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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Reproductive System Primary sex organs (gonads)
testes in males
ovaries in females
Gonads produce sex cells called gametes and secrete sex hormones
Accessory reproductive organs – ducts, glands, and external genitalia
Sex hormones
Androgens (males),
Estrogens and progesterone (females)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Male Reproductive System
The male gonads (testes) produce sperm and lie within the scrotum
Sperms are delivered to the exterior through a system of ducts: epididymis, ductus deferens, ejaculatory duct, and the urethra
Accessory sex glands:
Empty their secretions into the ducts during ejaculation
Include the seminal vesicles, prostate gland, and bulbourethral glands
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
The Scrotum and associated structures Sac of skin and superficial fascia that hangs outside
the abdominopelvic cavity at the root of the penis
Contains paired testicles separated by a midline septum
Its external positioning keeps the testes 3C lower than core body temperature (needed for sperm production)
Each testis is surrounded by two tunics:
The tunica vaginalis, derived from peritoneum
The tunica albuginea, the fibrous capsule of the testis
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Testicular Thermoregulation Sperms are not produced at core body temperature
In the scrotum, the testes are kept 2-3°C cooler than in the pelvic cavity. This is essential for sperm production.
Cooling mechanisms
The cremaster muscle contains strips of the internal abdominal oblique muscle around the spermatic cord.
It can elevate or lower the testes.
The dartos muscle is a subcutaneous layer of smooth muscle that wrinkles skin reducing surface area of scrotum. Can lifts testis upwards
The pampiniform plexus is an extensive network of veins that surround the testicular artery in the spermatic cord, keeping the testes cooler countercurrent heat exchange that cools arterial blood entering testis
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
The Testes Septa divide the testis into
250-300 lobules, each containing 1-4 seminiferous tubules
Seminiferous tubules:
Produce the sperm
Converge to form the tubulus rectus
The straight tubulus rectus conveys sperm to the rete testis
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Cells in the testes
Between the seminiferous tubules are clusters of interstitial (Leydig) cells, the source of testosterone.
A seminiferous tubule
lumen lined with germinal epithelium consisting of several layers of germ cells in the process of becoming sperm
Sustentacular (Sertoli) cells.
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The functions of Sertoli cells and BTB Sustentacular cells protect the germ cells and promote their
development. Tight junctions between adjacent sustentacular cells form a blood-testis barrier (BTB)
The fluid inside the tubules contains high levels of androgens, potassium and amino acids
The BTB prevents the immune system from attacking the developing spermatozoa (contain specific Ag that are not found on any other cell)
Sertoli cell supply nutrients to the developing sperms
Phagocytize cytoplasm shed by spermatids
Secrete inhibin (we will talk about this hormone later)
Secrete androgen-binding-protein (ABP) – binds testosterone inside tubules to maintain high levels
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Spermatic Ducts from rete testis to urethra
Epididymis (head, body and tail)
6 m long coiled duct adhering to posterior of testis
site of sperm maturation and storage (fertile for 60 days)
Ductus deferens/vas deferens (peristalsis during orgasm)
muscular tube 45 cm long passing up from scrotum through inguinal canal to posterior surface of bladder
Ejaculatory duct
2 cm duct formed from ductus deferens and seminal vesicle and passing through prostate to empty into urethra
Spermatic cord – encloses PNS and SNS nerve fibers, blood vessels, and lymphatics that supply the testes
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Epididymis The epididymis functions:
The duct of the epididymis has stereocilia that:
Absorb testicular fluid
Pass nutrients to the sperm
Recycling center for damaged spermatozoa
Storage place for spermatozoa
Facilitate functional maturation preparing them for capacitaion.
The spermatozoa mature in the epididymis but are not motile yet
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Ductus Deferens and Ejaculatory Duct
Runs from the epididymis through the inguinal canal into the pelvic cavity
Its terminus expands to form the ampulla and then joins the duct of the seminal vesicle to form the ejaculatory duct
Propels sperm from the epididymis to the urethra
Vasectomy – cutting and ligating the ductus deferens, which is a nearly 100% effective form of birth control
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Urethra
Conveys both urine and semen
Consists of three regions
Prostatic – portion surrounded by the prostate
Membranous – lies in the urogenital diaphragm
Spongy, or penile – runs through the penis and opens to the outside at the external urethral orifice
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
The Penis A copulatory organ designed to deliver sperm into the female
reproductive tract
Consists of an attached root and a free shaft that ends in the glans penis
Foreskin – cuff of skin covering the distal end of the penis
Erectile tissue – spongy network of connective tissue and smooth muscle riddled with vascular spaces
Corpus spongiosum – surrounds the urethra and expands to form the glans and bulb of the penis
Corpora cavernosa – paired dorsal erectile bodies bound by fibrous tunica albuginea
Erection – during sexual excitement, the erectile tissue fills with blood causing the penis to enlarge and become rigid
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Accessory Glands: Seminal Vesicles Lie on the posterior wall of the bladder and secrete 60% of the volume of
semen
Join the ductus deferens to form the ejaculatory duct
The composition of the gland secretions include:
High concentration of fructose that is easily metabolized by spermatozoa
Prostaglandins that stimulate smooth muscle contractions in both male and female reproductive tract
Fibrinogen that forms temporary clot within the vagina after ejaculation
When the inactive sperms mix with the seminal fluid they undergo the first step of activation and the flagella start moving (in some book this is done by the help of the prostate)
The secretion of the seminal gland are discharged into the ejaculatory duct under the control of the sympathetic system
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Accessory Glands: Prostate Gland
Doughnut-shaped gland that encircles part of the urethra inferior to the bladder
Produces 20-30% of the semen volume
Contains citrate (nutrient source) and enzymes
Fluid enters the prostatic urethra during ejaculation
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Accessory Glands: Bulbourethral Glands (Cowper’s Glands)
Pea-sized glands inferior to the prostate
Produce thick, clear mucus prior to ejaculation that neutralizes traces of acidic urine in the urethra
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
semen
The combination of sperm and the fluids secreted by the accessory glands.
The ejaculate (fluid produced during ejaculation) contains 20-100 million spermatozoa/ml
The volume is about 2-5 ml
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Ejaculation
The propulsion of semen from the male duct system
At ejaculation, sympathetic nerves serving the genital organs cause:
Reproductive ducts and accessory organs to contract and empty their contents
The bladder sphincter muscle to constrict, preventing the expulsion of urine
Propulsion of semen from the urethra (peristaltic contractions)
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Meiosis
The sequence of events that produces sperm in the seminiferous tubules of the testes
Each cell has two sets of chromosomes (one maternal, one paternal) and is said to be diploid (2n chromosomal number)
Humans have 23 pairs of homologous chromosomes
Gametes only have 23 chromosomes and are said to be haploid (n chromosomal number)
Gamete formation is by meiosis, in which the number of chromosomes is halved (from 2n to n)
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Chromosomes in Mitosis and Meiosis
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Spermatogenesis
Cells making up the walls of seminiferous tubules are in various stages of cell division
These spermatogenic cells give rise to sperm in a series of events
Mitosis of spermatogonia, forming spermatocytes
Meiosis forms spermatids from spermatocytes
Spermiogenesis – spermatids form sperm
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Mitosis of Spermatogonia
Spermatogonia – outermost cells in contact with the epithelial basal lamina
Spermatogenesis begins at puberty as each mitotic division of spermatogonia results in type A or type B daughter cells
Type A cells remain at the basement membrane and maintain the germ line
Type B cells move toward the lumen and become primary spermatocytes
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Spermatocytes to Spermatids
Primary spermatocytes undergo meiosis I, forming two haploid cells called secondary spermatocytes
Secondary spermatocytes undergo meiosis II and their daughter cells are called spermatids
Spermatids are small round cells seen close to the lumen of the tubule
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Spermiogenesis: Spermatids to Sperm
Late in spermatogenesis, spermatids are haploid but nonmotile
Spermiogenesis – spermatids lose excess cytoplasm and form a tail, becoming sperm
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings http://distance.stcc.edu/AandP/AP/AP2pages/reprod/spermato.htm
spermatogenesis
spermiogenesis
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Spermiogenesis: Spermatids to Sperm
Sperm have three major regions
Head – contains DNA and has a helmetlike acrosome containing hydrolytic enzymes that allow the sperm to penetrate and enter the egg
Midpiece – contains mitochondria spiraled around the tail filaments
Tail – a typical flagellum produced by a centriole
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Brain-Testicular Axis
Hormonal regulation of spermatogenesis and testicular androgen production involving the hypothalamus, anterior pituitary gland, and the testes
Testicular regulation involves three sets of hormones:
GnRH, which indirectly stimulates the testes through:
Follicle stimulating hormone (FSH)
Luteinizing hormone (LH)
Gonadotropins, which directly stimulate the testes
Testicular hormones, which exert negative feedback controls
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Hormonal Regulation of Testicular Function
The hypothalamus releases gonadotropin-releasing hormone (GnRH)
GnRH stimulates the anterior pituitary to secrete FSH and LH
FSH causes sustentacular cells to release androgen-binding protein (ABP)
LH stimulates interstitial cells to release testosterone
ABP binding of testosterone enhances spermatogenesis
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Testosterone
The principal androgen (male sex hormone) is testosterone.
This steroid is manufactured by the interstitial (Leydig) cells of the testes.
Secretion of testosterone increases sharply at puberty and is responsible for the development of the secondary sexual characteristics of men.
Testosterone is also essential for the production of sperm.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Male Secondary Sex Characteristics Male hormones make their appearance at puberty and
induce changes in nonreproductive organs, including
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 and mass
Testosterone is the basis of libido in both males and females