Male Reproductive System Physiology Flashcards
What are the two cell types in the epithelial lining of the seminiferous tubules?
Sustentacular/Sertoli Cells and developing spermatozoa and their precursor germ cells
What type of shape do the seminiferous tubules have and why?
Irregular coiled shape because they encircle developing germ cells
Where do the sustentacular cells extend?
From the base of the epithelium to the lumen of the seminiferous tubules
What do sustentacular cells do?
Secrete a fluid that covers the developing germ cells and assists with the transport of spermatozoa from the seminiferous tubules to the rete testis after they’re released from the sustentacular cells
What is one component of the fluid released from sustentacular cells and what does it do?
Androgen-binding protein which transports androgens from where they are made in the testis to the epididymis, where they are needed for spermatozoa to mature
Where are Interstitial/Leydig cells found and what do they do?
They are found in the connective tissue between seminiferous tubules and secrete testosterone, which is the main androgen originating from the testicles
Why is the composition of fluid between sustentacular cells and typical interstitial fluid different?
There is a selectively permeable blood-testis barrier between the sustentacular fluids and the fluids outside the seminiferous tubules
What contributes to the barrier between sustentacular fluid and typical fluid?
Cell junctions between adjacent sustentacular cells and between between myoid cells that surround the tubules
What effect does the barrier between sustentacular fluid and typical fluid cause?
The concentrations of cellular secretions, like androgens and androgen-binding proteins, in the lumen of the seminiferous tubules are higher than in typical fluid because the barrier sequesters the types of fluids
What is spermatogenesis?
The term for all processes involved in formation of mature male gametes from undifferentiated germ cells
What does spermatogenesis include in terms of meiosis and mitosis?
There are several mitotic cell divisions, followed by two meiotic cell divisions. During meiosis, the chromosome number is reduced from diploid to haploid
What is the process of mitotic and meiotic cell divisions during spermatogenesis called?
Spermatocytogenesis
Some cells don’t enter spermatogenesis after mitosis, what happens to them?
Remain at the base of the epithelium to maintain the supply of stem cells
What does meiosis entail and when does it occur?
It entails two cell divisions and only occurs during the development of gametes in the testis and ovary
Before meiosis, how does DNA replicate during mitosis?
Very similar to mitotic cell division: it results in chromosomes that consist of two identical chromatids
What happens to chromosomes when preparing for meiosis?
Homologous chromosomes pair up along the middle of the cell
What are homologous chromosomes?
Similar chromosomes of a typical pair, each of which was contributed by one of the parent animals
How many chromosomes from a homologous pair moves into a daughter cell?
One of each homologous pair
How are chromosomes of homologous pairs distributed to daughter cells?
Randomly
What provides genetic variation among offspring?
Mixing homologous pairs
Before the first meiotic division, what type of cell is it, and how many chromosomes and chromatids does it have?
It is a diploid cell with 4 chromosomes (diploid = 2 pairs) and 8 chromatids (2 chromatids per chromosome)
After the first meiotic division, what type of cell is each daughter cell, and how many chromosomes and chromatids does the daughter cell have?
It is a haploid cell, with 2 chromosomes (haploid = 1 pair) and 4 chromatids
After the second meiotic division, what type of cell is each daughter cell and how many chromosomes and chromatids does it have?
Each daughter cell is a haploid cell, with no full chromosomes, but 2 chromatids
How many of the daughter cells from meiosis contain an X chromosome and how many daughter cells contain a Y chromosome?
Two daughter cells have an X chromosome and two daughter cells have a Y chromosome
What is the gene combination for a male and female offspring?
Male = XY
Female = XX
What type of chromosome does the ovum contain?
An X chromosome
In avians, what type of chromosome does the male daughter cell contain?
All sperm cells contain a Z chromosome
In avians, what type of chromosome does the female ovum contain?
The ovum can contain wither a W or Z chromosome, so the ovum determines sex in avians
What is the difference in shape among early and fully formed spermatids?
Spermatids are round, immobile cells when first produced, but are mobile and have a head and a tail when fully formed
What does the head of the spermatid consist of?
The nucleus, which has condensed genetic material, and an acrosome, which is a membranous sac directly below the plasma membrane at the tip of the head and extends over the nucleus
What does the tail of the spermatid consist of?
A central core of microtubules and filaments that provide motility
What is in the middle piece of the tail of the spermatid?
A dense collection of mitochondria that provide energy for motility
What is within the acrosome?
Hydrolytic (reacts with water) enzymes like acrosin and hyaluronidase
What do some of the enzymes in the acrosome do?
They are released during fertilization to help the fusion of male and female gametes
What is the release of enzymes from the acrosome during fertilization called?
The acrosome reaction
What is the starting place for fertilization to occur?
The acrosome reaction
What does the conversion of the round spermatid to the elongated spermatozoon require?
Reshaping of the original spermatid, synthesis and packaging of acrosomal enzymes, organization of microtubules, and elimination of excess cytoplasm and cell mebrane
How do the sustentacular cells assist with the conversion of the spermatid shape?
They phagocytose bodies of excess cytoplasm and membrane after fully formed spermatozoa have been released
What is the average length of spermatogenesis in farm animals?
Around 2 months
How do testicular size and sperm production relate to animals that are seasonal breeders?
Both testicular size and sperm production increase during breeding season
Where do fully formed spermatozoa pass through after being released from the seminiferous tubules?
They pass through the rete testis into the epididymis
The epididymis is the major site of what?
Spermatozoa storage
Where is most spermatozoa contained within each epididymis?
Tail
What is the structure of spermatozoa entering the head of the epididymis?
They are immotile and incapable of fertilization since their tail hasn’t been fully formed yet
When do spermatozoa acquire the capacity for motility and fertilization?
During their passage through the epididymis
What do the functional changes in spermatozoa that occur during their passage through the epididymis depend on?
They depend on epididymal secretions and the presence of male sex steroids, testosterone, dihydrotestosterone in the epididymal fluids
What does semen consist of?
Spermatozoa suspended in fluid secretions of the male accessory sex organs
What is the fluid portion of semen called and what does it do?
It’s called seminal plasma and it transports the spermatozoa
What substances are included in the fluid part of the semen?
Electrolytes, fructose, citric acid, and sorbitol
What is the function of the substances in the seminal plasma?
They provide a favorable environment that allows sperm to survive and creates an environment in the female that supports semen
What is the function of fructose in the seminal plasma?
It is a potential source of energy for the spermatozoa
What are the characteristics of semen that are evaluated and appear to have correlation with potential fertility?
Motility characteristics, morphologic shape, and concentration of spermatozoa per mL of semen
What needs to be added to semen to divide the semen sample into breeding doses and freeze it for long term storage?
Cryoprotectants to increase the volume and protect the spermatozoa
Different species’ semen responds differently to the freezing process, what does this imply about the spermatozoa from different species?
The spermatozoa have unique metabolic and/or structural differences depending on species
What type of hormones are follicle-stimulating hormone (FSH) and luteinizing hormone (LH)?
Glycoprotein hormones
Where do follicle-stimulating hormone (FSH) and luteinizing hormone (LH) originate from?
Adenohypophysis/Anterior pituitary gland
What are the primary endocrine regulators of testicular function?
Follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
Why are FSH and LH considered gonadotropins?
Because their overall effect is to stimulate testicular function
What does FSH act on?
Germ cells in the seminiferous tubules and sustentacular cells
What is the function of FSH acting on sustentacular cells?
Supports the development of spermatozoa
What does LH act on?
Testicular interstitial cells
What is the function of LH acting on interstitial cells?
Promotes the secretion of androgens, mainly testosterone, which is necessary to complete spermatogenesis
What hormone do the sustentacular cells produce when FSH binds to them?
Inhibin
What hormone do the interstitial cells produce when LH binds to them?
Testosterone
Where is gonadotropin-releasing hormone (GnRH) released from?
Hypothalamus
What is the function of gonadotropin-releasing hormone (GnRH)?
To stimulate the release of FSH and LH from the gonadotropes of the adenohypophysis/anterior pituitary gland
What regulates gonadotropin-releasing hormone (GnRH)?
Negative feedback to the hypothalamus, provided by the testosterone produced by the LH stimulating the interstitial cells
How is LH regulated?
By stopping the release of gonadotropin-releasing hormone (GnRH).
Testosterone also has direct effects on the adenohypophysis/anterior pituitary gland that directly suppresses LH release
How is FSH regulated?
By stopping the release of gonadotropin-releasing hormone (GnRH)
Inhibin also has a negative feedback effect on the adenohypophysis/anterior pituitary gland that suppresses FSH release
What type of hormone is testosterone and what does it do?
Testosterone is a steroid hormone that enters a target cell to exert effects
What happens to testosterone inside target cells?
It is converted to dihydrotestosterone, which binds to intracellular receptors
Besides maturation of spermatozoa, what is the function of testosterone?
It promotes development and function of male accessory sex organs, causes development of secondary sex characteristics, and promotes male sexual behavior
What is libido?
Sex drive
