Physiology 2

Question 1

What type of bonds link the individual amino acids in a protein sequence?

Answer 1

Covalent peptide bonds

Question 2

What are the two most common secondary structures of proteins?

Answer 2

Alpha helix

Beta pleated sheet

Question 3

What type of bonds produce a protein’s secondary structure?

Answer 3

Hydrogen bonds

Question 4

What type of bonds produce a protein’s tertiary structure?

Answer 4

Hydrogen bonding
Ionic bonding
Hydrophobic interactions
Covalent disulphide bonding (cysteine)

Question 5

Contrast the ‘lock and key’ and the ‘induced fit’ models of enzymatic action

Answer 5

Lock and key requires ‘perfect fit’

Induced fit suggests conformational change of the enzyme occurs as a result of the substrate.

Question 6

Name some metal ion co-factors for enzymatic reactions and their associated enzymes

Answer 6

Mg2+: Hexokinase
Zn2+: Carbonic anhydrase
Fe2+: Cytochrome oxidase

Question 7

Name some organic co-enzymes and their associated reactions

Answer 7

Co-enzyme A: Acyl group reactions

Co-enzyme B12: Alkyl group reactions

Question 8

What effect does temp have on rate of enzymatic reaction?

Answer 8

Increased temp -> increased rate until enzyme denatured

Question 9

What effect does pH have on rate of enzymatic reaction?

Answer 9

Enzymes are pH-specific. H+ ion concentration affects Hydrogen bonding and amino acid charge leading to conformational change.

Question 10

Michaelis-Menten equation?

Answer 10

V0 = Vmax[S] / Km + [S]

Where V0=initial reaction velocity
Vmax=max velocity
Km=Michaelis constant
[S]=substrate constant

Question 11

How is the Michaelis constant derived?

Answer 11

k-1 + k2
/ k1

E + S -> ES (k1)
ES -> E + P (k2)
ES -> E + S (k-1)

Question 12

What happens to the Lineweaver-Burke slope when a competitive inhibitor is added to an enzymatic reaction?

Answer 12

Increase in slope around 1/Vmax (point of crossing y-axis)

Question 13

What happens to the Lineweaver-Burke slope when a non-competitive inhibitor is added to an enzymatic reaction?

Answer 13

Increase in slope from -1/Km (where meets x-axis)

Question 14

Define an allosteric enzyme

Answer 14

Enzyme that has multiple subunits and exhibits conformational change (and subsequent effects on substrate binding) in the presence of additional molecules

Question 15

What effect does allosteric binding have on Michaelis-Menten characteristics?

Answer 15

The hyperbolic curve is replaced by a sigmoid curve.

Question 16

Outline the fluid compartments of the body

Answer 16

70kg male (standard)
60% water - 42L
2/3 ICF - 28L
1/3 ECF - 14L

In the ECF:
Intravascular - 4L (9.5%)
Interstitial - 9L (21%)
Transcellular - 1L (2%)
Bone/connective tissue - 1L (2%)

Question 17

How much of the intravascular volume is accounted for by plasma?

Answer 17

55%

Question 18

What is an approximate calculation for total intravascular volume?

Answer 18

70-75ml/Kg

Question 19

Contrast osmolality and osmolarity

Answer 19

Osmolality: osmol/Kg water
Osmolarity: osmol/L water (temperature dependent)

Question 20

What is a normal plasma osmolality?

Answer 20

280-305 mOsmol/Kg

Question 21

How does osmolality relate between body water compartments?

Answer 21

Is is equal across compartments due to free movement of water across membranes

Question 22

Formula for estimating plasma osmolality?

Answer 22

= Urea + K + 2Na

Question 23

Where are osmoreceptors found?

Answer 23

Hypothalamus

Question 24

What features of capillaries make them effective vessels for exchange?

Answer 24

1. Low flow velocity (0.05-0.1cm/s)
2. Large area for diffusion
3. Thin walls (to minimise diffusion distance)

Question 25

What is the structure of a capillary?

Answer 25

Endothelial tube Basal lamina Average diameter 5-9 um

Question 26

What types of capillary exist?

Answer 26

Continuous | Fenestrated

Question 27

What are the subtypes of continuous capillary?

Answer 27

- Typical - Tight junctions (eg. BBB) - Discontinuous/sinusoidal (liver)

Question 28

Where are fenestrated capillaries found?

Answer 28

``` Endocrine organs Choroid plexus Glomerular capillaries GI tract Hypothalamus ```

Question 29

Size of molecules filtered by glomerular apparatus?

Answer 29

<4nm freely filtered | >8nm excluded

Question 30

What are the functions of the capillary and venular pericytes?

Answer 30

1. Contractile alteration of luminal diameter 2. Production of basement membrane and extracellular matrix 3. Release vasoactive agents 4. Regulate flow through endothelial cell junctions

Question 31

Define vasomotion

Answer 31

Vasomotion is the cycling of contraction and relaxation controlled by a smooth muscular response to local metabolites.

Question 32

What factors affect capillary sphincter tone?

Answer 32

``` NO low pO2 or high pCO2 Raised temperature Rising [K+] or [H+] Lactic acid Prostocyclin, thromboxane, endothelins ```

Question 33

What is the Starling equilibrium equation?

Answer 33

Q (fluid movement) = KA[Pc-Pi0 - s(PIc-PIi)] ``` Where: K=permeability constant A=area of membrane Pi=interstitial hydro press Pc=capillary hydro press s=albumin reflection coeff. PIi=interstitial oncotic press PIc=capillary oncotic press ```

Question 34

Why do alveoli not fill with water?

Answer 34

Hydrostatic pressure in the capillaries of the lung is less than colloid osmotic pressure, hence osmotic pressures prevent water entering the alveolus

Question 35

What factors may lead to development of oedema?

Answer 35

Excess capillary filtration (increased osmotic gradient) Protein deficiency Increased capillary leak

Question 36

What substances increase capillary permeability?

Answer 36

``` Substance P Histamine IL1, IL4, IL6 Kinins eg bradykinin, Kallidin Burns Acute lung injury Reperfusion injury ```

Question 37

What is meant by the term transcytosis?

Answer 37

The movement of extracellular material through a cell using vesicles, comprising endocytosis on one surface of the cell and exocytosis on another

Question 38

Which three proteins are important for transcytosis?

Answer 38

Caveolin: Involved in protein endocytosis Clathrin: stabilises vesicular structure Dynamin: 'Pinches off' the vesicle forming spherical structures

Question 39

Which electrolyte does exocytosis rely upon?

Answer 39

Calcium | Also requires ATP

Question 40

Explain the Gibbs-Donnan effect

Answer 40

Proteins exert the effect of binding permeable ions eg. albumin binding Na and Cl, which increases the colloid osmotic pressure.

Question 41

What is the Nernst equation?

Answer 41

Calculates the equilibrium potential across a membrane E = RT ln (c1/c2) + Zfv Where E: electrochemical potential in joules/mol R: universal gas constant (8.31 J/K/mol) T: Absolute temp (K) c1, c2: osmolarity of compartments (c1>c2) Z: valence of ion f: Faraday constant (96500 C/mol) v: volts (J/coulomb)

Question 42

What is the rearranged Nernst equation?

Answer 42

Eion = 61.5 log [ion1]/[ion2] | at 37 degrees C

Question 43

What is the Goldman equation?

Answer 43

Calculates the membrane potential taking into account the contributions of multiple diffusible ions. V = RT/F ln ((Pk[k]o + Pna[na]o + Pcl[cl]i) / Pk[k]i + Pna[na]i + Pcl[cl]o))

Question 44

Describe the structure of lymphatic vessels

Answer 44

Begin as blind-ended tubes close to capillaries in the interstitial space. Extremely thin endothelial lining and incomplete or absent basement membrane. Collagenous anchoring fibrils exert radial traction keeping lumen open in the interstitial space. Larger lymph vessels resemble venules and veins, with smooth muscle, elastin and collagenous walls.

Question 45

How is the flow of lymph fluid maintained?

Answer 45

Relies on hydrostatic pressure gradient Peristalsis of lymph vessels Large vessels have valves Aided by: -Negative intrathoracic pressure during respiration -Suction effect of high velocity flow at terminal junction with brachiocephalic veins

Question 46

How long is the thoracic duct in an adult?

Answer 46

~45cm

Question 47

``` Into which lymph nodes do the following organs drain? Abdominal wall Intestines Adrenals/gonads/posterior abdo wall Liver Pelvic viscera/perineum/lower limb ```

Answer 47

Abdominal wall: Axillary, anterior mediastinal, superficial inguinal Intestines: Preaortic Adrenals/gonads/post wall: Paraaortic Liver: Superficial + deep plexi -> anterior and posterior mediastinal Pelvis/perineum/legs: Iliac -> paraaortic

Question 48

What is the protein content of hepatic lymph drainage?

Answer 48

6.2 g/dL Lower than plasma (7g/dL) but higher than other tissues eg. heart (4.4 g/dL), GIT (4.1 g/dL), lung (4 g/dL), skin + skeletal muscle (2 g/dL)

Question 49

What factors are most important in determining absorption of water-soluble substances in the gut?

Answer 49

Concentration gradient | Diffusion distance

Question 50

How is fat absorbed in the intestine?

Answer 50

Large molecules emulsified by bile salts + lecithin -> droplets 0.5-1 um Lipase + colipase + droplets -> FFA + 2-monoglycerides Micelles formed containing ~20 fat molecules monoglycerides absorbed passively, FFA may be transported by fatty acid transport proteins (eg. FATP4)