✅16 - Homeostasis Flashcards
What is homeostasis?
The maintenance of an internal environment within restricted limits in organisms
What does homeostasis involve?
Trying to maintain the chemical make-up, volume and other features of blood and tissue fluid within restricted limits
What does homeostasis ensure?
That the cells of the body are in an environment that meets their requirements and allows them to function normally despite external changes
What are some examples of things maintained by homeostasis?
pH
Temperature
Water potential
What is the optimum point?
The point at which the system operates best
What is the optimum point monitored by?
A receptor
What is a coordinator?
Coordinates the information from receptors and sends instructions to appropriate effectors
What is a feedback mechanism?
The way by which a receptor responds to a stimulus created by the change to the system brought about by the effector
What is negative feedback?
When the change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off.
What is positive feedback?
When a deviation from an optimum causes changes that result i an even greater deviation from the normal
What is an example of positive feedback?
When a stimulus leads o a small influx of sodium ions in a neurone and the permeability of the neurone to sodium ions is increased.
Control systems normally have many…
…receptors and effectors
What are endotherms?
Animals which generate heat from inside their bodies
What are exotherms?
Animals which obtain a proportion of their body heat from sources outside their bodies
Where are hormones produced?
In glands, which secrete the hormone directly into the blood (endocrine glands)
What do hormones act on?
Target cells, which have specific receptors on the cell surface membrane that are complementary
What is the secondary messenger model?
One mechanism of hormone action, used by the two hormones in blood glucose regulation, adrenaline and glucagon
How does the secondary messenger model work for adrenaline and glucagon?
Adrenaline binds to a transmembrane protein receptor within the cell surface membrane of a liver cell
The binding causes the protein to change shape on the inside of the membrane
The change in protein shape leads to activation of an enzyme adrenal cyclase which converts ATP to cyclic AMP
The cAMP acts as a second messenger that binds to protein kinase enzyme, changing its shape and activating it.
The active protein kinase enzyme catalysed the conversion of glycogen into glucose which moves out of the liver cell by facilitated diffusion and into the blood, through channel proteins
What is the role of the pancreas in regulating blood glucose?
It produces enzymes for digestion and hormones insulin and glucagon for regulation of blood glucose
Which cells produce the hormones?
Islets of Langerhans
What do the islets of langerhans include?
Alpha cells and Beta cells?
What is the function of alpha cells?
Larger cells which produce glucagon
What is the function of Beta cells?
Smaller cells which produce insulin`
What is the role of he liver in regulating blood glucose?
The hormones produced by the pancreas take effect in the liver
What is glycogenesis?
Conversion of glucose into glycogen when glucose concentration is higher than normal
What is glycogenolysis?
The breakdown of glycogen to glucose, when blood glucose concentration is lower than normal
What is gluconeogenesis?
The production of glucose from sources other than carbohydrate such as glycerol and amino acids
What are the consequences if blood sugar falls too low?
Cells will be deprived of energy and die, as glucose is a substrate for respiration. Brain cells are especially sensitive
What happens if blood glucose concenration is too high?
It lowers the water potential of the blood and creates osmotic problems that can cause dehydration
What are the three sources of blood glucose?
Directly from the diet via hydrolysis of other carbohydrates
From the hydrolysis in the small intestine of glycogen (glycogenolysis)
From glconeogenesis
What is insulin?
A globular protein made up of 51 amino acids
How is insulin detected by cells?
Almost all body cells have glycoprotein receptors on their cell surface membrane which bind specifically with insulin