Placental Hormones & Endocrine Adaptations During Pregnancy

Pituitary Adaptations

Anterior lobe is regulated by the hypothalamus. The placenta secretes hormones and the pituitary gland adaps and adjusts. 1. Enlargement of gland 2. Decreases in TSH at first, then returns to baseline 3. Decrease in growth hormone (GH) and inhibition of FSH and LH due to hCG occur

Prostaglandin Adaptations

1. Control processes including inflammatory response, blood flow and formation of clots, and the induction of labor [plays important role in contraction of uterus during labor] Levels remain in their typical range throughout pregnancy. Unlike most hormones, the prostaglandins are not secreted from a gland to be carried in the bloodstream and work on specific areas around the body. Instead, they are made by a chemical reaction at the site where they are needed and can be made in nearly all the organs in the body. Prostaglandins are part of the body's way of dealing with injury and illness. The prostaglandins act as signals to control several different processes depending on the part of the body in which they are made. Prostaglandins are made at sites of tissue damage or infection, where they cause inflammation, pain and fever as part of the healing process. When a blood vessel is injured, a prostaglandin called thromboxane stimulates the formation of a blood clot to try to heal the damage; it also causes the muscle in the blood vessel wall to contract (causing the blood vessel to narrow) to try to prevent blood loss. Another prostaglandin called prostacyclin has the opposite effect to thromboxane, reducing blood clotting and removing any clots that are no longer needed; it also causes the muscle in the blood vessel wall to relax, so that the vessel dilates. The opposing effects that thromboxane and prostacyclin have on the width of blood vessels can control the amount of blood flow and regulate response to injury and inflammation. Prostaglandins are also involved in regulating the contraction and relaxation of the muscles in the gut and the airways. Prostaglandins are known to regulate the female reproductive system, and are involved in the control of ovulation, the menstrual cycle and the induction of labour. Indeed, manufactured forms of prostaglandins - prostaglandin E2 and F2 can be used to induce (kick-start) labour.

Pancreas Adaptation

1. Glucose crosses to the fetus, insulin does NOT! 2. hPL acts against insulin causing higher incidences of glucose issues in the 2nd half of pregnancy [insulin resistance]

Adrenal Gland Adaptations

1. Increase in cortisol [important to respond to stress] and aldosterone secretions - as early as 15 weeks in the pregnancy *Cortisol:* Cortisol is a steroid hormone, one of the glucocorticoids, made in the cortex of the adrenal glands and then released into the blood, which transports it all round the body. Almost every cell contains receptors for cortisol and so cortisol can have lots of different actions depending on which sort of cells it is acting upon. These effects include controlling the body's blood sugar levels and thus regulating metabolism, acting as an anti-inflammatory, influencing memory formation, controlling salt and water balance, influencing blood pressure and helping development of the foetus. In many species cortisol is also responsible for triggering the processes involved in giving birth. The secretion of cortisol is mainly controlled by three inter-communicating regions of the body; the hypothalamus in the brain, the pituitary gland and the adrenal gland. This is called the hypothalamic-pituitary-adrenal axis. When cortisol levels in the blood are low, a group of cells in a region of the brain called the hypothalamus releases corticotrophin-releasing hormone, which causes the pituitary gland to secrete another hormone, adrenocorticotropic hormone, into the bloodstream. High levels of adrenocorticotropic hormone are detected in the adrenal glands and stimulate the secretion of cortisol, causing blood levels of cortisol to rise. As the cortisol levels rise, they start to block the release of corticotrophin-releasing hormone from the hypothalamus and adrenocorticotropic hormone from the pituitary. As a result, the adrenocorticotropic hormone levels start to drop, which then leads to a drop in cortisol levels. This is called a negative feedback loop. *Aldosterone:* Aldosterone is a hormone produced in the outer section (cortex) of the adrenal glands, which sit above the kidneys. It plays a central role in the regulation of blood pressure mainly by acting on organs such as the kidney and the colon to increase the amount of salt (sodium) reabsorbed into the bloodstream and to increase the amount of potassium excreted in the urine. Aldosterone also causes water to be reabsorbed along with sodium; this increases blood volume and therefore blood pressure. Aldosterone is part of a group of linked hormones, which form the renin-angiotensin-aldosterone system. Activation of this system occurs when there is decrease in blood flow to the kidneys following loss of blood volume or a drop in blood pressure (e.g. due to a haemorrhage). Renin is an enzyme that leads to a series of chemical reactions resulting in the production of angiotensin II, which in turn stimulate aldosterone release. Aldosterone causes an increase in salt and water reabsorption into the bloodstream from the kidney thereby increasing the blood volume, restoring salt levels and blood pressure.

Human Placental Lactogen (hPL)

1. Modulates fetal and maternal metabolism. Helps regulate the mother's metabolism by increasing maternal blood levels of nutrients for use by the fetus. 2. Promote the growth of the mammary glands (breasts) in preparation for lactation. 3. Decreases maternal insulin sensitivity to increase its availability for fetal nutrition -Glucose is the main energy substrate for intrauterine growth and is transmitted in a steady stream from mother to fetus. Glucose is produced as a result of maternal metabolism principally from carbohydrate in the diet and from the gluconeogenic amino acids. The hormone insulin, in turn, regulates glucose. - Purpose of insulin resistance (IR) adapted by mother is to deliver enough quantity of nutrients to the growing fetus. Low insulin sensitivity is known as insulin resistance. The cells do not absorb as much glucose, which might lead to excessively high blood sugar levels. 4. Levels of hPL rise to stimulate lipolysis as glucose levels decrease -major role is the effect in inducing resistance to insulin action in the mother. This limits maternal glucose utilization, while ensuring an appropriate supply of free fatty acids derived from lipolysis for the mother during fasting, sparing glucose for fetal energy needs to protect against fetal hypoglycemia.

Human Chorionic Gonadotropin (hCG)

As early as 3 days after conception, the trophoblasts [produced by the fertilized egg after it implants in the uterus] make hCG, a hormone that ensures that the endometrium will be receptive to the implanting embryo. hCG preserves the corpus luteum and its progesterone production so that the endometrial lining of the uterus is maintained; this is the basis for pregnancy tests. -We recall that the corpus luteum is the structure that remains in the ovary after the egg has been discharged. If the egg is unfertilized, the corpus luteum degenerates, and the woman progresses through her normal monthly cycle. As mentioned, hCG is produced by the fertilized egg. Therefore, it is *the first detectable hormone of a pregnancy and can be detected by blood or urine tests within the first month of conception*. For this reason, hCG is the hormone that is tested for when performing a pregnancy test. hCG levels *double every 2-3 days for the first 4 weeks* of pregnancy! HCG hormone levels found in the mother's *blood and urine RISE a lot during the first trimester*. They may play a part in the nausea and vomiting often linked to pregnancy.

Relaxin

Relaxin is a hormone produced by the ovary and the placenta with important effects in the female reproductive system and during pregnancy. In preparation for childbirth, it relaxes the ligaments in the pelvis and softens and widens the cervix. In women, relaxin is secreted into the circulation by the corpus luteum in the ovary. During pregnancy it is also released from the placenta, the membranes which surround the fetus, and the lining of the uterus. Relaxin levels in the circulation rise after ovulation, during the second half of the menstrual cycle. 1. At this stage it is thought to relax the wall of the uterus by inhibiting contractions, and it also prepares the lining of the uterus for pregnancy. If pregnancy does not occur, relaxin levels drop again. During pregnancy, relaxin levels are at their highest in the first trimester. 2. At this time it is believed to promote implantation of the developing fetus into the wall of the uterus and the growth of the placenta. 3. Early in pregnancy, relaxin also inhibits contractions in the wall of the uterus, to prevent premature childbirth. 4. Relaxin can regulate the mother's cardiovascular and renal systems to help them adapt to the increase in demand for oxygen and nutrients for the fetus, and to process the resulting waste products. -It is thought to do this by relaxing the mother's blood vessels to increase blood flow to the placenta and kidneys. Towards the end of pregnancy relaxin... 5. Promotes rupture of the membranes surrounding the fetus and the growth 6. Opening and softening of the cervix and vagina to aid the process of childbirth. 7. There is also some evidence that relaxin can relax the ligaments at the front of the pelvis to ease delivery of the baby.

Endocrine System

The endocrine system is made up of glands that make hormones. Hormones are the body's chemical messengers that carry information and instructions from one set of cells to another. Endocrine hormones help control mood, growth and development, the way our organs work, metabolism, and reproduction. Major Glands of the Endocrine System: -hypothalamus [links the endocrine system and nervous system. Nerve cells in hypothalamus create chemicals that control the release of hormones from the pituitary gland. The hypothalamus gathers info sensed by the brain and sends it to the pituitary.] -pituitary ["master gland": also secretes hormones that signal the reproductive organs to make sex hormones and controls ovulation and menstrual cycles]: makes many hormones: -Growth Hormone: stimulates the growth of bone and other body tissues and plays a role in the body's handling of nutrients and minerals -Prolactin: activates milk production -Thyrotropin: stimulates the thyroid gland to make thyroid hormones -Corticotropin: stimulates adrenal glands to make certain hormones -Antidiuretic: helps control body water balance through its effect on the kidneys -Oxytocin: triggers the contractions of uterus during labor -thyroid [makes thyroid hormone thyroxine and triiodothyronine. These hormones control the rate at which cells burn fuels from food to make energy. The more thyroid hormone in the bloodstream, the faster chemical reactions happen in the body. Also play a role in the development of the brain and nervous system] -parathyroid [attached to the thyroid are four tiny glands that work together. They release parathyroid hormone, which controls the level of calcium in the blood with the help of calcitonin, which they thyroid makes] -adrenals [2 glands that sit on top of each kidney. Have two parts, each of which makes a set of hormones and has a different function. *Adrenal Cortex:* (outer part) makes hormones called corticosteroids that help control salt and water balance in the body, the body's response to stress, metabolism, the immune system, and sexual development and function. *Adrenal Medulla:* (inner part) makes catecholamines, such as epinephrine (aka adrenaline). Epinephrine increases BP and HR when body is under stress] -pineal body [secretes melatonin, a hormone that may help regulate when we sleep at night and wake in the morning] -ovaries and testes [Gonads are the main source of sex hormones. In boys the male gonads (or testes) are in the scrotum. They secrete hormones called androgens, such as testosterone. A girl's gonads (ovaries) make eggs and secrete female hormones estrogen and progesterone] -pancreas [makes insulin and glucagon]

Placenta

The placenta is an endocrine gland ["glands of internal secretion"; a gland that secretes hormones into the bloodstream] that is only present during pregnancy. The precursor cells of the placenta - the *trophoblasts*- first appear 4 days after fertilization as the outer layer of cells of the blastocysts. These early blastocyst trophoblasts differentiate into all the cells that form the placenta. When fully developed, the placenta serves as the interface between the mother and the developing fetus. During the next few weeks the placenta begins to make hormones that control the basic physiology of the mother in such a way that the fetus is supplied with the nutrients and oxygen needed for growth. The placenta also... -protects the fetus from immune attack by the mother -removes waste products from the fetus -induces the mother to bring MORE food to the placenta -near the time of childbirth, produces hormones that ready fetal organs for life outside the uterus Placenta function depends on the maternal blood pressure supplying circulation. If there is any interference with blood flow to the placenta, it cannot carry out its functions to the embryo or fetus. Theoretically, at NO time during pregnancy does the mother's blood mix with fetal blood bc there is no direct contact between their bloods; layers of fetal tissue always separate the maternal blood and the fetal blood. These fetal tissues are called the *placental barrier.* Materials can only be interchanged through *diffusion.* The maternal uterine arteries deliver the nutrients to the placenta, which in turn provides nutrients to the developing fetus; the mother's uterine veins carry fetal waste products away. The structure of the placenta is usually completed by week 12. The placenta is not only a transfer organ but a hormone factory as well. Placental hormones have profound effects on maternal metabolism, initially building up her energy reserves and then releasing these to support fetal growth in later pregnancy and lactation postnatally. Placental hormones include: -Human Chorionic Gonadotropin (hCG) -Estrogen -Progesterone -Human Placental Lactogen (hPL) -Relaxin

Estrogen [Estriol]

This group of hormones is normally formed in the ovaries. However, it is also made by the placenta during pregnancy to help maintain a healthy pregnancy. You may recognize estrogen as the hormone that stimulates the development of the female secondary sex characteristics during puberty, such as breast development, hip widening and body hair growth. During pregnancy, it serves as an additional function - it helps maintain the pregnancy and prepare the breasts for milk production. Estrogen levels increase steadily during pregnancy and reach their peak in the third trimester. The rapid increase in estrogen levels during the first trimester may cause some of the nausea associated with pregnancy 1. Causes enlargement of a woman's breasts, uterus, and external genitalia 2. Stimulates myometrial contractility

Progesterone [Progestin]

This hormone is made by the ovaries and by the placenta during pregnancy! Levels rapidly increase during the first trimester and remain high during pregnancy. High levels are required throughout pregnancy with levels steadily rising until the birth of the baby. During the first few weeks of pregnancy, progesterone is produced from the corpus luteum and is sufficient to maintain pregnancy. At this early stage, progesterone has many diverse functions which are vital to the establishment of pregnancy including: 1. Increasing blood flow to the womb by stimulating the growth of existing blood vessels 2. Stimulating glands in the lining of the endometrium to produce nutrients that sustain the early embryo -Provides nourishment for the early conceptus [embryo in the uterus - during early stages of pregnancy] 3. Stimulating the endometrium to grow and become thickened, producing the decidua: a unique organ that supports the attachment of the placenta and allowing implantation of the embryo 4. Helping to establish the placenta As the placenta forms and grows, it develops the ability to produce hormones. The cells that make up the placenta - trophoblasts - are able to convert cholesterol from the mother's bloodstream into progesterone. Between weeks 6-9 of pregnancy, the placenta takes over from the ovaries as the main producers of progesterone. As well as being vital to the establishment of pregnancy, progesterone also has many functions during mid to late pregnancy, including: 1. Progesterone *decreases the contractility of the uterus* ["pregnancy hormone" bc it calms the uterus]. -Prevents the muscles of the uterus from contracting until the onset of labor 2. Stimulates maternal metabolism and breast development 3. Prevents lactation until after pregnancy 4. Strengthening the muscles of the pelvic wall in preparation for labor If the egg is fertilized and pregnancy occurs, the corpus luteum is maintained thanks to the hormone hCG. This is important because the corpus luteum produces the hormone progesterone. Sufficient progesterone in a woman's body ensures that the lining of the uterus stays intact and provides a nourishing environment for the egg to implant and develop. Without progesterone from the corpus luteum, the lining of the uterus would slough off, ending the pregnancy. In the later stages of pregnancy, the job of progesterone production is taken over by the placenta. At that time, the corpus luteum, along with the ovaries, become inactive for the remaining months of the pregnancy.

Thyroid Adaptation

Thyroid hormones are critical for development of the fetal and neonatal brain, as well as for many other aspects of pregnancy and fetal growth. 1. Slight enlargement and increased activity 2. Thyroid hormone transfers to the fetus for critical brain development until 20 weeks, then T4 continues to be provided. 3. Hypothyroidism in either the mother or fetus frequently results in fetal disease; in humans, this includes a high incidence of mental retardation.