Answer:
The correct option is b. lower esophageal sphincter
Explanation:
The esophagus is the initial part of the digestive tract and its function is the transport of the alimentary bolus from the pharynx to the stomach, through the thorax and avoid the reflux thereof. It begins and ends in two sphincter structures, the upper esophageal sphincter and the lower esophageal sphincter, which separate it from the pharynx and stomach. The lower esophageal sphincter has two functions: relax during swallowing and prevent reflux of the gastric contents into the esophagus in the postdeglutory period. After swallowing, there is a relaxation of the lower esophageal sphincter, pressure dropping to levels similar to those of the gastric fundus, which allows the bolus to enter the stomach. This relaxation lasts a few seconds and is followed by a strong contraction that prevents backflow of food.
Answer:
C) production of sperm and eggs
Explanation:
Sperms and eggs are the male and female gametes respectively. Formation of sperms and egg cells require meiotic cell division. Meiosis in sperm mother cells and egg mother cells reduces the chromosome number of half in the sperms and eggs. Meiosis also adds new gene combinations in these gametes by the process of crossing over.
Mitosis cannot reduce the chromosome number to half in the sperms and eggs. Absence of crossing over in mitosis leads to the formation of genetically identical progeny cells from mitosis.
Hence, mitosis can not form sperms and egg cells. If it does, the sperms and egg cells would not have genetic variations and there would be doubling of chromosome number with each round of sexual reproduction.
Effacement: The cervix – which is normally long and thick, measuring about 1-2 inches, starts to get shorter and thinner. This process is known as effacement. As the cervix gets more and more effaced, it gets shorter and shorter and “pulled up” into the lower part of the uterus.
Dilation: At the same time, the cervix softens and begins to open up – known as dilation. This widening, allows a smooth passage for the baby’s head and the rest of the body from the uterus into the vaginal canal.
