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A negative feedback loop predominantly controls the synthesis and secretion of both FSH and LH. Low blood concentrations of testosterone stimulate the hypothalamic release of GnRH. GnRH then stimulates the anterior pituitary to secrete LH into the bloodstream. In the testis, LH binds to LH receptors on Leydig cells and stimulates the release of testosterone. When concentrations of testosterone in the blood reach a critical threshold, testosterone itself will bind to androgen receptors on both the hypothalamus and the anterior pituitary, inhibiting the synthesis and secretion of GnRH and LH, respectively. When the blood concentrations of testosterone once again decline, testosterone no longer interacts with the receptors to the same degree and GnRH and LH are once again secreted, stimulating more testosterone production. This same process occurs with FSH and inhibin to control spermatogenesis.

Aging and the… feature

Male reproductive system

Declines in Leydig cell activity can occur in men beginning at 40 to 50 years of age. The resulting reduction in circulating testosterone concentrations can lead to symptoms of andropause, also known as male menopause. While the reduction in sex steroids in men is akin to female menopause, there is no clear sign—such as a lack of a menstrual period—to denote the initiation of andropause. Instead, men report feelings of fatigue, reduced muscle mass, depression, anxiety, irritability, loss of libido, and insomnia. A reduction in spermatogenesis resulting in lowered fertility is also reported, and sexual dysfunction can also be associated with andropausal symptoms.

Whereas some researchers believe that certain aspects of andropause are difficult to tease apart from aging in general, testosterone replacement is sometimes prescribed to alleviate some symptoms. Recent studies have shown a benefit from androgen replacement therapy on the new onset of depression in elderly men; however, other studies caution against testosterone replacement for long-term treatment of andropause symptoms, showing that high doses can sharply increase the risk of both heart disease and prostate cancer.

Chapter review

Gametes are the reproductive cells that combine to form offspring. Organs called gonads produce the gametes, along with the hormones that regulate human reproduction. The male gametes are called sperm. Spermatogenesis, the production of sperm, occurs within the seminiferous tubules that make up most of the testis. The scrotum is the muscular sac that holds the testes outside of the body cavity.

Spermatogenesis begins with mitotic division of spermatogonia (stem cells) to produce primary spermatocytes that undergo the two divisions of meiosis to become secondary spermatocytes, then the haploid spermatids. During spermiogenesis, spermatids are transformed into spermatozoa (formed sperm). Upon release from the seminiferous tubules, sperm are moved to the epididymis where they continue to mature. During ejaculation, sperm exit the epididymis through the ductus deferens, a duct in the spermatic cord that leaves the scrotum. The ampulla of the ductus deferens meets the seminal vesicle, a gland that contributes fructose and proteins, at the ejaculatory duct. The fluid continues through the prostatic urethra, where secretions from the prostate are added to form semen. These secretions help the sperm to travel through the urethra and into the female reproductive tract. Secretions from the bulbourethral glands protect sperm and cleanse and lubricate the penile (spongy) urethra.

The penis is the male organ of copulation. Columns of erectile tissue called the corpora cavernosa and corpus spongiosum fill with blood when sexual arousal activates vasodilatation in the blood vessels of the penis. Testosterone regulates and maintains the sex organs and sex drive, and induces the physical changes of puberty. Interplay between the testes and the endocrine system precisely control the production of testosterone with a negative feedback loop.

Watch this video to learn about vasectomy. As described in this video, a vasectomy is a procedure in which a small section of the ductus (vas) deferens is removed from the scrotum. This interrupts the path taken by sperm through the ductus deferens. If sperm do not exit through the vas, either because the man has had a vasectomy or has not ejaculated, in what region of the testis do they remain?

Sperm remain in the epididymis until they degenerate.

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Watch this video to explore the structures of the male reproductive system and the path of sperm that starts in the testes and ends as the sperm leave the penis through the urethra. Where are sperm deposited after they leave the ejaculatory duct?

Sperm enter the prostate.

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Questions & Answers

There was this time when the teacher is explaining about something that involves calculating.When the teacher calculate that (2×4)-(1×-3)=11.I was confused and think that the answer is wrong, so I asked the teacher.Then,I realized I calculate wrongly and then my head feels hot. Why?
Dicky Reply
I mean... (2 x 4)- (1 x -3) = 11
Dicky
But since I don't really care about it. My head slowly goes back to normal.
Dicky
blood is unique it is the only flueid tissue in the body
yeh
Ayoub
this is fascinating
mery
for real
Musa
what is blood
sujon Reply
lol. the red substance in your body. that circulates food nutrients and oxygen
Nii
Blood is composed of plasma and formed elements. The plasma is about 55% of blood and is about 80-90% water usually. The other 20-10% accounts for solutes such as ions, nutrients, gases, and hormones.
Carmelo
Blood is a fluid type of connective tissue and it's formed elements (cells) include RBC, WBC, and plalets.
Carmelo
what is sasamoid bone?
hafeez Reply
how many types of bone on the base of shape
hafeez
5
Husna
i want join the conversation
juwar Reply
Alright
Haya
feel free to do so
Vida
where are you from ?
Haya
hi what's up
Mar
well hello
emad
Im from kashmir,but I'm studying in punjab
Aabid
Hello
Aabid
I'm studying pharmacy at JUST University in jordan
emad
so am i emad 😅
shereen
afg
Ayoub
I am Javed Ali
Javedali
hello i am hafeez from gilgit
hafeez
explain the mechanism(release and control) of hormonal interplay for fluid and electrolyte.
Cassie Reply
There are three main ways in which hormones may be released. Humoral stimulus - occurs when their is an inbalance in electrolytes in the body. Neural stimulus - occurs when autonomic nerve fibers stimulate glands to release hormones.
Carmelo
Hormonal stimulus - occurs when a hormone causes another hormone to be released from another gland.
Carmelo
what are the main pumps found in the cell membrane
pauline Reply
calcium
Schmidt
sodium potassium pump
Husna
Differences between ligaments and catilage
joy Reply
differences between catilage and ligaments
joy
Both are different types of connective tissues. Second difference is that cartilage contains chondroblasts rather than fibroblasts. Their is also slight differences on their extracrullar matrix. For ex, cartilages tend to contain more collagen than tendons and ligaments.
Carmelo
Both types of connective tissue also function differently. Ligaments connect bone to bone, while cartilage have a variety of function like cushioning bones and giving structural support like on the nose and ears.
Carmelo
explain the causes of the refractory period of a nerve fiber
Sophia Reply
Refractory period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation. Brief pause in stimulus or excitation.
Nii
To add on, the brief pause is produced because of the event of establishing a resting membrane potential that needs to be produced before depolarization (another action potential) can occur again.
Carmelo
The refractory period also gives a chance for neurotransmitters to be replenished on the axon terminal.
Carmelo
what is hypoxia
Akas Reply
I guess it's low supply the oxygen to the tissues
famuyiwa
yup
Natalie
A condition in which tissues (especially the blood) are deprived of an adequate supply of oxygen
Panthera
hanifa pia uko hapa
Panthera
Hypoxia is the lack of oxygen concentration in the blood. Therefore, tissues will receive a low concentration of oxygen. Usually our bodies respond to Hypoxia by stimulating erythropoiesis in red bone marrow.
Carmelo
hypoxia is the lack of oxygen in blood absolutely.
hafeez
hypoxia: is a condition in wich the concentration of oxygen goes down in tissue or all over the body but the low concentration of oxygen in blood is called hypoxiemia.
Ayoub
where is present Glenoid Cavity ?
A- Reply
what is the muscular tissue
Md Reply
muscular tissue is a type of tissue that provide to help in cotraction to aur body.
A-
What's the difference in epithelial, connective, muscular and muscle tissue
Gifty
and it's similarities
Gifty
what is limb bone
Akshu Reply
this are bone attaching or joining to the axial bone.axial bone including skull,vertebrate and ribcage
Eliasi
how many bones make up the skull?
Matthew
22 bones
Husna
22bones
Bhanu
where is present Glenoid cavity ?
A-
how many bone in skull
Md
almost there are 8 bones in skull
hafeez
Explain the stages of mitosis and cell division
Bella Reply
Bella, this is a very long process to detail by text. However, to keep it brief, mitosis has four phases in order: prophase, metaphase, anaphase, and telophase which sometimes followed by cytokinesis. Note that some cells do not always do the cytokinesis phase.
Carmelo
As a result, some of the cells in the body are multinuclear (osteoclasts for ex).
Carmelo
explain further
Nana
difference between mitosis and meosis
Nana
In mitosis, two genetically exact daughter cells (somatic cells) are produced and they are diploid. In meiosis, four genetically unique cells (gametes) are produced and they are haploid.
Carmelo
Meiosis only occurs in reproductive organs. Mitosis is a type of asexual reproduction and is involved in tissue growth and regeneration(repair).
Carmelo
mitosis > Diploid to Diploid meiosis > Diploid to Haploid
Carmelo
systems of human body
Udezue Reply

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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