Lec 5 Gynaecology (2) PDF

## Coitus, Ovulation and Fertilization ### Coitus or Copulation - Insertion of the erected penis inside the vagina with subsequent ejaculation. - The site of semen deposition (ejaculation) differs according to the animal: - **Cattle, buffalo**: Dorsal Fornix of vagina (Portio Vaginalis) -...

## Coitus, Ovulation and Fertilization ### Coitus or Copulation - Insertion of the erected penis inside the vagina with subsequent ejaculation. - The site of semen deposition (ejaculation) differs according to the animal: - **Cattle, buffalo**: Dorsal Fornix of vagina (Portio Vaginalis) - **Mare**: Cervix, uterus - **Sow**: Uterus - **Ram**: There is a urethral process which doesn't enter the external cervical os of the ewe during coitus. However, it is responsible for forcibly spraying the semen over the cervix and cranial portion of the vagina. - The urethral process allows the semen to be sprayed around the portio vagainalis. - The semen volume in the ram is very low (1-5 ml), but it is highly concentrated and needs to be distributed in the portio vagainalis; otherwise, the semen will clump together. ### Duration of Coitus - **Cattle and sheep**: Few seconds - **Stallion**: 15 - 30 seconds - **Dog**: 15 - 30 minutes - **Due to Copulatory tie**: - The bulbus glandis enlarges slowly until it is large enough to dilate the caudal portion of the vagina. - **Swine**: 3-8 minutes average (5.7 minutes copulatory tie) - **Failure of ejaculation**: Is easy ### The dangers of coitus to the female animal include: - The young and small heifer may injure its uterus by an overweight bull. - Laceration and trauma may be produced and cause swelling, hemorrhage, hematoma, discharge, and straining after coitus. ### Pregnancy - Artificial insemination is preferable for heifer growth. - Natural breeding is better for full-grown heifers, especially for heifers that have reached the age of breeding. - The first insemination should be natural to ensure the size of the female is suitable for the bull’s head size. - The use of foreign breeds can lead to dystochia (difficult labor) or over-sized ova. - Artificial insemination is recommended for: ### NB: - The penis of a bull and stallion is much longer than the vagina (may reach 1m). - Copulation may cause bleeding (8-15 cm). ### Metrorrhagia - It is bleeding after coitus. - Metrorrhagia after coitus may be normal, but it can be a sign of a problem. ### Maturation of Oocyte and Follicle **Ovogenesis** - The transformation of oogonia to oocytes. 1. **During fetal development**: Meiosis I begins. 2. **After puberty**: The primary oocyte completes meiosis 1. This produces a secondary oocyte and the first polar body. The first polar body may or may not divide. 3. The secondary oocyte begins meiosis 2, then the secondary oocyte and the first polar body is ovulated. 4. **If fertilization occurs**: The secondary oocyte completes meiosis 2, dividing into an ovum and a second polar body. 5. **If no fertilization occurs**: The secondary oocyte does not complete meiosis 2. 6. **The nucleus of the sperm cell and the ovum unite forming a diploid zygote.** ### NB: - Mature Graafian follicles contain a secondary oocyte and the first polar body, which are ovulated. - After fertilization, the secondary oocyte completes meiosis 2 and extrudes the first polar body. The first polar body is the product of meiosis 1. ### Folliculogenesis 1. **Primordial follicle** 2. **Primary follicle** 3. **Secondary follicle** 4. **Mature Graafian follicle**: Ovulation of oocyte. 5. **Corpus luteum** 6. **Corpus albicans** ### Mature Graafian Follicle (From outside to inside): - **Theca externa** - **Theca interna** - **Membrana granulosa** - **Granulosa cell** - **Antrum** - **Corona radiata** - **Zona Pellucida** - **Oocyte** ### Cumulus oocyte complex: - The cumulus oocyte complex consists of the oocyte and surrounding follicular fluid, zona pellucida, and corona radiata cells. - These cells have nutritive and protective functions. ### ZP: - The zona pellucida is a tough, acellular glycoprotein layer located on the outside of the oocyte. It is produced by the oocyte itself. - It acts as a barrier to sperm penetration and has species-specific receptors, preventing fertilization by sperm of other species. ### Corona radiata - The corona radiata is the outermost layer of cells surrounding the oocyte. It is composed of cumulus oophorus cells. ### Regulation of follicular growth: - **Growth differentiation factor 9 (GDF9):** This is a protein that plays a role in ovarian follicle development and growth. Theca cells produce GDF9, which targets the granulosa cells. GDF9 acts as a paracrine factor, meaning it acts locally, but it is not a hormone. - **Growth differentiation factor 9B (GDF9B):** Produced by both the granulosa cells and the theca cells of the ovarian follicle. GDF9B acts in an autocrine manner to inhibit follicle growth. - **Activin**: A protein hormone produced by the granulosa cells of the ovarian follicle. Its main function is to act as a paracrine factor, enhancing the growth and maturation of the dominant follicle. ### Mechanism of Ovulation: - **Estrus**: Estrogen levels increase, stimulating the release of LH. - **Pre-ovulatory LH surge**: - The pre-ovulatory LH surge causes expansion of the cumulus cell layer, which separates the oocyte from the follicular wall. - The pre-ovulatory LH surge also increases blood supply to the ovary and follicle, increasing vascular permeability. - This increase in vascular permeability allows the entry of plasminogen and prostaglandins into the follicle. - **Plasminogen activation**: - The plasminogen activator converts plasminogen to plasmin. - Plasmin is an enzyme that degrades collagen. - Plasmin also activates collagenase which degrades collagen. - This degradation of collagen weakens the follicular wall. - **Prostaglandin synthesis**: - Prostaglandins E and F are synthesized and released during the pre-ovulatory LH surge. - Prostaglandins E and F contract smooth muscle, which helps to expel the oocyte from the follicle. ### Fimbria - The fimbria are finger-like projections, located on the infundibulum of the fallopian tube. - They move and contract to guide the oocyte into the fallopian tube. - Under the influence of estrogen, the fimbria become more active. ### Time of Ovulation: - **Cow**: 10 to 12 hours after the end of estrus. - **Mare**: 2 days before the end of heat. - **Ewe**: 6 to 12 days before the end of heat. - **Goat**: 4 to 6 hours before the end of heat. - **Sow**: 24 to 48 hours after the start of estrus. - **Cat**: Induced 24 hours after coitus. - **Camel**: Induced 24 to 36 hours after coitus. ## Fertilization - Fertilization is the process of the union of a mature male gamete (sperm) with a mature female gamete (ovum) to produce a zygote. - **Factors facilitating fertilization**: - **Ovum maturation:** - **Epididymis**: Sperm matures in the tail of the epididymis. - **Sperm capacitation**: Sperm capacitation is a functional change that allows sperm to fertilize an egg. - **Acrosomal reaction**: The acrosomal reaction involves the breakdown of the acrosome of the sperm cell, releasing enzymes that help to penetrate the zona pellucida of the egg. - **Sperm maturation**: - Immature sperm cannot move and fertilize an egg. - This is due to a protoplasmic droplet that inhibits movement. - Mature sperm have lost the protoplasmic droplet. - **Gamete transport and meeting:** - The transport of the sperm to the egg is a highly complex process that is influenced by a number of factors: - **Fallopian tube length**: The fallopian tube is 25-35 cm long in cows. - **Fallopian tube site**: The fallopian tube is located between the ovary and the tip of the horn. - **Sperm transport**: - Sperm are ejaculated in the dorsal fornix of the vagina. - The cervical mucus provides a pathway for sperm to move through the cervix. - The selection of sperm occurs in the uterus. - Hormones such as oxytocin and prostaglandin play important roles in sperm movement. - The sperm reaches the ampullary isthmic junction where they wait for the ovum. - The sperm motility is essential for fertilization. - **Ovum transport**: - The fimbriae on the terminal oviduct pick up the ovum. - The follicular fluid is released during ovulation and serves as a medium for free-floating. - The coordinated action of cilia and muscle contractions assist with moving the ovum to the site of fertilization. - The ovum travels through the fallopian tube via peristaltic movements. ### Mechanisms of Sperm Transport: - **Site of fertilization**: ampullary-isthmic junction. - **Sperm ejaculation**: In the dorsal fornix of the vagina. - **Estrual mucus:** - During estrus, there is a *estrual mucus* which allows the sperm to move through the cervix. - Estrual mucus is ultra-channeled (not solid) allowing the sperm to move. ### The selection of sperm occurs in the uterus. ### Hormones that contribute to sperm transport: - **Oxytocin**: Present in semen. - **Prostaglandin**: Also present in semen. - **Oxytocin and prostaglandin**: Cause contractions that help to move the sperm in the uterus. ### Ampullary isthmic junction: - This is the final destination of the sperm. - In the ampullary-isthmic junction, the sperm can wait for the ovum. - Abnormal or dead sperm is either phagocytized (engulfed and broken down) or lost via the cervix. ### Mucus: - Cervical mucus has a number of important functions: - **Protection of sperm**. - **Nutrition of sperm**. - **Antimicrobial**. ### Attachment of the sperm to the Fallopian Tube: - The sperm attaches temporarily to the epithelium of the fallopian tube via ductal epithelium for protection and capacitance. - The sperm is then released to allow for fertilization. ### Sperm: - The average size of a sperm cell is 3 mm. - The average speed of sperm is 2 mm per second. ### Barriers for sperm: - The most difficult barrier for sperm to pass is the cervix: - This is due to the mucus and the presence of the *annular ring*, a ring-shaped structure made of muscles. - **Utero-tubal junction**: This is the point where the uterus joins with the fallopian tubes. ### Sperm Viability: - Sperm are viable in the female tract for 24 hours, but in the mare, they can be viable for up to 5 days. - It is estimated that only approximately 200 sperm cells reach the site of fertilization, and the rest degenerate and are absorbed by the female genital tract. ### **Mechanism of ova transport**: 1. **Ova pick up:** The fimbria on the terminal oviduct act like a funnel to pick up the ovum. 2. **Fluids**: - The fluid escaping from the follicle during ovulation acts as a medium for free-floating. - Ductal fluid is another important factor in ova transport. 3. **Movement:** - **Ciliary activity**: The coordinated action of cilia in the oviduct helps with the movement of the ovum to the site of fertilization. - **Muscle contraction**: Muscle contractions also play a role in ova transport. - **Peristaltic movements**: The rhythmic contractions of the oviduct help to move the ovum towards the uterus. - The combination of these factors ensures that the ova are transported in the right direction. ### The Site of Fertilization: - The site of fertilization is the *ampullary isthmic junction* of the fallopian tube. - This is the area where the sperm and the ovum meet and fertilization occurs. - The ampullary isthmic junction is blocked in the first 150 to 180 hours after estrus due to the presence of estrogens. ### **Ovum Release: - The *block* at the ampullary isthmic junction releases and allows the ovum to travel to the uterus after four days due to the effects of progesterone. ### Life Span of Ova: - The lifespan of the ova is 12 to 24 hours, except for the bitch, which may be fertile for 4-8 days. ### Fertilization of the Ovum: - The fertilization of the ovum occurs in the *ampulla* of the oviduct within 1 to 2 hours after ovulation if spermatozoa are present at the site of fertilization. ### **Factors facilitating fertilization:** 1. **Capacitation:** 2. **Acrosome reaction:** 3. **Meeting of ovum and sperm:** 4. **Reaction between fertilizin and anti-fertilizin:** ### Capacitation: - Capacitation is the process of functional changes in the sperm cell that enable it to fertilize the ovum. It occurs within the female reproductive tract. - Capacitation involves a number of changes, including: - **Removal of decapacitating factors**: - The decapacitating factors, which are present in the seminal plasma, inhibit sperm from fertilizing the ovum. - These factors are removed during capacitation. - **Changes in membrane permeability**: - The sperm cell membrane becomes more permeable, allowing the entry of calcium and other ions. - **Changes in the acrosome**: - The acrosome is a cap-like structure that covers the sperm cell head and contains enzymes that are needed to penetrate the zona pellucida. - During capacitation, the acrosome undergoes changes that prepare it for the acrosome reaction. ### Acrosome Reaction: - The acrosome reaction is triggered when the sperm cell binds to the zona pellucida of the ovum. - During the acrosome reaction, a series of events occur, leading to the release of enzymes from the acrosome: - **Fusion between the outer acrosomal membrane and the plasma membrane of the sperm**: - This fusion exposes the *perforatorium*, a structure within the acrosome that contains enzymes. - **Release of lytic enzymes**: - The perforation releases *lytic enzymes*, such as *hyaluronidase* and *acrosin*. - These enzymes break down the zona pellucida, allowing the sperm to penetrate. ### Penetration: - Penetration is the process by which the sperm cell penetrates the zona pellucida and then the plasma membrane of the ovum. - This process involves: - **Hypermotility**: This is an increase in the motility of the sperm cell. - **Lytic enzymes**: This refers to the enzymes released during the acrosome reaction, which break down the zona pellucida. - **Corona penetrating enzymes**: The corona penetrating enzymes break down the corona radiata, allowing the sperm cell to penetrate the zona pellucida. - **Zona lysin and acrosin**: These enzymes are released during the acrosome reaction and soften the zona pellucida. - The sperm cell creates a tunnel through the zona pellucida. - The sperm cell then penetrates the vitelline membrance (plasma membrane) of the ovum. - Once the sperm cell has penetrated the vitelline membrane, the sperm cell is inside the ovum. ### Stages After Penetration: - **Completion of Meiosis**: - The secondary oocyte completes meiosis 2 upon penetration of the sperm. - The second polar body is extruded. - **Cortical Reaction**: - The *cortical reaction* involves the release of cortical granules, which are located in the cytoplasm of the ovum. - Cortical granules contain enzymes that harden the zona pellucida, creating a barrier that prevents the entry of other sperm. ### **Syngamy:** - Syngamy is the fusion of the male and female pronuclei. It results in the formation of a zygote. **Other terms**: - **Cleavage**: The zygote undergoes rapid mitotic divisions (mitosis). - **Blastocyst**: The zygote differentiates into a multicellular structure called a blastocyst. - **Morula**: This is a solid ball of cells, approximately 12–16 cells, formed during the early stages of embryonic development. ### Abnormal Fertilization - **Polyspermy**: - Polyspermy occurs when more than one sperm cell penetrates the ovum. - This results in a triploid zygote (3N) instead of a diploid zygote (2N). - The zygote typically dies. - **Polygyny**: - Polygyny is the maturation of the egg without the expulsion of the second polar body. It results in a triploid zygote (3N). - The zygote typically dies. - **Gynogenesis**: - In gynogenesis, the male pronucleus fails to develop and the embryo remains haploid. - The embryo typically dies without developing. - **Androgenesis**: - In androgenesis, the female pronucleus fails to develop, resulting in a haploid embryo that will not develop normally. - **Wandering of Ovum**: - The ovum can wander from one ovary to the other. - **External wandering**: - The ovum travels through the peritoneal cavity. - **Internal wandering**: - The ovum travels through the fallopian tube. - **Superfecundation**: - This occurs when a female is impregnated by two different males. - This is common in bitches. - **Superfetation**: - Superfetation is the gestation of two or more fetuses from separate ovulations. - It is also common in bitches, but it is generally much rarer than superfecundation. ### Twins: - **Identical Twins (Monozygotic Twins)**: - Identical twins are formed when a single fertilized egg (zygote) splits into two developing zygotes at a very early stage of development. - Identical twins have the same sex and same DNA. - **Fraternal Twins (Dizygotic Twins)**: - Fraternal twins are formed when two separate eggs are fertilized by two different sperm cells. - Fraternal twins share half of their DNA, like normal siblings. - **The incidence of twins increases with the mother’s age**. ### Advantages of Twins: - The production of more offspring. ### Disadvantages of Twins: - **Mother:** - **Uterus Overstretching:** The uterus is stretched beyond its normal limits, which can cause uterine inertia. - **Dystocia:** This occurs when there is difficult labor, and the calf cannot be delivered naturally. - **Retained Placenta:** The placenta fails to detach from the uterus after birth. ### Other Disadvantages: - **Endometritis:** Inflammation of the lining of the uterus. - **Uterine Involution:** The uterus takes longer to return to its normal size and shape after birth. - **Increased Calving Interval:** The time between births is longer. ### Abortions in Cattle: - **Abortion or Retus:** - **Small in size**: - **Free-Martinism**: This occurs when a female calf is born co-twin with a sterile male calf. The female calf will often be sterile. - If twins are identified by ultrasound in a cow, the best action is to manually dilate the cervix or administer oxytocin. - It is not recommended to use prostaglandin in heifers due to potential side effects. - The use of *dexamethasone* hormone can be used for abortions, but it only works in later stages of pregnancy.