Sex Hormones & Cycling

What does the endocrine system link?

links the brain to organs that control body metabolism, growth and development, and reproduction

In which follicle will the granulosa cells start producing receptors for LH?

preovulatory so it can receive the LH signals to ovulate and push it’s ovum out.

What is the feedback loop for testes?

When there is low estrogen levels….

acts as a negative feedback loop and keeps GNRH, and LH and FSH LOW

When there are high estrogen levels….

acts as a positive feedback loop and will shift to up regulate keeps GNRH, and LH and FSH HIGH

• This mechanism is how we can get that peak that signals ovulation

What causes the LH surge that drives the preovulatory to ovulation

High blood levels of estradiol for 48 hours secreted by the developing gransoula that switch the negative feedback to postive,

What is the main mode of communication in the endocrine system?

•is via hormones

What are hormones?

are chemical messengers that are released into the bloodstream or tissue fluid affecting target cells some distance away

What are the three basic categories of hormones?

1) steroids

2) peptides

3) monoamines

What are steroids involves with and what are the two sources?

•Involved in Stress and Reproduction

•Come from two main sources in the body

–Testes/Ovaries

–Adrenal Cortex

In what form does steroid hormones enter the body?

•Come into the body as Cholesterol (27-C)

•Fat Soluble (dissolve in fats)

What can steroid hormones pass and where do they bind the corresponding receptors?

•Easily pass the blood-brain barrier, pass from mother to fetus, excretions

Receptors: found within the cells

What are peptide hormones two sources?

• Major Sources

  –Hypothalamus

  –Pituitary

• Tend to be larger molecules

How fast do peptide molecules break apart and what are the soluble in?

They are more fragile, break up within second.

They are also water soluble which means the action is much shorter

Where are peptide receptors found?

• found in the plasma membrane

What are the three categories of SEX STEROID (fat) hormones?

• lipid molecules derived from cholesterol

1. Androgens

2. Estrogens

3. Progestins

In a general sense explain the order of cholesterol → up to testerone molecules

Cholesterol - 4 enzymatic steps→ Progesterone - 3 enzymatic steps→ Testosterone

what happens during the enzymatic steps during the formation of cholesterol → up to testerone molecules and how can we tell?

Undergoes cleavage, which allows it to break down into SMALLER numbers of carbon

What are the two directions that testerone can enter based on the enzymes present?

Testosterone -aromatase→ Estradiol-17β

Testosterone -5α-reductase→ 5α-dihydrotestosterone (DHT)

What is the amount of carbons cholesterol have?

27-C

What is the amount of carbons progestins have?

21-C

What is the amount of carbons androgens have?

19-C

What is the amount of carbons estrogens have?

18-C

What is the amount of carbons corticoids have?

21-C

Write the order of steroids in decreasing Carbons starting with 27-C cholesterol to 21-C corticoids, write out all carbons

What are the two groups of 21-C steroids, and the sub chromosomes for each?

Progestins= progesterone or pregnenolone

Corticoids= mineralocorticoids (aldosterone) or glucocorticoids (cortisol/corticosterone)

What is progesterone?

A form of Progestins (steroid)

Responsible for: pregnancy, mating behaviour (tested on lab animals)

What is pregnenlone?

A form of Progestins (steroid)

Responsible for: a important precursor to progesterone but also for estrogens and androgens

Draw the hormonal loop for the follicular phase?

Draw the hormonal loop for the luteal phase?

What are mineralocorticoids?

A form of corticoids (steroid)

Responsible for: essential for metabolism which is needed for healthy body

ex) aldosterone

What are glucoocorticoids?

A form of corticoids (steroid)

Responsible for: stress

ex) cortisol (for humans), corticosterone (animals in lab)

Explain two major examples of androgens?

19-C steroids

1) DHT

2) Testosterone

What is DHT responsible for?

• Critical function in the sexual development of XY individuals, beginning early in prenatal life (begins in utero)

•  role of DHT differs as the person progresses through the different stages of development

• various impacts on their physiology during childhood, puberty, and even throughout adult life.

Explain two major examples of estrogens?

18-C steroids

• 17β-estradiol, estrone, estriol

What is the weakest form of estrogen, when is it higher, and what does it do?

• Estrone is the weakest type of estrogen

• Typically higher after menopause

• it’s typically higher after menopause.

When is estriol the highest, and what does it do?

• Estriol levels rise throughout pregnancy, helping to keep the uterus and unborn baby healthy.

• The levels are at their highest right before childbirth.

• They help prepare the body for labor and delivery.

Why is it hard to measure testosterone cycles in men?

They constantly fluctuate which can make determining a healthy range difficult unless it’s a extremely high or a very low low.

Explain the overall layout of the developing ovarian follicle?

A developing follicle requires supports which is usually surrounded by first granulosa cells and then the thecal cells.

• More follicles more testerone

What is the order of hormone production from cholesterol into the blood to he hromonesx secreted inside of the oocyte?

1. Cholesterol from blood enters thecal cell → Progestins → Androgens

2. As androgen it enters the granulosa cells and gets converted into estradiol by aromatase

3. Secreted into developing ovarian follicle

What other hormones do granulosa cells release?

Inhibin and Activin

What is inhibin and activin responsible for?

Important in suppressing and enhancing, respectively, hormone secretion from the hypothalamus and pituitary gland

What hormones does anterior pituitary release?

GH, TSH, ACTH, FSH, LSH, Prolactin

What hormones does posterior pituitary release?

ADH and Oxytocin

What is GH responsible for?

Long bone growth

What is TSH responsible for?

Thyroid stimulating hormone

T4 and T3 in thyroid

What is ACTH responsible for?

Activates the adrenal corticosteroids in kidneys

What is FSH/LH responsible for?

follicle stimulating, ovaries (estrogen, progesterone) or testis (testerone)

What is prolactin responsible for?

Milk production

What is oxytocin?

Responsible for milk letdown, and uterine contractions

What is ADH useful for?

Kidney and Water retention

Whats the general format of hormone secretions from the hypothalamus to the posterior pituitary gland?

Starts from two nucleuses (Supraoptic nucleus/Paraventricular nucleus) in the hypothalamus→send their axons to the posterior lobe of the pituitary and the capillary bed.

• Direct maximizes efficiency

What are monoamines?

Smaller-sized peptides can go and bind to the receptors, need the molecular structures, there’s a debate on whether they are considered hormones

What are som examples of monoamines?

Dopamine, Norephedrine, Serotonin and Histamine

What are dopamine, norepinephrine, and epinephrine categorized as?

Categorized as catecholamines

What are catecholamines?

Catecholamines act both as neurotransmitters and hormones vital to the maintenance of homeostasis through the autonomic nervous system.

What are the three layers of the adrenal cortex and what do they secrete

1. Glomerulosa (Aldosterone)

2. Fasciculata (Cortisol)

3. Reticularis (Androgens)

Secrete various steroid hormones

What are the one layer of the adrenal medulla and what do they secrete

Medulla (Catecholamines) in conjunction with the sympathetic nervous system,

What is GnRH responsible for men?

stimulates the release of gonadotropins which then stimulate the Leydig cells to secrete testosterone.

What is FSH responsible for men?

stimulates the Sertoli cells to produce sperm.

What is LH responsible for men?

stimulating the Leydig cells in the testes to produce testosterone

How is the Hypothalamic-Pituitary-Testicular Control System regulated?

VIA negative feedback

What are the two negative feedback systems of the hypothalamic-pituitary-testicular control system regulated?

1) From androgens (testerone) from leydig cells to hypothalamus

2) From inhibin from sertoli cells to the anterior pituitary gland

What are sertoli cells responsible for?

• Provide nourishment to the developing sperm

• Produce the peptide hormone, inhibin, important in regulating gonadotropins from the pituitary

Where are Leydig cells located?

Between the seminiferous tubules are occupied by leydig cells.

What do leydig cells secrete?

• secrete peptide hormones that control the process of spermatogenesis

• the steroid hormone testosterone.

Why is there lots of vasculature in the anterior lobe of the pituitary?

Get into the blood supply target organ aay

• Allows for lots of movement in blood

What’s Pathway for Control of Gonadotropin from hypothalamus to anterior lobe?

Median eminence (hypothalamus) → portal veins → glandular cells i(n anterior lobe of pituitary)

What is hCG?

–secreted by the conceptus and placenta, is a useful indicator of pregnancy status

Am I pregnant?

What is AMH?

–AMH is produced by the granulosa cells in ovarian follicles, the production of AMH is reflective of ovarian reserve

A proxy of the # of eggs you have

Can my body support a preg?

What is inhibin secreted by?

secreted by the Sertoli cells and by the granulosa cells

What is the purpose of inhibin?

• inhibits the synthesis and release of the FSH in the pituitary gland

• reduces the hypothalamic LH - releasing hormone content

• inhibits the multiplication of spermatogonia (undifferentiated germ cell) in the gonads

• inhibits the production of progesterone by the ovaries

What does the hypothalamus stimulate?

Hypothalamus secretes GnRH, which stimulates the secretion of LH and FSH by the anterior lobe of the pituitary gland

What does LH stimulate?

in turn stimulates the synthesis and secretion of androgens (primarily testosterone) by the Leydig cells of the testes

What does FSH stimulate in male?

Stimulates the Sertoli cells of the testes to increase the production of sperm (spermatogenesis).

What is needed to be make sertoli cells?

Promote high levels of sperm production only when both FSH and androgens are present

What are the two ways of negative feedback from testerone?

• A direct effect of testosterone on the LH-secreting cells in the anterior lobe of the pituitary, depressing their response to the GnRH pulses coming from the hypothalamus

• Second is an effect of testosterone on the hypothalamus, decreasing the frequency of GnRH pulses.

What are the twos ways to regulate spermatogenesis?

• Since testosterone controls the secretion of GnRH and because GnRH stimulates both LH and FSH secretion by the pituitary gland, increasing testosterone levels tend to have a negative feedback effect on FSH as well as LH.

• Sertoli cells also send a signal back to the pituitary gland that is more directly related to spermatogenesis, in the form of inhibin.

What does testerone help with”?

•Most internal and external genital structures require testosterone for normal functioning

•Testosterone influences sexual behaviour (not cause and effect tho)

•Testosterone promotes tissue growth

•Testosterone also influences the erectile capacity of the penis

•Testosterone promotes tissue growth

• Penile erections occur during REM sleep

What happens with nocturnal erections after castration?

cease some weeks after castration (removal of testes) and return with testosterone treatment

What are some ways those who are castrated may have returned testosterone treatment?

• Return with testosterone treatment

• Non-testicular sources—most likely the adrenal glands—for those who can still experience an erection after castration have higher circulating levels of testosterone than those who cannot

How does testosterone promote tissue growth?

•Anabolic effects are easiest to see in the musculature

•Androgens are the main reason why XY individuals tend to be more muscular than XX after puberty

•Androgens also promote the formation of red blood cells

Androgens also promote the formation of red blood cells:

Increases the oxygen-carrying capacity of the blood, and they increase the mass of the liver and kidneys as well

• Anabolic effects of androgens is the reason they are abused by athletes (XX and XY), but such use carries significant health risks

What does secretions of estrogens do in males?

–Estradiol facilitates maturation and concentration of sperm in the epididymis

–Estradiol terminates growth at the end of puberty

–Estradiol maintains normal bone density

What is Menstruation?

Vaginal discharge of endometrial tissue & blood experienced at roughly monthly intervals during fertile years, except when a person is pregnant or intensively nursing an infant

What organs are responsible for menstruation?

• complex internal mechanism that involves the ovaries, the brain, and the uterus

What is the ovarian cycle responsible for?

Hormonal interactions between the ovaries, the hypothalamus, and the pituitary gland

What is the menstrual cycle responsible for?

Changes in the endometrium of the uterus, which is responsible for menstrual periods

What is the Follicular Phase marked by?

AKA preovulatory in ovaries/proliferative phase in uterus

• phase is marked by the maturation of follicles in the ovary

Day 6-14

What is the Luteal or postovulatory phase marked by?

AKA postovulatory in ovaries/secretory phase in the uterus

• by the presence of a corpus luteum (CL)

Day 15-28

What is the corpus luteum?

CL is a hormone-secreting structure formed from a follicle ruptured at ovulation

What the proliferative phase and secretory phase?

Follicular or Secretory phase processes that take place in the uterus

What is the most constant phase in the menstrual cycle?

• The luteal phase is the most constant

• It usually lasts 14 day, give or take 2 days

Where is the variation more prominent in the other two phases?

In total cycle length is accounted for by variation in the other two phases

• Menstrual or Follicular

How long does the menstrual cycle?

A typical 28-day cycle

When is the menstrual phase?

The menstrual phase occupies days 1 through 5

What structures are involved with the menstrual phase?

Ovaries, Brain, Pituitary, and Uterus

When does ovulation occur?

Day 14

What is the menstrual phase is triggered by?

A drop in progesterone and estradiol levels

What hormone falls at the start of the menstrual cycle and what occurs after?

As estrogen levels fall at the beginning of the menstrual cycle, negative feedback diminishes, and gonadotropins rise