15 - Homeostasis Flashcards
What is homeostasis
The bodies maintenance of a dynamic equilibrium with a narrow range of conditions
How effectors and receptors respond to a stimulus
A receptor in a sense organ detects a stimulus which sends an impulse from the sensory neuron the brain (Relay Neuron), Which either processes this info into the senses for example or sends an impulse toward the motor neurone towards an effector (muscle/gland)
Difference between pos and neg feedback
A positive feedback loop amplifies a change from normal conditions, a negative feedback loop minimises the change from normal conditions.
What is a neg feedback loop
initiates a corrective mechanism whenever the internal environment deviates from its normal or acceptable level. Thermoregulation (Example) temp increase—>Corrective mechanism–>Norm Temp temp decrease–>Corrective mechanism—>Norm Temp
What is pos feedback with example
Deviation from normal conditions, amplified, leads to more deviation (rare in biology, leads to unstable + harmful conditions) Example childbirth:release of oxytocin stimulates uterine contractions which trigger release more pos feedback eg: More oxytocin is more contractions.Levs increase->pos feedback->further increase Set PointLevs decrease->pos feedback->further decrease
Why is homeostasis important (Use examples)
enzymes operate best in optimum conditions so maintenance of Ph and temp in body cells occur so enzyme linked reactions proceed efficiently .Cell Size: Water potential of blood cells will affect amount of water in tissue fluid and cells. Animal cells could desiccate or swell and burst. Independence from external environment: animals with constant internal environment maintain constant level of activity regardless of environment.
Kinesis
A movement or activity in response to a stimulus (Direction not important)
Taxies
direction of stimulus important EG: woodlouse moves away from sunlight.
Ectotherms and Endotherms
Ectotherms: Cold blooded animals that rely on the external environment to control their internal temperature. Endotherms: Warm Blooded mammals and birds, their internal core temp independant of the external environment.
How is temp change detected
Temp receptors in the skin sense changes in surface temp and temp sensors in the brain/hypothalamus detect and coordinate responses to changes in the temperature of the blood
Factors that affect an organisms core temp
Decrease: Evaporation: of water on the skin cools the skin down Convection: heating and cooling by currents of air and water, warm air/water rises and cooler air/water sinks setting a convection current. Increase: Radiation: transmission of electromagnetic waves to and from the ground/water/air.
Ectotherms behavioural responses
“To warm up/increase body temp so metabolic reactions become fast enough to be active:They bask in the sun, orientate their bodies so max SA exposed to the sun, conduction by pressing their bodies into the ground.
To COOL DOWN they: seek shade/hide in burrows, conduction by pressing their bodies against cool surfaces, minimise movement so less metabolic heat generated through respiration, orientate their bodies away from the sun.”
Ectotherm physiological responses
They need less food as a result of as less energy used to regulate temp (Food not used to generate heat eg) so can survive in habitats with difficult environments. Inactive in cold environments, greater proportion of energy used for growth.
Thermoregulation in Endotherms
use internal metabolic reactions to keep them warm (respiration). Have same behavioural mechanisms as ectotherms tho some hibernate during winter.
Physiological features in endotherms
“ways to cool down: Vasodilation: Arterioles near-surface of the skin dilate and vessels that connect arterioles with venules constrict so blood forced through capillaries near the skin and cools due to increased radiation, if skin pressed to cool surface then cools due to conduction. Sweating: sweat spreads across the skin and when it evaporates heat is lost cooling the skin below. Hair: Sits down which minimizes the layer of air and therefore insulating layer.
Warming up: Opposite of cooling down. Shivering: Involuntary contract and relaxation of muscles where the respiration used to move the muscles generate heat.”
Action Potential Mechanism
1: Neurone at resting potential, some potassium ion channels (PIC) open (Mainly those that aren’t voltage gated), sodium channels CLOSED 2: Energy of stimulus triggers opening of sodium ion channels (SIC), membrane more permeable to sodium ions so they diffuse into axon down electrochemical gradient making inside of neurone less negative 3: Change causes more SIC to open, more sodium ions diffusing into the axon, example of pos feedback 4:When PD reaches +40mv, voltage gated SICs close and voltage gated PICs open, sodium ions can no longer enter the axon but membrane more permeable to potassium ions 5:Potassium ions diffuse out of the axon down the electrochemical gradient, reducing the charge, resulting in the inside of the axon becoming more negative than the outside 6: Initially lots of potassium ions diffuse out, so axon becomes negative (compared to outside and normal resting state) Known as hyper-polarisation. Voltage-gated potassium channels close, sodium-potassium pump causes sodium ions to move out and potassium ions in, axon re-polarised and returned to resting state.
Propagation of an action potential
the initial stimulus causes change in sensory receptor triggering action potential in sensory receptor so first region of axon membrane depolarised which acts as stimulus for next region of membrane. Process continues along the length of the axon forming wave of depolarisation. Once sodium ions in axon, they’re attracted by the negative charge ahead and conc gradient to diffuse further into the axon triggering depolarisation of next section. Once action potential triggered, first region of axon membrane has been depolarised, this acts as a stimulus for depolarisation of the next region of the membrane. The process continues along the axon causing a wave of depolarisation. Localised electrical circuits are established by the influx of Na ions, causing the opening of the Na voltage gated channels a little further along the neurone.
Propagation in an unmyelinated neurone saltatory conduction
Myelin sheath acts as insulation, action potentials occur at nodes of ranvier where Na ions can pass through the protein channels. Therefore longer localised circuits arise between adjacent nodes of ranvier.Action potentials jump from node to node in a process called saltatory conduction - much faster then a wave of depolarisation along the whole length of the axon membrane.
What is excretion?
The removal of metabolic waste from the body
What are the 3 main metabolic waste products of the body?
- Carbon Dioxide 2. Bile Pigments 3. Urea
What blood vessel brings oxygenated blood to the liver?
Hepatic artery
What does the hepatic portal vein do?
Brings deoxygenated blood, rich in digested nutrients, from the small intestine to the liver
What does the hepatic vein do?
Takes deoxygenated blood away from the liver and joins the vena cava
What is a lobule?
Many vertical rows of hepatocytes arranged around a central vein