Reproductive System PDF

**Testis** - Each testis is an oval structure about 5cm long and 3cm in diameter. - Located in the scrotum. - Covered by: **tunica albuginea** - a fibrous capsule that covers each testis. - The **tunica albuginea** gives rise to **septa** (partitions) that divide the testis into...

**Testis** - Each testis is an oval structure about 5cm long and 3cm in diameter. - Located in the scrotum. - Covered by: **tunica albuginea** - a fibrous capsule that covers each testis. - The **tunica albuginea** gives rise to **septa** (partitions) that divide the testis into lobules (about 250 lobules). - Each lobule contains 3 or 4 highly coiled **seminiferous tubules.** - These converge to become **rete testis** which transport sperm to the **epididymis.** **SEMINIFEROUS TUBULES** Seminiferous tubules cut in various planes of section. The seminiferous tubules are highly convoluted and are lined by: **Germ cells** in various stages of spermatogenesis and spermiogenesis, which are collectively referred to as the spermatogenic series. Non--germ cells, called **Sertoli cells,** which support and nourish the developing spermatozoa are also found within the seminiferous tubules. In the interstitial spaces between the tubules, endocrine cells called **Leydig cells** (which produces male sex hormone testosterone), are found either singly or in groups in the supporting tissue **Spermatogenesis** - Spermatogenesis is a tightly regulated developmental process that involves sequential mitotic and meiotic cellular divisions, by which developing germ cells differentiate from spermatogonia to spermatocytes, spermatids and finally to spermatozoa. - Spermatogenesis occurs within the seminiferous tubules and is orchestrated by Sertoli cells. To complete spermatogenesis, differentiating germ cells must migrate through the seminiferous epithelium while maintaining transiently attached to Sertoli cells - Usually 4 to 5 concentric layers of morphologically distinct spermatogenic cells at various stages of development occurs within the **seminiferous epithelium.** - As the cells proliferate and differentiate, they gradually move from the **basement membrane (BM)** of the seminiferous tubule towards the **lumen** of the tubules. **Interstitial cells of Leydig** - Leydig cells are the principal cell type found in the interstitial tissue between the seminiferous tubules. - Produces testosterone in the presence of lutenizing hormone (LH). **Structure of Leydig cells:** - Polyhedral in shape, - Has a large prominent ovoid nucleus, containing 1-3 prominent nucleoli & large amounts of dark-staining peripheral heterochromatin. - Eosinophilic cytoplasm, - Several lipid-filled vesicles. **Rete Testis** - The seminiferous tubules converge upon the mediastinum testis, which consists of a plexiform arrangement of channels, the **rete testis RT**, surrounded by highly vascular collagenous supporting tissue containing myoid cells. Rete testis is lined by a single layer of low cuboidal epithelial cells with surface microvilli and a single cilium **Ductulus Efferens** - Rete testis drains into the head of the epididymis via some 15 to 20 convoluted ducts, **the ductuli efferentes (DE)**. - The ductuli are lined by a single layer of epithelial cells, some of which are (i) tall columnar and ciliated (ii) and others which are short and non-ciliated. - Ciliary action in the ductuli propels the still non-motile spermatozoa towards the epididymis. - The non-ciliated cells reabsorb some of the fluid produced by the testis. A thin band of circularly arranged **smooth muscle (SM)** surrounds each ductulus and aids propulsion of the spermatozoa towards the epididymis **Epididymis** - Receives ductuli efferentes. - Divided into **head, body and tail**. - **Pseudostratified epithelium** consisting of **principal** and **basal cells**. - **Principal cells** → primary columnar cell of the epididymis and their function is protein secretion & endocytosis. - **Basal cells** → located on the basement membrane throughout the epididymis → regulates the microenvironment where the functionally incompetent sperm cells produced by the testis are matured and stored. - From the proximal to the distal end of the epididymis, the muscular wall increases from a single circular layer smooth muscle, to three layers organised in the same manner as in the ductus deferens. - **Smooth muscle** in head and tail contract spontaneously; smooth muscle in tail requires sympathetic innervation for contraction. - The major function of the epididymis is accumulation, storage and maturation of spermatozoa in the epididymis, the spermatozoa develop motility. **Vas (ductus) deferens** - The vas deferens conducts spermatozoa from the epididymis to the seminal vesicles. - It is a thick-walled muscular tube consisting of inner and outer longitudinal layers and a thick intermediate circular layer. - Like the distal part of the epididymis, the vas deferens is innervated by the sympathetic nervous system, producing strong peristaltic contractions to expel its contents into the urethra during ejaculation. **Similar to that of the epididymis:** - The vas deferens is lined by a pseudostratified columnar epithelium. - Smooth muscle arranged in 3 layers. **Seminal Vesicles** - Seminal vesicles secrete 50--70% of the total volume of seminal fluid. - The epithelial lining is a pseudostratified tall columnar type and consists of secretory cells with lipid droplets in the cytoplasm, giving it a foamy appearance. - The lumen of each seminal vesicle is highly irregular. - The seminal vesicles produce a yellowish viscid alkaline fluid containing a wide range of substances, including fructose, fibrinogen, vitamin C and prostaglandins. - The prominent muscular wall is arranged into inner circular and outer longitudinal layers and is supplied by the sympathetic nervous system; during ejaculation, muscle contraction forces secretions from the seminal vesicles into the urethra via the ampullae **Prostate gland** - The secretory product of the prostate, makes up about 30--50% the seminal fluid volume. - The prostate gland is composed of **glands** and **stroma**. - The **supporting stroma SS** is a mixture of collagenous fibrous tissue and smooth muscle fibres. The **glands G** show a convoluted pattern with the epithelium thrown up into folds - The epithelium of the prostate gland contains tall columnar secretory cells with prominent round basal nuclei and pale-staining cytoplasm. There is also a scanty population of small, flat, **basal cells B** at the base of the gland in contact with the basement membrane **Penis** - The erectile tissues of the penis is arranged into three columns. \- Two dorsal columns are called the **corpora cavernosa (CC)** and \- a single ventral column is called the **corpus spongiosum (CS).** - The **penile** **urethra (U)** runs through the centre of the corpus spongiosum. - The corpus spongiosum expands at its distal end to form the glans penis. - The erectile corpora (columns) are enclosed within and separated by a **fibrocollagenous capsule (F).** - A sheath of **skin (S)** encloses the erectile centre of the penis. - The erectile tissues consist of lacunae, spaces that fill with blood, surrounded by collagenous connective tissue (the tunica albuginea). **Penile Urethra** - The penile urethra is lined by stratified or pseudostratified columnar epithelium. - There may also occur some small areas containing stratified squamous epithelium in human adult males. - The external opening called the urethral meatus is lined by stratified squamous epithelium which is continuous with the glans epithelium. - The urethra is lubricated by mucous secretions from the **para-urethral glands P** and the bulbo -urethral glands of Cowper. **Follicle development - Primordial follicles** Undeveloped follicles known as **primordial follicles** are inactive structures, awaiting stimulation from FSH before reentering their developmental pathway. Primordial follicles are composed of a primary oocyte surrounded by a single layer of flattened follicular cells. The primary oocyte has a large nucleus with dispersed finely granular chromatin, a prominent nucleolus and little cytoplasm. **Follicle development - Primary follicles** Once stimulated, by FSH, 30-50 primordial follicles re-enter development, and become **primary follicles** The primary follicle oocyte (O) has greatly enlarged and the follicular cells (F) have multiplied by mitosis and become cuboidal in shape. They are now known as **granulosa cells.** A **zona pellucida (ZP)** layer develops between the oocyte and the granular cells -- this is a thick homogeneous layer containing glycoprotein and acid proteoglycans. **Follicle development -- Secondary follicle** The **zona granulosa (ZG)** continues to proliferate. In addition, small fluid-filled spaces begin to develop between the granulosa cells, and these fuse to form the **follicular antrum (FA).** This is now referred to as the **secondary follicle.** At this stage, **the oocyte (O)** has nearly reached full size and becomes situated eccentrically within a thickened area of the zona granulosa called the **cumulus oophorus (CO).** The **zona pellucida (ZP)** can also be seen in this image. Stroma around the developing follicle differentiates into **thecal cells.** At the periphery of the follicle, the theca folliculi has developed two layers: \(i) the **theca interna TI,** comprising several layers of rounded cells, \(ii) and the less well-defined **theca externa TE,** consisting of spindle-shaped cells that merge with the surrounding stroma **Follicle development -- Graafian follicle** - On approaching maturity, further growth of the oocyte ceases. This stage in follicular development occurs just before ovulation. - At this stage, the oocyte (O) is known as the **secondary oocyte.** - The **follicular antrum (FA)** is markedly enlarged. - **Zona granulosa (ZG)** forms a layer of even thickness around the periphery of the follicle. - At this stage, the maturing follicle has reached between 1.5 and 2.5 cm in diameter and appears as a bulge beneath the ovarian surface. - **Cumulus oophorus** diminishes, and the oocyte O is instead surrounded by the **corona radiata CR** (i.e a thickened cell layer), which remains attached to the zona granulosa (ZG) by thin bridges of cells. At ovulation, the mature follicle ruptures, thus expelling the ovum (comprising secondary oocyte, zona pellucida and corona radiata), into the peritoneal cavity close to the entrance of the Fallopian tube **Corpus Luteum** - Following ovulation, the ruptured follicle collapses and fills with a **blood clot (B)** to form the corpus luteum of menstruation. - The blood clot B is surrounded by a wide zone of **granulosa lutein cells G**, penetrated by **septa S** containing large blood vessels. - A thin zone of **theca lutein cells T** can be seen peripherally. - Externally, the corpus luteum is bounded by condensed stromal tissue, that represents the theca externa of the Graafian follicle. The corpus luteum serves to provide hormones that are necessary for implantation and early development of a fertilized ovum **Corpus Albicans** - If fertilization does not occur, the corpus luteum (C) degenerates & regresses (over approx. 14 days) to become the **corpus albicans** → i.e inactive fibrous tissue mass. - Secretory cells of the degenerated corpus luteum undergo autolysis and are therefore phagocytosed by **macrophages M.** **[Female Genital Tract]** - **The female genital tract consists of the:** - fallopian tubes - uterus - vagina - All above consists of the same basic structure: - a wall of smooth muscle, - an inner mucosal lining and, an outer layer of loose supporting tissue **Fallopian Tube (Uterine Tube/Oviducts)** - The Fallopian tubes serve to carry the released ovum from the ovary to the uterine cavity. - It is also the site of fertilization. - Structurally, the Fallopian tube appears as an elongated funnel that is divided anatomically into four distinct regions as follows: - **Fimbria** (finger-like projections) - **Infundibulum** - **Ampulla** - **Isthmus** **Fallopian Tube (Ampulla)** - The mucosal lining of the Fallopian tube appears as branching longitudinal folds, a feature that is most prominent in the **ampulla** (a), i.e. the usual site of fertilisation. - Micrograph (b) depicts a mucosal fold of the ampulla. These contain a branching core of vascular supporting tissue **ST** which comprises a single layer of tall columnar epithelial cells **E.** - Micrograph (c) depicts the end of a mucosal fold at high magnification. The columnar epithelial cells are of three types: (i) ciliated, (ii) non-ciliated secretory and (iii) intercalated cells. **Uterus (Proliferative)** In the **proliferative stage** of the uterine cycle, under control of rising estrogen from the developing follicles, the stratum basalis is regrowing the stratum functionalis, which was shed during the previous menstrual flow. The diagnostic feature of this stage are the long and straight uterine glands which are not yet functional. **Uterus (Secretory)** In the **secretory stage** of the uterine cycle, under the control of estrogen and progesterone from the corpus luteum, the uterine glands of the stratum functionalis begin to be functional, producing glycogen. The diagnostic feature of this stage are the curvy, serrated-looking glands **Uterus (Menstrual)** In the **menstrual stage** of the uterine cycle, under the control of lack of estrogen and progesterone from the dead corpus luteum, the stratum functionalis dies and loses its anatomical integrity, breaking lose and shedding from the stratum basalis **Vagina** **The vaginal wall consists of:** - a mucosal layer lined by stratified squamous epithelium **(E),** - a layer of smooth muscle **(SM)** -- SM bundles are arranged as inner circular & outer longitudinal layers. - an outer adventitial layer **(A)** - A fibrous lamina propria **(LP)** layer that contains several elastin fibres, has a rich plexus of small veins and is devoid of glands. - The vagina is lubricated by cervical mucus, a fluid transudate from the rich vascular network of the lamina propria, along with mucus secreted by the glands of the labia minora.