Exam 2 Flashcards
The hypothalamus is inherently ____________? Why?
Female because testosterone androgenizes the surge center
The estradiol produced by the ovary binds to what in order for it to be too big to cross the blood-brain barrier, essentially allowing the surge center to develop in females?
Alpha feto-protein
An increase in average daily gain (ADG) results in a
Decreased age at puberty.
List the five environmental factors that affect puberty onset in females.
1) Breed
2) Exposure to male
3) Season of birth
4) Photoperiod
5) Group size and density
What two factors affect GnRH neuron development?
1) Body condition
2) Exposure to environmental and social cues
Females need to have a completely functional ______ in order for puberty to be maintained?
Surge center
Define the estrous cycle.
Events that happen between periods of sexual receptivity
What are the two phases of the estrous cycle? What hormone is high in each phase? What structure is present on the ovary during each phase?
1) Follicular Phase; Estradiol; Follicle
2) Luteal Phase; Progesterone; CL
What is the term used for an animal not cycling at a given time?
Anestrus
List the 5 (maybe 7) times in a female’s life that she will most likely not be cycling.
1) Pregnancy
2) Lactation
3) Season
4) Stress
5) Disease and illness
6) (presence of offspring)
7) (Prior to puberty)
List the three types of cycles we talked about in class, be able to explain how they work, and give a species example of each.
1) Monoestrous: once a year, dog
2) Polyestrous: normal, cow
3) Seasonally polyestrous: seasonally, horses, sheep
Proestrus + Estrus = ?
Follicular phase
Metestrus + Diestrus = ?
Luteal phase
What is superfecundation?
Multiple oocytes are fertilized by spermatozoa from different males (in one ovulation cycle)
In the bitch, which stage of the estrous cycle is the longest?
Anestrus
What phase of the estrous cycle is not present in the bitch?
Metestrus
Queens are induced _____ ?
Ovulators
Queens are in the follicular phase until copulation when the ____ surge is initiated.
LH
Queens only ovulate after ______?
Copulation
What are the four major events that occur in the follicular phase?
1) Ovulation
2) Sexual receptivity
3) Follicular growth
4) Elevated gonadotropin secretion, FSH, & LH
What is the level of concentration of estradiol during the follicular phase?
High
The tonic center is responsible for what type of secretion of which hormone?
Basal secretions of GnRH
The surge center is responsible for what type of secretion of which hormone?
Episodic surges of LH, which causes ovulation
If ______ is dominant, complete follicular development and ovulation cannot occur
Progesterone
What is the primary function of LH?
Complete follicular development & cause ovulation
What is the fate of most follicles and what causes this?
Atresia, because there is a lack of LH receptors
What type of cells are in the preovulatory follicles? What are their functions?
a. Theca externa - structural support and integrity
b. Theca interna - LH receptors
c. Granulosa - FSH receptors
What is luteinization?
Formation of the CL; transformation of follicle cells to luteal cells
Progesterone has what type of feedback on the GnRH neurons?
Negative
What structure forms after the functional CL regresses?
CA (corpus albicans)
What immune cells are present at luteolysis?
Cytokines
When we synchronize estrous, what are we trying to do?
Either kill or maintain the CL
What are two ways to manipulate the estrous cycle?
1) Progestogen - maintains the CL
2) Prostaglandin - kills the CL
Where does spermatogenesis take place?
Seminiferous tubules
What hormones do we need for spermatogenesis that are under endocrine control?
FSH, LH, & GnRH
LH acts on ________ cells and dervive from what tissue?
Leydig; same tissue as theca interna cells
FSH acts on _______ cells and derive from what type of tissue?
Sertoli; granulosa
What are the three phases of spermatogenesis? Give a brief description of what is happening in each.
1) Proliferation phase - mitotic divisions
2) Meiotic phase - meiotic division
3) Differentiation phase - no cell division
What are the four things we measure when looking at male fertility?
1) Producing ability
2) Viability
3) Morphology
4) # of normal spermatozoa
What are the two methods to preserve sperm?
1) Extender
2) Freeze
Which hormone is a glycoprotein?
FSH
Type of receptors that bind protein hormones
Plasma membrane
Sustained hormone secretion during pregnancy
P4
Major limiting factor for the onset of puberty
Secretion of GnRH
Which hormone negatively affects the development of GnRH surge center?
Testosterone
Which of the estrous phases is the longest?
Diestrus
Which hormone acts as a positive feedback messenger?
Estradiol (E2)
List 3 species that don’t experience lactational anestrus
1) Cats
2) Llama
3) Alpaca
Most effective method of estrous synchronization in sows?
Weaning
Order of follicular dynamics
1) Recruitment
2) Selection
3) Dominance
4) Atresia
Luteal phase begins with
Ovulation
Luteal phase ends with
Luteolysis
The male hypothalamus does not have a
Surge center
2 main factors impacting hypothalamic GnRH neuron development
1) Exposure to environmental or social cues
2) Threshold body size
Considered the onset of puberty in the female
1) First confirmed pregnancy
2) First ovulation
3) First estrus
Why can’t neurons in the surge center secrete much GnRH prior to puberty in the female?
Estradiol concentrations are too low
Considered onset of puberty in the male
1) Age at first ejaculation
2) Age at first ejaculation with adequate spermatozoa
3) Age at first ejaculation with live spermatozoa
Which hormone defeminizes the hypothalamus in the male during prenatal differentiation?
Testosterone
Prior to puberty in females, low estradiol is due to
Little follicular growth
Best definition for the onset of puberty in both males and females
To accomplish reproductive sucess
After puberty in females, the surge center is responsible for
Preovulatory surge of GnRH
In the male, testosterone is converted to estradiol via
Aromatase
After puberty in the female, basal levels of GnRH are higher because
Pulse frequency increases
If progesterone is high, which structure is present on the ovary?
CL
Which phase of the estrous cycle is characterized by the CL formation and the beginning of P4 secretion?
Metestrus
Which phase is characterized by sexual receptivity?
Estrus
Causes of anestrus
1) Negative energy balance
2) Disease
3) Pregnancy
4) Season of the year
5) Lactation
High levels of preovulatory estradiol engages the
Surge center
In a cycling female, what physiological event must happen for the follicular phase/proestrus to begin
Luteolysis/removal of negative feedback
Another name for the surge center
Preovulatory center
How is LH regulated?
GnRH
What hormone is produced by the CL?
Progesterone
Luteolysis is caused by
Protsaglandin
What are protein/peptide hormones?
Ex: Insulin; Act via plasma membrane receptors; Exert effects on the cytoplasm; cannot feed in their diet because protein will be absorbed.
What are steroid hormones?
Ex: Progesterone & Testosterone; Act via nuclear receptors that regulate transcription factors - slow responses; act through plasma membrane receptors - rapid responses
Sensory neurons
Afferent neurons taking neural signals to the spinal cord
Efferent neurons
Taking neural signals from the spinal cord and to the target tissue
Target tissues
Organs that respond to a specific set of stimuli or hormone
What kind of reflex does a neurotransmitter have?
Simple neural reflex
What kind of reflex does a neurohormone have?
Neuroendocrine reflex
What does a simple neural reflex do?
The nerves release neurotransmitters directly to the target tissue
What does a neuroendocrine reflex do?
Requires a neurohormone to enter the bloodstream and acts on remote target tissues
What is the sella turcica?
A cavity in the sphenoid bone; develops in bone around the pituitary for protection
What is the Hypothalamo-Hypophyseal Portal System?
Connects the hypothalamus to the anterior pituitary; Its main function is the transport and exchange of hormones to allow fast communication between both glands
What is neurohypophysis?
A structure that is located at the base of the brain; it is the posterior lobe of the pituitary gland.
Negative feedback = _____ of GnRH neurons
Suppression
Positive feedback = _____ of GnRH neurons
Stimulation
The surge center is sensitive to
positive feedback
What are kisspeptins?
The “gatekeepers” for GnRH release; Neuropeptides by the hypothalamus; an important regulator of sexual differentiation of the brain
What is the kisspeptins affected by?
Pheromones, stress, photoperiod, nutrition, age, etc.
Reproductive hormones have short ____
Half-lives
Reproductive hormones are classified by:
1) Source
2) Mode of action
3) Biochemical classification
Reproductive Hormones: Source Example
Pituitary hormones (FHS, LH, Oxytocin, Prolactin)
Reproductive Hormones: Mode of Action Example
Gonadotrophins (FHS, LH)
Reproductive Hormones: Biochemical Classification Example
Glycoproteins (FSH, LH)
Reproductive hormones originate from
1) Hypothalamus
2) Pituitary
3) Gonads (testis/ovaries)
4) Uterus
5) Placenta (if pregnant)
Reproductive hormones can cause:
1) Release of other hormones
2) Stimulation of the gonads
3) Sexual promotion
4) Pregnancy maintenance
5) Luteolysis
What is the hormone from the tissue of origin: Hypothalamus
GnRH
What is the hormone from the tissue of origin: Pituitary
FSH, LH, & Prolactin
What is the hormone from the tissue of origin: Gonadal
Estrogens, Progesterone, Inhibin, & Testosterone
What is the mode of action of Neurohormones?
Synthesized by neurons - released directly into the blood to target tissues
What is the mode of action of releasing hormones?
Synthesized by neurons in the hypothalamus
What is the mode of action of gonadotropins?
FSH & LH
What is the mode of action of sexual promoters?
Secreted by gonads
What do sexual promoters do?
1) Stimulate the reproductive tract
2) Regulate the function of the hypothalamus
3) Regulate reproductive behavior
4) Development of secondary sex characteristics
What is the mode of action of general metabolic hormones?
Promote metabolic well-being
What is the mode of action of luteolytic hormones?
Destroy CL
What is a pheromone?
Substances that are secreted to the outside of the body
What detects pheromones?
The olfactory system by the vomeronasal organ
Steroid hormones have what two types of receptors?
1) Fast response (similar pathway to protein hormones)
2) Slow response
How does steroid transport work?
Transported in the blood by a complex system
How does movement through the cell membrane and cytoplasm work?
Disassociates with transport proteins
How does the binding of steroids to nuclear receptors work?
Similar to protein-receptor binding; initiates DNA-directed messenger RNA synthesis
How does mRNA synthesis and protein synthesis work?
New mRNA leaves the nucleus and attaches to ribosomes
What are the three patterns of hormone secretion?
1) Episodic
2) Basal
3) Sustained
What is episodic secretion?
Associated with hormones under the nervous control; When nerves in the hypothalamus fire, neuropeptides are released in a sudden burst/pulse
What is basal secretion?
Hormone level stays low, but fluctuates with low amplitude pulses; “Background noise”
What is sustained secretion?
Hormone level remains elevated; Relatively steady, stable fashion for a long period of time; “Consistent”
What are the four “strengths” of hormone action?
1) Pattern and duration of secretion
2) Half-life
3) Receptor density
4) Receptor-hormone affinity
Hypothalamic GnRH neurons must be able to _______ BEFORE they can induce ovulation
Respond to estradiol
How does testosterone cross the blood-brain barrier? How does it defeminize/kill the surge center?
Testosterone does not bind to anything, so it can easily cross the blood-brain barrier; Testosterone will convert/defeminize to estradiol which will then kill of the surge center
How are females able to keep the surge center?
Females have no testis to secrete testosterone, so it cannot defeminize; estradiol binds to alpha-fetoprotein, so it cannot cross the blood-brain barrier
