Regulating homeostasis Flashcards
What is an external environment?
The environment outside an organism
What is an internal environment?
The fluid surrounding the cells (in a multicellular organism). It is also called the extracellular fluid
What are some examples of extracellular fluid?
Tissue fluid, plasma, cerebro-spinal fluid, lymph
What is intracellular fluid?
The fluid inside the cell (cytosol)
What is homeostasis?
The ability of an organism to regulate and maintain a stable internal environment (within tolerable limits) in response to internal or external changes
What is another word for homeostasis?
Dynamic equilibrium
Why is being able to regulate an internal environment important?
Allows the organism to survive a greater range of conditions
What can happen if the internal environment is not adapting?
Cellular damage, death
What is the process of homestasis?
Detection of change from a stimuli by receptors, stimulating a response from effectors
What systems control homeostasis in animals?
Endocrine and nervous system
What systems control homeostasis in plants?
Endocrine system
How is homeostasis maintained?
Feedback loop systems
What is the feedback loop mechanism?
- A stimulus/initial event effects a key variable from a stable state, creating a signal
- The signal is detected by a receptor
- The signal is transferred to the control centre
- The control centre sends a signal to the effector
- The effector works to respond to the signal
What is an osmoconformer?
The solute concentration of internal environment is isotonic to external environment
What is an example of an osmoconformer?
Decorator crab
What is a benefit to being an osmoconformer?
No energy expended
What is a negative to being an osmoconformer?
Less tolerable to external changes
What is an osmoregulator?
Internal solute concentration is able to be controlled
What is the benefit to being an osmoregulator?
Tolerating fluctations in external environment
What is the negative to being an osmoregulator?
Energy expended tolerating changes
How does a negative feedback system work?
They respond to stimuli by reversing the direction of change, to bring back to the original state
What is an example of a negative feedback system?
Producing perspiration that cools the body by evaporative cooling. This assists to reduce the core temperature of the body thus decreasing the original stimuli
What is a positive feedback loop?
Response causes an increase in the original stimulus (not a part of homeostasis)
Are positive feedback loops mechanisms to maintain homeostasis?
No
What is an example of a positive feedback loop?
Pressure on the cervix in childbirth releases the hormone oxytocin, stimulating more contractions and greater pressure on the certix. This is then progressing labour
What is the stimulus-response model?
- Stimuli affecting a key variable from a stable signal, causing a signal
- Detected by a receptor.
- Signal is transferred to the control centre
- Control centre sends a message to an effector
- Effector works to respond to the signal
What are receptors?
Substances that detect stimuli and respond by triggering a response to the release of a hormone or initiating signals in the nervous system
How many receptor types are there?
4
Which receptors are stimulated by chemical change?
Chemoreceptors
Examples of what stimulates a chemoreceptor
Respiratory gases, water, glucose
Where are chemoreceptors located?
Blood (major arteries), taste buds, nose, lungs, brain
What are mechanoreceptors?
a receptor stimulated by mechanical forces or pressure changes. They are stimulated by forces that change the shape of a sensory nerve ending
Examples of what stimulates a mechanoreceptor
Sound, vibration, touch, pressure
Where are mechanoreceptors located?
Skin, ears, blood vessels, lungs, joints
What stimulates a photoreceptor?
Light
Where are photoreceptors located?
Eyes
Where are thermoreceptors located?
Skin, brain
What stimulates thermoreceptors?
Temperature changes
What are hormones?
Signalling molecules that are responsible for communication between organs and tissues
Where are hormones commonly involved in?
The response arm of the negative feedback loop
What are hormones produced by?
Specialised cells. In complex animals, these cells are clumped together in organs called ‘endocrine glands’
How do hormones exert their effect?
Passing directly through the plasma membrane or interacting with the receptor on the outside of the cell
What is the hypothalamus?
The collecting centre, receiving information/stimuli form all parts of the body about inernal condition. It uses this information to control the secretion of homrones by the pituitary glands
What is the exception to a body system not regulated by the hypothalamus?
Blood glucose levels, which is monitored by the pancreas
Why are hormones highly specific?
Only released with a specific simuli from a specific gland
Only certain receptors can react
Where is the pituitary gland located?
Underneath (and connected to) the hypothalamus)
What is the role of the pituitary gland?
To secrete hormones that affect target cells or that regulate secretion from other glands
What does the anterior gland do?
Produce hormones involved in growth and regulation
What does the posterior lobe do?
Stores hormones produced by hypothalamus
What is the mode of action of hormones?
Transported to where they are required by circulatory system (animals) or diffusion (signals)
How do hormones create an effect?
Act by transmitting signals to target cells, which possess a specific receptor for a specific hormone.
How do hormones exert their effect?
By passing through a plasma membrane or interacting with the receptor on the outside of the cell
How much energy do hormones require?
Very little -> they are free of charge
What is the source of the hormone insulin?
Pancreas - islets of Langerhands B cells
What is blood glucose required for?
Cellular respiration
Where is glucose stored?
As glycogen in the liver
What is the site of action for insulin?
Body cells
What does insulin regulate?
Blood sugar levels
What is the source of glucagon?
Pancreas - alpha cells
What is the site of action for glucagon?
Liver
What does glucagon regulate?
Blood sugar levels
What happens when blood glucose is high?
Pancreas (specifically Islets of Langerhans) detects it. More insulin is secreted by beta cells. This decreases blood glucose by increasing blood glucose uptake by cells. Alpha cells decrease glucagon production, moving glucose from bloodstream into liver and converting it into glycogen. Fat cells take up more glucose.
What happens when blood glucose is low?
Pancreas detects it. Alpha cells secrete more glucagon, which has the effect of converting glycogen back to glucose and releasing it back into the blood stream.
Beta cells produce more insulin, which decreases rate of glucose uptake by liver and body cells
How does adrenaline play a role in increasing blood glucose levels?
Its actions on fat, muscle and liver
What does antidiuretic hormone (ADH) regulate?
Amount of water intake
What is the source of ADH?
Hypothalumus makes it. Pituitary gland secretes it
What is the source of Thyroid stimulating hormone (TSH)?
Anterior pituitary
What is the site of action for TSH?
Thyroid
What does TSH regulate?
Release of thyroxine
What is the source of thyroxine?
Thyroid
What is the site of action for thyroxine?
Body cells
What does thyroxine regulate?
Cellular metabolic rate
What does adrenaline regulate?
Fight or flight response
What is the site of action for adrenaline?
Heart and muscles
What is the source of adrenaline?
Adrenal glands
Why is the nervous system faster acting than the endocrine system?
Because nerve action is due to electrical impulses (which travel very quickly), while hormones travel from production site to target cells via bloodstream
Why are hormones longer lived than nerve signals?
Because hormones must be metabolised before actions stop + inactivation time can take hours to days, while transmitter signals act for a fraction of a section and then are inactivated
What is blood glucose required for in the body?
Main source of energy, required for cellular respiration, stored in the body as glycogen in liver + muscle
How is blood glucose regulated?
2 antagonistic hormones (secreted by Islets of Langerhans)
- insulin: beta cells
- glucagon: alpha cells
What level is blood glucose meant to be at?
4-6mmol/L in the blood
What effect does insulin have?
Increasing the rate of glucose uptake by cells, stimulating the conversion of glucose to glycogen by liver cells, having fat cells take up glucose when insulin is present (makes more fat)
What happens when blood glucose is low?
Pancreas detects problem. Pancreas secretes glucagon, targeting liver and muscle cells. Glucagon decreases the rate of glucose uptake by liver cells, as well as a converting the glycogen back to glucose and releasing it into bloodstream. Adrenaline also contributes to raising blood glucose levels with its effect of fat, muscle and the liver
What is hyposecretion?
Underproduction of hormones
What is hypersecretion?
Overproduction of hormones
What types of cancer are linked to diseases of the endocrine system?
Cancers of the endocrine glands
What is diabetes characterised by?
Hyperglycaemia (higher than normal blood glucose levels) particularly after a meal. Excretion of glucose in urine
What is Type 1 Diabetes?
An autoimmune condition in which the immune system destroys the insulin-producing beta cells in the Islets of Langerhans in the pancreas
What is Type 2 Diabetes?
Failure of the muscle and liver cells to respond sufficiently to insulin
When looking at a graph of a glucose tolerance test, what are the signs of diabetes?
Higher initial concentration of blood glucose (over 8mmol/L). When glucose is taken in (glucose tolerance test), the blood glucose rises at a much greater rate and takes longer to return to original level
What are the diabetes symptoms caused by?
High glucose levels
What can high glucose levels lead to?
The kidneys work hard to get rid of excess glucose. This results in increased urine production, glucose in urine, excessive thirst and dehydration, excessive hunger, etc. This can lead to blurred vision and vessel damage
How can diabetes be managed?
Glucose intake is balanced with insulin injections and exercise
What is the name of regulating temperature?
Thermoregulation
What temperature does the thermoregulatory centre regulate in most mammals?
37.5 (+ or - 0.5)
What is it called when the internal temperature is too high?
Hyperthermia
What happens in hyperthermia?
Enzymes denature
What is the name of the state in which the human body is below temperature set point?
Hypothermia
What is an example of when the temperature set point can be regulated?
During a fever. Certain chemicals (pyrogens) released by white blood cells raise the set point. This causes the whole body temp. to increase by 2-3C -> kills bacteria, inhibits viruses, explains why you shiver even though hot
What is a homeotherm/endotherm?
An animal that controls their own body temperature
What is a poikilotherm/ectotherm?
An animal that depends on their external environment from heat supply
What is an example of a poikilotherm?
Reptiles
What is conduction?
Heat moves from a warm object to an object at a lower temperature
What is radiation?
Heat radiated from warm objects and absorbed by cooler objects
What is convection?
Currents in air or water move heat from one area to another
What is evaporation?
Heat is lost as water evaporates from the surface of a warm object (cools object)
Where is the thermoregulatory centre in the body?
Hypothalamus
What are the two sets of thermoreceptors that give input to the hypothalamus?
- Receptors in the hypothalamus monitor the temperature of the blood as it passes through the brain (measures core temperature)
- Receptors in the skin monitor the skin temperature and neurons transmit information to the hypothalamus
Which systems regulate temperature?
Endocrine and nervous
What happens when the body temperature falls?
Hypothalamus detects problem. It relays messages via motor neurons to activate skeletal muscles shivering and constrict arterioles to reduce heat loss from skin. Hypothalamus secretes thyrotropin-releasing hormone from neurosecretory cells. TRH signals pit. gland to make TSH. TSH stimualtes thyroid gland to release thyroxine. This causes a metabolism increase, so heat production rises. Furthermore, sweat glands don’t secrete fluid
What happens when the body temperature rises?
The hypothalamus picks up this signal. It tells the blood vessels to dilate, allowing heat loss. It tells the sweat glands to secrete fluid. It reduces metabolism
What are some processes that occur when body temperature lowers?
Blood vessels constrict
Sweat glands do not secrete fluid
Shivering (involuntary contractions) generate heat
What are some processes that occur when body temperature rises?
Blood vessels dilate, sweat glands secrete fluid
What happens when blood water levels are low?
It is detected by the hypothalamus, which signals the pituitary gland to start or increase ADH production. High ADH signals kidneys to produce a small amount of con. urine
What happens when blood water levels are high?
Hypothalamus detects, signalling pituitary gland to stop or decrease ADH production. Low ADH menas a large amount of dilute urine is made.
How does seeking shelter reduce heat loss?
Traps heat, extra insulation
How does changing body shape reduce heat loss?
Alters SA:V of skin, reducing exposed surface area
How does putting on more clothes reduce heat loss?
Insulating layer betweeen body and environment. traps layer of air
How does voluntary reduce heat loss?
Metabolic processes, convert stores to energy, increased blood flow to muscles
How does vasoconstriction of vessels reduce heat loss?
Amount of blood near exposed surface decreases
How does piloerection reduce heat loss?
Constricts of piloerector muscles around hair follicles (goosebumps), which increases insulation of hairs.
How does non-shivering thermogenesis reduce heat loss?
Increased cellular activity in brown adipose tissue (tissues warm). Brown fat breaks down for more energy
How does shivering thermogenesis reduce heat loss?
Metabolic heat increased
How does increasing metabolism reduce heat loss?
Increased metabolism
How does sweating increase heat loss?
Evaporation, increased blood flow
How does decreasing metabolism increase heat loss?
Less heat is made by processes
How does vasodilation of blood vessels increase heat loss?
More blood is sent to extremities
How does decreasing activity increase heat loss?
Less heat made by processes. Lower metabolism
How does covering body with water increase heat loss?
Water absorbs heat and then evaporates
How does changing body shape increase heat loss?
Increased exposed SA, more heat loss
How does removing clothing increase heat loss?
More exposed skin so more radiation, skin comes in direct contact with cool surfaces
How does moving out of sun into shade increase heat loss?
Decreased sunlight, more convective cooling
How does bathing in cool water increase heat loss?
Water absorbs heat
What part of the brain overseas the release of hormones?
Hypothalamus
Which part of the brain links the endocrine and nervous sytem?
Hypothalamus
