Module 5: Homeostasis. Flashcards
What are hormones?
They are chemical messengers that are released into the bloodstream.
They are proteins, peptides or steroids.
Hormones are secreted when an endocrine gland is stimulated - can be stimulated by electrical impulses or a change in concentration of a specific substance.
State the stages of hormonal communication.
Stimulus - receptors - hormones released - effectors - response.
Describe the action of hormones in terms of cell signalling.
- A hormones is called a first messenger as it carries the chemical message the first part of the way, from the endocrine gland to the receptor on the target cells.
When a hormone binds to its receptors, it activates an enzyme in the cell membrane - the enzyme catalyses the production of a molecule inside the vell called a signalling molecule and this molecule signals to other parts of the cell to change how the cell works.
The signalling molecule is called a second messenger because it carries the chemical message the second part of the way, from the receptors to the other parts of the cell. Second messengers activate a cascade - a chain of reaction inside the cell.
Describe the structure and function of adrenaline.
It is a hormone that is secreted from the adrenal glands in the pancreas.
It is secreted when their is a low concentration of glucose in the blood, when stressed or exercising.
This hormone gets the body ready for action by making more glucose available for muscles to respire by activating glycogenolysis - the breakdown of glycogen to glucose.
Describe what happens when adrenaline is secreted.
It is a first messenger and it binds to receptors in the cell membranes of many cells such as liver cells.
When adrenaline binds, it activates an enzyme in the cell membrane called adenylyl cyclase.
Activated adenylyl cyclase then catalyses the production of a second messenger called cyclic AMP (cAMP) from ATP.
cAMP activates a cascade. For example a cascade of enzyme reactions makes more glucose available to the cell by catalysing the breakdown of glycogen into glucose.
Explain what the adrenal glands are.
they are endocrine glands that are found just above the kidneys.
It has an outer part called the adrenal cortex and an inner part called the adrenal medulla.
Both these parts play different roles in our response to stress, producing effects which help to prepare the body for the ‘fight or flight response’
Describe the function of the adrenal cortex.
- Secretes steroid hormones such as cortisol and aldosterone.
Their effects include:
- Stimulating the breakdown of proteins and fats into glucose. This increases the amount of energy available so the brain and muscles can respond to the situation.
- Increasing blood volume and pressure by increasing the uptake of sodium ions and water by the kidneys.
- Suppressing the immune system.
Describe the function of the adrenal medulla.
- Secretes catecholamine hormones (modified amino acids) such as adrenaline and noradrenaline.
-These act to make more energy available in the short-term by increasing heart and breathing rate, causing cells to break down glycogen into glucose and constricting some blood vessels so that blood is diverted to the brain and muscles.
Describe the structure and function of the pancreas.
The areas of the pancreas that contain endocrine tissue are called the islets of Langerhans - they are found in clusters around the blood capillaries and they secrete hormones directly into the blood.
They are made up of two types of cells - beta and alpha cells
Alpha cells - secrete a hormone called glucagon (pink stained)
Beta cells - secrete a hormone called insulin (purple stained)
Glucagon and insulin help to control blood glucose concentration.
What is homeostasis?
It is the maintenance of a constant internal environment.
How does temperature affect the rate of metabolic reactions?
When temperature increases = the rate of metabolic reactions also increases.
More heat = more kinetic energy and so molecules move faster.
This makes the substrate molecules more likely to collide with the enzymes active sites. The energy of these collisions also increases, which means each collision is more likely to result in a reaction.
If temperature goes too high, this vibration breaks some the hydrogen bonds that hold the enzyme in its 3D shape. The active site changes shape and the enzyme and substrate no longer fit together. At this point, the enzyme is denatured - it no longer functions as a catalyst.
optimum temperature in humans = about 37 degrees Celsius.
What is Negative feedback?
A mechanism that restores levels back to normal.
Only works within certain limits - is the change is too big then the effectors may not be able to counteract it.
What is Positive feedback?
In contrast, positive feedback mechanisms will amplify a detected change, moving conditions away from the normal level. They are used to accelerate a biological pathway, for example, the formation of a blood clot after an injury.
At the site of a wound, activated platelets release a chemical which results in further platelet activation. This causes platelets to rapidly accumulate at the site of the wound, forming a blood clot.
Positive feedback is not involved in homeostasis, because it does not keep internal conditions within a normal range.
What are Ectotherms?
Reptiles + fish
They cannot control their body temperature internally - they control their temperature by changing their behaviours.
e.g. when a lizards internal temperature drops, it will move to find a warmer area such as a place in the sunshine. When its internal temperature gets too high, it will move to somewhere cooler such as a burrow beneath the sand.
Ectotherms have a variable metabolic rate because they cannot keep their internal temperature constant. They generate very little heat themselves. This means the activity level of ectotherms depends on the external temperature too - they are more active at higher temperatures and less active at lower temperatures.
What are Endotherms?
Mammals + birds
They control their body temperature internally by homeostasis, as well as by altering their behaviour.
They have a constantly high metabolic rate because they can keep their internal temperature constant.
They generate a lot of heat from metabolic reactions, this means the activity level of endotherms is largely independent of the external temperature - they can be active at any temperature (within certain limits)
