Homeostasis and Blood Glucose Levels Flashcards
Homeosatsis
The maintenance of stable/constant internal environment
Within strict limits
Importance of homeostasis
Maintaining a constant internal environment means enzyme controlled biological reactions take place at a constant optimum rate
So changes in the internal or external environment aren’t dangerous/deadly
Why are organisms that control their own internal environment more independant of their environment
Greater geographical range so able to colonise more habitats and ecosystems
Greater chance of finding food, shelter and mates
Explain an example of positive feedback (threshold potential)
Initial membrane depolarisation Opening of voltage gated Na+ channels Increased Na+ flows through the membrane Further membrane depolarisation Typically along unmyelinated axons
Positive feedback
Occurs when a deviation from an optimum causes changes that result in an even greater deviation from the normal
Negative feedback
When there is an increase/decrease from the set point, the opposite effect is instigated to produce a response that returns the value to normal
Endotherms
Maintain body temperature by both physiological and behavioural means
Independant of area/environment so not relying on it
Can migrate to find a mate, reproduce all year round
Ectotherms
All animals except mammals and birds
Maintain body temperatures by behavioural means only
Exposing themselves to sun or taking shelter
Gaining warmth from the ground
Hypoglycaemia
Very low levels of glucose below the strict set range
Can be fatal
Hyperglycaemia
Very high levels of glucose above the strict set range
Can be fatal
What controls blood glucose concentration
Pancreas
Has glucose receptor cells that monitor the concentration of blood glucose
And endocrine cells called the islets of Langerhans which secrete hormones
What are the Islets of Langerhans composed of
alpha cells which secrete the hormone glucagon
beta cells which secrete the hormone insulin
Advantage of Islets of Langerhans having lost of capillaries
Can get the hormones straight into the blood so they can be transported
Insulin
A peptide hormone secreted by beta cells in the pancreas
When blood glucose levels are too high
In order to help reduce blood glucose levels to the normal range
How does insulin work
Binds to complementary receptors on cell surface membrane of target cells in liver
This controls the uptake of glucose by regulating the inclusion (addition) of glucose carrier proteins in the surface membranes of target cells so more glucose taken into cells
Insulin activates enzymes that stimulate glycogenesis
To decrease the blood glucose levels
Glucagon
A peptide hormone secreted by alpha cells in the pancreas
When blood glucose levels are too low
In order to help increase blood glucose levels to the normal range
How does glucagon work
Binds to receptors on the cell surface membrane of liver cells
Activates enzymes involved in the hydrolysis of glycogen to glucose (glycogenolysis)
Activates enzymes involved in the conversion of glycerol and amino acids into glucose (gluconeogenesis)
Describe the role of glycogen formation and its role in lowering blood glucose levels
Glucose concentration in liver cells falls
Below that in the blood
Creating a glucose concentration gradient
Glucose enter the cells and leaves the blood via facilitated diffusion through carrier proteins
Describe how blood glucose levels can be increased with hormones
Release of glucagon from alpha cells
Leads to formation of glucose in liver cells
From non-carbohydrates/amino acids/fatty acids
Explain the changes to blood glucose levels after a meal
Glucose absorbed from the ileum into the hepatic portal vein
Blood glucose concentration increases
Detected by pancreas
Insulin secreted from beta cells
Causes glucose to be taken up by the liver and converted into glycogen
Reducing blood glucose levels
Detected by the pancreas
Stops secreting insulin
If levels fall to far, alpha cells secrete glucagon
Causes liver to hydrolyse some glycogen to store glucose
Glucose diffuses into the blood down a concentration gradient by facilitated diffusion
Increasing blood glucose concentration
Pancreas stops secreting glucagon
Can insulin and glucagon be in the body at the same time
Yes
