Smooth muscle occurs in the airways of the gas exchange system. Explain how the smooth muscle cells in the bronchiolar walls help these airways to function.
Viewed in longitudinal section (LS), smooth muscle cells are long and taper at both ends. This shape is called fusiform. Each cell has a central nucleus, which also appears elongated. Fig. 1.1 shows a diagram of a smooth muscle cell to illustrate the fusiform shape.
A student used a microscope fitted with a calibrated eyepiece graticule to estimate that one smooth muscle cell was $250\,\mu\text{m}$ long. Name the type of microscope slide the student used to calibrate the eyepiece graticule.
The smallest object the student can see without using a microscope is $0.2\,\text{mm}$ long. Explain whether a cell of length $250\,\mu\text{m}$ could be seen without using a microscope.
Fig. 1.2 shows a photomicrograph of smooth muscle tissue in the intestinal wall. A capillary can be seen as well as smooth muscle cells. Outline the features that allow the blood vessel in Fig. 1.2 to be identified as a capillary.
Explain how the structure of a capillary is linked to its function in smooth muscle.
Caldesmon is a large protein with multiple binding sites for attachment to other proteins. It exists in two forms, H-caldesmon and L-caldesmon. H-caldesmon helps regulate contraction and relaxation in smooth muscle cells. L-caldesmon is found in some non-muscle cells, where it also functions as a regulatory protein. Caldesmon is encoded by the gene known as $\textit{CALD1}$. $\textit{CALD1}$ contains 17 exons. The primary structure of H-caldesmon has a repeating sequence in the middle of the amino acid chain that is absent from L-caldesmon. Researchers have found that a gene mutation is not responsible for the two different forms of caldesmon. Explain what is meant by a gene mutation.
Researchers now know that the two caldesmon forms arise from events taking place immediately after transcription of DNA. Alterations happen to the primary transcript produced by transcription. Suggest how smooth muscle cells and non-muscle cells can make different forms of caldesmon from the same primary transcript.
Suggest how the two forms of caldesmon can still have similar functions even though their primary structure is different.