Ch 8: Homeostasis Flashcards
What is the definition of homeostasis?
the maintanence of a constant internal environment despite changes to external factors within a certain range at optimal levels, process is done actively (expending energy)
What are the principles of communication?
- production of a signal that contains information to be transferred
- detection of the signal
- transfer of this signal until it reaches its target
- a respones to the signal by the target
- switching off a signal by the target
What are the different types of receptors?
def: a structure that detects/receives a stimulus
exteroreceptors: a receptor that receives signals from the external environment, they work by receiving information and converting it to a chemical signal that can then be relayed between body cells
interoreceptors: a receptor that receives signals from the internal environment and ensures it is maintained within narrow limits allowing maximum cellular efficiency
What are the main types of receptors?
- chemoreceptors
- stimuli:
- ex.- substances that have smell, olfactory receptors, or taste (location in animals: nose, mouth)
- int. - detection of oxygen and ion levels (location in animals:aorta, cartoid arteries)
- stimuli:
- mechanoreceptors
- stimuli: pressure, touch, tension, sound vibrations, balance (location in animals: ear, skin)
- photoreceptors
- stimuli: ext. - light (location in animals: eyes, light sensitive cells in body surface of some invertebrates)
- thermoreceptors
- stimuli:
- ext. - external temp. variations (location in animals: skin)
- int. - internal temp. variations (location in animals: hypothalamus)
- stimuli:
- pain receptors
- stimuli: pain (location in animals: free nerve endings in the skin)
What is the nervous system?
the network of nerve cells and fibres that transmits nerve impulses to provide communication between parts of the body
Provide an overview of the nervous system
central nervous system: responsible for processing, storing and coordinating information - formed by brain and spinal chord
peripheral nervous system: transmits information to and from the CNS - comprises all other neurons
- somatic sensory system: nerves associated with a voluntary response - incl. sensory and motor
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autonomic nervous system: nerves associated with an involuntary response
- parasympathetic nervous system: controls homeostasis and ‘rest and digest’ response i.e. smooth muscle
- sympathetic nervous system: controls body’s respons during percived threat (fight or flight response) i.e. cardiac muscle
What are neurons?
- are the basic units of the nervous system
- have extensions called fibres, along which nerve impulses travel. A bundle of these comprise a nerve and each nerve is wrapped in a tube of connective tissue, as nerve impulses travel along axons, they can skip from node to node, greatly speeding up the impulse
- the insulating sheath surrounding the axon is called myelin, made up of Schwann cells, which wrap around the axon, spaces between the Schwann cells are called nodes. The myelin sheath is essential as it assists in the transmission of electrical impulses along sensory and motor neurons, acting like insulation - it allows the impulse to travel faster and keeps the message from accdentally corssing over to adjacent neurons
What is the endocrine system?
def: the bodily system responsible for the production and secretion of hormones, which are released into the bloodstream to act on specific target cells and organs
- not all responses require rapid change, some take time and are under the control of hormones.
- Hormones are chemical substances that are secreted by ductless glands directly into the bloodstream, they can be proteins, steroids, fatty acids and amino acids. Hormones act upon their particular target cells and tissues to bring about a response. Only the cells that express a receptor for a hormone will respond to it
- the pituitary gland is often connected with the coordination of activities associated with the endocrine system - it is known as the master gland because it produces many hormones that affect hormone production by other endocrine glands.
- Large protein hormones such as insulin are generally detected by receptors that are expressed on the cell surface. Small hydrophobic hormones such as cortisol can easily pass through the plasma membrane and so their receptors are intracellular.
Describe the endocrine organs
- Hypothalamus: body’s thermostat, regulates appetite, regulates the pituitary gland
- Pituitary gland: regulates hormone release by other glands
- Thyroid gland: regulates growth and metabolism
- Adrenal glands: responsible for ‘fight or flight’ response
- Pancreas: regulate glucose metabolism and homeostasis
- Ovaries and testes: regulate sex-related phenotypes and reproduction
What are the reasons for a response?
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Developmental processes, growth and reproduction
- failure in the signalling pathways that cause genes to switch on and off and trigger mitotic divisions can lead to uncontrolled cell division and cancer
- apoptosis is important in foetal development and failure to respond to signals for this can lead to malformations
- during reproduction, particular cells differentiate to function differently; these processes all occur in response to certain signals both from the external and internal environment
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Homeostasis: the maintanence of a relatively constant internal environment within small tolerance limits, despite changes in the internal or external environments
- cell function, movement of materials, enzyme activities and biochemical processes all depend on responses to changes in the environment and correcting them back to normal
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Surviving challenges in the external environment
- a coordinated response to immediate threaths that may cause injury or death requires signals from the external environment to be detected and conveyed to cells that then respond appropriately
Describe the body systems involved in homeostasis and define key terms
organisms have narrow ranges in which they keep internal temp. and fluid concentration - all disturbances to the optimal level must be controlled quickly for cells to continue to function effectively
stimulus: a signal that causes a response
receptor: a structure that detects or receives a stimulus
feedback mechanism: a mechanism in which the ouput/response affects the input or stimulus - processes that respond to small disturbances to keep concentrations of substances within narrow limits for optimal cellular function
How is the response controlled in feedback?
once a signal has been responded to, it is important that it is switched off - an over response is a waste of energy and can often lead to cell damage
- disrupting the signal transduction pathway
- removal of the original stimulus
- responding in a way that alters the orginial signal - feedback
What is negative feedback?
def: when a change of variable/stimulus occurs, a response that reverses the direction of the change, extremely important in homeostasis as the response always aims to restor the internal environment to a constant set of conditions
- A stimulus is detected by a receptor
- The information is transferred to a processing centre
- The processing centre sends the information to an effector
- The effector carries out a response
- The stimulus is corrected and no longer stimulates the response
What is positive feedback?
def: when a change of variable/stimulus occurs, a response that changes the variable even more in the same direction
- this positive feedback is usually associated with growth and development rather than homeostasis.
- for example, positive feedback stimulates and reinforces the process of metamorphosis of a tadpole to a frog. Once the process has begun, it continues to completion.
- another example is the release of prostaglandins from the placenta during childbirth. These stimulate contractions, and the positive feedback only discontinues when the placenta is delivered.
What is a tolerance range?
def: the range within which an organism can function and reproduce
How do animals keep warm in the cold?
- Insulation - feathers, fur and blubber prevent heat loss by trapping a layer of air close to the body
- Piloerection is raising of body hairs to trap a layer of air
- Countercurrent heat exchange - warm blood travelling to extremities via arteries transfers its heat to cool blood returning from extremities in adjacent veins - the outgoing blood to the extremity is cooled in the process, but not enough to affect cell activities, as the temp. gradient between the extremity and the surroundings is reduced, heat loss is minimised
- shape and size - adaptations that lower surface area to volume ratio reduces heat loss, heat loss is less in larger, rounder organisms i.e. large SA of an elephant’s ears assist heat loss. Some animals reduce heat loss by behaviour i.e. uddling provides insulation and reduces an organism’s surface area to volume ratio (penguins)
- metabolism - Increasing the metabolic rate generates more heat i.e. via exercise which increases the metabolic rate and also shivering is an adaptation to increase metabolic heat
- shut down - sometimes behaviours and physical features are inadequate in stabilising temperature
Hibernation When heat-generating behaviour and adaptations are not sufficient to keep an organism’s body temperature above the lower critical temperature, it may enter a state of hibernation as the increase in metabolic activity requires a supply of energy which for some proves difficult if food is scarce. The set point is lowered considerably and the metabolic rate falls to a level that just sustains life. Aestivation, another kind of seasonal dormancy, is a response to dry conditions.Snails retreat into their shell and seal it off, for example. On the other hand, the upper critical temperature is reached when cooling mechanisms fail and the metabolic rate increases as the external temperature increases.
Describe the kidneys and their osmoregulatory role
Osmoregulatory function
- Remove nitrogenous wastes from the body - essential as nitrogenous wastes i.e. ammonia are toxic and can severely affect the pH level of cells
- Regulate water concentration in the blood
- Maintain ion levels in the blood
Nitrogenous wastes come from the synthesis of proteins. Different organisms have adapted the use of one of these different waste forms depending on their environmental demands.They occur in three biological forms:
- Ammonia – least toxic
- Urea – intermediate toxicity
- Uric acid – least toxic
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How do the kidneys regulate the water/solute balance
the functional unit of the kidney is the nephron.
- In the glomerulus, blood plasma is filtered from fine capillaries.
- Filtrate is collected in the Bowman’s capsule.
- Filtrate travels through the loop of Henle, along which nutrients and proteins are reabsorbed back into the bloodstream.
If water level decreased
- Hypothalamus detects too little water in the blood
- Stimulates pituitary gland which releases vasopressin
- Travels via circulation to kidneys, stimulates water reabsorption by kidneys and secretion of Na+ ions
- Less water is excreted by kidneys. More Na+ is secreted into urine
- Blood osmolarity returns to normal (negative feedback)
What are osmoregulators?
def: organisms that have specialised mechanisms for regulating internal water and solute concentrations, despite concnetration changes in the external environment
Structural features
Animals
- waterproof or impermeable outer layer (integument) can reduce water loss
Plants
- thick waxy cuticle on the leaf surface
- more stomata on the under side of the leaf than the upper
- sunken stomata
- cylindrical or rolled leaves
- hairs on leaves
- tap roots
Physiological adaptations
- reptiles and birds reabsorb water from their cloaca, the cavity into which their ureter and rectum open.
- terrestrial vertebrates can slow the production of urine by reducing the glomerular filtration rate, the Australian desert frog can also swell and store its urine for use in the dry season.
- having longer loops of Henle allow organisms to concentrate their urine i.e. the desert hopping mouse Notomys alexis can concentrate its urine more than any other known rodent
- camels can tolerate water loss and concentration of their body’s fluids.
- some marine organisms have body fluids with a higher water concentration (that is, they are hypotonic) than their surroundings. For example, marine fish live in salty water and have hypotonic body tissues. As water is lost via osmosis from the gill surfaces, marine animals drink copious amounts of sea water, this increases salt intake as well, marine vertebrates actively remove salts by special chloride secretory cells in the gills. Also a slow filtration rate and the excretion of concnetrates nitrogenous waste helps them reduce water loss. Other organisms have body fluids with a lower water concentration (that is, they are hypertonic) than their surroundings. For example, fresh water fish have higher solute concentrations than their surroundings. In aquatic environments, osmoregulators must overcome osmosis.
Behaviours
- some terrestrial animals living in dry environments can undergo aestivation, a hibernation state in which the metabolic rate slows for several months until water is available.
- other animals inhabit burrows, in which the humidity is higher and the temperature lower.
- notomys alexis wraps the bushy end of its tail around its face to trap a humid layer of air between itself and the environment.
