Reproduction 2 Flashcards
Where does spermatogenesis occur?
Across the Sertoli cells until the lumen of the Seminiferous tubule
Where are the Spermatogonia and Spermatozoa located?
Spermatogonia (early stage) are located outside of the tubule, as we go inside the sperm cells differentiate more -> Spermatozoa in the lumen, where it can enter Epididymis later
Sequence of differentiation:
Spermatogonia -> Mitosis: 1x stays spermatogonium and 1x becomes primary spermatocytes -> Meiosis: secondary spermatocytes with haploid chromosome set -> 2nd meiosis: 4 spermatids with only 1 chromatid -> differentiation to spermatozoa in the lumen
How is the flagellum able to move?
With ATP through oxidative phosphorylation in the mitochondria in the midpiece of the sperm
Where is the nucleus located in the sperm cell?
In the head, the sperm needs to be as light weighted as possible
How are sperm cells able to penetrate the egg cell?
Acrosomes = pocket of enzymes that helps to penetrate the coatings of the egg cell
How does the differentiating sperm cell (primary spermatocytes) migrate to the lumen?
The tight junctions disassemble -> primary spermatocytes passes -> and will resemble behind the primary spermatocytes
As the sperm cells differentiate they are perceived as foreign molecules (from diploid to haploid) -> Why are these cells not attacked by the immune system?
Because from the stage: secondary spermatocytes they are protected by the blood-testis barrier, and are not exposed to the blood and the immune cells
What are Gonadotropins?
sexual hormones. FSH and LH
What are the functions of Sertoli cells?
provide protection to developing sperm cells -> blood-testis-barrier
-provide fluid for movement, ATP, and nutrients
-target for testosterone and FSH for spermatogenesis
-synthesize inhibin -> together with testosterone negative feedback to gonadotropin release: inhibit pituitary FSH
How is the release of Gonadotropins stimulated?
Pulsatile secretion (every 90 min) of GnRH from hypothalamus -> travels through hypophyseal portal system of the anterior pituitary where gonadotropins FSH and LH are secreted
What is the target of LH and FSH?
LH targets Leydig cells -> produces testosterone
FSH targets Sertoli cells together with testosterone -> and stimulates spermatogenesis
FSH targets Sertoli cells to produce inhibin -> negative feedback on anterior pituitary to produce fewer gonadotropins
-Testosterone provide negative feedback on anterior pituitary on LH production
Functions of testosterone?
-Spermatogenesis in Sertoli cells together with FSH
-stimulates the release of EPO (more RBCs)
-secondary sexual characteristics: sex organ development, hair growth, body hair, skin darkening, thickening, acne (sebum increased), lower vocal tone, muscle and bone mass, sex drive
To which molecule is testosterone converted with 5-a-reductase?
Dihydrotestosterone
Where is Dihydrotestosterone present and how can it be reduced?
In the skin and prostate, reduced by blocking 5-a-reductase (FINASTERIDE)
What types of erectile tissues are present in the penis?
-Corpora cavernosa: paired dorsal erectile bodies -> those tissues are provided with more blood during erection through vasodilation
-Corpus spongiosum (also provided with more blood): surrounds the urethra and expands to form the opening of the penis
Which neurons and neurotransmitters are involved in erection?
Parasympathetic NS (usually release ACh -> muscarinic): release nitric oxide (vasodilator) + decrease of sympathetic
Why is the activity of sympathetic neurons decreased during erection?
bc it would release NE -> alpha receptor, and cause vasoconstriction - we don´t want that during erection
How is erection maintained during erection?
Compression of veins
How does ejaculation occur?
By sympathetic activity: semen stored in Epididymis -> Vas deferens -> ejaculation duct -> Urethra
The semen is expelled from the urethra by contraction of urethra smooth muscle
How is the Ovary (carrying oocytes) connected with Fallopian tube?
-Through ovarian ligaments at one side
-Fimbria = fringe -> Cilia extensions beat in the direction of the Fallopian tube to attract the oocytes
Structure of the uterine wall:
Outside to inside:
-Perimetrium surrounding the muscular wall (Myometrium)
-Myometrium: smooth muscles responsible for oxytocin causing uterine contractions in process of birth
-Endometrium: thickness varies, under hormonal control
How is Oogenesis different from Spermatogenesis?
Oogenesis occurs early during prenatal development, millions of oogonia are formed through mitosis -> and many are degraded -> No new oogonia are built and degenerate with age - only 400-500 germ cells are released from ovary
How does Oogenia differentiation proceed?
It differentiates into primary oocytes through meiosis 1 during prenatal development and they halt in meiosis 1 metaphase until puberty
What happens in puberty that stimulates Oogenesis
Pulsatile release of GnRH -> release of FSH and LH from anterior pituitary -> FSH and LH targets ovaries -> release of estrogen -> activation of primary oocytes to complete meiosis 1
What results from meiosis 1?
Two haploid cells with 2 chromatids per chromosome:
1. The secondary oocyte (haploid) - “quality cell”
2. The first polar body (haploid), bc all necessary things are put together in one cell bc it will form the very first cell of the developing human
What happens with the secondary oocyte after meiosis 1?
It starts with meiosis 2 and it halts again -> is now ovulated: the Fimbria (cilia) is trying to pull (by beating) it into Fallopian tube
What happens if the Oocyte is penetrated?
Completion of meiosis 2 and formation of one large Ovum (functional gamete) with only 1 chromatid -> loss of the second polar body (with the other duplicated DNA)
In what structures do oocytes exist in the ovary?
Follicles
-Primordial follicles: single layer of squamous epithelial cells
-Primary follicles: one or more cuboidal-shaped cells
-Secondary follicle (pre-antrum): has pockets with fluid (antrum)
-Tertiary and mature follicle: Follicle gets bigger and volume of antrum increases
How many follicles start and finish development with each menstrual cycle?
6-20 preantral and early antral follicles begin to develop
after 1 week only 1 becomes dominant throughout the cycle (surrounded by granular cells - corona radiata)
What happens with the ruptured follicle after ovulation?
After ovulation, the oocyte leaves the Ovary (some of the granular cells comes with it)
-the raptured follicle becomes the corpus luteum
