progesterone in their bodies.

Sexual Reproduction is a Problem for Sessile, Burrowing or Parasitic animals. Solution?

Hemaphroditism Have both male and female reproductive organs.

Sequential Hemaphroditism Species switch sexes during their lifetime.

Protogynous - female first Protandrous - male first Reef fish call wrasses switch from female to male based on

size

Spermatogenesis

The Sperm

Oogenesis

Preparation For Implantation

of the egg in the Uterus

Menstral Cycle Ovarian Cycle

Preparing the eggPreparing the Uterus

Menstral CyclePreparing the Endometrium

• There are three phases– Proliferative - endometrium thickens

– Secretory – endometrium becomes vascular and creates glandular structures.

– Menstral flow – endometrium is expelled.

Ovarian CyclePreparing the Egg

• There are three phases

• Follicular – several follicles begin to grow– Ovulation – one follicle matures and breaks

out of the ovary– Luteal phase – remaining follicular tissue

becomes glandular.• Secretes estrogen and progesterone to support the

growing endometrim.

There are Five Hormones that Synchronize the ovarian and Menstral Cycles

• GnRH, FSH, LH, Estrogen, and Progesterone

• GnRH– Gonadotropin releasing hormone– Released by the hypothalamus– Causes the pituitary to releases FSH and LH

• FSH– Follicle stimulating hormone– Respond to receptors on the follicle and encourage growth– Growing follicles secrete estrogen– Small amounts of estrogen inhibit the release of FSH and LH from the

pituitary.– A steep rise in the release of estrogen from the follicle cause the

opposite effect and stimulate the release of FSH and LH from the pituitary.

– The follicle now respond to receptors for LH.

• LH– Lutenizing Hormone– Cause the maturation of the follicle and it is released from the ovary– The follicular tissue left behind now becomes the corpus luteum which is

glandular in function and secretes estrogen and progesterone.

• Estrogen and Progesterone– An increase in the production of these hormones inhibit the

hypothalamus and pituitary which inhibits the release of FSH and LH.– Progesterone supports the endometrium– Without LH the corpus luteum disintegrates– Without progesterone the endometrium disintegrates.

• Blood vessels are choked off and the uterus undergoes spasms.• The endometrium is expelled

– Without the corpus luteum the hypothalamus and pituitary can once again release FSH and LH and the follicular phases begins again.

Zygote Formation

Placental Circulation