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AY23/24 - MD1140 Foundation > Homeostasis > Flashcards

Homeostasis Flashcards

Fluid compartments, feedback loops, skin as an example of homeostasis

1
Q

What fluid compartments are there in the human body?

A

Plasma (liquid component of blood)
Interstitial fluid (surrounds and bathes body cells)
Intracellular fluid

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2
Q

Describe the fluid distribution in the human body.

A

2/3 - Intracellular fluid
1/3 - Extracellular fluid

1/4 EF - Plasma
3/4 EF - Interstitial fluid

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3
Q

Define interstitial fluid.

A

Fluid that bathes and surrounds the body cells

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4
Q

What does the lymphatic system do with regard to interstitial fluid?

A

Lymphatics remove excess interstitial fluid from interstitial space by draining it into the bloodstream

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5
Q

What are 5 means of fluid output?

A

Kidney
Faeces
Skin
Sweat
Lungs

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6
Q

What are the factors affecting body water content?

A

Gender (males 60% > females 55%)
Age (young > old)
Body fat (more body fat - less water)

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7
Q

Reasons for increased output of fluid.

A

Diarrhoea, vomiting

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8
Q

Reasons for decreased output of fluid

A

Kidney failure leading to decreased urination, causing accumulation of water in the body

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9
Q

Define osmolarity.

A

A measure of the concentration in solution expressed as the number of solute molecules per litre of solvent

Unit - mOsm/L

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10
Q

Define osmolality.

A

A measure of the number of solute molecules per kilogram.

Unit - mOsm/kg

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11
Q

Compare the osmolarity of the three fluid compartments.

A

Same throughout due to osmotic equilibrium

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12
Q

Compare the ionic composition of the three fluid compartments.

A

Potassium: Intracellular fluid > Plasma, Interstitial fluid

Sodium and chloride: Plasma, Interstitial fluid > Intracellular fluid

Plasma and interstitial fluid contain phosphate

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13
Q

Compare the protein content of the three fluid compartments.

A

Intracellular fluid: Intracellular proteins
Plasma: Plasma proteins
Interstitial fluid: Only a small amount of proteins

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14
Q

How is interstitial fluid formed?

A

Through filtration of fluids across capillaries

Capillaries have highly permeable walls to solutes and water

Arteries and veins are usually impermeable to solutes and water

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15
Q

Define the Starling forces.

A

Forces that determine the movement of fluid between capillaries and interstitial space, and they determine the rate of filtration across capillary.

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16
Q

What are the Starling forces?

A

1) Hydrostatic pressure: force generated by the pressure of fluids

2) Colloid osmotic pressure / Oncotic pressure: force generated by proteins in plasma or interstitial fluid attracting water (works like a sponge)

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17
Q

How does hydrostatic pressure act as a Starling force?

A

Hydrostatic pressure of capillary (Pc) is higher than that of interstitial space (Pi)

Hence, pressure gradient forces fluid out of the capillary into the interstitial space

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18
Q

How does colloid osmotic pressure act as a Starling force?

A

More proteins in plasma, more pressure generated, hence more water is drawn out of interstitial space into the plasma.

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19
Q

What is oedema?

A

Accumulation of excessive fluid in the body

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20
Q

How do low plasma protein concentration cause oedema?

A

Low plasma proteins
Low colloid osmotic pressure
Reduced forces promoting fluid reabsorption into capillary
Increased interstitial fluid volume, oedema

21
Q

Define homeostasis.

A

Maintenance of a relatively stable internal environment.

22
Q

What are some examples of homeostatically-regulated functions?

A

1) Fluid volume
2) Blood glucose levels
3) Concentration of mineral content (electrolytes)
4) Blood pressure
5) Concentration of O2 and CO2
6) Adequate nutrients
7) Temperature
8) pH
9) Concentration of waste products

23
Q

What are homeostatic control systems?

A

Functionally interconnected network of body components that operate to maintain a given factor in the internal environment at a relatively constant level

24
Q

What must homeostatic control systems be able to do?

A

1) [SENSOR] Detect a deviation of a particular factor in the internal environment from set point
2) [INTEGRATOR/CONTROLLER] Integrate this information
3) [EFFECTOR] Make changes to the internal environment to restore the deranged variable

25
Q

Which systems control the homeostatic response in the body?

A

Nervous and endocrine

26
Q

How does a feedback loop work?

A

1) Controlled variable is measured b y sensor
2) Sensor sends input to integrator
3) Integrator sends input to effector
4) Effector changes controlled variable

27
Q

What kind of feedback drives homeostasis?

A

Negative feedback

28
Q

Example of a positive feedback loop

A

Oxytocin release during birth

1) nerve impulses from cervix transmit signals to brain
2) brain stimulated pituitary gland to release oxytocin
3) oxytocin carried to uterus through blood stream
4) oxytocin stimulates uterine contractions, pushes baby towards cervix

29
Q

How does genetic markup affect homeostasis?

A

Genetic markup determines one’s individual characteristics and set pointsn

30
Q

Name and describe one illness where homeostasis is disrupted.

A

Diabetes; despite high blood glucose concentration, liver is not stimulated to secrete insulin to take up glucose to convert to glycogen, leads to high blood glucose and damage to blood vessels, kidneys, heart and eyes

31
Q

What are the roles of skin in the human body?

A

1) Protective
2) Thermoregulation
3) Water balance
4) Vitamin D synthesis

32
Q

How does skin fulfil its function as a form of protection?

A

Forms a mechanical barrier between internal and external environment
Prevents water from leaving the skin
Prevents microorganisms from entering

33
Q

How to measure body surface temperature? (places)

A

Forehead
Armpit
Oral
Ear
Rectal

34
Q

Which one is higher: body core or body surface temperature?

A

Body core temperature

35
Q

How does internal heat production occur?

A

1) Metabolism in al cells
2) Muscle activity
3) Hormone action (thermogenic effect)
4) Sympathetic stimulation
5) Digestion, absorption, storage of food

36
Q

What are the 4 methods of heat transfer between body and external environment?

A

1) Evaporation
2) Conduction - direct transfer of thermal energy from molecule to molecule
3) Convection - transfer of heat by air currents
4) Radiation - transfer of heat via electromagnetic waves

37
Q

What are the two types of thermoreceptors?

A

Peripheral thermoreceptors and central thermoreceptors (in the hypothalamus, abdominal organs)

38
Q

What is non-shivering thermogenesis?

A

Thermogenesis stimulated by cold stress. Cold stress leads to sympathetic nervous system activation, releasing NE and adrenaline that stimulates increase in metabolic activity and heat generation.

39
Q

Describe three ways that skin is involved in thermoregulation.

A

1) Skin and subcutaneous fat act together as a heat insulator
2) Vasoconstriction and vasodilation of the blood vessels in the skin
3) Sweating

40
Q

What causes hyperthermia?

A

Excessive rise in body temperature

41
Q

What causes hypothermia?

A

Excessive drop in body temperature

42
Q

Name the causes of hypothermia.

A

Severe hypothyroidism (inability to generate heat)
Severe infections (vasodilation, increased heat loss)
Extremely cold weather
Burns (natural insulator is damaged)

43
Q

Name the effects of hypothermia.

A

Confusion (leading to further inability to respond to temperature changes)
Respiratory depression
Abnormal heart rhythms
May be fatal

44
Q

Name the causes of hyperthermia.

A

Severe hyperthyroidism (high thyroxin levels; too much heat generation)
Infections
Hypothalamic disorders (damage to temperature control centre)
Heat exhaustion/Heat stroke
Certain drugs

45
Q

How is the skin involved in water balance?

A

Acts as a barrier to prevent/minimise water loss.
Stratum corneum acts as a mechanical barrier between skin and external environment.
Lipids in stratum corneum create a hydrophobic barrier that prevents evaporation of water.

46
Q

How is water lost through skin?

A

1) Transepidermal water loss (TEWL) - diffusion through skin layers
2) Sweating (mediated by autonomic control)

47
Q

How is the skin involved in pain?

A

Presence of nociceptors (pain receptors) in the skin

48
Q

Describe the pain pathway.

A

Pain receptors stimulated
First order neuron transmits nerve impulse
Second order neuron in spinal cord transmits nerve impulse
Reaches brain via spinothalamic tract

49
Q
A

AY23/24 - MD1140 Foundation (2 decks)

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