Puberty
It is a Sexual Maturity or Reproductive Competence, Ability for an animal to release gametes and to manifest complete sexual behavior sequence. the Gradual process Not a single event and Occurs over a period of time
Reproductive endocrine system maturity
1. Hypothalamic-Pituitary-Gonad Axis
Initiated by hypothalamic neuron development Release of GnRH and Feedback mechanisms evolve
2. Influences
Development of threshold body size Exposure to a variety of environmental and social cues Genetics of the Animals
Onset of Puberty
A. Age at Puberty (Farm Animals)
Puberty Age
SpeciesMaleFemale
Cattle11 mo. (7-18) 11 mo. (9-24)
Sheep 7 mo. (6-9) 7 mo. (4-14)
Swine 7 mo. (3-8) 6 mo. (3-7)
Horses 14 mo. (10-14) 18 mo. (12-19)
B. Age at Puberty (Other Mammals)
Rabbits3 to 4 months
Cat8 to 9 months
Dog10-12 months
Humans10-16 years
Endocrine Mechanism of Puberty
A.Maturation of Hypothalamus
1.Pituitary and Gonad can function before puberty Exogenous hormones
2.Hypothalamus need to mature for puberty to occur Gradual process Proportional to growth
B.Maturation of GnRH release centers (Hypothalamus)
1.Two release centers
a.Tonic release center Sensitive to negative feedback of steroid hormones
b.Surge release center Sensitive to positive feedback of estradiol LH surge Ovulation
C.TonicCenter
1Circulating gonadotropins increase pulsatility
2.Frequency controlled by Pulse Generator
a.Senses internal and external stimuli
i.Internal--Nutrients, Metabolites, Steroid Hormones, etc.
ii.External Day length, Pheromones, etc.--
3.Steroid hormones undergo gradual rise to adult levels
D.SurgeCenter
1.Characteristics of prepubertal female: Lack of gonadal estradiol to stimulate surge center and Lack of sensitivity to estradiol at surge center
2.Increase in tonic pulsatility: increases gonadal estradiol(GnRH,LH/FH, Increase Follicular Development Increase Steroidogenesis (Estradiol)
3.Increase in sensitivity to estradiol
a.Sensitivity increases with age/body weight
i.Increase in estrogen receptor numbers
b.Estradiol much reach threshold concentration to cause surge
Positive Feedback
Parturition
Parturition is the act or process of giving birth to offspring. The terms used to describe parturition vary with the species of animal it is being used to describe. The following are examples of parturition terminology:
A dog whelps and gives birth to puppies
A cow calves and give birth to a calf
A sow farrows and gives birth to piglets
A ewe lambs and give birth to lambs
A horse foals and give birth to a foal
Stages of Parturition
Just as there are 3 phases of pregnancy, there are also 3 stages of parturition. It is important to recognise each stage and monitor the dam to make sure she is progressing from one stage to the next in a timely fashion.
TheFirst Stage of Parturition is the Preparatory Stage. During this stage, a number of important things happen, including:
*Positioning of the fetus for birth - The normal position of a fetus is with the front feet pointing out the cervex, right-side up with the chin resting on forelegs. With cattle, sheep and horses, any other position is considered an abnormal position and may result in dystocia.
*Dilation of cervix
*Exposure of fetal membranes through the vulva with possible rupture
In the cow, this stage can last for up to 6 hours. During this time, it is inadvisable to attempt to assist the dam with delivery. If, however, the dam does not progress to the second stage of parturition within 6 hours, it is likely that there are problems with positioning of the fetus that will require assistance. In a full breech position, where the rump is presented to the cervix and the hind feet are tucked under the calf's belly, the cervix will not dilate properly due to lack of stimulation by the nose and front feet of the fetus.
TheSecond Stage of Parturition is the Expulsion Stage. During this stage, the following takes place:
- Uterine contractions intensify, leading to
- Abdominal pressing by the dam, followed by
- Expulsion of the fetus
In the cow, this stage of parturition can take up to 4 hours; in the mare, the foal must be delivered within 15 minutes of the rupture of the amniotic sac, or the foal is likely to sufficate. The ewe usually delivers each lamb at about 15 minute intervals. The sow normally delivers piglets at approximately 5-6 minute intervals. One should assist the dam only after the cervix is fully dilated or you may damage the cervix and uterus.
The Third Stage of Parturition is the "Cleaning" Stage. During this stage, the placental membranes (afterbirth) are expelled. This happens after each birth in cattle, sheep and horses, however the sow may deliver all the piglets from one uterine horn, expell the placental membranes from that horn and then deliver the pigs from other horn, or she may deliver all of the piglets before she "cleans". It is very important to make sure that the animal finishes the third stage of parturition, because any remnants of placental membranes left in the uterus will serve as a nidus for infection and could lead to the death of the dam. In the horse, the placental membranes should be expelled within 15 minutes of expulsion of the fetus. Swine can take up to 1 hour to expell the placental membranes, and cattle may take as much as 12 hours to deliver the placental membranes. After the appropriate length of time, if the membranes are not expelled, the animal has a retained
Placental Hormones
In addition to its role in transporting molecules between mother and fetus, the placenta is a major endocrine organ. It turns out that the placenta synthesizes a huge and diverse number of hormones and cytokines that have major influences on ovarian, uterine, mammary and fetal physiology, not to mention other endocrine systems of the mother. This section focuses only on the major steroid and protein hormones produced by the placenta. Additional details on placental endocrinology can be found in the Placental Hormones section of the Endocrine System text.
Steroid Hormones
Sex steroids are the best known examples of placental hormones. Two major groups are produced by all mammals:
Progestins: Progestins are molecules that bind to the progesterone receptor. Progesterone itself is often called the hormone of pregnancy because of the critical role it plays in supporting the endometrium and hence on survival of the conceptus.
The placentae of all mammals examined produce progestins, although the quantity varies significantly. In some species (women, horses, sheep, cats), sufficient progestin is secreted by the placenta that the ovaries or corpora lutea can be removed after establishment of the placenta and the pregnancy will continue. In other animals (cattle, pigs, goats, dogs), luteal progesterone is necessary throughout gestation because the placenta does not produce sufficient amounts.
Progestins, including progesterone, have two major roles during pregnancy:
Support of the endometrium to provide an environment conducive to fetal survival. And Suppression of contractility in uterine smooth muscle.
Progesterone and other progestins also potently inhibit secretion of the pituitary gonadotropins luteinizing hormone and follicle stimulating hormone. This effect almost always prevents ovulation from occurring during pregnancy.
Estrogens: The placenta produces several distinct estrogens. In women, the major estrogen produced by the placenta is estriol, and the equine placenta synthesizes a unique group of estrogens not seen in other animals. Depending on the species, placental estrogens are derived from either fetal androgens, placental progestins, or other steroid precursors.
. Two of the principle effects of placental estrogens are:
Stimulate growth of the myometrium and antagonize the myometrial-suppressing activity of progesterone and Stimulate mammary gland development. Estrogens are one in a battery of hormones necessary for both ductal and alveolar growth in the mammary gland.
Protein Hormones
Several protein and peptide hormones are synthesized in placentae of various species. They have effects on the mother's endocrine system, fetal metabolism and preparation of the mother for postpartum support of her offspring.
Chorionic gonadotropins: As the name implies, these hormones have the effect of stimulating the gonads, similar to the pituitary gonadotropins. The only species known to produce a placental gonadotropin are primates and equids.
The human hormone is called human chorionic gonadotropin or simply hCG. This hormone is produced by fetal trophoblast cells. It binds to the luteinizing hormone receptor on cells of the corpus luteum, which prevents luteal regression. Thus, hCG serves as the signal for maternal recognition of pregnancy. The first hormone you produced was hCG!
Equine chorionic gonadotropin is also produced by fetal trophoblast cells. It is actually the same molecule as equine luteinizing hormone.
Placental lactogens: These hormones are molecular relatives of prolactin and growth hormone. These hormones have been identified in primates, ruminants and rodents, but not in other species.
The functions of placental lactogens are not well understood. They are thought to modulate fetal andmaternal metabolism, perhaps mobilizing energy substrates for fetal use. In some species they have been shown to stimulate function of the corpus luteum, and to participate in development of the mammary gland prior to parturition.
Relaxin: Relaxin is a hormone thought to act synergistically with progesterone to maintain pregnancy. It also causes relaxation of pelvic ligaments at the end of gestation and may therefore aid in parturation. In some of the species in which relaxin is known to be produced, it is produced by the placenta, while in others, the major source is the corpus luteum. In some species, relaxin is produced by both the corpus luteum and placenta.
Animal Pregnancy StageAndrew Bret Wallis/Photodisc/Getty Images
The development of animals is extremely interesting, because we get to see how it is similar and how it is different from the development of human beings in the womb. In the development of animals, the new life grows in its own right and in preparation for its own children.
Early Cellular Changes
Immediately after conception occurs, cleavage of the cell into many smaller cells occurs. They come together in a form known as the blastula. The cells begin to take on different positions in relation to one another. When they are doing this, the cells-which are now an embyro- are referred to as being in the gastrula stage. Due to this process, the cell has three germ layers, known as the ectoderm, endoderm and mesoderm
Formation of Organs
One of the most fascinating processes of the pregnancy cycle is the creation of organs in the womb. Organogenesis is the process of organ and tissue formation. This process can occur because the three germ layers are now interacting with one another. Instead of the typical breakdown from organ to tissues, we are looking at the build up process of these materials. Once the organs have been formed, the cells begin to move to where they are going to remain for the organism's life. Virtually all of the distinct features of the body are formed at this point. In a human's pregnancy, the sexual organs could be used to determine the gender of the baby.
Preparation for the Future
Even at this early stage of life, the body begins to prepare itself for future generations. Most of the cells in the body are referred to as somatic cells. However, there are also germ cells which are mainly composed of gametes. These cells are for the developing organism's own sexual reproduction in the future. The germ cells will go into the sexual organs of the developing fetus. However, this process is a continual one. Gametes, which allow the animal to produce a child during sexual intercourse, will not appear until the creature is sexually mature. Sexually maturity in animals is the equivalent of puberty in human beings.