Reproductive Physiology The Male Reproductive System Dr. Khalid Al-Regaiey.
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Transcript of Reproductive Physiology The Male Reproductive System Dr. Khalid Al-Regaiey.
![Page 1: Reproductive Physiology The Male Reproductive System Dr. Khalid Al-Regaiey.](https://reader034.fdocuments.us/reader034/viewer/2022051214/56649e5e5503460f94b57c64/html5/thumbnails/1.jpg)
Reproductive Physiology
The Male Reproductive System
Dr. Khalid Al-Regaiey
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Sex Determination: Overview
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• Bipotential tissues: genes & hormones direct differentiation
• Gonad testis or ovary
• Wolffian duct Vas deferens,
• Mullerian duct oviduct
Sexual Differentiation: Internal Embryonic Development
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Sexual Differentiation: Internal Embryonic Development
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Sexual Differentiation: External Genitalia
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Male Development
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Role of hCG in Male Development
• Human chorionic gonadotropin (hCG) which is secreted by the placenta has LH-like effects
• If the fetus is male, hCG stimulates testosterone production from the testes of the fetus which helps in development of male sexual organs
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Regulation of Reproduction: General Pathways
• Hypothalamus: pulse generator
• Gonadotropin releasing H
• (GnRH)
• Anterior Pituitary
• Lutenizing H (LH)
• Follicle stimulating H (FSH)
• Ovary: progesterone
• Estrogen, inhibin• Testis: testosterone
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Regulation of Reproduction: General Pathways
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Male Reproductive System
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Male Reproductive Anatomy and Physiology
• Testis
• Epididymis
• Vas deferens
• Seminal vesicle
• Prostate
• Bulbourethral
• Ejaculatory duct
• Urethra• Penis
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Male Reproductive Anatomy
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The Male Reproductive System in Anterior View
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The Structure of the Testes
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• Takes about 74 days
• Seminiferous tubules
• Contain spermatogonia
• Stem (germ) cells involved in spermatogenesis
• Contain Sertoli cells
• Sustain and promote development of sperm
Spermatogenesis
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The Seminiferous Tubules
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The Seminiferous Tubules
Sertoli cells
Leydig cells
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Spermatogenesis
(2N)
(4N)
(2N)
(1N)
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Spermiogenesis and Spermatozoon Structure
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Spermatozoa Structure and Functions in Review
• Head• Acrosome: formed
from Golgi apparatus, contains proteolytic enzymes
• Nucleus
• Midpiece
• Centrioles:
• Mitochondria:
• Tail: flagellum• Microtubules:
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• GnRH LH Leydig cells testosterone growth and division of germ cells
• GnRH FSH Sertoli cells spermatoctye maturation
• Inhibin feedback – FSH
• Testosterone – short & long loops
Regulation of Spermatogenesis
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Regulation of Spermatogenesis
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Maturation of Sperm in Epididymis • Sperms in the early portion of epididymis
are nonmotile
• After 18-24 h they develop capability of motility
• Most of sperms are stored in vas deferens, maintaining their fertility for at least a month
• After ejaculation they become motile
• Activity of a sperm is greatly enhanced in neutral to slightly alkaline medium and depressed in acidic medium
• The life expectancy of ejaculated sperm in the female genital tract is 1-2 days
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Seminal Vesicles
• S Vs produce nutrients as well as prostaglandins and fibrinogen
Prostate
• Slightly alkaline milky fluids that help in neutralizing other seminal fluids as well as the vaginal fluids
• Prostates fluids also contain clotting protein and profibrinolysin
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Semen
• Milky white, sticky mixture of sperm and accessory gland secretions:
• Sperm and fluid from vas deferens 10%
• Seminal plasma (70% seminal vesicles, 20% prostate, and small amounts from other glands)
• Provides a transport medium and nutrients (fructose), protects and activates sperm, and facilitates their movement
• Average pH is 7.5
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Semen
• Prostaglandins in semen:
• Decrease the viscosity of mucus in the cervix
• Stimulate reverse peristalsis in the uterus
• Facilitate the movement of sperm through the female reproductive tract
• Clotting factors coagulate semen immediately after ejaculation, then fibrinolysin liquefies the sticky mass during the next 15-30 minutes
• After ejaculation, sperms can live 24-48 h
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• Freshly ejaculated semen undergoes a process called capacitation: 1. inhibitory factors are washed out by uterine and fallopian fluids, 2. the sperm swims away from cholesterol vesicles, 3. the membrane of the sperms becomes more permeable to Ca++
• Only 2-5 ml of semen are ejaculated, but it contains 35-200 million sperm/ml (<20 million infertile)
• When the majority of the sperm are morphologically abnormal or nonmotile then person is likely to be infertile
Semen
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Hormonal Regulation of Testicular Function• The hypothalamus releases gonadotropin-
releasing hormone (GnRH) in pulses
• GnRH stimulates the anterior pituitary to secrete FSH and LH
• FSH causes Sertoli cells to release androgen-binding protein (ABP) and help in sperm maturation
• LH stimulates interstitial (Leydig) cells to release testosterone
• Binding of testosterone to ABP enhances spermatogenesis
• GH: promotes early division of spermatogonia
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HPG Axis
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Hormonal Regulation of Testicular Function
• Feedback inhibition on the hypothalamus and pituitary results from:
• Rising levels of testosterone
• Increased inhibin
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Mechanism and Effects of Testosterone Activity• Testosterone is synthesized from
cholesterol
• It binds to testosterone –binding globulin (TeBG), serum albumin, or to corticosterone-binding globulin (CBG)
• Once it diffuses to cells it either binds to androgen receptor or converted to DHT which then binds to the androgen receptor
• Testosterone targets all reproductive and accessory organs and its deficiency causes these organs to atrophy
• Increases metabolic rate and red blood cell formation
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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
• Closure of epiphyseal plates in long bones
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Male Secondary Sex Characteristics
• Testosterone is the basis of libido in both males and females
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Male Sexual Act
• Erection is initiated by sexual stimuli including:• Touch and mechanical stimulation of
the penis • Erotic sights, sounds, and smells
• Erection can be induced or inhibited solely by emotional or higher mental activity
• Enlargement and stiffening of the penis from engorgement of erectile tissue with blood
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• During sexual arousal, a PNS reflex promotes the release of nitric oxide
• Nitric oxide relaxes the penis arteries and causes erectile tissue to fill with blood
• Expansion of the corpora cavernosa:
• Compresses their drainage veins
• Retards blood outflow and maintains engorgement
Male Sexual Act (cont.)
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• When the sexual stimulus becomes extremely intense, spinal cord begins to send sympathetic impulses to initiate emission
• Filling of the internal urethra with semen elicits signals that promotes ejaculation
• After orgasm, the excitement disappears within 1-2 minutes (resolution)
Male Sexual Act (cont.)
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The Erection Reflex