Chapter 10 - Homeostasis and thermoregulation Flashcards
Homeostasis
The maintenance of a constant internal environment within tolerance limits despite fluctuations in the external environment
what is the purpose of homeostatic regulation
To maintain internal factors around a set normal value. When the factors deviate away from the value, homeostatic adaptations will attempt to bring the factor back to the normal value
Metabolism
The sum of all the chemical reactions occurring within an organism to maintain life. Includes reactions enabling an organism’s growth, homeostasis and reproduction
enzymes
A reusable, biological catalyst that lowers the activation energy of chemical reactions, making them proceed faster. It is a protein that is sensitive to factors such as temperature and pH
negative feedback
feedback that reduces the effect of, or eliminates the original stimulus. eg aircon in building
receptors
A cell or tissue that detects a stimulus (change in the environment). May be internal or external
what are the five main types of receptors
- Chemoreceptors (chemical stimuli - aorta, carotid arteries)
- Mechanoreceptors (mechanical stimuli)
- Photoreceptors (light signals - eyes)
- thermoreceptors (change in temperature - skin, hypothalamus)
- nociceptors (pain)
- Osmoreceptors (osmotic pressure - hypothalamus)
Interstitial fluid
fluid that lies in spaces between cells
what does the nervous system consist of
- The central nervous system (brain and spinal cord) - receives sensory information from receptors, interprets and processes the information and produces a response
- The peripheral nervous system (sensory and motor neurons) transmit info to and from the CNS
what is the pathway of nerve impulses
Follow sensory neurons from source of stimulation, via the PNS to the CNS. Interconnecting neurons located in the CNS relay the electrical impulses from the sensory neurons to the appropriate motor neurons. From the CNS, motor neurons relay information signals via the PNS to the effectors.
Afferent
From receptor to CNS
Efferent
From the CNS to the effector
What are the four differences between the actions of nerves and hormones
- Nervous responses are more rapid than hormonal as nerve impulses travel rapidly along nerve fibres while hormones are transported in the bloodstream
- Nerve impulses bring about an immediate response which lasts for a short time. Hormones are slower acting but can last a considerable time
- Nervous messages are an electrochemical change that travels along membrane of neuron. Endocrine messages are hormones that are transported by blood
- Nervous impulses travel along a nerve fibre to a specific part of the body and often influence just one effector. Hormones travel to all parts of the body and effect a number of different organs
example of hormone regulation in humans
ADH secreted by the pituitary gland effecting the kidneys, stimulating the reabsorption of water, helping maintain an appropriate water balance in the body
example of hormone regulation in other organisms
Female ring doves coo during courtship to stimulate the release of the hormones that result in egg development.
what are the three types of neurons on their function
- Sensory (receptors –> CNS)
- Interconnecting (Sensory neurons –> motor neurons)
- Motor (CNS –> effector)
examples of factors that can vary in the environment
Temperature, water availability, nutrients, oxygen and carbon dioxide
Positive feedback
feedback model that strengthens and intensifies the effects of the stimulus. EG, blood clotting, childbirth, development of frogs and toads
Five parts of a negative feedback model
- Stimulus: change in internal or external environmental factors. Involves a deviation away from normal value
- Receptor: Cell or tissue that detects the stimulus. May be internal or external
- Modulator (coordinating centre): Structure that receives messages from receptors (via sensory neurons), coordinates a response, send instruction to effector
- Effector: Muscle or gland that receives message from control centre and carries out the response
- Response: the action of the effector that counteracts the stimulus
- Negative feedback: factor returns to normal value
set point
optimal value for an internal variable such as temperature
Tolerance ranges
the range of a factor within which an organism can function and reproduce. If factors go outside of this range, it may be fatal for the organism. LEARN DIAGRAM
Optimal range
the narrower range, within an organism’s tolerance range for a particular factor at which the organism functions best
Zone of physiological stress
The zone that is outside the optimal range but inside tolerance range. Is not optimal but survival is possible
Zone of intolerance
the zone that is outside the tolerance range for survival
Internal factors that have a tolerance limit
temperature, nitrogenous waste, water, salts and gases
Increase in temperature
- Enzymes denature, leading to slow cell metabolism
- Cells can die
- Membranes such as cell membranes become too fluid, allowing some unwanted substances into or wanted substance out of cells
- Rate of photosynthesis slows
Decrease in temperature
- Decrease in the activity rate of enzymes, which results in a decrease in metabolic rate
- the activity of some other proteins decreases
- Membranes such as cell membranes become rigid (instead of fluid), slowing cell membrane transport of substances
- mammals can suffer hypothermia, may lose limbs and cannot reproduce
increase in Nitrogenous waste
- As nitrogenous wastes build up, they increase in concentration and become more toxic
- An increase in ammonia (a base) in the blood can lead to an increase in the pH of body fluids
- Enzyme activity can decrease, enzymes will denature if the pH gets too high.
- High levels of nitrogenous waste can affect water balance. Cells may lose water to dilute the waste, affecting water homeostasis
Nitrogenous waste pathway
Ammonia (highly toxic) –> urea (moderately toxic) –> uric acid (least toxic, little water, energy cost)
Hypothermia
A state in which an organism’s internal temperature drops below the lower tolerance limit
Hypotonic
(water enters cell) At a lower concentration than another solution. When a cell is surrounded by a hypotonic solution, water moves out of the cell via osmosis to dilute the cell, so the cell swells. (animal cells which have no cell wall sometimes burst)
Hypertonic
(water leaves cell) At a higher concentration than another solution. When a cell is surrounded by a hypertonic solution, water moves out of the cell via osmosis to dilute the surroundings, so the cell shrinks
Isotonic
At the same concentration as another solution. If a cell and its surrounding solution are isotonic, there is no net movement of water between them and the cell maintains a constant volume
Plasmolysis
The state of a plant cell in which the cell membrane has pulled away from the cell wall due to water moving out of the cell
Physiological adaptations
Related to how an organism, system, organ, tissue or cell functions.
Structural adaptations
related to an organism’s shape, specialised features and size.
Behavioural adaptions
Relate to how the organism acts
Physiological processes that maintain an organism’s internal environment within tolerance limits
- Reducing carbon dioxide concentration by increasing breathing rate. This passes more blood through lungs, releasing carbon dioxide and blood is oxygenated faster.
- The changed internal temperature is detected by thermoreceptors in the hypothalamus which signals to the sweat glands to activate
Structural adaptations that maintain an organism’s internal environment within tolerance limits
Thick insulating fur that keeps a bear warm, the thin flat leaves of a tree that maximise sunlight capture, the vast capillary network over the alveoli that creates a large surface area for gas exchange
Behavioural adaptations that maintain an organism’s internal environment within tolerance limits
Burrowing in mud helps desert frogs avoid drying out. In humans, removal of clothing or moving to shade.
hyperthermia
A state in which an organism’s internal temperature rises above the upper tolerance limit
what are endotherms
An animal that uses metabolic processes to generate its own heat to maintain its internal temperature within the tolerance range. Endotherms also have a range of adaptations that serve as mechanisms for controlling heat gain or loss.
examples of endotherms
Birds, mammals, some reptiles, fish and insects
what are ectotherms
An animal whose body temperature is determined by the external environment. Ectotherms rely on structures and behaviours for thermoregulation. Ectotherms may obtain heat from the sun or from objects in their surroundings, which means their body temperature fluctuates with that of the external environment
examples of ectotherms
Amphibians, some reptiles, fish, most invertebrates
why do scientists avoid using the terms ‘warm blooded’ and ‘cold blooded’
Because they are misleading. For example, if an ectothermic lizard is basking in the sun, its body temperature may be ‘warmer’ than an endothermic seal that is using faster metabolism to warm up
Costs of endotherms
To maintain a stable internal temperature, they may have a higher metabolic rate, need to spend more energy to maintain a higher metabolic rate. Results in higher food requirements and more time spent finding food
costs of ectotherms
Body temperature is dependent on external temperature. These animals are limited to living in environments with less extreme temperatures. They cannot tolerate very high or very low external temperatures
benefits of endotherms
Body temp is independent of external temperature. This enables endotherms to live in more extreme environments. They can be active at night or more often during day and cold weather. Being more active may reduce chance of predation
benefits of ectotherms
Their heat source is mainly the environment, so there are lower energy requirements for these animals. Therefore they need to consume less food, spend less time hunting, can tolerate larger fluctuations in their internal body temperature compared with endotherms
Temperature gradient
Produced when two objects in close proximity have different temperatures due to different amounts of heat energy. this causes heat to travel from the hotter object to the colder object
evaporative cooling
A mechanism of heat transfer from an organism to its surroundings. Water on the surface of the skin draws heat energy from the body for the change of state from liquid water to vapour. The vapour diffuses into the surrounding air, taking heat away from the body and cooling the body down
