Homeostasis Flashcards
Define homeostasis
Homeostasis is the maintenance of constant internal environment, allowing them to function normally despite internal or external changes such as changes in temperature pH in water potential
Organisms that control the environment and more independent of their environment
What does this lead to?
Greater geographical range, so can colonise more habitats and ecosystems
Greater chance of finding food, shelter and mates
Basic control mechanism
The set point- optimum or Norm at which the system operates at for example body temperature
A receptor - detects changes from the set points and informs the controller for example, baroreceptors
Controller - coordinates information from various receptors and sends instructions to an appropriate effect
For example, the brain
The effector- brings about the changes needed to return the system to the set point
For example, a grand
Feedback loop - informs the Receptor of the changes to the system brought about by the effector
Define negative feedback
When there is an increase or decrease from the set point, the opposite effect is instigated producing a response that returns the value to norm
Define positive feedback
When a deviation from an optimum causes even greater deviation from the normal
Explain how insulin reduces the blood glucose concentration
More insulin binds to receptors
Simulates uptake of glucose by channel proteins
Activate enzymes which converts glucose to glycogen
Explain the action of glucagon
Attaches to receptors on target cells and activates enzymes
Glycogen to glucose
Gluconeogenesis
Explain the effect of sweating or panting on temperature control
Evaporation of water from lining of mouth or skin
Heat transferred from blood
Describe how a change in blood PH of blood pressure can cause a change in heart rate.
Carbon dioxide detected by chemoreceptors or pressure detected by baroreceptors
Cardiac centre
More impulses to the Sino atrial node along the sympathetic nerve
Decrease PH detected my chemo receptors in carotid artery
Send more impulses to the medulla
More nerve impulses sent by the sympathetic nervous system to sinoatrial node
Less carbon dioxide in blood leads to a reduction in heart rate
Explain how
Less carbon dioxide in blood detected by chemoreceptors
Chemoreceptors located in aorta or carotid artery
Fewer impulses to the cardiac centre
Less impulses along the sympathetic nerve
To Sino atrial node
Describe the secondary messenger model
Second messenger produced
Activate enzymes in c cell
So Glyco neogenesis occurs
Describe the role of glycogen information and its role in lowering the blood glucose levels
Glucose concentration in cells fall
Below that in blood
Maintains glucose concentration
Glucose into cells by facilitated diffusion using carrier channel proteins
Describe how blood glucose levels can be increased using hormones
Release of glucagon
Leads to formation of glucose in the liver
From non carbohydrates
Describe how ultrafiltration occurs in glomerulus
High blood pressure
Water and glucose pass out
Through gaps in endothelium
Through capillaries basement membrane
Explain why a thicker medulla leads to more concentrated urine
Thicker Medela means longer loop of Henle
Increase in sodium ion concentration, so sodium ion gradient maintained for longer
So water potential gradient maintained so more water reabsorbed by osmosis
Describe the action of ADH in the kidney
Permeability of membrane is increased
More water absorbed from collecting duct
Smaller volume of urine
Urine becomes more concentrated
Explain why glucose is found in the urine of a person with untreated diabetes
High concentration of glucose in the blood
Not all glucose is reabsorbed at the proximal convoluted tubule
Co transport proteins and carrier proteins are working at maximum rate
Control of high blood glucose concentration
Insulin is synthesised and secreted by beta cells in the pancreas
Insulin binds to complimentary receptors on the cell surface membrane of target cells
This controls the uptake of glucose by regulating the inclusion of glucose carrier proteins in the surface membrane of target cells
Insulin also activates enzymes that stimulate the conversion of glucose to glycogen- glycogenesis
Decreasing blood glucose
Control of low, blood glucose concentration
Glucagon is synthesised and secreted by alpha cells in the pancreas
Glucagon binds to receptors on the cell surface membrane of target cells
Activating enzymes involved in the hydrolysis of glucagon to glucose- glycogenolysis
Activating enzymes involved in the conversion of glycerol and amino acids into glucose -glyconeogenesis
Which cells in the pancreas secrete hormones
Islets of Langerhans
Control of blood glucose after a meal
Glucose is absorbed from the ileum into the hepatic portal vein
Blood glucose concentration increases which is detected by the pancreas
Pancreas secretes insulin from beta cells
Insulin causes, gout, close to be taken up by the liver and converted into glycogen
This reduces blood glucose, which is detected by pancreas which stops secreting insulin
If glucose levels fall too far, this is detected by the pancreas
Pancreas secretes glucagon from his alpha cells
Glucagon causes deliver to hydrolyse some of its glycogen store to glucose
Diffuses into the blood down a concentration gradient by facilitated diffusion
Increases blood glucose, which causes Pancras to stop secretin glucagon
Negative feedback loop
Second messenger model of hormone action- adrenaline and glucagon
- Adrenaline and glucagon both bind to specifiic receptor on the surface of target cell= first messenger
- Hormone- receptor complex causes a change in receptor protein change tertiary structure
- Also activates adenylate cyclase resulting in the conversion of atp into cyclic AMP= secondary messenger
- Secondary messenger causes series of chemical changes that produce the required rapid response
- CAMP is secondary messenger and activates kinase enzymes which produce a cascade of chain reactions that catalyse the glycogen to glucose
Glucagon
Hormone
Glycogen
Energy store
Glycogenesis
Glucose to glycogen
Glycogenolysis
Glycogen to glucose
Gluconeogenesis
Glucose from amino acids and glycerol
Diabetes
Type one
Insulin dependent
Severe insulin deficiency due to autoimmune killing beta cells or faulty gene
Diabetes
Type two
Non insulin dependent
Insulin produced but insulin receptors in target cells are unresponsive so insulin has no effect
How diabetes occurs
Very high blood glucose concentration after a meal
Active transport pumps into proximal convoluted tubule of the kidney which can’t re absorb it all from kidney filtrate
So glucose excreted into urine
Symptoms of diabetes
High thirst due to osmosis of water from cells to blood which had low water potential
Large volumes of urine production due to excess water in the blood
Poor vision due to osmotic loss of water from eye lens
Tiredness due to loss of glucose in urine and poor uptake of glucose by liver and muscle cells
Treatment diabetes
Insulin injections
Managed diet
