Blood (table 5.8) is a fluid connective tissue that travels through tubular vessels. Its primary function is to transport cells and dissolved matter from place to place. Blood consists of a ground substance called plasma and of cells and cell fragments collectively called formed elements. Eryth-rocytes22 (eh-RITH -ro-sites), or red blood cells, are the most abundant formed elements. In stained blood films, they look like pink discs with a thin, pale center. They have no nuclei. Erythrocytes transport oxygen and carbon dioxide. Leukocytes, or white blood cells, serve various roles in defense against infection and other diseases. They travel from one organ to another in the bloodstream and lymph but spend most of their lives in the connective tissues. Leukocytes are somewhat larger than erythrocytes and have conspicuous nuclei that usually appear violet in stained preparations. There are five kinds, distinguished partly by variations in nuclear shape: neutrophils, eosinophils, basophils, lymphocytes, and monocytes. Their individual characteristics are considered in detail in chapter 18. Platelets are small cell fragments scattered amid the blood cells. They are involved in clotting and other mechanisms for minimizing blood loss, and in secreting growth factors that promote blood vessel growth and maintenance.

Before You Go On

Answer the following questions to test your understanding of the preceding section:

  1. What features do most or all connective tissues have in common to set this class apart from nervous, muscular, and epithelial tissue?
  2. List the cell and fiber types found in fibrous connective tissues and state their functional differences.
  3. What substances account for the gelatinous consistency of connective tissue ground substance?
  4. What is areolar tissue? How can it be distinguished from any other kind of connective tissue?
  5. Discuss the difference between dense regular and dense irregular connective tissue as an example of the relationship between form and function.
  6. Describe some similarities, differences, and functional relationships between hyaline cartilage and bone.
  7. What are the three basic kinds of formed elements in blood, and what are their respective functions?

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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