Session 1

Question 1

define homeostatis

Answer 1

‘the ability of a living organism, cell or tissue to keep the conditions inside it the same, despite any changes in the conditions around it’

maintaining a state of internal balance… dynamic equilibrium

Homeo = sameness
Statis = standing still

main homeostatic controls: water, temperature + pH

Question 2

what elements make up a feedback loop

Answer 2

stimulus = detectable change in the environment

sensor = something that monitors the current value of the variable

control centre = something that retains the desired value of the variable (and has a way of comparing that to the current value provided by the sensor)

effector = something that has the ability to change the value of the variable in a way that is determined by the control centre

Question 3

positive vs negative feedback loops

Answer 3

negative is when a stimulus causes an effector response to bring the body back to it’s normal conditions, ie to counteract the change.
(eg body temp control and blood glucose control)

negative feedback stops when the effector ceases

positive is when the output enhances or exaggerates the original stimulus.
(eg regulation of blood clotting and the process of uterus contraction/childbirth)

positive feedback stops when the stimulus ceases

Question 4

percentage of water in standard 70kg male

Answer 4

60% of total body weight is water
of that…
- 0.66 is intracellular fluid (inside cells)
- 0.33 is extracellular fluid

of the extracellular fluid…
- 0.75 is interstitial fluid (ie surrounds cells, but outside blood vessels
- 0.25 makes up blood plasma (more on next card)

Question 5

calculating blood volume (in standard 70kg male)

Answer 5

0.25 of extracellular fluid (ie 5%) of total body weight is blood plasma in standard human

this is calculated to be 3.5 L (1kg = 1L)
- minus 0.5 L which is found in transmembrane space (ie plasma membranes).
- this fluid isnt plasma or intracellular fluid
- add 2 L of RBCs to add to the plasma
- therefore 5 L of total blood volume in standard male

however… actually 4.9 L due to approximations in calculations

Question 6

state the body compartments where fluids accumulate

Answer 6

extracellular is fluid outside cells
- interstitial fluid is fluid that surrounds cells but outside blood vessels
- blood plasma makes up the total blood volume

intracellular fluid is fluid that is inside cells

transmembrane space isnt plasma or intracellular fluid. It is the space inside plasma membranes

Question 7

compare and contrast water balance in males and females, and in early and late life

Answer 7

• females have lower % water content than men (due to higher fat content)
• babies have greater water content
• obese people have lower water content
• lean people have higher water content
• elderly people have less water content as they have increased body fat

Question 8

dehydration and overhydration (water toxicity) and their effect on osmolality

Answer 8

dehydration
- osmolality increases
- cells and tissues initially absorb water from intersitial space
- then from each other (sacrafice of cells)
- then as tissues die, water absorbed from organs and then brain, liver, kidneys and lastly heart

water toxicity
- osmolality decreases
- osmotic pressure high
- enzymes and proteins stop working
- cells keep swelling until they burst (lysis)

Question 9

what is osmolality

Answer 9

a function of the concentration of particles in solution
expressed in milliOsmoles
mOsm/kg

Question 10

why is acid-base balance important

Answer 10

• measure of the concentration of H+ in blood
• higher conc of H+ means more acid, and therefore lower pH value

normal pH is 7.35 - 7.45

• normal cellular metabolism requires optimum otherwise proteins and enzymes denatured

Question 11

what organs are required for maintaining acid base balance

Answer 11

lungs = respiratory balance
kidneys = metabolic balance

Question 12

what are the normal ranges for pH, and their symptoms

Answer 12

acidosis: lower than 7.35
headaches, tremors, confusion, diarrhoea, nausea, arrythmia etc

normal: 7.35 - 7.45

alkalosis: greater than 7.45
tremors in hand, numbness in face, nausea, confusion and muscle twitching

below 7 and above 7.8 are likely to cause death

Question 13

what are ranges for core body temperature

Answer 13

normal is 36.5 - 37.5

• heat exhaustion is above 40 (fitting, seizures, dizzy, confused)
• heat stroke is above 40 (hot to touch, flushed, strong bounding pulse)
• fever is above 38 (pale sweaty skin, cramps)
• mild hypothermia is 32.1 - 35 (shivering, fatigue, confusion, muscle stiffness)
• severe hypothermia is 28 - 32 (shivering stops, muscles rigid, very slow and weak pulse)
• below 28 is no vital signs, dilated pupils, unconscious, appeareance of death, go blue/grey lips and gums

hyper = too much
hypo = too little

Question 14

what is the relationship between pH and [H+]

Answer 14

double [H+] for every 0.3 decrease in pH

remember 7.4 pH and 40 nanomoles/L [H+]

ie when pH decreases, [H+] increases

Question 15

mechanisms of pH control in the body (in broad terms)

Answer 15

each part of the body works at a different optimum of pH

buffer systems
- proteins as buffers as they can act as H+ donors or acceptors
- phosphate buffers too
- buffers help when there are minor changes in pH eg due to exercise where acidic CO2 in blood

respiratory control
- eg during exercise, CO2 levels increase due to respiration
- CO2 dissociates into carbonic acid in the tissues
- this lowers pH
- therefore the resp rate increases to increase blood flow to lungs and remove CO2 more quickly (gas exchange)

renal control
- kidneys control pH of extracellular tissues
- if pH too high, secretes H+ ions
- if pH too low, retains H+ and secretes HCO3- ions

Question 16

mechanisms of temperature control in the body (in broad terms)

Answer 16

sensor = skin and hypothalamus
control centre = hypothalamus
effectors = muscles, blood vessels, hairs on skin, fat and sweat glands

if too hot…
- vasodilation where arterioles dilate so more blood enters capillaries, so heat is lost
- sweating glands secrete sweat, which uses excess heat energy from the body to evaporate off the skin surface
- pilorelaxation where the hairs flatten, trapping less hot air and allowing more evaporation
- stretching out where the body is making use of a larger surface area

if too cold…
- vasoconstriction to keep core warm
- shivering to generate heat by respiration
- piloerection
- curling up

main heat source is respiration

Question 17

describe mechanism of oedema

Answer 17

oedema = fluid retention aka dropsy

where the hydrostatic pressure is greater than the osmotic pressure…
- capillaries have tiny holes throughout length, called fenestrations which allow ultrafiltration of water
- if tissues are damaged, fenestrations increase in size, allowing albumen to exit capillary (plasma loss), so now oncotic pressure is outside blood stream, sucking more water out capillary
- normally water that leaks out during ultrafiltration is returned to bloodstream by lymphatic system
- if lymphatic system fails/is blocked, water accumulates, causing oedema

oedema can also cause drop in BP, due to water leaving bloodstream, causing lower blood volume, and therefore lower BP… also causing less O2 delivery to cells

Question 18

describe mechanism of ultrafiltration (broad terms)

Answer 18

• there is a higher pressure at the arteriole end of capillary than the venule end, and this is due to higher BP
• fenestrations in capillary only let small molecules, such as water through
• larger proteins, eg albumen, remain in capillary
• high hydrostatic pressure at arteriole end forces small molecules out
• most water re-enters at venous end by osmosis, due to osmotic pressure, created by albumen remaining in capillary
• water also re-enters venous end due to hydrostatic pressure gradient
• rest of water is removed by lymphatic vessel, part of lymphatic system, which drains back into the blood near the heart, into veins

Question 19

tonicity (hypo/hyper etc and where water moves in and out of cells)

Answer 19

water movement is always down concentration gradient by osmosis

cell in hypotonic solution
- the solute concentration is lower outside cell
- water moves into cell
- cell swells and bursts
- osmotic lysis / haemolysis

cell in isotonic solution
- the solute concentration is equal in and out of the cell
- no net movement of water
- the same amount of water on both sides of plasma membrane

cell in hypertonic solution
- the solute concentration is higher outside cell
- water moves out of cell
- cell shrinks

Question 20

what are tissues (and give the 4 main different types)

Answer 20

tissue = a collection of cells specialised for a specific function. It is a Latin word meaning ‘woven’

1. Muscle tissue eg cardiac muscle
2. Nerves eg sympathetic nerve
3. Epithelial eg skin
4. Connective (holds other tissues together)

Question 21

relationship between milli, micro and nano metres

Answer 21

milli x1000 = micro
micro x 1000 = nano

Question 22

what is histology used for

Answer 22

• examines cells and tissues
• checks for changes in structure of cells ie if cell has mutated
• can diagnose things like cancer from appearance of cells

Question 23

common biopsy techniques

Answer 23

• surgery and then later dissection from histopathologist
• scraping ie curettes, scalpel scrapes
• sharps eg needle biopsy, pipelle (endometrial), trephine (to go through bone to get bone marrow), punch biopsy
• venepuncture ie blood smears or for haematological disease assessment
• transvascular where device travels through blood vessels to highly vascularised tissues biopsy site (eg kidney, lung, brain or heart)

Question 24

why do tissues need to be fixed + state which fixatives are commonly used

Answer 24

fixation needs to be used in order to preserve tissues in a life-like state.
- works by cross-linking all proteins so they cannot move
- often by 10% formalin solution (buffered and dissolved in sodium chloride ie saline, to prevent osmotic damage)
- for electron microscopy, glutaraldehyde fix is often used instead

Question 25

how can tissue processing lead to the formation of shrinkage and artefacts

Answer 25

shrinking
- can occur during dehydration process where water is removed, which may cause organelles etc to shrink
- also may be due to the wax cooling

artefacts
- could be caused by damage when lifting sample with forceps etc
- pigments in the stains may appear as artefacts

Question 26

why are stains used, and some common ones

Answer 26

stains are used to visualise cell components in more detail
haematoxylin + eosin
- H only stains nucleus blue (anything acidic)
- E only stains cytoplasm and extracellular matrix pink (anything alkali)
- H+E together show more detail

masson’s trichrome
- red = keratin and muscle
- green and blue = collagen + bone
- pink = cytoplasm
- dark brown = nuclei

periodic acid-schiff
- anything with a sugar is dyed pink
- ie anthing ‘glyco-‘

immunohistochemistry
- primary antibody complimentary to protein added
- secondary labelled antibody binds to complimentary primary antibody
- label is either flourescent tag or an enzyme that turns a dye a different colour

Question 27

what are the advantages of phase contrast, dark field, flourescence and confocal light microscopy

Answer 27

can see things in more detail

phase contrast allows you to see things that are living, and for clear samples that don’t absorb light (ie cells in culture), so you can see details like villi

dark field allows you to see things with a high amount of contrast, and can view live and unstained samples

flourescent allows for specific and sensitive staining, to visualise the distribution of very specific proteins (that are complimentary to primary antibody)

confocal light microscopy allows for high-res imaging, where you can remove out of focus areas, control the depth and produce a 3D image by taking a series of images and combining them using Z-stack.

Question 28

what is limit of resolution

Answer 28

the smallest distance by which two objects can be separated and still distinguishable as two seperate objects

Question 29

why are electron microscopes capable of finer resolution than light microscopes

Answer 29

electron microscopy involves using an electromagnetically controlled beam of electrons focussed at sample to produce an image
- electrons have a much shorter wavelength than visible light
- can therefore produce an image of much higher resolution images

Question 30

main cell organelles and their main functions (broad terms)

nucleus, golgi apparatus, vesicles and plasma membrane

Answer 30

• nucleus has nuclear envelope with pores (to allow substances to move between nucleus and cytoplasm). Contains all genetic content of cell, inc chromosomes. Nucleolus has membrane and makes ribosomes
• golgi apparatus is membrane enclosed, fluid filled sacs. Processes and packages lipids + proteins, and makes lysosomes. vesicles store L+P and transports them out of cell
• plasma membrane mainly made up of lipids + proteins, regulates movement of substances in and out of cell, and has receptor molecules on surface to allow responses to chemicals. Made of phospholipid bilayer.

Question 31

main cell organelles and their main functions (broad terms)

mitochondria, lysosome, ribosome

Answer 31

• mitochondria are double membrane. Has matrix (contains enzymes for respiration) and cristae (folded inner membrane). Site where ATP is produced
• lysosome made by golgi apparatus. Has outside membrane but no clear internal structure. Type of golgi vesicle. Contains digestive enzymes known as lysozymes. Used for digesting invading cells and breaking down worn out cell components.
• ribosome is not surrounded by membrane. Has large and small subnit. Floats free in cytoplasm or attached to RER. Made up of proteins and RNA. Involved in protein synthesis