WEEK 1: GAMETOGENESIS, OVULATION AND MOVEMENT OF THE EGG AFTER OVULATION Flashcards
Define the following terms:
Gametogenesis
Fertilization
Implantation
Differentiation
- Gametogenesis is the process of producing sex cells (gametes) by a specialized type of cell replication known as meiosis.
- Fertilization is the fusion of male and female gametes to form a zygote.
- Implantation is the method of blastocyst (a ball of cells formed from the zygote) attaching to the uterus wall.
- Differentiation is the process by which cells become specialized for different functions in the developing organism.
Define the following terms:
1. Menstrual cycle
2. Fertilization
3. Zygote
4. Blastocyst
5. Implantation
Menstrual cycle: Tightly coordinated cycle of stimulatory and inhibitory effects that results in release of a single mature oocyte from a pool of primordial oocytes
Fertilization: process where the sperm and egg unite to form a zygote
Zygote: a diploid cell formed from fusion of egg and sperm
Blastocyst: a structure/cluster of cells from dividing zygote. Consists of inner cell mass (embryoblast) and outer layer (trophoblast)
Implantation: process where blastocyst hatches from zona pellucida to adhere to the endometrium
What is Spermatogenesis?
Describe the process of spermatogenesis.
What is site of maturation involving meiosis and spermatogenesis?
What is the reductive cell division called?
Describe the genotype for spermatogonia.
*Process of spermatogonia mature into spermatozoa (sperm)
Primary spermatocyte -> secondary spermatocyte-> spermatid->sperm
Seminiferous Tubule is site of maturation involving meiosis and spermatogenesis.
meiosis is reductive cell division.
1 spermatogonia (diploid) 46XY = (haploid); 23X & 23Y
State the 2 phases of spermatogenesis.
*Spermatocytogenesis
*Spermiogenesis
What is spermiogenesis?
The process by which a spermatid becomes a spermatozoa.
Spermiogenesis is the final stage of spermatogenesis during which haploid spermatids, resulting from meiosis, undergo a series of structural and functional changes to transform into mature and motile spermatozoa.
Describe the first phase of spermatogenesis.
- Mitosis (Proliferation):
a. Type A Spermatogonia:
Spermatogonia are the undifferentiated germ cells located along the basal membrane of the seminiferous tubules in the testes.
Type A spermatogonia are the stem cells that give rise to spermatocytes through mitotic divisions.
Type A spermatogonia divide into two types: Type A1, which maintains the pool of stem cells, and Type A2, which differentiates into primary spermatocytes.
b. Primary Spermatocytes:
Type A2 spermatogonia undergo mitosis to produce primary spermatocytes.
Primary spermatocytes are diploid cells that are committed to entering meiosis.
- Meiosis (Reduction Division):
a. Meiosis I:
Primary spermatocytes enter meiosis I, resulting in two secondary spermatocytes.
Each secondary spermatocyte is haploid (contains half the chromosome number).
b. Meiosis II:
Secondary spermatocytes then undergo meiosis II, resulting in four haploid spermatids.
The reduction in chromosome number ensures that each sperm cell contributes only half of the genetic material to the eventual offspring.
Describe the process of spermiogenesis.
- Formation of the Acrosome:
The Golgi apparatus in the spermatid forms the acrosome, a cap-like structure located at the anterior (head) of the developing sperm.
The acrosome contains enzymes, such as hyaluronidase and acrosin, which are essential for penetrating the protective layers surrounding the egg during fertilization.
- Nuclear Condensation:
The nucleus of the spermatid undergoes condensation, resulting in a more compact and streamlined structure.
This condensation ensures that the genetic material is tightly packed and ready for delivery to the egg during fertilization.
- Formation of the Flagellum (Tail):
The centrioles near the nucleus organize microtubules to form the axial filament of the flagellum, the tail of the sperm.
The flagellum provides the sperm with motility, allowing it to swim toward the egg in the female reproductive tract.
- Reduction of Cytoplasm:
Excess cytoplasm is shed from the developing sperm, reducing its overall size and contributing to its streamlined shape.
This reduction in cytoplasm is essential for optimizing the sperm’s motility and ensuring that it can efficiently navigate through the female reproductive system.
Describe what happens to the sperms after spermiogenesis in the seminiferous tubules.
SPERMIATION:
During spermiogenesis, the haploid spermatids undergo significant structural and functional changes to transform into fully mature and functional spermatozoa. Once this transformation is complete, the mature spermatozoa are released from the Sertoli cells into the tubular lumen in a process called spermiation.
Maturation and Migration to the Epididymis:
The mature spermatozoa, now equipped with an acrosome and a flagellum, are released into the lumen of the seminiferous tubules.
They then move to the epididymis, a coiled tube located on the surface of the testes, where they undergo further maturation and gain the ability to swim.
Storage in the Epididymis:
Sperm are stored in the epididymis until they are fully mature and capable of fertilization.
The epididymis provides an environment conducive to the acquisition of motility and the ability to recognize and bind to eggs.
Completion of Maturation:
During their time in the epididymis, sperm undergo additional changes, including modifications to their plasma membrane proteins.
These modifications enhance the sperm’s ability to interact with the female reproductive tract and prepare it for fertilization.
Ejaculation and Fertilization:
Upon ejaculation, sperm are propelled through the vas deferens, mixing with seminal fluid from the seminal vesicles and prostate gland.
The resulting mixture, known as semen, is ejaculated through the penis during sexual intercourse.
What is oogenesis?
Oogenesis is the process by which female germ cells, or oogonia, develop into mature egg cells, or ova. It occurs in the ovaries and involves several stages, including mitosis, meiosis, and maturation.
Describe the process of oogenesis.
What is the purpose of forming secondary polar bodies?
- Formation of Oogonia:
*Fetal Development:
During fetal development, oogonia undergo mitotic divisions, producing a pool of primary oocytes.
Primary oocytes are diploid cells that are arrested in prophase I of meiosis until puberty.
- Follicular Development:
*Puberty:
At puberty, under the influence of hormonal changes, a limited number of primary oocytes resume development each menstrual cycle.
A group of surrounding cells forms a structure called a follicle around the developing oocyte.
- Meiosis I:
*Before Birth:
Meiosis I begin before birth, but it is arrested at prophase I.
The primary oocytes remain in this state until puberty.
*At Puberty:
At each menstrual cycle, one or a few primary oocytes resume meiosis I.
Meiosis I is completed, resulting in the formation of a secondary oocyte and a polar body.
The secondary oocyte is arrested at metaphase II until fertilization.
- Ovulation:
Release of the Egg:
The mature follicle, now called a graafian follicle, ruptures, releasing the secondary oocyte from the ovary.
This release of the egg is called ovulation.
- Meiosis II:
*If Fertilization Occurs:
If fertilization occurs, the secondary oocyte resumes meiosis II.
Meiosis II is completed, resulting in the formation of a mature ovum and another polar body.
*If No Fertilization:
If fertilization does not occur, the secondary oocyte degenerates, and meiosis II is not completed.
- Maturation of the Ovum:
If Fertilization Occurs:
The mature ovum, with a haploid set of chromosomes, is now capable of fusing with a sperm during fertilization.
- Formation of Polar Bodies:
Purpose:
*Polar bodies are small, nonfunctional cells that contain the excess genetic material.
They are formed during both meiotic divisions and often degenerate.
Describe the hormonal changes leading to ovulation.
Hormones play a crucial role in regulating the ovulatory process.
At the beginning of the menstrual cycle, the anterior pituitary gland releases follicle-stimulating hormone (FSH), which stimulates the development of ovarian follicles.
As the follicles mature, they produce increasing amounts of estrogen.
Rising estrogen levels, as a result of follicular development, eventually trigger a surge in luteinizing hormone (LH) from the pituitary gland.
The LH surge is a key signal for ovulation.
The LH surge causes the mature graafian follicle to rupture.
Ovulation is the release of the mature egg (secondary oocyte) from the ovary into the abdominal cavity.
Describe the movement of the egg after ovulation.
- Fimbriae:
The fallopian tube is connected to the ovary by fimbriae, finger-like projections that help capture the released egg.
The fimbriae create a gentle sweeping motion, guiding the egg from the surface of the ovary into the opening of the fallopian tube.
- Ciliary Action:
Cilia in the fallopian tube’s epithelium play a crucial role in egg transport.
The coordinated beating of cilia helps move the egg toward the uterus by creating a flow of fluid within the tube.
- Peristaltic Contractions:
The muscular walls of the fallopian tube undergo rhythmic contractions known as peristalsis.
Peristaltic contractions help propel the egg through the fallopian tube toward the uterus.
- Smooth Muscle Contractions:
Smooth muscle in the walls of the fallopian tube contracts to assist in the transport of the egg.
These contractions are regulated by hormonal signals and neural influences.
- Time Frame:
The journey of the egg from the ovary to the uterus typically takes a few days.
The egg is viable for fertilization for about 12 to 24 hours after ovulation.
