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Growth Demands (growth + demand)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

160 Copepodology for the Phycologist with Apologies to G. E. Hutchenson

JOURNAL OF PHYCOLOGY, Issue 2003
P. A. Tester
Heterocapsa triquetra is one of the most common bloom forming dinoflagellates found in estuaries and near shore regions around the world. In order to bloom, H. triquetra optimizes a suite of factors including low grazing pressure, increased nutrient inputs, alternative nutrient sources, and favorable salinity and hydrodynamic conditions, as well as the negative factors of temperature-limited growth, short day lengths, and periods of transient light limitation. The prevailing environmental conditions associated its wintertime blooms are largely the result of atmospheric forcing. Low-pressure systems moved through coastal area at frequent intervals and are accompanied by low air temperatures and rainfall. Runoff following the rainfall events supplies nutrients critical for bloom initiation and development. Heterocapsa triquetra blooms can reach chl a levels >100 mg L,1 and cell densities between 1 to 6×106 L,1. As the blooms develop, nutrient inputs from the river became insufficient to meet growth demand and H. triquetra feeds mixotrophically, reducing competition from co-occurring phytoplankton. Cloud cover associated with the low-pressure systems light limit H. triquetra growth as do low temperatures. More importantly though, low temperatures limit micro and macrozooplankton populations to such an extent that grazing losses are minimal. [source]

Relationship between cribra orbitalia and enamel hypoplasia in the early medieval Slavic population at Borovce, Slovakia

INTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 3 2008
Z. Obertová
Abstract Cribra orbitalia and enamel hypoplasia were examined in an early medieval (8th to beginning of 12th century AD) skeletal sample of 451 individuals from Borovce, Slovakia. More than 40% of these individuals died before reaching 20 years of age. The relationship between the occurrence of orbital and enamel lesions was analysed by focusing on the age-specific distribution, and on its influence on demographic parameters. Both features were found in 11.2% of the observed skulls. The presence of orbital and dental lesions showed a considerable impact on mortality as well as the life expectancy. Generally, the highest mortality was observed among 0,4 year old individuals. The greatest discrepancy in the demographic parameters, however, appeared between the affected and unaffected individuals aged 10,14 and 15,19 years. In these two age groups the co-occurrence of both lesions was most frequently recorded. These individuals obviously had a history of sickness, and thus could not cope with further bouts of disease and with the increased physiological demands of pubertal growth. The missing correlation in younger age categories can be largely explained by the difficulty of macroscopically examining the permanent dentition, since an interrelationship between the age at hypoplasia development and the occurrence of cribra orbitalia was detected. Several differences between the individuals with enamel defects and both conditions were observed in the distribution of age at hypoplasia formation. According to these results, several factors, such as impaired health status, growth demands and diet, influence the development of enamel hypoplasia and cribra orbitalia in a particular population. It is possible that after reaching a certain threshold, the underlying factors act synergistically in a kind of vicious cycle as the balance between the immune system, metabolism, and exogenous factors such as pathogens and nutrition, is disturbed. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Reproductive adaptations to a large-brained fetus open a vulnerability to anovulation similar to polycystic ovary syndrome

AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 3 2003
Deborah K. Barnett
During the ovarian or menstrual cycle, prior to ovulation, many female primates exhibit a relatively prolonged follicular phase and terminate the postovulatory luteal phase with menstrual bleeding. The prolonged follicular phase is a trait that distinguishes primate from nonprimate species. It enables extended estrogen-induced proliferation and growth of the uterine endometrium prior to progesterone-induced maturation during the luteal phase to accommodate a potential pregnancy with a rapidly invading placenta. Progressive development of both an extended duration of estrogen-induced, preimplantation endometrial proliferation and a rapidly invading placenta across the Primate order may well have been necessary to accommodate differentiation and growth of an increasingly large fetal brain. Prolongation of the follicular phase in primates has also led to the isolation of the final stages of follicle selection (growth deviation of the dominant follicle from its contemporaries) solely within the follicular phase and thus outside the protection of luteal phase progesterone inhibition of pituitary luteinizing hormone (LH) secretion. Such primate reproductive characteristics put the latter stages of ovarian follicle selection at risk of exposure to excessive pituitary secretion of LH. Excessive secretion of LH during follicle selection could result not only in impaired follicle development, excessive ovarian androgen secretion, and ovulation failure, but also in excessive estrogenic stimulation of the uterine endometrium without intervening menstrual periods. Such reproductive abnormalities are all found in a single, prevalent infertility syndrome afflicting women in their reproductive years: polycystic ovary syndrome (PCOS). We propose that successful female reproductive adaptations to accommodate the growth demands of large-brained primate fetuses have facilitated a particular vulnerability of higher primates to hypergonadotropic disruption of ovulatory function, as found in PCOS. Am. J. Hum. Biol. 15:296,319, 2003. © 2003 Wiley-Liss. [source]

Adaptations in placental nutrient transfer capacity to meet fetal growth demands depend on placental size in mice

THE JOURNAL OF PHYSIOLOGY, Issue 18 2008
P. M. Coan
Experimental reduction in placental growth often leads to increased placental efficiency measured as grams of fetus produced per gram of placenta, although little is known about the mechanisms involved. This study tested the hypothesis that the smallest placenta within a litter is the most efficient at supporting fetal growth by examining the natural intra-litter variation in placental nutrient transfer capacity in normal pregnant mice. The morphology, nutrient transfer and expression of key growth and nutrient supply genes (Igf2P0, Grb10, Slc2a1, Slc2a3, Slc38a1, Slc38a2 and Slc38a4) were compared in the lightest and heaviest placentas of a litter at days 16 and 19 of pregnancy, when mouse fetuses are growing most rapidly in absolute terms. The data show that there are morphological and functional adaptations in the lightest placenta within a litter, which increase active transport of amino acids per gram of placenta and maintain normal fetal growth close to term, despite the reduced placental mass. The specific placental adaptations differ with age. At E16, they are primarily morphological with an increase in the volume fraction of the labyrinthine zone responsible for nutrient exchange, whereas at E19 they are more functional with up-regulated placental expression of the glucose transporter gene, Slc2a1/GLUT1 and one isoform the System A family of amino acid transporters, Slc38a2/SNAT2. Thus, this adaptability in placental phenotype provides a functional reserve capacity for maximizing fetal growth during late gestation when placental growth is compromised. [source]