Tolerance limits
All organisms share tolerance limits for a number of different factors. This does not include: water availability, light intensity, body temperature or nutrient availability.
Light intensity
Recall the stimulus response model.
Stimulus🡪receptor🡪sensory neuron🡪interneuron (in brain or spinal cord)🡪 motor neuron 🡪 effector 🡪 response
Define a hormone.
Chemicals produced by the endocrine system, transported by the circulatory system that have an effect on target cells through complementary binding to cell receptors
Explain how the nervous and endocrine systems work together to regulate the "fight or flight" response.
During the "fight or flight" response, the nervous system quickly activates the adrenal medulla via the sympathetic nervous system, leading to the release of adrenaline (epinephrine) into the bloodstream. This hormone enhances the body's ability to respond to stress by increasing heart rate, blood pressure, and energy availability, demonstrating the coordinated action of both systems.
List five responses associated with the ‘flight or fight’ response.
Dilation of pupils
Increased HR and BP (increase oxygen to muscles)
Dilation of blood vessels to muscles.
Increase blood glucose
Increase rate of breathing
Hormones help to increase body temperature by increasing: the release of water from the sweat glands, blood flow through the capillaries near the surface of the skin, metabolic activity or shivering.
Metabolic activity
Compare the structure and function of the three different types of neuron.
Sensory: Detect/send impulses to the CNS from sense organs. Cell body joined by axon and Dendron.
Interneuron: connection between sensory and motor. Short axon.
Motor: from CNS to effector. Short dendrites, long axon.
Describe the body’s response to low blood sugar.
Alpha cells on pancreas release glucagon, which binds to liver cells stimulating glycogenolysis. Liver releases glucose into blood.
Compare the roles of neurotransmitters and hormones in maintaining homeostasis, and discuss how their mechanisms of action reflect the differences between the nervous and endocrine systems.
Neurotransmitters are chemical messengers used by the nervous system to transmit signals across synapses between neurons, allowing for rapid and localized responses. Hormones, on the other hand, are released by endocrine glands into the bloodstream, affecting distant target organs and maintaining homeostasis over a longer duration. The rapid action of neurotransmitters is suited for immediate adjustments, such as reflex actions, while hormones regulate long-term processes like growth, metabolism, and reproduction, reflecting the complementary roles of these systems in maintaining homeostasis.
Using the ‘fight or flight’ response, describe how the response to stimuli can be coordinated by the nervous or other endocrine messages
Danger is detected and response initiated by the brain (CNS). Link to hypothalamus, which stimulates the adrenal gland to release adrenalin.
State the impact on a mammal, if body temperature increased above tolerance limit.
Enzymes may denature and not function.
Homeostatic mechanisms: sweat, decreased metabolism, vasodilation, hairs sit flat (pilorelaxation)
Which of the following is not a correct description of an element in the stimulus- response model for the homeostatic response to an increase in the body temp of a human? stimulus: high temp of blood; receptor: hypothalamus; transmission: nervous or response: decrease in blood flow near the skin surface
4. response: decrease in blood flow near the skin surface
Tea and coffee contain caffeine, which increases the volume of urine produced by the kidneys. The most likely response of the nephrons in the kidney to caffeine would be to decrease the rate of: active transport of Na ions into the tubule from the blood capillaries, filtration at the glomerulus, reabsorption of sodium ions into the blood capillaries from the tubule OR active transport of urea into the tubule from the blood capillaries
reabsorption of sodium ions into the blood capillaries from the tubule
Explain the roles of feedback mechanisms in the nervous and endocrine systems, using examples to show how they maintain homeostasis.
Feedback mechanisms help maintain homeostasis by adjusting system activities. In the nervous system, negative feedback regulates body temperature via the hypothalamus. In the endocrine system, blood glucose levels are controlled by insulin and glucagon. These feedback loops ensure stability by responding to changes in the body's internal environment.
How vasodilation and the inhibition of shivering result in a decrease in a human body during anaesthesia?
Vasodilation is the expansion of blood vessels, increasing blood flow near the skin. This increases the rate of heat loss. The inhibition of shivering prevents the involuntary contraction of muscles ->decreases the rate of heat gain
During a bacterial infection, WBC release a protein that changes the set point of the brain 'thermostat' from 37degrees to 40 degrees C. When this protein breaks down after about 3 days, the temp is reset to 37 degrees. What response is most likely to occur?
a decrease in sweating at 80 hrs after the onset of the infection, when the body temp is about 39 degrees.
Hyperventilation results in an increase in the rate of breathing (more CO2 removed by the lungs->the amount of CO2 in the blood will decrease-> an increase in pH of the blood; less H+ ions will be in the blood, due to less carbonic acid being present as there is less CO2)
Describe the difference in action between steroid hormones with peptide and protein hormones.
Steroid hormones are small and lipid soluble, therefore bind to intracellular receptors.
Peptide and protein hormones bind to extracellular receptors, as they are usually unable to pass through the cell membrane.
How might a dysfunction in the hypothalamic-pituitary-adrenal (HPA) axis affect both the nervous and endocrine systems, and what could be the potential effects on the body?
A dysfunction in the HPA axis can lead to imbalances in cortisol production, affecting both systems. Excess cortisol can cause prolonged stress responses, impacting mood and cognitive functions (nervous system) and leading to conditions like high blood pressure and weakened immune response (endocrine system). Insufficient cortisol can result in fatigue and low blood pressure.
Explain how thyroxine affects body temperature.
Thyroxine increases the metabolic rate of cells->increases heat production->an increase in body temp
Which statement about an animal's tolerance limits is not correct: may be defined by the environmental conditions required by the species, they relate to abiotic factors in the environment of the organism, they are fixed characteristics of all individuals of that species, or they determine distribution and abundance of the animal?
Fixed characteristics of all individuals of that species
Describe how receptors in the brain detect an increase in the pH of blood.
The brain cannot directly detect the pH of blood as H+ ions cannot diffuse across the blood-brain barrier of the brain. CO2 is able to cross the said blood. CO2 diffuses, reacts with H2O to form carbonic acid, and then dissociates into H+ ions which is detected by chemoreceptors in the brain.
Describe the action of thyroid stimulating hormone and thyroxine in metabolism.
TRH is produced by the hypothalamus, which stimulates the pituitary to produce TSH.
TSH travels through the blood stream to thyroid gland, releasing thyroxine. Thyroxine increases metabolism, producing heat.
Describe how the nervous and endocrine systems might respond differently to short-term versus long-term stress, and the implications for health.
In short-term stress, the nervous system quickly activates the sympathetic nervous system, causing immediate changes like increased heart rate. The endocrine system releases adrenaline for sustained response. In long-term stress, prolonged cortisol release can lead to health issues such as immune suppression and high blood pressure, while the nervous system may experience changes affecting mood and cognition
Describe how a lowered respiration rate (hypoventilation) could lead to respiratory acidosis.
Respiratory acidosis (build up of carbonic acid) caused by excess CO2 dissolved in blood. Hypoventilation, less carbon dioxide exiting body, therefore builds up in blood, lowering pH.