Sperm and Fertility L16 Flashcards
Where does spermatogenesis (sperm production) take place?
In the basal compartment of the seminiferous tubules of the testes
Three phases to spermatogenesis
Mitotic division, meiotic division, cytodifferentiation
What happens when the mitotic divisions are complete?
The spermatogonia move between adjacent sertoli cells to the adluminal compartment of the seminiferous tubules.
Process of spermatogenesis (mitosis + meiosis)
Each of these primary spermatocytes starts with n-46. The primary spermatocytes undergo meiosis 1. The DNA content doubles - each of the spermatocytes still has 46 chromosomes. (Meiosis 1) The primary spermatocytes then divide to produce secondary spermatocytes.
Secondary spermatocytes have 23 chromosomes, each chromosome has two chromatids.
Secondary spermatocytes divide very rapidly - Meiosis II - to give four spermatids each with 23 chromosomes.
In the adluminal compartment the cells are called _________ __________________ - they undergo meiosis.
In the adluminal compartment the cells are called primary spermatocytes - they undergo meiosis.
Cytodifferentiation (spermiogenOsis)
Spermatids are still round cells. During spermiogenosis the round spermatids differentiate their shape and become spermatozoa (sperm). Sperm move into the lumen of the seminiferous tubules.
Structure and function of sperm
The round spermatids form a tail, a mid-piece, and a head. The mid-piece is packed with mitochondria to produce energy. The head contains the DNA and is covered by the acrosome - a compartment filled with enzymes that are required for egg penetration.
The excess cytoplasm of the spermatid is also lost into a structure called the residual body that is phagocytosed (eat and recycle) by the sertoli cells after the sperm leaves.
Leydig (interstitial) cell
Located in the connective tissue (interstitium) between the seminiferous tubules in the testes. Leydig cells play a crucial role in the male reproductive system by producing and secreting testosterone, the primary male sex hormone.
Summary of spermatogenesis
Spermatogonial stem cells (n=2)
■ Basement membrane of tubule
Spermatogonia (n=2)
■ divide by mitosis, basal compartment of the tubules
Primary spermatocytes (n=2)
■ divide by meiosis I, in adluminal compartment
Secondary spermatocytes – (n=1)
■ divide by meiosis II, two chromatids, in adluminal compartment
Spermatids (n=1)
■ cytodifferentiate, in adluminal compartment
Sperm (n=1)
■ move to lumen and exit the tubules
Hormonal control of spermatogenesis (spermatogonia do not develop into sperm without testosterone)
Sertoli cells
Cells found within the seminiferous tubules of the testes which help pre-sperm cells become sperm cells and produce androgen binding proteins (important to get androgens from tests to travel around the body to produce the secondary sexual characteristics as they are FAT and therefore bind to the androgen binding protein)
What happens with too much DHT? (Dihydrotestoterone)
Male pattern baldness
Secretion of inhibition
Sertoli cells produce and secrete the hormone inhibin, which provides feedback to the pituitary gland to regulate the production of FSH. This negative feedback mechanism helps control the rate of spermatogenesis.
Function of Kisspeptin
By binding to receptors on GnRH neurons in the hypothalamus, kisspeptin promotes the secretion of GnRH, which then stimulates the pituitary gland to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These hormones are essential for the development of the reproductive organs and the initiation of gametogenesis (sperm production in males and oocyte development in females).
Causes of male infertility
Reduced sperm count (>20 million/ml)
Also known as oligospermia
Or even no sperm azoospermia
Or the sperm may be immotile - cannot swim
In Vitro Fertilization (IVF)
The process begins with ovarian stimulation, where a woman is given hormone injections (typically FSH and LH) to stimulate the ovaries to produce multiple mature eggs, rather than the single egg that is normally released during a menstrual cycle.
Egg Retrieval:
Once the eggs are mature, they are retrieved from the ovaries using a minor surgical procedure called transvaginal ultrasound aspiration. This procedure is usually done under sedation or light anesthesia, and a needle is used to extract the eggs from the follicles in the ovaries.
Sperm Collection:
Sperm is collected from the male partner or a sperm donor. The sperm sample is then processed in the laboratory to select the healthiest and most motile sperm.
Fertilization:
The collected eggs and sperm are combined in a laboratory dish to facilitate fertilization. In some cases, a single sperm may be directly injected into an egg in a process called intracytoplasmic sperm injection (ICSI), particularly when there are issues with sperm quality or quantity.
Difference between IVF and ICSI
Parts of the male reproductive system
