Lecture 15: Male Reproductive System

Question 1

explain penis during resting state

Answer 1

Resting State→ flaccid penis
-Arterioles supplying erectile tissues are
constricted
-Muscular partitions are tense
-Blood flow into erectile tissue is restricted

Question 2

explain penis during erection

Answer 2

-When aroused (touch, mechanical stimulation,
erotic sights, sounds, smells), sacral segment
triggers parasympathetic reflex → releases NO
-Smooth muscles in walls penile blood vessels relax
-Arterioles dilate and erectile tissues filled
-Penis stiffens and elevates to upright position

Question 3

explain effect of NO (nitric oxide) release in erection

Answer 3

-Causes relaxation of local vascular smooth muscle
-When smooth muscles relax, arterioles dilate
-Corpora cavernosa expands and retards venous drainage, leading to engorgement of erectile tissues with blood, and enlargement and stiffening of penis → erect penis
-Corpus spongiosum keeps urethra open

Question 4

describe random (spontaneous) erections

Answer 4

-Unexpected erection in the absence of any known stimulus → out of the blue
-Normal, and indicates good blood flow
-Indicates problem if flaccid in the presence of sexual stimuli (e.g. on bed)
-Nocturnal erection (morning wood) – random process, penis is erect on waking up from sleep
-High testosterone levels in the morning; contact with clothing, bedsheets, etc.
-Indicates healthy penile blood flow

Question 5

what is emission

Answer 5

-Release of small amount of semen before ejaculation; occurs under sympathetic stimulation
-Due to peristaltic contraction across the duct system:
a) Peristaltic contractions of ampullae of ductus deferens: Push seminal fluid and sperm into prostatic urethra
b) Contractions in seminal glands and prostate: Move seminal mixture along spongy urethra

Question 6

what are the 4 steps in ejaculation

Answer 6

1. contraction
2. spinal reflex
3. resolution
4. latent (refractory) period

Question 7

describe ejaculation

Answer 7

Powerful release of semen from the duct system to the exterior
-Spinal reflex is initiated over sympathetic nerves serving genital organs

Question 8

what is step 1 in ejaculation

Answer 8

-Ductus deferens, prostate, and seminal glands contract and empty contents into prostatic urethra;
–Bladder internal sphincter muscle constricts, preventing expulsion of urine or reflux of semen into bladder

Question 9

what is step 2 in ejaculation

Answer 9

-Semen in urethra triggers spinal reflex through somatic neurons
-Bulbospongiosus and ischiocavernosus muscles undergo rapid series of contractions → stiffens penis
-Push semen toward external urethral opening → causes intense pleasurable sensations → climax (orgasm), associated with increased heart rate and blood pressure

Question 10

what is step 3 in ejaculation

Answer 10

Resolution
-Follows ejaculation, period of muscular and psychological relaxation
-Blood vessels constricted by signals from sympathetic nerves reducing blood flow to penis
-Blood begins to exit erectile tissues → Detumescence (process of losing erection)

Question 11

what is step 4 of ejaculation

Answer 11

Latent/ Refractory Period
-Time during which man is unable to achieve another orgasm
-Can last minutes to hours
-Latent period lengthens with age

Question 12

describe tje male sexual response cycle

Answer 12

1. Excitement Phase: vasocongestion results in erection, the testes begin to elevate, skin on the scrotum tenses and thickens
2. Plateua Phase: the tip of the penis turns a deep reddish-purple, the testes become completely elevated, droplets of semen may be released from the penile opening from the penile opening before ejaculation
3. Orgasm Phase: sensations o impending ejaculation lasting 2-3 seconds precede to ejaculatory reflex, orgasmic contractions propel semen through the penis and out of the body
4. Resoultion Phase: men become physiologically incapable of acheiving another orgasm for ejaculation for a period of time called the refractory period

Question 13

what is spermatogenesis

Answer 13

-process of sperm formation; occurs in seminiferous tubules
-begins at puberty; continues past age 70
-complete process takes about 64 days
three steps: mitosis, meiosis, spermiogenesis

Question 14

slide 6 neural activation of erection

Answer 14

Look at graph

Question 15

what is the mitosis phase of spermatogenesis

Answer 15

first step
each division of a diploid spermatogonlum produces two daughter cells, one is a spermatogonlum that remains in contact with the basement membrane of the seminiferous tubule and the other is a primary spermatocyte that is displaced toward the lumen, these events from spermatogonlum to primary spermatocyte take 16 days

Question 16

what is the meiosis I step in spermatogenesis

Answer 16

second step
as meiosis I begins, each primary spermatocyte contains 46 individual chromosomes. at the end of meiosis I, the daughter cells are called secondary spermatocytes. every secondary spermatocyte contains 23 chromosomes, each with a pair of duplicate chromatids. this pahes of spsermatogenesis takes ~24 days

Question 17

what is the meiosis II step in spermatogenesis

Answer 17

the secondary spermatocytes soon enter meiosis II, which yeilds four haploid spermatids, each containing 23 chromosomes. for each primary spermatocyte that enters meiosis, four spermatids are produced. this phase lasts only a few hours

Question 18

what is the spermiogenesis step in spermatogenesis

Answer 18

physical maturation
this is the last step of spermatogenesis, each spermatid matures into a single sperm. the rpocess of spermiogenesis, from spermatids to sperms, takes 24 dyas

Question 19

describe the last part of spermiogenesis

Answer 19

-Each spermatid matures into one sperm
-Involves major structural Changes:
*Spherical spermatids change into elongated, slender sperm cell
*Acrosomal formation and tail development

Spermiation – a sperm cell:
-Loses attachment to nurse cell
-Enters lumen of seminiferous tubule
-Fluid from nurse cells direct sperm into the ducts of testes

Question 20

what is capacitation

Answer 20

-Series of cellular and physiological changes spermatozoa undergo to fertilize female egg
-Sperm leaving epididymis:
*Mature but immobile
*To become motile (actively swimming) and fully functional: Sperm must undergo capacitation

Question 21

what are the two steps in capacitation

Answer 21

1. Sperm become motile
   -When mixed with secretions of seminal glands
2. Sperm become capable of fertilization
   -When exposed to female reproductive tract

Question 22

describe the anatomy of sperm

Answer 22

sperm is designed to reach and penetrate the secondary oocyte in order to acheive fertilization and create a zygote
-parts: head, neck, middle piece, principal piece & end piece

Question 23

describe head of sperm

Answer 23

genetic region, contains nucleus with 23 chromosomes; Acrosome covers the head and contains hydrolytic enzymes to help with penetration

Question 24

describe the neck of sperm

Answer 24

contains centrioles that form the microtubules that make up the rest of the tail

Question 25

describe the middle piece of sperm

Answer 25

spiral around mitochondria that make ATP to power sperm motility

Question 26

describe the principal piece & end piece of sperm

Answer 26

constitute the tail used for movement

Question 27

describe mature sperm

Answer 27

Lacks:
-Endoplasmic reticulum
-Golgi apparatus
-Lysosomes and peroxisomes
-Inclusions

Loss of organelles reduces size and mass

Sperm must absorb nutrients (primarily fructose) from surrounding fluid

Question 28

describe the hormonal controls of spermatogenesis

Answer 28

1. the hypothalamus releases GnRH, which reaches the anterior pituitary via the hypophyseal portal veins
2. GnRH causes anterior pituitary gonadotropic cells to release FSH and LH
3. FSH indirectly stimulates spermatogenesis by causing sustentocytes to release ABP, which keeps the local concentration of testosterone high
4. LH stimulates interstitial endocrine cells to secrete testosterone, which is essential for spermatogenesis
5. testosterone acts at other body sites [ex. to stimulate maturation of sex organs, development and maintenance of secondary sex characteristics, and libido (sex drive)]
6. negative feedback by testosterone inhibits FSH and LH release from the anterior pituitary and GnRH release from the hypothalamus
7. inhibin released by sustentocytes feeds back on anterior pituitary, decreasing FSH release

The Hypothalamic-Pituitary-Gondadal Axis

Question 29

what are the 4 hormones responsible for control of spermatogenesis

Answer 29

-GnRH= gonodotropin-releasing hormone
-FSH= follicle-stimulating hormone
-LH= luteinizing hormone
-ABP= androgen-binding protein

Question 30

what is erectile dysfunction (ED)

Answer 30

Parasympathetic nerves of penis release too little NO (nitric oxide) leading to inability to attain erection

Question 31

what cauese a temporary ED episode

Answer 31

psychological factors, alcohol or drugs (antihypertensives, antidepressants, etc.)

Question 32

what causes chronic ED

Answer 32

problems with blood vessels (atherosclerosis, varicose veins) or nervous system (stroke, penile nerve damage, multiple sclerosis)
–Diabetes mellitus is often underlying cause
-New drugs, sildenafil (Viagra) and others enhance effect of existing NO (nitric oxide)

Question 33

what is priapism

Answer 33

painful and persistent erection in absence of sexual arousal that lasts for hours
-Due to medications used to attain erection; induce abnormalities of blood vessels, nerves

Question 34

what is premature ejaculation

Answer 34

ejaculation occurs while at foreplay or just immediately after penetration
-Caused by hypersensitive glans penis or foreskin; anxiety; psychological and emotional trauma

Question 35

what is infertility in males

Answer 35

Problems associated with sperm quality or quantity → inability to impregnate the female
Causes:
* Ingested foreign molecules – environmental toxins, phthalates (oily solvents from plastics), pesticides, herbicides, etc.
* Estrogen-like compounds block action of male sex hormones

Question 36

causes of infertility in males

Answer 36

• Ingested foreign molecules – environmental toxins, phthalates (oily solvents from plastics), pesticides, herbicides, etc.
• Estrogen-like compounds block action of male sex hormones
• Antibiotics such a tetracycline may suppress sperm formation
• Radiation, lead, marijuana, and excessive alcohol can cause
  abnormal sperm to be produced (two-headed, multiple-tailed)
• Defects in calcium channels, hormonal imbalances and oxidative stress
• Thermal related events, such as sperm or overuse of hot tubs
  may inhibit sperm maturation