1 – Hormonal Basis of Reproduction Flashcards
Hormones
- Chemical messengers
- Released into circulations
- Targets need to have specific receptors (extracellular or intracellular)
Hormone Transportation
o Free (ex. water-soluble)
o Bound (ex. lipid-soluble)
Hormone classification
o Biochemical structure
o Source
o Mode of action
Half-life
- Determines how fast a hormone is metabolized
Systemic regulation
- Controls processes ANYWHERE in the body (only target tissues respond)
o Neuroendocrine
o Endocrine
>Travel slower, but response is longer-lasting and widespread (MULTIPLE tissues at the same time)
Point-to-point regulation
- Controls specific processes at specific cells/tissues connected by NERVES (‘landline phone’)
Biochemical structure
- Peptide (ex. GnRH)
o Shorter half life (shorter the chain=shorter the half life) - Glycoprotein (Ex. LH, FSH)
- Steroid (Ex. E2, P4)
- Modified fatty-acids derived (prostaglandins)
o Autocrine/paracrine function, so not really hormone
Secretion Patterns
- Pulsatile
- Surge
- Cyclic
- Circadian & circannual
- Pulsatile
a. Most hormones
b. Reach a peak, then decline to basal levels (dependant on half-life)
c. Single blood sample inadequate for diagnosis
d. Ex. LH, testosterone
- Surge
a. Preovulatory GnRH/LH surge
b. ONLY in females: surge centre for large pulses back-to-back to stimulate LH surge and cause ovulation
- Cyclic
a. Reproductive aged females: influenced by HPG axis and ovarian activity
- Circadian & circannual
a. Circadian: 24hrs
i. LH increases in urine of boys at night
b. Circannual: vary by season
i. Reproductive hormones in seasonal breeders
c. Melatonin: reflects length of night
Negative feedback
- Acts to MINIMIZE deviation from setpoint
- Leads to STABILITY
- Main control for most hormones
- 2 hormones keep each other within normal range
- GnRH asks for LH, LH signals that it has been received
Positive feedback
- Acts to INCREASE deviation from setpoint
- Leads to INSTABILITY
- Occurs only in a few situations
- Increased target hormone potentiates initial hormone release
- *cycle continues until something gives in
- Ex. babies head against cervix, tells uterus to contract, oxytocin released=contraction of uterus (stops at parturition)
G protein-coupled receptors (GPCRs)
- 7-pass transmembrane domains
- Involved in link between 1st and 2nd messengers
o Gs or GI act to get or not get cAMP
o Gq activates PLC to get IP3+DAG to get Ca2+ - Molecular switches
- Can be activated by various ligands
Hypothalamic control of anterior pituitary
-Parvicellular neurosecretory cells secrete RELEASING or INHIBITORY factors
-Portal vessels: link 2 capillary networks
Parvicellular neurosecretory cells secrete RELEASING or INHIBITORY factors
o Released near capillaries of HYPOPHYSEAL PORTAL SYSTEM at the median eminence
o Transported efficiently to the anterior pituitary gland to regulate the secretion of pars distalis hormones
Hypophyseal portal system
- Ensures regulatory hormones reach cells in A. pituitary before entering general circulation
Median eminence
- Swelling near attachment of infundibulum where hypothalamic neurons release regulatory hormones into interstitial fluids
o Enter the bloodstream through fenestrated capillaries
Gonadotropes
* Hypothalamic regulator
o GnRH: 10 AA, stimulatory
Gonadotropes
* Tropic hormone secreted
o FSH: 213AA, 3 hr half life
o LH: 210AA, 0.5 hr half life
o Alpha subunit=common
o Beta subunit=hormone-specific subunit
o *pulsatile
o hCG works on same receptor as LH
* *GnRH pulse, FSH sluggish pulses, LH sharper pulse (due to shorter half life)
Gonadotropes
* Target endocrine gland
o Ovary: granulosa & theca cells
o Testis: Sertoli & Leydig cells
Gonadotropes
* Receptor
o FSH and LH receptors (Gs protein coupled)
Gonadotropes
- Negative feedback hormone
-estrogen
-progesterone
-testosterone
-inhibin
