week 1- homeostasis & energy balance

homeostasis definition

maintaining a constant internal environment despite changes to the external environment

which system controls the homeostatic response to blood glucose levels?

endocrine (hormones released)

what happens when blood glucose levels are too high?

beta cells in the pancreas secrete insulin

what effect does insulin have?

increased rate of glucose transport into cells, increased glycogenesis in the liver & skeletal muscle, increased aa absorption and protein synthesis, increased triglyceride synthesis in adipose tissue

what happens when blood glucose is too low?

alpha cells in the pancreas secrete glucagon

what effect does glucagon have?

increased glycogenolysis in the liver & skeletal muscle, increased breakdown of fats to fatty acids in adipose tissue, increased synthesis and release of glucose

where do glycogenolysis, synthesis of glucose and glycogenesis take place?

liver

what are insulin and glucagon?

antagonistic pair

why is it bad to have too little blood glucose?

brain needs glucose to function

metabolic rate

rate at which chemical energy is expended by the body

factors that influence metabolic rate

age, sex, body surface area, muscular activity, environmental temperature

what can you measure to determine metabolic rate?

rate of heat produced by the body, rate of oxygen consumption

why is oxygen consumption used to measure metabolic rate?

oxygen is used during oxidation to extract energy from nutrients, so rate of oxygen is proportional to rate of metabolism

why is heat production used to measure metabolic rate?

when nutrients are oxidised to release energy, heat is produced. rate of heat production is a direct measurement of metabolic rate

factors affecting basal metabolic rate (BMR)

body weight, body SA, lean body mass, age, sex, pregnancy

physiological factors affecting metabolic rate (not BMR)

exercise, eating food, fever, fasting & malnutrition, sleep

which hormones can affect energy metabolism?

catecholamines, thyroid hormones, growth hormone, male sex steroids

what affect do catecholamines have on energy metabolism?

increase metabolic rate

what affect do thyroid hormones have on energy metabolism?

if they are lost, metabolic rate significantly decreases causing weight gain

what affect do growth hormones have on energy metabolism?

(minor effect) more energy needed for growth so rate increases

what affect do male sex steroids (eg. testosterone) have on energy metabolism?

(minor affect) rate increases

which is the absorptive state?

anabolic

where is energy in the anabolic/absorptive state?

stored in macromolecules

which is the postabsorptive state?

catabolism

where is energy in the catabolic/postabsorptive state?

mobilised into the blood

which metabolic reactions happen in the anabolic/absorptive state?

glycogenesis, glycolysis- conversion of glucose to pyruvate which is stored as fatty acid

which metabolic reactions happen in the catabolic/postabsorptive state?

glycogenolysis, gluconeogenesis

what causes the transition between absorptive and postabsorptive state?

insulin

which hormones are secreted by the pancreas to cause the transition between anabolic and catabolic states, and where specifically are they secreted from?

alpha cells secrete glucagon, beta cells secrete insulin

ideal range for blood glucose levels

70-140 mg/dl / 4-8 mmol/l