6C Flashcards
What is Homeostasis?
Changes in your external environment can affect your internal environment. Homeostasis is the maintenance of a stable internal environment. It involves control systems that keep the internal environment roughly constant, meaning it is in a state of dynamic equilibrium (Fluctuating around a normal level)
Why is Homeostasis important? Temperature
It is important as temperature affects enzyme activity, and they control the rate of metabolic reactions (Chemical reactions in living cells) As the temperature increases, so does the metabolic rate. The more heat, the more kinetic energy, so molecules move faster. This makes the substrate molecules more likely to collide with the enzymes’ active sites. However if the temperature is too high, it disturbs the hydrogen bonds in the Enzymes tertiary structure by the molecules vibrating too much, denaturing it and stopping the reaction from taking place.
Too cold of temperatures reduces the enzymes activity, slowing the metabolic reactions.
Why is Homeostasis important? pH
If blood pH is too high or low, enzymes become denatured, as the ionic and hydrogen bonds that hold the enzymes tertiary structure are disrupted, changing the enzymes active site and denaturing it, stopping the enzymes from catalysing any metabolic reactions.
How can pH be calculated?
pH is based on the conc. of Hydrogen ions in the environment. The greater the conc. the lower the pH number. The formula is:
pH = -Log10 (H+)
What does Log10 tell you about pH?
Log10 is expressed on a logarithmic scale, which uses logarithm of a number instead of the number itself. Each value using log10 is ten times more than the value before - So pH3 has ten times more H+ than pH4 (Measured in mol dm-3) As the conc. can vary so much, converting the values to a logarithmic scale makes it easier to plot both very small and very large values on the same axis of a graph.
What is another use for a Logarithmic scale, other than measuring pH
Microbial growth, where the number of organisms increases exponentially
What happens if the Blood Glucose concentration is too high?
The water potential of the blood is reduced to a point where water molecules diffuse out of the cells, and into the blood by Osmosis. This can cause the cells to shrivel up and die
What happens if the Blood Glucose concentration is too low?
The cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide energy
What is Negative Feedback?
Receptors detect when a level is too high or low, and is communicated through The Nervous/Hormonal system to effectors. The effectors respond to counteract the change, bringing the level back to normal. This is the Negative Feedback Mechanism. This only works within certain limits though, if the change is too big then the effectors may not be able to counteract it
Multiple Negative Feedback Mechanisms
Homeostasis involves multiple negative feedback mechanisms for each thing being controlled, giving more control over the changes, meaning it can actively increase or decrease a level so it returns to normal, instead of one mechanism, which can only turn things off or on, and it would be a slower response
What is Positive Feedback?
Some changes trigger a Positive Feedback mechanism, which amplifies the change. Effectors respond to further increase the level away from the normal level. The mechanism that amplifies a change away from the normal is called a Positive Feedback Mechanism. It isn’t involved in Homeostasis as it doesn’t keep the internal environment constant, however it can be rapidly activate processes in the body, such as releasing chemicals to trigger more pellets to form a blood clot at an open scar - which ends with Negative Feedback when the body detects the blood clot has been formed)
Glucose Concentration in the blood - How much Is normally in the blood and what monitors it?
The Pancreas monitors the Blood Glucose, which is normally around 90mg per 100cm3 of blood
Hormonal Control of Blood Glucose concentration (BGC)
Hormonal system controls the BGC using two hormones - Insulin and Glucagon. These are chemical messengers which travel in the blood to their target cells (Effectors) They are both Secreted by clusters of cells in the pancreas, called the Islets of Langerhans. They contain Alpha and Beta cells. Alpha releases Glucagon, whilst Beta releases Insulin. They then act on effectors, which respond to restore the BGC
Insulin
Insulin lowers the BGC when its too high. It binds to specific receptors on the cell membranes of muscle and liver cells, increasing the permeability of the membranes to Glucose, so the cells can take up more Glucose. This also Involves increasing the number of channel proteins in the membranes. Insulin also activates enzymes in the muscle and liver cells to convert Glucose to Glycogen. The cells then store the Glycogen in their cytoplasm, as an Energy Source.
What is the process of forming Glucose to Glycogen
Glycogenesis
Glucagon
Glucagon raises the BGC when its too low. It binds to specific receptors on the cell membranes of liver cells and activates enzymes to break down Glycogen to Glucose. It can also activate enzymes that are involved in the formation of Glucose from Glycerol and Amino acids.
What is the process of breaking down Glycogen to Glucose?
Glycogenolysis
What is the process of breaking down Glycerol and Amino acids to glucose?
Gluconeogenesis
Why are hormones used instead of the nervous system?
Although the responses are slower using hormones than The Nervous System, Hormones occur all over the body if their target cells are widespread, unlike nervous impulses that are localised to one area. Hormones aren’t broken down as quickly as neurotransmitters as well, so their effects tend to last for longer
Rise in BGC
When the Pancreas detects the BGC is too high, Beta cells secrete Insulin, and the Alpha cells stops secreting Glucagon. Insulin binds to the receptors on liver and muscle cells (The effectors) which respond to decrease the BGC by making their cell membrane more permeable to Glucose, so they take up more Glucose. Glycogenesis is activated and the cell respires more so the BGC returns to normal
Fall in BGC
When the Pancreas detects the BGC is too low, Alpha cells secrete Glucagon, and the Beta cells stops secreting Insulin. Glucagon binds to the receptors on liver cells (The effector) which responds to increase the BGC by activating glycogenolysis and Gluconeogenesis. Cells will also respire less Glucose so the BGC returns to normal
What are Glucose Transporters?
They are channel proteins which allow Glucose to be transported across the cell membrane. Skeletal and cardiac muscle cells contain a glucose transporter called GLUT4. When insulin levels are low, GLUT4 is stored in vesicles in the Cytoplasm of cells, but when Insulin binds to receptors of the cell-surface membrane, it triggers the movement of GLUT4 to the membrane. Glucose can then be transported into the cell through the GLUT4 protein by facilitated diffusion
Adrenaline
Adrenaline is a hormone that’s secreted from your adrenal glands when there’s a low Conc. of Glucose in your blood. Adrenaline binds to receptors on the cell membrane of the liver cells and activates Glycogenolysis and inhibits Glycogenesis. It also activates the secretion of Glucagon and inhibits Insulin, which increases the BGC. It gets the body ready for acton by making more glucose available for muscles to respire
What are Second Messengers and what do they do?
Both Adrenaline and Glucagon can activate Glycogenolysis inside a cell even though they bind to receptors on the outside of the cell. They can do this by the Second Messenger Model - The binding of the hormone to cell receptors activates an enzyme on the inside of the cell membrane, which then produces a chemical known as a second messenger, which then activates other enzymes in the cell to bring about a response
