ANIMAL REPRODUCTION AND DEVELOPMENT

Reproduction

processes by which organisms produce offspring

Diversity of reproductive patterns

animal behaviors and anatomy vary to ensure reproductive success

Asexual reproduction

reproduction from a single parent without gamete fusion

Asexual offspring genetics

clones of the parent with no genetic variation

Budding

form of asexual reproduction where part of parent pinches off to form new individual

Budding examples

occurs in cnidarians such as Hydra

Regeneration

formation of new organism from a body fragment

Regeneration examples

seen in sponges and echinoderms like sea stars

Parthenogenesis

development of offspring from unfertilized egg found in some invertebrates

Asexual advantage isolation

animals can reproduce without locating a mate

Asexual advantage speed

rapid reproduction allows fast population growth

Sexual reproduction

reproduction involving fusion of sperm and egg gametes

Gametes

haploid reproductive cells that fuse to form diploid zygote

Sexual reproduction advantage

produces genetic variation aiding survival

Gametogenesis

formation of gametes in testes and ovaries

Spermatogenesis

formation of haploid sperm from diploid germ cells

Primary spermatocytes

diploid cells undergoing Meiosis I to form secondary spermatocytes

Secondary spermatocytes

haploid cells undergoing Meiosis II to form spermatids

Oogenesis

formation of haploid eggs from primary oocyte

Primary oocyte

diploid cell undergoing meiosis to form secondary oocyte and polar body

Polar body

small cell produced during oogenesis that degenerates

Secondary oocyte stage

enters Meiosis II and stops at metaphase II

Fertilization

fusion of sperm and secondary oocyte nuclei producing diploid zygote

Zygote

fertilized egg that develops into an adult animal

External fertilization

fertilization occurring outside the female body typically in water

Internal fertilization

sperm deposited in female reproductive tract

Scrotum

sac of skin housing testes outside abdominopelvic cavity

Testicular temperature regulation

sperm produced at ~3°C below body temperature

Dartos muscle

smooth muscle wrinkling scrotum

Cremaster muscle

skeletal muscle raising testes

Testes

oval plum-sized male organs forming external genitalia

Tunica vaginalis

double-layered outer covering of testes derived from peritoneum

Tunica albuginea

fibrous capsule dividing testes into lobules

Testicular lobules

250–300 compartments per testis

Seminiferous tubules

sperm-producing structures in testicular lobules

Myoid cells

contractile cells aiding movement of sperm and fluids

Tubulus rectus

straight tubule conveying sperm to rete testis

Rete testis

network of tubules receiving sperm from seminiferous tubules

Efferent ductules

ducts through which sperm leave testis toward epididymis

Leydig cells

cells producing androgens primarily testosterone

LH stimulation of Leydig cells

luteinizing hormone triggers testosterone production

Sustentacular cells

support cells providing nutrients and producing inhibin

Penis

male organ delivering sperm into female tract

Glans penis

enlarged distal tip covered by prepuce

Prepuce

foreskin often removed via circumcision

Corpus spongiosum

erectile body surrounding urethra forming glans

Corpora cavernosa

paired erectile tissues enabling erection

Epididymis

duct absorbing nutrients and storing sperm

Sperm ejaculation site

sperm ejaculated from epididymis not testes

Vas deferens

18-inch muscular tube transporting sperm via peristalsis

Vasectomy

procedure cutting vas deferens

Ejaculatory duct

tube entering prostate and delivering sperm to prostatic urethra

Urethra male function

terminal duct carrying semen and urine

Prostatic urethra

passes through prostate

Membranous urethra

2-inch segment in urogenital diaphragm

Penile urethra

6-inch segment running through corpus spongiosum

Seminal vesicles

paired glands secreting alkaline fructose-containing seminal fluid

Prostate gland

single gland secreting slightly acidic milky fluid

Bulbourethral glands

pea-sized glands secreting mucus to neutralize acidic female tract

Vulva

external female genitalia

Vestibule

cleft between labia minora containing urethral and vaginal openings

External urethral orifice

urethra opening between clitoris and vagina

Vaginal orifice

opening to vagina bordered by hymen and bulb of vestibule

Paraurethral glands

mucus-secreting glands homologous to prostate

Bartholin’s glands

glands secreting lubricating fluid homologous to bulbourethral glands

Ovaries

paired almond-shaped female sex glands producing ova and hormones

Ovarian germinal tissue

houses thousands of follicles containing eggs

Ovary functions

oogenesis ovulation and hormone secretion

Germinal epithelium

outer covering of ovaries

Ovarian follicles

oocytes in developmental stages

Graffian follicle

large fluid-filled follicle containing immature ovum secreting estrogen

Corpus luteum

post-ovulation structure secreting progesterone

Corpus albicans

degenerated corpus luteum with white fibrous tissue

Stroma

connective tissue between follicles

Uterus

pear-shaped pelvic cavity organ housing embryo

Uterus functions

menstruation pregnancy and labor

Fallopian tubes

paired tubes extending from uterus to ovaries

Infundibulum

funnel-like end of tube with fimbriae

Fimbriae

finger-like projections sweeping egg into tube

Fallopian tube function

transports egg via cilia and muscle contractions

Fertilization site

typically fallopian tubes

Vagina

canal opening to outside at vaginal orifice

Vagina functions

birth canal penis receptor menstrual passage

Mammary glands

glands under pectoralis major producing milk

Mammary adipose tissue

fat filling breast structure

Mammary lobes

15–20 sections separated by adipose

Alveoli

milk-secreting cells

Erection

process enabling penetration into the vagina

Parasympathetic impulses in erection

release nitric oxide causing vasodilation of arteries and vasoconstriction of veins

Erectile tissue filling

penis enlarges and becomes rigid as corpora cavernosa and spongiosum fill with blood

Emission

movement of semen from ducts and glands into prostatic urethra

Ejaculation

sympathetic reflex closing urethral sphincters and expelling semen externally

Oogenesis

egg formation in ovaries beginning at puberty

Oogenesis hormonal control

regulated by FSH

Menstrual cycle hormones

coordinated by GnRH FSH LH estrogen and progesterone

GnRH function

hypothalamic hormone triggering anterior pituitary to release FSH and LH

FSH ovarian role

stimulates ovum growth and estrogen release

LH ovarian role

induces ovulation and forms corpus luteum

LH progesterone role

stimulates corpus luteum to produce progesterone

Estrogen menstrual role

stimulates endometrium growth and secondary sex characteristics