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
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
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
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
5
Q
What are the 6 endocrine glands?
A
(glands that produce hormones)
- kidneys & liver
- EPO (erythropoietin, stimulates RBC production) - heart (atrial cells)
- ANP (atrial natriuretic peptide, inhibits sodium reabsorption at DCT and CD of kidney nephrons) - 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) - adrenal glands
- mineralcorticoids (including aldosterone)
- glucocorticoids (including cortisol, cortisone)
- androgens (DHEA and androstenedione) - thyroid glands
- T3 and T4 - pancreas (endocrine portion)
- insulin (lowers blood glucose levels)
- glucagon (raises blood glucose levels)
6
Q
What are paracrines?
A
- chemical messengers with locally activated effects (within the same tissue)
7
Q
What are the 3 categories of hormones?
A
- Amino acid based
- adrenaline and noradrenaline
- T3 and T4
- GH, ACTH, TSH, ADH, pancreatic hormones
- water soluble; use second messengers - Steroids
- gonadal (oestrogen, progesterone, androgens)
- corticosteroids (cortisol, aldosterone)
- lipid soluble; direct gene activation - Eicosanoids
- hormone like chemical (not true hormones)
- act as paracrines
- prostaglandins, leukotrienes
8
Q
What are the 2 primary mechanisms for hormone activation upon an effector cell?
A
- 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 - 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)
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
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)
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
12
Q
What are amino acid based hormones?
A
Hormones produced in the adrenal medulla (epinephrine and norepinephrine) and thyroid (T3 and T4)
13
Q
What are the 5 main actions of hormones?
A
- alter cell membrane permeability
- alter cell membrane excitability
- stimulate synthetic activity
- activate or deactivate enzymes
- stimulate mitosis
14
Q
Describe the cyclic AMP second messenger system
A
- used by amino acid based hormones (epinephrine / norepinephine, T3 and T4)
- amino acid based hormones bind to membrane receptors and activate a G protein
- G protein activates adenylyl cyclase
- adenylyl cyclase catalyzes the conversion of ATP to cAMP (second messenger)
- cAMP activates protein kinases
- protein activates phosphylarate proteins in cytoplasm and alters their activity
15
Q
Describe the steps of direct gene activation
A
- for steroid hormones (aldosterone, cortisol, oestrogen, progesterone, testosterone)
- hormone diffuses through plasma membrane
- binds with receptor in cytoplasm to form a hormone-receptor complex
- complex enters nucleus and triggers gene transcription
- transcribed mRNA is translated into proteins that alter cell activity
16
Q
What are the 3 mechanisms that regulate the release of hormones?
A
- 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 - Neural stimulus
- short term stress response: SNS triggers adrenal medulla to release adrenaline and noradrenaline - 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
- LH:
- luteinizing hormone
- stimulates ovulation and converts ruptured follicle into corpus luteum in females, stimulates production of testosterone in males - 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 - PRL:
- prolactin
- stimultes milk production and mammary gland development - GH:
- growth hormone
- anabolic hormone that stimulates somatic growth; and use of fats as energy source - TSH:
- thyroid stimulating hormone
- stimulates release of T3 and T4 - 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
- oxytocin
- stimulates ejection of milk from mammary glands - 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
- Mineralcorticoids
- released by outer cortex / zona glomerulosa
- most abundant: aldosterone (increases sodium chloride reabsorption at DCT and CD of nephron in kidney) - Glucocorticoids
- released by middle cortex / zona fasciculata
- cortisol, cortisone, corticosterone (promote gluconeogenesis, enhance SNS effect on smooth muscle, anti-inflammatory) - Androgens
- released by inner cortex / zona reticularis
- DHEA and androstenedione (support sexual behaviour, sense of wellbeing) - 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
What are the actions of GH and from where is it released?
- 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
What are the actions of LH and from where is it released?
- 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
What are the actions of FSH and from where is it released?
- 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
What are the actions of ACTH and from where is it released?
- 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
What are the actions of TSH and from where is it released?
- produced by the anterior pituitary and released in response to GnRH from hypothalamus
- triggers secretion of T3 and T4 from thyroid
30
What are glucocoroticoids?
- 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
What are mineralcorticoids?
- 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
What are androgens?
- produced by zona reticularis (inner cortex) of adrenal gland
- DHEA and androstenedione
- sexual function, wellbeing
33
What are catecholamines?
- released by adrenal medulla
- epinephrine and norepenephrine
- augment SNS activity, increase HR, increase cardiac contractility, cause vasoconstriction to increase BP, increase blood glucose
