Animal phys exam 3 pt 3

Progestins

• From the ovaries

• Primary role is in maintaining pregnancy

Female reproductive hormones

• Negative feedback control, both short and long loop

• Negative feedback also through the hormone inhibin from the follicle

What kind of feedback is used for ovulation?

Positive feedback through LH

What cells respond to LH by producing androgens?

Theca cells

Where do androgens diffuse to after being produced and where is aromatase expressed?

Granulosa cells

What hormones stimulate the proliferation of the granulosa cells?

FSH and estrogen

What type of control is the system under during the early follicular phase of the estrus (or menstrual) cycle

Negative feedback control

The surge in ____ triggers ovulation

• LH

• LH and estrogen levels increase rapidly just before ovulation and the negative feedback loop switches to a positive feedback loop

What feedback control is the luteal phase of the estrus cycle (or menstrual cycle) under?

Negative feedback from the corpus luteum

What happens to progesterone and estrogen levels during pregancy?

Progesterone and estrogen continue to increase, first from the CL and then from the developing placenta

Estrous cycle (heat) - Proestrus

hormonal changes that bring about ovulation

Estrous cycle (heat) - Estrus

coincides with ovulation, when the female is receptive to the male

Estrous cycle (heat) - Diestrus

Period between estrus and the next breeding period

• No menses, uterine lining is reabsorbed

In which organisms does the menstrual cycle usually occur?

Primates, bats, and elephant shrew

What characterizes the menstrual cycle?

The shedding of the lining of the uterus (menses)

Longer gestation period is associated with

Larger log body weight

Which mammals have longer gestation periods? Precocial or Atricial?

• Precocial mammals

• Need more time to develop so can do more after birth

Spontaneous ovulators

• No external physical cue needed

• Rodents, humans

Induced ovulators

• Vaginal stimuation needed

• Many carnivores, rabbits, voles

Two reasons why induced ovulation may be necessary

• Short lifespan » rapid transition to reproductive state

• Solitary living » only reproduce when social conditions are right

How do birth control pills work?

• Mix of low levels of progesterone and estradiol

• Trick the body into thinking its pregnant, so no ovulation

Ovary releases egg into ____

Fallopian tube (oviduct)

What do ovaries produce?

• Gametes - secondary oocytes that develop into mature ova (eggs)

• Hormones including progesterone, estrogens

What are Theca cells?

Triggered by LH to produce androgens

What are Granulosa cells?

Triggered by FSH to produce aromatase which converts the androgens to estrogens

What is the Corpus Luteum?

Source of progesterone in early days following ovulation

What is the role of the fallopian tubes / oviducts?

• Provide a route for sperm to reach an ovum

• Transport secondary oocytes and fertilized ova from ovaries to uterus

Perimetrium

• Outer layer of the Uterus

• Part of visceral peritoneum

Myometrium

• 3 layers of smooth muscle in the uterus

• Contractions in response to oxytocin from posterior pituitary

Endometrium

• Inner layer of uterus

• Highly vascularized

Stratum functionalis

lines uterine cavity, sloughs off during menstruation

Stratum basalis

permanent, gives rise to new stratum functionalis after each menstruation

Where does the blood supply come from in the uterus?

Uterine arteries, arcuate arteries, radial arteries

Vagina

Canal extending from exterior of body to uterine

cervix

Muscularis

2 layers of smooth muscle

Adventitia

Anchors vagina to adjacent organs

Hymen

Forms border around and partially closes vaginal orifice

Breast / Mammary glands

• Defining character of mammals

• Nipple has openings of lactiferous ducts

• Areola - Pigmented area

Mammary gland

Modified sudoriferous gland that produces milk

Oogenesis and follicular development

• Formation of gametes in ovary

• Oogenesis begins before females are born

• Same steps of meiosis as spermatogenesis

Primary oocytes

• Before birth, most germ cells degenerate – atresia

• A few germ cells develop into primary oocytes that enter meiosis I during fetal development

• Each covered by single layer of flat follicular cells – primordial follicle

Follicular development

Each month from puberty to menopause, FSH and LH stimulate the development of several primordial follicles

• Usually only one reaches ovulation

Primordial follicles develop into

primary follicles

Primary follicles develop into

secondary follicles

Parturition

Fetus signals it’s ready to leave, stress hormones (CRH) from the fetal placenta increase

• Oxytocin secreted from posterior pituitary causes smooth muscle contractions in uterus.

• Oxytocin also causes smooth muscle to release prostaglandins which also cause further contractions.

• Fetus presses against cervix, stimulating mechanoreceptors that send signal to hypothalamus to stimulate more oxytocin release (positive feedback).

• Birth

Oviparous

• Lay eggs

• All birds, most amphibians, some fish

• Lower latitude squamate (lizards and snakes) reptiles

Viviparous

• Give live birth

• Almost all mammals, some fish

• Higher latitude squamate reptiles

Hemipenes

• Found in reptiles

• Two testes and two penises

• Each testis pipes to its own hemipene

Snake hemipenes

• Have paired hemipenes but use only one at a time to mate

Which side do snakes prefer to use?

• Right!

• Right testis, kidney and hemipene are bigger

• Prefer to use right

Avian Sex differentiation

• Males homogametic (ZZ) and females hetero (WZ)

• Female “decides” sex of offspring

Cloacal protuberance

• Copulatory organ in birds

• Pair of testes but only one copulatory organ

• Enlarged during breeding season and is used to store sperm for mating

Oviduct in female birds

Only one active ovary and oviduct for mating, the other is regressed and inactive

Duck penises

• Corkscrew shaped and exceptionally long

• Develop anew this year

• Changes size when hanging out with rivals, more competition

Gastrotheca frogs

• Females lay eggs while clasped and the male shoves them into pouch on back

• Eggs hatch and tadpoles / frogs emerge (depends on species)

Gastric brooding frogs

• Female turns off digestive processes

• Swallow eggs and babies undergo metamorphosis in her gut

• Extinct

Marsupial frogs

• brood their direct developing larvae in a fully enclosed pouch

• Like kangaroos

Protandry

Fish species that begin life as males and switch to females

Protogyny

Fish species that begin life as female and switch to male

Parthenogenesis

involves the development of an embryo from an unfertilized egg or one where sperm & egg nuclei did not fuse

Ameiotic or Mitotic parthenogenesis

no meiosis, egg is formed by mitosis (diploid). Offspring are clones of mom

Meiotic parthenogenesis

haploid ovum formed by meiosis, it may be activated by a male (or not). Offspring not necessarily clones due to recombination

In which organisms does parthenogenesis occur?

Vertebrates, some fishes, amphibians, lizards

Parthenogenic lizards

• Desert Whiptail lizard

• Triploid species (arose from hybridization of two diploids)

• All eggs are daughters

• Alternate between displaying “male” and “female” like behaviors

C. uniparens (Whiptail) Female behavior

Observed when E2 levels are high

C. uniparens (Whiptail) Male behavior

Observed when progesterone levels are high (postovulatory)

Giant sperm

• Found in fruit flies that produce giant sperm longer than they are

• Requires a special reproductive tract, both for male and female (equal reproductive investment)

Evolutionary basis of homosexuality

• Advantage of having males around without risk of cuckoldry

• One study shows that females who have homosexual offspring have higher overall fecundity

Homosexuality in sheep

• 8% of Rams are “male oriented”

• Sexual preference doesn’t change through life

• Sexual behavior is male like

• Castration has no effect

• No difference in testosterone levels / testis size

Heterosexual rams have an ___ that is twice as large in homosexual rams

oSDN (Nuclei in the hypothalamus)

• Aromatase activity in oSDN also different

• heterosexual rams » homosexual rams » ewes

Monotreme mammals

• Only platypus and 2 echidnas

• Mammals that lay eggs

• Have mammary glands to suckle young

Marsupial mammals

• Kangaroos the most common

• No real placenta

• Young born very immature and crawl into pouch where they permanently attach to a nipple

Female Hyenas

• Most masculinized female animal

• Have a peniform clitoris with a single urogenital canal, through which they copulate, void, and give birth

• Females are larger and more dominant (including cubs) to adult males

How do female hyenas copulate?

Retract clitoris or mounting

Why have biological rhythms?

• Allows animals to prepare for predictable events

• Promote efficient functioning

Period

Length of time to complete one cycle

Frequency

number of completed cycles per unit time

Amplitude

amount of change above or below average

Phase

point in rhythm relative to some objective time point

Exogenous factors

factors outside the organism that WERE thought to drive rhythmic patterns. Mostly zeitgebers

Endogenous mechanisms

rhythms from inside the animal that drive many of the physiological and behavioral rhythms. Seen in ALL animals and plants

Evidence of Endogenous Clocks

• Animals maintained in constant conditions, orbiting the earth, display rhythms

• Adjacent animals kept without cues display rhythms with different periods

• The period or phase of an individual can be transferred to another through tissue transplants

Circadian

daily cycles: activity, metabolism, behavior (24 hours)

Circatidal

tide cycles: intertidal animals (12.4 hours)

Circalunar

phase of the moon: nocturnal predators (29.5 days)

Circannual

seasons of the year: migration, reproduction (365.25 days)

Zeitgeber

environmental cue used to entrain rhythm

Characteristics of circadian clocks

• Inherited

• Relatively independent of temperature

• Relatively independent of chemical influence

• Entrained

• Independent of behavioral feedback

• Found at every level of organization (cell to organism) and throughout the body

Biological rhythms - Entrainment

synchronization of an endogenous rhythm to a periodic environmental cue

Biological rhythms - Free Running

biological rhythm not synchronized with an environmental cue

Why breed seasonally?

• Resources vary throughout year

• Time breeding so the young emerge when resources are most abundant (breeding season later for those with shorter gestation)

What regulates seasonal breeding?

The environment!

Initial predictive cues

Initiate gonadal growth

• Larger during breeding season

Supplementary cues

Fine tune gonadal development, onset of breeding

• Have flexibility to respond to environmental cues

Social cues

Coordinate breeding within a pair

Photoperiod

• Initial predictive cue, follows day length

• Melatonin becomes important

Short day breeders

• Short days equal long periods of melatonin

• Stimulates breeding

Long day breeders

• Long days equals short periods of melatonin

• Stimulates breeding

Gonadal growth in sparrows

• Internal clock regulates photosensitivity

• With appropriate environmental conditions, gonadal growth begins

How do animals measure daylength?

• Melatonin plays a role

• Secreted at night