5:1:1 Communication and Homeostasis Flashcards
Define homeostasis
The body’s responses to changes in their internal and external environment in order to maintain optimal conditions for enzyme action and cell function
How is the body’s internal environment controlled
Physiological control systems:
- Nervous system
- Endocrine system
What is the nervous system
- Allows us to respond to our surroundings and coordinate and regulate bodily functions
- Information sent through the nervous system as nerve impulses (electrical signals) through neurones
- Neurones coordinate the activity of sensory receptors, decision making centres in the central nervous system, and effectors
What does the nervous system consist of
- Central nervous system (CNS): brain, spinal cord
- Peripheral nervous system (PNS): all nerves in body
What is the endocrine system
- System which has hormone producing glands (endocrine glands), allowing these chemicals to transmit information within the organisms
- Hormones can alter activity of target organs, and used to control functions that don’t need instant responses
Label diagram of the endocrine system in humans
What are the main factors that need controlling in organisms
- Temperature (vital for enzyme activity)
- pH (vital for enzyme activity)
- Blood glucose concentration
Why does pH have to be controlled
- Enzymes have optimum pH’s, and can be denatured at pH extremes
- Denaturing occurs when the H and ionic bonds holding the tertiary protein structure break which alters the shape of the active site
- Enzyme-substrate complex can’t form
Why does blood glucose concentration have to be controlled
- Amount of glucose present affects water potential of the blood and the availability of respiratory substrates for cells
- Usual glucose concentration for humans is 90mg/100cm^3
- Glucose is essential for cellular respiration
Why does the opening/closing of stomata have to be controlled
- Plants require a constant supply of CO2, and well as controlling the water levels in the plant
- Stomata respond to internal and external stimuli (e.g. darkness/water stress)
- Regulation of stomata balances the need for CO2 uptake and water loss
What are negative feedback loops
- A majority if homeostatic control mechanisms use negative feedback to maintain homeostatic balance
- The loops involve:
- A receptor to detect a stimulus
- A coordination system (nervous/endocrine) to transfer the information
- An effector (muscles/glands) to carry out the response
What is the outcome of a negative feedback loop
- The stimulus is continuously monitored
- If there is an increase in the factor, the body responds to make it decrease
- If there is a decrease in the factor, the body responds to make the factor increase
- They reduce the initial effect of the stimulus
What are the two corrective methods used by negative feedback loops to control homeostasis
- One for when the factor becomes too high
- One for when the factor becomes too low
What are positive feedback loops
- Where the original stimulus produces a response that causes the factor to deviate even more from the normal range
- They enhance the effect of the original stimulus
Describe how positive feedback loops work (e.g. bone repair)
- Osteoblasts secrete a hormone called osteocalcin in an inactive form
- The osteoclasts secrete acid which lowers the pH and the acidic conditions to cause the inactive form of osteocalcin to the active one
- The active from of osteocalcin binds to a receptor on beta cells in the pancreas which stimulates then to release insulin
- Osteoblasts have insulin receptors which release more osteocalcin when stimulated
- The osteoblasts cells enhance the effect of the original stimulus (insulin)
What is cell signalling and why is it important
- Cell signalling is the process by which cells communicate with each other
- It is important as it allows multicellular organisms to control and coordinate their bodies to respond to their environments
What occurs in cell signalling pathways
- A stimulus is received by a receptor cell
- The stimulus is converted to a signal (chemical) that can be passed on (process called transduction)
- Signal is transmitted to a target cell (effector) that detects it
- An appropriate response is made
What are the two categories of cell signalling pathways
- Paracrine signalling (signalling between close together cells)
- Endocrine signalling (signalling between far apart cells using hormones as the signalling molecules)
How are cell membranes involved in cell signalling
- Transmission of messages in cell signalling pathways requires crossing barriers (cell membranes)
- The membranes control what moves in and out of the cell, therefore signalling molecules are very small for easy transport across the membrane
- Receptor molecules on/in the cell surface membrane are proteins or glycoproteins
- Signalling molecules bind to the receptor molecule cause in specific changes in the receiving cell
What is thermoregulation and why is it important
- Thermoregulation is the control of internal body temperature
- It’s control is vital for enzyme activity
- As well as rate of reactions
What are endotherms
Animals that posses physiological mechanisms to control their internal body temperature (using heat generated within tissue) (e.g. mammals and birds)
What are ectotherms
Animals that rely on behavioural adaptations to ensure their internal body temperature doesn’t get too high or low (absorbing heat from their environment) (e.g. reptiles and amphibians)
How does thermoregulation work in endotherms
- They detect external temperatures via peripheral receptors (for both heat and cold)
- These receptors communicate with the hypothalamus to bring about a physiological response
- The hypothalamus can also regulate body temperature by monitoring the temperature of the blood flowing through it and initiating homeostatic responses when it’s too low or high
What are examples of endotherms cooling mechanisms
- Vasodilation
- Sweating
- Flattening of hairs
What are examples of endotherms warming mechanisms
- Vasoconstriction
- Boosting metabolic rate
- Shivering
- Erection of hairs
How does vasodilation work as a cooling mechanism
- Heat exchange occurs at the bodies surface
- To increase heat loss, the capillaries are supplied with a greater volume of blood (carries heat energy) which loses heat via radiation
- During vasodilation the muscles in arteriole walls relax, causing the arterioles near the skin to dilate and allow more blood to flow
How does sweating work as a cooling mechanism
- Sweat is secreted by sweat glands
- The sweat cools the skin by evaporation which uses heat energy from the body to convert the liquid water into water vapour
- Sweating is less effective in humid environments
How does the flattening of hairs work as a cooling mechanism
- Hair erector muscles in the skin relax, causing the hairs to lie flat
- This stops then from forming an insulating layer by trapping air, and instead allows air to circulate over the skin so heat can leave by radiation
How does vasoconstriction work as warming mechanism
- Supplying the capillaries with less blood volume minimises heat loss by radiation
- The muscles in the arteriole walls contract, causing constrictions which reduced the blood flow
- Blood is instead diverted through shunt vessels further down in the skin to preserve heat
How does boosting metabolic rate work as a warming mechanism
- Most of the metabolic reactions in the body are exothermic and provide warmth to the body
- The hormone thyroxine is released in cold environments, where is increases the basal metabolic rate, increasing heat production
How does shivering work as a warming mechanism
- Reflex action in response to the decrease in temperature
- The muscles are the effectors, and they contract rapidly in a regular manner
- The metabolic reactions required to power this shivering generate warmth for the body
How does the erection of hairs work as a warming mechanism
- Hair erector muscles in the skin contract, causing the hairs to stand on end
- This forms an insulating layer over the skin by trapping air between the hairs, stopping heat being lost via radiation
Why do aquatic ectotherms have little difficulty thermoregulating
Due to the water temperature varying much less than land temperatures, due to the high specific heat capacity of water
How do ectotherms heat up
Seek out the sun or warm surfaces to bask in until their body temperatures have increased
How do ectotherms cool down
By seeking shade or water, until their body temperature has decreased
What are the disadvantages and advantages of ectotherms thermoregulation mechanisms
- Advantage: they require very little energy, so they would be able to survive better in environments with little food
- Disadvantage: their behaviour is more restricted by environmental temperatures, so they can’t easily colonise areas that have extreme temperatures
