S1 - Homeostasis, pH, Core Body Temperature and Body Fluids

Question 1

Define Homeostasis

Answer 1

• Home = sameness and stasis = standing still - ability of an organism to maintain a state of internal balance.
• A state of dynamic equilibrium affected by intrinsic and extrinsic factors.
• 4 components: variable, sensor, control centre and effector

Question 2

What needs to be maintained constant in the internal environment?

Answer 2

Mainly: Temperature (for enzyme optimum temp.), pH (for enzyme and protein opt. pH), Water (volume and pressure)

O2, CO2, Nutrients (glucose, amino acids), Waste (ammonia, water)

Question 3

Describe negative and positive feedback loops

Answer 3

Negative: when the sensor or control centre inhibits further action by the effector in order to remove stimulus - it stops when effector ceases.
Stim- rising blood glucose level, Sens and Con- high BG detect by beta cells in pancreas, Eff- pancreas secretes insulin, Return to normal BG

Positive: when the sensor or control centre increases effector action in order to increase stimulus - it stops when initiator/stimulus ceases.
Stim- baby pushes against cervix, Sens and Con- nerve impulses sent to brain and brain stimulates pituitary to release oxytocin, Eff- oxytocin causes uterus to contract, Baby continues to push against cervix

Question 4

Examine the normal range of core body temperature

Answer 4

• Normal human body temperature is 37 +- 0.5 degrees Celsius.
• Most biochemical processes will not function efficiently outside of this range.
• At v. high temp, enzymes can denature and lose their activities; at . low temp, there is insufficient energy to maintain metabolic processes.

Question 5

How to measure temperature?

Answer 5

• Infra-red thermometer - on chest/head
• Tympanic thermometer - forehead
• Temporal film - as temp increases the colour changes; used on children
• Oral/rectal/axillary(armpit) thermometer - not suitable for children
• Traditional - mercury therm. are toxic

Question 6

Control of body temperature mechanism

Answer 6

Sensor: skin (internal), hypothalamus (external)
Control centre: Hypothalamus (Thermostat)
Effectors:

To increase temp:
- Vasoconstriction - arterioles get smaller to reduce blood flow to keep core warm
- Shivering of skeletal muscles - rapid contraction and relaxation allows heat production by respiration
- Piloerection - hairs on skin stand to trap layer of air
- Curling up - smaller surface area
- Increased metabolism of white fat in adults
- Burning of brown fat in infants

To reduce temp:
- Vasodilation - arterioles dilate to allow increased blood flow allowing heat loss by radiation
- Sweating - glands secrete sweat which removes heat when water evaporates
- Pilorelaxation - surface of body cools
- Stretching out - larger surface area

Question 7

What happens when body temp. is over the normal range?

Answer 7

> > 40 - Heat exhaustion: Unconsciousness/seizures, confused/restless, headache, dizzy
40 - Heat stroke: Flushed dry skin, strong bounding pulse, hot to touch
38 - Fever - Pale sweaty skin, cramps in stomach, arms and legs
—
32.1 - 35 - Mild hypothermia - Shivering, fatigue, slurred speech, confusion, forgetfulness, muscle stiffness
28 - 32 - Severe Hypothermia - Shovering stops, muscles become rigid, very slow and weak pulse, drowsiness
< 28 - No vital signs - Severe reduction in response levels, unconsciousness, dilated pupils, pulse undetectable, darker skin changes to grey and gums to blue, appearance of death BUT not dead until warm and dead

Question 8

Examine normal range of pH

Answer 8

• Acid-base balance is the precise regulation of hydrogen ion concentration.
• Normal pH is 7.35-7.45: normal cellular metabolism occurs within this
• pH = -log10[H+] and a pH of 7 represents 10^-7 moles of free hydrogen ions in every litre of pure water.
• 2 major organs responsible for maintaining acid base balance are the lungs (respiratory balance) and the kidneys (metabolic balance).
• The limits of human tissue survival are from pH 6.8-7.8
• A change in [H+] nanomoles by a factor of 2 causes a pH change of 0.3.
• Artery blood is more alkali(pH 7.45) than vein blood (pH 7.35).

Question 9

What happens when body pH is over normal range?

Answer 9

3.5 - Human body cannot sustain life
5.8 - Cancer cells begin to form
6.8 - Disease symptoms begins
[ Death likely pH < 6 for long ]
< 7.35 - Acidosis - headaches, confusion, feeling tired, tremors and coma
> 7.45 - Alkalosis
[ Death likely pH > 8 for long ]

Two types of acidosis & alkalosis: Metabolic or Respiratory

Question 10

Metabolic and Respiratory acidosis

Answer 10

Metabolic acidosis:
- Due to increased production of metabolic acids (lactic acid) or an inability to excrete acid via kidneys

Respiratory acidosis:
- Due to excessive build up of CO2 due to hypoventilation.
- Can also occur as a compensatory response to metabolic alkalosis.

Treatment:
- Infusion of bicarbonate solution to increase blood pH
- Mechanical ventilation to drive the CO2 out of lungs

Question 11

Acid based issues in the body

Answer 11

• Gastric (stomach) pH normally 1.5-3.5 and if it goes in oesophagus is can cause oesophagitis (inflammation) or stricture (when oesp. closes down).
• If stomach loses mucus protection it can cause ulceration and perforation.
• In acid attack if gases are inhaled it can be dangerous for trachea.
• Vomiting causes gastric juice to irritate the epithelial cells in oesophagus and pharynx that do not have protection (mucus). This can lead to heartburn or indigestions-like symptoms or burning sensation in mouth
• TREATMENT: over-the-counter antacids that have weak basic salts like aluminium hydroxide, magnesium hydroxide and calcium salts. Antacids w/ aluminium hydroxide are preferred as they are milder, long acting and have fewer side effects as it has more insoluble.

Question 12

How to analyse blood pH?

Answer 12

• Blood gas analysis is conducted - Arterial Blood Gas
• Artery blood is slightly alkali due to O2 - it is bright red because haemg. bonds to O2
• Venous blood is more acidic and darker

Question 13

Buffering systems in the body

Answer 13

ICF: Intra Cellular Fluid:
- Phosphate buffer system - Sodium Phosphate buffering to regulate intracellular pH and transport system
- Protein buffer system - Haemoglobin buffer system

ECF: Extra Cellular Fluid:
- Carbonic acid-Bicarbonate buffer system - regulate Blood pH and uses erythrocytes as an intermediary.

Both uses protein buffer systems - Amino acid buffers

Question 14

Calculate how much water is in a ‘standard human male’ and where does water go?

Answer 14

• 70kg man is made of 60% water = 42L of total body water
• 1/3 (14L) Extracellular; 2/3 (28L) Intracellular
  WITHIN EXRA.
• 3/4 (10.5L) Interstitial water + 0.5L Transmembrane water (space occupied by endothelial cell membranes)
• 1/4 (5L) Circulating Blood Volume: 3L plasma + 2L red cells

Question 15

Determine the amount of water in females, aged and young, and infants

Answer 15

• Infants (up to 1 year old) have the highest percentage of TBW (70%)
• The higher the percentage of body fat, the lower the percentage of TBW
• Females have a lower TBW (50%)
• As age increases TBW decreases

Question 16

Importance of fluid balance

Answer 16

• Approx. 2.5L of fluid is needed each day
• Cells, tissue, organs need the right amount of water as almost all chemical reactions that happen in the human body happen in solution.

Not enough:
- Water absorbed from interstitial space and then from other cells
- As tissues die, water absorbed from organs
- As organs die, water absorbed from brain, liver and lastly kidney and heart

Too much:
- As osmotic pressure is high, cells absorb water and swell
- Enzyme and proteins stop working
- Swelling until they burst

+ Isotonic solutions are used in IV drips for patients (physiological saline concetration 0.9% NaCl)

Question 17

Importance of Tonicity

Answer 17

Iso - same on both sides of plasma membrane
Hypo - more water outside - cells burst
Hyper - less water outside/more solute outside - cells shrink

Question 18

Explain the concept of osmolality

Answer 18

• Osmolality is the concentration of a solution expressed as the total number of solute particles per kilogram (calculated considering the mass of solution).
• Contributes to osmotic pressure
• MilliOsmoles (mOsm/kg)
• If a solute that ionises has two diff. ions that are independently osmotically active (when moving across membrane it takes water w/ it) , then it each millimole in solution = 2 mOsmoles
  e.g. NaCL which is 140 mmol/L = 260 mOsm/kg

Question 19

How does water flow?

Answer 19

• (Blood or Interstitial) Hydrostatic pressure = force exerted by the fluid on the vessel wall - created by pumping action of the heart (OUT)
• Osmotic pressure = force applied by solute/colloid(small particle) to prevent osmotic movement across membrane - created by conc. of solute particles (IN)
• Colloid osmotic pressure = oncotic pressure
• Albumin is a protein found in blood that is made in the liver which adds to oncotic pressure.
• Capillaries have fenestrations that allow blood to enter and exit cells.

Question 20

Explain what is oedema

Answer 20

• Oedema is fluid retention - called “dropsy”
• Body fluids become diluted and there is a reduction of Na conc. in extracellular fluid which increases hydrostatic pressure, causing shift in osmotic pressure, making water move into interstitial spaces, making cells and tissue swell.
• Peripheral oedema is known as “swollen ankles” resulting from retention of fluid.
• Lymphatic obstruction may cause lymphedema, which means swelling due to a blockage of the lymph passages.
• This occurs in congestive heart failure, liver cirrhosis and renal disease. rRisk is increased in diabetes patients.
• Pitting oedema = when pressure is applied to the swollen area, a “pit” or indentation will remain.