Mar 4th Flashcards
What is gametogenesis?
The formation and genetic/phenotypic maturation of gametes.
How many chromosomes do gametes have compared to somatic cells?
Gametes are haploid, meaning they have half the number of chromosomes as somatic cells.
How many phases are there in gametogenesis?
4 phases
Which phase of gametogenesis is identical in both males and females?
The first phase.
What are the four phases of gametogenesis?
1️⃣ Migration of extraembryonic primordial germ cells (PGCs) to the gonads
2️⃣ Increase in PGCs by mitosis
3️⃣ Reduction of chromosomal material by meiosis
4️⃣ Structural and functional maturation (oogenesis/spermatogenesis)
What are primordial germ cells (PGCs)?
They are the earliest recognizable precursors of gametes.
Where do PGCs migrate to during early embryonic development?
They migrate into the gonads.
Where do PGCs originate?
Outside of the gonads, in the hindgut.
Is crossing over random?
No, it occurs at “hot spots” based on protein configurations that organize chromosomes early in meiosis.
Where does crossing over occur in sex chromosomes (X & Y)?
Within a small region of homology between the X and Y chromosomes.
What role does histone hypermethylation play in recombination?
It marks specific sites where DNA strands break and are repaired after crossing over.
What is the function of cohesion?
It holds sister chromatids together during cell division.
What is condensin’s role in cell division?
It is important for chromosomal compaction and is necessary for both mitotic and meiotic divisions.
Where does spermatogenesis occur?
testes
How long does spermatogenesis last?
It is an indefinite process, continuously producing sperm.
How many gametes are produced per cycle in spermatogenesis?
Four sperm cells per cycle.
What is spermatogenesis?
The process of producing spermatozoa from male primordial germ cells via mitosis and meiosis.
What are the initial cells in spermatogenesis called and how do they become spermatocytes
- Spermatogonia
- through mitosis
What are spermatogonia?
Diploid stem cells that give rise to two daughter cells.
What happens to the two daughter cells produced by spermatogonia?
One remains a stem cell at the basement membrane, and the other becomes a primary spermatocyte.
What occurs in the first meiotic division of spermatogenesis?
The primary spermatocyte duplicates its DNA and divides into two haploid secondary spermatocytes.
What happens in the second meiotic division of spermatogenesis?
The secondary spermatocytes divide into four haploid spermatids.
What are the four phases of spermatogenesis?
- Spermatocytogenesis – Formation of primary & secondary spermatocytes.
- Spermatidogenesis – Formation of spermatids from secondary spermatocytes.
- Spermiogenesis – Maturation of spermatids into immotile spermatozoa.
- Spermiation – Final maturation into motile spermatozoa.
What is spermatocytogenesis?
The process of forming spermatocytes with half the normal genetic material.
What are the three types of spermatogonia, and what do they do?
- Type A dark (Ad): Stem cells of the seminiferous epithelium.
- Type A pale (Ap): Committed to differentiation.
- Type B: Differentiated from Type A, giving rise to primary spermatocytes.
What happens during spermatidogenesis?
Secondary spermatocytes undergo meiosis II to form haploid spermatids.
Why are secondary spermatocytes rarely seen in histological studies?
Because they rapidly enter meiosis II.
What key changes occur during spermiogenesis?
- Tail formation: Microtubules grow from one centriole (axoneme).
- Mitochondrial arrangement: Energy supply in the midpiece.
- Chromatin condensation: DNA becomes tightly packed & inactive.
- Acrosome formation: Golgi surrounds nucleus to form acrosome.
- Testosterone-driven changes: Removes excess cytoplasm via Sertoli cells.
What is the result of spermiogenesis?
Mature but immotile spermatozoa.
What happens in spermiation?
Mature, immotile spermatozoa become motile spermatozoa.
4 phases of spermiogenesis
- Golgi Phase
- Cap Phase
- Acrosomal Phase
- Maturation Phase
What is the Golgi phase in spermiogenesis?
The phase where the Golgi apparatus organizes and contributes to acrosome formation.
What do small Golgi vesicles fuse to form?
Proacrosomic granules.
Where do proacrosomic granules remain?
On one side of the nucleus.
What happens to the centrioles during the Golgi phase?
They migrate to the opposite side of the nucleus.
What does continued Golgi vesicle fusion result in?
The formation of a large acrosomic vesicle with a dense acrosomic granule.
What is the function of the proximal centriole (PC)?
Forms the attachment point for the flagellum.
What is the function of the distal centriole (DC)?
Gives rise to the flagellum.
What happens during the cap phase of spermiogenesis?
The acrosomic vesicle forms a cap over the anterior portion of the nucleus.
Which organelles migrate during the cap phase?
The Golgi apparatus and other cytoplasmic organelles migrate toward the distal portion of the cell.
What structure begins to form during the cap phase?
The flagellum starts to form from the distal centriole.
What major change happens to the nucleus during the acrosomal phase?
The nucleus begins to elongate.
What structure forms from reorganized microtubules in the acrosomal phase?
The manchette.
What two structural components are formed during the acrosomal phase?
The neck and annulus.
What continues to develop during the acrosomal phase?
The flagellum.
What structure does the manchette form during the maturation phase?
The post-nuclear cap.
Where do mitochondria migrate, and what do they form?
They migrate to the posterior side of the nucleus and form a spiral assembly, defining the midpiece.
What is the function of the annulus in sperm maturation?
It forms the connection between the middle and principal pieces of the flagellum.
What is the function of the acrosome in sperm?
It contains hydrolytic enzymes that help break down the outer layers of the egg during fertilization (acrosomal reaction).
What part of the sperm head lies posterior to the acrosome?
The postnuclear cap.
Why is the plasma membrane important for sperm function?
It is crucial for cell survival and fertilization capability.
What is the function of the capitulum?
It serves as the neck that connects the flagellum to the head.
Which part of the sperm tail contains mitochondria, and why?
The middle piece contains mitochondria in a spiral arrangement to generate ATP for movement.
What is the main function of the principal piece of the flagellum?
It is the longest part and is essential for sperm motility.
What is the function of the terminal piece?
It contains the final part of the microtubule fibers that support the tail structure.
What is spermiation?
The release of mature spermatozoa from Sertoli cells into the lumen of the seminiferous tubule.
How are immotile spermatozoa transported to the epididymis?
By testicular fluid secreted by Sertoli cells and aided by peristaltic contractions.
Why is meiosis crucial in sperm production?
Because only ~1000-2000 stem cells migrate to the embryonic testes, continuous sperm production relies on meiosis.
What is oligospermia?
A condition where sperm concentration is <20 million sperm/mL, leading to decreased fertility.
How long can spermatozoa survive after ejaculation?
Approximately 80 hours.
How does female cervical mucus help sperm survival?
It maintains the metabolic requirements of spermatozoa.
What happens to sperm after entering the female reproductive tract?
They are rapidly separated from seminal plasma and resuspended in female genital fluid.
What is capacitation?
A process sperm undergo while traveling through the female reproductive tract, allowing them to fertilize the egg.
Why do only a few sperm reach the site of fertilization?
Most sperm are eliminated at selective barriers (cervix & uterotubal junction) or removed by phagocytosis.
testes produce what kind of cells
- Sperm (supported by Sertoli cells)
- Testosterone (Leydig cells)
What is the primary function of Sertoli cells?
They provide structural and metabolic support for developing sperm.
How do Sertoli cells protect spermatids from the immune system?
By maintaining the blood-testis barrier and using FAS-ligand to trigger apoptosis in T-cells.
What is the role of the blood-testis barrier?
t isolates developing sperm from the immune system to prevent an immune attack.
How do Sertoli cells assist in sperm maturation?
They phagocytose residual cytoplasm from developing sperm.
What is the function of androgen-binding protein (ABP)?
It concentrates testosterone near developing sperm to support spermatogenesis.
Which hormone secreted by Sertoli cells regulates the pituitary gland?
Inhibin, which helps control spermatogenesis by regulating FSH secretion.
GnRH
gonadotropin releasing
hormone secreted into portal vessels
FSH
follicle stimulating hormone
LH
luteinizing hormoneT
Testosterone
will travel to other target cells, resulting in development of secondary sex characteristics
How does testosterone regulate GnRH secretion?
Testosterone inhibits GnRH secretion from the hypothalamus.
What effect does testosterone have on the anterior pituitary?
It inhibits the anterior pituitary’s response to GnRH, reducing LH and FSH secretion.
Which hormone do Sertoli cells secrete to regulate FSH?
Sertoli cells secrete inhibin, which specifically inhibits FSH secretion from the anterior pituitary.
Does inhibin affect LH secretion?
No, inhibin only inhibits FSH secretion without affecting LH.
what cells is testosterone secreted from
Leydig cells
why is there an increased risk of infertility in males taking anabolic steroids
- mimic the effects of testosterone
- excess testosterone shuts down pathway
- testes stop producing sperm
- testes stop producing testosterone
- decreased libido and fertility
Role of nitric oxide in erection
- NO acts on vascular smooth muscle cell, activating guanylate cyclase, which catalyzes conversion of GTP to cGMP
- cGMP causes Ca2+ channels in vascular smooth muscle cell to close (cytoplasmic Ca2+
concentration decreases) - Vascular smooth muscle cell relaxes, resulting in vasodilation of penis & engorgement of erectile tissue
What triggers an erection?
Parasympathetic nerve-induced vasodilation of arterioles through smooth muscle relaxation.
What happens to blood flow during an erection?
Blood flows into the corpus cavernosum, compressing veins and reducing outflow, increasing intracavernosal pressure.
Which neurotransmitter mediates erection?
Nitric oxide (NO).
viagra mechanism of action
- Inhibits the
phosphodiesterase (PDE)
that catalyzes the
breakdown of cGMP - This increases the
availability of cGMP,
promoting erection
