6 Homeostasis Flashcards
Homeostasis
The maintenance of an internal environment within certain limits of an organism
Importance of Homeostasis
- changes to pH and temperature affects the rate of reaction of enzymes
- maintaining blood glucose concentrations ensures a constant water potential
- some organisms that maintain a constant internal environment have wider geographical ranges and so are more adapted to surviving
Control mechanisms
- optimum point
- receptor
- coordinator
- effector
- feedback mechanism
Negative feedback
The change produced by the control system leads to a change in the stimulus detected by the receptor, turning the system off
E.g regulation of blood glucose
Positive feedback
When a deviation from the optimum point causes changes leading to more deviation from the normal
E.g a stimulus leads to influx of sodium ions in neurones
Hormones
- produced in glands
- carried in blood plasma to target cells that have specific receptors complementary to a specific hormone
- effective in low conc, widespread and has long-lasting effects
Second Messenger Model
- adrenaline binds to a protein receptor in a liver cells membrane
- changes shape of protein
- this leads to activation of enzyme adenyl cyclase- converts ATP to cAMP
- cAMP is a second messenger, binds to protein kinase enzyme- changing its shape and activating it
- enzyme catalyses conversion of glycogen to glucose
- glucose moves out of liver cell via facilitated diffusion into bloody through channel proteins
Role of Pancreas in Regulating Blood Glucose
- produces insulin and glucagon
* has groups of hormone-producing cells called “islets of Langerhans”
Islets of Langerhans
Includes:
•a-cells that produce glucagon
•B-cells that produce insulin
Glycogenesis
- conversion of glucose into glycogen
* when blood glucose is higher than normal, liver removes glucose from blood to convert into glycogen
Glycogenolysis
- the breakdown of glycogen to glucose
- when blood glucose concentration is lower than normal, liver converts stored glycogen into glucose
- glucose diffuses into blood to raise conc back to normal
Gluconeogenesis
- production of glucose from sources that aren’t carbohydrates
- when there is less glycogen stores, liver can produce glucose from glycerol and amino acids
Regulation of Blood Glucose Conc
- if conc is too low, cells won’t have enough energy and will die
- if conc is too high, water potential of blood decreases creating osmotic problems that can lead to dehydration
Factors for Blood Glucose Conc
- diet from absorbing glucose or hydrolysis of carbohydrates
- hydrolysis in small intestine of glycogen (glycogenolysis)
- producing glucose from other sources of carbohydrate (gluconeogenesis)
- changes in rate of respiration
B-cells in the Pancreas
- have receptors that detect the rise in blood glucose conc
- responds by secreting insulin into blood plasma
- most body cells have receptors specific to insulin molecules, so combine to change the tertiary structure of the glucose transport carrier proteins, causing them to open and more glucose to enter cells
- rise in insulin leads to an increase in glucose transport carrier proteins
- insulin activates enzymes to convert glucose to glycogen
