What are primordial germ cells?
A cell that will eventually give rise to mature gametes after a process of first mitosis then meiosis.
Where do primordial germ cells originate and where must they migrate to?
Primordial germ cells are made from the epiblast layer and must move from the yolk sac to sit in the dorsal mesentery of the high lumber/lower thoracic region. (Or the region where the gonads develop)
From what tissue does the gonad arise from?
What gene determines testes development and where is it found?
SRY gene - Sex determining Region Y Found on the short arm of the Y chromosome
What changes occur in the primitive gonad if testes are to develop?
Medullary cords develop (become patent in puberty and form seminiferous tubules) No cortical cords Thick tunica albuginea
What changes occur in the primitive gonad if ovaries are to develop?
Medullary cords degenerate Cortical cords develop No tunica albuginea
Describe the duct system in an embryo when sex has not yet been determined:
There exists mesonephric ducts which run from the embryonic kidney to the urogenital sinus. And paramesonephric ducts (Mullein ducts) which run laterally to the urogenital ridge and terminate at the urogenital sinus.
What changes happen to the duct system in males?
Lydia cells produce testosterone which causes the mesonephric ducts to remain. Sertoli cells which line the seminiferous tubules produce Mullerian Inhibiting Hormone which causes the Mullerian ducts to regress.
What changes happen to the duct system in females?
In the absence of testosterone the mesonephric duct regresses. And in the absence of Mullerian Inhibiting Hormone the Mullerian ducts remain.
What are the adult derivatives of the mesonephric ducts?
Epididymis Vas Deferens Seminal Vesicle
What are the adult derivatives of the Mullerian ducts?
They fuse in the midline and form: Fallopian tubes Uterus Cervix Top 1/3 of Vagina The paramesonephric duct joins the urogenital sinus which forms the lower 2/3rd of the vagina.
What three structures are common starting points for the formation of male and female external genitalia.
Genital tubercle Genital Swellings Genital Folds
How is the male external genitalia formed?
Under the influence of dihydrotestosterone (from testosterone) there is an elongation of the genital tubercle to form the shaft of the penis. The genital folds fuse to form the spongy urethra. The genital swellings become the scrotal swellings.
How is the female external genitalia formed?
No fusion of the genital folds and the urethra opens into the vestibule. The genital swellings become the labia majora, the genital folds the labia minora and the genital tubercle becomes the clitoris.
Describe the original position of the testes?
Retroperitoneal organs that are attached by their caudal pole to the labioscrotal swellings.
Describe the layers of the testes from the outside in:
Tunica albuginea, external spermatic fascia, cremasteric muscle and fascia, internal spermatic fascia, tunica vaginalis, testis.
Describe the descent of the testis:
The testis moves caudally firstly due to elongation of the trunk of the embryo. Then the shortening of the gubernaculum draws the testis through the inguinal canal and into the scrotum.
What are the contents of the spermatic cord?
Blood supply: Testicular artery, Cremasteric artery, Pampiniform plexus, Three Others: Vas deferens, lymphatics, tunica vaginalis, Nerves: Nerve to cremaster muscle, (genital branch of genitofemoral) Sympathetics Layers - Internal spermatic fascia, cremasteric muscle, external spermatic fascia
Describe the descent of the ovary:
The ovaries descend mainly due to the expansion of the trunk of the embryo.
What does the gubernaculum in females become?
Ovarian ligament - connects ovary to uterus Round ligament - connects uterus to labia (only structure in inguinal canal in females)
What are common abnormalities of male genital development?
Hypospadias - genital folds fail to fuse properly so there may be openings of urethra of the urethra on the underside of the penis. Cryptorchidism - undescended testicle - increased risk of cancer.
Describe the process of spermatogenesis:
1. Spermatogonia (primordial germ cell) are found at the basal surface of a seminiferous tubule. This undergoes mitosis - one cell replaces the parent cells the authored becomes a primary spermatocyte. 2. The primary spermatocyte undergoes meiosis I to form a secondary spermatocyte. 3. The secondary spermatocyte undergoes meiosis II to form a spermatid. 4. As these divisions occur the cytoplasms of all cells are still connected and they are gradually moving towards the lumen of the seminiferous tubule. 5. As spermatids pass through the tubule, rete testis, ducti efferentes and epididymis they are further remodelled to spermatazoa.
What is a spermatogenic cycle?
The duration between consecutive divisions of spermatogonia.
What is a spermatogenic wave?
Different parts of the seminiferous tubule undergo spermatic cycles at different times therefore ensuring there is constant spermatozoa production and therefore constant fertility.
Describe the production and structure of a primordial follicle: (1)
A primordial follicle is formed from a germ cell. During gestation 7 million germ cells are formed but only 2 million remain. A germ cell begins meiosis but this is halted at an early stage. This forms a primary oocyte. A primary oocyte is surrounded by a single layer of granulosa cells so form a primordial follicle.
What changes to primordial follicles happen during puberty? (2)
Independent of hormones a zona pellucida develops and the granulosa layer develops further. A theca also develops. This is now called a pre-antral follicle.
How is a pre-ovulatory follicle formed? (3)
From a pre-antral follicle. Fluid is formed between granulosa cells and this fluid collects to form an antrum, Under the influence of FSH and LH the follicle grows to 20mm. The theca secretes increasing amounts of oestrogen.
What events occur just before ovulation to the pre-ovulatory follicle? (4)
Meiosis restarts so that the first division is completed, generating the first polar body. An LH surge triggers rupture of the follicle to release the ovum causing ovulation.
What occurs to the ovum after ovulation? (5)
A corpus luteum is formed. This involves reorganisation of the follicle, growth under the influence of LH, secretion of oestrogen and progesterone. Corpus luteum dies after 14 days. (needs to grow large enough so can signal to mother its presence)
Label the microscopic structure of the testis:
ST - Seminiferous tubules C - capsule (tunica albuginea) R - Rete testis DE - ductus efferentes H/B/T - head, body and tail of epididymis V - Vas deferens
Describe the structure of the seminiferous tubules:
Seminiferous tubueles are made from sertoli cells which can be seen at the base of each tubule. The other cells seen in the tubule are the developing spermatozoa.
In between the tubules in the interstium are Leydig cells which produce testosterone.
What is need to prep the sertoli cells for spermatozoa development?
Describe the epithelium present in the rete testis and the fucntion of the rete testis:
Cuboidal and ciliated columnar cells.
Cuboidal cells serve an absorptive function to absorb fluid secreted by sertolid cells.
The ciliated columanr cells move sperm through the tubules.
The outermost part of the wall of the rete testis contains contractile elements.
What are the efferent ductules?
Channels that connect the rete testis and the epididymis.
The channels are characterised by scalloped epithelium.
Describe the epithelium found in the epididymis and its function?
Pseudo-stratified columunar epithelium with lots of stereocilia
4-6m highly coiled tube.
Outside layer of smooth muscle with increases in amount as you approach the vas deferens.
This is where sperm maturation is completed. E.g. the sperm become motile.
Describe the structure of the vas deferens and the function?
Has three layers:
Epithelium - pseudostratified columnar with few sterocilia
Muscular layer - three layer: inner and outer layer and longitudinal and the middle layer is circular.
Muscular layer contracts powerfully during ejaculation.
Describe the structure and function of the seminal vesicles?
Paired outgrowths of the ductus deferens.
Coiled tubulosaccular glands.
Have highly folded mucosa with a lamina propria and muscular coat.
Lined by pseudeostratified columnar epithelium.
What does the seminal vesicle secrete and what % of the ejaculate volume does it contribute?
Seminal vesicle secretes fructose, proteins and prostaglandins.
Not a storage site
Makes up 85% of ejaculate volume.
Describe the structure of the prostate gland:
Walnut shaped gland which surrounds the urthra at the base of the bladder.
Has a fibromuscular capsule from which septae invelope the prostate and divide it into lobules.
Secretory elements sit in the fibromuscular connective tissue stroma.
Contains tubuloalveolar glands with are aranged in three groups around the urethra: mucosal, submucosal and main glands.
Prostate gland can also be divided into two separate zones: peripheral and transitional.
What does the the prostate gland secrete?
Prostate Specific antigen
Which areas of the prostate gland does benign prostatic hyperplasia occur?
Where in the prostate gland does neoplasia usually affect?
Where are the bulbourethral glands located and what is thier structure?
Two pea shaped glands that lie beneath the prostate gland and the beginning of the internal portion of the penis.
The glands are made up of several lobules and have a fibrous covering.
Acini are made from simple columnar epithelium. These acini join the urethra.
What is the function of the bulbourethral gland?
Produce a mucous like fluid that clears the urethra of any residual fluid and neutralises any acid prior to ejaculate.