Male Reproductive Systems

HAN 202

Chromosomal Sex Determination

One of the 23 pairs of chromosomes in body sells are sex chromosomes (X and Y)

Female Offspring

X egg + X sperm (XX)

Male Offspring

X egg + Y sperm (XY); SRY gene on Y chromosome initiates testes development

Primary Sex Organs/Gonads

Testes and ovaries that produce sex cells/gametes and secrete steroid sex hormones (androgens and estrogens/progesterone)

Secondary/Accessory Reproductive Organs

Ducts, glands, and external genitalia

Development of External Genitalia

Genital tubercle → glans of penis and clitoris

Urethral fold → urethra and labia minora

Labioscrotal folds → scrotum and labia majora

Descent of Gonads

About two months before birth

Testosterone stimulates the migration of the testes toward the scrotum; ovaries also descend, but are stopped by the broad ligament at the pelvic brim

Gubernaculum

Fibrous cord from each testis to the scrotum or from ovary to labium majus; guides the descent

Puberty

In response to rising level of gonadal hormones; reproductive organs grow to adult size and become functional; secondary sexual characteristics appear; earliest time that reproduction is possible

Sexually Transmitted Infections

Gonorrhea, syphilis, chlamydia, genital warts, genital herpes

The Scrotum

Pouch of skin, muscle, and connective tissue; lies externally to the pelvic cavity; contains paired testes that are 3 degrees C lower than core body temps for sperm production

Dartos Muscle

Smooth muscle; contracts when cold, wrinkling the scrotum & holds testes against warm body; reduces surface area of scrotum and heat loss; outermost muscle

Cremaster Muscles

Skeletal muscle; contracts when cold to hold testes closer to body; when warn, relaxes and moves testes further from body; innermost muscle

The Testes

Combined endocrine & exocrine glands that produce sex hormones and sperm; surrounded by two tunics (tunica vaginalis and albuginea)

Septa/Septum

Divides the testis into 250-300 lobules, each containing 1-4 seminiferous tubules (site of sperm production)

Interstitial (Leydig) Cells

Located outside of seminiferous tubules and produce androgens → testosterone

Sperm Pathway in Testes

Created in the seminiferous tubules then travels trough tubulus rectus, rete testis, efferent ductules, epipdiymis

The Spermatic Ducts

Epididymis, ductus deferens, ejaculatory duct, urethra

Epididymis

Site of sperm maturation and storage

Ducts include head, body, tail (head contains efferent ductules)

Nonmotile sperm enter, pass slowly through, and become motile

During ejaculation, the epididymis contacts, expelling the sperm into the ductus deferens

Ductus Deferens/Vas Deferens

Tube between epididymis and seminal vesicle; passes through inguinal canal

Expands to form the ampulla and then joins the duct of the seminal vesicle to form the ejaculatory duct

Vasectomy

Cutting and ligating the ductus deferens; nearly 100% effective form of birth control

Ejaculatory Duct

2 cm duct formed where ductus deferens and duct of seminal vesicle merge; passes through prostate and empties into urethra

Urethra

Conveys both urine and semes; has three regions (prostatic, membranous, spongy/penile)

The Accessory Glands (Male)

Seminal vesicles, prostate, bulbourethral glands (cowper’s glands)

Seminal Vesicles

Produces viscous alkaline seminal fluid (70% of the volume of semen)

Duct of seminal vesicle joins the ductus deferens to form the ejaculatory duct

Prostate

Encircles the ejaculatory duct and part of the urethra inferior to the bladder

Secretes milky, slightly acidic fluid; forms 30% of semen; plays a role in the activation of sperm

Prostate DIseases

Benign prostatic hyperplasia (BPH) and prostate cancer

Bulbourethral Glands/Cowper’s Glands

Pea-sized glands inferior to the prostate

Prior to ejaculation, produce thick, clear mucus; lubricates the glans penis and neutralizes trace of acidic urine in the urethra

The Penis

Root and shaft ends in the glans penis

Prepuce/foreskin is cuff of loose skin covering the glans

Penile Shaft

Contains 3 cylindrical bodies called erectile tissues - corpus spongiosum and corpora cavernosa

Erection

Erectile tissue fills with blood, causing the penis to enlarge and become rigid

Semen

Mixture of sperm and accessory gland secretions

Contains nutrients (fructose), protects and activates sperm, and facilitates their movement

Alkalinity neutralizes the acid in the male urethra and female vagina

Clotting factors coagulate semen just after ejaculation, then fibrinolysin liquefies it

Prostaglandins in Semen

Decrease the viscosity of mucus in the cervix and stimulate reverse peristalsis in the uterus

Spermatogensis

Sequence of events that produces sperm in the seminiferous tubules of the testes; spermatic cells give rise to sperm

Meiosis

Gamete formation

Nuclear division in the gonads in which the umber of chromosomes is halved (from 2n to n); two consecutive cell divisions following one round of DNA replication; introduces genetic variation

Mitosis in Spermatic Cells

Spermatogonia form spermatocytes

Meiosis in Spermatic Cells

Spermatocytes form spermatids

Spermiogenesis in Spermatic Cells

Spermatids become sperm; lose excess cytoplasm and form a tail, becoming spermatozoa

Spermatozoon/Sperm

Head: genetic region, nucleus, acrosome contains hydrolytic enzymes that allow sperm to penetrate an egg

Midpiece: metabolic region; mitochondria

Tail: locomotor region; flagellum

Hypothalamic-Pituitary-Gonadal (HPG) Axis

A sequence of hormonal regulatory events involving the hypothalamus, anterior pituitary gland, and testes

Step 1 HPG Axis

Hypothalamus releases gonadotropin-releasing hormone

Step 2 HPG Axis

GnRH stimulates the anterior pituitary to secrete FSH and LH

Step 3 HPG Axis

FSH causes sustentacular cells to release androgen-binding protein (ABP), which makes spermatogenic cell receptive to testosterone

Step 4 HPG Axis

LH stimulates interstitial cells to release testosterone

Step 5 HPG Axis

Testosterone is the final trigger for spermatogenesis

Step 6 HPG Axis

Feedback inhibition on the hypothalamus and pituitary results from rising levels of testosterone or inhibin (released when sperm count is high)

Testosterone

Synthesized from cholesterol

Transformed to exert its effects on some target cells (dihydrotestosterone [DHT] in prostate and estrogen in some neurons in the brain)

Prompts spermatogenesis

Targets all accessory organs; deficiency leads to atrophy

Has multiple anabolic effects throughout the body

Is the bases of sex drive/libido in males

Secondary Sexual Characteristics Males

Features induced in the non-reproductive organs by male sex hormones (mainly testosterone): appearance of pubic, axillary, and facial hair; enhanced growth of the chest and deepening of the voice; skin thickens and becomes oily; bones grow and increase in density; skeletal muscles increase in size & mass