chapter 9 - homeostasis and hormonal control Flashcards
homeostasis
maintenance of a constant internal environment, that requires geative feedback to reverse the effects of the stimulus through a corrective mechanism to reverse the condition back to normal
principle of homeostasis in terms of negative feedback
normal (set point) → stimulus (change from normal) → receptors (detects stimulus) → control centre → corrective mechanism → condition returns to normal
target organ
organ with receptors to bind to specific hormones to carry out its response
thermoregulation (hot day)
blood and skin temperature increases. thermoreceptors in the skin and the hypothalamus in the brain will be stimulated. increasing production of sweat as the sweat glands become more active and produce more sweat, causing more latent heat of vapourisation to be lost when more water in sweat evaporates. vasodilation of arterioles allows for more blood to flow to the skin surface blood capillaries, allowing more heat to be lost by conduction, convection and radiation. rate of metabolic activities like respiration slows down, causing less heat to be produced. increased heat loss and reduced heat production allows the body temperature to decrease and blood and skin temperature returns to normal.
thermoregulation (cold day)
blood and skin temperature decreases. thermoreceptors in the skin and the hypothalamus in the brain will be stimulated. decreasing production of sweat as the sweat glands become less active and produce less sweat, causing less latent heat of vaporisation to be lost when less water in sweat evaporates. vasoconstriction of arterioles allows for less blood to flow to the skin surface blood capillaries, allowing less heat to be lost by conduction, convection and radiation. rate of metabolic activities like respiration increases, causing more heat to be produced. shivering, which is the repeated relaxation and contraction of the skeletal muscles, also generates more heat which increases the body temperature. decreased heat loss and increased heat production allows the body temperature to increase and blood and skin temperature returns to normal.
hormones
chemical substances produced in minute quantities by endocrine glands. they are transported by blood to one or more specific target organs and after performing their functions, they are destroyed in the liver and excreted by the kidneys. they also help to control and coordinate body activities such as growth and development of an organism.
endocrine glands
ductless glands that transport their secretions through the blood (eg. islets of langerhans in the pancreas secrete insulin and glucagon through the blood to regulate blood glucose concentration)
blood glucose concentration (increases)
concentration of blood glucose increases above the norm. islets of langerhans in the pancreas will be stimulated to secrete more insulin into the bloodstream, which is transported to the liver and muscles. rate of glucose uptake increases and the permeability of cell membranes to glucose increases, stimulating the liver and muscles to convert excess glucose to glycogen to be stored in the liver and muscles . oxidation of glucose during tissue respiration also increases. insulin production falls and the concentration of blood glucose decreases back to normal.
blood glucose concentration (decreases)
concentration of blood glucose decreases above the norm. islets of langerhans in the pancreas will be stimulated to secrete more glucagon into the bloodstream, which is transported to the liver and muscles. rate of glucose uptake decreases, stimulating the liver and muscles to convert stored glycogen that was stored in the liver and muscles to glucose to be released into the bloodstream. glucagon production falls and the concentration of blood glucose increases back to normal.
diabetes mellitus
insufficient insulin secretion hence unable to regulate blood glucose concentration leading to persistently high level of glucose in blood. kidneys are unable to completely glucose in body, causing glucose to be excreted in urine.
type 2 diabetes mellitus
insulin is produced but target cells like liver and muscles do not respond well to insulin. kidneys are unable to completely glucose in body, causing glucose to be excreted in urine
risk factors and managements of type 2
risk factors of type 2 : unhealthy diet, sedentary lifestyle, obesity, age
management : changes to diet and lifestyle (more active lifestyle)
relationship between sweat and urine production
when sweat production increases, more water in sweat is lost through evaporation. the water potential of blood plasma decreases, causing more ADH to be released by the pituitary gland, and more water to be reabsorbed back into the blood, causing a decrease in urine volume
how does reduced secretion of ADH affect the composition of urine
reduced secretion of ADH decreases the permeability of the cells on the walls of collecting duct to water [1]. hence, less water is reabsorbed at the collecting duct into the blood capillaries [1] and higher volume of water is found in the urine, making the urine less concentrated/more diluted
