Endocrinology of Pregnancy Flashcards
Where is tubular fluid reabsorbed and what controls this process?
Tubular fluid reabsorbed in the efferent ducts (vasa efferentia)
- This is induced by oestrogen
- This acts to concentrate the sperm prior to entering the epididymis
NOTE:
The tubular fluid produced by the sertoli cells in the seminiferous tubules functions to:
- Provide nutrition for the developing sperm
- Provides a means of transport to carry the develpoing sperm to the epididymis
What takes place in the epididymis and what controls this process?
In the epididymis, nutrients (e.g. fructose) and glycoproteins are secreted into the epididymal fluid
- This is stimulated by androgens
NOTE: Epididymis is where the sperm mature and attain their motility
What is ejaculation?
Ejection of semen from the body
What does semen consist of?
- Spermatozoa (15-120 million/ml)
- Seminal fluid (2-5ml)
- Leucocytes
- Potentially viruses e.g. hepatitis B, HIV (if the man is infected)
What are the proportions of sperm that reach different parts of the female reporoductive tract after ejaculation?
- 1/100 of spermatozoa in ejaculate enter the cervix
- 1/10,000 cervix to ovum
- Overall 1/million reach ovum
Which structures contribute to the production of the seminal fluid?
Small contibution from:
- Testis (seminiferous tubules, rete testis - essentially the part before the epididymis)
- Epididymis
Mainly from accessory sex glands:
- Seminal vesicles
- Prostate gland
- Bulbourethral glands
What is capacitation of sperm?
This is when sperm achieve fertilising capability
- Takes place in the female reproductive tract
What 3 changes take place in capacitation?
- Loss of glycoprotein coat
- Change in surface membrane characteristics
- This allows the acrosome reaction when in close proximity to the ovum
- Change in membrane → increased permeability to Ca2+
- Whiplash movements of the tail
Where exactly does capacitation take place and what is it dependent on?
Takes place in ionic & proteolytic environment of the Fallopian tube
Dependent on:
- Oestrogen
- Calcium
Describe the acrosome reaction.
- The capacitated sperm binds to ZP3 (sperm receptor)
- Once bound to ZP3, progesterone stimulates calcium influx into the sperm
- Hyaluronidase & proteolytic enzymes are released from acrosome
- This allows the spermatozoon to penetrate the Zona Pellucida (glycoportein layer surrounding egg)
Where does fertilisation normally occur?
Fallopian tube
What does fertilisation result in the formation of?
Second meiotic division
- There is unequal distribution of cytoplam
- Cell with cytoplasm and chromosomes = ovum
- Cell with just chromosomes = polar body
- This polar body is then expelled
Describe the cortical reaction.
The cortical reaction is triggered by fertilisation
- Cortical granules release molecules that degrade the zona pellucida (including ZP3 and ZP2)
- This prevents further binding of other sperm
- As ZP3 and ZP2 are sperm glycoprotein receptors present in the zona pellicuda
- So their degradation prevents further sperm binding as there are no receptors
- The nuclei fuse: haploid → diploid
Describe how the conceptus develops before implantation
- Continues to divide as it moves down Fallopian tube to uterus (3-4 days)
- Receives nutrients from uterine secretions
- This free-living phase can last for approx. 9-10 days
Describe the process of implantation.
Attachment phase: outer trophoblast cells contact uterine surface epithelium
THEN
Decidualisation phase: changes in underlying uterine stromal tissue (within a few hours)
NOTES:
- Stroma = the part of the tissue which has a structural or connective role (i.e. parts which are not specific to the function of the tissue = everything except parenchyma)
- e.g. connective tissue, BVs, nerves etc.
- Blatocyst:
- Trophoblast → placenta
- Inner cell mass → embryo
What hormone environment is required for implantation?
Progesterone dominance in the presence of oestrogen
Describe the molecules involved in the attachment phase.
Leukaemia inhibitory factor (LIF):
- From endometrial secretory glands (and maybe blastocyst)
- Stimulates adhesion of blastocyst to endometrial cells
Interleukin-11 (IL11):
- Also from endometrial cells is released into uterine fluid (i.e. released into uterine cavity)
- May be involved
- Leads to trophoblast migration and decidualisation
Many other molecules involved in process - e.g. HB-EGF (growth factor from endometrial cells which interact with receptors on trophoblast)
What happens in the decidualisation phase?
Endometrial changes due to progesterone
- Glandular epithelial secretion
- Glycogen accumulation in stromal cell cytoplasm
- Stromal cells - refers to connective tissue cells, i.e. fibroblasts
- Growth of capillaries
- Increased vascular permeability (→ oedema)
Factors involved:
- Interleukin-11 (IL11)
- Histamine
- Certain prostaglandins
- TGFβ - promotes angiogenesis
NOTE:
- This process forms the decidua
- Decidua = modified endometrium which lines the uterus during pregnancy and is shed with afterbirth
Describe the hormone changes which take place during pregnancy.
NOTES:
- Oestriol is E3 and synthesised by placenta
- Different to oestradiol (E2) which is produced by the ovarian follicles in the menstrual cycle
- Human placental lactogen = growth hormone that can have prolactin like effects but is important for the growth and development of the foetus
- ↓ maternal insulin sensitivity, leading to an increase in maternal blood glucose levels
- ↓ maternal glucose utilization, which helps ensure adequate fetal nutrition
- ↑ lipolysis with the release of free fatty acids
Describe progesterone and oestrogen production during pregancy initially.
First 40 days:
- Produced in corpus luteum in maternal ovary
- Stimulated by hCG which acts on LH receptors (i.e. mimics the effects of LH)
- hCG produced by trophoblasts
- Stimulated by hCG which acts on LH receptors (i.e. mimics the effects of LH)
- Essential for developing fetoplacental unit
- Inhibits maternal LH & FSH (-ve feedback)
From day 40:
- Placenta starts to take over production
Describe oestrogen and progesterone production over the course of pregancy, more at later stages.
NOTES:
- Cholesterol → pregenolone → any steroid hormone
- DHEAS = Dehydroepiandrosterone sulfate
- DHEA is a steroid which can be converted to oestrogens
- Conjugation/deconjugation refers to addition/removal of sulphate
Describe how maternal hormones change in pregnancy.
NOTE:
Placental GH-variant:
- Secreted from placenta during pregancy
- Predominant form of GH is maternal circulation (over one secreted by somatotrophs in anterior pituitary)
- Associated with foetal growth
Explain what happens during partruition (childbirth).
You get contraction of the uterus via two main ways
DIRECT:
- Intracellular Ca2+ concentration increases
- i.e. calcium release from stores triggered by prostaglandins, influx from extracellular enviroment
- This stimulates muscle contraction directly by acting on actin-myosin in uterine smooth muscle cells in the myometrium
INDIRECT:
- Oxytoxin is release by posterior pituitary
- It acts on the oxytocin receptor on cells making up the myometrium and endometrium
- i.e. receptor expressed by smooth musle cells and epithelial cells
- This stimulates uterine contraction
Additional:
- Foetal cortisol and placental oestrogen bind to oxytocin receptor → indirect contraction
- Placental oestrogen can increase release of Ca2+ from intracellular stores → direct contraction
What does oxytocin stimulate?
- Uterine contraction
- Cervical dilation
- Milk ejection
How is lactation (breastfeeding) controlled?
