 This video will cover the following objective from the reproductive system, describe the location, structure, and function of the testes, define spermatogenesis, describe the location and functions of the spermatagonia, spermatocytes, spermatids, spermatizoa, sertoli cells, and lydig cells or interstitial cells of lydig. The testes are found within the scrotum. The scrotum is a sack of skin located just inferior to the pelvic cavity. The scrotum contains the testes outside of the pelvic cavity in order to maintain the optimal temperature for spermatogenesis, the formation of sperm. The scrotum has a layer of smooth muscle in the dermis of the scrotum known as the dartose muscle that can contract involuntarily in order to produce the wrinkled appearance of the scrotum that helps to draw the testes closer to the pelvic cavity, helping to increase the temperature inside of the testes. Similarly, there's a skeletal muscle known as the cremaster muscle that can contract to pull the testes closer to the pelvic cavity to warm the testes. And both the cremaster and the dartose can relax in order to move the testes further from the pelvic cavity to help cool down the testes. So the cremaster muscle is found within a bundle of connective tissue known as the spermatic cord. So the other structures that are deep to the cremaster muscle within the spermatic cord are the testicular artery, which is the male gonadal artery carrying blood into the testes. There's also the testicular vein or the pampiniform plexus of testicular veins that carry blood out of the testes. And the testicular artery and the plexus of testicular veins have a countercurrent flow mechanism that helps to conserve the heat within the blood and prevent that heat from flowing into the testes. And so the heat is transferred directly from the testicular artery into the plexus of testicular veins as blood is flowing in the opposite direction through those vessels. Another structure found within the spermatic cord is the ductus deference or vas deferens, the tube that will transport the sperm from the scrotum into the pelvic cavity to the ejaculatory duct in the prostate gland. Here we can see the internal structure of the testes. The testes contain small tightly coiled tubes known as the seminiferous tubules that are responsible for sperm production. So the sperm are first produced inside of the seminiferous tubules and then they move into the epididymis, a long tightly coiled tube system located just superior and posterior to the testes. The sperm will be stored and matured inside of the epididymis and then they will travel out into the ductus deference, also known as the vas deferens that travel up into the pelvic cavity and will then transport the sperm into the ejaculatory duct within the prostate gland during ejaculation. So the cells that form the seminiferous tubule include the spermatogonia and spermatocytes that are involved in spermatogenesis. So the spermatogonia are found in the most superficial layer of each seminiferous tubule and as they divide producing primary spermatocytes, the primary spermatocytes are pushed deeper towards the lumen and the primary spermatocytes enter into meiosis. Each primary spermatocyte will produce four spermatids in the two rounds of myotic cell division and so as each of these daughter cells is produced they will be pushed further towards the lumen so that the spermatids are found adjacent to the lumen and are released into the lumen as they enter into the process of spermeogenesis where a spermatid will mature into a spermatizoa or mature sperm cell that will develop a tail in order to be able to swim to propel itself through the female reproductive tract to find the developing oocyte and initiate the process of fertilization. So the other type of cell that's found in a seminiferous tubule is known as a sertoli cell. So the sertoli cells are surrounding the spermatocytes within the seminiferous tubule and they function to help support the process of spermatogenesis. The sertoli cells produce a hormone known as inhibin that will be important for regulating the production of another hormone from the anterior pituitary known as follicle stimulating hormone. So follicle stimulating hormone will stimulate the process of spermatogenesis and will stimulate the sertoli cells to make a protein called androgen binding protein. Androgen binding protein helps to concentrate testosterone inside of the seminiferous tubule and testosterone will stimulate the process of spermatogenesis. But when follicle stimulating hormone stimulates the sertoli cells to make androgen binding protein it also stimulates those cells to make inhibin and inhibin will have a negative feedback function to decrease the production of follicle stimulating hormone helping to maintain the homeostatic level of follicle stimulating hormone and androgen binding protein. So testosterone is produced by another cell that's found just outside of the seminiferous tubule known as the interstitial cell of LIDIG or just LIDIG cell. So the LIDIG cell or interstitial cell of LIDIG produces testosterone in response to another hormone that comes from the anterior pituitary called luteinizing hormone. So luteinizing hormone stimulates the interstitial cells of LIDIG to make testosterone and then testosterone will have a function inside of the seminiferous tubules to stimulate spermatogenesis and testosterone will also have effects all through the body stimulating masculinization like the effects that would stimulate increased facial hair growth or stimulate growth of the larynx to produce the lower pitch voice in men or stimulating the growth of the skeletal muscle. Here we see the histology of the testes at low magnification where you can see there are numerous seminiferous tubules responsible for spermatogenesis where the spermatagonia will divide by mitosis to produce primary spermatocytes that enter into meiosis to produce the spermitids. The spermitids then enter into the lumen of the seminiferous tubule and go through spermogenesis to form the mature sperm cells known as spermatozoa. The outer layer of the testes is a layer of fibrous connective tissue known as the tunica albuginia. You can see the tunica albuginia surrounding all of the seminiferous tubules of the testes. Here we have a higher magnification view focused in on the seminiferous tubules where the spermatagonia and spermatocytes form the seminiferous tubules and those spermatocytes are surrounded by larger sertoli cells and the sperm are released into the lumen where they will then travel out through the seminiferous tubules into the epididymis. Adjacent to the seminiferous tubules we can see regions where there are interstitial cells. The interstitial cells of lydig or lydig cells are those cells that produce testosterone. Here we have a higher magnification view of a seminiferous tubule where we can see the spermatocytes that are going through meiosis to produce spermatids that are released into the lumen to form the sperm or spermatazoa. We can also see the adjacent interstitial cells or lydig cells that produce testosterone. Here is another low magnification view of the testes with a different staining pattern. We can see the fibrous connective tissue capsule called the tunica albuginia surrounds the tightly coiled seminiferous tubules within the testes that are responsible for spermatogenesis where the spermatocytes go through myotic cell division to produce the spermatids that mature into spermatazoa. Here's a higher magnification view where we can see the spermatocytes in the walls of the seminiferous tubules and the interstitial cells of lydig that are adjacent to each of the seminiferous tubules. And here at high magnification we can see a seminiferous tubule with numerous spermatocytes forming the wall of the seminiferous tubule and the sperm that have been released from the tubule into the lumen and then adjacent to the seminiferous tubules. We can see interstitial cells of lydig the cells that make testosterone are found adjacent to the seminiferous tubules. The process of spermatogenesis is regulated by the endocrine system. The hypothalamus produces a releasing hormone known as gonadotropin releasing hormone or GNRH. So GNRH is released from the hypothalamus into the hypothysyl portal and it travels in the blood into the anterior pituitary where it will then stimulate the cells in the anterior pituitary to release FSH and LH follicle stimulating hormone and luteinizing hormone. Luteinizing hormone will then bind to receptors on the surface of the interstitial cells of lydig and stimulate the production of testosterone. Then testosterone will act locally in the seminiferous tubules. Testosterone will stimulate the process of spermatogenesis but testosterone will also travel through the blood having effects all through the body to have masculinizing effects and then in the hypothalamus and anterior pituitary gland testosterone will have a negative feedback function to decrease the production of GNRH and LH. Now follicle stimulating hormone produced by the anterior pituitary will bind to the receptors on the sertoli cells in the seminiferous tubules. Then the sertoli cells will respond by producing androgen binding protein and a hormone called inhibin androgen binding protein functions to bind to testosterone inside of the seminiferous tubule helping to increase the local concentration of testosterone in the seminiferous tubule helping to promote the process of spermatogenesis inhibin functions as a negative feedback hormone to decrease the production of follicle stimulating hormone from the anterior pituitary and so both inhibin and testosterone have negative feedback functions leading to a decreased production of FSH and LH as a homeostatic control mechanism maintaining a stable concentration of FSH and LH in the blood.