Reproduction Liang Huawei( 梁华为 ) E-mail: liang.huawei@yahoo.com.cn
Reproduction Reproduction is the biological process by which new individual organisms are produced. An individual does not need the system to survive, but the human race does. Types Sexual reproduction Asexual reproduction
Human reproduction belongs to sexual reproduction ( 配子 )
Reproductive system Primary sexual organ Gonad (Testis, Ovary) Accessory sexual organ
Reproductive Physiology Functions of sexual organs (testis and ovary) Regulation of the reproductive functions Sex physiology
Male Reproductive Function
Male reproduction system
Testis 睾丸 Seminiferous tubules( 生精小管 ) Spermatogonia( 生精细胞 ) Sertoli cell( 支持细胞 ): inhibin( 抑制素 ), ABP Leydig cell( 间质细胞 ): androgen( 雄激素 )
Functions of the Testis Spermatogenesis( 生精作用 ) Endocrine functions
Spermatogenesis In all the seminiferous tubules during active sexual life Stimulated by gonadotropic Hs Begin at an average age of 13 years Decreasing markedly in old age The entire period: 64 days
Steps of spermatogenesis Spermatogonia ( 精原细胞 ) Primary spermatocyte( 初级精母细胞 ) Meiosis I T, FSH Secondary spermatocyte ( 次级精母细胞 ) Meiosis II Spermatid( 精子细胞 ) Spermatozoa (sperm, 精子 ) Male sperm Female sperm
精子细胞 精子 Spermatogenesis is the testicular process in adult males that generates haploid gametes capable of fertilizing ova. The overall result is that the set of 23 pairs of homologous chromosomes is reduced to a set of 23 chromosomes per sperm the corresponding 23 pairs are present in ova.
Sertoli cells support spermatogenesis in the seminiferous tubules in response to testosterone and FSH.
Spermatozoon Head Acrosome: enzymes Tail (flagellum) To and fro movement 1-4 mm/min in a fluid medium
Factors that affect spermatogenesis Hormonal factors that stimulate spermatogenesis Testosterone LH FSH Temperature T (-) spermatogenesis Scrotum ( 阴囊 ) As a cooling mechanism Maintain 2 differential Cryptorchidism ( 隐睾症 )
Lifetime of sperm Many weeks in the male genital ducts 24-48 hrs in the ejaculated semen( 精液 ) Several weeks at lowered temperature Years below - 100 C
Sperm count Ejaculated semen during each coitus: 3~6 ml An average of about 120 million sperm/ml semen 35 ~ 200 million/ml < 20 million/ml infertile
Sperm morphology and motility Infertile Abnormal physically Nonmotile or relatively nonmotile
Sperm bank
Male sex hormones Androgens( 雄激素 ) Leydig cells Inhibin( 抑制素 ) Sertoli cells Estrogen( 雌激素 ) Sertoli cells
Androgens Steroid hormones (Leydig cells) Types Testosterone,T( 睾酮 ) More abundant Dihydrotestosterone,DHT( 双氢睾酮 ) More active Dehydroisoandrosterone,DHIA( 脱氢异雄酮 ) Androstenedione( 雄烯二酮 )
Source Testes Adrenal glands Synthesis From cholesterol P450ssc
Secretion Pulsatile pattern Circadian rhythm: 日周期
Transportation + Albumin + Gonadal steroid-binding globulin (GBG) Metabolism T DHT (tissue) or Estrodiol Degradation into inactive products in the liver Excretion From the kidney or gut
Functions of testosterone
Required for initiation and maintenance of spermatogenesis Stimulus for descent of the testes The testes usually descend into the scrotum during the last 2 to 3 months of gestation. If undescended, administration of T or gonadotropic hormones Induce differentiation of male accessory reproductive organs and maintain their function
Induce male secondary sexual characteristics
Effect on the distribution of body hair growth of hair over the pubis, on the face and chest growth of hair on the top of the head -- boldness
Effect on the voice Causing hypertrophy of the laryngeal mucosa and enlargement of the larynx A relatively discordant cracking voice typical adult masculine bass voice Effect on the skin and development of acne thickness of the skin secretion by the sebaceous glands( 皮脂腺 )
Effect on muscle development muscle mass Synthetic androgens Used by athletes Used in old age as a youth hormone
Effect on bone growth and calcium retention size and strength of bones total quantity of bone matrix Causes calcium retention Often used in older men to treat osteoporosis Stimulate cessation of bone growth Specific effect on the pelvis A funnel-like shape
Effect on metabolism Stimulate protein anabolism Effect on red blood cells red blood cells RBC Hb man 4.0~5.5 x 10 12 /L 120~160g/L woman 3.0~5.0 x 10 12 /L 110~150g/L Required for sex drive and may enhance aggressive behavior
Effect on cardiovascular system Jackson G. Int J Clin Pract. 2008 Aug;62(8):1131
To be continued