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DISCUSSION QUESTIONS:
1) The four basic tissue types combine to form organ systems which perform the many diverse functions that occur in the human body, but what does each tissue type bring to the functioning organ/organism?
2) Discuss why gastrulation may be considered the most important event in embryogenesis.
3) Which of the 11 major organ systems are involved in homeostasis and what is their contribution to the maintenance of stable internal environment?
INDICATIVE ANSWERS TO DISCUSSION QUESTIONS:
1) Nervous tissue comprises the means to gather, process and control sensory, motor and cognitive functions through the formation of the central and peripheral nervous systems. Muscle tissue provides the motor functions of the body, not only in terms of locomotion and interaction with the environment but also in terms of the functional activities of the internal organ systems (eg cardiovascular and digestive systems). Epithelial tissues form the boundaries between organ systems, allowing them to act as discreet functional entities but they also serves to isolate the whole organism from the environment while allowing selective entry of some substances. Connective tissue is the more diverse group and is essentially responsible for most of the other functions not covered by the three previous tissue types!
2) Gastrulation is the key event in embryology involving the formation of the three primary germ cell layers (ie ectoderm, mesoderm and endoderm) and the establishment of the basic body plan (ie the generation of the three-dimensional body axes: the anterior-posterior, dorsal-ventral and left-right). Reorganization of the germ cells enables neurulation and organogenesis to follow.
3) It could be argued that all of the organ systems make some contribution to homeostasis to greater or lesser extents. Traditionally, however, the major contributors to maintaining homeostatic balance are considered to be the respiratory and the urinary systems, principally controlled by the nervous and endocrine systems. The contribution of the different systems varies greatly. At one end of the scale you have the control of acid/base balance, principally affected by the urinary and respiratory systems where major imbalances can occur rapidly if not controlled, and at the other end of the scale, the subtle effects of the skeletal system (controlled by the endocrine system) on the control of mineral levels. Other examples to be considered could be the control of blood pressure and tissue fluid volumes by the cardiovascular and lymphatic systems, control of pathogenic organisms by the immune system, barrier properties of the integumentary system etc.