L#31 - Adrenal glands, testes, and penis

Adrenal glands

  • The adrenal glands / suprarenal glands — are a pair of pyramid-shaped endocrine organs that sit on top of the kidneys

  • They are structurally and functionally 2 glands in a single organ

  • The outer adrenal cortex is 3 layers of glandular tissue that make and secrete at least 24 different hormones called corticosteroids

  • The inner adrenal medulla is nervous tissue, part of sympathetic nervous system, and produces the hormones epinephrine and norepinephrine

Adrenal cortex hormones

  • Corticosteroids are steroidal hormones (made from cholesterol) that are produced by the cortex

  • The zona glomerulosa produces mineralocorticoids (because they affect sodium, a mineral), mostly aldosterone. These hormones regulate electrolytes in extracellular fluids, raise blood Na+ and lower K+

Aldosterone — stimulates reabsorption of Na+ (and water, by osmosis) and secretion of K+ in the kidney distal convoluted tubules and collecting ducts. This increases blood volume and blood pressure

  • The zona fasciculata produces glucocorticoids (corticosteroids that help to regulate glucose)

  • Glucocorticoids, such as cortisol — are released in response to stress through adrenocorticotropic hormone and primarily cause gluconeogenesis, as well as the use of fats and amino acid by body cells

  • Cortisol used as medication is hydrocortisone. It is an anti-inflammatory and immunosuppressive drug to reduce allergic reactions such as anaphylaxis or angioedema (swelling of the dermis)

  • The zona reticularis produces gonadocorticoids (corticosteroids that target reproductive organs)

Gonadocorticoids — are inactive precursor steroid hormones or weak adrenal androgen steroids that are released into the blood, absorbed by the ovaries and testes, and then converted into sex hormones

  • The ovaries produce estrogen and progesterone as well as low levels of testosterone. The testes produce testosterone and low levels of estradiol — a form of estrogen

Adrenal medulla hormones

  • The adrenal medulla contains medullary chromaffin cells that synthesize the catecholamine hormones epinephrine and norepinephrine

  • Adrenal catecholamines produce short-term stress-mediated responses, increasing heart rate, respiratory rate, blood pressure and blood sugar

Reproductive systems

  • Biological sexes do not exist as 2 completely distinct categories of female and male

  • Because of evolution, most individuals have one set of reproductive organs

  • Sexual reproduction is easier if those organs are physically compatible w/ someone else’s reproductive organs

  • Secondary sex characteristics, hormone levels, chromosomes, organs and tissues can all develop and mature in myriad natural variations, that can not be easily classified as exclusively female or male

  • The primary sex organs (gonads) are ovaries and testes — they produce gametes (sex cells) which are ova and sperm

  • They also secrete steroid sex hormones, which are androgens from testes and estrogens and progesterone from ovaries

    • the development of secondary sex characteristics is stimulated by increased levels of these sex hormones

  • The accessory reproductive organs are the ducts, glands and external genitalia

People and diseases

  • Sometimes biomedical sciences focus on people and sometimes biomedical sciences focus on tissues and organs and diseases

    • If someone has a uterus, they are at risk of endometriosis, regardless of whether they are a man or women

    • If someone has a prostate, they are at risk of prostate cancer

  • Organs don’t define identities, but they affect our disease risks

The testes within the scrotum

  • The scrotum hangs outside the abdominopelvic cavity at the root of the penis and houses the testes. Since viable sperm can’t be produced at body temp, the scrotum provides an environment 3 degrees Celsius below the core body temp

  • The testes are a primary reproductive organ, producing both sperm and testosterone

  • within the seminiferous tubules of the testes are spermatogenic cells embedded in sustentocytes (support cells) called Sertoli cells

Testicular tissues

  • LH / Luteinizing hormone — stimulates Leydig cells (interstitial cells) in connective tissue around the seminiferous tubules to produce testosterone

  • FSH / Follicle-stimulating hormone — stimulates Sertoli cells to bind testosterone and keep hormone levels high near the spermatogenic cells

  • Testosterone — initiates spermatogenesis, causes ducts, glands and the penis to develop, and can induce male secondary sex characteristics. It uses direct gene activation to exert its effects

Reproductive ducts

  • Sperm pass from seminiferous tubules, through the rete testis, into the epididymis. These coiled tubes provide a place for immature sperm to develop until they are expelled during ejaculation

  • Immature sperm take 2-6 days to pass through the epididymis through fluids containing antimicrobial proteins and defensins

  • While in the epididymis, sperm gain the ability to swim

  • The ductus deferens / vas deferens — extends as part of the spermatic cord from the epididymis, through the inguinal canal, into the pelvic cavity, where it passes over the bladder, and into the ejaculatory duct, which pass through the prostate gland, to join the urethra

  • The urethra is the terminal portion of the testis-associated duct system and carries both urine and sperm (not at the same time) to the exterior environment

Testis-associated accessory glands

  • The seminal glands produce 60-70% of semen, through secretions that contain fructose (for sperm to make ATP), vitamin C (an antioxidant), a coagulating enzyme (to make semen gel-like), and prostaglandins (hormone-like signalling molecules that can facilitate sperm transport in the uterus)

  • The prostate gland produces 20-30% of semen. These secretions contain citrate (for sperm Ca2+), several enzymes, and prostate-specific antigen that liquefies semen to help sperm swim more easily. It also plays a role in sperm activation

Testis-associated accessory glands

  • The bulbo-urethral glands produce a clear mucous prior to ejaculation that neutralizes any acidic urine in the urethra

  • Semen is a milky, white, somewhat sticky mixture of sperm and accessory gland secretions that provides a transport medium for sperm, as well as performing supportive and protective roles for sperm within the uterine reproductive tract

The penis

  • The penis is a copulatory organ

  • The penis is made of an attached root and a free body that ends in an enlarged tip, the glans penis

  • The prepuce / foreskin, covers the penis and may be slipped back to form a cuff around the glans

    • Circumcision is surgery to remove the foreskin, often for cultural or religious reasons

Erection

  • Internally, the penis contains the urethra and 3 cylindrical bodies of erectile tissue: the corpus spongiosum surrounding the urethra and the paired corpora cavernosa

  • Erection occurs when nitric oxide causes dilation of penile arterioles, allowing blood to fill erectile tissues — the corpora cavernosa then compresses penile veins, reducing blood flow out of the penis

  • Ejaculation is the propulsion of semen triggered by the sympathetic nervous system