Female Reproductive System: Anatomy and Oogenesis

Female Reproductive System

• Focuses on female reproduction
• Details anatomical structures
• Explains the processes of oogenesis, follicular growth, and hormonal regulations

Components of the Female Reproductive System

• Uterus: The hollow, muscular organ where a fertilized egg implants and develops
• Includes the endometrium (lining), myometrium (muscle layer), and cervix
• Conditions like fibroids, adenomyosis, and endometrial cancer can negatively affect the uterus
• Fallopian Tubes: Paired tubes carry eggs from the ovaries to the uterus where fertilization typically happens
• Vagina: The muscular canal connecting the external genitalia to the uterus
• Serves as the passageway for menstrual blood, sexual intercourse, and childbirth
• Ovary: Paired organs produce eggs (oocytes) and secrete hormones like estrogen and progesterone
• Involved in oogenesis, follicular development, and hormonal regulation

Oogenesis

• Oogenesis: Egg (oocyte) development, starts with oogonia (primordial germ cells)
• Primordial Germ Cells (Oogonia): These cells undergo mitosis during fetal development
• Primary Oocytes: Arrested in prophase of meiosis I at birth. These are early-stage oocytes that remain dormant until puberty
• Secondary Oocytes: Oocytes resume meiosis at ovulation and finish meiosis II only if fertilized

Follicle

• Follicular Growth: Oocytes develop within follicles in the ovaries
• Follicular growth starts with the primordial follicle and progresses to the Graafian follicle
• Mature follicle is ready for ovulation
• Ovulation: The release of a mature oocyte from the dominant follicle in response to hormonal signals (primarily LH and FSH)
• Corpus Luteum: After ovulation, the remaining granulosa and theca cells of the ruptured follicle form a corpus luteum
• Corpus luteum produces progesterone to support early pregnancy
• Follicle Selection: Only one (sometimes two) typically becomes dominant and ovulates
• This process involves hormonal cues that prioritize one follicle over others

Hormonal Control

• Two-Cell Theory: Interaction between granulosa and theca cells in the ovary
• Theca cells produce androgens (e.g., testosterone), converted to estrogens by granulosa cells
• This cooperation is essential for follicular maturation
• Follicular Growth: Hormones like FSH and LH regulate follicular growth
• FSH stimulates granulosa cells, LH stimulates theca cells, and this balance influences follicular development and oocyte maturation
• Ovulation: A surge in LH, triggered by high estrogen levels, induces ovulation
• This hormonal surge leads to the final maturation and release of the oocyte
• Corpus Luteum: Following ovulation, the corpus luteum produces progesterone
• Progesterone is essential for the maintenance of the uterine lining and early pregnancy
• Cytokines also play a role in follicular growth, ovulation, and the function of the corpus luteum
• Number of Ovulating Follicles: Typically, one follicle is selected to ovulate, but in some species/conditions multiple may ovulate

Female Reproductive System Components

• Uterus: Composed of the endometrium (inner lining), myometrium (muscle layer), and cervix.
• Responsible for receiving and nurturing a fertilized egg
• Fallopian tubes: Transport eggs from the ovaries to the uterus where fertilization usually occurs
• Vagina: Serves as the birth canal and the passage for menstrual blood and sperm Ovaries: Produces oocytes and hormones that regulate the reproductive system

Female Sexual Characteristics

• Primary: Uterus, ovaries, fallopian tubes, and vagina
• Secondary: Development of breasts, wider hips, and pubic hair

Functions of the Ovary

• Produces oocytes
• Secretes hormones like estrogen and progesterone
• Supports follicular development and ovulation

Stages of Oogenesis

• Primordial Germ Cells (during fetal development)
• Primary Oocytes (arrested in meiosis I at birth)
• Secondary Oocytes (resume meiosis at ovulation).

Follicle Progression

• Primordial follicle: Contains a primary oocyte surrounded by a layer of flattened granulosa cells
• Primary follicle: Granulosa cells become cuboidal
• Secondary follicle: Development of the antrum (fluid-filled space)
• Graafian follicle: Fully mature, large antrum, and ready for ovulation

Pre-Ovulatory Follicle Changes

• The Graafian follicle increases in size, the antrum enlarges, granulosa cells proliferate, and the oocyte completes its first meiotic division

The Oocyte and Follicle at Ovulation

• The oocyte is a secondary oocyte arrested in metaphase of meiosis II
• The follicle ruptures, releasing the oocyte into the fallopian tube

Corpus Luteum Formation

• After ovulation, the remaining granulosa and theca cells undergo luteinization to form the corpus luteum.

Follicular Atresia

• Follicular atresia: Process where non-dominant follicles undergo apoptosis, reducing the number of follicles available for ovulation

Dominant Follicle Selection

• The dominant follicle is selected based on higher sensitivity to FSH and LH, also local production of favorable growth factors and cytokines

The Two-Cell Model of Cellular Cooperation

• Theca cells produce androgens, which granulosa cells convert into estrogens
• This cooperation is critical for the follicle to mature and be capable of ovulating a viable oocyte

Cell Similarities

• Granulosa cells are similar to Sertoli cells: They both support and nourish the developing gametes (oocytes and sperm)
• Theca cells are similar to Leydig cells: They produce steroid hormones; theca cells produce androgens, and Leydig cells produce testosterone

Hormonal Control of Follicular Growth

• FSH promotes granulosa cell proliferation, while LH stimulates theca cells
• Both hormones are essential for follicular maturation and estrogen production

Male Anatomy

• Testes (testicles): Produce sperm and testosterone
• Male sex accessory ducts: Epididymis, vas deferens, ejaculatory duct, urethra
• Sex accessory glands: Seminal vesicles, prostate gland, bulbourethral glands
• External genitalia: Penis, scrotum

Intratubular Compartment

• Germ Cells: Undergo spermatogenesis; includes spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids, and spermatozoa
• Sertoli Cells: Support and nourish developing sperm; maintain blood-testis barrier
• Sertoli Cells secrete androgen-binding protein (ABP), inhibin, and anti-Müllerian hormone during fetal development

Functions of Sertoli Cells

• Support and nourish developing sperm through nutrient provision
• Adjust plasma membranes to allow sperm migration
• Secrete testicular fluid
• Phagocytosis of degenerated germ cells
• Maintain the blood-testis barrier

Seminiferous Tubules

• Seminiferous tubules: Subcompartment where spermatogenesis occurs

Extratubular Compartment

• Leydig Cells: Located between seminiferous tubules, they secrete androgens, primarily testosterone
• Functions of Leydig cells: Produce testosterone, essential for spermatogenesis, secondary sexual traits, and maintenance of male reproductive organs
• Role of LH in steroidogenesis: LH stimulates Leydig cells to produce testosterone
• StAR (Steroidogenic Acute Regulatory Protein) and TPSO (Testicular Peroxisomal Sperm Organizing Protein): Facilitate the transport and conversion of cholesterol to testosterone within Leydig cells

Spermatogenesis

• Spermatogenesis: The process of sperm formation that involves mitotic proliferation, meiotic division, and spermiogenesis

Stages of Spermatogenesis

• Mitotic Proliferation: Spermatogonia divide by mitosis to form primary spermatocytes
• Meiotic Division: Primary spermatocytes undergo meiosis I and II to produce haploid spermatids
• Spermiogenesis: Spermatids mature into spermatozoa (sperm)

Spermatozoon Structure

• Head: Contains genetic material (DNA), acrosomal vesicle (for fertilization)
• Midpiece: Contains mitochondria (energy for movement)
• Tail: Flagellum for motility

Spermatogenic Cycle & Wave

• Spermatogenic Cycle: Duration for a spermatogonium to progress through all stages of spermatogenesis
• Length: About 64 days in humans
• Stages: 12 stages in the seminiferous tubule during spermatogenesis
• Spermatogenic Wave: Sequential arrangement of spermatogenesis across different regions of the seminiferous tubules at any given time
• Length: The cycle happens in waves, so different regions of the seminiferous tubule contain sperm at different stages of development

Biochemical Aspects of Spermatogenesis

• DNA, RNA Synthesis: Essential for proper replication and expression of genes during spermatogenesis, especially during meiotic division
• Protein Synthesis: Important for developing sperm proteins necessary for sperm function and structure
• Haploid Gene Expression: After meiosis, haploid spermatids express genes necessary for sperm development and motility

Hormonal Control

• Testicular Hormone: Testosterone, produced by Leydig cells, is crucial for spermatogenesis and secondary sexual characteristics
• Endocrine Support:
  • FSH (Follicle-Stimulating Hormone): Acts on Sertoli cells to support spermatogenesis -LH (Luteinizing Hormone): Stimulates Leydig cells to produce testosterone

Male Reproductive Organs

• Testes, male sex accessory ducts (epididymis, vas deferens, ejaculatory duct, urethra), external genitalia (penis, scrotum)

Male Accessory Reproductive Organs

• Seminal vesicles, prostate gland, bulbourethral glands

Testis Anatomy

• Intratubular compartment: Contains germ cells (undergo spermatogenesis) and Sertoli cells (support and nourish sperm)
• Extratubular compartment: Contains Leydig cells (produce testosterone), blood vessels, interstitial tissue

Stages of Spermatogenesis

• Mitotic proliferation
• Meiotic division
• Spermiogenesis

Spermatogenesis Stages in Seminiferous Tubule

• Mitotic proliferation: Spermatogonia divide by mitosis, occur near the basal membrane of seminiferous tubules
• Meiotic division: Primary spermatocytes undergo meiosis to form haploid secondary spermatocytes and spermatids, occurs in the central regions of seminiferous tubules
• Spermiogenesis: Spermatids mature into spermatozoa, and it occurs in the lumen of seminiferous tubules.

LH and FSH: Mode of Action

• LH: Stimulates Leydig cells to produce testosterone
• FSH: Acts on Sertoli cells to promote spermatogenesis and regulate ABP secretion

Sertoli Cell Functions

• Sertoli cells: Nourish/support developing sperm, maintains the blood-testis barrier, phagocytose degenerated germ cells
• Sertoli cells secrete testicular fluid, ABP, and inhibin to regulate spermatogenesis

Leydig Cells

• Leydig cells: Produce testosterone; LH stimulates steroidogenesis by acting on Leydig cells
• StAR: Facilitates the transport of cholesterol into Leydig cells, and TPSO assists in steroidogenesis.

Spermatozoon Structure

• Head: Contains DNA and acrosome for fertilization
• Midpiece: Contains mitochondria for energy production
• Tail: Flagellum for motility

Spermatogenic Cycle vs. Wave

• Spermatogenic cycle: Process for a spermatogonium to go through spermatogenesis (~64 days)
• Spermatogenic wave: Sequential arrangement of spermatogenesis across seminiferous tubules

Human Spermatogenic Cycle & Wave

• Spermatogenic cycle: A cycle is ~64 days. Stages occur in a wave: 12
• It takes about 4 cycles for type A spermatogonia to become an elongated spermatid

Blood-Testis Barrier

• Protects developing sperm from immune system attacks and maintains the appropriate chemical environment for spermatogenesis

Spermatogenesis Hormones

• Hormones: Testosterone (produced by Leydig cells), FSH (acts on Sertoli cells), and LH (stimulates Leydig cells) are needed to ensure successful spermatogenesis

Explore the female reproductive system, including the uterus, fallopian tubes, vagina, and ovaries. Understand the process of oogenesis, follicular growth, and hormonal regulation. Learn about the anatomical and physiological components essential for reproduction.