BI0005 - Lecture 15 - Physiology of pregnancy
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What does the female reproductive system consist of?
– Produce hormones
– Develop the ova
Fallopian (uterine) tube
– Connects ovaries to uterus
– Site of fertilisation
– Site of implantation of fertilised ovum
– Where foetus develops
What is the Uterus?
• Cavity lined with epithelial cells (endometrium) and an underlying muscle layer (myometrium)
– Changes each month to receive fertilised egg
– If fertilisation occurs develops to placenta
– Required for muscular contractions to give birth
What are the fallopian (uterine) tubes made of?
Epithelial cells (2 types)
• Hairs waft ova along tube towards uterus
• Produce mucus lubricates and keeps hydrated
– Peristaltic movement
– Propels ova & sperm
– Then fertilised egg
How do the gametes develop?
– form in testes
– mature as pass through series of ducts
– final maturation occurs in female reproductive tract
– produced in ovary
• occurs in multiple phases
• starts in utero but only completes if fertilisation occurs
What is the female reproductive cycle?
• Combination of events that occur in uterus (uterine cycle) and ovaries (ovarian cycle)
• Controlled by hormones
Hormone is a chemical released from an endocrine gland into blood that causes a reaction often by another organ
What is the purpose of the female reproductive cycle?
• to release a mature ovum
• to prepare the uterus for implantation of fertilised ovum
What are the uterine and ovarian cycles?
• Proliferative phase
• Secretory phase
• Follicular phase
– Development & expansion of the follicular cells
– Release of ovum
– Secretion of progesterone
What is the summary of the Ovarian cycle?
• Release of follicle stimulating hormone (FSH)
• Stimulates follicle growth
• Follicle contains an egg (ova)
• At ovulation, follicle breaks open to release ovum
• Ruptured follicle develops into corpus luteum
How do Ova develope?
– Process of formation female gametes
– Eggs form during early foetal development
– Undergo mitosis to form
– Division to give millions of eggs
– Most die without further development
– Remainder develop to primordial oocytes
What are the hormones of the Ovarian cycle?
Growth of follicles
– Stimulated by luteinising (LH) & follicle stimulating hormone (FSH) (FOLLICULAR PHASE) • Corresponds to proliferative phase of uterine cycle
Release of ovum stimulated by surge of LH
– oestrogen levels increase (OVULATION)
• Oestrogen secreted by follicles
Transformation of empty follicle to form corpus luteum
– (LUTEAL PHASE)
– Due to LH
– Secretes oestrogen & progesterone
• = Secretory phase of uterine cycle
What are the phases of the Uterine Cycle?
– Oestrogen stimulates thickening of endometrium
• Part of uterus
• Preparing for implantation
– Corpus luteum maintains development of endometrium
• Because it secretes hormones
– Endometrial glands secretes nutrient fluid
• Feed embryo before and as implants
– Loss of corpus luteum & ovarian hormones
• As levels of LH fall
– Disintegration of some of endometrium
– Menstrual (blood) flow
What is the process of fertilisation?
• Released ovum swept by cilia into fallopian tube
• Fertilisation takes place in oviduct (fallopian tube)
• 12-24 hours after release
• Oocyte only viable for 24hr
• When sperm penetrates the oocyte
• Triggers reaction to prevent another sperm being able to fertilise the oocyte
• Sperm enters egg that is much larger
What are the numbers for sperm?
• 300 million into vagina
• 60 million reach cervix
• 6 million pass through cervix
• 100 survive to fallopian tubes where fertilisation takes place
• Sperm viable for approx 48 hours
• Fresh sperm are infertile
• Need to be in female reproductive system approx 7 hours & undergo “capacitation” to be fertile
– Removal of substances (glycoprotein) from plasma membrane around head surface
What are the steps of fertilisation?
1. Interaction of sperm with outer region of egg
2. Release of enzymes from sperm head
3. Digest path through outer oocyte
4. Interact plasma membrane of oocyte
5. Sperm moves into egg
What are the trimesters?
• Divide pregnancy to 3 trimesters
• Each approx 3 months long
• Length of pregnancy
– 266 days (38 weeks) from ovulation
– 280 days (40 weeks) from last menstrual period
What happens in the first trimester?
• Development of placenta
• All organs in place by 8 weeks
– Not mature but present
– Heart starts to beat during week 4
• Known as embryo from implantation to week 8
• Once organs formed known as foetus
What is the Placenta?
• Develops from mother and embryo
• Mother’s contribution
– Endometrium of uterus
• From embryo
– Cells called trophoblasts
– Form villi
– Inside villi foetal blood supply
Comment on the Placenta & blood supply?
• Mother and foetal circulations do NOT mix
• Materials exchange across villi
• Blood taken to embryo via umbilical vein
• Blood returns from embryo via umbilical artery
What are the functions of the placenta?
• Synthesis of hormones
• Respiratory gas exchange
• Nutrient transfer
• Waste product removal
• Heat transfer
– Ensure maintain foetus at constant temperature
• Protection of foetus
What passes between the mother and the foetus?
From Mother to Foetus
• Oxygen; Nutrients; Hormones; Antibodies
From Foetus to Mother
• Carbon dioxide; Other metabolic waste; hormones; Water
What happens in the second trimester?
• Foetus grows to 30cm
• Very active
• Uterus grows to cope with needs of growing foetus
What happens in the third trimester?
• Growth main factor
– 3-4 kg weight
– to 50cm length
• Foetal activity decrease
– Lack of space
• Trigger of labour
Why are there maternal adaptations to pregnancy?
– to cope with the demands placed on the body by the foetus
– to prepare for labour and lactation
• Hence most systems affected
How does pregnancy affect the cardiovascular system?
• Increase blood volume and blood cells
– To make sure sufficient blood to placenta
• Increase cardiac output
– Push more blood round the body
• Blood flow increases to
– Kidney for waste disposal
– Uterus take substances to and from placenta
– Skin for heat loss
– Breasts for mammary development to prepare for lactation
How does pregnancy affect the respiratory system?
• Increase in oxygen taken in to lungs
• Increase in oxygen passing across alveoli
• Rapid removal of carbon dioxide
• Result ensures sufficient oxygen for foetus
How does pregnancy affect the Gastrointestinal system?
• Increase food in-take
• Slow transit through GI tract
• Increase absorption from GI tract
• Result ensure good nutrient supply
How does pregnancy affect metabolic function?
• Reduce mother’s dependence on glucose
• Increase fat breakdown
• Inhibit amino acid breakdown
• Result: increase glucose levels for foetus and fatty acids for mother
How does pregnancy affect renal function?
• Kidney enlarged
• Increase blood flow to kidney
• Increase urine production
• Reduce loss of salt and water
• Result increased waste removal and retention of salt and water
What is a brief summary of the physiology of pregnancy?
• Development of ovum correlates with preparation of endometrium to receive fertilised egg
• All stages require correct balance of hormones
• Placenta development essential to provide good exchange system between mother and foetus
• Maternal adaptations to ensure that foetus gets oxygen and nutrients and waste is removed
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BI0005 - Lecture 15 - Physiology of pregnancy
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