Chapter 41: Homeostasis (Part 2, Week 9) Flashcards
[Start 41.3 General Principles of Homeostasis]
T/F External conditions are rarely constant.
True
What types of environmental changes are animals exposed to that could be harmful or even fatal if an animal did not respond appropriately?
Fluctuations in air and water temperatures, nutrient and water supplies, pH, and, in some cases, oxygen availability.
What is a example of homeostatic variables in animals that is influenced by eating food and excreting wastes? (3)
Mineral levels are affected such as Na+ and K+
- Establish resting membrane potentials across plasma membranes in all cells and transmit electrical signals in excitable tissues (muscles and nervous tissue)
Ca 2+
- Important for muscle contraction; neuron function; skeleton and shell formation
Fe 2+
- Binds and transports oxygen in blood or body fluids (some invertebrates use copper instead of iron)
What is a example of homeostatic variables in animals that is influenced by eating food and expending energy?
Energy sources are affected such as glucose
- Broken down to provide energy for use by all cells, especially brain cells
Fat
- Provides an alternate source of energy, particularly for cells not in the nervous system; major component of plasma membranes
ATP
- Provides energy to drive most chemical reactions and body functions; modifies function of many proteins by transferring a phosphate group to proteins
What homeostatic variable has factors that influence it such as rate of energy expenditure, environmental temperature, behavioral mechanisms?
Body temperature
Its function determines the rate of chemical reactions in an animal’s body.
What homeostatic variable has factors that influence it such as hydrogen ion transporters in cells, buffers in body fluids, rates of energy expenditure, and breathing rate?
pH of body fluids
Its function affects enzymatic activity in all cells.
What homeostatic variable has factors that influence it such as movement of air or water across respiratory surfaces (for example, lungs and gills), and the metabolic rate?
Oxygen and carbon dioxide.
Example of function
Oxygen circulates in body fluids and enters cells, where it is used during the production of ATP; carbon dioxide is a waste product that is eliminated to the environment, but it is also a key factor that regulates the rate of breathing.
What homeostatic variable has factors that influence it such as drinking, eating, excretion of wastes, perspiration, osmosis across body surface (skin or gills)?
Water
Example of function
Numerous biological functions including participating in chemical reactions; helping to regulate body temperature; acting as a solvent for biologically important molecules
What concentration in the plasma may increase or decrease, depending on whether an animal has recently eaten?
Plasma glucose concentration
However, even after a sugary meal or a prolonged fast, homeostatic mechanisms either return glucose concentration to normal or enable it to remain within the range required for survival.
Traditional units for glucose concentration used in the U.S. appear on the vertical axis; as a reference, a value of 100 mg/dL is equal to 5.5 mM.
What is the extracellular fluid?
The internal environment of cells, tissues, or organs.
What is a system designed to regulate particular variables in an animal’s body, such as body temperature; consists of a set point, sensor, integrator, and effectors?
Homeostatic control system
In a homeostatic control system, what is the normal value for a controlled variable, such as blood pressure, in an animal?
Set point
In a homeostatic control system, what is a structure such as a sensory receptor or a nucleus in the brain that detects a signal with in the system?
Sensor; monitors the level or activity of a particular variable.
In a homeostatic control system, what is typically a nucleus in the brain, in which the value of a variable is compared to a set point?
Integrator; compares signals from the sensor with the set point.
In a homeostatic control system, what is a molecule that directly influences a cellular response?
In animals, this structure is one that compensates for a deviation of a physiological variable from its set point.
Effector; compensates for deviation between actual value and the set point.
What is a homeostatic mechanism in animals in which a change in the variable being regulated brings about responses that move the variable in the opposite direction?
Negative feedback loop.
Example: a negative feed back loop involving homeostatic changes to blood pressure.
- When the blood pressure of an animal decreases due to blood loss, pressure sensors in the heart and certain blood vessels detect the change in pressure and send the information to the integrator—the brain.
- In the brain, the signal is compared with the normal set point for blood pressure. The brain responds to the deviation from the set point in two ways.
- First, signals are sent along nerves to the effectors—in this case, the kidneys, heart, and blood vessels.
- Second, the brain stimulates the release of certain hormones into the blood; these hormones provide an additional signal to the effectors.
- The result is that the heart beats more rapidly and forcefully, the kidneys produce less urine and thereby retain more water in the body, and the blood vessels direct blood to the most vital organs such as the brain. These responses raise the animal’s blood pressure back toward the set point.
To prevent overcompensation. like in maintaining blood pressure, what happens when blood pressure returns to its set point?
Stimulus is removed from the sensor.
This negative feedback, in turn, shuts off further production of the hormonal and neural responses. If this did not happen, blood pressure may reach incredibly high levels and possibly put the organism at risk.
What, in animals, is a mechanism that accelerates or amplifies a process, leading to what is sometimes called an explosive system?
Positive feedback loop
A positive feedback loop moves a system away from homeostasis, because a change in a variable or process leads to events that amplify that change.
In the example of reduced blood pressure, the body shivers to generate heat, and if not controlled, could lead to dangerously high body temperature.
This is contrary to the principle of homeostasis, in which large fluctuations in a variable are minimized and reversed.
In this example, how would an organism prevent higher body temperatures that could be detrimental to an organism by utilizing positive feedback when an injury reduced blood pressure?
The process of blood-clotting in mammals.
If an animal receives a wound that results in bleeding, various blood-borne factors contribute to sealing the damaged blood vessels and preventing further blood loss from occurring.
In mammals, this response includes the actions of fragments of cells called platelets, which are produced by the bone marrow and released into the blood.
When a blood vessel is cut, damaged cells secrete chemicals in the local area that attract platelets to the site and activate them. Activated platelets seal a damaged blood vessel in two general ways.
First, they physically help seal off the wound by clustering together at the injury site, and second, they secrete chemicals that attract and activate even more platelets to the site.
Those platelets, in turn, secrete more chemicals, which attract more platelets, and so on. The cycle ends when the wound is fully sealed.
What is a process by which an animal’s body begins preparing for a change in some variable before it even occurs?
What are some examples of this process that aids homeostatsis?
Feedforward regulation
- Mammalian body temperatures raise slightly before waking to help with increased metabolic demands of being active.
- Dogs salviate and their stomachs churn to create acids before feeding if they see or smell food.
What does feedforward regulation use?
Sensory detectors that recognize odors and sights. (like with Pavlov and his dogs)
What can the mechanisms that affect feedforward regulation result from or are modified by?
Learning.
The nervous system LEARNS to anticipate a homeostatic challenage.
Familiar examples are the increased heart rate and breathing rate that occur just before an athletic competition—demonstrated, for example, in trained racehorses before the start of a race.
The process of training, in which a horse’s body learns to prepare for the exertion of the ensuing race, prevents any delay between the start of exercise and the adequate flow of blood and nutrients to skeletal muscle.
What is a common thread that links all homestatic processes together?
Communication between cells, whether the cells are close to each other or in different parts of an animal’s body.
Some homeostatic responsesare highly localized, occurring only in the area of a disturbance.
For example, damage to an area of skin causes cells in the injured area to release molecules that help contain the injury, prevent infections, and promote tissue repair in the immediate vicinity.
Local responses provide areas of an animal’s body with mechanisms for local self-regulation. It is
no benefit to an animal to promote tissue repair in regions of the body that are not injured.
What is a type of cellular communication in which molecules are released into the interstitial fluid and act on nearby cells?
Paracrine signaling
Another example of extremely localized signaling occurs between neurons. A common way in which neurons communicate is through the release of neurotransmitters, small signaling molecules that are synthesized and stored in neurons.
When a neuron releases neurotransmitters, they diffuse and then bind to receptor proteins on an adjacent neuron (or in some cases a muscle or gland cell), altering the activity of that cell.
This type of cell-to-cell communication is typically very rapid, finishing within milliseconds.
Consequently, neurotransmitter responses can make immediate homeostatic adjustments, like those associated with reflexes.
Other than paracrine signaling and neurostransmitter release, what is a way cells can communicate over long distances by releasing chemical messenger molecules into the blood?
This type of signaling is mediated by hormones.
In animals, a chemical signal that is produced in a gland or other structure and released into the blood or hemolymph, where it acts on distant target cells. In plants, a signaling molecule that is important in coordination of plant development or plant response to the environment.
A hormone released in response to a homeostatic disturbance, such as the decrease in blood pressure described earlier, can influence the activities of many different cells, tissues, and organs simultaneously because the hormone is carried throughout the entire blood circulation.
Some hormones act quickly—within seconds—whereas others take minutes or even hours for their effects to occur.
[Start 41.4 Homeostatic Control of Internal Fluids]
Most of the water in an animal’s body is contained inside its cells; what is this fluid called?
What is the fluid in an organism that is outside of the cells called?
Intracellular fluid (intra means inside of)
Extracellular fluid
What separates intracellular and extracellular fluids?
Plasma membranes
