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Genetic Material
- in nucleus of each cell in the body
- genes passed on to next generation via the gametes
- - ova in female
- - spermatozoa in male
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Genetic sex of an animal
- established at fertilization
- depends on whether the spermatozoan carries the X or Y chromosome
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Phenotype
- physical expression
- depends on the action of sex-determining genes (trigger gonad development)
- secretion of reproductive hormones from the gonads
- action of these hormones leads to the development of the reproductive system
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Reproductive hormones
- estrogen and testosterone are the biggies
- control ovulation and fertilization
- implantation and growth of the embryo into a fetus
- parturition
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Reproductive physiology
control starts in the brain - hypothalmus and pituitary
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Hypothalmus
- governs the reproductive system
- send signals to the pituitary gland (hypophysis or hypophyseal gland)
- lies below the thalmus at the base of the brain
- actually is part of the brain
- main action is to control the amount and type of gonadotropic hormones secreted by the pituitary gland
- other actions:
- - is responsible for the timing and onset of puberty
- - sexual interest and the mating drive
- - supresses production of prolactin
- - secretes gonadotropin releasing hormone (GnRH), which acts upon pituitary
- receives neural input from other parts of the brain and its secretion is influenced by...
- - daylight length
- -- influences the pineal gland (secretes melatonin during the hours of darkness)
- - smell
- -- pheremones (animals smells) can trigger hypothalmic secretions
- -- eg "ram effect" - ram secretes hormones to bring ewe into season
- - nutrition
- -- very thin animals stop their reproductive cycles
- -- body can't support a pregnancy
- - sound
- -- calling cats will bring a tom cat - trigger hypothalmic secretion increasing tom's libido
- - fear
- -- of a dominant male
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Pituitary gland (hypophyseal gland or hypophysis)
- controls the gonads - testes or ovaries
- is an extension of the brain
- hollow stalk is a part of the 3rd ventricle of the brain
- divided into 2 parts:
- - anterior pituitary or anterior lobe (adenohypophysis)
- - posterior pituitary
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Anterior pituitary or anterior lobe (adenohypophysis)
- secretes 4 reproductive hormones:
- - luteinizing hormone (LH)
- - follicle stimulating hormone (FSH)
- - prolactin
- - adrenocorticotropic hormone
- LH and FSH are the pituitary gonadotropins (act upon the gonads)
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Testes or ovaries
release hormones that influence other parts of the reproductive tract
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Male reproductive hormones control...
- production of spermatozoa in the testes
- development of the male type phenotype:
- - thickened cheek pouches of the male tom cat - will shrink a bit if neutered
- - crest or curve of the neck in the stallion
- development of the male libido (sex drive)
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Female reproductive hormones control...
- development of the follicles and maturation of the oocytes (ova or eggs)
- maintenance of pregnancy and lactation
- development of female behavior
- more complex reproductive cycle than male
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Hypothalamo-hypophyseal axis
describes the relationship between the hypothalmus and the pituitary gland
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Luteinizing hormone
release of LH is stimulated by gonadotropic releasing hormone (GnRH) from the hypothalmus
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Luteinizing hormone in the female
- high levels
- - a surge of LH stimulates ovulation
- low levels
- - assists FSH in stimulating the development of the follicle in the ovary
- - supports the corpus luteum in the ovary
- - stimulates the production of progesterone by the luteal cells (in corpus luteum)
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Luteinizing hormone in the male
- stimulates the Leydig cells of the testes to secrete testosterone
- high levels
- - acts as a negative feedback on the hypothalmus and reduces the amount of GnRH produced
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Follicle Stimulating Hormone
release is stimulated by gonadotropin releasing hormone (GnRH)
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Follicle Stimulating Hormone in the female
- stimulates production of follicles in the ovary
- high levels
- - acts as a negative feedback on the hypothalmus and reduces the amount of GnRH produced
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Negative feedback
used as a check and balance mechanism
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Follicle Stimulating Hormone in the male
- stimulates the Sertoli cells of the testis to produce androgen binding protein
- - which stimulates spermatogenesis
- high levels
- - acts as a negative feedback on the hypothalmus and reduces the amount of GnRH produced
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Prolactin
- high levels
- - stimulates production of milk
- low levels
- - maintains the corpus luteum in the ovary
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Adrenocorticotropic hormone (ACTH)
stimulates the adrenocortex to release corticosteroids
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Corticosteroids in reproduction
initiate the cascade of events that result in parturition
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Posterior Pituitary
- secretes oxytocin which:
- - causes milk letdown
- - causes smooth muscle contraction (uterus)
- - acts as a prostaglandin precursor (causes corpus luteum regression)
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Hormones in female reproductive system
- hypothalmus makes:
- - gonadotropin-releasing hormone (GnRH)
- pituitary gland makes:
- - follicle stimulating hormone (FSH)
- - luteinizing hormone (LH)
- ovaries make:
- - estrogen (Graafian follicles)
- - progesterone (corpus luteum)
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How a cycle works
- 1. The hypothalmus secretes gonadotropin releasing hormone (GnRH)
- 2. This stimulates the pituitary gland to release follicle stimulating hormone (FSH)
- 3. Its presence in the blood causes the Graafian follicles to grow
- 4. As they grow, they produce estrogen
- 5. The higher levels of estrogen in the blood causes the pituitary gland to stop releasing FSH and start releasing luteinizing hormone (LH)
- 6. This causes the Graafian follicles to rupture, releasing eggs.
- 7. The ruptured follicle, now a corpus luteum, starts releasing progesterone (needed to maintain pregnancy) into the blood.
- 8. Its presence stops the pituitary gland from releasing LH and FSH.
- 9. If conception occurs, the corpus luteum becomes functional and produces progesterone to maintain pregnancy.
- 10. If conception does not occur, the corpus luteum disappears and progesterone level lowers to the point where cycle ends.
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Gonadotropin-releasing hormone (GnRH)
- produced in the hypothalmus
- secreted by the pituitary gland to release gonadotropins (LH, FSH)
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Graafian follicles
- small sac in the ovaries the enclose an ovum
- immature follicles contain an undeveloped egg cell
- mature follicles break open and release an ovum => ovulation
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Prolactin
- promotes growth of mammary tissue
- stimulates and sustains milk production in postpartum animals
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Pineal gland
- attached to cerebrum of brain
- functions as a light receptor
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Melatonin
- synthesized and secreted by the pineal gland (during the hours of darkness)
- suppresses GnRH, which stops reproductive activity
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Luteinizing hormone in the female
- stimulates ovulation of mature follicles
- stimulates the development of the follicle in the ovary
- supports the corpus luteum formation
- stimulates the production of progesterone
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Luteinizing hormone in the male
stimulates Leydig cells of testes to secrete testosterone
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Follicle stimulating hormone in the female
stimulates the production of follicles in the ovary
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Follicle stimulating hormone in the male
stimulates Sertoli cells of testis to stimulate spermatogenesis
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Adrenocorticotropic hormone (ACTH)
stimulates adrenal cortex to release corticosteroids (parturition)
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Oxytocin
- causes milk letdown
- causes smooth muscle contraction in uterus during parturition
- prostaglandin precursor - secretion causes corpus luteum regression
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Prostaglandin
- naturally occurring
- chemically related long-chain fatty acids
- used in the treatment and regulation of activity of the female reproductive system
- luteolytic - regression of the corpus luteum
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Testis
- two different cells produce hormones:
- - Sertoli cells
- - Leydig cells
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Sertoli cells
- found within the seminiferous tubules next to the spermatogonia that divide to produce sperm
- are stimulated by FSH from the anterior pituitary and produce:
- - Androgen binding protein
- - Inhibin
- - Estrogen
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Androgen Binding protein
binds testosterone to stimulate spermatogoenesis
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Inhibin
- depresses secretion of FSH (but has no effect on LH)
- "seesaw" method of hormone secretion:
- - as inhibin goes up, FSH goes down
- - as inhibin goes down, FSH goes down (produces more FSH)
- - series of checks and balances
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Estrogen produced by Sertoli cells
- testosterone is converted to estrogen (low levels in the male)
- high levels in the male, inhibit secretions from the anterior pituitary
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Leydig cells
- found between the seiniferous tubules (interstiial cells)
- stimulated by LH from the anterior pituitary and secrete testosterone
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Actions of testosterone
- inhibit the secretion of LH and FSH, acting as a negative feedback
- stimulate the growth and activity of the male reproductive tubular genitalia and accessory sex glands and scrotum
- stimulate spermatogenesis in the presence of androgen binding protein
- stimulate hypertrophy of cells and organs in general; anabolic (building) activity
- stimulate male behavior
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Male reproductive tubular genitalia
- epididymis
- vas deferns
- ampullae
- seminal vesicles
- prostate
- urethra
- prepuce
- penis
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Ovary
- Granulosa cells
- Luteal cells
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Granulosa cells
- line the tertiary of Graafian follicles in the ovary
- stimulated by FSH to produce estrogen
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Graafian follicles
small sac in the ovary that encloses the ovum
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Actions of estrogen
- develop and maintain cyclic changes in the female tubular genitalia
- develop the secretory ducts of the mammary gland and uterine gland
- stimulate female estrous behavior (mating behavior)
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Female tubular genitalia
- Fallopian tube
- uterine horn
- uterine body
- cervix
- vagina
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Luteal cells
- cells of the corpus luteum produce:
- - progesterone
- - relaxin
- - oxytocin
- - estrogen
- the corpus luteum and the secretion of progesterone is supported by LH secretion
- LH is luteotropic (stimulates the formation of the corpus luteum)
- LH & FSH cause ovulation of mature follicles
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Progesterone
- the hormone of pregnancy
- actions are to:
- - cause development of uterine glands in an estrus primed uterus
- - block normal myometrial contractivity of the uterus (prevents premature contractions)
- - stimulate glandular development of the mammary gland
- - inhibit GnRH
- levels rise just before eggs are released
- testing for progesterone in bitch is a more accurate way to determine the heat cycle than testing for estrogen
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Relaxin
- actions are to:
- - cause relaxation of the pelvic ligaments and the cervix, enlarging the birth canal
- - suppress lactation
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Oxytocin
- action is to:
- - attach to receptors in the uterus and act as a precursor to prostaglandin (which causes regression of the corpus luteum)
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Estrogen, progesterone and testosterone
are steroid hormones
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Pineal gland
- aka epiphyseal cerebri
- receives messages about day length from other parts of the brain and secretes melatonin
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Melatonin
- turns the hypothalmus on and off
- synthesized during the hours of darkness
- action is to supress GnRH
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Absence of GnRH
- no stimulation of the anterior pituitary gland
- reproduction activity stops
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Physiology of parturition
- onset requires a live fetus
- secretions from the fetus trigger a cascade of events leading to parturition
- 1. Trigger for parturition is the secretion of adrenocorticotropic hormone (ACTH) from the anterior pituitary of the fetus brought about by...
- 1a. stress - fetus reaches a size where placenta can no longer supply nutrients for further growth
- 2. ACTH cause the fetal and maternal adrenal cortex to release cortisol
- 3. Raised cortisol levels stimulate production of enzymes that allow conversion of progesterone to estrogen
- 4. Fall in progesterone removes the block of contraction of smooth muscle of the uterus (myometrium)...
- 4a. frequency and amplitude of uterine contractions increases
- 5. Raised levels of estrogen stimulates the production of oxytocin (increases uterine contractions)
- 6. Regression of the corpus luteum - progesterone levels fall even further
- 7. Increased uterine contractions cause fetus to move towards the cervix
- 8. Dilation of cervix causes release of oxytocin
- 9. Oxytocin induces more uterine contractions which further engage fetus in the cervix and pelvis
- 10. Relaxin is produced by the placenta and/or the maternal corpus luteum and causes relaxation of the cervix
- 11. Presence of th fetus in the pelvis stimulates contraction of the abdominal muscles and straining
- 11a. Abdominal muscle straining is responsible for the final expulsion of the fetus through the birth canal
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First stage of labor
- begins with the onset of increased uterine contractions
- encompasses numbers 1-7 above
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Second stage of labor
- begins when the fetus enters the birth canal and abdominal straining starts
- number 8 through period when the fetus is expelled
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Third stage of labor
- expulsion of the placenta (fetal membranes)
- occurs after the expulsion of the fetus in animals that have one fetus or interspersed with the fetus in litter-bearing animals
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Presentation
describes the relationship of the head and body of the fetus to the long axis of the dam
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Anterior presentation
fetal head is coming first
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Posterior presentation
tail comes first
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Transverse presentation
fetus is across the birth canal
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Position
describes where the fetal verterbral column is relative to the birth canal
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Posture
describes the arrangement of the fetal head and limbs
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Normal parturition
anterior presentation and dorsal position with one foreleg slightly in front of the other so that the head and 2 forelegs form a cone
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Lactation
- mammary glands
- - modified sweat glands
- - lie along either side of midline of ventral abdomen
- - development is triggered by rising levels of prolactin and milk
- - letdown is triggered by oxytocin
- colostrum
- - milk released in the first few hours after parturition
- - high levels of antibodies
- - passive immunity to newborn
- - antibodies absorbed undamaged by newborn in first few hours of life because pH of stomach is neutral
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Androgens
- hormones that determine the expression of the male phenotype...
- including outward development of secondary sex characteristics and initiation and maintenance of spermatogenesis
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Estrogen
- hormone formed in the ovary
- responsible for secondary female characteristic development
- act on female genitalia to produce and environment suitable for fertilization, implantation and nutrition of the early embryo
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Testosterone
- most important male sex hormone
- produced by the Leydig cells of the testes
- chief function is to stimulate the development of the male reproductive organs and the secondary sex characteristics
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Corpus luteum
a progesterone secreting yellow glandular mass in the ovary formed from the wall of an ovarian follicle that has matured and released its ovum
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Luteotropic
stimulating the formation of the corpus luteum
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Parturition
act or process of giving birth
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Adrenal cortex
- outer part of the adrenal gland
- produces 3 main groups of hormones: glucocorticoids, mineralocorticoids and androgens
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Myometrium
smooth muscle layer of uterus
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