Lecture 1 - Homeostasis Flashcards
What is homeostasis?
(Short definition)
Homeo = sameness
Stasis = standing still
What is homeotstasis?
(Long definition)
The ability of an organism or cell to maintain a stable internal environment by marinating a dynamic equilibrium of conditions despite any changes going on around it.
What type of mechanisms maintain homeostasis?
Feedback loops
What are the 2 types of feedback loops?
Positive feedback
Negative feedback
How do negative feedback loops work?
Stimulus is detected by a receptor
Control centre produces response to act against the change
Effector carries out the response determined by the coordination centre
How does a positive feedback loop work?
Stimulus is detected by receptors
The control centre decides to enhance/add to the stimulus
Effector actually enhances the stimulus
Give 3 examples of conditions that are regulated by negative feedback loops:
-Temperature
-pH
-Water balance
Give 2 examples of events that are under positive feedback control:
-Child birth (Ferguson reflex)
-Blood clotting cascade
In negative feedback loops, when does the negative feeback stop?
When the effector ceases
IN positive feedback, when does the positive feedback stop?
When the initiator /stimulus ceases
What is the normal core body temperature range?
36.5ºC - 37.5ºC
What devices can be used to measure core body temperature?
Infra-red skin thermometer
Tympanic thermometer
Temporal thermometer
Where is the temperature control centre in the body?
Hypothalamus
What are the responses to thermoreceptors detecting low body temperature?
Vasoconstriction
Shivering
Piloerection
Curling up
How does Vasoconstriction help keep core body temperature warm?
Arterioles constrict reducing blood flow to skin
How does shivering help increase core body temperature?
Rapid contraction and relaxation of skeletal muscle produces heat via respiration
What are the responses to thermoreceptors detecting the body temature is too high?
Vasodilation
Sweating
Pilorelaxation
Stretching out
Between what temperature is a person classed as being normal but cold?
36.5º - 35º
What is the temperature range for having Mild Hypothermia?
35ºC - 32.1ºC
What is the temperature range for having Severe Hypothermia?
32ºC - 28ºC
What happpens when the core body temature is below 28ºC?
No vital signs
When can you classify someone ass being dead when their core body temperature is below 28ºC?
They’re not dead until they are WARM AND DEAD
What temperature range is somebody classed as being normal but warm?
37.5ºC - 38ºC
What temperature range doe somebody have a fever?
38ºC - 39.9ºC
What temperature range can somebody have heat stroke and heat exhaustion?
Over 40ºC
What is the Acid-Base balance?
The homeostasis of pH within a very narrow range in the body
What is the normal plasma pH value?
7.35 - 7.45
What are the 2 major organs responsible for maintaining acid-base balance?
Lungs-Respiratory balance
Kidneys-Metabolic balance
How does a change in [H+] by a factor of 2 change pH?
Changes pH by 0.3
What is used to measure blood pH?
Arterial Blood Gas test
What are the 3 blood buffer systems in the body which help maintain the acid-base balance?
Carbonic acid - Bicarbonate buffer for blood pH
Sodium Phosphate buffering system
Protein buffer systems
What do antacids do?
Neutralise acids
How does solubility affect the effectiveness of an antacid?
Insoluble = better
What are the pH limits of human tissue survival?
6.8 - 7.8
What happens when cells receive too little water?
Dehydration
Cell death
What happens when a cell receives too much water?
Swelling
Toxicity, metabolic failure and cell death
How much does the average male weigh?
70kg
Approximately, what percentage of the average man is water?
60%
Approximately how much water does the average man contain?
42L
How much of the average mans water content is intracellular and how much of it is extracellular?
Extracellular = 1/3 = 14L
Intracellular = 2/3 = 28L
How is the 14L of extracellular water in the average man distributed through the body?
10.5L interstitial fluid
0.5L transmembrane fluid
3L Plasma
How many litres of blood are there in the average 70kg male? How is this volume comprised?
5L
3L Plasma
2L Actual blood cells
What is the weight of the average female?
58kg
How does the total body water of a female differ to a male?
Females = 50% water
Male = 60%
Why do females total body water differ to males?
They have a higher fat content
How does fat content affect Total Body Water (TBW)?
Higher the fat content, the lower the TBW
Do infants have a higher or lower TBW than adults?
HIGHER
What is meant by a isotonic celll?
There is an equal amount of water on both sides of the plasma membrane
What is meant by a hypertonic cell?
There is MORE water inside the cell than outside
The solute concentric outside the cell is higher than the inside
Water moves OUT OF the cell via osmosis
What is meant by a Hypotonic cell?
There is LESS water inside the cell compared to the outside
The solute concentration inside the cell is higher than the outside
Water moves INTO the cell via osmosis
What is Osmolality?
The conc of a solution expressed as the total number of SOLUTE PARTICLES PER KG
What is Osmolarity?
The conc of a solution expressed as Osmolality of solute particles PER LITRE OF SOLUTION
What is the normal range of osmolality for a patient?
280 - 300 mOsm/kg
What happens when there isn’t enough water?
Cells absorb water from each other
As tissues die water absorbed from organs
As organs die water absorbed from brain, liver and then the kidneys and heart
What happens if there’s too much water?
Osmotic pressure high
Cells swell
Enyzmes and proteins stop working
Cells burst
If a patient has too much water and they need fluids, what type of fluids must you give them?
Isotonic solutions
IV drip of 0.9% NaCl
How does lots of water move across a membrane into a cell?
Via aquarporins
What is Oedema?
Fluid retention in tissues
What causes Oedema to occur?
Hydrostatic pressure > oncotic pressure
What conditions can lead to hydrostatic pressure increasing leading to oedema?
Congestive heart failure
Liver cirrhosis
Renal disease
What is pitting oedema?
When the oedema affected skin is pressed, the dent remains
How can you tell if someone with Oedema may have Congestive Heart Failure?
The Oedema will be pitting
When pressed it will remain dented
What produces the Oncotic pressure (the force that draws water back into the blood vessels/capillaries)?
Plasma proteins like Albumin
What occurs if Albumin moves out of the capilaries into the Intersitial space?
Water is drawn out of capillary and remains in interstital space because interstitial fluid osmolarity increases
What is pyrexia?
Increase in core body temperature
What can cause pyrexia?
Infections
How is pyrexia triggered by infections?
When fighting infections white blood cells (mainly macrophages) release pyrogens which travel to the hypothalamus causing the bodies thermostat to be increased
Who has the highest total body water % and why?
Lean infants since they have the lowest amount of fat
Less fat = more water
What temperature may an elderly patient with hypothermia wake up from being comatosed?
32ºC
