Chapter 27: Pt. 1 Male Reproductive Flashcards
Human Reproductive Systems:
o Gonads = primary reproductive organs. o Males: (2) testes. o Females: (2) ovaries. o Function of gonads: o 1. produce gametes. o 2. secrete sex hormones. o Gametes = sex cells (haploid number of chromosomes). • Male: spermatozoa. • Female: ova. • Zygote = 1 spermatozoon + 1 ovum.
Human Chromosomes:
o Somatic cells (diploid cells)
o 23 pairs of chromosomes for a total of 46.
• Each pair is homologous–contains similar genes in same order.
• One member of each pair is from each parent.
o 22 autosome pairs and1 pair of sex chromosomes.
• Sex chromosomes are either X or Y.
• Females have two X chromosomes.
• Males have an X and a smaller Y chromosome.
o Gametes (haploid cells):
• Single set of chromosomes for a total of 23.
• Produced by special type of division: meiosis.
Loss of Y Chromosomes:
o Male somatic cells all contain X and Y chromosomes.
o Starting ~age 40, some males starting losing the Y chromosome, this is associated with an increased cancer risk and a decreased lifespan.
o By age 70, about 15 percent of men have noticeable loss of the Y chromosome from a proportion of their blood cells.
o Smoking increases risk of loss of Y chromosome.
Accessory Reproductive Organs:
o Accessory reproductive organs:
o Essential for reproduction.
o Include ducts, glands, and supporting structures.
o Secondary sex characteristics:
o Features not essential for reproduction, but attract sexes to each other.
o Physique, breasts, voice, scent, skin, body hair distribution, metabolic rate.
Testes:
o Paired oval glands (2” x 1”).
o Develop in utero in abdominal cavity (near kidneys), descend thru inguinal canal at about 7th month of fetal life.
o Lie in scrotum outside abdominopelvic cavity to regulate ideal temperature for sperm production.
o Spermatogenesis requires temps 2 to 3 degrees C below body temp.
o Controlled by cremaster muscles, dartos muscle, and pampiniform plexus.
o Temperature is regulated by the pampiniform venous plexus removing heat from incoming warm blood in testicular arteries.
o Exocrine function: releasing spermatozoa into ducts.
o Endocrine function: releasing hormones into blood.
o Testosterone.
o Inhibin.
o Testes are regulated primarily by other hormones:
o LH from anterior pituitary stimulates secretion of testosterone.
o FSH from anterior pituitary stimulates spermatogenesis.
o LH and FSH are regulated by GnRH (gonadotropin releasing hormone) secreted by hypothalamus.
Descent of Testes:
o Develop in utero in abdominal cavity (near kidneys).. Descend thru inguinal canal at about 7th month of fetal life.
o CRYPTORCHIDISM = failure of testes to descend into the scrotum.
o 30 percent of premature infants.
o 80 percent spontaneously descend within 1st year of life.
o If do not descend, must be surgically corrected by 18 mos.
Membranes Around Testes:
o Tunica vaginalis:
o Serous membrane derived from peritoneum (remnant of testicular descent).
o Tunica albuginea:
o Forms a capsule around testes.
o Extends inward to form SEPTA that divide each testis into 200 to 300 testicular lobules.
o Each lobule contains 1 to 4 seminiferous tubules—where spermatogenesis occurs.
Seminiferous Tubules:
o “Spermatozoa factories”. o 2 cell populations. o Sertoli cells (sustentocytes)). • Nourish and protect spermatozoa. • Form BLOOD-TESTIS BARRIER. • Secrete INHIBIN (hm that inhibits release of FSH from anterior pituitary when spermatozoa count is high). • Secrete ABP = androgen binding protein to mediate the effects of testosterone diffusing in from INTERSTITIAL ENDOCRINE CELLS (LEYDIG CELLS). o Spermatogenic cells (mitosis and meiosis). • Spermatogonia (stem cells). • Primary spermatocytes. • Secondary spermatocytes. • Spermatids and Spermatozoa.
Spermatogenesis:
o Spermatocytogenesis
• Spermatogonia undergo mitosis to produce primary spermatocytes (begins at puberty).
o Meiosis I
• Primary spermatocytes undergo Meiosis I to produce haploid number of chromosomes… Prophase I takes 22 days!
o Meiosis II
• Secondary spermatocytes undergo Meiosis II.
o Spermiogenesis
• Spermatids mature into spermatozoa.
Initiation of Spermatogenesis:
o Puberty !!!!
o Hypothalamus increases release of GnRH, a hormone which targets the anterior pituitary.
o Anterior pituitary increases secretion LH and FSH.
o LH stimulates Leydig cells to secrete testosterone:
o An enzyme in prostate & seminal vesicles converts testosterone into dihydrotestosterone (DHT-more potent).
o FSH stimulates spermatogenesis:
o With testosterone, stimulates SERTOLI CELLS to secrete ABP (androgen-binding protein) (keeps hormones levels high).
o Testosterone stimulates final steps spermatogenesis.
Control of Testosterone Production:
o Negative feedback system controls blood levels of testosterone.
o Receptors in hypothalamus detect increase in blood level.
o Secretion of GnRH slowed.
o Anterior pituitary (FSH and LH hormones) slowed.
o Leydig cells of testes slowed.
o Blood level returns normal.
Blood and Nerve Supply to Testes:
o Blood and lymph vessels travel within spermatic cord.
o Testicular artery branches off of abdominal aorta, capillaries, testicular veins arise from pampiniform plexus.
o Both divisions of the ANS supply testes, MANY associated sensory nerves (agonizing pain if injured).
Testicular Cancer:
o Rare (3 in 100,000 males).
o Most common cancer in men ages 15 to 35 years.
o Risk factors:
o Cryptorchidism.
o Mumps virus.
o Cure rate is 90 – 95 percent if orchiectomy and chemotherapy.
Exocrine Duct System:
o Epididymis o 1.5 - 3” long on posterior side of testis (20 feet of coiled ductwork inside!) o Stereocilia = long microvilli. o Temporary storage site for immature spermatozoa, may remain viable for 40 to 60 days. o Takes 20 days minimum to reach “tail”. o Vas Deferens = Ductus Deferens. o Ejaculatory Duct. o Male urethra.
Function of Epididymis:
o Epididymis absorbs 90 percent of fluid leaving the testis.
o Epididymis secretes substances that continue maturation of spermatozoa (start process of becoming motile).
o Storage of spermatozoa (40 – 60 days).
o Propulsion of sperm into ductus deferens (vas deferens), innervated by the sympathetic nervous system.
Vas Deferens:
o 18” long muscular tube that propels spermatozoa towards the ejaculatory ducts.
o Smooth muscle is innervated by sympathetic nervous system.
o Leads from epididymis into pelvis as part of the spermatic cord.
o In pelvis, expands to form an ampulla at its distal end.
o Ampulla joins the duct from the seminal vesicle to form the ejaculatory duct.
Spermatic Cord:
o Includes all structures passing to and from the testes: o Testicular artery. o Pampiniform plexus of veins. o Autonomic nerves. o Lymphatic vessels. o Ductus (vas) deferens. o Cremaster muscle.
Ejactulatory Ducts:
o Very short duct (less than 1”) formed by the merging of the ampulla of the vas deferens with the duct from the seminal vesicle (on each side).
o Pierces the prostate gland and empties into the prostatic urethra.
Male Urethra:
o Special duct that is shared by both the urinary system and the reproductive system, urine and semen cannot pass through it at the same time.
o Male urethra is about 20 cm (8”) long.
o 3 general regions of male urethra:
o Prostatic urethra (surrounded by prostate).
o Membranous urethra (enclosed within urogenital diaphragm).
o Spongy (penile) urethra (within penis).
Accessory Glands:
o Secrete most of the liquid portion of semen.
o 3 types of accessory glands:
o (2) Seminal vesicles.
o (1) Prostate gland.
o (2) Bulbourethral glands.
o Composition of semen:
o Liquid from seminiferous tubules, including spermatozoa.
o Liquid from all 3 types of accessory glands.
Seminal Vesicles:
o Contribute about 60-70 percent to volume of semen.
o Secretions contain:
o Fructose.
o Citric acid, Vit. C.
o Prostaglandins.
o Thin the mucous barrier of female cervix.
o Pro-seminogelin.
o Precursor to fibrous protein– entangles sperm and makes it stick to vaginal wall.
Prostate Gland:
o Contributes about 30 percent to volume of semen.
o Secretions empty into prostatic urethra via about 20-30 tiny ducts.
o Contains:
o Citric acid
o PSA = prostate specific antigen (proteolytic enzyme) = Serine protease (breaks down seminogelin), liquifies semen.
o Sits inferior to urinary bladder, encircling prostatic urethra.
o Lies immediately anterior to rectum, can be palpated by digital rectal exam.
o Hypertrophies with age, constricting the prostatic urethra.
o BPH = benign prostatic hyperplasia.
o TURP (transurethral resection of prostate).
o TUNA (transurethral needle ablation).
o Meds (e.g., Finasteride, Avodart) and MICROWAVES to shrink prostate.
Prostate Cancer:
o Very common cancer in men.
o Affects 9 percent of men over the age of 50.
o Tends to form near the periphery of the gland (does not usually affect urine flow at first, goes unnoticed).
o Diagnosed by DRE and/or by unusual jumps in the level of serum PSA test.
o Can be slow-growing (controversial to treat) or fast-growing, need biopsy.
Bulbourethral Glands:
o Also known as Cowper’s glands.
o Contribute less than 5 percent to volume of semen.
o Produce clear, alkaline fluid that lubricates the head of the penis during sexual arousal (and alkalinizes the penile urethra from any acid traces of urine).
Semen:
o Each mL contains 50 to 125 million spermatozoa !
o Typical ejaculate = 2.5 to 5 mL (thus, contains 125 – 625 million spermatozoa).
o If less than 20 million spermatozoa/mL, may contribute to infertility.
o Sperm motility is also a factor in infertility.
o pH (spermatozoa are inactive if pH is low).
External Genitalia:
o Scrotum (1):
o External sac containing the two testes.
o Scrotal septum compartmentalizes the two testes.
o Penis (1):
o Copulatory organ that delivers spermatozoa to female vagina.
o 3 structural parts:
• Root (attaches penis to body wall).
• Shaft (body): contains erectile tissue.
• Glans penis: distal expanded “head”.
Penis Structure:
o Root: o Bulb. o Crura. o Shaft (body): o Corpus spongiosum. o Corpora cavernosa. o Glans Penis: o Covered by prepuce in uncircumcised males. o External urethral orifice (meatus).
Hypospadias:
o Fairly common congenital anomaly.
o Occurs 1 in 125 live male births.
o Result of arrested development of the urethra, the prepuce, and the underside of the penis, external urethral orifice may be anywhere along the shaft or even with the scrotum.
o Multifactorial etiology, including disruption of gene expression by environmental endocrine disruptors (estrogen mimics).
o Controversial, EPA is screening thousands of industrial chemicals for endocrine effects.
Androgen Insensitivity Syndrome:
o Male (XY) person has female sex appearance.
o Testes produce normal amounts of testosterone, but target cells lack the proper receptor for testosterone.
o External genitalia develop as females because they can’t respond to testosterone.
Male Sexual Response:
Erection
o Penis has rich sensory and motor neural innervation.
o As male becomes excited, the parasympathetic nervous system (S2 thru S4) releases ACh and NO which relax the smooth muscles of the arterioles supplying the penis.
o Erectile tissues (corpora cavernosa) fill with blood, thought that this congestion compresses the veins so that the blood is trapped, penis becomes erect.
o Viagra works by causing increased vasodilation of penile blood vessels (but also vasodilation in other areas of body).
Male Sexual Response:
Ejaculation
o Ejaculation = propulsion of semen out of the male duct system, which is under control of the sympathetic nervous system (primarily L1 and L2 levels).
o Somatic Motor Nervous System also involved with local muscles, causing spasmodic contractions at the root of the penis, compresses urethra, ejaculation.
o Sympathetic output causes:
o Rapid heart beat (up to 180 bpm).
o Increased BP.
o Increased respiratory rate (up to 40 breaths/minute).
Erectile Dysfunction:
o Impotence = inability to attain/sustain an erection.
o Many possible causes:
o Decreased testosterone production (endocrine).
o Defective stimulation of erectile tissue by nerve fibers (nerve damage from surgery, peripheral neuropathy).
o Decreased response of blood vessels to neural stimulation (atherosclerosis).
o Restricted blood circulation to genital areas.
o Inability to concentrate on sexual stimulation (stress).
o Certain meds (Minoxidil, Proscar).
o Treatment: Phosphodiesterase inhibitors allow NO cascade to remain effective.
o Sildenafil (Viagra)
o Vardenafil (Levitra)
o Tadalafil (Cialis)
