L 34. Adaptation to pregnancy, Physiology of parturition & lactation

Learning objectives To discuss the physiological adaptations during normal pregnancy, cardiovascular, respiratory, gastrointestinal, renal and the uterine changes during pregnancy.

Learning outcomes At the end of this lecture students should be abele to; Describe the physiological adaptations during the normal course of pregnancy Describe the cardiovascular & respiratory changes during pregnancy Describe the renal function and electrolyte balance during pregnancy

Learning outcomes cont Gastrointestinal changes during pregnancy Uterine changes during pregnancy Describe the physiology of parturition Describe the role of hormones in functioning mammary gland Describe the physiology of lactation

MATERNAL CHANGES IN PREGNANCY 5

Duration of pregnancy is 280 days or 40 weeks from the first day of last menstrual period. 6

The uterus Uterus gains weight from 50g to 1000g. Length, thickness and volume Mainly hypertrophy of existing muscle cell and hyperplasia. There is increase in connective tissue and elastic tissue. 7

Mammary Glands Hyperplasia of the ductal and alveolar tissue Pigmentation of the nipple and the areola 8

Changes in blood Blood volume increases by 30% Haematocrit decreases. aldosterone and estrogens increased in pregnancy Increased fluid retention by the kidneys Haematocrit decreases. Plasma volume increases much more than RBC volume Increase in fibrinogen level Increase in ESR. 9

Changes in circulatory system Cardiac output increases to 30 to 40% above normal. Blood volume increases by 30%. Blood pressure Systolic remains same There is fall in diastolic pressure Vasodilation (Kinin,Nitric oxide,EDF) Increase in blood flow to uterus and kidneys 10

Respiratory changes Increase in O2 consumption – 20% more than normal Minute ventilation increases by 50% Respiratory rate is increased. Higher levels of progesterone during pregnancy Increased sensitivity of respiratory centre to CO2 No change in vital capacity. 11

CHANGES IN GIT Morning sickness Decrease in motility Increase in absorption Increased appetite 12

Changes in urinary system Increased fluid intake and increased load of excretory products GFR increases as much as 50%. Reabsorption capacity of renal tubules is increased by 50% Increased production of hormones by the placenta and adrenal cortex 13

Skin Hyperpigmentation Increased secretion of ACTH and MSH during pregnancy 14

CNS Changes in mood. Craving for unusual diet. 15

Metabolism Increased basal metabolic rate (BMR) Increased secretion Thyroxin, Adrenocortical hormones, Sex hormones 16

Increased requirement of iron Likely to develop iron deficiency without supplementation Increased requirement of calcium and phosphorus 17

OTHER CHANGES Weight gain 10-12 kgs Water retention. Fetus Uterus , mammary glands Placenta and amniotic fluid Increase in blood volume Fat deposition Water retention. 18

Physiology of PARTURITION 19

Childbirth process of giving birth Also called “labor” 20

Increased uterine contractility Hormonal factors Increase in estrogen to progesterone ratio Oxytocin Fetal hormones Mechanical factors Stretch of uterine musculature Stretch of cervix 21

Circulating estrogens Increases the number of gap junctions between myometrial cells Production of prostaglandins Increase in myometrial contractile proteins Increase in number of oxytocin receptors 22

Effect of cortisol Increase in cortisol formation in the fetus. CRH secretion by the fetal hypothalamus increases Increased placental production of CRH. This increases circulating adrenocorticotropic hormone (ACTH) in the fetus 23

Positive feedback theory for onset of labour

Head descends into the cervix Initiates the cervical stretch Stretch of cervix Head descends into the cervix Initiates the cervical stretch Increase in contractility of the uterine body Head descends further Cycle repeats 25

Stretch of cervix and distention of vagina Uterine contractions Stretch of cervix and distention of vagina Afferents from cervix and vagina positive feedback to the hypothalmus Oxytocin from posterior pituitary Formation of Prostaglandins in the decidua 26

Two types of positive feedback mechanisms increase uterine contractions during labor: Stretching of the cervix causes the entire body of the uterus to contract Cervical stretching also causes the pituitary gland to secrete oxytocin 27

Parturition Intermittent contractions of the uterus Delivery of the fetus Separation and delivery of Placenta Shearing effect between walls of uterus and placenta 350 ml of blood loss

Physiology of LACTATION

Role of estrogens Causes the ductal system of the breast to grow and branch. Stroma of the breast increase in quantity and large quantities of fat are laid in the stroma. Growth hormone, adrenal glucocoticoids, prolactin & insulin are also needed for ductal growth.

Role of progesterone Acts synergistically with estrogen causes additional growth of the breast lobules, budding of alveoli development of secretory characteristics in the cells of the alveoli.

Initiation of Lactation-Function of Prolactin Estrogen and progesterone inhibits secretion of milk. Prolactin is required for actual secretion of milk.

Increase lactogenic effect Function of prolactin: prolactin Promotes the secretion of milk Estrogen and progesterone Birth Decrease [estrogen + progesterone Increase lactogenic effect (prolactin) Increase [milk] in the alveoli of the Breast – not the ducts!!!!!

Galactopoiesis (maintainance of lactation) Prolactin GH, Cortisol, PTH, Insulin Oxytocin

Milk Ejection Reflex 36

Ejection of Milk: Oxytocin Milk let down reflex or Suckling reflex Neuroendocrine reflex spinal cord Suckling of breast Afferent conduction of APs Contraction of the myoepithelial cells Ejection of milk Oxytocin secretion hypothalamus Prolactin secretion Increase [milk] in the alveoli of the breast

Role of hormones Estrogen & Progesterone specific effect of both these hormones is to inhibit the actual secretion of milk Prolactin: stimulates milk production Oxytocin: stimulates milk release Human chorionic somatomammotropin :Has lactogenic properties and supports the action of prolactin

Effect of lactation on menstrual cycles Lactation amenorrhea Nursing stimulates prolactin secretion Prolactin inhibits GnRH secretion Action of gonadotropins on ovaries inhibited “No ovulation”