Ch. 27 - Male Reproductive System

External Genitalia of Males

scrotum and penis

• Occupy the perineum

  • Bordered by the pubic symphysis, ischial tuberosities, and coccyx

• Main function is to deliver gametes

Scrotum

pouch of skin, muscle, and fibrous connective tissue containing the testes

• Left testicle usually hangs lower than the right so the two are not compressed against each other

• Skin has sebaceous glands, sparse hair, rich sensory innervation, and dark pigmentation

• Internal median septum divides scrotum into right and left sides

• left side has the longer testicular vein, so it is very prone to having circulatory issues

Spermatic Cord

bundle of fibrous connective tissue containing the ductus deferens, blood and lymphatic vessels, and testicular the nerve

• Continues through the inguinal opening into the pelvic cavity

  • External inguinal ring: inferior entrance to inguinal canal

  • Internal inguinal ring: superior exit to pelvic cavity

Why are testes in the scrotum?

Human testes reside in the scrotum because of its cooler environment

• Cannot produce sperm at core body temperature of 37°C

• Must be held at about 35°C (95 degreees F)

Testes (testicles)

combined endocrine and exocrine glands that produce sex hormones and sperm

• Each teste is oval and slightly flattened

• white in color

• covered by tunica albunginea (white fibrous capsule) which has another membrane around it called the tunica vaginalis, forming a serous membrane with a bit of fluid between

• testes have septa that divide them into 250-300 lobes

• testes secrete high levels of testosterone throughout their life

Seminiferous Tubules

Ducts in the testes where sperm are produced

• One to three in each lobule

• Each tubule is lined with a thick epithelium of germ cells and nurse cells

  • germ cells become sperm

• surrounded by interstitial endocrine cells

Nurse Cells in Seminiferous Tubules

Nurse cells are in between the germ cells

• Protect the germ cells, and promote their development

• Germ cells depend on them for nutrients, waste removal, growth factors, and other needs

Interstitial Endocrine (Leydig) Cells

Clumps of cells that are between the tubules that produce testosterone

Blood–Testis Barrier (BTB)

formed by tight junctions between nurse cells

• protects sperm from pathogens and the immune system

Why do we need to protect germ cells from our immune system?

Germ cells are immunologically different from body cells and would be attacked by the immune system if we did not have this barrier

Spermatic Ducts

Carry sperm from testis to the urethra

• includes:

  • Efferent Ductules

  • Epididymis

  • ductus deferens

  • ejaculatory duct

Efferent Ductules

12 small ciliated ducts that collect sperm from the testes and transport it to the epididymis

• start in the testes

• connects testes to epididymis

Epididymis

Is a single coiled duct, (6 m long), that attaches to the back of the testes

• Site of sperm maturation and storage (fertile for 40 to 60 days)

• Sperm mature as they travel through the duct

• If not ejaculated in the 40-60 days, they disintegrate and the epididymis reabsorbs them

• includes a head, body, and tail

Ductus (vas) Deferens

Muscular tube passing up from the scrotum through the inguinal canal to the back of the bladder

• Duct widens behind the bladder and widens into the terminal ampulla

• Duct ends by uniting with the duct of the seminal vesicle

• Has a thick wall of smooth muscle well innervated by sympathetic nerve fibers

  • causes parastaltic waves that moves sperm up through the inguinal opening to the back of the bladder

  • widens at the back of bladder to store sperm

• during arousal, smooth muscle contractions will push the sperm to the ejaculatory duct

Ejaculatory Duct

Short duct formed from the ductus deferens and seminal vesicle

• passes through prostate to empty into the urethra

• allows secretions from seminal vesicle and sperm to mix and create semen

Seminal Vesicles

Pair of glands posterior to bladder

• Empties into ejaculatory duct

• Forms 60% of semen

Prostate Gland

• Single gland

• Surrounds urethra and ejaculatory duct just below the bladder

• Empty through about 20 pores in the prostatic urethra

• Thin milky secretion forms 30% of semen

Bulbourethral glands

• Near bulb of penis, right on either side of the midsaggital plane

• During sexual arousal, they produce a clear, alkaline, slippery fluid that lubricates the head of the penis in preparation for intercourse

• Protects the sperm by neutralizing the acidity of residual urine in the urethra

Penis

• Penis serves to deposit semen in the vagina

• Half of the penis is an internal root

• Half is an externally visible shaft and glans (head)

• External portion is about 4 in. long when flaccid

  • 5 to 7 in. long when erect

• Skin over shaft loosely attaches to allow expansion

  • Extends over the head as a prepuce (foreskin) that is removed by circumcision

What can circumcision lead to?

leads to development of less sensitive epidermis on the glans (head)

• pros is that it leads to less STIs

Internal Structure of the Penis

• Has 3 cylindrical bodies of erectile tissue that fill with blood during sexual arousal and create an erection

• the 3 bodies are…

  • one corpus spongiosum along the ventral side of penis

  • Two corpora cavernosa

• Prepubescent boys only have 2 bodies of erectile tissue instead of 3

Corpus Spongiosum

Erectile tissue that runs along the front side of the penis

• Encloses the spongy (penile) urethra

• Distal end enlarges and forms the glans penis (penis head)

Corpora Cavernosa

erectile tissue that makes up the rest of the penis

• Diverge like arms of a Y from the corpus spongiosum

• Each arm, called a crus, attaches the penis to the pubic arch 

• is covered with ischiocavernosus muscle

What state is the reproductive system in for several years after birth?

Reproductive system remains dormant for several years after birth

• 10 to 12 years in most boys

• 8 to 10 years in most girls

• Surge of pituitary gonadotropins awakens the reproductive system, leading to onset of puberty

Adolescence

The period from the onset of gonadotropin secretion and reproductive development to when a person attains full adult height

• adolescence ends when person stops growing taller

• for most males, adolescence ends at around 18 years old

Puberty

first few years of adolescence, until the first menstrual period in girls or the first ejaculation of viable sperm in boys

• Typically around age 14 in boys and age 12 in girls

How does the concentration of testosterone fluctuate from utero to adult male?

• The testes secrete testosterone in utero at levels about as high as they are midpuberty

• Then testes becomes dormant until puberty

• From puberty through adulthood, reproductive function is regulated by hormonal links between the hypothalamus, pituitary gland, and gonads

Gonadotropin-Releasing Hormone (GnRH)

produced by the hypothalamus

• stimulates the anterior pituitary to secrete FSH and LH which will go to the testes do serve different functions

Follicle-Stimulating Hormone (FSH)

Stimulates nurse cells to secrete androgen-binding protein that binds testosterone,

• this keeps testosterone in the seminiferous tubule to stimulate spermatogenesis

Luteinizing hormone (LH)

LH goes to interstitial endocrine cells and stimulate testosterone production

• sometimes called interstitial cell–stimulating hormone (ICSH)

What hormone do nurse cells release and what does it do?

Inhibin

• inhibin down-regulates FSH, which down-regulates androgen binding proteins so we maintain homeostasis for sperm production

What does testosterone do in the male reproductive system?

• testosterone down-regulates GNRH and gonadotropin release

• testosterone also has potent secondary sex characteristics

What does testosterone do during puberty (5 things)?

• Stimulates growth of sex organs

  • Penis, testes, scrotum, ducts, glands

• Testosterone stimulates generalized body growth

  • Limbs elongate, muscle mass increases, and larynx enlarges

• Stimulates erythropoiesis, basal metabolic rate, and appetite

• Pubic hair, axillary hair, and facial hair develop in response to dihydrotestosterone (DHT)

  • apocrine and sebaceous glands also develop

• Stimulates sperm production and libido

What do hormones do during adulthood?

• Testosterone sustains the male reproductive tract, sperm production, and libido

  • gradual decline in libido as testosterone declines

• Inhibin from nurse cells suppresses FSH output, reducing sperm production without reducing LH and testosterone secretion

Spermatogenesis

process of sperm production in the seminiferous tubules

• Involves 3 principal events

  • Division and remodeling of large germ cells into small, mobile sperm cells with flagella

  • Reduction of chromosome number by half

  • Shuffling of genes (crossing over) so each chromosome contains new gene combinations that did not exist in the parent

    • Ensures genetic variation in the offspring

• Meiosis produces 4 haploid daughter cells that will become sperm

6 steps from spermatogonium to sperm

1. Spermatogonium

2. Primary Spermocyte

3. Secondary Spermocyte

4. Early Spermatid

5. Late Spermatid

6. Sperm

Spermatozoon (Sperm Cell)

Has two parts: head and tail

• Head is pear-shaped

  • contains the nucleus

    • has haploid set of chromosomes

  • has the acrosome

    • enzyme cap that contains enzymes that will help it penetrate the egg

• Tail is divided into 3 regions:

  • Midpiece

    • contains mitochondria

    • produces ATP for flagellar movement

  • Principal piece

    • the middle axoneme portion surrounded by supporting fibers

    • Constitutes most of tail

  • Endpiece

    • very narrow tip of flagella

Semen (seminal fluid)

Fluid expelled during orgasm

• 2 to 5 mL of fluid is expelled during ejaculation

• Semen is 60% seminal vesicle fluid, 30% prostatic fluid, and 10% sperm and spermatic duct secretions

• Normal sperm count is 50 to 120 million/mL

• Anything lower than 20 to 25 million/mL indicates infertility

To help make semen, what does the prostate produce?

Prostate produces a thin, milky white fluid

• Contains calcium, citrate, and phosphate ions

• also contains a clotting enzyme

  • this causes semen to grow a thick coagulated mask to keep the sperm together to make it easier for it to reach female reproductive tract

• also contains a protein-hydrolyzing enzyme called serine protease (prostate-specific antigen) to break that thick mask and release the sperm freely

To hep make semen, what do the seminal vesicles produce?

Seminal vesicles produces a viscous yellowish fluid

• Contains fructose and other carbohydrates, citrate, prostaglandins, and protein called proseminogelin

• the prostaglandins help stimulate smooth muscle contractions to help move sperm

How does the stickiness of semen promote fertilization?

• Clotting enzyme from prostate activates proseminogelin and converts it to a sticky fibrin-like protein called seminogelin

• This entangles the sperm and causes it to stick to the inner wall of the vagina and cervix

• This ensures semen does not drain back into vagina

• Promotes the uptake of sperm-filled clots of semen into the uterus

• 20 to 30 minutes after ejaculation, serine protease from prostatic fluid breaks down seminogelin, and liquifies the semen so it can swim freely up the tract

2 requirements for sperm motility:

elevated pH and an energy source

• Prostatic fluid buffers vaginal acidity from pH 3.5 to 7.5

• Seminal vesicles provide fructose and other sugars to the mitochondria of sperm for ATP production

How do semen make it to the female reproductive tract?

• Active sperm crawl up vagina and uterus

• Prostaglandins in semen may thin the mucus of the cervical canal and can stimulate waves of contractions in the uterus to help move the semen

• female orgasm also gives sperm a kickstart in moving

4 Phases of Male Sexual Response

• Excitement

• Plateau

• Orgasm

• Resolution

Excitement Phase

characterized by vasocongestion (swelling of genitals with blood), myotonia (muscle tension), and increases in heart rate, blood pressure, and pulmonary ventilation

• Bulbourethral glands secrete fluid

• Erection is primarily due to parasympathetic NS triggering the secretion of nitric oxide (NO)

  • NO is a potent vasodilator

• arteries dilate and fill erectile tissue with blood

• penile veins constrict so less can flow out

• Erection allows for entry into vagina

Plateau Phase

• variables such as respiratory rate, heart rate, and blood pressure stay increased

• increase in engorged tissue and muscle tension

• Lasts for a few seconds or a few minutes before orgasm

Orgasm

a short but intense reaction that is usually marked by the discharge of semen

• Lasts 3 to 15 seconds

• Heart rate, blood pressure, and breathing greatly elevate

• tightening of skeletal muscles can occur

2 Stages of Ejaculation

Emission:

• when the different ingredients of semen are being premixed

• sympathetic nervous system stimulates peristalsis which propels sperm through the ducts once mixed

Expulsion:

• also stimulated by sympathetic nervous system

• semen in urethra activates reflexes that stimulate muscular contractions that lead to expulsion

• internal urethral sphincter constricts so urine cannot enter urethra and semen cannot enter bladder

*Ejaculation and orgasm are not the same

Resolution Phase

• body variables return to their preexcitement state

• Sympathetic signals constrict arteries to reduce blood flow to penis

• Penis becomes soft and flaccid

• Cardiovascular and respiratory functions return to normal

• important bc stagnant blood can lead to blood clotting

Refractory Period

period following resolution where it is usually impossible for a male to attain another erection or orgasm

• May last from 10 minutes to a few hours

Senescence of Male Reproductive System

• Gradual decline in testosterone secretion, sperm count, and libido

• Men are fertile into old age, but ED may occur due to atherosclerosis, hypertension, medication, or psychological reasons

• Testosterone secretion declines with age

  • bc of decline in number and activity of interstitial endocrine cells

• Andropause (male climacteric) may occur

Andropause

A period of declining reproductive function that may be first seen in early 50s

• Although sperm counts decline, men can still father children throughout old age

• not all men experience andropause

What do drops in testosterone and inhibin from age trigger?

An age-related drop in testosterone and inhibin triggers a rise in FSH and LH

• Although most men do not notice this, some experience mood changes, hot flashes, “illusions of suffocation”

Erectile Dysfunction (impotence)

the inability to produce or maintain an erection sufficient for intercourse

• 20% of men in 60s to 50% of those in 80s

What age range has the highest rate of ED?

highest rate of ED currently is in males in their 30s

• this change is due to smartphones and overconsumption of sexually explicit material

Treatments for ED

Viagra, Levitra, and Cialis

• These are all phosphodiesterase inhibitors

How does the ED medication work in the body?

Sexual stimulation triggers nitric oxide secretion, which activates cGMP, which then increases blood flow into erectile tissue

• These drugs slow the breakdown of cGMP by phosphodiesterase to prolong the duration of the erection

When should you not take ED meds?

if taking meds for High BP, then you shouldn’t take meds for ED bc both meds lower BP