Estrous Behaviour + Cycles Flashcards
Follicular Phase
Starts with luteolysis and ends with ovulation
-characterized by high E2 levels
Luteal Phase
Starts with ovulation and ends with luteolysis
-characterized by high P4 levels
Estrus
Noun denoting state of being: synonymous with “heat”
Estrous
Adjective describing characteristics of estrus
Anestrous (AKA anovulation)
Female is not having repeated estrous cycles because animal is prepubertal, pregnant, postpartum, sick, has poor nutrition or seasonally affected
Estrous behaviour
Sexual receptivity (lordosis), increased physical activity, mounting behaviour, bellowing, and trailing other females
What characterizes beginning of estrus?
Female accepts mounting from males or females
What signals muscles for lordosis and mounting?
Sensory information is fed to hypothalamus which releases neurotransmitters into the spinal cord to signal specific muscles
What is the luteal phases subdivided into?
Metestrus, diestrus, proestrus and estrus
-proestrus and estrus = follicular phase
Metestrus
Begins with ovulation, ends when CL is fully establishes, P4 levels are rising
Diestrus
Begins when CL becomes fully functional, high P4 until luteolysis
Proestrus
decreasing P4 from CL and increased E2 from follicle - increased GnRH - increased FSH and LH
Why does FSH increase during estrus?
Due to the GnRH surge, it overpowers inhibin feedback
Primordial follicles
Activated, and develop into primary/secondary follicular stages
Secondary follicles
Acquire FSH/LH receptors and are recruited for antral follicle development
What happens to follicles that aren’t selected?
The die off
Follicular Wave
Coordinated growth of follicles in groups, occurs 2-3 times/cycle
E2 from Growing follicle
Positive feedback on surge center - more GnRH production - more LH production
Preovulatory LH surge
Induces ovulation through multiple pathways
High LH from surge
Leads to accumulation of fluid in antrum, loosening of ovary and increased blood flow to ovary - follicle rupture and ovulation
When is E2 highest?
At ovulation and when the follicle ovulates, E2 drops and remnants of the follicle become corpus luteum producing large amounts of P4
At what stage do P4 levels drop?
Drop at luteolysis, but stay high throughout luteal phase
Luteolysis
Degradation on CL that occurs when no implantation has taken place
What does P4 prevent?
Production of prostaglandins which prevents contraction of myometrium
P4 synthesis
Requires LDL cholesterol and LH stimulus in order to convert cholesterol to P4
Uterine Hormones
Prostaglandins have local effect, PGF2-alpha constricts spiral arteries which causes tissue necrosis, sloughing and cramping
Do prostaglandins from uterus have a short half-life?
Yes, meaning they do not survive systemic circulation, they diffuse directly from uterine veins to ovarian arteries
What does posterior pituitary secrete?
Oxytocin in pulses because it releases from neurons, rather than endocrine tissue
Why are PGF-2-alpha pulses needed?
For luteolysis. It downregulates its own receptor expression after a certain period of time (8-10 days)
What do prostaglandins binds to?
Luteal cell receptors and induce influx in Ca2+ which then induces apoptosis
Synthetic GnRH
Used to induce growth of follicles
Progesterone
May be used to promote maintenance of pregnancy
FSH
May be used to promote growth of multiple follicles to increase the number available to choose
Monovulatory
During selection, only one follicle expresses LH receptors and reaches dominance
