W13 Physiology of Pregnancy and Lactation (MAH)

Question 1

Pregnancy
Split into ? trimesters andhow long is each?

Answer 1

Pregnancy is the fertilisation and development of one or more offspring, known as an embryo or fetus in a woman’s uterus

9 months(ish) 40 weeks
* 1st Trimester 1-13
* 2nd Trimester 14-26
* 3rd Trimester 27-40

Question 2

Early pregnancy symptoms?

Answer 2

• Late or missing menstrual period
• Hormone associated side effects

Missed period, vaginal discharge, tender breasts, polyuria, lethargy, morning sickness, headaches, a change in tastes, bloating cramps and backache, skin changes

Question 3

Physiological changes during pregnancy?

Answer 3

➢Hormonal system ➢Cardiovascular System Adaptations ➢Respiratory System
➢Renal and Urinary Adaptations ➢Musculoskeletal and Skin Changes ➢Gastrointestinal Adaptations ➢Metabolic and Endocrine Changes

Question 4

Fertilization and Implantation

Answer 4

Ovulation and Fertilization:
* Ovulation: Release of a mature ovum from the ovary
* Fertilization: Occurs in the fallopian tube when a sperm penetrates the ovum, forming a zygote.

Zygote Formation:
* The zygote undergoes cell division (cleavage) as it moves toward the uterus.

Implantation in the Uterine Wall:
* Around day 6-7 post-fertilization, the blastocyst implants into the endometrial lining.
* Trophoblast cells facilitate implantation and later form part of the placenta.

Question 5

Recap of menstrual cycle: (for info?)

Answer 5

• An ovum is released from a single follicle (ovulation).
• The ovum is collected by the fimbria and wafted along one of the uterine tubes where fertilisation may occur if sperm are present.
• The ruptured follicle persists and develops into a yellow structure called the Corpus Luteum. During the luteal phase of the menstrual cycle, the Corpus Luteum secretes large amounts of oestrogen and progesterone, which maintains the highly vascularised endometrium.
• If fertilisation does not occur, the Corpus Luteum starts to break down and menstruation occurs.
• If fertilisation has occurred, the developing embryo – known as a blastocyst – travels down the uterine tube into the uterus, a journey taking 3–4 days.

Question 6

Implantation

Answer 6

• Fertilisation: The process begins with fertilization, where a sperm cell merges with an egg in the fallopian tube to form a zygote.
• Cell Division and Blastocyst Formation: The zygote travels down the fallopian tube towards the uterus, dividing to form a multi-cellular cluster known as a morula. Further division leads to the formation of a blastocyst, which consists of an outer layer called the trophoblast (which later forms part of the placenta) and an inner group of cells that will develop into the embryo.
• Uterine Preparation: While the blastocyst is developing, hormonal changes prepare the uterus for implantation. The lining of the uterus, known as the endometrium, becomes thicker and enriched with blood and nutrients.
• Blastocyst Arrival and Attachment: Around the 6–7th day after fertilisation, the blastocyst reaches the uterus. It then attaches itself to the endometrium in a process facilitated by enzymes and hormonal signals. This attachment typically occurs in the upper part of the uterus.
• Penetration and Embedding: The blastocyst burrows into the eroded endometrium around the 6–7th day, a process known as implantation, and becomes completely surrounded by the syncytiotrophoblast (9th day). The trophoblast cells proliferate and form projections (villi) that invade deeper into the uterine lining, establishing a connection with maternal blood vessels. The trophoblast develops into the placenta and – by the 13th day – a basic utero-placenta circulatory system already exists. This connection will eventually develop into the placenta, providing oxygen and nutrients to the growing embryo.
• Hormonal Signal to Sustain Pregnancy: The trophoblast cells start to secrete human chorionic gonadotropin (hCG), the hormone detected by pregnancy tests. hCG signals the corpus luteum (remnant of the follicle that released the egg) in the ovary to continue producing progesterone, a hormone vital for maintaining the endometrial lining and supporting the early stages of pregnancy.

Question 7

3. Hormonal Changes During Pregnancy

Answer 7

Human Chorionic Gonadotropin (hCG): Secreted by trophoblast cells after implantation. Maintains the corpus luteum, ensuring continued production of progesterone and oestrogen.
Oestrogen: Promotes uterine growth, blood flow, and breast development.
Progesterone: Maintains the uterine lining, inhibits uterine contractions, and supports immune tolerance of the fetus.
Relaxin: Relaxes ligaments and softens the cervix in preparation for childbirth.
Human Placental Lactogen (hPL): Modulates maternal metabolism to supply nutrients to the fetus.

Unique interplay between the foetus, the placenta and the mother.
At 6-8 weeks, there is a transfer of function from the corpus luteum to the placenta.

Question 8

Endocrine Changes in Early Pregnancy

Answer 8

• The syncytiotrophoblast plays a vital endocrine function by secreting the hormone hCG. This signals the Corpus Luteum to persist and keep synthesising progesterone
• The Corpus Luteum, which becomes enlarged in early pregnancy, also secretes the hormones oestrogen and relaxin
• At around 10 weeks’ gestation, the function of the Corpus Luteum declines
• If there is ‘progesterone insufficiency’ in hormone production by the placenta, the pregnancy will miscarry. Miscarriage is common at around 10–12 weeks

As the pregnancy progresses, prostaglandins, protein hormones (e.g. hCG, hCS and relaxin) and steroid hormones (e.g. estrogens and progesterone) are produced by the placenta and the fetal-placental unit.

Question 9

Progesterone- In addition to preparation for implantation and maintaining the uterine lining progesterone has a role in:

Answer 9

• Supporting Fetal Development: promotes the growth of blood vessels in the endometrium and stimulates glands in the uterus to secrete nutrients, supporting the growing foetus. It also aids in the development of the placenta, which will take over the role of progesterone production from the corpus luteum around the end of the first trimester
• Preventing Premature Contractions: prevents premature contractions of the uterus. It helps to keep the uterine muscles relaxed, thus reducing the risk of early labour. This relaxation effect is also important to accommodate the growing foetus and prevent miscarriage.
• Preparing the Breasts for Lactation: Progesterone, along with oestrogen, prepares the breasts for milk production and breastfeeding. It stimulates the growth of milk-producing glands in the breasts.
• Modulating the Immune Response: Pregnancy requires the mother’s immune system to tolerate the foetus, which is genetically different. Progesterone modulates the immune response to prevent rejection of the foetus.
• Regulating Other Hormones: It helps regulate the production of other hormones necessary for pregnancy, like human chorionic gonadotropin (hCG) and oestrogen

Question 10

Oestrogen:

Answer 10

1. Stimulating Uterine Growth
2. Preparing the Endometrium
3. Breast Development
4. Placental Growth and Function
5. Fetal Development
6. Regulating Other Hormones
7. Water Retention and Circulation
8. Cervix and Pelvic Ligaments
9. Maternal Metabolism
10. Mood and Well-being

E1 is the predominant oestrogen in menopause
E2 Is the predominant oestrogen secreted by the ovary
E3 is almost exclusively produced in pregnancy by the placenta

Question 11

Physiological Adaptations in Maternal Systems

Answer 11

Cardiovascular Changes:
* Increased Blood Volume: By 30-50% to supply
the placenta.
* Cardiac Output: Increases due to elevated heart rate and stroke volume.
* Blood Pressure: Slight decrease due to vasodilation.

Respiratory Adaptations:
Increased Oxygen Demand: Metabolic rate rises. Tidal Volume: Increases to enhance oxygen intake.
Diaphragm Elevation: Compensated by rib cage expansion

Renal Function Adjustments:
* Increased Glomerular Filtration Rate (GFR): To
eliminate fetal waste.
* Sodium and Water Retention: Supports increased blood volume.

Metabolic Changes:
* Increased Nutrient Requirements:Especially
protein, iron, and folic acid.
* Insulin Resistance: Due to hPL, raising blood glucose levels for the fetus

Question 12

5. Fetal Development

Answer 12

Fetal Development
* Embryonic Period (Weeks 1-8):
* Formation of major organs and structures.
* High sensitivity to teratogens. Fetal Period (Weeks 9-40):
* Growth and maturation of organ systems.
* Fetal movements begin (quickening).

Placental Function:
* Gas Exchange: Oxygen and carbon dioxide between mother
and fetus.
* Nutrient Delivery: Glucose, amino acids, fatty acids. * Waste Removal: Urea and bilirubin.
* Hormone Production: hCG, oestrogen, progesterone.

Question 13

Dating a pregnancy

Answer 13

• The duration of a pregnancy is taken from the first day of the last menstrual period – this is known as the gestational age

Question 14

6. Parturition (Childbirth)
   What are the 3 stages?

Answer 14

Hormonal Triggers:
* ↓ Progesterone: Removes inhibition of uterinecontractions.
* ↑ Oestrogen: Stimulates uterine muscle sensitivity. Stages of Labor:
1.Dilation Stage: Cervix dilates to 10 cm; regular contractions begin.
2.Expulsion Stage: Delivery of the baby through the birth canal.
3.Placental Stage: Delivery of the placenta.

Oxytocin: From the posterior pituitary, stimulates uterine contractions.
Prostaglandins: Produced by the uterus, enhance contractions

Question 15

The placenta

Answer 15

• The placenta is a temporary organ that develops during pregnancy.
• Its genetic characteristics are identical to those of the developing child
• It attaches to the lining of your uterus and delivers oxygen and nutrients to your growing baby through the umbilical cord
• Highly specialised organ of pregnancy that supports the normal growth and development of the foetus
• Circle desk with a diameter of 15 to 20 cm and the thickness of 2.5 cm at its centre
• Two sides
• Important to analyse postpartum

Question 16

7. Physiology of Lactation

Answer 16

Breast Development:
* Oestrogen and progesterone stimulate growth of mammary glands during pregnancy.
* Prolactin: From the anterior pituitary, promotes milk production.
Hormonal Control of Milk Production:
* Prolactin: Initiates and maintains milk synthesis.
* Oestrogen and Progesterone: High levels during pregnancy inhibit lactation; levels drop after birth, allowing lactation to commence.
Milk Ejection Reflex (Let-Down Reflex):
* Oxytocin: Released in response to infant suckling, causes contraction of myoepithelial cells, ejecting milk

Question 17

7. Physiology of lactation
   Lactation can be divided into 5 stages
   Milk composition?

Answer 17

1. Mamaogenesis: Development of breasts to a functional state
2. Lactogenesis: synthesis and secretion of milk from the breast alveoli
3. Galactokinesis: Injection of milk outside the breast
4. Galactopoiesis: Maintenance of lactation
5. Involution: regression and atrophy post lactation

Milk composition
* Colostrum (1-5 days): Richer in proteins, minerals, amino globulins, anti-inflammatory factors, PGE1 and PGE2, cytokines, phagocytes, lymphocytes
* Mature milk (> 30 days): Larger quantity than colostrum.
* Foremilk: thin proteins, lactose, water and other nutrients
* Hindmilk:morefat,thereforewhiterand provides much of the energy of the feed.
Other components include human growth factors, cortisol, insulin, thyroxine, and prolactin

Question 18

Complications of pregnancy

Answer 18

• Gestational Diabetes
• Preeclampsia and Eclampsia
• Preterm Labour and Birth
• Placenta Previa
• Placental Abruption
• IUGR
• Miscarriage
• Stillbirth
• Hyperemesis Gravidarum
• Infections including maternal sepsis
• DVT / PE
• Amniotic Fluid Complications
• Rh Incompatibility
• Gestational Hypertension

Question 19

Risk factors for adverse outcomes?

Answer 19

• Age of either parent
• Exposure to environmental toxins
• Exposure to recreational drugs and alcohol
• Pharmaceutical drugs
• Multiple pregnancies
• Social and socioeconomic factors
• Weight
• Disease - diabetes mellitus, thyroid disease

Question 20

Preterm birth (PTB)

Answer 20

• Preterm is defined as babies born alive before 37 weeks of pregnancy are completed. There are sub-categories of preterm birth, based on gestational age: extremely preterm (less than 28 weeks) very preterm (28 to less than 32 weeks) moderate to late preterm (32 to 37 weeks).
• Major global health problem rate has increased by 33% over the last few decades.
• About 15 million(~11%) of all infants worldwide are born premature. PTB is a leading cause of
  newborn deaths and the second leading cause of death in children under the age of 5.
• 1.1 million babies die from cheap PTB complications each year.
• Pathophysiological mechanisms underlying PTB or largely unknown but might relate to the premature activation of normal labour processes and/or a maternal insult [uterine over distension; Maternal stress; Infection and inflammation; or other immunological mediated processes]
• Irrespective of the triggering event, local and systemic inflammation tends to be a feature of
  preterm labour and delivery.

Question 21

Test your knowledge
1.Summarize the key physiological adaptations that occur in the maternal cardiovascular and respiratory systems during pregnancy.
2.Explain the hormonal regulation of parturition and how it leads to the onset of labour. 3.Describe how lactation is initiated and maintained postpartum.

Question 22

Cardiovascular system adaptations:
Blood Pressure Variations:

Answer 22

Despite the increase in blood volume and cardiac output, blood pressure usually drops during the first two trimesters due to the hormonal effects causing vasodilation.
Blood pressure typically reaches its lowest point in mid- pregnancy and then gradually rises to pre-pregnancy levels by the end of the third trimester.
The heart may be displaced upwards and laterally as the uterus enlarges. There may be slight hypertrophy of the heart muscle due to increased workload.

Question 23

Cardiac Output Changes:
Vascular Adaptations:

Answer 23

Cardiac output gradually but significantly increases, by as much as 30-50%. This is due to an increase in both the heart rate (by 10-20 beats per minute) and stroke volume
This increase in cardiac output is essential to supply adequate blood flow to the uterus, kidneys, and other organs, and to meet the metabolic demands of the mother and foetus.

Systemic vascular resistance decreases due to progesterone and other pregnancy-related factors on the vascular smooth muscle. This reduction in resistance helps accommodate the increased CO without causing a significant increase in BP.
The body also develops additional blood vessels, particularly in the uterine region, to support the placenta and foetus.

Question 24

Increased Blood Volume: 1.5litres
Changes in Blood Composition:

Answer 24

Increase in blood volume during pregnancy, starting as early as the first trimester and peaking in the second trimester. This increase can be up to 30-50% above pre-pregnancy levels. The purpose is to support the growing foetus and placenta. More dramatic with multiple pregnancy.

Increase in RBC mass (not number) due to raised maternal EPO
Plasma volume increases by 10-15% in early pregnancy&raquo_space;> net decrease in Hb&raquo_space;> physiological anaemia of pregnancy.
Coagulation factors also increase, which is a protective mechanism against bleeding during childbirth but can increase the risk of thrombosis.
Platelets decreased esp. in 3rd trimester&raquo_space;>thrombocytopaenia
WBC increase in pregnancy due to physiological stress of the pregnancy

Question 25

Respiratory System Changes

Answer 25

• Increased Oxygen Consumption: by ~20% during pregnancy to accommodate the metabolic demands of the mother and the growing foetus
• Elevated Diaphragm: The diaphragm is elevated by as much as 4 cm due to the enlarging uterus
• Breathing Mechanics: As pregnancy progresses, breathing becomes more diaphragmatic than
  thoracic due to the restricted movement of the ribcage
• Changes in Blood Gases: slight increase in arterial oxygen tension and a decrease in arterial carbon dioxide tension due to hyperventilation
• Nasal and Airway Changes: Hormonal changes can lead to swelling of the nasal mucosa and increased nasal congestion, commonly experienced by pregnant women
• Increased Progesterone Effect: Progesterone increases the sensitivity of the respiratory centre to carbon dioxide, enhancing the ventilatory response and ensuring adequate oxygen levels for the mother and fetus

Question 26

Renal and Urinary Adaptations

Answer 26

• Increased Kidney Size
• Increased Renal Blood Flow
• Elevated Glomerular Filtration Rate
• Changes in Renal Tubular Function
• Altered electrolyte balance and fluid retention
• Dilatation of the Renal Pelvis and Ureters
• Increased Urinary Frequency
• Increased Risk of Urinary Tract Infections
• Altered Drug Excretion

Changes in kidney function approximately follow changes in cardiac function.
By week 20, the kidneys are filtering 30 to 50% more bloods.
There is a greater reabsorption of sodium and increased elimination of sugars, amino acids and creatinine

Question 27

Musculoskeletal Changes:

Answer 27

• Postural changes, joint laxity, and weight distribution – lower centre of gravity – increased weight/mass to the front which we need to counterbalance
• Relaxin causes the pelvic ligaments and the pubic symphysis to relax, widen and become more flexible&raquo_space;> beneficial increases motility and prepares us for birth
• Abdominal muscles lengthen weaken
• Reduced support for the spine
• Increased ligament and intervertebral disc elasticity
• Increased lordosis.

Question 28

Skin Changes

Answer 28

• Stretch Marks (Striae Gravidarum)
• Hyperpigmentation: Increased levels of oestrogen and progesterone can lead to hyperpigmentation. The most common manifestation is the linea nigra, a dark line running from the navel to the pubic area.
• Melasma or “the mask of pregnancy” is another form of hyperpigmentation, where dark patches appear on the face.
• Flushing, spider veins and varicose veins.
• Sweaty, oily skin
• Lustrous hair and nail growth

Question 29

Maternal weight gain in pregnancy

Answer 29

• Varies
• Interventions beneficial 10-20 weeks
• See NHS webpages

Question 30

Gastrointestinal Adaptations

Answer 30

• Growing uterus puts pressure on the digestive organs
• Impairs their function, leading to:
  ➢Constipation ➢Gallstones
  ➢Reduced bile transport ➢Emesis gravidarum ➢Dysgeusia
• General slowing of the digestive process due to lower levels of Gastrin
• Progesterone and relaxin causes a lax cardiac sphincter&raquo_space;> reflux
• Altered motility, increased nutritional demands

Question 31

Metabolic and Endocrine Change

Answer 31

• Metabolic rates increase substantially by just 15 weeks gestation . This increased metabolic rate may put pregnant women at a higher risk of hypoglycemia, or low blood sugar.
• There are changes in carbohydrate, lipids, and protein metabolism
• Gestational diabetes and insulin resistance
• Thyroid function changes