Изменить текст на жирный или добавить изображения с помощью Google Script

Это код, который у меня есть, и он отлично работает! Я просто хочу знать, как изменить текст на жирный и добавить изображения, если это возможно. Для тех, где он говорит, растет, светится, по поводу. Я бы хотел, чтобы это было выделено жирным шрифтом, например.

       function sendEmails() {
  var allData,counter,emailAddress,fourRowsOfData,i,lastRow,
      message,messageStart,messageEnd,numRows,
      row,sheet,startRow,studentName,subject;

  //USER INPUT
  startRow = 2;  // First row of data to process
  numRows = 4;   // Number of rows to process
  subject = "Camp Pursuit: Report Card ";
  messageStart = "Dear Parents,"+'\n' +'\n' +
  "Every week at Camp Pursuit, we ask the teachers to make observations about how the kiddos did." +'\n' +
  "We know that one week isn't enough to truly know a child, so we call this our " +"Glows, Grows, & Apropos." +'\n' +
    "Meaning..." + '\n' +'\n' +
    "Glows: Positive things the teacher noticed" +'\n' +
    "Grows: Areas for continued growth" +'\n' +
    "Apropos: Ways to continue your son/daughter enrichment" +'\n' +
    "We hope you appreciate seeing what the teachers saw last week, and perhaps you can use some of"+'\n' +
    "the recommendations for further enrichment this summer.  Feel free to let us know your thoughts on the camp through our anonymous online survey."+'\n' +
     "Your feedback helps us improve the experience for all kiddos! "+'\n' + 
"Survey Link: https://docs.google.com/forms/d/1g4LvA9a8sdKECr1yvp5uOoPnvKACFm3HvbTBfvQGRyo/viewform?usp=send_form" +'\n' +
"We look forward to seeing your child at our programs throughout the year!" +'\n' +
"Sincerely, "+'\n' +
"The Camp Pursuit Team"
+'\n';
  //END USER INPUT

  sheet = SpreadsheetApp.getActiveSheet();
  lastRow = sheet.getLastRow();

  allData = sheet.getRange(startRow, 1, lastRow-startRow, 10);// Get All data first

  counter = 0;

  while (counter < lastRow-startRow) {
    Logger.log('counter: ' + counter)

    fourRowsOfData = sheet.getRange(startRow + counter, 1, numRows, 6).getValues();
    emailAddress = fourRowsOfData[0][0];  // First column of first row
    Logger.log('emailAddress: ' + emailAddress)

    studentName = fourRowsOfData[0][1];

    messageEnd = "";//Reset on every outer loop

    for (i = 0; i < numRows; i++) {//loop numRows times - once for each row
        row = fourRowsOfData[i];

        messageEnd = messageEnd + '\n' +
            "Class: " + row[2] + '\n' +'\n' +
              "Glows: " + row[3]+ '\n' +
              "Grows: " + row[4] +'\n' +
                "Apropos: " + row[5] +'\n';  
    }

    message = messageStart + "\n" + studentName + "\n" + messageEnd;

    MailApp.sendEmail(emailAddress, subject, message);//Send the email outside of inner loop    
    counter+=numRows;//Increment counter by number of rows to process
  }
}