Homeostasis, pH, core body temperature + body fluids Flashcards
(38 cards)
1
Q
define homeostasis
A
the process whereby cells, tissues and organisms maintain the status quo
(the ability or tendency of a living organism, cell, or tissue to keep the conditions inside it the same despite any changes in the conditions around it, or maintaining a state of internal balance)
2
Q
what needs to be maintained constant in the internal environment
A
- temperature
- pH
- water (volume and pressure)
- gases: oxygen, CO2
- nutrients, glucose, amino acids, electrolytes
- waste products: ammonia, urea
3
Q
examples of homeostasis
A
- acid-base balance
- fluid balance
- control of body temperature
4
Q
four components of a homeostatic mechanism
A
- variable (temperature, cell volume, pH)
- sensor (monitors current value of variable)
- control centre (retains desired value of variable and compares to current value)
- effector (ability to change value of variable)
5
Q
positive feedback
A
- increases effect of stimulus
- e.g. blood clotting
- stops when initiator ceases
6
Q
negative feedback
A
- decreases effect of stimulus to return to normal level
- e.g. blood glucose regulation
- stops when effector ceases
7
Q
70 kg man water compartments
A
- 60% water - 42l
- 2/3 intracellular fluid - 28l
- 1/3 extracellular fluid - 14l
- 11l interstitial fluid
- 3l plasma
8
Q
circulating blood volume
A
5 litres (3l plasma + 2l red cells)
9
Q
what is interstitial fluid
A
fluid that surrounds cells but is outside the blood vessels
10
Q
how many litres of fluid is needed a day to maintain a helathy adult
A
2.5l
11
Q
compare total body water in males and females (lean and obese)
A
- 60% adult males (70% and 50%)
- 50% adult females (60% and 42%)
- 70% infants (80% and 60%)
- 50% elderly
12
Q
tonicity
A
- isotonic = same amount of water on both sides of plasma membrane
- hypotonic = more water outside cell
- hypertonic = more water inside cell
13
Q
what is osmolality
A
concentration of particles in solution expressed as mOsm/kg
- measurement of osmotic pressure
14
Q
what is osmolarity
A
concentration of particles in solution expressed as mOsm/l
15
Q
normal osmolality of body fluids
A
280-300 mOsm/kg
16
Q
body compartmetns where fluids accumulate
A
- intracellular
- extracellular (interstitial + blood plasma)
17
Q
what happens if there is not enough water (dehydration)
A
- plasma osmolality increases
- cells and tissues absorb water from interstitial space and plasma
- absorb water from each other e.g. RBCs lose water and shrink
- as tissues die, water absorbed from organs
- as organs die, water absorbed from brain, liver, kidney and heart
18
Q
what happens if there is too much water (water toxicity)
A
- osmotic pressure is high (osmolality decreases)
- cells absorb water and swell
- enzyme and proteins stop working
- cells keep swelling until they burst
19
Q
why do patients need isotonic solutions
A
- to avoid cells shrinking or bursting
- IV drips need physiological saline concentrations (0.9% NaCl)
20
Q
movement of water between compartments and cell membranes determined by
A
- hydrostatic forces created by pumping of heart
- osmotic pressures created by concentration of solute particles
21
Q
what is oedema
A
- fluid retention
- makes cells and tissues swell
- dangerous in the brain - can cause coma and death
- peripheral oedema commonly found in limbs
22
Q
process of oedema
A
-
hydrostatic pressure > osmotic pressure so water doesnt move back into capillary and accumulate in interstitial space
1. raised hydrostatic pressure in the capillary (vasodilation, congestion e.g. heart failure)
2. decreased oncotic pressure in capillary (liver disease - low albumin)
3. increased oncotic pressure in interstitial space (leakage of plasma proteins - albumin)
4. impaired lymphathic drainage (lymphoedema)
23
Q
oncotic pressure (colloid-osmotic pressure)
A
osmotic pressure from the proteins (albumin) in blood vessels that causes fluid to be pulled back into the capillary
24
Q
2 major organs responsible for maintaining acid-base balance
A
- lungs - respiratory balance
- kidneys - metabolic balance
25
what is pH
- free hydrogen ion concentration
- pH = -log[H+]
26
important of acid-base balance for normal human physiology
- **normal pH is 7.35-7.45** (blood in arteries more alkali than veins)
- normal cellular metabolism occurs within this range
- change in [H+] by factor of 2 causes pH change of 0.3
- **acidosis** occurs if blood pH < 7.35
- **alkalosis** occurs if blood pH > 7.45
- if **below 6.8 or above 8.0 **for a significant period of time then **death** is likely
27
arterial blood gas (ABG)
analysis of pH and gases in an arterial blood sample
28
metabolic acidosis
- increased production of metabolic acids like lactic acid
- inability to excrete acid via kidneys
29
respiratory acidosis
- excessive buildup of carbon dioxide due to hypoventilation
- compensatory response to metabolic alkalosis
30
acid damage
- **gastric juice has pH 1-3.5**
- **goblet cells** lining stomach wall secrete substances (mucus) to protect cells against acid
- **regurgitation** damages epithelial lining oesophagus and pharynx (oesophagitis, stricture)
- stomach losing protection can cause **gastric ulceration and perforation**
31
pH buffering systems
- **carbonic acid-bicarbonate** buffer important in blood pH
- **sodium phosphate** buffering system regulate intracellular pH and transport systems
- **calcium** can raise pH
- **antacids** (aluminium hydroxide, magnesium hydroxide, calcium salts) neutralise acidic pH e.g. indigestion
- **aluminum hydroxide** preferred as it's milder, long- acting and insoluble
32
core body temperature
- normal range is **36.5–37.5 °C**
- fluctuates throughtout day - **circadian rhythm**
- enzymes lose activities at high temps
- insufficient energy to maintain metabolic processes at low temps
33
how do we measure temperature
- infra-red skin thermometer
- tympanic thermometer
- temporal film
- oral/rectal/axillary thermometer
- traditional
34
components of negative feedback loop in regulating temperature
**stimulus**
- low or high temperature
**sensor**
- skin
- hypothalamus
**control centre**
- hypothalamus
**effector**
- muscles
- blood vessels
- hairs on skin
- fat
- sweat glands
35
mechanisms of reducing temperature
- **vasodilation** - arterioles dilate so more blood enters skin capillaries and heat is lost
- **sweating** - sudorific glands secrete sweat which removes heat when water changes state
- **pilorelaxation** - hairs flatten
- **stretching out** - larger surface area
36
mechanisms of increasing temperature
- **vasoconstriction** - arterioles get smaller to reduce blood going to skin keeping core warm
- **shivering** - rapid contraction and relaxing of skeletal muscles, heat produced by respiration
- **piloerection** - hairs on skin stand up
- **curling up** - smaller surface area
37
effects of core body temperature being out of normal range
- **no vital signs < 28°C** - unconciousness, dilated pupils, pulse undetectable, death appearance
- **severe hypothermia 28.0- 32.0°C** - shivering stops, muscles become rigid, very slow and weak pulse, drowsiness
- **mild hypothermia 32.1-35°C** - shivering, fatigue, slurred speech, confusion, forgetfulness, muscle stiffness
- **normal 36.5-37.5°C** - normal core body temperature
- **fever >38°C** - pale sweaty skin, cramps in stomach, arms and legs
- **heat stroke > 40°C** - flushed dry skin, hot to the touch, strong bounding pulse
- **heat exhaustion >40°C** - unconsciousness/fitting/seizures, confused/restless, exhaustion, headache, dizzy, uncomfortable
38
mechanism of high temperature when infected
- toxins from bacteria and chemicals from immune system (interleukin-6) **increase set point** in hypothalamus to higher temperature
- **initiates heat generation** through shivering and increased metabolic rate so increased temperature is achieved
- **above 38.5°C is fever (pyrexia)**
- high temperature important as **immune system works optimally**
