The Reproductive System
The Male Reproductive System • Basic Functions – Production of sperm – Transportation of sperm – Production of androgenous hormones
Components • Anatomical Components – The scrotum – skin and superficial fascia surrounding the testes • Positioning provides an environment 3 ˚ cooler than body temperature – Dartos muscle – layer of smooth muscle – Cremaster muscle – bands of skeletal muscle surrounding the testes – Testes & associated structures – Ducts – Accessory Glands – Penis • Neural component – ANS?
The Male Reproductive System Figure 24.1
The Scrotum – Containing the Testes and Spermatic Cord Figure 24.2
The Testes • Are enclosed in a serous sac – the tunica vaginalis vaginalis =“sheath like” • Tunica albuginea – fibrous capsule of the testes – Divides each testis into 250 ‐ 300 lobules • Lobules contain 1 ‐ 4 coiled seminiferous tubules
Schematic drawing of a cross-section through the vaginal process. 1 Testicle 2 Epididymis 3 Mesorchium 4 Visceral Lamina of Tunica vaginalis 5 Parietal Lamina of Tunica vaginalis 6 Vaginal cavity (Cavum vaginale) 7 Mesepididymis 8 Internal spermatic fascia This should look familiar... and remind you of the visceral and parietal peritoneum and formation of the mesenteries
The Seminiferous Tubules and Spermatogenesis • Seminiferous tubules – separated by areolar connective tissue • contains interstitial cells of Leydig (Leydig cells) that are responsible for producing testosterone • Epithelium consists of – Spermatogenic cells – sperm ‐ forming cells – Columnar sustentacular cells – support cells • Also called Sertoli cells or “nurse cells”
The Seminiferous Tubules and Spermatogenesis
Spermatogenesis • Spermatogenesis – sperm formation – Begins at puberty* – 400 million sperm per day – Spermatogenesis takes place in the seminiferous tubule. – Cells differentiate and are moved toward the lumen (by the sustentacular cells) • Stage 1 – spermatocytogenesis • Stage 2 – spermatidogenesis • Stage 3 – spermiogenesis * pre ‐ pubescent development of the type Ad spermatogonia which does not lead to sperm formation does occur.
Spermatogenesis Stage 1: Spermatocytogenesis (formation of haploid secondary spermatocytes) Type Ad (dark type A spermatogonium) 1. Spermatogonium divides • Outcome depends partially on age: – Mitotic division produces two Ad cells during prepubescency – After puberty division of Ad cells produce Ap (pale Type A spermatogonium) These (Type Ap spermatogonium) undergo 2. another mitotic division and become a Type B spermatogonium Type B spermatogonium undergo mitosis and 3. becomes a primary spermatocyte (still diploid or 2n at this stage) Primary spermatocytes undergo meiosis I and 4. becomes a secondary spermatocyte (which are haploid or n at this stage) • Small cytoplasmic bridges between secondary spermatocytes ensures equal rates or synchronous development
Spermatogenesis Stage 2: Spermatidogenesis (formation of spermatids from 2 spermatocytes) – Secondary spermatocytes quickly undergo meiosis II (still haploid) to produce early spermatids Stage 3: Spermiogenesis (formation of spermatozoa from spermatids) – Spermatids start developing flagella from the axoneme (cytoskeletal structure) – Midpiece becomes defined and mitochondria inhabit this area – Chromosomes become highly condensed and becomes inactive (no transcription). – Golgi apparatus becomes the acrosome – Excess organelles and cytoplasm ejected from spermatid and absorbed by the Figure 24.4b surrouding sustentacular (Sertoli) cells
Spermiation and Capacitation • Spermatozoa are released from the sustentacular (Sertoli) cells and enter the lumen (spermiation) along with testicular fluid produced by the sustentacular cells • Still immotile, peristalsis moves the spermatozoa to the epididymis where they gain motility and the capacity to fertilize (capacitation)
Sperm Structure
Supporting Cells • Sustentacular Cells (aka Sertoli cells): – surround spermatogenic cells – extend from basal lamina to the lumen – tight junctions between cells • form the blood ‐ testis barrier – “move’” the developing stages of the eventual spermatozoa from the basal lamina to the lumen – Consume the unneeded portions of spermatozoa during maturation – produce ABP (androgen binding protein) & AMH (anti ‐ müllerian hormone), transferrin, estradiol ‐ aromatase, GDNF (glial derived neurtrophic factor), inhibins & activins – produce testicular fluid • Myoid cells – surround seminiferous tubules & are contractile • Interstitial cells of Leydig (Leydig cells) – secrete testosterone
The Epididymis • Duct of the epididymis is 6m long (when uncoiled) • Dominated by pseudostratified columnar epithelium – Bears tufts of stereocilia – immotile, long microvilli • 20 ‐ day journey for sperm to move through – Gain the ability to swim and to fertilize an egg (capacitation) Figure 24.3a
The Ductus Deferens Tubular structure which conducts fluid and spermatozoa from the tail of the epididymis to the ejaculatory duct Transverse section through ductus deferens – showing the muscularis and the pseudostratified epithelium (with non-motile stereocilia) lining the lumen, and a thick muscularis layer. Figure 24.1
The Spermatic Cord spermatic cord ductus deferens ANS nerves pampiniform plexus testicular artery cremaster muscle external spermatic fascia internal spermatic fascia Figure 24.2
Spermatic Cord Histology ductus deferens Region of pampiniform plexus
The Urethra Figure 24.8a, b • the epithelium of the urethra starts as transitional cells as it exits the bladder. Most of the length of the urethra are stratified columnar cells, and finally stratified squamous cells near the external urethral orifice • Also contains small mucus ‐ secreting urethral glands, that help protect the epithelium from the corrosive urine
Accessory Glands • The seminal vesicles – Lie on the posterior surface of the urinary bladder – Secretes about 60% of the volume of semen • Fluid contains – Fructose to nourish sperm – Other substances » proteins, enzymes, fructose, mucus, vitamin C, flavins, phosphorylcholine and prostaglandins.
Accessory Glands ‐ Prostate • The prostate gland – Encircles the prostatic urethra – Consists of 20 ‐ 30 compound tubuloalveolar glands – Secretes about 25 ‐ 30% of seminal fluid – Contains: • nutrients such as zinc, amino acids, citric acid, vitamins and sugars that are thought to keep sperm healthy, but are not essential for reproduction, • enzymes such as acid phosphatase and prostatic specific antigen (PSA) which help to increase semen fluidity so sperm can swim more easily and dissolve the mucous cap of the cervix, • hormone ‐ like chemicals (prostaglandins) which have effects on the female genital tract, such as making the cervix 'pout' slightly so sperm can swim through more easily, and perhaps causing the female tract to contract
Accessory Glands ‐ Prostate Figure 24.9a, b
Accessory Glands • The bulbourethral glands – Pea ‐ sized glands inferior to the prostate gland – Produce a mucus • Mucus enters spongy urethra prior to ejaculation – Cleanses urethra and enhances pH for fertilizations Notice how it looks a little like the mucus production portion of the salivary glands…
Figure 24.8a, b The Penis
The Reproductive System PART 2 The female system
The Female Reproductive System • General Functions – Produces gametes (ova) – Prepares to support a developing embryo & fetus – Provide changes according to the menstrual cycle or pregnancy
The Female Reproductive System Figure 24.11a
The Ovaries • Small, almond ‐ shaped organs • Held in place by ligaments and mesenteries – Broad ligament – Suspensory ligament – Ovarian ligament • Ovarian arteries – arterial supply
Structure of the Ovary Figure 24.12a
The Ovarian Cycle Figure 24.13
The Ovarian Cycle • Ovulation – occurs about halfway through each ovarian cycle – Oocyte exits from one ovary • Enters the peritoneal cavity – Is swept into the uterine tube • Luteal Phase – occurs after ovulation – Remaining follicle becomes a corpus luteum • Secretes progesterone • Acts to prepare for implantation of an embryo
Oogenesis • Includes chromosomal reduction division of meiosis • Takes many years to complete Figure 24.15
The Uterine Tubes Figure 24.11a
The Uterus Figure 24.10
The Uterine Wall Endometrium – ciliated simple columnar – Thick underlying connective tissue (stroma) – Layers • Functionalis • Basalis – Highly vascular and glandular • Myometrium • Perimetrium
The Uterine Cycle • Series of cyclic phases of the endometrium • Phases coordinate with the ovarian cycle • Endometrial phases directed by FSH and LH • Phases of uterine cycle – Menstrual phase – days 1 ‐ 5 • Stratum functionalis is shed – Proliferative phase – days 6 ‐ 14 – Secretory phase – days 15 ‐ 28
The Menstrual Cycle • Structural and hormonal changes Figure 24.19a, b Figure 24.19c, d
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