Communication and homeostasis Flashcards
Endocrine glands
groups of cells specialised to secrete hormones
When are endocrine glands stimulated to release a hormone?
when there’s a change in concentration of a specific substance (sometimes another hormone) or by an electrical impulse
Where do hormones bind to?
receptors on the membranes of target cells
What are tissues that contain target cells called?
target tissues
Pathway of hormonal communication
stimulus, receptors, hormone, effectors, response
What is a first messenger?
a hormone, as it carries the chemical message from the endocrine gland to the receptor on the target cells
What happens when a hormone binds to its receptor?
it activates an enzyme in the cell membrane which catalyses the production of a signalling molecule
What is a signalling molecule?
a molecule that signals to other parts of the cell to change how the cell works. it is a second messenger.
Why is the signalling molecule a second messenger?
it carries the chemical message from the receptor to other parts of the cell. it activates a cascade inside the cell.
When is adrenaline secreted?
when there’s a low concentration of glucose in your blood, when you’re stressed, or when you’re exercising.
How does adrenaline get the body ready for action?
by making more glucose available for muscles to respire by activating glycogenolysis.
How does adrenaline act as a first messenger?
- binds to specific receptors in the cell membranes of many cells e.g. liver cells
- activates the enzyme adenylyl cyclase in the membrane
- this catalyses the production of a second messenger called cAMP from ATP
- cAMP activates a cascade of enzyme reactions making more glucose available by glycogenolysis.
Where are adrenal glands found?
just above the kidneys
What is the outer part of each adrenal gland called?
cortex
What is the inner part of each adrenal gland called?
medulla
What does the cortex of the adrenal glands do?
-secretes steroid hormones, e.g. cortisol and aldosterone, when you’re stressed
What effects do steroid hormones have on stress?
- stimulate gluconeogenesis to increase the amount of energy available for the brain and muscles to respond
- increases blood volume and pressure by increasing the uptake of Na+ and water by the kidneys
- suppressing the immune system
What does the medulla of the adrenal glands do?
-secretes catecholamine hormones (modified amino acids) e.g. adrenaline and noradrenaline, when you’re stressed.
What effects do adrenaline and noradrenaline have on stress?
make energy more available in the short term by:
- increasing heart and breathing rate, causing glycogenolysis
- constricting some blood vessels so blood is diverted to the brain and muscles
Where is the pancreas found?
below the stomach
What are the areas of the pancreas that contain endocrine tissue called?
islets of Langerhans
What are islets of Langerhans?
- clusters of endocrine tissues around blood capillaries that secrete hormones directly into the blood
- it is made up of alpha and beta cells
What do the alpha and beta cells of the islets of Langerhans secrete?
- alpha: glucagon
- beta: insulin
Homeostasis
the maintenance of a constant internal environment
How does a high temperature affect enzyme activity?
The rate of metabolic reactions increases with temperature. More heat = more kinetic energy, molecules move faster. Substrate molecules are more likely to collide with active sites. the energy of collisions also increases so each collision is more likely to result in a reaction.
How does a temperature too high affect enzyme activity?
the reaction stops as the vibrations break some of the hydrogen bonds that hold the enzyme in its 3D shape. the active site changes shape and the substrate can no longer fit. the enzyme has denatured.
Negative feedback mechanism
when the changed level is brought back to normal
Negative feedback mechanism- steps
1- normal level 2- level changes from normal 3- receptors detect a change 4- communication via the nervous or hormonal system 5- effectors respond
Does negative feedback always work?
No, not when the change is too large
Positive feedback mechanism
amplifies a change away from the normal
Is positive feedback involved in homeostasis?
No, as it doesn’t keep internal environment constant
When is positive feedback useful?
to rapidly activate processes in the body
e.g. when forming a blood clot after injury, platelets are activated and produce a chemical to trigger more to be activated.
What are ectotherms?
animals that can’t control their body temperature internally- control it by changing their behaviour.
Example of an ectotherm
Lizard- when their internal temp drops, they move to a warmer area such as sunshine. when it is too high, they move to somewhere cooler like a burrow underneath sand.
What does the internal temperature of an ectotherm depend on?
the external environment.
Why do ectotherms have a variable metabolic rate?
they cant keep their internal temperature constant. they generate very little heat themselves.
How is the activity level of ectotherms?
depends on the external environment. more active at higher temperatures and less active at lower temperatures.
What are endotherms?
they control their body temp internally by homeostasis, as well as altering their behavior.
Example of an endotherm
Elephant- temp mainly controlled by homeostasis but also by behavior so it wallows in mud or flaps ears to cool down.
Mechanisms to reduce body temp
1- sweating- water in sweat evaporates from the skin’s surface and takes heat with it.
2- hairs lie flat- erector pili muscles relax. less heat is trapped so skin is less insulated.
3- vasodilation: arterioles near the skin’s surface dilates. more blood flows through the capillaries. more heat is lost from the skin by radiation.
Mechanisms to increase body temp
1-shivering 2- vasoconstriction 3- less sweat 4- hairs stand up 5- hormones: body releases adrenaline and thyroxine which increase metabolism so more heat is produced
How is body temperature controlled by the hypothalamus?
1- normal body temp (37) 2- rise/fall in body temp 3- thermoreceptors detect a change 4- hypothalamus sends impulses to effectors 5- effectors respond
Which thermoreceptors detect both the internal and external environments?
those in the hypothalamus detect the internal environment and those in the skin (peripheral temperature receptors) detect the external environment
How do thermoreceptors send messages to the effectors?
they send impulses along sensory neurones to the hypothalamus which sends impulses along motor neurons to the effectors
What id the normal blood glucose concentration?
around 90 mg per 100cm3 of blood
Which cells monitor blood glucose conc.?
pancreatic cells
How does insulin lower blood glucose concentration?
- binds to specific receptors on the cell membranes of liver cells and muscle cells and increases the permeability of the membranes to glucose, so they take up more.
- also activates enzymes for glycogenesis
- also increases the rate of respiration of glucose, especially in muscle cells
What is glycogenesis?
when glucose is converted into glycogen which is stored in the cytoplasm of liver and muscle cells.
How does glucagon increase blood glucose concentration?
- binds to specific receptors on the cell membranes of liver cells and activates enzymes for glycogenolysis.
- also causes gluconeogenesis in liver and kidneys
- also decreases respiration of glucose in cells
What is glycogenolysis?
breaking down glycogen into glucose
What is gluconeogenesis?
forming glucose from glycerol and amino acids
What happens when there’s a rise in blood glucose conc?
- pancreas detects it
- beta cells secrete insulin, alpha cells stop secreting glucagon
- insulin binds to receptors on liver and muscle cells (Effectors)
- liver and muscle cells respond e.g. activate glycogenesis.
What happens when there’s a fall in blood glucose conc?
- pancreas detects it
- alpha cells secrete glucagon, beta cells stop secreting insulin
- glucagon binds to receptors on liver cells
- liver cells respond e.g. gluconeogenesis or glycogenolysis.
What do beta cells contain and have?
- contain insulin in vesicles
- have potassium ion (K+) channels and calcium ion (Ca2+) channels in their membrane
When blood glucose conc is normal (or lower), how are beta cells?
the K+ channels are open and the Ca2+ channels are closed. K+ ions diffuse out of the cell through the K+ open channels so the inside of the cell membrane is more negatively charged than the outside. the membrane is polarised.
What happens when the beta cells detect a high blood glucose conc?
- more glucose enters the beta cells via facilitated diffusion. this causes the rate of respiration to increase, making more ATP.
- more ATP triggers K+ channels to close so K+ ions build up inside the cell, making the inside less negative. the membrane is depolarised.
- depolarisation triggers Ca2+ channels to open, Ca2+ ions diffuse into the beta cell. this causes vesicles to move to and fuse with the plasma membrane, releasing insulin by exocytosis.
Describe type 1 diabetes
- autoimmune disease where the body attacks and destroys the beta cells
- they don’t produce insulin
- after eating, their blood glucose levels stay high which can result in death if not treated.
- the kidneys can’t reabsorb all of this glucose so some is excreted in the urine
Who is likely to develop type 1 diabetes?
- children or young adults
- those with a close family history of the disease
How is type 1 diabetes treated?
- Insulin therapy: regular injections of insulin throughout the day or an insulin pump.
- Islet cell transplantation (although usually still need additional insulin therapy)
- need to monitor blood glucose levels and think carefully about their diet and level of activity
Describe type 2 diabetes
- beta cells don’t produce enough insulin or body cells don’t respond to insulin properly as receptors on their membranes don’t work properly so cells don’t take up enough glucose
- usually acquired later in life than type 1 and is often linked with obesity
Who is likely to develop type 2 diabetes?
certain ethnic groups e.g. African or Asian and those with a close family history of the disease
How is type 2 diabetes treated?
- Initially through lifestyle changes: balanced, healthy diet, regular exercise and losing weight for both prevention and control of effects
- If it still isn’t treated, medication is used. e.g. metformin, sulfonylureas, thiazolidinediones.
How does medication for type 2 diabetes work?
- Metformin: usually the first medication used. It acts on liver cells, reducing the amount of glucose released into the blood. Also increases the sensitivity of cells to insulin so more glucose is taken up with the same amount of insulin.
- Sulfonylureas: stimulate the pancreas to produce more insulin
- Thiazolidinediones: make the body cells more sensitive to insulin
How is human insulin made nowadays?
by GM bacteria
How is insulin made by GM bacteria better than it being extracted from animal pancreases?
- cheaper
- larger quantities of insulin
- makes human insulin, more effective than pig or cattle insulin + less likely to trigger an allergic response or be rejected by the immune system
- some prefer it due to ethical or religious reasons
How can stem cells treat diabetes?
they can be grown into beta cells and implanted into the pancreas of a person with type 1 diabetes
