Human Digestion: Processes, Health, and Food Safety
Chewing
During chewing, food is fragmented, and its presence in the mouth stimulates the secretion of saliva (which moistens and lubricates the food bolus) by the salivary glands.
Swallowing
Once the bolus is crushed and insalivated, it passes from the mouth into the esophagus. This act is called swallowing. Swallowing is a voluntary phase, in which the tongue pushes the bolus against the palate and elevates the soft palate, and two involuntary phases: the first, when the bolus passes into the pharynx,
Read MoreEvolution and the Origin of Life: From Darwin to Modern Theories
The Origin of Variability
Darwin could not explain how such variability arises on which natural selection acts, and how such variability is maintained generation after generation. Many of the differences between individuals are due to genetic variations, and these are generated by two processes: mutation and sexual reproduction.
Mutations as a Source of Variability
Mutations are changes that occur randomly in genes. Those that affect the gametes are transmitted to offspring. Types:
- Harmful mutations:
DNA Replication, Transcription, and Translation in Molecular Genetics
Molecular Genetics: DNA Replication, Gene Expression, and Mutation
Concept of Gene
A gene is a fragment of DNA containing encoded information for the synthesis of structural and regulatory proteins.
Characteristics of Genes
- Prokaryotes: Genes are continuous units; all information contained in the gene leads to protein synthesis.
- Eukaryotes: Genes are fragmented. Sequences consist of information to synthesize proteins (exons) and other sequences that are eliminated in the transcript (introns).
Replication
Replication
Read MoreEnvironmental Science: Combustion, Conductivity, Climate, and Photosynthesis
Objective 7: Environmental Contamination by Combustion
The combustion process generates toxic gases, such as carbon dioxide. It also generates heat, affecting the environment and producing smog. This contributes to the greenhouse effect, which is the increase in temperature that occurs in the terrestrial globe due to environmental contamination.
Objective 8: Electrical Conductivity
Electrical currents are classified as chemical properties. When passed through solutions of acids or salts, they produce
Read MoreCellular Respiration: Krebs Cycle, Electron Transport, and Fermentation
Krebs Cycle
The Krebs cycle is the common pathway in all aerobic cells for the complete oxidation of carbohydrates, fats, and proteins. It can also be the starting point of biosynthetic reactions. This is because there are intermediate metabolites, which may go to the cytosol and act as anabolic precursors. In this sense, we say that the Krebs cycle is amphibolic. The process involves the complete oxidation of acetyl-CoA, which is excreted as carbon dioxide. The e-/H+ obtained in the successive oxidations
Read MoreSmooth Muscle, Striated Muscle, and Heart Function
Smooth Muscle Cells
Smooth muscle cells are the simplest of the three muscle types.
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Aspect
- Smooth muscle cells are fusiform, elongated, with sharp ends and an enlarged central portion with an elongated nucleus.
- Most are 5-20 µm in diameter (and up to 200 µm in the gravid uterus), and their length can vary between 20 µm and 1 mm or more (e.g., in the gravid uterus).
- These descriptions are of isolated cells, as they usually form narrow beams and homogenous bundles, making it difficult to see their