Hormones and Homeostasis Flashcards
What can we call a plant “hormone”
A PGR or Plant Growth Regulator
What is a positive or negative tropism?
Plants can sense and respond to stimuli. Many of these responses are directional growth responses, called tropisms. Tropisms can be positive (growing towards the stimulus) or negative (growing away from the stimulus) and occur in response to a variety of stimuli:
What is IAA?
Indoleacetic acid - a PGR
Where is IAA produced?
In the tip of roots and shoots
Explain phototropism in a coleoptile tip.
Auxin is synthesized in the coleoptile tip; asymmetric illumination is detected by the coleoptile tip and this causes auxin to move into the darker side; auxin diffuses down the coleoptile; and the higher auxin concentration on the darker side causes the coleoptile to bend toward the light
How do auxins work?
- Binding to a receptor protein in the target cell membranes and activating a proton pump.
- This pump pumps protons (hydrogen ions) from the cytoplasm of these cells to their cell walls.
- The resulting decrease in pH activates an enzyme that breaks the bonds between cellulose microfibrils.
- This loosens the cell wall and so allows the cell to elongate under the internal turgor pressure.
How do roots and shoots behave differently?
Auxin accumulates on the lower side of both but stimulates growth in shoots and inhibits growth in roots. Therefore roots go down and are positively geotropic and shoots are the opposite.
Explain how the body of a mammal may respond to a rise in the environmental temperature.
Reducing body temp Heat receptors in skin; nervous impulse; to hypothalamus; blood temperature monitored; heat loss centre involved; vasodilation / dilation of arterioles; more blood to surface / heat lost by radiation; piloerector muscles relax; hairs flatten on skin surface; less insulation; sweating initiated / increased; panting / licking; evaporation removes latent heat; drop in metabolic rate / use less brown fat; accept long term changes such as less fat deposition; thinner fur; migration; accept one behavioural process;
Cross-channel swimmers experience a large decrease in external temperature when they enter the water. Describe the processes involved in thermoregulation in response to this large decrease in external temperature. (7)
Raising body temp
1. hypothalamus (contains the thermoregulatory centre);
2.has receptors which detect temperature changes of blood;
3.receives impulses from receptors in skin;
4.nerve impulses transmitted (from hypothalamus / brain);
5.results in vasoconstriction / constriction of arterioles / dilation
of shunt vessels;
6.diversion of blood to core / specified organ / less blood to skin;
7.muscular contraction /shivering generates heat via respiration;
8.release of thyroxine / adrenaline;
9.increase in metabolic rate / respiration;
10.correct reference to negative feedback mechanisms;
Describe the role of insulin in the control of blood glucose concentration. (4)
increase in blood sugar leads to lower blood sugar - glycogenesis
(homeostatic principle)/ (more) insulin secreted;
binds to (specific) receptors on (liver/muscle) cells;
leads to more glucose
entering cells/carrier activity/
increased permeability to glucose;
glucose leaves the blood;
glucose entering cell converted to glycogen;
Describe how a small amount of glucagon in the body could cause a rapid increase in the concentration of glucose in the blood plasma. (3)
Ref to cascade / amplification effect; (1)
1 molecule of cyclic AMP formed per glucagon (molecule);
each cyclic AMP activates (1) enzyme(molecule) ;
each enzyme causes breakdown of (1 ) glycogen (molecule);
each glycogen gives (1) glucose / glycogen is a polymer;
glucose diffuses into blood /
glucose moves high to low concentration; (1)
Explain how the hormone glucagon brings about its changes in the body.
It acts on liver cells;
causing conversion of glycogen into glucose;
via action of an enzyme- glycogenolysis
Also through gluconeogenesis;
What is negative feedback?
Negative feedback
An initial stimulus causes a response that reduces the magnitude of the initial stimulus
What is positive feedback?
Positive feedback
A stimulus causes a response that intensifies the initial input
Tell me about hormones…
Hormones…
Chemicals secreted from endocrine glands
Carried in the blood stream to their target organs
Target organs have specific receptors that compliment the shape of the hormone
Small molecules
Transported in the plasma
Effective in small amounts
Tell me about the 1st and 2nd messengers…
2nd Messenger Model/cascade effect of hormones
Hormone (1st messenger) does not enter the cell but attaches to a receptor on the cell membrane
Attachment starts a cascade system through the action of a second messenger cAMP
Example of cascade effect specific to glucagon
Attachment of a molecule of glucagon activates an enzyme adenylate cyclase
Active Adenylate cyclase converts many molecules of ATP to many cAMP’s
Each molecule of cAMP activates more than one glycogen phosphorylase enzyme
Each glycogen phosphorylase enzyme catalyses the hydrolysis of more than one glycogen molecule
Each glycogen molecule is made up of many glucose monomers
In this process a small amount of a hormone (glucagon) causes a series of amplified steps that causes a big response.
What is environmental temperature monitored by?
Environmental temperature monitored by thermoreceptors in skin send impulses to the hypothalmus
What is blood temperature monitored by?
Blood temperature monitored by thermoreceptors in hypothalamus
How can we generate a higher body temperature?
Shivering- increased muscle activity, increases respiration, releasing heat energy that transfers to blood flowing through the organs.
Increased metabolism- due to increase in release of adrenaline from adrenal glands and increased thyroxine from the thyroid glands.
Brown fat oxidation (infants and animals). Rich in mitochondria and oxidation of fat releases heat energy. Brown fat is located at the back of the neck and warms blood flowing to the brain
What is vasoconstriction?
Vasoconstriction impulses sent along the sympathetic nerves cause pre capillary sphincters in arterioles to contract and reduce blood flow in the capillaries supplying the skin. Blood is diverted through the arteriovenous shunt vessel, so less heat loss by radiation occurs.
How do hairs keep you warm?
Piloerection impulses along the sympathetic nerves to the erector pili muscles cause them to contract and the hair stands up trapping a layer of insulating air
Trapped layer of air warms up and reduces the temperature gradient between the blood and environment.
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How does sweating decrease physiologically?
Reduced sweating, impulses via the parasympathetic nerves causes less sweating
What is vasodilation?
Impulses sent via parasympathetic nerves to the precapillary sphincters in arterioles and they relax causing vasodilation allowing more blood to flow in the capillaries in the surface of the skin causing more heat loss by radiation
Describe how blood glucose concentration is controlled by hormones in an individual who is not affected by diabetes.
Insulin / glucagon secreted by pancreas / islets of Langerhans;
Hormone receptors in membrane (of target cells);
(insulin stimulates) conversion of glucose to glycogen / glycogenesis:
activates / involves enzymes;
stimulates uptake by cells;
conversion of glucose to lipid / protein;
glucagon stimulates conversion of glycogen to glucose;/ glycogenolysis;
glucagon stimulates conversion of lipid / protein to glucose /
gluconeogenesis;
What do the alpha cells in the islets of Langerhans produce?
Secrete glucagon
Causes glycogenolysis (glycogen to glucose)
Through the action of glycogen phosphorylase
What do the beta cells in the islets of Langerhans produce?
Secreting insulin
Causes glycogenesis (glucose glycogen)
Through the action of glycogen synthase
What is the role of insulin?
Binds to specific receptors on the membrane and opens channel proteins in the membrane increasing the permeability of the cells (mainly in the liver and muscle) to glucose
Increases respiration so that more glucose is used
Causes the activation of enzymes involved in the conversion of glucose to glycogen (glycogenesis)
Causes the conversion of glucose into fat in adipose tissue
What is the role of glucagon?
Only affects the liver cells
Acts through the cascade effect through a second messenger
Causes the activation of an enzyme (glycogen phosphorylase) that causes the hydrolysis of glycogen to glucose. It also encourages the formation of glucose from non glucose substrates (amino acids, fatty acids) in a process called gluconeogensis
Adrenaline (sometimes called epinephrine) causes increased glycogenolysis
What is the fasting blood glucose level and how is it used?
Fasting blood glucose level: this is the amount of glucose in the blood after fasting overnight (about 10hours). It tells us the amount of glucose required by the cells to maintain resting metabolic rate
Tell me about Diabetes mellitus….
Diabetes is a condition in which there are higher than normal blood glucose levels in the body. Symptoms can be, excessive thirst, hunger and urination. Sweet smelling breath (Ketosis: due to the high level of ketones form fat metabolism), glucose in the urine.
Type I- pancreas does not secrete enough insulin
Type II – liver no longer responds to insulin
Which organ cleans the blood?
The kidney
