Biol 417 Exam 1

neurons

• Electrically excitable cells that transmit signals throughout the body

neurotransmitters

• Chemical messengers that allow neurons to communicate with eachother

• Diffuse across synapses (short distance)

• Effects are rapid and short lived

hormone

• Chemical messengers that travel in the bloodstream to act on target tissues

• Travel long distances

• Slower onset but longer lasting effects

neurosecretory neuron

• A special type of neuron that produces and releases hormones instead of just neurotransmitters

• Primarily located in the hypothalamus

autocrine signaling

• Hormonal signaling

• Signal targets the same cell that secreted it

Paracrine signaling

• Hormonal signaling

• Signaling affects nearby cells

Endocrine signaling

• Hormonal signaling

• Signal travels long distances vis the bloodstream to reach target cells throughout the body

macrolecithal eggs

• Eggs characterized by having a large amount of yolk

• Primary food source for the developing embryo

• Ancestral trait

• Most vertebrates

mesolecithal eggs

• Eggs characterized by having a moderate amount of yolk

• Concentrated in one hemisphere (vegetal pole)

• Has a larval stage, the limited yolk can’t support full development inside the egg

• Amphibians and Lampreys

microlecithal

• Eggs that contain a very small amount of yolk

• The devleloping embryo gets nutrients from another source like a placenta

• Mammals

lecithotrophy

• A developmental strategy where an embryo obtains its nutrition soley from the yolk contained within its egg

matrophy

• A mode of embryonic development in which the mother provides nutrients directly to the developing embryo (e.g. placenta)

oviparity + lecithotrophy

• The female lays eggs and embryonic development occurs outside the mother

• Nutrients come from yolk inside the egg

viviparity + matrophy

• The embryo develops inside the mother’s body, live birth

• Nutrients come from the mother (placenta)

• Internal fertilization

• Benefits: embryo protection, higher survivial rate, stable developmental environment

• Costs: high energetic demands, reduced mobility, fewer reproductive events (longer gestation)

viviparity + lecithotrophy (ovoviviparity)

• Eggs are retained inside the body

• Embryos get their nutrients only from the yolk

• Live birth, but from hatched eggs

oviparity + matrophy

• Monotremes, mammals that lay eggs

• Embryos recieve additional nutrients (milk) from the mother after hatching

• Platypus

amniotes

• An animal whose embryo developes in an amnion

• An amnion is a membrane that encloses the embryo in a fluid filled cavity, used for protection

• Lizards, snakes, turtles, crocodiles, birds, mammals

• Advantages:

  • sturdy and porous eggshell

  • eggs can “breathe” and handle waste

  • ability to lay eggs on land or give live birth

  • free from dependence on water for reproduction in fish and amphibians

yolk sac

• Present in all vertebrates

• Extraembryonic membrane that provides the embryo with nutrients

chorion

• Present in amniotes

• The outermost membrane surrounding the embryo

• Good for protection and gas exchange

allantois

• Extraembryonic membrane found in amniotes that aids in gas exchange and waste handling during embryonic development

placenta

• An organ that develops in the uterus during pregnancy

• Provides oxygen and nutrients to the developing embryo

• Mammals, lizards, snakes

chondrichthyes phylogeny

traits shared by mammalian carnivores and elasmobranchs

• Internal fertilization

• Direct development (no metamorphosis)

• Viviparity (live birth)

• Long gestation

• Larger and fewer offspring

• Long-lived

viviparity in chondrichthyes

• Viviparity is widespread in chondrichthyes

• Viviparity evolved more than once in the chondricthyes

• Oviparity never evolved from a viviparous ancestor

• Co-evolved with increasing body size, shallower depth, and tropical distribution

• Benefits:

  • Protection and increased embryo survival

  • Well developed offspring, more likely to survive on their own after birth

aplacental viviparity

• 51% of chondrichthyes use this mode of reproduction

• Development of unattached embryos within the uterus

• Three modes:

  • Oophagy/Adelphophagy

  • Lipid histotroph viviparity

  • Yolk-sac viviparity

lecithotrophic oviparity in chondrichthyes

• Ancestral trait

• Egg laying reproduction, embryo nourished by yolk

• The developing embryo and yolk are surrounded by a tough, protective egg case

• Outer surface of egg cases are keratinized

• Deep cold-water species lay eggs near hydrothermal vents

Yolk sac (lecithotrophic) viviparity

• A mode of aplacental viviparity

• Observed in guitarfish and dogfish sharks

• Energy supplied soley via a yolk sac

• Embryos develop inside the mother, live birth

Lipid histotroph viviparity

• A mode of aplacental viviparity

• Embryo starts out with a yolk sac but recieves extra nutrition via uterine milk secretions (matrophy)

• The trophonemata (uterine villi) secretes uterine milk (lipid histotrophy)

• California butterfly ray and stingrays

oophagy/adelphophagy

• A mode of aplacental viviparity

• Matrophy

• Developing embryos feed on unfertilized eggs that are released from the ovaries (oophagy)

• Ingestion of smaller embryos (adelphophagy)

uterine lamellae

• Folds in the lining of the uterus that increases the surface area for gas exchange

• Allows the mother to efficiently supply oxygen and remove CO2 from the uterine environment

• Help non placental sharks like the great white efficiently deliver oxygen to their pups

placental viviparity in sharks

• Nourishment via a yolk sac placenta

• Once the yolk sac has been depleted, it attaches to the uterine wall acting as a pseudoplacenta that provides the embryo with nutrients from the mother (matrophy)

• Blacktip shark

What is the goal of sexual reproduction?

• Making a diploid zygote

• Increasing the genetic variation within a population (benefit over asexual reproduction)

anisogamy

• A form of sexual reproduction where males and females produce gametes of different sizes

• Unequal investment in offspring

• Males produce small gametes, females produce large gametes

gonads

• Testes and ovaries

• The organs that produce gametes

• Where meiosis occurs to produce haploid gametes

spermatogenesis

• The process of producing sperm in the testes

• Takes place inside the seminiferous tubules

• Males can produce up to a trillion gametes in their lifetime

• 4 gametes are produced by a single spermatogonium

• Begins after the onset of puberty and continues throughout life

spermatogonia

• Germ cells that undergo meiotic divisions to become sperm

• Divides by mitosis to produce one cell that remains a spermatogonium (self-renewal) and another that differentiates into a primary spermatocyte which will enter meiosis to eventually form sperm

• Present at birth

primary spermatocyte

• Spermatocyte that has duplicated its DNA but not undergone a meiotic division

• Diploid cell (2n)

secondary spermatocyte

• Spermatocyte that has gone through the first meiotic division

• Chromosome number reduced by half

• Produces two haploid (n) daughter cells

• Divides into spermatids in second meiotic division

spermatids

• An immature sex cell formed from a secondary spermatocyte

• Mature into sperm

• Second meiotic division produces four haploid gametes (n)

seminiferous tubules

• Region of the testes where sperm and hormones are produced

• Contain two types of cells:

  • Spermatogonia

  • Sertoli cells

epididymis

• Duct from seminiferous tubules to vas deferens where sperm complete their maturation and are stored

• Sperm become motile and gain the ability to recognize and fertilize the egg

vas deferens

• Tube that carries sperm from the epididymis to the urethra

• Smooth muscle

ejaculatory duct

• Formed by the union of the vas deferens and seminal vesicle duct

• Sperm from the vas deferens and fluid from the seminal vesicles mix together to form semen

• Passes through the prostate gland before it opens into the urethra, prostatic gland adds prostatic fluid to the mixture

• Propels semen into the prostatic urethra during ejaculation

pathway of sperm

seminiferous tubules —> epididymis —> vas deferens —> ejaculatory duct —> urethra —> penis

seminal vesicle

• Male accessory glands that contribute enzymes and other secretions to semen

prostate gland

• Male accessory organ that contributes enzymes, nutrients, and other secretions to semen

• Surrounds the urethra

• Activates sperm

• Enlarges with age

bulbourethral gland

• Male accessory gland that produces components of semen

• Located below the prostate

• Contribute <5% of semen volume

• Secrete a small amount of thick, alkaline mucus prior to ejaculation (pre-ejaculate)

• Helps neutralize the acidic environment of the vaginal canal to protect the sperm

• Lubricates the urethra to reduce friction during ejaculation

acrosome

• Lysosome-like vesicle of sperm that contains powerful enzymes essential for fertilization

midpiece of sperm

Mitochondria to produce energy for sperm movement concentrates in the midpiece of the sperm body, along with microtubules that extend into the tail

flagellum

• Tail-like structure that is used for swimming

• Flagellum uses dynein to move

sertoli cells (nurse cells)

• Testicular cells that support sperm production

• Provide nourishment for the developing spermatogonia

• Located inside the seminiferous tubules

blood testes barrier

tight junctions between Sertoli cells that prevent free exchange between the extracellular fluid and the lumen of the seminiferous tubules

interstitial (Leydig) cells

• Cells in the testes that produce testosterone

• Found between the seminiferous tubules

oogenesis

• The process of forming female gametes (eggs)

• At birth, the normal female ovary contains about 1-2 million oocytes

• 1 functional gamete is produced from a primary oocyte

• Oogonia are produced during fetal development

ampulla

• The widest part of the fallopian tube

• Site of fertilization (sperm cell penetrates oocyte)

endometrium

• The secretory inner lining of the uterus

• Functional layer (stratum functionalis): the superficial layer shed during menstruation

• Basal layer (stratum basalis): deeper, more stable layer that remains during menstruation

• Contains glands that secrete nutrient-rich fluid to nourish a potential embryo after ovulation

• Goes through cyclic changes each month as a part of the menstrual cycle

menstruation

a process that occurs when the body sheds the endometrial lining

proliferative/follicular phase

• Phase of the menstrual cycle when the endometrium thickens and the ovarian follicles grow

• Occurs before ovulation in anticipation of pregnancy

• Estrogen levels rise as the dominant follicle in the ovary matures

• Rising estrogen levels stimulate the endometrium to proliferate and thicken

luteal phase

• Postovulatory phase of the uterus when it develops into a secretory structure

• If no pregnancy occurs, the superficial layers of the endometrium are lost during menstruation

• Ideal time for embryo implantation when the endometrium is thick and nutrient rich

ovulation

the release of an egg from the ovaries

primordial follicles

• Consists of a primary oocyte in early meiosis surrounded by a single layer of granulosa cells

• Present at birth and remain dormant until they begin to grow in reponse to hormonal signals during puberty

primary follicle

• An undeveloped primary oocyte and its outer layer of granulosa cells

• Oocyte begins to grow, number of granulosa cells increases

mature follicle

• Follicle selected for ovulation

• Meiosis resumes to form secondary oocyte

• Large fluid-filled follicle that ruptures during ovulation to release the secondary oocyte

primary oocyte

• Oocyte that has duplicated its DNA but not undergone a meiotic division

• Females are born with all of their primary oocytes

• Meiosis I begins during embryonic development and is arrested in prophase I

secondary oocyte

• The ovulated egg which has gone through the first meiotic division

  • Meiosis I resumes in the dominant follicle that is selected for ovulation to produce a secondary oocyte and a polar body

• Meiosis II begins (only completed if sperm penetration occurs)

corpus luteum

• Ovarian structure that produces estrogen and progesterone after ovulation

• Formed from the ruptured follicle

• No pregnancy = degenerates into corpus albicans

• Pregnancy = hormones sustain pregnancy

scrotum

• The external sac into which the testes descend so that they can stay cooler than body temperature

dartos muscle

• Smooth muscle that contracts to cause scrotal wrinkling

• Reduces the surface area available for heat loss

• Important for regulating the temperature of the testes

cremaster muscle

• Skeletal muscle that contracts to pull the testes closer to the body, increasing their temperature

• When it relaxes, the testicles hang lower, decreasing their temperature

pampiniform (venous) plexus

• A network of veins arising from the testicular venous outflow

• A key part of the countercurrent heat exchange system in the testes

• Absorbs heat from the warmer arterial blood as it travels toward the testes

  • Cools the arterial blood before it reaches the testes, helping to maintain the lower temperature (2 degrees cooler than body temp) needed for sperm production

varicocele

• Veins of the pampiniform plexus are enlarged

• Dilated veins cause blood to pool and move more slowly, reducing the temperature difference between the venous and arterial blood, weakening heat exchange

  • Heat has more time to transfer into the slow moving venous blood

  • Venous blood becomes less cool by the time it reaches the artery

  • Smaller temperature difference between the artery and vein reduces efficiency of heat exchange

• Results in higher testicular temperatures which negatively impacts sperm motility and production

path the egg takes to leave the body

• Egg is released from the ovary during ovulation

• Fimbriae at the entrance of the fallopian tube catch and transport the egg into the tube

• The egg travels through the fallopian tube where fertilization can occur if sperm are present

• If not fertilized, the egg enters the uterus and is eventually broken down

• The egg and the uterine lining pass through the cervix

• The unfertilized egg and uterine lining exit the body through the vagina during menstruation

vestibular glands

• Female accessory sex glands

• Produces a mucus-like secretion that lubricates the vagina during sexual intercourse

male and female parts with the same developmental origins

• The clitoris is homologous to the penis

• The labia is homologous to the scrotum

• The vestibular glands are homologous to the bulbourethral glands

female external genitalia

• Labia majora - outer folds of skin

• Labia minora - inner folds that surround the vaginal and urethral openings

• Clitoris

• Urethral opening

• Vaginal opening

male external genitalia

• Penis

• Scrotum

uterus

• A hollow, muscular organ

• Structure in which fertilized eggs implant and develop during pregnancy

• Myometrium - middle layer made of smooth muscle, produces uterine contractions during labor

• Contains more muscle than epithelium in comparison to the vagina

cervix

• Neck of the uterus that opens into the vagina

• Lined with mucous glands whose secretions create a protective barrier between the vagina and the uterus, can block or allow sperm to pass depending on the time in the menstrual cycle

• Creates mucous plugs that forms in the cervical canal during pregnancy and seals off the uterus to protect the fetus from infection

• Dilates during childbirth

clitoris

• Female external genitalia important for sexual arousal

• Has more than 10,000 nerve fibers

• Clitoral stimulation leads to increased vaginal blood flow, lubrication, and temperature. It also neutralizes the vaginal acidicity and increases the chances of conception.

fallopian tube

• Tube that transports eggs from the ovary to the uterus

• Ciliated cells actively beat to propel the ovum (egg) from the ovary towards the uterus

• Microvilli secrete nutrients

What signals do sperm move in response to?

• Rheotaxis - movement in response to fluid flow, they swim against the flow of fluid which helps guide them toward the uterus and fallopian tubes

• Thermotaxis - movement in response to temperature differences, sperm are attracted to the slightly warmer temp of the area near the ovulated egg

• Chemotaxis - movement in response to chemical signals, the egg secretes chemical attractants

vaginal epithelium

• The vagina is lined with stratified squamous epithelium, protects against abrasion

• Prior to menopause, the high estrogen levels stimulate the vaginal epithelium to thicken and maintain an acidic pH that protects against infection. The epithelium is thick, moist, and elastic.

• After menopause, the decline in estrogen causes the epithelium to become thinner and the vaginal pH to become more alkaline. This leads to increased dryness, reduced elasticity, and a higher risk of infection.

factors that may contribute to earlier onset of puberty and menstruation (menarche)

• Improved nutrition and higher body fat

• Exposure to endocrine-disrupting chemicals (interferes with hormonal signaling)

HPG axis

• Hypothalamus → Pituitary Gland → Gonad

• The hypothalamus contains neurosecretory cells that secrete releasing hormones (GnRH) into the portal system.

• GnRH stimulates the anterior pituitary to release tropic hormones (LH and FSH) that target the gonads

• The gonads (endocrine organ) produce sex hormones in response to tropic hormones (testosterone, estrogen)

tropic hormone

• A hormone that has an endocrine gland as their target

• FSH and LH

short-loop negative feedback

• A pituitary hormone feeds back to decrease hormone secretion by the hypothalamus

long-loop negative feedback

• Negative feedback from an endocrine gland hormone to the hypothalamus and anterior pituitary

gonadotropin-releasing hormone (GnRH)

• Hypothalamic hormone that stimulates release of FSH and LH from the anterior pituitary

• Release from the hypothalamus occurs in small pulses every 1-3 hours

• Continuous administration of GnRH fails to stimulates secretion of FSH and LH (receptors become desensitized and downregulated)

luteinizing hormone (LH)

• Anterior pituitary hormone that acts on the gonads to influence hormone production

• Stimulates the Leydig (interstital) cells to produce testosterone from cholesterol

• Stimulates theca cells to produce androgens

• Levels are low during the follicular phase, rise dramatically just before ovulation, and then decline in the luteal phase

• LH surge triggers ovulation

follicle-stimulating hormone (FSH)

• Anterior pituitary hormone that stimulates gamete production in the gonads

• Stimulates sertoli cells resulting in:

  • Synthesis of ABP

  • Stimulation of spermatogenesis

  • Secretion of inhibin

• Induces aromatase expression so granulosa cells can convert androgens into estrogens

• Stimulates the growth of follicles

• FSH levels rise at the very beginning of the cycle (due to drop in estrogen and progesterone), rising estrogen levels from the follicles inhibits FSH secretion causing levels to decline, levels rise right before ovulation, high progesterone after ovulation causes levels to drop

testosterone

• Sex hormone dominant in males

• Secreted by Leydig (interstitial) cells and diffuses into nearby seminiferous tubules where sertoli cells help maintain a high local concentration of testosterone by binding it to ABP

• Long loop negative feedback: inhibits the release of GnRH, FSH, and LH

androgen-binding protein

• Sertoli cell protein that binds testosterone to keep it in the lumen of the seminiferous tubule

inhibin

• Peptide hormone from the gonads that inhibits FSH secretion from the anterior pituitary

• Secreted by sertoli and granulosa cells in response to FSH

aromatase

• Convert androgens (testosterone) into estrogens

theca cell

• The outermost layer of the ovarian follicle

• Stimulated by LH to produce androgens (e.g. testosterone)

• No aromatase activity

• Androgens diffuse into granulosa cells

• Progesterone made in granulosa cells acts as a precursor that diffuses to theca cells, where it is converted into androgens

granulosa cell

• Innermost layer of the ovarian follicle

• Stimulated by FSH to secrete estrogens and inhibin

  • FSH stimulates granulosa cells to convert androgens recieved from theca cells into estrogen using the enzyme aromatase

estrogen

• Steroid hormone associated with female reproductive organs

• Estrogen levels rise during the mid-follicular phase and then drop after ovulation. This is followed by a secondary rise in estrogen during the mid-luteal phase with a decrease at the end of the menstrual cycle.

progesterone

• Primarily produced after ovulation during the luteal phase

• After the mature follicle releases the egg, the granulosa and theca cells of the ruptured follicle transform into luteal cells, forming the corpus luteum

• These luteual cells are now specialized to produce large amounts of progesterone

hormonal control of the menstrual cycle

1. The hypothalamus releases GnRH, which stimulates the anterior pituitary to secrete FSH and LH

2. FSH promotes the growth and maturation of follicles in the ovary. Granulosa cells are stimulated by FSH to secrete estrogen and inhibin.

3. Estrogen and inhibin act on the hypothalamus and pituitary gland to reduce the release of GnRH and FSH. This causes a decline in FSH levels which causes smaller follicles to degenerate, resulting in the emergence of a single dominant follicle

4. As the dominant follicle grows, it produces more estrogen which triggers a positive feedback loop that stimulates a surge of LH (and FSH).

5. This rise in LH leads causes ovulation

6. The ruptured follicle transforms into the corpus luteum which produces high levels of progesterone (also produces estrogen)

7. Progesterone inhibits GnRH, FSH, and LH secretion through negative feedback (inhibin also exerting negative feedback)

   • If pregnancy does not occur, the corpus luteum degenerates and progesterone levels fall, removing the inhibition on GnRH and allowing FSH levels to rise again to trigger the next cycle

kisspeptin

• Hypothalamic neuropeptide that acts upstream of GnRH

• Stimulates the release of GnRH

• Released by KNDy neurons in pulses

• Sensitive to feedback from low levels of sex steroids

• Factors that may impact release:

  • Day length

  • Food intake/body fat

  • Stress level

  • Environmental estrogens