Page 36 - Control Theory in Biomedical Engineering

Modeling and control in physiology 23

Fig. 17 Blood glucose homeostasis. (The figure has been adopted from Abozenadah, H.,
et al., 2018. Allied Health Chemistry, Foundations of General, Organic, and Biological
Chemistry.)

external stimuli, such as eating or physical activity, affect the equilibrium of
glucose blood level. The blood glucose level can so increase or decrease and
affect the body’s equilibrium. In order to maintain blood glucose homeosta-
sis, the control process includes a closed feedback loop involving the pan-
creatic islet cells, the liver, the brain and the muscle, as described in Fig. 17.

3.3 Control strategies in homeostasis
In the literature, three basic control strategies guaranteeing homeostasis are
reported (Houk, 1988): (1) negative feedback control, (2) feed-forward con-
trol and (3) adaptive control. The control process of the human body via
negative feedback is described by the block diagram shown in Fig. 18.In
this strategy, natural sensors detect stimulus as external or internal perturba-
tions related to a given physiological variable, compare their levels to a given
set point and then send the error information in the form of electrical signals
to the brain. Then, the brain transmits the control signal to one or more nat-
ural effectors (muscles and glands), which respond to the instruction of the
brain as a corrective action in order to maintain the physiological variable in
a stable steady state.