Chapter 15 - Homeostasis Flashcards
Latent heat of evaporation
➜ objects cool down as water evaporates from a surface
Radiation
➜ the transmission of EM waves to and from the air, water or ground
- transfer of heat between two objects through the air
Convection
➜ the heating and cooling by currents of air or water, warm air of water rises and cooler air of water sinks setting up convection currents around an organism
- The transfer of heat through moving air
Conduction
➜ the heating as a result of the collision of molecules. Air is not a good conductor of heat but the ground and water are
- transfer of heat from direct contact between two objects.
Ectotherms behavioural responses
behaviour when too cold:
➜ basking
➜ change body shape (increasing surface area)
➜ pressing body against warm ground (conduction)
behaviour when too hot:
➜ finding shade or burrowing
➜change body shape (decreasing surface area)
➜ pressing body against cool surfaces (conduction)
Endotherms behavioural responses (cold)
behaviour when too cold:
➜ less sweat - less heat loss
➜ hairs raised - layer of insulating air is trapped
➜ vasoconstriction - less flow of blood to surface so less heat loss
➜ high metabolic rate in liver cells - respiration generates more heat
➜ shivering - skeletal muscles contract - heat generated from respiration
Endotherms behavioural responses (hot)
behaviour when too hot:
➜ sweat - evaporates, heat loss, cools blood at surface
➜ hairs lie flat on surface - radiation
➜ Vasodilation - blood flows closer to surface of skin - more heat loss
➜ low metabolic rate in liver cells - respiration generates less heat
Excretion
➜ the removal of metabolic waste products from the body
➜ CO2
➜ Urea - (Co(NH2)2) - produced in the liver from ammonia and CO2 (breakdown of excess amino acids by liver)
➜ Bile pigments - formed when haemoglobin is broken down by Kupffer cells (specialised macrophages in the liver)
Egestion
➜ the removal of undigested material from the body
Deamination
- removal of an amine group from a molecule
- body cannot store either proteins or amino acids
- deaminate amino acids, remove the amino group + converting it to ammonia which is toxic, to urea
- urea is toxic in ↑ conc but not in blood conc
-remainder of amino acids can be converted into lipids for storage or cellular respiration - ammonia produced is converted to urea in the ornithine cycle
2NH3 + CO2 –> CO(NH2)2 + H2O
Transamination
➜ conversion of one amino acid to another
Detoxification
➜ a metabolic waste product is converted to water and oxygen by catalase
➜ e.g hydrogen peroxide, ethanol to ethanal
What do animals + plants need to be able to do?
Animals and plants need to be able to respond to changes in their internal and external environment and to coordinate the activities of their different organs.
Why is homeostasis important?
ensures the maintenance of optimal conditions for enzyme action and cell function
What are the 2 communication systems in mammals that require information to be transferred between different parts of the body?
- nervous system
- endocrine system
What does the human nervous system consist of?
- central nervous system (CNS) – the brain and the spinal cord
- peripheral nervous system (PNS) – all of the nerves in the body
What does the nervous system allow us to do?
allows us to make sense of our surroundings and respond to them and coordinate and regulate body functions
How is info sent through nervous system?
nerve impulses – electrical signals that pass along nerve cells known as neurones
What do neurones do ?
coordinate the activities of sensory receptors (eg. those in the eye), decision-making centres in the central nervous system, and effectors such as muscles and glands
What is a hormone?
- a chemical substance produced by an endocrine gland and carried by the blood
- transmit information from one part of the organism to another and bring about a change -> alter the activity of one or more specific target organs
What is endocrine system?
- endocrine glands that produce hormones in animals are known collectively as that
What is a gland?
- a group of cells that produces and releases one or more substances (secretion)
What does homeostatic control mechanisms in organisms use?
- negative feedback to maintain homeostatic balance
What does negative feedback control loops involve?
-receptor -> detects a stimulus that is involved with a physiological factor
- coordination system (nervous system and endocrine system) –> transfer information between different parts of the body
- effector (muscles + glands) – to carry out a response
What is the outcome of a negative feedback loop?
- stimulus is continuously monitored
- increase in the factor, body responds to make the factor decrease
- decrease in the factor, the body responds to make the factor increase
What do negative feedback loops do?
- reduce the initial effect of the stimulus
What do receptors do ?
- detect any deviations from stimuli which results in a corrective mechanism to return the factor back to normal
What do positive feedback loops do?
- enhance the effect of the original stimulus
What is homeostasis?
- regulation of the internal conditions of a cell or organism to maintain optimum conditions for function, in response to internal and external changes.
What is cell signalling?
- process in which cells communicate with each other
Why is cell signalling important?
- allows multicellular organisms to control and coordinate their bodies and to respond to their environments
What do cell signalling pathways do?
- coordinate the activities of cells, both between cells that are very close to each other and between cells that are large distances apart within the organism
What are the basic stages of cell signalling?
- stimulus is received by a receptor cell
- stimulus is converted to a signal (chemical) that can be passed on - this process is known as transduction
- signal is transmitted to a target cell (effector) that can detect it (via receptors in its cell membrane)
- response is made
What are the 2 cell signalling pathways categorised into?
- Paracrine signalling (signalling between cells that are close together)
- Endocrine signalling (signalling between cells that are far apart, which involves the signalling molecule being transported in the circulatory system)
What does transmission of messages in cell signalling pathways require?
- crossing cell surface membranes
Why is cell surface membrane important?
- membrane controls which molecules can move between the internal and external environments of the cell
Why are signalling molecules are usually very small ?
- for easy transport
What do signalling molecules do?
binds to the receptor molecule, causing specific changes in the receiving cell
What is thermoregulation?
control of internal (core) body temperature
With regards to the process of thermoregulation, what 2 groups can animals be separated into?
- Endotherms
- Ectotherms
What are endotherms?
- animals that possess physiological mechanisms to control their internal body temperature eg. mammals + birds
-> they can maintain their body temperatures using heat generated within their body tissues
What are ectotherms?
- animals that rely on behavioural adaptations to ensure their internal body temperature does not get too high or low eg. reptiles and amphibians
-> they regulate their body temperatures by absorbing heat from their environment
Vasodilation
The warmer the environment, the less heat is lost from the blood at the body’s surface
- increase heat loss by supplying the capillaries in the skin with a greater volume of blood, which then loses heat to the environment via radiation
- Arterioles (small vessels that connect arteries to capillaries) have muscles in their walls that can relax or contract to allow more or less blood to flow through them
- During vasodilation these muscles relax, causing the arterioles near the skin to dilate and allowing more blood to flow through skin capillaries
Sweating
- secreted by sweat glands
- cools the skin by evaporation which uses heat energy from the body to convert liquid water into water vapour
- sweating is less effective as a cooling mechanism in humid environments, as humid air is less effective at evaporating water
How do endothermic animals detect external temperatures?
via peripheral receptors
What are peripheral receptors?
- thermoreceptors found in the skin and mucous membranes
- receptors for both hot + cold
- communicate with the hypothalamus to bring about a physiological response to changing external temperatures
How does the hypothalamus also help to regulate body temperature ?
monitoring the temperature of the blood flowing through it + initiating homeostatic responses when it gets too high or too low
Flattening of hairs
- hair erector muscles (effectors) in the skin relax, causing hairs to lie flat
- stops them from forming an insulating layer by trapping air and allows air to circulate over skin and heat to leave by radiation
Vasoconstriction
- decrease heat loss by supplying capillaries in the skin with a smaller volume of blood, minimising the loss of heat to the environment via radiation
- muscles in the arteriole walls contract, causing the arterioles near the skin to constrict and allowing less blood to flow through capillaries
- blood is diverted through shunt vessels, which are further down in the skin and therefore do not lose heat to the environment
- reduces heat loss from the blood as it flows through the skin
Boosting metabolic rate
- Most of the metabolic reactions in the body are exothermic (heat-producing) and this provides warmth to the body
- In cold environments, the hormone thyroxine (released from the thyroid gland) increases the basal metabolic rate, increasing heat production in the body
Shivering
- reflex action in response to a decrease in core body temperature (nervous mechanism)
- muscles are the effectors and they contract in a rapid and regular manner
- metabolic reactions required to power this shivering generate sufficient heat to warm the blood and raise the core body temperature
Erection of hairs
- hair erector muscles in the skin contract, causing hairs to stand on end
- forms an insulating layer over the skin’s surface by trapping air between the hairs and stops heat from being lost by radiation
What do ectotherms do to heat up?
- ectotherms seek out the sun or warmer surfaces and rest or ‘bask’ in these locations as they warm, until their body temperature has been increased sufficiently
What do ectotherms do to cool down?
- ectotherms seek shade/ water
