Other hormones bind to nuclear receptors and act by directly regulating gene transcription.
Vija L, Ferlicot S, Paun D. Testicular histological and immunohistochemical aspects in a post-pubertal patient with 5 alpha-reductase type 2 deficiency: case report and review of the literature in a perspective of evaluation of potential fertility of these patients. BMC Endocr Disord. 2014;14:43.
Upon completion of this chapter the student should be able to answer the following questions: 1.
Explain the different requirements for and utilization by different cells of fuels during the digestive phase as opposed to the interdigestive and fasting phases.
2.
Integrate the structure, synthesis, and secretion of insulin with circulating fuel levels, especially glucose.
3.
Utilize the different signaling pathways regulated by insulin to link insulin to itscellular effects at the molecular level.
4.
Integrate the structure, synthesis, and secretion of glucagon with the levels of circulating fuels, insulin, and catecholamines.
5.
Map out and integrate the actions of insulin on the utilization and storage of glucose, free fatty acids (FFAs), and amino acids (AAs) by hepatocytes, skeletal muscle, and adipocytes during the digestive phase.
6.
Map out and integrate the actions of counterregulatory hormones (glucagon, catecholamines) on the utilization of glucose, the sparing of glucose, and the utilization of FFAs and AAs by hepatocytes, skeletal muscle, and adipocytes during the interdigestive and fasting phases.
7.
Integrate the changes in fuel utilization and hormonal signaling in hepatocytes during the interdigestive and fasting phases that allow for and promote hepatic glucose production and ketogenesis.
8.
Compare signaling pathways that have orexigenic and anorexigenic actions via the hypothalamus.
9.
Link several pathologies related to metabolism, especially those caused by the absolute or relative absence of insulin and by obesity.
Continual Energy Supply and Demand: The Challenge
There are an estimated 40 trillion cells in the human body, not including the approximately 40 trillion nonhuman cells that comprise the human microbiome. All these cells must continually perform work to stay alive. This work includes maintenance of cellular composition and structural integrity, along with the integrated synthesis and breakdown (i.e., turnover) of macromolecules and organelles. This work also involves the functions of cells that contribute to the human body as a whole (e.g., contraction of the muscle fibers of the diaphragm). Additional work is required of cells when the human body is engaged in a variety of activities, including (but not limited to) manual labor, exercise, and outdoor play; body growth spurt and maturation of the reproductive systems at puberty; pregnancy and breastfeeding; combating a serious infection or cancer; and the healing of damaged tissues/organs (e.g., a broken bone or healing from surgery). On average the resting metabolic rate of a relaxed, awake, stationary, healthy adult human accounts for about 70% of their total energy expenditure each day (
Fig. 39.1
To perform this work, cells need fuels, along with the capability to convert fuels into potential chemical energy in the form of adenosine triphosphate (ATP). Cells then convert the energy within ATP into chemical and mechanical work (see