Anatomy and physiology Flashcards
Describe the sexual differentiation of the internal and external genitalia during embryogenesis
In both sexes, the Mullerian and Wolffian ducts originate from the mesoderm. Gonadal development is dependent on the SRY gene on Chromosome Y.
In male embryos, Sertoli cells produce AMH (Anti-Mullerian hormone), which causes suppression of the Mullerian duct. The Wolffian duct develops into the external genitalia.
In female embryos, there is no AMH produced, so the Mullerian duct develops into the internal genitalia.
Describe the external female genitalia.
- Mons pubis
- Clitoris
- Labia majora and labia minora
- Urethral opening
- Vaginal opening
What are the natural barriers to pathogens in the vagina?
- Stratified squamous epithelium with tight junctions
- Glycogen rich epithelium (stimulated by E2), which provides substrate for Bacillus to produce lactic acid, maintaining the pH of the vagina at ~4.5
Describe the organs/tissues bordering the vagina (Ant-post + lateral).
Anteriorly: base of the bladder + 2/3s of urethra (fused)
Posteriorly:
- Upper 1/3: Pouch of Douglas
- Middle 1/3: Middle rectum
- Lower 1/3: Perineal body
Laterally: Levator ani muscles, ureters, pelvic fascia.
Describe the support of the vagina. Why is this important?
Main support comes from the levator ani muscles (pelvic floor/pelvic diaphragm). These are: iliococcygeus, pubococcygeus, and puborectalis.
Also 3 levels of ligaments and fascia:
-Level 1: Apical support. Uterosacral ligaments attach cervix to sacrum, cardinal ligaments attach lateral fornices to pelvic wall.
-Level 2: Midvaginal support. Pelvic fascia.
-Level 3: Perineal body.
**Defects in any of these structures will predispose to prolapse. eg. Level 1- uterine/vaginal vault prolapse, Level 2- rectocele/cystocele, Level 3- ant/post wall prolapse
Describe the gross anatomy of the uterus
- Body
- Fundus (top)
- Cornu (where tubes enter)
- Isthmus (lower part into cervix)
- Cervix
Through which ligament do the Fallopian tubes run through?
Broad ligament
Describe the attachments of the ovaries
- Attached to pelvic wall by suspensory ligament of the ovaries (receive blood supply + nerves through this)
- Attached to uterus by ovarian ligament and mesovarium of the broad ligament
Describe the blood supply of the pelvic organs. What is significant about the uterine artery?
- Ovary receives blood supply from the ovarian artery (branch of the aorta)
- Anterior branch of the internal iliac forms the uterine A, vaginal A, vesical A, middle rectal A, pudendal -> vulval A
The uterine A supplies uterus, ureters, cervix, upper vag. It runs in the broad ligament with the ureter, and thus both are at risk of damage during hysterectomy.
Describe the lymphatic drainage of the pelvic organs. Why is this relevant and important to know?
Overall: inguinal -> ex iliac -> common iliac -> para-aortic
External genitalia-> femoral + superficial inguinal nodes
Cervix-> stepwise or straight to para-aortic
Ovaries -> straight to para-aortic
- Infections of the external genitalia eg. HSV can cause enlarged inguinal nodes
- Ovarian cancer can disseminate quickly
Which is the main nerve supplying the external genitalia?
Pudendal nerve (S2-S4). Supplies sensation to vulva, anus, and levator ani
What are some possible Mullerian tract abnormalities? How common are they?
- Affect up to 6% of the population
- Obstruction: eg. Imperforate hymen
- Duplication: eg. partial, total, uterine septum
- Agenesis: Rokitansky syndrome (no uterus, cervix)
Describe the physiology of the normal menstrual cycle
Hypothalamus releases pulsatile GnRH –> stimulates pituitary FSH and LH production
-LH stimulates theca cells to produce androgens
-FSH stimulates follicles to grow, and stimulates aromatase to convert androgens to oestrogen
As follicles grow, they produce more oestrogen, which downregulates FSH. This leads to a relative lack of FSH, causing only one dominant follicle (that has become independent of FSH) to keep growing. The other follicles undergo atresia. The dominant (Graffian) follicle develops fully and produces large amounts of oestrogen. High oestrogen triggers the pituitary to go from negative feedback to positive –> big LH surge triggering ovulation.
After ovulation, the follicle becomes the corpus luteum, and produces progesterone and oestrogen. This stimulates the endometrium to undergo hyperplasia (oestrogen) and secrete glycoproteins (progesterone) to prepare for implantation. When implantation does not occur, the corpus luteum degrades and the lack of hormonal support causes the endometrium to shed in the process of menstruation.
Describe the role of prostaglandins during the menstrual cycle and clinical relevance.
PGs are involved in the process of ovulation and in menstruation. Supposedly, blocking PGs may inhibit ovulation. Blocking PGs (with NSAIDs) during menstruation also decreases blood loss and pain.
Describe the process of puberty in females
GnRH pulsatility begins around 8-9 years, causing LH and FSH release –> oestrogen increase.
The rising oestrogen stimulates the development of secondary sex characteristics, starting with breast development, then pubic and axillary hair, and finally menstruation.
Define precocious puberty and name some causes.
Onset of puberty before the age of 8 years in F.
Causes can be divided into central (increase in LH and FSH) or peripheral (independent oestrogen production).
Central PP is usually idiopathic in girls, though other causes include any CNS pathology such as pituitary tumours, infection, injury.
Peripheral precocious puberty is usually caused by congenital adrenal hyperplasia, or by sex steroid producing tumours in the adrenals or gonads.
Define delayed puberty and name some causes.
Delayed puberty is lack of development of secondary sex characteristics by the age of 14 years. This is not the same thing as primary amenorrhoea.
Causes can be divided into hypergonadotrophic (high LH + FSH) and hypogonadotrophic (low LH + FSH).
Hypergonadotrophic causes include Turner syndrome, Fragile X, iatrogenic causes eg. pelvic radiotherapy, or immunological.
Hypogonadotrophic causes include Kallmann syndrome, CNS tumours, FHA, or chronic illness.
Describe the features of Turners syndrome. Why is there often delayed puberty?
Turners syndrome is a genetic condition caused by the absence of one X chromosome (in all cells or some cells eg. mosaicism), with the genotype 45XO.
Affected individuals may have short stature, webbed neck, wide carrying angle, barrel chest with widely-spaced nipples, etc. There is also an association with several medical complications, including aortic coarctation, deafness and renal anomalies.
In Turner’s, the ovaries do not fully develop and are termed ‘streak gonads’. As a result, LH and FSH production during the onset of puberty fails to stimulate oestrogen production, and secondary sex characteristics do not develop and menarche does not occur.
