BIOS 131 Chap 27

Under the influence of androgens, the embryonic mesonephric duct develops into the male reproductive tract. Androgens are male sex hormones that play a crucial role in the development of male reproductive organs. The mesonephric duct, also known as the Wolffian duct, is a structure present in both males and females during embryonic development. However, under the influence of androgens, this duct differentiates into the male reproductive tract, including the epididymis, vas deferens, and seminal vesicles. This process is essential for the formation of the male reproductive system.

Spermatozoa obtain energy for locomotion from fructose in the semen. Fructose is a type of sugar that is present in the semen. It serves as a source of energy for the sperm cells, allowing them to swim and move towards the egg during fertilization. This energy supply is essential for the sperm's motility and ability to reach and penetrate the egg for successful fertilization.

Germ cells are the cells that give rise to gametes (sperm or eggs) and are genetically different from the rest of the body cells. Secondary spermatocytes are the cells that are formed after the first round of meiosis in spermatogenesis. These cells have undergone genetic recombination and are genetically different from the original germ cells. The blood-testis barrier is a specialized structure that protects germ cells from harmful substances and immune responses, ensuring their proper development into mature sperm. Therefore, secondary spermatocytes, being genetically different from the rest of the body cells, need to be protected by the blood-testis barrier.

The fibrous capsule that surrounds both the corpora cavernosa and the testes is known as the tunica albuginea. This protective layer provides structural support and helps maintain the shape and integrity of these organs. It also plays a role in regulating blood flow and pressure within the corpora cavernosa, which is important for achieving and maintaining an erection.

The correct answer is seminal vesicles. Seminal vesicles are a pair of glands that contribute to the production of semen. They secrete a fluid that makes up over half of the volume of semen. This fluid contains various substances, including fructose, prostaglandins, and enzymes, which provide nourishment and support for sperm. The seminal vesicles play an important role in fertility and reproduction.

The blood-testis barrier is formed by tight junctions between the sustentacular cells. These cells, also known as Sertoli cells, are found in the seminiferous tubules of the testes and provide support and nourishment to developing sperm cells. The tight junctions between sustentacular cells create a physical barrier that prevents harmful substances from entering the seminiferous tubules and interfering with sperm production. This barrier helps to maintain the optimal environment for sperm development and protects the developing sperm cells from potential damage.

The earliest haploid stage of spermatogenesis is the secondary spermatocyte. Spermatogenesis is the process of sperm cell development, which involves several stages. It begins with the division of spermatogonia (diploid cells) into primary spermatocytes. These primary spermatocytes then undergo the first meiotic division, resulting in the formation of secondary spermatocytes. Secondary spermatocytes are haploid cells, meaning they have half the number of chromosomes as the original diploid cells. Further divisions of secondary spermatocytes lead to the formation of spermatids, which eventually mature into sperm cells.

Erection of the penis occurs when nitric oxide causes the deep arteries to dilate. Nitric oxide is a signaling molecule that relaxes the smooth muscles in the walls of the deep arteries, allowing them to widen and increase blood flow to the penis. This increased blood flow is what causes an erection.

The acrosome is a specialized structure found in the head of a sperm cell. It contains enzymes that help the sperm penetrate the outer layer of the egg during fertilization. These enzymes break down the protective coating of the egg, allowing the sperm to enter and fertilize it. Therefore, the correct answer is acrosome.

The correct answer is "autonomic somatic cervical sexual nongenital abolished". This means that after a spinal cord injury at the cervical level, both autonomic (involuntary) and somatic (voluntary) reflexes related to sexual function are abolished. This includes the ability to have erections and ejaculate. However, it is important to note that sexual responses to non-genital stimuli and psychological factors can still occur.

Hemoglobin unloads less oxygen at lower temperatures than at higher ones, as shown by the oxyhemoglobin dissociation curve. Thus, it unloads less oxygen to the testes than elsewhere, and the sperm develops in a hypoxic environment. According to one theory, this hypoxia induces sperm to develop their unusually large mitochondria and preconditions them for vigor in the hypoxic environment of the female reproductive tract.

Antihypertensive medications lower blood pressure by dilating blood vessels, including those in the penis. This can lead to reduced blood flow to the erectile tissues of the penis, making it difficult to achieve or maintain an erection. Therefore, the medication could potentially cause erectile dysfunction or impotence in the patient.

If the corpus spongiosum becomes as engorged and rigid as the corpora cavernosa, it would compress the urethra and interfere with ejaculation. The corpus spongiosum surrounds the urethra and helps to keep it open during sexual arousal, allowing for the passage of semen during ejaculation. If it becomes too engorged and rigid, it can put pressure on the urethra, obstructing the flow of semen and interfering with the ejaculation process. Therefore, it is important for the corpus spongiosum to remain less engorged and rigid compared to the corpora cavernosa to ensure proper ejaculation.

Erection is caused by parasympathetic stimulation of the penile arteries. The parasympathetic nervous system is responsible for promoting relaxation and increasing blood flow to various parts of the body, including the penis. When the parasympathetic nerves are activated, they release a neurotransmitter called nitric oxide, which causes the smooth muscles in the penile arteries to relax. This relaxation allows for increased blood flow into the penis, leading to an erection. Therefore, the statement that erection is caused by parasympathetic stimulation of the penile arteries is true.

Luteinizing hormone (LH) is produced by the pituitary gland and plays a crucial role in the reproductive system. In males, LH stimulates the Leydig cells in the testes to produce and secrete testosterone, which is the primary male sex hormone. Therefore, it is correct to say that LH stimulates the testes to secrete testosterone.

Sperm are stored primarily in the epididymis prior to ejaculation. The epididymis is a coiled tube located on the back of each testicle. It serves as a site for sperm maturation and storage. Sperm produced in the testes enter the epididymis where they undergo a process of maturation and gain the ability to swim. When ejaculation occurs, the sperm are expelled from the epididymis into the vas deferens and then travel through the ejaculatory ducts to be released during sexual intercourse.

Sperm development requires a temperature that is lower than the core body temperature. The testicles, where sperm is produced, are located outside the body in the scrotum, which helps keep them at a lower temperature. If the testicles were inside the body, the higher core body temperature would inhibit sperm development. Therefore, it is true that sperm cannot develop at the core body temperature.

The male scrotum is homologous to the female labia majora because both structures are derived from the same embryonic tissue, the genital tubercle. During development, the genital tubercle can differentiate into either the scrotum in males or the labia majora in females. Both structures also serve similar functions in protecting and supporting the reproductive organs. Therefore, it is true that the male scrotum is homologous to the female labia majora.

The seminal vesicles are responsible for producing and secreting a significant portion of the fluid that makes up semen. They contribute about 70-80% of the seminal fluid volume, which provides nutrients and protection for sperm. The remaining components of semen, including sperm cells, are produced by other reproductive organs such as the testes and prostate gland. Therefore, it is true that most of the semen is produced by the seminal vesicles.

Sperm are stored in the epididymis.

The corpora cavernosa are erectile tissues located within the penis that become engorged with blood during sexual arousal, causing an erection. These tissues are attached to the pubic arch by crura, which are elongated structures that anchor the penis to the pelvic bones. This attachment helps support the penis and maintain its position during sexual activity. The other options listed, such as the corpus spongiosum, perineal membrane, bulbospongiosus, and ischiocavernosus, are not directly involved in the attachment of the penis to the pubic arch.

Female development results from a low testosterone level, not from estrogen.

There is no such phenomenon as male menopause, and sperm production normally continues throughout old age.

The ductus deferens, also known as the vas deferens, is a tube that carries sperm from the testes to the urethra. It develops from the mesonephric duct, which is a structure that forms during embryonic development in males. The mesonephric duct plays a crucial role in the development of the male reproductive system, including the formation of the ductus deferens. Therefore, the correct answer is mesonephric duct.

In meiosis, sister chromatids separate from each other during anaphase II. During this phase, the centromeres holding the sister chromatids together divide, allowing them to move to opposite poles of the cell. This ensures that each daughter cell receives one copy of each chromosome. Anaphase II is the final stage of meiosis II, following the separation of homologous chromosomes in anaphase I.

Type B spermatogonium is the correct answer because it is the stage in spermatogenesis where four spermatozoa arise from each primordial germ cell. Spermatogenesis is the process of sperm cell development, and it begins with the differentiation of spermatogonia. Type B spermatogonia undergo mitotic division to produce primary spermatocytes, which then undergo meiosis to form secondary spermatocytes. These secondary spermatocytes further divide to form spermatids, which eventually mature into spermatozoa. Therefore, the correct stage in which four spermatozoa arise from each primordial germ cell is type B spermatogonium.

The pampiniform plexus prevents the testes from overheating.

Inhibin is the correct answer because it is a hormone secreted by the sustentacular cells in the testes. Its main function is to inhibit the secretion of follicle-stimulating hormone (FSH) from the anterior pituitary gland. By inhibiting FSH, inhibin helps to regulate sperm production without affecting testosterone secretion. This allows for a reduction in sperm production while maintaining normal levels of testosterone in the body.

Gonadotropin-releasing hormone (GnRH) is the first hormone secreted at the onset of puberty. GnRH is released by the hypothalamus and stimulates the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the pituitary gland. FSH and LH then act on the gonads (ovaries in females and testes in males) to stimulate the production of sex hormones such as estrogen and testosterone, which are responsible for the physical changes of puberty. Therefore, GnRH plays a crucial role in initiating the cascade of hormonal changes that occur during puberty.

Only the testis are the primary sex organs.

Seminogelin is the protein responsible for clotting and causing the stickiness of semen. It is produced by the seminal vesicles and helps in the formation of a gel-like substance that aids in sperm retention and transportation within the female reproductive tract. Prostaglandin, fibrin, phosphodiesterase, and serine protease are not directly involved in the clotting and stickiness of semen.

The correct answer is trabecular. The trabecular muscles are responsible for forcing blood out of the penile lacunae through contraction. These muscles help in maintaining and regulating blood flow within the penis during sexual arousal and ejaculation.

The expulsion of semen occurs when the bulbospongiosus muscle is stimulated by somatic efferent neurons. These neurons carry signals from the central nervous system to the muscle, causing it to contract and expel semen. Somatic efferent neurons are responsible for voluntary movements, and in this case, they play a crucial role in the control of ejaculation.

The pampiniform plexus is a network of veins located in the spermatic cord. Its main function is to regulate the temperature of the testes by cooling them down. This is important because the testes need to be kept at a slightly lower temperature than the rest of the body in order to produce healthy sperm. The pampiniform plexus achieves this by allowing cool blood from the surrounding tissues to absorb heat from the testicular arteries, thus cooling down the blood supply to the testes.

Testosterone may be considered both an endocrine and a paracrine secretion of the testes because it acts as a hormone when it is secreted into the bloodstream and affects organs throughout the body. It also acts as a paracrine secretion when it diffuses from the interstitial cells to the nearby seminiferous tubules and stimulates spermatogenesis.

Spermatogonia have the same diploid genome as the somatic cells of the body and therefore do not stimulate an immune response. However, primary spermatocytes must migrate to the other side of the blood-testis barrier before they undergo meiosis I because meiosis I renders the cells genetically different from the somatic cells and thus capable of stimulating an immune attack if they are exposed to the blood.

The answer suggests that blood capillaries would not be expected to be found in the walls of the seminiferous tubules because the presence of blood capillaries would allow T cells or antibodies from the circulatory system to attack the germ cells, leading to germ sterility. Therefore, the absence of blood capillaries in the tubule walls helps to maintain the blood-testis barrier and protect the germ cells from the immune system.

Castration is followed by a rise in FSH and LH levels because of the sudden absence of negative feedback inhibition of the pituitary by the gonads. When the gonads are removed, there is no longer production of sex hormones such as estrogen or testosterone. These hormones normally provide negative feedback to the pituitary gland, inhibiting the release of FSH and LH. Without this feedback, FSH and LH levels increase.