Chromosomal Distribution in Sexual Reproduction
Haploid from the mother and father at fertilization make a diploid ovum and meiosis to occur
Germ cell migration
-primordial germ cells that originate outside in the yolk sac. It goes to the genital ridge and start procuring sex organs
Male development
Genetic sex is determined at fertilization, the 1 cell Zygote will develop three germ layers. Mesoderm will go on to form the reproductive system. the germ cells arise outside the body.
-Gonadal sex is determined by the expression of SRY during embryonic
Formation of the Testis
SRY +ve
-The forming Sertoli cells secrete testosterone and Mullerian Inhibiting Factor.
-Mullerian Inhibiting Factor causes degradation of M�llerian duct.
-Testosterone promotes survival of the Wolfian duct
-Sertoli cells produce the enzyme 5-alpha reduc
Formation of the Testis
-The germinal epithelium invade the mesenchyme to form the primary sex chords which will continue to develop into seminiferous tubules
-SRY induces the expression of Sox9 which activates FGF9. FGF9 drives the formation of Sertoli cells which surround the
Functional Anatomy of the Testis
-Under a tough membranous shell, the tunica albuginea, the testis contains very fine coiled tubes called seminiferous tubules. The tubules are lined with a layer of cells (germ cells) that form from puberty into old age, develop into sperm cells (also kno
Within the seminiferous tubules
-germ cells develop into spermatogonia, spermatocytes, spermatids, and spermatozoa through the process of spermatogenesis.
-Sertoli cells- the epithelium of the seminiferous epithelium are critical for the support of germ cell development into spermatozoa
Between tubules (interstitial cells)
-Leydig cells- cells localized between seminiferous tubules produce and secrete testosterone and other androgens important for sexual development and puberty.
--Sertoli cells constantly envelope developing sperm cells into spermatozoa. "nurse cells" carry
Sertoli cells
nurse cell" of the the testes and is an integral part of a seminiferous tubule. It is activated by follicle stimulating hormone and has FSH-receptors on its membranes
-As spermatocytes divide, they maintain cellular bridges between daughter cells allowin
Functional anatomy of Testis
Translocation of germ cells from base to the lumen of the seminiferous tubules occurs by conformational changes in the lateral margins of the Sertoli cells.
--engulf germ cells and allow to pass closely to membrane of Sertoli cell. How intimately controll
The blood testis barrier
large molecules cannot pass from the blood into the lumen of a seminiferous tubule due to the presence of tight junctions between adjacent Sertoli cells. Therefore the spermatogonia are in the basal compartment and the more mature forms such as primary an
The function of the blood-testis barrier
is to prevent an auto-immune reaction. Mature sperm (and their antigens) arise long after immune tolerance is established in infancy. Therefore, since sperm are antigenically different from self tissue, a male animal can react immunologically to his own s
Functional Anatomy of the Testis
-Leydig cells are found adjacent to the seminiferous tubules in the testicle. They produce testosterone in the presence of luteinizing hormone (LH).
--Need to consume cholesterol for precursors for hormones.
Leydig cells functional anatomy
Leydig cells release a class of hormones called androgens. They secrete testosterone, androstenedione, and dehydroepiandrosterone (DHEA), when stimulated by the pituitary hormone LH. LH increases cholesterol demolase activity (an enzyme associated with th
Mechanisms of controlling Differentiation
Intrinisic: SRY-> Sox9 -> FGF9 -> Sertoli cells
Extrinsic: Germ stem cells become sperm or oocytes based on signals within their niche produced by the Sertoli cells.
Testis kept outside
They are kept outside of the body to maintian omeostatic temperature through regulation. gubernaculum and development ensues and descends into what was vagina. inguinal ring will have temp sensors to monitor blood, whether to raise or lower. cryptorchidis
Cryptorchidism
is the failure of testis to descend; unilateral or bilateral; decreased fertility; increased risk of germ cell tumor
Puberty
is the process of physical changes by which a child's body becomes capable of reproduction
Puberty cont.
It is initiated by hormone signals from brain to the gonads (the ovaries and testis)
-nutrition- achieving a certain weight or ration of fat to muscle.
-season- animals will come into season based on light cycles
-disease- may interfere with the onset of
Testis
-descent is usually complete by seven month of gestation
-descend into scrotum
--location provides cooler environment essential for spermatogenesis
-Perform dual function
--Produce sperm: occurs within seminiferous tubules
--Secrete testosterone: produced
Testosterone
-steroid hormone derived from cholesterol precursor molecule
-Five categories of testosterone effects
--Reproductive system before birth
--sex-specific tissues after birth
--other reproductive-related effects
--secondary sexual characteristics
--non-repro
Follicle Stimulating Hormone (FSH)
is a hormone synthesized and secreted by gonadotrophs of the anterior pituitary gland. FSH regulates the development, growth, pubertal maturation, and reproductive processes of the body. FSH and LH act synergistically in reproduction.
Inhibin
Potently inhibits pituitary follicle-stimulating hormone (FSH) synthesis and secretion
Luteinizing Hormone
a hormone produced by anterior pituitary gland
IN males, it stimulates Leydig cell production of testosterone
**maintenance of spermatogenesis
Exocrine Glands
are a type of ductal glands that secrete their products (including hormones and other chemical messengers) into ducts that lead directly into the external environment **Short range
Endocrine Glands
secrete their products (hormones) directly into the bloodstream or release hormones (paracrines) that affect only target cells nearby the release site **long range
Hormonal Control Spermatogenesis
**Testis have dual function- Exocrine and Endocrine
-LH secretion from the anterior pituitary stimulates testosterone production by the Leydig cells (only Leydig cells have LH receptors)
-testosterone will feedback to the hypothalamus to decrease LH produ
Hormones
At the onset of puberty the hypothalamus begins pulsitile secretion of GnRH.
Gonadotropin-Releasing Hormone (GnRH) is a trophic peptide hormone responsible for the release of follicle-stimulating hormone (FSH) and LH from the anterior pituitary
**pulse fr
Hormonal Control of Spermatogenesis
Through these complex feedback loops, the production of Testosterone is initiated which induces the development of secondary sexual characteristics
In the presence of Testosterone, FSH initiates the process of meiosis (spermatogenesis) within the seminife
Hormonal control of Spermatogenesis animation
Fast pulse of LH causes the release of testosterone through the final maturation of Leydig cells and mitosis of cells from development of testis
Once goes back to hypothalamus will slow pulse, which will stop release of LH and start release of FSH. FSH wi
Spermatogenesis
Results in many highly specialized, mobile sperm
Complex process by which undifferentiated diploid primordial germ cells (spermatogonia) are converted into haploid spermatozoa (sperm)
Three major stages of Spermatogenesis
-Meiotic proliferation:
sperm forming daughter cell divides mitotically twice more to form four identical primary spermatocytes
-Meiosis:
Each primary spermatocyte forms two secondary spermatocytes yielding four spermatids after the second meiotic divisio
Spermatozoan
-Remains closely associated with Sertoli cells throughout development
-Consists of 4 parts: Head, acrosome, midpiece, tail
Head
consists primarily of the nucleus (contains DNA)
Acrosome
-Enzyme-filled vesicle that caps tip of head
-used to penetrate ovum
-formed by endoplasmic reticulum and Golgi complex before these organelles are discarded
Midpiece
area where mitochondria are concentrated
Tail
provides mobility for spermatozoan
Two stages of Spermatogenesis
-Spermatocytogenesis: all stages lacking sperm morphology
-Spermiogenesis: change in cellular morphology to "sperm shape
Spermatogenesis
-A spermatogonium sitting on the basement membrane divides mitotically. one daughter cell will replace the mother cell while the other cell goes forward into spermatogenesis
-the lateral margins of the Sertoli cells alter their conformation and allow the
Spermatogenesis
-spermatogonia start meiosis and duplicate their chromosomes to 4N and become primary spermatocytes
-the spermatocytes travel towards the lumen of the tubule
-the primary spermatocytes divide meiotically to form secondary spermatocytes (2N)
-the secondary
Spermiation
-During the morphological maturation of spermiogenesis, the nucleus of the spermatid is compressed and the histones are replaced with protamines.
-The head of the sperm called the acrosomal cap derives from Golgi apparatus
-the tail of the sperm becomes o
Functions of Sertoli cells located in seminiferous tubules
-form blood-testis barrier
-provide nourishment
-phagocytic function: cytoplasmic drop
-Secrete seminiferous tubule fluid which flushes released sperm from tubule into epididymis for storage and additional processing
-secrete androgen-binding protein
-Sit
Epididymis and ductus deferens
-store and concentrate sperm
-increase sperm motility and fertility prior to ejaculation.
*during ejaculation
-sperm are mixed with secretions released by accessory glands: seminal vesicles, prostate gland, bulbourethral glands
Seminal vesicles
-supply fructose for energy
-supply prostaglandins: promote smooth muscle motility in both male and female reproductive tracts (enhances sperm transport)
-provide more than half the semen
-secrete fibrinogen
Prostate gland
-contributes alkaline fluid that neutralizes acidic vaginal secretions.
-provides clotting enzymes and fibrinolysin
Bulbourethral glands
release lubricating mucus
Spermatogenic Cycle
-as spermatocytes divide they maintain cellular bridges between each daughter cells allowing each cell to communicate with one another
-because of this close communication, the control of cellular division and differentiation during spermatogenesis is syn
Sperm Maturation
-the sperm that are eventually released into the lumen of the somniferous tubules are immature and incapable of fertilization.
Maturation of sperm occurs in the epididymus and involves incorporation of epididymal proteins that enhance motility, stabilize