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Human Phys

Reproductive physiology

QuestionAnswer
Gonads - ovaries in women - testes in men Roles: 1. gamete production: sperm/ovum 2. production of sex hormones: androgen, estrogen, progesterones
Gametogenesis: gamete production Two phases: 1) mitosis - oogonia/spermatogonia 2) meiosis I and II - primary 1 and 2 oocytes/1 and 2 spermatocytes - further maturation of spermatids into spermatozoa
Mitosis Chromosome duplication Daughter cells are diploid (2n): 23 pairs of maternal and paternal chromosomes Occurs in spermatogonia from prenatal – adult life Occurs in oogonia only during fetal life
Meiosis 1) replication 2) Homologous chromosome pairing + random distribution 3) crossing over 4) homologous chromosome separation/first meitotic division (1n)
Meiosis: females 1° oocytes Fetal development 2° oocytes Fertilization
Meiosis: males 1° spermatocytes Embryo/puberty - adulthood 2° spermatocytes Puberty - adulthood
Sex steroid production Androgens predominate in males; estrogens and progesterone predominate in females Similarities with adrenal cortex: Cholesterol precursor Production of weak androgens (DHEA and androstenedione) and progesterone
Endocrine regulation Reproductive hormone synthesis is regulated by the hypothalamo-pituitary-gonadal (HPG) axis
Endocrine regulation Gonadotropin releasing hormone (GnRH) secreted by the hypothalamus Luteinizing hormone (LH) and follicle stimulating hormone (FSH) gonadotropins secreted by the anterior pituitary gland
Endocrine regulation Kisspeptin neurons activate GnRH neurons in the hypothalamus Negative feedback regulation at the level of the anterior pituitary and hypothalamus
Steroidogenic and Supporting Cells Specialized cells within the gonads produce the sex hormones Estrogen: Granulosa cells produce aromatase Theca cells produce androgens Progesterone: Granulosa cells and theca cells Corpus luteum
Steroidogenic and Supporting Cells Testosterone Leydig cells Supporting cells (granulosa cells and Sertoli cells) also secrete a protein hormone inhibin
Sexual development 1) Sex determination Determined at the moment of fertilization by the genetic inheritance of the sex chromosomes
Sexual development 2) Sex differentiation SRY (sex-determining region of the Y chromosome) protein expression → testes formation Anti-Müllerian hormone (AMH) expression → regression of the female (Müllerian) duct system
Sexual development Testosterone secretion → development of the male (Wolffian) duct system DHT → development of penis, scrotum, prostate Absence of SRY expression → development of the Müllerian duct system, vagina and external genitalia
Male reproduction Four major components - Paired testes - Duct system Epididymis Ductus deferens Ejaculatory duct Urethra - Glands Seminal vesicle Prostate Bulbourethral gland - Penis
Testicular Macrostructure Epididymis Rete testes Testicular parenchyma Scrotum Testicular capsule
Testicular Microstructure Interstitial tissue Seminiferous epithelium Lumen Seminiferous tubule
Testicular Integument The testis, epididymis and spermatic cord are enclosed by the scrotum, which consists of four main layers: Skin Dartos muscle – regulates scrotal surface area Scrotal fascia Parietal vaginal tunica
Testicular Integument The testicular capsule provides additional support for the testis and is comprised of the: Visceral tunica vaginalis Tunica albuginea – collagen interspersed with smooth muscle cells Tunica vasculosa – rich in blood vessels
Testicular blood supply Spermatogenesis proceeds best at temperatures ~2C cooler than core body temperature
Testicular blood supply Blood entering the testis is cooled by contact with the venous pampinform plexus where heat was lost through the scrotal skin in a counter-current heat exchange mechanism
Tubular compartment Contains the seminiferous tubules Comprise 70-90% of the testicular parenchyma in mammals Combined length of 250 m in humans
Tubular compartment Consists of germ cells and somatic cells (Sertoli “nurse” cells) May be further subdivided into the basal (peripheral) and adluminal (adjacent to the lumen) compartments
Interstitial Compartment Contains the interstitial tissue Consists of Leydig cells, peritubular myoid cells, blood and lymphatic vessels, connective tissue, immune system cells and nerves
Testicular function In the testicular parenchyma: Spermatogenesis Production of sperm Takes place in the tubular compartment Steroidogenesis Production of sex hormones (mostly androgens) Takes place in the interstitial compartment (Leydig cells)
Spermatogenesis: Sertoli Cell Involvement Sertoli cells are connected with every cell type in the seminiferous epithelium Germ cells – gap junctions Sertoli cells – tight junctions → blood-testis barrier
Spermatogenesis: Sertoli Cell Involvement Target cell for FSH and testosterone Supports proliferation and differentiation of the germ cells Maintain a high level of testosterone in the luminal fluid by secreting androgen-binding protein
Spermiogenesis Spermatids undergo extensive cytoplasmic re-organization Formation of the acrosome Development of the flagellum Nuclear condensation Released into the seminiferous tubule lumen as spermatozoa
Sperm transport Sperm are non-motile after release from seminiferous epithelium Carried through seminiferous tubule → rete testis → efferent ductules → epididymis by luminal fluid secreted by Sertoli cells
Sperm transport Carried from epididymis → vas deferens by peristaltic contractions from layer of smooth muscle tissue Distal epididymis and vas deferens store sperm until ejaculation
Sperm transport Fluid which suspends ejaculated sperm (i.e., semen) contains chemicals which aid in sperm motility Full motility is not acquired until encountering the female reproductive tract (i.e., capacitation)
Endocrine regulation Hypothalamus secretes gonodotropin-releasing hormone (GnRH) ~ every 90 mins GnRH stimulates the pituitary gland to secrete pulsatile release of gonadotropins Luteinizing hormone (LH) Follicle stimulating hormone (FSH)
Endocrine regulation LH and FSH stimulate gonads to secrete testosterone and inhibin, respectively Testosterone and inhibin negatively feedback to pituitary gland and hypothalamus
Early Postnatal Reproductive Hormone Profile A transient early rise in gonadotropins initiates pubertal onset Induces a transient rise in testosterone Magnitude and time corresponds with pubertal timing
Prepubertal Reproductive Hormone Profile Mitotic phase: decreasing gonadotropin levels, low steroidogenesis Post-mitotic phase: increasing steroidogenesis, low gonadotropin levels
Prepubertal Testicular Development: Histomorphology Mitotic phase: Spermatogonia or primary spermatocytes as most mature germ cell type Small lumen Post-mitotic phase: All germ cell types present Lumen formation and enlargement
Postpubertal Development and Aging In the postpubertal period, there is increasing seminiferous tubule size, testosterone concentration and semen output to adult levels
Postpubertal Development and Aging With aging, testosterone levels decline, accompanied by decrease in libido and sperm motility Androgen production and spermatogenesis continue throughout life
Created by: reub8n
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