Intro to Physiology and Homeostasis Flashcards
What is homeostasis?
Staying the same
Maintaining conditions within the body in a relatively constant state of equilibrium - NOT FIXED STATE BUT WITHIN LIMITS
What are examples of cellular homeostasis?
Generation of membrane potential (excitability of cells)
Ionic homeostasis eg channels and transporters (use environmental chemistry to their advantages)
Volume homeostasis (osmolarity)
pH homeostasis (maintain optimal environemnt for enzymes as well as organic and inorganic molecules)
What are the three homeostasis control mechanisms?
Receptors / sensors
Control centre / set point
Effectors
How do receptors, set points, and effectors work to maintain homeostasis?
- Stimulus (a change in variable due to internal or external factors) is picked up on by receptors / sensors
- The variable is compared to a set point in the control centre
- Depending on how the variablerelates to the set point, effectors cause a response; either negative or positive feedback
What is negative feedback control?
Effectors always act to move the variable in the opposite direction of the stimulus
What does ectotherm and endotherm mean?
Ectotherm = body temp changed with surrounding environment temp
Endotherm = body temp does NOT change with the surrounding environment temp
Explain negative feedback control using thermoregulation (the ability of an organism to keep its body temperature within certain changes)
- Stimulus = change in core body temperature due to interal / external factors
- Changes in temperature are received by skin (receptors / sensors)
- This information is compared to the set point (~37 C) in the hypothalamus (control centre)
- Hypothalamus triggers effector response in muscles and/or glands to see that the core body temperature is raised / lowered by either heat production or loss
What are examples of heat production?
Basal metabolism
Muscular activity (shivering)
Thyroxine adn epinephrine (stimulating effects on metabolic rate)
Temperature effect on cells
What are examples of heat loss?
Radiation
Conduction / convection
Evaporation
Smooth muscle in arterioles in the skin are one example of thermoregulater effectors. How do respond to hot and cold stimulus?
Hot = Relax, vasodilation, more heat is carried to the surface/skin, radiation, convection, skin turns red
Cold = Contract, vascoconstriction, skin turns bluish
Sweat glands are one example of thermoregulater effectors. How do they respond to hot and cold stimulus?
Hot = secrete sweat, evaporation (high humidity reduces evaporation)
Cold = No sweat
Arrector pili muscles in skin (attached to skin hairs) are one example of thermoregulater effectors. How do they respond to hot and cold stimulus?
Hot = Relax, hair flattens, allow surface air circulation, encourage convection and evaporation
Cold = Contract, raising skin hair / goosebumps, trapping an insulating layer of still and warm air next to the skin
Skeletal muscles are one example of thermoregulater effectors. How do they respond to hot and cold stimulus?
Hot = No shivering
Cold = Contract and relax repeatedly (shivering) to generate heat by friction and metabolic reactions
Adrenal and thyroid glands are one example of thermoregulater effectors. How do they respond to hot and cold stimulus?
Hot = Stop secreting adrenaline and thyroxin - reduce metabolic rate
Cold = Secrete adrenaline and thyroxin - increase the metabolic rate
Behaviour are one example of thermoregulater effectors. How do they respond to hot and cold stimulus?
Hot = Stretching out, finding shade etc
Cold = Curling up, huddling etc
What are ways to measure core temperature and surface temperature?
Core temperature = oral cavity, ear canal, rectum
Surface temperature = forehead, armpit
What is the difference between signs and symptoms?
Signs = objective findings elicited by a physician
Symptoms = subjective features of a disease as reported by a patient
How does a fever affect body temperature homeostasis?
A fever increases the hypothalamic set point to ? 38 C due to trauma, exercise, or pyrogens
Therefore, normal body temperature reads as below the hypothalamic set point leading to activation of temperature raising mechanisms
What are pyrogens and what do they do?
Chemical substance released by white blood cells (endogenous) and / or invading microorganisms (exogenous)
They are a protection mechanisms (kills abcteria, inhibits viruses)
They raise the set point on the thermoregulatory dentures causing the whole body temperature to increase
What is positive feedback control?
Amplifies the detected change (eg hot becomes hotter)
A sign that one cannot maintain homeostasis and requires additional mechanisms to break the feedback loop
How is blood clot formation and hameostasis an example of a positive feedback loop?
- Break or tear occurs in blood vessel wall
- Platelets adhere to site and release chemicals
- Released chemicals attract more platelets
- Cycle only ends when plug is formed
How is the reproductive system or paturition (childbirth) an example of a positive feedback loop?
- Oxytocin from foetus and mother’s posterior pituitary stimulates uterus to contract
- Contractions stimulate placenta to make prostaglandins which stimulate more vigours contractions from uterus
- This produces more oxytocin and stimulates the placenta more via contractions
