How the Fallopian Tube Supports Fertilization and the Menstrual Cycle
The fallopian tubes or the oviducts/uterine tubes are structures found in the female reproductive system. They are pivotal in transporting the ova or the egg released as a result of the ovulation process from the ovary into the lumen (central channel) of the uterus every month. In case of fertilization as a result of the presence of sperms, the fallopian tubes conduct the transportation of the fertilized egg to the uterus for its firm implantation. The other structures of the female reproductive system include ovaries, uterus, cervix and vagina.
The fallopian tubes are uterine appendages bilaterally situated at the superior part of the uterine cavity. They are the long, slender tubes connecting ovaries to the uterus. It leaves the uterus via the cornua leading to the formation of a link between the peritoneal and endometrial cavities.
The fallopian tubes show fine hair-like projections known as cilia on cells of the lining. These cilia of the tube are necessary for egg-movement from the tube to the uterus. If these cilia are caused any harm as a result of any infection, it may hinder the movement of the egg forward and may continue to stay in this tube itself. Additionally, it may also lead to complete or partial blocking of the tube with scar tissue thereby preventing the egg from physically entering the uterus.
Structure of Fallopian Tubes
Each of the fallopian tubes is 4-5 inches long with a diameter of approximately 0.2–0.6 inches. The channel of the fallopian tubes is lined with a mucous membrane which has several papillae and folds. Papillae are small cone-shaped projections of the tissue.
The mucous membrane has three layers of muscle tissue – the outermost layer has longitudinal fibres ending in several fimbriae (finger-like branches) near the ovaries, leading to the formation of infundibulum – funnel-shaped depository. The middle layer has circular fibres while the innermost layer has fibres arranged spirally.
The infundibulum is the outermost, wide distal section of each of the fallopian tubes. It grasps the eggs released and channels it. The extremities of the fimbriae spread over the ovary contracting close to the surface of the ovary during the ovulation to guide the freely moving egg suitably.
Following the infundibulum is the central, long part of these uterine tubes known as the ampulla. The ampulla and the infundibulum are linked to the uterus through the isthmus – a small area close to 0.8 inches long. The intramural, the last part of the tube is situated in the fundus of the uterus. The intramural duct offers a channel which is the narrowest part of the tube. This structure is the narrow tube in line with the isthmus leading to the uterine wall and the uterine cavity. This is the region where the fertilized eggs typically secure themselves and go on to develop.
This mucous membrane which lines the fallopian tube produces secretions helping the smooth transportation of the sperm and the egg for it to thrive. This fluid mainly comprises sodium, calcium, proteins, chloride, glucose, lactic acid and bicarbonates. The last two constituents are key to the usage of oxygen by sperms in addition to helping the egg in developing after fertilization. While the other constituents mentioned render a suitable environment for fertilization, glucose serves as a nutrient for the sperms and eggs.
The mucous membrane possesses cells containing cilia – fine hair-like projections. They help in the movement of the sex cells. The sperms once deposited in the female reproductive tract typically arrive at the infundibulum in a matter of some hours. In any case, the eggs arrive in the uterine cavity in about 3-4 days. The peristaltic movement in the form of rhythmic muscular contractions in sync with the sweeping motions of the cilia together assist and rightly guide, channelizing the movement of the sperm or the egg. Any damage or abnormalities to the fallopian tube affects the fertility of a woman.
Menstrual Cycle
The monthly cycle of changes in the ovaries and the lining of uterus or endometrium is termed as the menstrual cycle. This menstrual cycle ceases when the egg is fertilized, and pregnancy begins. The menstrual cycle occurs in two phases: the follicular phase of the menstrual cycle and the Ovulatory phase of menstrual cycle. The follicular phase is the first day of the period. The following events occur during this follicular phase:
Hormones like Follicle stimulating Hormone (FSH) and Luteinizing Hormone (LH), are released from the brain and travel in the blood to the ovaries.
The hormones stimulate the growth of about 15 to 20 eggs in the ovaries which have a separate shell known as a follicle.
The FSH and LH also trigger a rise in the production of the female hormone called estrogen.
FAQs on Fallopian Tube: Structure, Functions & Importance
1. What is the primary role of the fallopian tube in the female reproductive system?
The primary role of the fallopian tube is to transport the egg (ovum) from the ovary to the uterus each month. It is also the site where fertilisation—the fusion of the egg and sperm—typically occurs. After fertilisation, the tube transports the resulting embryo to the uterus for implantation.
2. What are the four main parts of a fallopian tube?
A fallopian tube is divided into four main parts, starting from the ovary and moving towards the uterus. The importance of understanding these parts lies in their specific functions:
Infundibulum: A funnel-shaped opening near the ovary, with finger-like projections called fimbriae that capture the egg after ovulation.
Ampulla: The widest and longest section of the tube. This is the most common site where fertilisation takes place.
Isthmus: A narrow, thick-walled section that connects the ampulla to the uterus.
Uterine Part (Intramural): The final, short segment that passes through the muscular wall of the uterus to open into the uterine cavity.
3. What is an ectopic pregnancy and why is it dangerous if it occurs in the fallopian tube?
An ectopic pregnancy is a complication where a fertilised egg implants outside the main cavity of the uterus, most commonly within the fallopian tube. It is a serious medical condition because the fallopian tube is not designed to expand like the uterus. As the embryo grows, it can cause the tube to rupture, leading to severe internal bleeding, intense pain, and life-threatening complications for the mother.
4. Are 'fallopian tube' and 'uterine tube' different structures?
No, 'fallopian tube' and 'uterine tube' refer to the same structure. Uterine tube is the more formal anatomical term, while fallopian tube (named after the 16th-century anatomist Gabriele Falloppio) is the more commonly used name. Another term for this structure is the oviduct. All three names describe the paired tubes connecting the ovaries to the uterus.
5. Why is the fallopian tube the usual site for fertilisation and not the uterus?
Fertilisation occurs in the fallopian tube, specifically the ampulla, due to critical timing and environmental factors. The egg is viable for only about 12-24 hours after ovulation. It takes several days for the egg to travel down the tube to the uterus. Sperm must travel up from the uterus into the fallopian tubes to meet the egg during this short window of viability. The fallopian tube provides the ideal environment for the fusion of gametes before the egg degenerates.
6. How does the structure of the fimbriae assist in the process of reproduction?
The fimbriae are delicate, finger-like projections at the ovarian end of the fallopian tube. Their structure is crucial for reproduction because they are not static. Around the time of ovulation, they become active and sweep over the surface of the ovary to capture the released egg and guide it into the infundibulum. This mechanism ensures the ovum enters the reproductive tract for potential fertilisation.
7. What is the impact of a blocked fallopian tube on fertility?
A blocked fallopian tube, a condition known as tubal occlusion, can prevent the sperm from reaching the egg or stop a fertilised egg (zygote) from reaching the uterus for implantation. This is a significant cause of female infertility. If only one tube is blocked, pregnancy is still possible, but if both tubes are completely blocked, natural conception cannot occur. In such cases, assisted reproductive technologies like In-Vitro Fertilisation (IVF) are often recommended.
8. What is the average length of a fallopian tube in an adult female?
The average length of a fallopian tube in an adult female is approximately 10 to 12 centimetres (about 4 to 5 inches). The length can vary slightly between individuals, but this range is typical for the muscular tube that provides the essential pathway from the ovary to the uterus.
