Animal Reproduction

Purpose of Reproduction?

Types of Reproduction• Asexual– Fission– Budding– Regeneration– PARTHANOGENESIS• Egg develops without

fertilization; haploid or diploid– Male worker bees; ants &

wasps– Komodo dragons– Some sharks

Asexual vs. Sexual ReproductionAsexual• Many offspring fast

– Each individual is capable of having their own “kids” w/o a partner

• No genders necessary• Variation comes only from

mutations, therefore slow to adapt to environment

• Occurs when environment is favorable – Successful genotypes

continuously passed on

Sexual• Takes longer to increase

population size• Need males & females• Genetic variation• Enhanced reproductive

success• Faster adaptation to

environment• Occurs when environment

is unstable, rapidly changing

Hermaphrodites• Each individual has male and female parts– Any two individuals can mate– Some can self-fertilize

• Allows sessile organisms to mate

Types of FertilizationInternal• Sperm deposited near

female reproductive tract; fertilization occurs within tract

• Few zygotes (fertilized eggs) produced

• More protection for developing embryo

External• Female releases eggs into

environment, male fertilizes them externally

• Many zygotes produced

• Less protection for developing embryo• More likely that damage will

happen to them, so the more you have, the more offspring will actually survive

External Fertilization• Spawning–Male and female

gametes released at the same time

– Can be in response to:• Chemicals• Lunar cycles• Temperature• Day length

Embryo Protection MethodsInternal• Hard – shelled eggs• Protective womb for

internal embryo development

External• Soft – shelled eggs• Ingestion of eggs• Gluing of eggs to a mate for

protection

Explain how the renin - angiotensin – aldosterone

system works.

What is its stimulus and how does it respond?

Human Reproduction

Male Reproductive Anatomy• Testes (testicles) – male gonads

– SEMINIFEROUS TUBULES – sperm maturation site• Surrounded by Leydig cells that produce hormones

– EPIDIDYMIS• Tubule where sperm mature

– VAS DEFERENS • Muscular duct which sperm are sent through to reach

the urethra during ejaculation

Male Reproductive System

• Semen - ejaculated sperm + secretions

– SEMINAL VESCICLES - secretion contains mucus, fructose, coagulating enzymes, and prostaglandins

– PROSTATE GLAND – secretion has anticoagulant and citrate

– BULBOURETHRAL GLAND – secretes mucus to neutralize acidity of urine

Male Reproductive Organs

• Penis – delivers semen to female reproductive tract– Fills with blood when stimulated and closes off

veins, preventing blood from leaving

• Viagra – acts like NO (nitric oxide) and causes relaxation of arteries enhancing blood flow

Female Reproductive Organs• Ovaries – female gonads– Contain hundreds of eggs (OOCYTES) that are

surrounded by FOLLICLES

• Oviduct - Fallopian tube– Oocyte is expelled from follicle and travels down

oviduct to the UTERUS– Lined with cilia to help propel the egg– Uterus has thick inner lining to nourish the egg

called the ENDOMETRIUM

Female Reproductive Organs

• Vagina – canal leading to the uterus

– Site of sperm deposition

– CERVIX – narrow opening of the uterus that connect to vagina

– LABIA – folds of skin protecting external vagina

Spermatogenesis & Oogenesis

What is in the acrosome? Why

Why the mitochondrial sheath?

Hormones of the Spermatogenesis• Gonadotropin Releasing Hormone released

from hypothalamus

• GnRH causes relase of follicle-stimulating hormone and luteinizing hormone

– FSH causes production of Sertoli cells• Nourish developing sperm

– LH stimulates Leydig cells• Leydig cells then secrete testosterone & other androgens

– Increases spermatogenesis

Before birth

At puberty

FSH from anterior pituitary

• Many follicles stimulated, one matures• Secondary oocyte is released and finishes division if fertilized

Spermatogenesis vs. Oogenesis• All 4 meiotic cells become

sperm

• Occurs from adolesence through all of adulthood

• Produces millions of functional sperm

• Continuous process

• Only 1 of 4 meiotic cells become an egg; the rest a polar bodies

• Starts before birth; ends around 50 yrs old

• Produces hundreds of functional eggs

• Many long interrupted pauses in production

Female Reproductive Cycle

The Ovarian Cycle• GnRH causes release of small amounts of FSH

and LH– FSH causes follicle growth– LH causes estradiol production by follicle cells• Low estradiol production inhibits FSH and LH levels

The Ovarian Cycle• Estradiol levels begin

to greatly increase– Causes FSH and LH

levels to go up• Positive feedback –

more estradiol = more LH

– Increase in LH causes follicle to grow and burst, releasing oocyte into fallopian tubes

The Ovarian Cycle• LH causes left over follicular tissue to become

the corpus luteum– Glandular tissue that secretes progesterone and

estradiol• Promote thickening of uterine wall• Levels cause negative feedback on hypothalamus and

causes decrease of LH & FSH• Low levels of LH & FSH cause corpus luteum to

disintegrate

The Uterine Cycle

The Uterine (Menstral) Cycle• Uterus must prepare to support a developing

embyo– Wall must be thick and vascularized– Estradiol & progesterone cause thickening after

follicle rupture

The Uterine Cycle

• As corpus luteum disintegrates, hormone levels drop– Causes vasoconstriction– Uterine lining disintegrates• Endometrium is shed and blood is lost during

MENSTRUAL PHASE