Basic science and biochemistry Flashcards
. In addition to macrophages, what type of alveolar epithelial cell type is responsible for major surfactant metabolism?
A. Type I
B. Type II
C. Type III
D. Type IV
B. At 16-26 weeks, embryologic processes taking place in the fetal lungs include the development of respiratory bronchioles, acinar saccules, thinning of capillary epithelial space, and differentiation of type I and type II epithelial cells. From 32 weeks to childhood, the events include septation of alveoli, maturation of type II cells, and surfactant production. Along with macrophages, type II alveolar epithelial cells are responsible for the major pathways involved in surfactant metabolism. Specific enzymes in the endoplasmic reticulum of type II cells use glucose, phosphate, and fatty acids as substrates for phospholipid synthesis. The major phospholipid in surfactant is synthesized by type II cells as a 2-acyl unsaturated molecule, which is minimally surface active. This phosphatidylcholine is then remodeled to yield phosphatidylcholine with palmitic acids in the 1-acyl and 2-acyl positions, referred to as saturated phosphatidylcholine. This lipid is very surface active but is solid at body temperature. Other phospholipids, such as phosphatidylinositol and phosphatidylglycerol, and the surfactant proteins facilitate surface adsorption of the saturated phosphatidylcholine and thus affect surfactant function. Once the type II cell has matured sufficiently to have surfactant stores, secretion can be stimulated from type II cells.
Which of the following molecules is MOST responsible for the coordination of contractions during labor?
A. Progesterone
B. Estrogen
C. Connexin-43
D. Vasopressin
C. Both with preterm and term labor, myometrial contractions are a hallmark of parturition. During labor, the individual myocytes contract together as a functional syncytium. This increased coordination is induced by gap junction formation, which increases cell-to-cell communication. Gap junctions develop in the myometrium before labor and disappear after delivery. Expression of gap junction protein, connexin-43, in human myometrium is similar in both term and preterm labor. These findings suggest that the appearance of gap junctions and increased expression of connexin-43 (contraction-associated proteins) are part of the underlying series of molecular and cellular events responsible for the switch from contractures to contractions before the onset of parturition. The connexin-43 gene encodes a protein with critical roles in synchronizing myometrial contractile activity. Increasing evidence suggests that the developing fetus may produce physical and hormonal signals that stimulate macrophage migration to the uterus, with release of cytokines and activation of inflammatory transcription factors, such as nuclear factor κB (NF-κB) and activator protein 1 (AP-1), which also is activated by myometrial stretch. It has been postulated that the increased inflammatory response and NF-κB activation promote uterine contractility via 1) direct activation of contractile genes (e.g. COX-2, oxytocin receptor, and connexin 43) and 2) impairment of the capacity of progesterone receptor to mediate uterine quiescence. The other molecules listed are hormones that do influence myometrial contraction, but do not participate in the synchronization of contractions to the same degree as the connexin proteins. 1. Creasy and Resnik’s Maternal-Fetal Medicine. 7th Edition. P 610. 2. Mendelson CR. Minireview: fetal-maternal hormonal signaling in pregnancy and labor. Mol Endocrinol. 2009 Jul;23(7):947-54 3. Saito T, Nishimura M, Kudo R, Yamasaki H. Suppressed gap junctional intercellular communication in carcinogenesis of endometrium. Int J Cancer. 2001 Aug 1;93(3):317-23. 4. Kilarski WM, Dupont E, Coppen S, et al. Identification of two further gap-junctional proteins, connexin 40 and connexin 45, in human myometrial smooth muscle cells at term. Eur J Cell Biol. 1998 Jan;75(1):1-8.
