_HD-201_-E01_T01_Histology-of-Male-Reproductive-System_compressed

• The urinary and reproductive systems are concurrent in males.
• The penile urethra is naturally acidic.
• Semen must be more neutral to a little basic.

Organs and Structures Overview

• Testes are the main organ for reproduction.
• Testes are paired organs, sized at approximately 5cm x 2.5 cm x 3 cm.
• Average temperature within the testes must be 34°C (3° lower than body temp).
• Undescended testis may become cancerous.
• Most distal portion of the processus vaginalis becomes tunica vaginalis during descent of the testis.
• Dartos and cremaster muscles move the testes towards or away from the body for temperature regulation.
• Warm temperature relaxes the muscles, moving them away from the body.
• Cooler temperature contracts the muscle, moving them towards the body.
• Testicular artery is cooled by the venous blood from the pampiniform plexus surrounding the artery in a countercurrent mechanism.
• The scrotum contains testes in sacs of multiple layers: skin, dartos fascia, tunica vaginalis, cremaster muscle, tunica albuginea.
• The inguinal canal has an evagination called the processus vaginalis, which becomes tunica vaginalis.
• Tunica albuginea is a white colored, fibrous coating of the testes composed of connective tissue.
• The testicular mediastinum drains into efferent ducts outside the testes.
• Efferent ducts coalesce to become the epididymis.
• The epididymis is found dorsally behind the testes, serving as a storage and maturation site for sperm.
• During ejaculation, spermatozoa are transported to the vas deferens.
• The vas deferens is an intra-abdominal duct that goes behind the bladder, joins the seminal vesicles, and becomes the ejaculatory duct inside the prostate.
• During ejaculation seminal fluid contains secretions from seminal vesicles, prostate gland, and Cowper's gland.
• Bulbourethral (Cowper's) gland is located at the base of the penis in the deep perineal pouch.
• Accessory glands include the seminal vesicles, prostate gland, and Cowper's gland.

Reproduction

• The main function of the male reproductive system is to reproduce.
• Right and left testes are located in the scrotum, separated by the scrotal septum.
• Seminiferous tubules are lined by germinal epithelium.
• Sperm cells are initially non-motile and immature when produced in the seminiferous tubules.
• Semen travels from the prostatic urethra → membranous urethra → penile (spongy) urethra → external urethral orifice.
• Coordinated contraction of the epididymis, vas deferens, seminal vesicles, prostate, and bulbospongiosus muscle ensures semen expulsion.
• Cowper's/Bulbourethral Glands produce fluid to prepare penile urethra; neutralizes the penile urethra.
• Penile urethra has urine & other components not good for semen.

Fertilization Pathway

• During coitus, semen is expelled out into the vaginal tract.
• Sperm with enough numbers travels through the vaginal tract to the uterus and fallopian tube, where an ovum is present.
• Capacitation happens in the fallopian tube where the ovum and sperms will meet.
• Many sperm cells are necessary in order to penetrate the thick zona pellucida of a single ovum.
• Fertilization occurs in the fallopian tube, specifically at the ampulla, if a sperm breaks through the zona pellucida.
• After fertilization, the fertilized egg travels towards the uterus and attaches itself to its lining.
• Implantation that happens in the fallopian tube will result in an ectopic pregnancy.

Male Histophysiology

• Hypothalamus releases gonadotropin-releasing hormone (GnRH), stimulating the anterior pituitary to release follicle stimulating hormone (FSH) and luteinizing hormone (LH).
• LH stimulates the Leydig cells to release testosterone, while FSH stimulates the Sertoli cells to release androgen-binding proteins (ABP).
• Testosterone gives rise to secondary male characteristics and promotes differentiation and maturation of gametes.
• FSH also stimulates the spermatogonium to promote spermatogenesis.
• Sertoli cells produce inhibin.
• Inhibin sends negative feedback to anterior pituitary to counter further FSH release, while testosterone sends negative feedback to the hypothalamus to counter further GnRH, FSH, and LH release.

Testes Histology

• The testis is surrounded by a dense connective tissue capsule, the tunica albuginea, thickened on the posterior side to form the mediastinum testis.
• The testes are divided into ~250 testicular lobules by septa with sparse connective tissue present.
• Interstitial tissue (interstitium) is testicular tissue between seminiferous tubules, containing fibroblasts, macrophages, mast cells, undifferentiated mesenchymal cells, lymphatics, blood vessels.
• Leydig cells (supporting cells) are stimulated by LH to produce testosterone.

Seminiferous Tubules

• 3-4 layers of smooth muscle cells (myoid cells, fibroblasts), connected to epididymis via rete testis and 10-20 efferent ductules.
• Where spermatogenesis and spermiogenesis occur.
• Germinal Epithelium (Seminiferous Epithelium) has basal and adluminal compartments. Basal compartment, which near basement membrane or basal lamina, has contractile soft tissue or myoid cells. Basal compartment's first layer after the basement membrane is the spermatogonia.
• Will give rise to spermatogonia type A or B.
• Type A will give rise to another type A or type B.
• Type B goes into lumen, becomes slightly enlarged, and preparation for meiosis, giving rise to primary spermatocyte.

Spermatocytes

• Primary spermatocytes, self, diploid (2N)
• Contain the same genetic material you are carrying.
• Slightly larger cell than secondary spermatocytes.
• Secondary spermatocytes, non-self, haploid (N)
• Lesser in cytoplasmic material than primary spermatocytes.
• Secondary spermatocytes become spermatids, which further differentiate into spermatozoa.
• Inside the lumen of the seminiferous tubules, you will find non-motile sperm cells.
• Cap consists of enzymes that penetrate the zona pellucida, a thick layer of the ovum.
• Centrioles go to south pole and develop the flagellum.
• As the cell/spermatozoa develops, cytoplasm starts to slough off.
• Sperm cells will move by hydrostatic movement, and they will have to go through straight tubules in a rallying area.
• The sperm cells move this way so they have enough and motile sperm counts to penetrate the ovum.
• Having low sperm count will not be able to penetrate the ovum.
• Only 1 sperm cell will fertilize the ovum.

Sertoli Cells

• Athletes that manifest with female genitalia but still with XY chromosome and male internal organ may have a condition called androgen insensitivity syndrome.
• There must be failure to develop male characteristics due to failure of Sertoli cells to produce ABP.
• Sertoli cells secretes Mullerian-Inhibiting Substance during fetal development.
• Prevents the development of Müllerian (paramesonephric) ducts, which would otherwise form female reproductive structures
• Blood-testes barrier is created by tight junctions between Sertoli cells.
• Protects developing sperm from autoimmune attacks by isolating germ cells from the immune system.
• Engulfs and removes excess cytoplasm from developing sperm, thus is phagocytic.

Rete Testes

• Simple cuboidal cells.
• May actually appear simple squamous epithelium, but books describe it as simple cuboidal embedded in dense connective tissue
• Looks like a maze.

Efferent Ducts

• From the rete testis, the sperm will drain now into your efferent ducts.
• The efferent ducts are lined by tall and short pseudostratified columnar cells
• Tall cells = ciliated and short cells = nonciliated, with absorptive properties.
• The efferent ducts facilitate getting the sperm into the epididymis:
• Absorbing fluid from a high (positive) gradient to a low (negative gradient), you create a hydrostatic imbalance.
• The volume coming from your seminiferous tubules is decreased here in the efferent ducts.
• Providing a hydrostatic force that will promote movement of fluid from the seminiferous tubules into the efferent ducts.
• The efferent ducts will drain into your epididymis.

Epididymis

• Where efferent ductules enter
• Where sperm cells undergo further subtle modifications
• Where sperm are stored until ejaculation
• Inside the epididymis, there is a very distinct pseudostratified columnar epithelium with stereocilia
• With very distinct lumen
• Columnar Principal cells remove most of the water and residual bodies entering the epididymis with the sperm.
• They secrete various products, greatly changing the fluid in which sperm are suspended.
• Stereocilia are involved in the absorption of excess fluid accompanying the spermatozoa from the testis.
• The epididymis will serve as a temporary storage of your sperm cells until they mature.
• Surrounding your epididymis are smooth muscle cells.
• These smooth muscle cells, during ejaculation, will propel the sperm cells from the epididymis into the vas deferens.

Vas Deferens

• A muscular, tubular organ structure.
• Its long course from extra-abdominal (testes) to abdominal, goes behind the bladder to join the seminal vesicle.
• The seminal vesicle and vas deferens will become ejaculatory ducts, with the ejaculatory ducts embedded within the substance of the prostate gland.
• Lining is composed of pseudostratified columnar epithelium, in contrast with ureter, which has transitional epithelium.
• With multiple layers of longitudinal outer, circular middle, and longitudinal inner smooth muscle due to its propulsive function.
• A surgical procedure to cut or seal the tubes that carry sperm to prevent pregnancy.
• Readily accessible by males and done through local anesthesia.
• Vasectomy does not decrease male characteristics.

Seminal Vesicle

• Located behind the bladder and the prostate gland.
• Best appreciated in a cut section of the bladder where the seminal vesicle and the prostate are visible.
• Joins the vas deferens to become the ejaculatory duct.
• Configuration of tubuloalveolar cells show very prominent glandular processes.
• Produce the majority of the contents of semen (fluid, fructose, fibrinogen, prostaglandin), forming 70% of the semen
• Consist of highly tortuous tubes, each about 15cm long enclosed with connective tissue
• Rich in secretory granules
• Fructose: Major energy source for sperm and Prostaglandin: Stimulate activity in the female reproductive tract
• Fibrinogen: Allows semen to coagulate after ejaculation
• Mucosa of the tube displays a great number of thin, complex folds which fill much of the lumen
• Lamina Propia contains elastic fibers
• Surrounded by smooth muscles with inner circular and outer longitudinal layers to empty the gland during ejaculation

Prostate Gland

• Ejaculatory ducts and the prostatic urethra are embedded within the prostate gland and produces 20% of seminal fluid.
• Lateral and medially contains varying tubuloalveolar gland patterns with a prominent fibrous stroma
• Stroma represents as more prominent/intervening tissue
• Contains primarily deposited glycoproteins and keratin sulfate but are of no clinical significance
• Apart from doing a rectal exam for the purposes of checking the prostate (i.e., prostatic examination), one can milk the seminal vesicle and the prostatic urethra
• This technique allows for the collection of samples for culture, particularly for cases of patients with suspected STDs
• Benign Prostatic Hyperplasia (BPH) is prostatic enlargement in the older population that can result in obstruction of the prostatic urethra in the urinary tract, causing a distended bladder and retrograde urinary excretion.

Prostatic Examination

• Done through rectal examination, the prostate is readily accessible through the anus.
• Prostatic enlargement may be a sign of cancer.

Cowper's/Bulbourethral Glands

• Also known as the Cowper's glands, which are found at the base of the penis, before the penile urethra
• Secretions that are produced by penile urethra and bulbourethral glands to prepare and lubricate the penile urethra before ejaculation
• Prepares the urethra for the passage of seminal fluid
• Does NOT contain sperm, hence, cannot impregnate
• To protect against STDs, barrier methods (e.g. condoms) must be used to aid in physically blocking the exchange of bodily fluids and significantly reduce the risk of transmission

Penis

• Engorging the penis with blood (as it is filled with capillaries), akin to inflating a balloon that provides erection and is sensitive to certain pharmacology (e.g. nitric oxide derivatives)
• Sildenafil was initially designed to treat pulmonary hypertension, vasodilating the pulmonary arteries affected by constriction in pulmonary hypertension
• Side Effect: Prolonged erection
• In the corpus spongiosum, there's the penile urethra
• During ejaculation, the ejaculate (semen) will pass through the penile urethra
• Erection of the penis is afforded by the presence of the cavernous artery and the venous plexus
• During coitus and ejaculation, the semen will be deposited in the vaginal tract and the semen and the sperm cells will now move from the vaginal tract and into the fallopian tube