EXAM LECTURE 1 BIO 221

What are some major forms of birth control and their mechanisms of action?

Barrier methods (e.g., condoms) physically block sperm. Hormonal contraceptives (e.g., pills, patches, implants) contain estrogen and progesterone, which prevent ovulation by inhibiting FSH and LH, and thicken cervical mucus. Hormonal IUDs release progesterone, thinning the endometrium and thickening cervical mucus. Sterilization permanently blocks gamete transport.

Where does fertilization typically occur?

In the ampulla of the fallopian tube.

What is the ball of cells called that develops from cleavages after fertilization, and what does it become?

After fertilization, the zygote undergoes mitotic cleavage, forming smaller cells called blastomeres. These compact into a solid ball known as the morula. As fluid collects inside, a cavity called the blastocoel forms, resulting in a blastocyst. The blastocyst, containing an inner cell mass and trophoblast, is the stage that implants into the uterine wall.

What are the two groups of cells in the blastocyst, and what do they ultimately become?

The blastocyst contains two main types of cells: the inner cell mass, which develops into the embryo, and the trophoblast, which forms the fetal portion of the placenta.

What is the source of human chorionic gonadotropin (hCG)?

The syncytiotrophoblast, which forms after implantation, is the structure that secretes human chorionic gonadotropin (hCG).

What is the target and action of hCG?

hCG targets the corpus luteum, maintaining progesterone and estrogen production to support early pregnancy.

What else is significant about hCG?

It prevents menstruation and is the hormone detected in pregnancy tests.

What are some possible triggers for parturition (childbirth)?

Possible triggers for parturition is rising fetal cortisol. Placental estrogen increases and progesterone decreases. Estrogen makes the uterus more sensitive to oxytocin and prostaglandins which causes the uterus to have stronger contractions. More cervical stretches will increase the release of oxytocin until labor.

Describe the positive feedback cycle of oxytocin secretion during labor/parturition.

Cervical stretch from the baby’s head signals the hypothalamus, causing the posterior pituitary to release oxytocin. Oxytocin strengthens uterine contractions, which increase cervical stretch and trigger more oxytocin release, continuing until birth.

Name the hormones involved in lactation and their function.

Prolactin stimulates milk production after childbirth. Oxytocin causes milk ejection by contracting breast muscle cells. Estrogen and progesterone prepare the breast during pregnancy but inhibit milk secretion until after birth. Human placental lactogen supports breast development and maternal metabolism for lactation.

What are the general functions of the male reproductive system?

Producing sperm and delivering it to the female reproductive system.

What are the general functions of the female reproductive system?

Produces ova (eggs) and provides a place for a new human to develop during pregnancy.

Name the reproductive glands for males

Testes

Name the reproductive glands for females

Ovaries

What are the two functions of the reproductive glands?

They produce gametes and secrete hormones. The male gametes are sperm the female are ova.

What is the gene which determines differentiation to male development?

The SRY gene, located on the Y chromosome, initiates male sex determination and development.

What does the SRY gene allow for the development of what structure and what hormone?

The development of testes and the production of testosterone.

What two cells do the testes contain?

The testes contain Leydig cells, which secrete testosterone, and Sertoli cells, which support and nourish developing sperm.

What main hormone do Sertoli (sustentacular) cells produce?

They produce the Anti-Mullerian Hormone (AMH), which inhibits the development of female reproductive structures. AMH causes regression of Müllerian ducts and prevents the uterus and fallopian tubes from developing in XY embryos.

What hormone do Leydig cells produce?

Leydig cells produce testosterone, a key hormone in male reproductive development.

What is testosterone converted into and why?

Testosterone is converted to dihydrotestosterone (DHT) by the enzyme 5-alpha reductase. DHT is more potent than testosterone and is crucial for the development of male external genitalia (penis, scrotum, prostate) and later secondary sexual characteristics.

What does testosterone from Leydig cells preserve?

Wolffian ducts and promotes the development of male internal reproductive structures. The ducts form the epididymis, vas deferens, seminal vesicles, and ejaculatory ducts.

What’s a good thing to remember?

AMH (from Sertoli cells) causes regression of the Müllerian ducts in males, while testosterone (from Leydig cells) maintains the Wolffian ducts. In females, the absence of AMH allows the Müllerian ducts to develop, and the absence of testosterone leads to regression of the Wolffian ducts.

What hormone is required for the development of the penis and prostate?

Dihydrotestosterone (DHT), formed from testosterone by 5-alpha reductase, is the more potent androgen responsible for the development of male external genitalia (penis and scrotum) and the prostate gland.

What enzyme catalyzes the formation of dihydrotestosterone?

5α-reductase

What happens if a male doesn’t have DHT?

An XY person can produce testosterone and AMH but male external parts won’t develop properly.

When do testes usually move into the scrotum?

Typically around the seventh month of fetal development.

What is spermatogenesis?

The process by which male gametes, or sperm cells, are produced in the testes through several stages of cell division and maturation.

Spermatogensis begins when and occurs where?

Begins at puberty (12-14) when rising testosterone levels activate the process. Spermatogenesis occurs inside the seminiferous tubules (where immature cells turn into sperm) of the testes. The spermatogonia (the first immature male germ cells) line the seminiferous tubules and mature into spermatozoa.

Name the stages of spermatogenesis and tell whether the stage is diploid or haploid.

Spermatogonium (46, diploid, 2n)

        │   (mitosis)

        ↓

Primary Spermatocyte (46, diploid, 2n)

        │   (meiosis I)

        ↓

Secondary Spermatocytes (23, haploid, n)

        │   (meiosis II)

        ↓

Spermatids (23, haploid, n)

        │   (spermiogenesis: shaping & maturation)

        ↓

Spermatozoa (23, haploid, n) → Mature sperm

Name the functions of the sustentacular cells or sertoli cells.

These are the nurse cells of the testes; they’re in the seminiferous tubules, and they support and nourish developing sperm. They provide nutrients and growth factors to sperm. They secrete AMH, and produce fluid to help transport sperm in the tubules.

What is a good way to remember the functions of the Sertoli cells?

S – Support & nourish developing sperm
P – Phagocytosis of excess cytoplasm from maturing sperm
E – Establish blood-testis barrier (immune protection)
R – Release hormones (Inhibin, ABP, AMH in fetus)
M – Move sperm with testicular fluid through seminiferous tubules

What is the temperature requirement for spermatogenesis?

Requires a temperature lower than core body temperature, so normal body temperature is 37 °C (98.6 °F) and optimal temperature for spermatogenesis is 34-35 °C (93-95°F).

What muscles help to regulate testes temperature?

The cremaster muscle and the dartos muscle.

What is the cremaster muscle and its function?

A skeletal muscle that surrounds the spermatic cord and testes, it pulls the testes closer to the body when cold and relaxes when warm.

What is the dartos muscle and what is its function?

A smooth muscle in the wall of the scrotum, it wrinkles the scrotal skin in the cold, which reduces surface area to consrve heat and relaxes in the heat (the skin smooths out, increasing surface area to release heat).

What is the total time required for sperm development and maturation?

Sperm development takes about 64–74 days in the testes plus 10–14 days in the epididymis, totaling 70–90 days.

Where is sperm primarily stored?

The main storage site for sperm is the epididymis.

Describe the parts of a sperm and their functions.

The sperm head contains 23 chromosomes and an acrosome with enzymes for egg penetration, enabling fertilization. The neck links the head and tail and holds centrioles for cell division. The midpiece, rich in mitochondria, provides ATP for movement, while the tail (flagellum) propels the sperm through the female tract.

What is the erection reflex?

The erection reflex is an autonomic response in which the nervous system, blood vessels, and penile tissues coordinate to allow blood to fill the corpora cavernosa, resulting in enlargement of the penis.

Describe the reflex arc for an erection.

An erection reflex begins with sexual stimulation, either by touch of the glans/skin or signals from the brain. Sensory afferents carry these impulses to the sacral spinal cord (S2–S4), which activates parasympathetic efferents. These nerves release nitric oxide in the penile arterioles and smooth muscle, causing vasodilation and increased blood flow into the corpora cavernosa, resulting in an erection.

Where are the primary sensory receptors for the erection reflex located?

Sensory receptors for the erection reflex are mainly in the glans penis and along the penile skin, sensing touch, pressure, and temperature.

Explain the roles of the sympathetic and parasympathetic nervous systems in penile function.

Parasympathetic nerves trigger vasodilation, allowing blood to fill the erectile tissues and cause an erection. Sympathetic nerves trigger vasoconstriction, reducing blood flow and ending the erection.

Describe the pathway of nitric oxide (NO) production leading to an erection.

1. Stimulation: Touch (glans/skin) or brain signals (arousal) activate parasympathetic nerves (S2-S4).

2. Enzyme Activation: In penile nerves and blood vessel lining, nitric oxide synthase (NOS) is activated.

3. NO Production: Nitric Oxide Synthase converts L-arginine into nitric oxide (NO) + citrulline. NO diffuses into smooth muscle cells.

4. Action in smooth muscle: NO activates guanylyl cyclase, increasing cGMP levels.

5. Effect: cGMP relaxes smooth muscle, arteries dilate, more blood flows in, veins compress, leading to an erection.

What is the physiological effect of nitric oxide (NO) in penile function?

Nitric oxide (NO) relaxes smooth muscle in penile arteries, causing them to widen (vasodilation). More blood flows in, veins are compressed, and blood is trapped — making the penis firm and erect.

What is the action of guanylyl cyclase?

Guanylyl cyclase is an enzyme that turns GTP → cGMP, which acts as a second messenger inside cells. cGMP then triggers effects like blood vessel relaxation (vasodilation), smooth muscle relaxation, controlling ion channels, preventing platelets from clumping, and aiding vision.

What is the action of Phosphodiesterase 5 (PDE-5)?

PDE-5 breaks down cGMP into GMP, ending cGMP signaling and reducing smooth muscle relaxation and vasodilation. In short: Guanylyl cyclase makes cGMP, PDE-5 destroys cGMP.

Describe the efferent responses involved in ejaculation.

• Sympathetic: Emission, contraction of the vas deferens, seminal vesicles, and prostate to propel semen into the urethra.

• Parasympathetic: Erection support, relaxes urethral and prostatic smooth muscle to allow semen passage.

• Somatic: Expulsion, rhythmic contraction of bulbospongiosus and ischiocavernosus muscles to eject semen.

Name key substances found in semen and their roles.

Semen contains:

1. Fructose: Energy for sperm.
2. Lubricant: Aids in movement.
3. H_2O: Fluid medium.
4. Citric acid and Zinc: Important for sperm viability and function.
5. Prostaglandins: Affect female reproductive tract motility.

Define sperm capacitation.

Removal of surface glycoproteins and cholesterol from sperm membrane in the female tract, enabling hypermotility and acrosome reaction for fertilization.

Define sperm activation.

Sperm activation refers to the functional changes following capacitation, including hyperactivated motility and initiation of the acrosome reaction, enabling penetration of the oocyte and successful fertilization.

Explain the hormonal regulation of testosterone and inhibin secretion.

The hypothalamus releases GnRH, which stimulates the anterior pituitary to secrete LH and FSH. LH acts on Leydig cells to produce testosterone, which feeds back to inhibit GnRH and LH release. FSH acts on Sertoli cells to support sperm production and secrete inhibin, which provides negative feedback to reduce FSH release

👉 In short: GnRH → LH & FSH → (LH → testosterone, FSH → inhibin) → both give negative feedback to keep hormone levels balanced

List the primary targets and actions of testosterone.

Testosterone stimulates growth and function of reproductive organs (testes, epididymis, seminal vesicles, prostate) and supports spermatogenesis. It promotes development of external genitalia (penis, scrotum) in the fetus and puberty. It induces secondary sexual characteristics, including facial/pubic hair, deepening of the voice, and increased muscle and bone mass. It enhances protein synthesis, red blood cell production, and sebaceous gland activity, and it regulates libido, sexual behavior, and aggression.

What is the action of the enzyme aromatase?

• Aromatase is an enzyme.

• Its job is to convert androgens (e.g., testosterone) into estrogens (e.g., estrone, estradiol).

• It is found in the ovaries, testes, fat tissue, brain, and placenta.

• The estrogens it makes are important for female reproduction, bone strength, and hormone balance (feedback on GnRH, LH, FSH).

👉 Super short: Aromatase changes testosterone into estrogen, helping control reproduction, bone health, and hormone levels.

What is the name for the cycle of hormonal and physical changes in a female?

Menstrual Cycle, cycle of 28 days that allow for preparation of fertilization and pregnancy.

What is the name of the first cycle?

Menarche.

Name the stages of oogenesis and indicate whether the stage is diploid or haploid.

1. Oogonium-diploid (2n)

2. Primary oocyte-diploid (2n) arrests in prophase I (Before Birth 1, 2)

3. Secondary oocyte—haploid (n) arrests in metaphase II (After puberty)

4. Ovum haploid (n): The first part of the menstrual cycle is prepping for fertilization; the second is preparing for pregnancy.

Name the 2 outer layers of cells of the ovarian follicle and indicate what hormone is released from each.

• Theca cells, which release androgens (testosterone), and granulosa cells, which convert androgens to estrogens

What is the thick layer of glycoproteins that surrounds the oocyte?

• Zona pellucida

Describe the follicular phase out of the 2 ovarian phases and indicate the days in the framework of a 28-day cycle.

• Follicular Phase (Day 1-14): Begins with menstruation. FSH stimulates follicle growth and granulosa cells secrete estrogen, which rebuilds and thickens the endometrium. Rising estrogen eventually triggers the LH surge, causing ovulation at mid-cycle.

What event separates the 2 phases?

• Ovulation (Day 14)

What structure is prominent in the second phase?

• Corpus luteum, a temporary gland formed from the ruptured follicle after ovulation. If fertilization doesn’t happen, it breaks down into a scar-like structure called the corpus albicans .

What triggers ovulation?

• A surge in LH , triggered by several days of high estrogen from the dominant follicle

What change occurs that signals ovulation has occurred?

Ovulation happens when the mature follicle bursts, releasing the secondary oocyte (egg) into the fallopian tube. Progesterone then causes a small rise in body temperature.

Name the 3 phases of the uterine cycle.

• Menstrual Phase (Day 1-5)- Proliferative Phase (Day 6-14)- Secretory Phase (Day 15-28)

What is occurring in the uterine endometrium in the menstrual phase?

• During the menstrual phase, low hormone levels of estrogen and progesterone cause the functional layer of the endometrium to shed resulting in menstrual bleeding.

What is occurring in the uterine endometrium in the proliferative phase?

• In the proliferative phase, rising estrogen rebuilds and thickens in the endometrium, forming new glands and blood vessels in preparation for possible implantation.

What is occurring in the uterine endometrium in the secretory phase?

• During the secretory phase, progesterone makes the endometrium glandular, vascular, and nutrient rich, preparing it for possible implantation.

What causes menstruation?

• Menstruation occurs when the corpus luteum degenerates, causing progesterone and estrogen levels to drop, which triggers shedding of the endometrial lining.

What chemical mediator mediates uterine contraction and vasoconstriction?

• Prostaglandins stimulate uterine contractions and constrict blood vessels.

What changes occur in the cervical mucous during the menstrual cycle and what hormones influence these effects?

Rising estrogen in the follicular phase makes it thin, watery, and stretchy to help sperm enter, while post-ovulation progesterone makes it thick and sticky, blocking sperm and pathogens.

Name the changes that occur in female reproductive tract during sexual intercourse.

• Increased vaginal lubrication, uterine and vaginal contractions, and thin cervical mucus to help sperm movement.

Describe the hormonal control by the hypothalamus and the anterior pituitary on the secretion of ovarian hormones.

• Hypothalamus releases GnRH → stimulates anterior pituitary → secretes FSH & LH → FSH promotes follicle growth & estrogen; LH triggers ovulation & corpus luteum → corpus luteum secretes progesterone → estrogen & progesterone provide feedback to hypothalamus and pituitary.

What are some of the targets and actions of the ovarian hormones?

• Estrogen builds the endometrium, develops breasts and secondary sex characteristics, and maintains bone health. Progesterone converts the endometrium to the secretory phase, prepares the breasts for lactation, and supports pregnancy.

What is the endometrium?

The endometrium is the inner lining of the uterus that undergoes cyclic changes each menstrual cycle. Under estrogen, it thickens and proliferates; under progesterone, it becomes secretory and glandular to support implantation. If no fertilization occurs, it sheds during menstruation.

Describe the luteal phase out of the 2 ovarian phases and indicate the days in the framework of a 28-day cycle.

Luteal Phase (Day 15-28): After ovulation, the corpus luteum secretes progesterone (and some estrogen) to maintain the endometrium for implantation; if no fertilization occurs, hormone levels fall, triggering menstruation.

What hormones are released during the follicular and luteal phases?

Follicular phase: The developing follicles release estrogen and inhibin B under the stimulation of FSH and LH.
Luteal phase: The corpus luteum releases progesterone, estrogen, and inhibin A under LH support.

What other hormones do Sertoli cells produce?

They produce inhibin B, which helps regulate spermatogenesis by inhibiting FSH secretion. They also produce androgen-binding protein (ABP) and support developing sperm cells.

How can parasympathetic efferents trigger vasodilation in an erection?

Parasympathetic efferents release ACh → ACh binds muscarinic receptors on endothelial cells → endothelial cells produce NO → NO increases cGMP in smooth muscle → smooth muscle relaxes → penile arteries dilate and veins compress → erection occurs.

The cardiovascular system consists of what?

Heart & blood vessels. Its job is to deliver blood to tissues.

What are the 3 circuits?

The systemic circuit, the pulmonary circuit, and the coronary circuit.

Name 5 characteristics of cardiac muscle cells

Cardiac muscle cells are striated, cylindrical shaped, involuntary, typically mono-nucleated, and linked by intercalated discs with gap junctions.

What are the 2 types of cardiac muscle cells?

Cardiac cells include pacemaker cells that trigger spontaneous action potentials and cardiocytes that contract in response to electrical signals.

Pacemaker cells create the signal, and cardiocytes carry out the contraction

What are the phases of the Pacer cell action potential and what ion events occur during each phase?

Phase 4 – Pacemaker potential: The membrane slowly depolarizes due to sodium (Na⁺) entry through funny channels and calcium (Ca²⁺) entry through T-type channels.

Phase 0 – Depolarization: A rapid upstroke occurs as calcium (Ca²⁺) enters the cell through L-type channels.

Phase 3 – Repolarization: Potassium (K⁺) leaves the cell, restoring the membrane potential back toward its resting level.

Where are pacer cells located and what are the inherent rates of firing in these areas?

Pacemaker cells are in the:

• Sinoatrial node (SA node): 60–100 bpm

• Atrioventricular node (AV node): 40–60 bpm

• Purkinje fibers (PF): 20–40 bpm

  The other nodes are backups, only taking over if the SA node fails or slows down too much.

What are the phases of the cardiocyte action potential and what ion events occur during each phase?

• Phase 0 – Depolarization: Rapid sodium (Na⁺) influx.

• Phase 1 – Initial repolarization: Brief potassium (K⁺) efflux.

• Phase 2 – Plateau: Calcium (Ca²⁺) enters through L-type channels while potassium (K⁺) leaves slowly.

• Phase 3 – Repolarization: Potassium (K⁺) efflux restores the membrane potential.

• Phase 4 – Resting: Stable resting potential maintained.

How is the depolarization generated by the pacer cells transmitted to the cardiocytes?

Pacemaker cells send their electrical signal to cardiocytes through intercalated discs, where gap junctions let ions pass so the heart muscle contracts together.

What are the steps in the process of converting the electrical signal of the action potential in a cardioctye to the mechanical response of muscle contraction?

When cardiocytes depolarize, calcium ions Ca^{2⁺} enters through L-type channels, causing more calcium ions Ca^{2⁺} to be released from the sarcoplasmic reticulum. These calcium ions bind troponin (a protein complex), allowing the muscle to contract.

Phase 2 = electrical plateau + calcium influx → triggers contraction.

Define systole and diastole

Systole is when the ventricles contract and push out blood, and diastole is when they relax and fill with blood.

Which mechanical events of the heart are produced by the electrical activity represented in each waveform of the EKG?

The P wave triggers atrial contraction, the QRS complex triggers ventricular contraction, and the T wave triggers ventricular relaxation.

What is the time of a single cardiac cycle if the heart rate is 75bpm?

A single cardiac cycle lasts 0.8 seconds.

What portion of the time is systole?

Systole lasts 0.3 seconds.

What portion of the time is diastole?

Diastole lasts 0.5 seconds.

If the heart rate goes up significantly which phase is affected the most?

When heart rate rises, diastole shortens the most, reducing the time the ventricles have to fill with blood.

What important events occur during diastole?

During diastole, the ventricles relax and fill with blood, first passively as the AV valves open, then actively by atrial contraction, while the semilunar valves remain closed to prevent backflow.

Write the blood flow pattern through the heart starting with the superior and inferior vena cava.

Superior/Inferior Vena Cava → Right Atrium → Tricuspid Valve → Right Ventricle → Pulmonary Valve →Pulmonary Trunk—>  Pulmonary Artery → Lungs → Pulmonary Veins → Left Atrium → Mitral (Bicuspid) Valve → Left Ventricle → Aortic Valve → Aorta → Body

Distinguish between active and passive ventricular filling.

Passive ventricular filling occurs as blood flows from the atria to the ventricles due to a pressure gradient, while active filling happens when atrial contraction pushes extra blood into the ventricles.

What causes the AV valve to open?

The AV valve opens when atrial pressure exceeds ventricular pressure.

What causes the semilunar valves to open?

The semilunar valves (aortic and pulmonary) open when the pressure in the ventricles rises higher than the pressure in the aorta and pulmonary trunk during ventricular systole.

The 2 valves include:

• Aortic valve: between the left ventricle and the aorta.

• Pulmonary valve: between the right ventricle and the pulmonary trunk.

What is the stroke volume?

Stroke volume is the amount of blood ejected by a ventricle with each heartbeat.