Obstetrics and Gynaecology Flashcards
Outline the Hypothalamic-Pituitary-Gonadal Axis (HPGA)
Hypothalamus releases gonadotrophin-releasing hormone (GnRH)
GnRH stimulates anterior pituitary to produce LH and FSH
LH and FSH stimulate development of follicles in ovaries
Theca granulosa cells around follicles secrete oestrogen
Oestrogen has negative feedback effect on hypothalamus and anterior pituitary to suppress release of GnRH, LH and FSH
What is produced by the anterior pituitary?
LH and FSH
Outline oestrogen
Steroid sex hormone produced by ovaries in response to LH and FSH
17-beta oestradiol- Acts on tissues with oestrogen receptors to promote female secondary sexual characteristics
What does oestrogen stimulate?
Breast tissue development
Growth and development of female sex organs (vulva, vagina and uterus) at puberty
Blood vessel development in uterus
Development of endometrium
Outline progesterone
Steroid sex hormone produced by corpus luteum after ovulation
In pregnancy- Progesterone produced mainly by placenta from 10wks
Acts on tissues previously stimulated by oestrogen
Outline role of progesterone
Thicken and maintain endometrium
Thicken cervical mucus
Increase body temperature
Outline hormonal changes during pregnancy
GH increases initially- Growth spurt
Hypothalamus starts to secrete GnRH- Initially during sleep
GnRH stimulates release of FSH and LH from pituitary gland
FSH and LH stimulate ovaries to produce oestrogen and progesterone
FSH levels plateau a yr before menarche
LH levels continue to rise and spike just before induce menarche
What age do boys and girls start puberty?
Girls- 8-14y
Boys- 9-15y
Overweight children tend to enter puberty earlier- Aromatase is enzyme in adipose tissue- Important in creation of oestrogen
Before puberty girls have little GnRH/LH/FSH/oestrogen/progesterone
List causes of delayed puberty in girls
Low birth weight
Chronic disease
Eating disorders
Athletes
Outline Tanner staging
Stage I- <10y- No pubic hair- No breast development
Stage II- 10-11y- Light and thin PH- Breast buds from behind areola
Stage III- 11-13y- Course and curly PH- Breast begins to elevate beyond areola
Stage IV- 13-14y- Adult-like PH but not reaching thigh- Areolar mound forms and projects from surrounding breast
Stage V- >14y- PH extending to medial thigh- Areolar mounds reduce and adult breasts form
Outline the follicular phase of menstruation
Start of menstruation to moment of ovulation (0-14d of cycle)
Outline luteal phase of menstrual cycle
Moment of ovulation to start of menstruation (14-28d)
After ovulation, follicle that released ovum collapses and becomes corpus luteum
Corpus luteum secretes progesterone and maintains endometrial lining- Becomes thick and no longer penetrable- Also secretes small amount of oestrogen
In fertilisation- Syncytiotrophoblast of embryo secretes hCG- Maintains corpus luteum
No fertilisation- No hCG- Corpus luteum degenerates and stops producing oestrogen and progesterone- Fall in oestrogen and progesterone causes endometrium to breakdown and menstruation
Stromal cells of endometrium release prostaglandins- Encourage endometrium to breakdown and uterus to contract
Negative feedback from oestrogen and progesterone on hypothalamus and pituitary gland ceases- Allows level of LH and FSH to begin to rise and cycle restart
Outline formation of follicles
Oocytes surrounded by granulosa cells, forming follicles
1. Primordial follicles
2. Primary follicles
3. Secondary follicles- Requires FSH stimulation to develop into antral follicle
4. Antral follicles (Graafian follicles)
As follicles grow- Granulosa cells secrete increasing amounts of oestradiol- Negative feedback effect on pituitary gland, reducing quantity of LH and FSH
Rising oestrogen causes cervical mucus to become more permeable- Allows sperm to penetrate cervix around time of ovulation
One follicle develops more than other and becomes dominant
LH spikes just before ovulation, causing dominant follicle to release ovum from ovary
What is menstruation?
Superficial and middle layers of endometrium separating from basal layer
Tissue broken down inside uterus, and released via cervix and vagina
Release of fluid containing blood from vagina lasts 1-8d
Outline development of primary follicle
Primordial follicles grow and become primary follicles
Primary follicles have 3 layers:
1. Primary oocyte in centre
2. Zona pellucida
3. Cuboidal shaped granulosa cells
Granulosa cells secrete material that become zona pellucida- Secrete oestrogen
Follicles grow larger and develop surrounding layer called theca folliculi
- Inner layer- Theca interna- Secretes androgen hormones
- Outer layer- Theca externa- Made of connective tissue containing smooth muscle and collagen
Outline development of secondary follicle
Primary follicle grows larger and develop small fluid-filled gaps between granulosa cells
Develop receptors for FSH
Further development after secondary follicle stage requires stimulation from FSH
At start of menstrual cycle, FSH stimulates further development of secondary follicles
Outline development of antral follicles
Secondary follicle develops single large fluid-filled area within granulosa cells- Antrum- Antral follicle stage
Antrum fills with increasing fluid- Follicle expands rapidly
Corona radiata- Made of granulosa cells- Surrounds zona pellucida and oocyte
One of the follicles becomes dominant follicle and matures, bulging through wall of the ovary- Others degrade
Outline ovulation
Surge of LH from pituitary
Causes smooth muscle of theca externa to squeeze and follicle bursts
Follicular cells release digestive enzymes that puncture hole in wall of ovary- Ovum passes and escapes
Oocyte released into surrounding area and swept up by fimbriae of fallopian tubes
Outline corpus luteum
Leftover parts of follicle collapse and turn yellow
Collapsed follicle becomes corpus luteum
Cells of granulosa and theca interna become luteal cells
Luteal cells secrete steroid hormones- Progesterone
Corpus luteum persists in response to hCG from a fertilised blastocyst when pregnant
If fertilisation doesn’t occur- Corpus luteum degenerates after 10-14d
Outline fertilisation
Just before time of ovulation- Primary oocyte undergoes meiosis- Splits 46 chromosomes in oocyte in 2
Secondary oocyte has 23 chromosomes
Oocyte surrounded by zona pellucida surrounded by corona radiata (granulosa cells)
Sperm enters fallopian tube and attempts to penetrate corona radiata and zona pellucida to fertilise egg
Outline development of blastocyst
Combination of chromosomes from egg and sperm- Zygote
Cell divides rapidly to create mass of cells- Morula- Mass of cells travels along fallopian tube toward uterus
Fluid-filled cavity gathers within group of cells- Blastocyst
Blastocyst contains embryoblast and blastocele surrounded by trophoblast
Gradually loses corona radiata and zona pellucida
Enters uterus
Outline implantation of blastocyst
Arrives at uterus 8-10d after ovulation and reaches endometrium
Cells of trophoblast undergo adhesion to stroma of endometrium
Outer layer of trophoblast= Syncytiotrophoblast- Produces hCG
Cells of stroma convert into decidua- Provides nutrients to trophoblast
hCG maintains corpus luteum and produces progesterone and oestrogen
Outline development of embryo
Week after fertilisation- Implanted blastocyst differentiates
Cells of embryoblast splits in 2- Yolk sac and amniotic cavity
Cells of embryonic disc develop into fetal pole, then fetus
Chorion surrounds complex- 2 layers- Cytotrophoblast and syncytiotrophoblast
Chorionic cavity forms around yolk sac, embryonic disc and amniotic sac
Suspended from chorion by connecting stalk- Eventually becomes umbilical cord
What occurs in the fetus at 5wks?
Embryonic disc develops into fetal pole
Contains 3 layers- Ectoderm, mesoderm and endoderm