Organ Architecture 6 - The Reproductive System PDF

THE FEMALE GENITAL TRACT Gonads —> uterine tube —> uterine cavity —> cervix —> vaginal canal —> vestibule of the vagina The female genital tract is largely covered by a fold of peritoneum that forms the broad ligament of the uterus. However the uterus is not an intraperitoenal organ. The outer lay...

THE FEMALE GENITAL TRACT Gonads —> uterine tube —> uterine cavity —> cervix —> vaginal canal —> vestibule of the vagina The female genital tract is largely covered by a fold of peritoneum that forms the broad ligament of the uterus. However the uterus is not an intraperitoenal organ. The outer layer of the ovaries is called germinative epithelium (not peritoneum) The broad ligament is divided into mesosalpinx, mesometrium and mesovarium There might be remnants of the mesonephros or mesonephric duct which form cysts in different parts of the broad ligament OVARIES They’re 3-5cm in length. Stroma —> fibroblast cells containing lipid droplets + collagen fibers + bundles of smooth muscle cells Cortex —> peripheral region of the stroma, it contains follicles at different stages of development Tunica albuginea —> superficial region of the cortex Germinative epithelium —> outermost layer, it is made of cuboidal cells and it is a continuation of the peritoneum. Might give rise to ovarian cancer Medulla —> central zone of the ovary, here we don’t find follicles but we do find lots of blood vessels Helicine arteries —> they’re 10 coiled arteries that give rise to straight arteries which will surround the follicles creating a capillary plexus Along the genital tract we find a basic structure: Wall of smooth muscle Inner mucosal lining Outer layer of loose supporting tissue What changes is the thickness of the mucosal and muscular layers along different locations to serve different functions. Other changes are attributed to the ovarian cycle (for example the number of cilia increase on the cells of the tubes when the oocyte has to be moved around) The changes happening during the ovarian cycle facilitate: Entry of the oocyte into the fallopian tube Entry and progression of the spermatozoa into the cervix and in the fallopians tube Passage of the ovum into the uterus Implantation and development of the ovum in the mucosal lining of the uterus UTERINE TUBES (Fallopian tubes or salpinges) Salpingitis = inflammation of the uterine tube (that’s why we need to remember the alternative name) The fallopian tubes are the site of fertilisation (usually in the ampullary region) and of cleavage and they propel the egg or blastocyst to the uterus. The secretions of the fallopian tube nourish the early embryo The uterine tube is divided into 4 a atomic regions: Infundibulum —> terminates with the fimbriae (which are close to the ovary). One of the fimbriae is attached to the surface of the ovary and it’s called ovaric fimbria Ampulla —> where fertilisation takes place Isthmus —> where capacitation occurs Uterine part —> connection with the uterine cavity  The tubes are made of: Mucosa —> The mucosa isn’t smooth, it makes lots of folds. These folds make up a labyrinth which is super important to slow down the egg and favour the meeting of the spermatozoa. The folds are higher in the ampulla Lamina propria —> highly vascularised Muscular layer Serosa NO SUBMUCOSA Cells of the tubes: Ciliated cells —> during the estrogenic phase they perform ciliogenesis (increase in the number of cilia) while during the luteal phase they undergo deciliation (loss of cilia) Non-ciliated cells (peg cells) —> they have a secretory activity and provide nourishment for the egg. They secrete nourishing substances in the lumen of the tubes to support the zygote. The secretion is regulated by the ovarian cycle Muscular layer —> organised into an inner circular spiral layer and an outer spiral layer. This layer allows the propulsion of the egg or zygote along the tubes. Gentle peristaltic movement (otherwise it would crush the egg). The muscular layer is very thick in the isthmus Close to ovulation the fimbriae are swollen with blood and enlarged PROBLEMS WITH THE TUBES UTERUS It is a muscular organ with a thick wall and it is located in the middle of the lesser pelvis. It is 7-8cm long The uterus is divided into a fundus, a corpus (or body) and a cervix (or neck) The corpus is flattened on the anterior surface due to the relationship with the bladder and it is convex posteriorly where it is in relationship with the intestine. Both faces are covered by peritoneum The upper portion is called fundus and it is above an imaginary line that goes from one tube to the other (uterine horn) The uterus is connected to the vagina through the cervical canal, which opens at the level of the internal os and closes at the level of the external os. In some books the site of transitioning between the body and the cervix is called isthmus (narrowing part) Part of the cervix is surrounded by a region of the vagina called vaginal fornixes A10 intravaginal portion of the cervix surround by the anterior and posterior fornix (arrows) the posterior vaginal fornix is deeper and functions as a reservoir of semen. B9 isthmus (passage from the body to the cervix) During pregnancy, the isthmus elongates and it’s called “inferior” uterine segment C13 external os of the uterus The lumen of the body of the uterus has a triangular shape. The lumen of the cervix has palmate folds that interdigitate with one another —> mechanism of protection of the uterine cavity (especially during pregnancy) to prevent the access of unwanted substances  When the bladder fills the uterus lifts up a bit as it is in relationship with it. We can describe two angles: Angle of anteflexion (between the axis of body of the uterus and the axis of the cervix) Angle of anteversion (between the axis of the vagina and that of the cervix) In some women the angle might be changed: Retroversion, retroflexion or prolapse (uterus prolapses inside the vagina due to a problem in the ligaments) Microstructure of the BODY of the uterus: Endometrium —> mucosa, it is made of simple columnar epithelia and a lamina propria (called endometrial stroma). The cells of the epithelium are ciliated and they invaginate as to form glands. The epithelium can vary in thickness (1-6mm) during the ovarian cycle. The endometrium is divided into a basal layer and a functional layer. The functional layer is further divided into a spongy and a compact layer Myometrium —> thickest layer located in the middle, the orientation of the muscle fibers is not well defined but we can still observe 3 muscle layers. The middle layer (or stratum vasculare) has circular fibers and abundant blood vessels while the other two layers are longitudinally or obliquely oriented Perimetrium —> adventitia or serosa During the menstrual phase the functional layer is shed while the basal layer remains intact Importance of the ARTERIAL SUPPLY —> arcuate arteries in the myometrium give rise to radial arteries, which give rise to spiral arteries and straight arteries. Straight branches supply the basal layer while spiral arteries supply the functional layer. The spiral portion is very sensitive to hormones produced during the menstrual cycle, especially progesterone. Towards the end of the cycle progesterone drops dramatically and spiral arteries respond by activating a mechanism of constriction-dilation. For this reason the blood arriving to the function layer is less and less and this leads to ischemia of the layer and breakdown of the distal portion of the arteries, leading to bleeding. The bleeding stops as the coiled arteries become even more coiled and block themselves During the menstrual period the muscle layer starts to contract to eliminate the ischemic layer of endometrium. Normally there are always contractile waves in the uterus, but these increase a lot during the menstrual phase. These powerful contractions are what lead to pain in women. Menstrual pain is called DYSMENORRHEA. SENSATION AMLEYTE ENDOMETRIOSIS Presence of ectopic endometrial tissue in other sites of the body. Areas of endometriosis bleed each moth giving rise to inflammation and scarring (which can create ligamental devices with other organs). Endometriosis can lead to pelvic pain (chronic or recurrent), dysmenorrhea, infertility, lower back pain and dysuria (due to inflammation) ENDOMETRIAL CYCLE: Menstrual phase Estrogenic phase (proliferative phase) Ovulation Progestinic phase (secretory phase) —> secretory because at this point the lumen of the endometrial glands we see lots of secretions to prepare for a importa possible implantation (secretions will go in the lacunae ONSET OF MENSTRUATION —> the stroma disaggregates and glands collapse. We can find lots of apoptotic bodies and blood in the stroma EARLY and LATE PROLIFERATIVE PHASE —> we can see lots of mitotic figures (increase in proliferation to substitute the damaged tissue). The lamina propria becomes larger (edematose) and the glands acquire a tortuous appearance EARLY- MID and LATE SECRETORY —> The glands start synthesising glycogen, which is initially stored in the basal compartment of the cells and then it moves to the apical one to be released in the lumen. Here glands are very coiled and full of content. Some of the fibroblasts of the lamina propria undergo a decidual-like reaction (they become larger and prepare for a possible implantation). In the meanwhile the most superficial part of the spiral arteries is reconstituted When a woman enters MENOPAUSE the process of folliculogenesis and of hormonal changes stops. The endometrium becomes thinner, the glands are still present to an extent and they’re are dilated and present concretions (they’re inactive) ABNORMAL UTERINE/VAGINAL BLEEDING (AVB) It is a bleeding that occurs between the menstrual periods or a menstrual flow that is lighter or heavier than normal. This is a type of bleeding that occurs at a time in life when it is not expected (for example in girls before the age of 9, during pregnancy or after menopause). The bleeding can be caused by structural and non-structural problems: Structural —> polyps, adenomyosis, leiomyosis, malignancy/hyperplasia (PALM) Non-structural —> coagulopathy, ovulatory dysfunction, endometrial, iatrogenic, not yet classified (COEIN) ADENOMYOSIS When the endometrium tissue grows into the muscular wall of the uterus. It can cause heavy or prolonged menstrual bleeding, severe dysmenorrhea, chronic pelvic pain or painful inter course FIBROIDS or UTERINE MYOMAS or UTERINE LEIOMYOMAS or FIBROMAS They’re solid tumors made by smooth muscle cells and fibrous tissue. They can be contained in the wall of the uterine cavity or they can protrude outside of the uterus. This can cause heavy or prolonged menstrual periods, abnormal bleeding between menstrual periods, pelvic pain (also due to compression of other organs if the fibroma is big), low back pain and pain during intercourse These are the most common types of tumors in women THE UTERINE CERVIX Functions: Admit spermatozoa during ovulation Protects the uterus and upper genital tract from bacterial invasion (thick mucous except from ovulation, folds that interdigitate with one another) Dilated during delivery Does not participate in the menstrual cycle (doesn’t undergo massive cyclical changes such as the uterus) It is divided into Endocervix (in the cervical canal) —> lined by columnar mucous secreting epithelium (the glands don’t undergo the same changes as those in the endometrium). Ectocervix (outside the cervical canal) —> lined by squamous stratified epithelium (as the vagina) Transition zone —> intermediate zone between the endocervix and the ectocervix. It is the zone of transition between columnar epithelium and squamous stratified and in majority of cases it is the site of development of tumours (95% of all cervical neoplasia) The mucous secretion changes during the menstrual cycle —> at ovulation the mucous is less viscous, hydrated and has an alkaline pH to favour sperm migration. During pregnancy the mucous is very thick and viscous to prevent exogenous substances from coming in (forming a sort of mucous plug) The crystallisation patterns of the mucous are different during ovulation and outside the time window for ovulation (useful to determine the optimal time or fertilisation) BELOW THE MUCOSA —> there’s not a lot of smooth muscle tissue, the main component is dense collagenous connective tissue with elastic fibers. Before parturition the cervix dilates and softens thanks to the lysis of collagen fiber bundles in response to hormones. ENDO Nociceptive/pain related information from the uterus, cervix and uterine tube reach the T10-L1, L2 segments of the spinal cord (same as lower ileum, sigmoid colon and rectum) VAGINA It is a fibromuscular canal (H shaped), the posterior wall is longer than the anterior wall (and the posterior vaginal fornix is deeper for this reason), the upper portion surrounds the lower cervix (vaginal fornix) while the lower portion opens into the vestibule of the vagina. The vagina is lubricated by the cervical mucous produced by the endocervix The vagina presents rugae vaginalis (transverse) and longitudinal crest folds where the vagina adheres to the urethra behind Microscopic structure of the vagina: Mucosa —> squamous stratified epithelium, non keratinised and rich in glycogen (metabolised into lactic acid by the microbiota of the vagina and responsible for its acidic pH). The acidic environment prevents proliferation of bacteria, however the pH fluctuates (for example with age) so the susceptibility to infections changes with time. Lamina propria —> it contains many elastic fibers and a rich plexus of small veins. It has no glands! The mucous comes form the endocervix Smooth muscle layer—> inner circular and outer longitudinal Adventitia —> it’s in the pelvic space, there’s no peritoneum around it (not mobile) The color, density and smell of the vaginal discharge give information about the health of the patient. If they’re abnormal they might be a sign of infection beveelasticfibers At MENOPAUSE there are some hormonal changes that lead to modifications of the vaginal tissue: it becomes thinner and less elastic (47% loss of elasticity), there are changes in the microbiota (56%), changes in pH and changes in glycogen content DISCHARGE (both from the vagina and from the male urethra) can be altered in STDs. In women we notice abnormal vaginal discharge, color and consistency while in males we can observe discharge form the penis. STDs can lead to painful urination (dysuria), painful sexual intercourse in women, bleeding between menstrual periods, painful testicles (epididymitis for example), pain in lower abdomen and pelvis, pain during bowel movements (they send messages to the same segments of the spinal cord), vaginal or penis itching and irritation, odor, fever, headache, sorethroat, rash, fatigue and swollen lymph nodes BARTHOLIN GLANDS or GREATER VESTIBULAR GLANDS These glands open in the vestibule of the vagina and they’re localised in the superficial perineal pouch (not in the vaginal pouch). They produce a mucous secretion for lubrication (for example during sexual intercourse). They’re analogous to the bulburehtral glands of Cowper in males. These glands may become inflamed (bartholinitis) and swell or form cysts FEMALE EXTERNAL GENITALIA or VULVA Vestibule of the vagina, labia minora, labia majora, hymen (breaks down spontaneously or at the first sexual intercourse) The labia minora come together superiorly to form the the frenulum of the clitoris (erectile tissue, vascular plexuses surrounding vagina and urethra) while the labia majora come together superiorly to form the prepuce of the clitoris. The crus of the clitoris come together forming the body of the clitoris CIRCUMCISION and INFIBULATION Female genital mutilation. "Infibulation" is the term used for the removal of the labia minora and the inner surfaces of the labia majora and the sewing together of the remaining tissue so that only a small hole for the passage of urine and menstrual blood remains. MALE GENITAL TRACT Male gonads —> gametes and hormones, seminiferous tubules System of ducts —> straight tubules, rete testis, ductuli efferentes, epididymis, vas deferens and ejaculatory ducts (that converge in the urethra) Two exocrine glands —> seminal vesicles and prostate glands (seminal fluid with nutritive and lubricating properties) Penis —> organ of copulation (bulbourethral gland also contributes to lubrication) TESTIS We can recognise a superior/inferior pole, a later/medial surface and an anterior/posterior margin. The superior pole and posterior margin are in contact with the epididymis. The testis in the scrotal bursa are surrounded by layers of the abdominal wall (deriving form the formation of the inguinal canal) —> tunica vaginalis (small serosa deriving from the peritoneum, formed by a parietal and a visceral layer, not connected to the peritoneum anymore), internal spermatic fascia, cremasteric fascia (comes from the cremasteric fascia, derivative from the internal oblique abdominal muscle) and an external spermatic fascia (derives from the outer oblique abdominal muscle). The seminiferous tubules are arranged in compartments called lobules and are delimited by septa made of fibroelastic tissue and originating from the tunica albuginea. The lobules converge at the level of the mediastinum of the testis (straight tubules come together at the level of the rete testis and enter the caput epidydimis). Length: 4-5cm, width: 3cm The testis are outside of the body to be kept at a lower temperature, however blood coming into them is at body temperature. To solve this problem we cool blood down through the COUNTERCURRENT HEAT EXCHANGE —> there is a plexus of veins called pampiniform plexus in the spermatic cords. This plexus surrounds the testicular artery and allows dissipation of heat of the arterial blood (from 36.66 °C to 33.88 °C VARICOCELE The pampiniform plexus can dilate due to aging or due to the weakening of the wall and give rise to varicocele. This can lead to infertility as the countercurrent mechanism doesn’t work very well anymore + the venous drainage doesn’t work very well and leads to an edema that damages the blood-testis barrier SEMINIFEROUS TUBULES The seminiferous tubules are around 1.000-2.000 and are 280-400meters long. The seminiferous tubules are organised in lobules (around 250) separated by septa. They all converge in the mediastinum of the testis. The mediastinum of the testis —> straight tubules to rete testis to ductuli efferentes  STRAIGHT TUBULES They keep the seminiferous tubules in communication with the rete testis. In the wall of the seminiferous we find Sertoli cells and developing gametes, but in the last portion, where they are in communication with the straight tubules, we can only find columnar Sertoli cells and no germ cells. At the level of the straight tubules the epithelium is simple cuboidal and it presents microvilli and a cilium. Microvilli reabsorb part of the seminal fluid produced in the seminiferous tubules. Here the tight junctions are located apically (while in the seminiferous tubules they were at the bottom) RETE TESTIS It is made by cavities lined by cuboidal epithelium (with microvilli for reabsorption and a motile cilium to move seminal fluid to the ductuli efferentes) and surrounded by a highly vascularised stroma (where the reabsorbed fluid is sent) containing myoid cells (contractile movements to help mix spermatozoa and move them forward) DUCTULI EFFERENTES Here there are cells with microvilli and cilia (to propel spermatozoa towards the epididymis). There is also a thin band of circular muscle surrounding the basal lamina of the epithelium to help propulsion. First appearance of the muscular component! (Before just myoid) There is a progressive increase in smooth muscle tissue —> in the rete testis we find myoid cells in a highly vascularised stroma, in the ductuli efferentes we find a thin layer of smooth muscle cells. Muscle will increase proceeding towards the head, body, tail of the epididymis and ductus deferens EPIDIDYMIS It is divided into a head, body and tail, it is around 6m long and has a 400 micron diameter. The mucosa is made mostly of pseudo stratified epithelium and there is a very clear smooth muscle layer The columnar cells of the epididymis have a non motile branching Stereocilia which is very important for absorption (90% of testicular fluid is reabsorbed in the ductuli efferentes and epidydimis) and secretion (substances for spermatozoa nutrition: carnitin, sialic acid, glycoproteins, glycerolhosphocholine which inhibits capacitation). Abundant ER and Golgi apparatus. The basal cells are stem cells The epithelium of the epididymis is androgen dependent (produced by Leydig cells and bound to ABP). The thickness of the smooth muscle layer increases from heat to tail. In the head the muscle layer makes spontaneous gentle peristaltic contractions while in the tail the contraction is stimulated by adrenergic innervation during sexual arousal. Androgens and ABP are present in the rete testis up to the epididymis to allow a progressive maturation of spermatozoa and motility EPIDIDYMITIS Inflammation of the epididymis. It can be due to STDs (like gonorrhea and chlamydia), coliform bacteria (like Escherichia Coli infecting the urinary system and expanding to the epidydimis). Epididymitis gives rise to scrotal pain and edema DUCTUS DEFERENS (vas deferens) It is lined by pseudo stratified columnar epithelium and basal cells + a lamina propria + a muscle layer (inner and outer longitudinal + intermediate circular). Its role is that of transporting, secreting and absorbing and it is 30-40cm long The muscle layer is very developed because this duct is responsible for ejaculation CONNECTION WITH THE URETHRA The distal dilated portions of the ductus deferens lead into the seminal vesicles and receive their short ducts forming the ejaculatory ducts. The ejaculatory ducts then come together in the prostatic urethra. opening prostaticplagienure of The two ejaculatory ducts open at the level of the vero montatum or seminal coliculus EJACULATORY DUCTS They pierce the parenchyma of the prostate gland and communicate with the region of the vero montatum. They’re lined by simple columnar epithelium surrounded by connective tissue and smooth muscle (tissue of the prostate gland surrounding it) SEMINAL VESICLES They’re a glandular diverticulum in origin but then they change very much so we refer to them as glands associated to the male genital tract. They’re associated to the ductus deferens and the mucosa presents branching folds (like in the fallopian tube). The epithelium is simple columnar or pseudo stratified and it is surrounded by a thick smooth muscle layer. During ejaculation the contraction of the smooth muscle layer forces secretion from the seminal vesicles into the urethra. The secretion of the seminal vesicles includes fructose, prostaglandins, vitamin C and seminal vesicles-specific proteins (coagulating proteins). These secretions allow the survival of spermatozoa in the vagina. The fluid is gellified and allows spermatozoa to remain in the vagina without falling out URETHRA PROSTATE GLAND It develops from the primitive urethra and surrounds its first portion 0 (the parenchyma of the prostate gland is right behind the urothelium). The smooth muscle at the level of the prostatic urethra is part of the prostate gland. The prostate gland is formed by a glandular and a stromal component surrounded by a capsule (made of fibroelastic tissue and smooth muscle fibers). The capsule gives rise to fibromuscular septa that divide the parenchyma. Anteriorly the fibromuscular stroma is denser. Glandular elements —> they’re classified according to their relation to the urethra —> mucosal, submucosal and main prostatic glands (branched tubuloacinar). Each of these glands opens independently in the urethra (many openings) The parenchyma of the prostate gland is best divided into 3 concentric zones that are relevant from the clinical point of view (can also be divided in lobules but it’s not important): shorterflounds Transition zone (5-10%) —> surrounds the proximal part of the urethra (mantellar zone) and it is clinically relevant because it’s the place where benign prostatic hyperplasia usually takes place Central zone (20%) —> it includes the ejaculatory ducts andelands longer the proximal part of the urethra (surrounds the transition zone) Peripheral zone (70%) —> it contains the main glands main and itglands is located posterolaterally to the central zone. It surrounds the distal prostatic urethra and in most case it’s the site of carcinoma The transition zone is most likely to cause dysuria if enlarged  The prostatic epithelium is made of tall columnar cells and basal cells + a lamina propria (fibroelastic) + smooth muscle cells in the septa The prostate gland secretion is an alkaline fluid (neutralises pH of the vagina), it is rich in citric acid and proteolytic enzymes (they liquefy semen that has been deposited in the vagina) and proteins such as prostate- specific acid phosphate and prostate specific antigen (marker for early detection of prostatic cancer). The aggregation of the secretion of the prostate gland and cell debris due to the renovation of the epithelium forms the corpora amilacea During puberty the prostate enters a period of accelerated growth and typically achieves its mature size. The prostate continues to change over time and in the fifth decade of life significant enlargement of the gland is common The prostate epithelium is androgen dependent —> one of the therapies against hyperplasia and tumours are drugs that reduce the androgen level. At the level of the prostate gland testosterone (produced by Leydig cells and arriving through the blood stream) is converted to dihydrotestosterone (DHT) by the cells of the stroma. DHT then acts in a paracrine fashion on epithelial cells favouring its proliferation (and the proliferation of stromal cells) BENING PROSTATIC HYPERPLASIA (BPH) Increase in the dimension of the prostate gland mostly due to an enlargement of mucosal glands, it leads to a partial strangulation of the urethra (causes dysuria). This leads to nocturia and sensory urgency and it affects 50% of man over 50yo and 80% of men over 80yo. Most common in the transitional zone of the prostate ADENOCARCINOMA OF THE PROSTATE GLAND It affects mostly the peripheral region. It metastasised to bones via blood vessels in 1/3 of men older than 75yo and its the second most common form of cancer in men MALE EXTERNAL GENITALIA The male external genitalia is made of the penis, which is divided into a root, body and glans (where there is the opening of the urethra) The penis is composed of 3 erectile columns (columns of erectile tissue) —> 2 corpora cavernosa and 1 corpus spongiosum. These structures have an attached portion and a free portion These three columns are kept together by a system of fasciae devices (in between their layers we can find lymphatics, nerves and vessels). There are also 2 suspensory ligaments that support the penis at the base (where the attached portion continues with the free portion) The fasciae are called Dartos fascia and Buck’s fascia At the root of the penis there are many different muscles that complete the abdominal pelvic cavity and maintain the mechanism of erection Inside each corpora cavernosa there is an artery called cavernous artery Both the corpus spongiosum and corpora cavernosa are covered by a layer of connective tissue (tunica albuginea) which contributes to the erectile mechanism. If the lacunae of the corpus spongiosum and cavernosa are filled with blood there is an enlargement of the organ. The tunica albuginea maintains the hardness of the penis to prevents it from enlarging too much lacunaein larger the cavernose corpora that spongious Structure of the CAVERNOUS BODIES Connective tissue —> the irregular vascular lacunae are lined by an endothelium and supported by elastic fibers, collagen fibers and smooth muscle fibers (important in the mechanism of controlling the amount of blood going into the lacunae) Tunica albuginea During erection blood flows in the vascular lacunae through helicine arteries (tortuous arteries). These arteries originate from the central cavernous artery. The veins are compressed (between the enlarged corpora cavernosa and tunica albuginea) to avoid blood from going back away and erection is maintained. When there is no erection the blood flow is impaired by the presence of myoepithelioid cushions in the walls of the lacunae, which prevent them from filling The parasympathetic nervous system is relevant for the mechanism of erection while the sympathetic contributes to the mechanism of relaxation. Smooth muscle cells and endothelial cells lining the lacunae also secrete factors that modulate the erection/relaxation of the penis. The spongy bone of the urethra is also made by erectile tissue but it is less developed than the cavernous. Here the tunica albuginea is thinner and more elastic and the caves are smaller with a thicker wall (more difficult to distend). The spongy body never reaches the same rigidity of the cavernous body and the urethra is never compressed allowing ejaculation