F214: Communication & Homeostasis

Cellular activity relies on enzyme action, therefore living organisms must maintain a limited set of cell conditions, such as a suitable temperature , pH  and an aqueous environment.

Internal environments; cells and tissues are not exposed to the external environment as they are protected by epithelial tissues. Consequently, the cell environment is the surrounding TISSUE FLUID.

Various cellular activities produce toxins. As a result cells are responsible for altering their own environment.

The accumulation of excess waste acts as a STIMULUS to cause a RESPONSE (waste removal)

Stimulus - environmental change that initiates a response

Response - change in the behaviour or physiology of an organism, as a result of a change in the environment

Negative feedback - process in which a change in a parameter brings about the reversal of that change in order to maintain optimum conditions; parameter remains fairly constant

Positive feedback - process in which a change in a parameter is increased in order to remain away from the optimum; parameter does not remain constant.

Homeostasis - maintenance of a constant internal environment, despite external changes

1. Optimum conditions

2. Deviation from optimum conditions ( stimulus)

3. Receptors detect the change

4. Communication system informs the effector through cell signalling

5. Effectors react to reverse the change, resulting in a return to the optimum .

1. deviation from the optimum

2. receptors detect the change in environment

3. Effectors are informed through cell signalling.

4. Effectors react to increases the change, therefore further increasing the  deviation from the optimum

A good communication system will enable SPECIFIC , RAPID communication with both SHORT and LONG TERM responses. This occurs in the form of 2 types of cell signalling :

Neuronal
* interconnected network of neurones
* signal across synaptic junctions using neurotransmitters
* conduct quick signals; rapid response

Hormonal 
* released from endocrine cells into the bloodstream
* specific target cells but an overall generalised effect
* responsible for coordination of longer-term responses

1. Changes in body temperature affect the tertiary structure of globular proteins such as enzymes.

2. Their structure is specific to their function; if an enzyme does not function properly, the level of cellular activity decreases.

3. Core body temperature is an important factor, as most vital organs are found in the thoracic cavity and abdominal region of the body.

4. Peripheral body parts e.g. extremities and limbs may increase of decrease temperature within reason, without affecting the survival of the individual.

1. Peripheral thermoreceptors monitor the temperature changes in the external environment

2. A rise or fall in core body temperature is detected by the thermoregulatory centre in the hypothalamus

3. Cell signalling; causes the effector to reverse the change through negative feedback

Endotherm: an organism able to regulate it's own body temperature

Physiological mechanism (COLD)

1. erector pili muscles contract causing hairs to 'stand on end' (Piloerection) trapping an insulating layer of air to reduce heat loss.

2. spontaneous contraction of muscle, causes an increase in respiration, which results in an increase in heat generation

Behavioural mechanism (COLD)

3. Increased rate of movement to generate heat in muscle

Physiological mechanism (HOT)

Vasodilation of arterioles increases the blood flow near skin surface to increase heat loss by radiation, convection or conduction.

Increase in sweat secretion from the sweat glands,  latent heat causes the sweat to evapourate to cool down the skin

decrease the rate of metabolism in hepatocytes,consequently less heat is generated through exergonic reactions.

Behavioural mechanism (HOT)

move into shaded area, reduces the surface area exposed to the sun.

remain inactive and spread out limbs to decrease heat absorption

Ectotherm - an organism that relies on the external environment to regulate it's own body temperature.

Physiological mechanism (COLD)

horned lizard expands ribcage to increase S.A to absorb more heat.

Behavioural mechanism (COLD)

locusts orientate body towards sun to increase heat absorption

Physiological mechanism (HOT)

locusts increase their abdominal breathing movement to increase water evaporation

Behavioral mechanism - HOT

lizards hide in burrows reducing  S.A exposure

Advantages

1. They possess a fairly constant core temperature, depite external temperature changes

2. Hence,activity is still possible even when the external temperature is relatively cool

3. As a result, they carry the ability to inhabit colder parts of the planet

Disadvantages

1. However, maintaining a constant core temperature is taxing; significant amounts of energy are used to sustain these optimum conditions.

2.For this reason, a greater intake of food is required to maintain energy stores.

3.Ergo, less energy from the metabolism of food is used for growth

Advantages
1. Relying on the external environment to regulate their body temperature, means that less food is in used respiration

2.less food used in respiration, means that they have greater reserves of energy, hence they can survive longer periods without food.

3. Additionally, a greater proportion of energy can be used for growth

Disadvantages
1. limited control of  internal temperature regulation inevitably reduces their activity in cooler climates or wintery environments as they do not warm up sufficiently.

Pacinian corpuscles -  detects mechanical deformation that is caused by pressure application to the skin

Olfactory cells - located in the nasal cavity, they detect the presence of volatile chemicals

Sound receptors - located in the cochlea and responsible for the detection  of vibrations in the air

Cones and rods - situated in the retina, they detect  wavelengths and intensity of light.

Taste buds - detect presence of soluble chemicals

Motor Neurone - coveys an action potential from the CNS to an effector.

Sensory neurone - transmits an action potential from a sensory receptor to the CNS

Diagram (right to left) dendrites -> dendron -> Cell body -> axon -> nerve endings

Changing membrane permeability

1. neurones contain specialised channel proteins which are specific to Na+ or K+ ions

2. when open, permeability to that particular ion increases

3. ion channels are generally closed, therefore the membrane is usually polarised

4. an action potential is created by altering the permeability of nerve cells to Na+ ions; movement of these ions across the membrane results in depolarisation.

1. In the generator region of sensory receptor cells, the gated ion channels open by energy changes in the environment.

e.g. gates in the pacinian corpuscle detect pressure change, and are opened by deformation.

2. voltage-gated channels further along open by responding to depolarisations of the plasma membrane.

3. In order for the action potential to be fired, sufficient generator potentials must combine via summation to be able to overcome the threshold potential (-50mv)

1.) -65mv = resting potential; neurone is polarised

2.) -50mv threshold potential(all or nothing law); gated Na+ ion channels open, results in an influx of Na+

3.) depolarisation of axon membrane

4.) +40mv voltage gated K+ ion channels opens, voltage gated Na+ channel closes

5.) K+ ions diffuse out of axoplasm down concentration gradient

6.) hyperpolarisation and refractory period, action potential cannot be fired

1. Na ion channels open at particular points along a neurone

2. Subsequently, Na+ ions  diffuse down their concentration gradient, into the axoplasm .

3. Consequently, upsetting the balance of ionic concentrations created by the Na+/ K+ pump

4. The concentration of Na+ rises at points where the Na+ ion channels are open, causes Na+ to diffuse down it's concentration gradient sideways

5. this movement of charged particles is referred to as a local current

6. Although, in a myelinated neurone, the Na+ ions appears to 'jump' from one Node of Ranvier to the next, this is called saltatory conduction.

1. higher internsity stimulus causes sensory receptors to produce more generator potentials

2. increases the frequency of action potentials in sensory neurones, in which it's arrival at a synaptic knob increases the release of neurotransmitters.

3. As a result, there is a higher action potential frequency in the postsynaptic neurone

4. Subsequently the increased frequency of signals to the brain, means heightened intensity of the response

1. amplify low level stimuli by summation

2. acclimatisation; after repeated stimulation the synapse uses up it's store of neurotransmitter, therefore an action potential cannot be fired. This avoids overstimulation of an effector.

3. filter unwanted low level stimuli

4. divergence: one presynaptic neurone may diverge to several postsynaptic neurones which allows one signal to be transmitted to several areas

Advantages of Myelination

1. transmit an action potential more quickly enabling a more rapid response to the stimulus

2. carry signals over long distances

3. myelinated neurones tend to be used in movement

Non-Myelination

1. used in coordination of breathing + digestion where increased speed of transmission is not so important

2. carry signals over shorter distances  

De-myelination

1. loss of myelin from myelinated neurones

2. results in loss of muscle coordination e.g. multiple scelrosis

3. autoimmune disorder; immune system may cause inflammation due to overproduction of cytokines

Adrenal medulla

1. releases adrenaline & noradrenaline (precursor)

Adrenal cortex

1. produces steroid hormones;

2. mineralcorticoids; responsible for controlling ion conc. of blood e.g. aldesterone

3. glucocorticoids; control metabolism of polysaccharides in liver e.g. cortisol

1. Adrenaline is an amino acid derivative therefore, it is unable to enter cells.

2. Adrenaline acts as a 1st messenger by binding to complementary shaped glycoprotein receptors on specific target tissues (e.g. hepatocytes).

3. This activates the enzyme adenyl cyclase which converts to ATP to cAMP

4. cAMP acts as a 2nd messenger by causing a cascade effect within the cell, in which, the final cascade pathway enzyme kinase, catalyses glycogenolysis.

Hormone - a chemical substance used in cell signalling which travels to a cell or organ to regulate it's activity.

Effect of adrenaline

1. relax smooth muscle in bronchioles

2. causes general vasoconstiction to raise BP

3. inhibits the action of the gut

Exocrine glands -duct
* Salivary gland
* sweat glands

Endocrine glands - ductless
* pituitary gland
* pancreas: Islets of Langerhans

Pancreas has both endocrine & exocrine functions

exocrine function : during digestion, it releases pancreatic amylase, into a duct leading to the duodenum of the small intestine.

Decrease

1. detected by alpha-cells in Islets of langerhans, stimulates the secretion of glugacon into the blood.
2. glucagon binds to complementary receptors on hepatocytes, stimulating glycogenolysis and gluconeogenesis

Increase

1. detected by Beta-cells in Islets of langerhans; insulin is secreted directly into the blood

2.  binds to complementary receptors on hepatocytes

3. Insulin increases uptake of glucose into the cell for respiration and stimulates glycogenesis

1.High glucose concentration causes it to diffuse down it's concentration gradient into the B-cell via facilitated diffusion.

2.glucose is metabolised to ATP, which causes ligand-gated K+ ion channels to close (ATP controlled).

3.This initiates a type of membrane depolarisation, which results in a change in potential difference

4.the change in potential difference causes voltage-gated CA2+ ion channels to open.

5.the diffusion of Ca2+ into the B-cell stimulates the fusion of insulin-containing vesicles to the plasma membrane, in which insulin is released by exocytosis.

Diabetes Mellitus - inability to control blood glucose, either because B-cells no longer produce insulin or the receptor cells are no longer responsive to insulin.

Type I
1.cause: autoimmune disease,in which Body's immune system recognises B-cells as foreign and initiates an immune response

2.treatment: insulin injections

Type II
1.cause: insulin receptors lose ability to detect insulin

2.contributing factors: diet, age, obesity and alcohol

3.treatment: monitering and altering diet

GM bacteria
1. exact copy of human insulin, therefore less chance of rejection
2. cheaper than manufacturing pig insulin, as bacteria do not occupy a lot of space for cultivation
3. less chance of moral objections

Stem cells
1. can differentiate into new B-cells
2. individual may require immunosupressants for life

Sympathetic nervous system

1. movement of muscles is detected by baroreceptors

2. decrease in blood pH is detected by chemoreceptors in carotid arteries

3. action potential is sent down the accelerator nerve to the heart from the cardiovascular centre in the medulla oblongata.

4. increases heart rate by increasing the rate in which the sino atrial node (SAN) releases the wave of electrical excitation

Parasympathetic nervous system

1. rise in blood pressure is detected by receptors in the carotid sinus

2. action potential is sent down the vagus nerve from the cardiovascular centre in the medulla oblongata

3. this decreases heart rate by slowing down the rate in which the SAN initiates wave of excitation

Adrenaline

1. released from the adrenal medulla of the adrenal gland

2. binds to complementary receptors on it's target tissue;cardiac muscle

3. increases cardiac output