Tissue and Organ Formation

The tissues just described form organs and organ systems that are much the same in all vertebrates. To get a general sense of how this happens, start with a sperm and egg. Recall that these develop from germ cells, which are immature reproductive cells. (All other cells in the body are “somatic”, after the Greek word for body.) After a zygote forms at fertilization, mitotic cell divisions produce an early animal embryo. In vertebrates, the cells soon become arranged as three primary tissues-ectoderm, mesoderm, and endoderm. These are embryonic forerunners of all tissues in the adult. Ectoderm gives rise to the skin’s outer layer and to tissues of the nervous system. Mesoderm gives rise to the tissues of muscle, bone, and most of the circulatory, reproductive, and urinary systems. Endoderm gives rise to the gut’s lining and organs derived from it.

You might think we are stretching things a bit when we say that each one of those systems contributes to the survival of all living cells in the body. After all, what could the body’s bones and muscles have to do with the life of a tiny cell? Yet interactions between the skeletal and muscular systems allow us to move about toward sources of nutrients and water, for example. Parts of those systems assist blood circulation, as when contractions of leg muscles help move blood in veins back to the heart. The bloodstream transports nutrients and other substances to individual cells, and transports secreted products and wastes away from them.

MUSCULAR SYSTEM
Movement of internal body parts movement of whole body maintenance of posture heat production.

INTEGUMENTARY SYSTEM
Protection from injury, dehydration, and some microorganisms; control of body temperature; excretion of some wastes; reception of external stimuli.

NERVOUS SYSTEM
Detention of external and internal stimuli control and coordination of responses to stimuli integration of activities of all organ systems.

URINARY SYSTEM
Maintenance of the volume and composition of extracellular fluid. Excretion of blood-borne wastes.

SKELETAL SYSTEM
Support, protection of body parts sites for muscle attachment, body cell production, and calcium and phosphate storage.

CIRCULATORY SYSTEM
Rapid internal transport of many materials to and from cells helps stabilize internal temperature and pH.

REPRODUCTIVE SYSTEM
Male: Production and transfer of sperm to the female. Female: Production of eggs provision of a protected, nutritive environment for developing embryo and fetus. Both systems have hormonal influences on other organ systems.

RESPIRATORY SYSTEM
Delivery of oxygen to cells removal of carbon dioxide wastes produced by cells pH regulation.

DIGESTIVE SYSTEM
Ingestion of food, water preparation of food molecules for absorption elimination of food residues from the body.

LYMPHATIC SYSTEM
Return of some tissue fluid to blood roles in immunity (defense against specific invaders of the body).

ENDOCRINE SYSTEMHormonal control of body functioning works with nervous system in integrative tasks.