Intro to Physiology and Homeostasis

Question 1

What is homeostasis?

Answer 1

Staying the same

Maintaining conditions within the body in a relatively constant state of equilibrium - NOT FIXED STATE BUT WITHIN LIMITS

Question 2

What are examples of cellular homeostasis?

Answer 2

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)

Question 3

What are the three homeostasis control mechanisms?

Answer 3

Receptors / sensors

Control centre / set point

Effectors

Question 4

How do receptors, set points, and effectors work to maintain homeostasis?

Answer 4

1. Stimulus (a change in variable due to internal or external factors) is picked up on by receptors / sensors
2. The variable is compared to a set point in the control centre
3. Depending on how the variablerelates to the set point, effectors cause a response; either negative or positive feedback

Question 5

What is negative feedback control?

Answer 5

Effectors always act to move the variable in the opposite direction of the stimulus

Question 6

What does ectotherm and endotherm mean?

Answer 6

Ectotherm = body temp changed with surrounding environment temp

Endotherm = body temp does NOT change with the surrounding environment temp

Question 7

Explain negative feedback control using thermoregulation (the ability of an organism to keep its body temperature within certain changes)

Answer 7

1. Stimulus = change in core body temperature due to interal / external factors
2. Changes in temperature are received by skin (receptors / sensors)
3. This information is compared to the set point (~37 C) in the hypothalamus (control centre)
4. 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

Question 8

What are examples of heat production?

Answer 8

Basal metabolism
Muscular activity (shivering)
Thyroxine adn epinephrine (stimulating effects on metabolic rate)
Temperature effect on cells

Question 9

What are examples of heat loss?

Answer 9

Radiation
Conduction / convection
Evaporation

Question 10

Smooth muscle in arterioles in the skin are one example of thermoregulater effectors. How do respond to hot and cold stimulus?

Answer 10

Hot = Relax, vasodilation, more heat is carried to the surface/skin, radiation, convection, skin turns red

Cold = Contract, vascoconstriction, skin turns bluish

Question 11

Sweat glands are one example of thermoregulater effectors. How do they respond to hot and cold stimulus?

Answer 11

Hot = secrete sweat, evaporation (high humidity reduces evaporation)

Cold = No sweat

Question 12

Arrector pili muscles in skin (attached to skin hairs) are one example of thermoregulater effectors. How do they respond to hot and cold stimulus?

Answer 12

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

Question 13

Skeletal muscles are one example of thermoregulater effectors. How do they respond to hot and cold stimulus?

Answer 13

Hot = No shivering

Cold = Contract and relax repeatedly (shivering) to generate heat by friction and metabolic reactions

Question 14

Adrenal and thyroid glands are one example of thermoregulater effectors. How do they respond to hot and cold stimulus?

Answer 14

Hot = Stop secreting adrenaline and thyroxin - reduce metabolic rate

Cold = Secrete adrenaline and thyroxin - increase the metabolic rate

Question 15

Behaviour are one example of thermoregulater effectors. How do they respond to hot and cold stimulus?

Answer 15

Hot = Stretching out, finding shade etc

Cold = Curling up, huddling etc

Question 16

What are ways to measure core temperature and surface temperature?

Answer 16

Core temperature = oral cavity, ear canal, rectum

Surface temperature = forehead, armpit

Question 17

What is the difference between signs and symptoms?

Answer 17

Signs = objective findings elicited by a physician

Symptoms = subjective features of a disease as reported by a patient

Question 18

How does a fever affect body temperature homeostasis?

Answer 18

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

Question 19

What are pyrogens and what do they do?

Answer 19

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

Question 20

What is positive feedback control?

Answer 20

Amplifies the detected change (eg hot becomes hotter)

A sign that one cannot maintain homeostasis and requires additional mechanisms to break the feedback loop

Question 21

How is blood clot formation and hameostasis an example of a positive feedback loop?

Answer 21

1. Break or tear occurs in blood vessel wall
2. Platelets adhere to site and release chemicals
3. Released chemicals attract more platelets
4. Cycle only ends when plug is formed

Question 22

How is the reproductive system or paturition (childbirth) an example of a positive feedback loop?

Answer 22

1. Oxytocin from foetus and mother’s posterior pituitary stimulates uterus to contract
2. Contractions stimulate placenta to make prostaglandins which stimulate more vigours contractions from uterus
3. This produces more oxytocin and stimulates the placenta more via contractions