Placenta, Umbilical Cord and Foetal Membranes: Definition, Structure and Functions

Placenta, Umbilical Cord and Foetal Membranes: Have you ever thought about your navel? This area of your body, commonly known as the belly button, was formerly the entrance site for the umbilical cord, a vital anatomical feature. In simple terms, the umbilical cord is the lifeline of a developing foetus. It’s a flexible tube-like structure that connects the foetus to the placenta of the mother.

The placenta is an organ that connects to the mother’s blood supply and is linked to the uterine wall. Fetal membranes are the membranes that surround the developing foetus. The amnion and chorion are the two chorioamniotic membranes that make up the amniotic sac, which surrounds and protects the foetus. The purpose of this article is to illustrate the most important characteristics of the placenta, umbilical cord, and foetal membranes.

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Definition of Placenta

Fig: Illustration of Placenta

The placenta is a temporary organ that exchanges nutrients and oxygen between the mother and the foetus. It’s crucial for modulating the mother’s immune response to antigens of paternal and foetal origin, as well as a source of a wide range of hormones that keep the gestation progressing. The placenta is a connection that connects the foetal membrane to the uterine wall. As a result, the placenta is both maternal and embryonic. The developing embryo receives nutrients and oxygen from the mother through the placenta, emitting carbon dioxide and nitrogenous waste.

Structure

Fig: Placenta Anatomy

1. It is the intimate connection between the foetus and the uterine wall of the mother. The foetal part of the placenta is the chorion, and the maternal part is the decidua basalis.
2. Chorionic villi are a group of finger-like projections that grow into the uterine tissue from the chorion’s outer surface. The placenta is formed when these villi penetrate the mother’s uterine wall tissue.
3. The foetal blood gets very close to the maternal blood in the placenta, allowing for the interchange of materials between the two. Food (glucose, amino acids, lipids), water, mineral salts, vitamins, hormones, antibodies, and oxygen pass from the maternal blood into the foetal blood, while metabolic wastes such as carbon dioxide, urea, and toxins pass from the foetal blood into the maternal blood.
4. As a result, the placenta acts as the foetus’s nutritional, respiratory, and excretory organ. In the placenta or anywhere else, the blood of the mother and the foetus do not combine. In the capillaries of the chorionic villi, the foetal blood comes into close contact with the mother’s blood in the tissue between the villi; nonetheless, they are constantly separated by a membrane, through which substances must diffuse or lie transferred by some active, energy-demanding mechanism.
5. Types of Placenta: The placenta can be classified into different types on the basis of nature of contact; the placenta is of two types indeciduate and deciduate.
   (a) Indeciduate placenta: Chorionic villi are simple, lie in contact with the uterus, they have loose contact, and there is no fusion. At the time of birth, the uterus is not damaged, e.g., Ungulates, Cetaceans, Sirenians, Lemurs, etc.
   (b) Deciduate placenta: The allanto chorionic villi penetrate into the uterine villi. They are intimately fused. Hence, at the time of birth, the uterus is damaged, and bleeding occurs, e.g., Primates, Rodentia, Chiroptera, etc
6. The human placenta is deciduate and hemochorial type, and it produces various hormones.

Hormones Produced by the Placenta

Functions of Placenta

1. Nutrition: The Placenta facilitates the passage of food materials from the mother’s blood into the foetal blood through the umbilical vein.
2. Digestion: Protein is digested by the trophoblast of the placenta before it is passed into the foetal circulation.
3. Respiration: Oxygen diffuses from maternal blood to foetal blood through the placenta, and carbon dioxide passes from foetal blood to maternal blood.
4. Excretion: Nitrogenous wastes such as urea move through the placenta into maternal blood and are filtered out by the mother’s kidneys.
5. Storage: Before the foetus’ liver is formed, the placenta stores glycogen, fat, and other nutrients for the foetus.
6. Barrier: The placenta serves as an effective barrier (defensive wall) that allows beneficial aerials to enter the social bloodstream. The placenta allows harmful compounds like nicotine from cigarettes and addictive narcotics like heroin to pass through. As a result, pregnant women should avoid smoking and using drugs. The placenta allows viruses and bacteria to get through.
7. Endocrine function: As an endocrine gland, the placenta secretes hormones such as oestrogen, progesterone, and human chorionic gonadotropin (HCG).

Definition of Umbilical Cord

The umbilical cord transports oxygenated blood and nutrients from the placenta to the foetus through the abdomen, passing through the navel. It also transports the fetus’s deoxygenated blood and waste products to the placenta. The umbilical cord is cut close to the baby’s body when they are born, and the stump comes off on its own. Let’s take a closer look at the umbilical cord’s anatomy and function.

Structure & Function

1. The umbilical cord begins to form around the fifth week of pregnancy and can reach a length of 20 inches when fully developed.
2. It’s a stiff, sinewy structure with two layers: a smooth muscle layer on the outside and a gelatinous fluid called Wharton’s jelly on the inside.
3. Within this material, there are usually three vessels: one vein and two arteries. The arteries convey deoxygenated and nutrient-depleted blood away from the foetus, while the veins deliver oxygen and nutrient-rich blood from the placenta to the foetus.
4. These two branches connect to the umbilical cord outside and form a circuit in the fetus’s body. The umbilical cord may not form properly in some situations or another issue during birth.
5. These issues can sometimes be detected via ultrasound before birth, although they are often not noticed until after the baby is born. Let’s take a look at a few of these concerns and how they could affect the fetus.
   a. Single umbilical artery:

Fig: Single Umbilical Artery

The umbilical cord may develop with a missing artery in rare situations. Although the source is unknown, it can result in birth abnormalities affecting the heart, nervous system, chromosomes, and urinary tract. This condition can be diagnosed even before the baby is born.

b. Umbilical cord prolapse:

Fig: Umbilical cord prolapse

The umbilical cord may prolapse or fall into the birth canal as the infant passes through, becoming crushed by the baby during delivery. If the infant is not born right away, this can cut off the baby’s blood flow and create a life-threatening situation.

c. Umbilical cord knots:

Fig: Umbilical cord knots

It’s not uncommon for the cord to coil around the baby’s neck, but this rarely results in major complications. However, it is possible that it will become tangled and cut off the baby’s blood supply in rare situations.

d. Umbilical cord cysts: Ultrasound can sometimes reveal cysts growing on the umbilical cord. This can cause problems with the kidneys, chromosomes, and abdomen.

e. Vasa Previa:

Fig: Vasa Previa

Umbilical cord blood vessels may shift outside of the cord’s protection and go underneath the newborn in rare situations. This can cause blood vessel tears and life-threatening hemorrhages.

Umbilical Cord Blood Storage

Cord blood is the blood inside the umbilical cord that contains undifferentiated (blood-forming) stem cells. This blood can be extracted from the cord and kept in private or public banks to treat diseases such as leukaemia and sickle cell anaemia. Some parents prefer to keep their child’s blood in a private bank in case the stem cells are needed later in life by the child or a family member. The practice of private banking is fraught with controversy. Many medical practitioners advise against storing cord blood for self-use because most health issues are already present in the cord blood, and the child is unlikely to utilise the cells. Furthermore, as compared to public banking, it is an extremely expensive procedure.

Foetal Membranes

Fig: Foetal Membranes

1. The membranes that enclose the embryo or foetus are known as foetal membranes. The amnion, chorion, allantois, and yolk sac are the membranes that make up the embryo. 
2. The cellular layer, the reticular layer, the basement membrane, and the trophoblast layer are the four layers that make up the chorion membrane.
3. The outermost layer is the trophoblast.
4. The amniotic sac is made up of the chorion and the amnion. The amniotic sac is a sac filled with a fluid called amniotic fluid. The fluid acts as a cushion for the foetus as it develops. The amnion is a membrane that connects the chorion to the amnion. It’s a sturdy and thin membrane. The amniotic cavity is lined with it.
5. The epiblast-derived extraembryonic ectodermal layer and the thin non-vascular extraembryonic mesoderm make up this cell layer. 
6. The allantois is a sac-like or diverticulum that emerges from the hindgut’s ventral wall. It is a part of amniotes’ conceptus (i.e., the embryo and its appendages, adjunct parts, or related membranes). In humans, it does not play a direct role in respiration or waste storage. The placenta and the umbilical vessels that develop in combination with the allantois perform these activities.
7. The hypoblast forms a membrane that forms the yolk sac. It’s linked to the establishment of the primordial gut and early embryonic blood supply. In mammalian embryos, the yolk sac is a ventral, endodermally walled organ that does not serve a nutritional purpose. The first blood cells and vessels are formed in the yolk sac’s wall by mesodermal blood islands. Although primordial germ cells can be seen in the yolk sac wall, they come from the extraembryonic mesoderm at the base of the allantois.

Amniotic Fluid

Fig: Amnion and Amniotic fluid

Amniotic fluid is essential for foetal growth and serves a variety of roles during the fetus’s existence inside the womb. The foetus may movely within the amniotic cavity while maintaining intrauterine temperature and protecting the growing foetus from damage due to amniotic fluid. Fluid abnormalities may obstruct normal foetal development and result in structural defects, or they may be an indirect symptom of an underlying problem, such as a neural tube defect or gastrointestinal illness. This section will cover amniotic fluid production and sonographic patterns, as well as amniotic fluid volume evaluation and abnormalities and the use of amniotic fluid volumes in the diagnosis of fetal disorders.

Derivation

Early in foetal development, the amniotic cavity develops and is filled with amniotic fluid. The embryo and, eventually, the foetus are totally surrounded and protected by the fluid. The amniotic membrane, a thin membrane bordered by a single layer of epithelial cells, is the main source of amniotic fluid early in pregnancy. During this stage of development, water readily passes through the membrane, and amniotic fluid is produced by the amnion’s active transport of electrolytes and other solutes, followed by passive diffusion of water in response to osmotic pressure changes. Amniotic fluid production and consumption change as the foetus and placenta mature. 

Characteristics of Amniotic Fluid

The six functions of amniotic fluid are as follows:

1. It protects the foetus by acting as a cushion.
2. It allows embryonic and foetal movement.
3. Amniotic fluid prevents the amnion from adhering to the embryo.
4. It allows for symmetrical development
5. Amniotic fluid keeps the temperature consistent
6.  Amniotic fluid stores foetal metabolites before they are excreted by the maternal system.

Summary

The placenta is a connection that connects the foetal membrane to the uterine wall. As a result, the placenta is both maternal and embryonic. The developing embryo receives nutrients and oxygen from the mother through the placenta while also emitting carbon dioxide and nitrogenous waste. The umbilical cord begins to form around the fifth week of pregnancy and can reach a length of 20 inches when fully developed. It’s a stiff, sinewy structure with two layers: a smooth muscle layer on the outside and a gelatinous fluid called Wharton’s jelly on the inside. The amniotic membrane, a thin membrane bordered by a single layer of epithelial cells, is the main source of amniotic fluid early in pregnancy. The membranes that enclose the embryo or foetus are known as foetal membranes. The amnion, chorion, allantois, and yolk sac are the membranes that make up the embryo. 

Frequently Asked Questions (FAQs)

Q.1: What are the 5 functions of the placenta?
Ans: The placenta serves as a link between the mother and the foetus. Gas exchange, metabolic transfer, hormone secretion, and embryonic protection are all functions of the placenta. Nutrient and drug transfer across the placenta are by passive diffusion, facilitated diffusion, active transport, and pinocytosis.

Q.2: Why is the placenta called endocrine?
Ans: The placenta secretes a variety of hormones. It’s known as an endocrine gland. The placenta, as an endocrine gland, produces estrogen, progesterone, and other hormones. hPL stands for “human placental lactogen” and Human chorionic gonadotropin (HCG).

Q.3: What is a foetal membrane?
Ans: The membranes that enclose the embryo or foetus are known as foetal membranes. The amnion, chorion, allantois, and yolk sac are the membranes that make up the embryo. The cellular layer, the reticular layer, the basement membrane, and the trophoblast layer are the four layers that make up the chorion.

Q.4: What is the function of the umbilical cord?
Ans: Because it transports the baby’s blood back and forth between the newborn and the placenta, the cord is also referred to as the baby’s “supply line.” It provides the newborn with nourishment and oxygen while also removing the baby’s waste products. At five weeks after conception, the umbilical cord begins to develop.

Q.5: How is the umbilical cord formed?
Ans: Between the 4th and 8th weeks, the expanding amnion envelops the body stalk, the ductus omphalo-entericus, and the umbilical coelom, forming the umbilical cord.

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