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Section 5G Reproductive Systems > Endocrine System > Flashcards

Endocrine System Flashcards

1
Q

What is the hypothalamic - pituitary - gonadal axis?

A
  • an axis of hormonal reactions between the hypothalamus, the anterior and posterior pituitary glands, and the gonads (ovaries and testicles)
  • hormones released by the hypothalamus and pituitary glands affect hormonal actions at the gonads
  • hormones released by the gonads create a negative feedback loop to the hypothalamus and pituitary gland
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2
Q

What are the effects of LH in males and females?

A

LH:

  • luteinizing hormone
  • released by anterior pituitary in response to GnRH from hypothalmus
  • affects gonads (ovaries and testicles)

Males:
- triggers interstitial (Leydig) cells in testes to release testosterone

Females:
- stimulates ovulation and formation of corpus luteum from ruptured follicle

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3
Q

What are the different effects of FSH in males and females?

A

FSH:

  • follicle stimulating hormone
  • released by anterior pituitary in response to GnRH from hypothalamus

Males:

  • triggers sustentacular cells in testes to release ABP (androgen binding hormone)
  • ABP maintains high concentration of testosterone for spermatogenic cells

Females:

  • stimulates follicular phase of ovarian cycle (selection and maturation of follicle)
  • stimulates oestrogen production from granulosa cells in ovaries
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4
Q

What is the endocrine system?

A
  • a system of hormones (chemical messengers) that interacts with the nervous system to co-ordinate bodily functions
  • nervous system: governs short term reactions; endocrine system: governs long-term reactions
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5
Q

What are the 6 endocrine glands?

A

(glands that produce hormones)

  1. kidneys & liver
    - EPO (erythropoietin, stimulates RBC production)
  2. heart (atrial cells)
    - ANP (atrial natriuretic peptide, inhibits sodium reabsorption at DCT and CD of kidney nephrons)
  3. anterior pituitary gland
    - 6 hormones
    - GH (growth hormone)
    - TSH (thyroid stimulating hormone, stimulates release of T3 and T4)
    - PRL (prolactin: milk production)
    - FSH (follicle stimulating hormone, maturation of ovarian follicle in females, production of ADP by sustentacular cells in males)
    - LH (luteinizing hormone, ovulation and conversion of corpus luteum in females, production of testosterone in males)
    - ACTH (adreno-corticotrophic hormone; promotes release of hormones from adrenal cortex)
  4. adrenal glands
    - mineralcorticoids (including aldosterone)
    - glucocorticoids (including cortisol, cortisone)
    - androgens (DHEA and androstenedione)
  5. thyroid glands
    - T3 and T4
  6. pancreas (endocrine portion)
    - insulin (lowers blood glucose levels)
    - glucagon (raises blood glucose levels)
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6
Q

What are paracrines?

A
  • chemical messengers with locally activated effects (within the same tissue)
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7
Q

What are the 3 categories of hormones?

A
  1. Amino acid based
    - adrenaline and noradrenaline
    - T3 and T4
    - GH, ACTH, TSH, ADH, pancreatic hormones
    - water soluble; use second messengers
  2. Steroids
    - gonadal (oestrogen, progesterone, androgens)
    - corticosteroids (cortisol, aldosterone)
    - lipid soluble; direct gene activation
  3. Eicosanoids
    - hormone like chemical (not true hormones)
    - act as paracrines
    - prostaglandins, leukotrienes
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8
Q

What are the 2 primary mechanisms for hormone activation upon an effector cell?

A
  1. Direct gene activation
    - all steroid hormones, thyroid hormones
    - lipid soluble hormone diffuses through plasma membrane of cell and binds with receptor in cytoplasm
    - receptor hormone complex enters nucleus of cell and triggers gene transcription that alters cell activity
  2. Second messenger system
    - water soluble hormones that cannot diffuse across cell membrane
    - hormones (first messenger) act upon intercellular signalling molecules (second messengers) that carry ‘message’ of hormone into cell
    - examples of second messenger systems are cyclic AMP (amino-acid based hormones) and tyrosine kinase (insulin)
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9
Q

Which hormones use the direct gene activation system?

A

Steroid hormones:

  • aldosterone, cortisol (adrenal glands)
  • testosterone, oestrogen, progesterone (sex hormones)

Thyroid hormones:
- T3 and T4

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10
Q

Which hormones use the second messenger activation systems?

A

Amino acid based hormones

  • epinephrine and norepinephrine (use cyclic AMP system)
  • insulin (uses tyrosine kinase system)
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11
Q

What are steroid hormones?

A
  • hormones synthesized from cholesterol
  • produced in the adrenal cortex, ovaries and testes

Adrenal cortex:
- aldosterone, cortisol

Ovaries:
- oestrogen, progesterone

Testes:
- testosterone

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12
Q

What are amino acid based hormones?

A

Hormones produced in the adrenal medulla (epinephrine and norepinephrine) and thyroid (T3 and T4)

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13
Q

What are the 5 main actions of hormones?

A
  1. alter cell membrane permeability
  2. alter cell membrane excitability
  3. stimulate synthetic activity
  4. activate or deactivate enzymes
  5. stimulate mitosis
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14
Q

Describe the cyclic AMP second messenger system

A
  • used by amino acid based hormones (epinephrine / norepinephine, T3 and T4)
  1. amino acid based hormones bind to membrane receptors and activate a G protein
  2. G protein activates adenylyl cyclase
  3. adenylyl cyclase catalyzes the conversion of ATP to cAMP (second messenger)
  4. cAMP activates protein kinases
  5. protein activates phosphylarate proteins in cytoplasm and alters their activity
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15
Q

Describe the steps of direct gene activation

A
  • for steroid hormones (aldosterone, cortisol, oestrogen, progesterone, testosterone)
  1. hormone diffuses through plasma membrane
  2. binds with receptor in cytoplasm to form a hormone-receptor complex
  3. complex enters nucleus and triggers gene transcription
  4. transcribed mRNA is translated into proteins that alter cell activity
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16
Q

What are the 3 mechanisms that regulate the release of hormones?

A
  1. Humoral stimulus
    - triggered by altered blood levels of ions or nutrients
    - low blood calcium triggers release of parathyroid hormone
    - high blood calcium triggers release of calcitonin from thyroid
  2. Neural stimulus
    - short term stress response: SNS triggers adrenal medulla to release adrenaline and noradrenaline
  3. Hormonal stimulus
    - hormone release caused by another (trophic) hormone
    - ie: hormones produced by hypothalamus regulate secretion of hormones from anterior pituitary that act on other organs
17
Q

What is the hormonal inhibition mechanism?

A
  • negative feedback loop used to ‘turn off’ hormonal mechanisms
  • when hormone levels rise sufficiently to cause target organ effects, the target organ effects feed back to reduce initial stimulus for hormone release (causes inhibition of further hormone release)
18
Q

What is the hypothalamic-pituitary axis, and the mechanisms of connection between the hypothalamus and the anterior and posterior pituitary glands?

A

Axis:

  • connection between hypothalamus and anterior and posterior pituitary glands
  • hypothalamus triggers hormonal release from anterior and posterior pituitary glands
  • anterior pituitary gland: synthesizes and releases 6 major hormones
  • posterior pituitary gland: stores and releases hormones received from hypothalamus (doesn’t manufacture hormones)

Neurohypophysis:

  • connection between hypothalamus and posterior pituitiary
  • neural tissue

Adenohypophysis:

  • connection between hypothalamus and anterior pituitary
  • composed of glandular tissue with vascular connections to hypothalamus via hypophyseal portal system (network of capillary plexii)
19
Q

Which aspect of the pituitary gland synthesizes hormones?

A

Anterior:
- synthesizes and releases 6 hormones

Posterior:
- stores hormones produced by hypothalamus

20
Q

What are the 6 hormones synthesized and released by the anterior pituitary gland?

A
  1. LH:
    - luteinizing hormone
    - stimulates ovulation and converts ruptured follicle into corpus luteum in females, stimulates production of testosterone in males
  2. FSH:
    - follicle stimulating hormone
    - stimulates oogenesis in females (selection and maturation of dominant follicle), stimulates production of androgen-binding protein by sustentacular cells in males
  3. PRL:
    - prolactin
    - stimultes milk production and mammary gland development
  4. GH:
    - growth hormone
    - anabolic hormone that stimulates somatic growth; and use of fats as energy source
  5. TSH:
    - thyroid stimulating hormone
    - stimulates release of T3 and T4
  6. ACTH:
    - adreno-corticotrophic hormone
    - stimulates release of corticosteroids and androgens from adrenal cortex
21
Q

Which 2 hormones are stored in and released by the posterior pituitary gland in response to hypothalamic stimulation?

A
  1. oxytocin
    - stimulates ejection of milk from mammary glands
  2. ADH
    - anti diuretic hormone
    - inserts aquaporins into collecting duct of nephrons in kidney to promote water reabsorption
22
Q

Which 4 types of hormones are released by the 4 different zones of the adrenal glands?

A
  1. Mineralcorticoids
    - released by outer cortex / zona glomerulosa
    - most abundant: aldosterone (increases sodium chloride reabsorption at DCT and CD of nephron in kidney)
  2. Glucocorticoids
    - released by middle cortex / zona fasciculata
    - cortisol, cortisone, corticosterone (promote gluconeogenesis, enhance SNS effect on smooth muscle, anti-inflammatory)
  3. Androgens
    - released by inner cortex / zona reticularis
    - DHEA and androstenedione (support sexual behaviour, sense of wellbeing)
  4. Catecholamines
    - neurotransmitters in SNS
    - stimulate and support functioning of SNS
    - norepinephrine, epinephrine
23
Q

What are the actions of ADH and from where is it released?

A
  • produced by hypothalamus and released from posterior pituitary
  • released in response to decreased blood volume or increased blood osmolarity, or in resonse to angiotensin II (RAAS system)
  • increases water reabsorption in kidneys by inserting aquaporins into DCT and CD
24
Q

What are the actions of oxytocin and from where is it released?

A
  • produced by hypothalamus and released by posterior pituitary in response to suckling at breast or uterine/ cervical stretching
  • stimulates uterine contractions (labour) and milk ejection (breastfeeding)
  • also causes bonding (psychoactive effect)
25
Q

What are the actions of GH and from where is it released?

A
  • growth hormone
  • produced and released by anterior pituitary in response to low GH levels
  • anabolic hormone that causes somatic growth
  • metabolizes fats for use as energy source (over glucose)
26
Q

What are the actions of LH and from where is it released?

A
  • produced and released by anterior pituitary, released in response to GnRH from hypothalamus
  • females: stimulates ovulation and converts ruptured follicle into corpus luteum
  • males: stimulates production of testosterone by interstitial / Leydig cells in testes
27
Q

What are the actions of FSH and from where is it released?

A
  • follicle stimulating hormone
  • produced by anterior pituitary and released in response to GnRH from hypothalamus
  • females: stimulates oogenesis (selection and maturation of oocyte in ovary)
  • males: stimulates production of androgen binding protein by sustentacular cells in testes (to support sperm production)
28
Q

What are the actions of ACTH and from where is it released?

A
  • adreno-corticotrophic hormone
  • produced by the anterior pituitary and released in response to corticotrophin releasing hormone from hypothalamus (release triggered by stressors ie fever)
  • promotes release of corticosteroids and androgens from adrenal cortex
29
Q

What are the actions of TSH and from where is it released?

A
  • produced by the anterior pituitary and released in response to GnRH from hypothalamus
  • triggers secretion of T3 and T4 from thyroid
30
Q

What are glucocoroticoids?

A
  • released from zona fasiculata (middle cortex) in adrenal cotex
  • cortisol, cortisone, corticosterone

Actions:

  • gluconeogenesis (production of glucose from non-carbohydrate sources)
  • enhances SNS effect on vascular smooth muscle (vasoconstriction) and contributes to BP regulation
  • anti-inflammatory immune effect
31
Q

What are mineralcorticoids?

A
  • released from zona glomerulosa (outer cortex) of adrenal cortex
  • most abundant: aldosterone

Actions:
- increases reabsorption of sodium chloride at PCT and CD of nephron in kidney to increase blood volume and blood pressure

32
Q

What are androgens?

A
  • produced by zona reticularis (inner cortex) of adrenal gland
  • DHEA and androstenedione
  • sexual function, wellbeing
33
Q

What are catecholamines?

A
  • released by adrenal medulla
  • epinephrine and norepenephrine
  • augment SNS activity, increase HR, increase cardiac contractility, cause vasoconstriction to increase BP, increase blood glucose

Section 5G Reproductive Systems (8 decks)

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