1
Q
Fluid Mosaic Model
A
50% Proteins and 50% Lipids - lipids form a bilayer where lipids can move freely
2
Q
Lipid bilayer is permeable to…
A
- Non-polar uncharged molecules
- Lipid soluble molecules (steroids)
- Small uncharged, polar molecules (H2O, urea, CO2, Glycerol)
3
Q
Lipid bilayer is impermeable to…
A
- Large, uncharged polar molecules (Glucose, amino acids)
- Ions
4
Q
What increases the rate of diffusion?
A
- Greater concentration gradient
- Higher temperature
- Increased surface area of the membrane
5
Q
What decreases the rate of diffusion?
A
- Larger size of diffusion molecule
- Increased diffusion distance
6
Q
Pd
A
- Permeability through the bilayer for water
- small
- temperature dependant (lipid fluidity)
- Mercury insensitive
7
Q
Pf
A
- Permeability through aquaporins
- large
- temperature independent
- Mercury sensitive
8
Q
Isosmotic
A
If 2 solutions have the same osmolarity
9
Q
Hyposmotic
A
The solution with the lower osmolarity
10
Q
Hyperosmotic
A
The solution with the higher osmolarity
11
Q
Isotonic
A
No effect on cell volume
12
Q
Hypotonic
A
Causes cell swelling and lysis
13
Q
Hypertonic
A
Causes cell shrinkage (crenation)
14
Q
Ion Channels Selectivity
A
- Specific amino acids line the channel and determine selectivity
15
Q
Carrier proteins exhibit
A
- Specificity
- Inhibition
- Competition
- Saturation
16
Q
Primary Active Transport
A
- Energy is derived from the hydrolysis of ATP
- E.g. electrogenic Na+/K+ ATPase generates a net current - pump works consistently as there is leakage of Na+ into the cell
17
Q
Secondary Active Transport
A
- Uses energy released by a substance diffusing down its concentration gradient (potential energy) to actively transport another substance against its concentration gradient
- Na+/Ca2+ Antiporter
- Na+/Glucose Symporter
- Na+/Amino Acid Symporter
18
Q
Phagocytosis
A
Cell eating
- Pseudopods forming vesicle around foreign substance and membrane receptor
- Phagolysosome
19
Q
Pinocytosis
A
Cell Drinking
- Directly ingested through vesicle
20
Q
Receptor Mediated Endocytosis
A
- Specific substances/ligands
- Substance binds to receptor protein in cathrin coated pit
- Substance injected and receptor moves back to surface
21
Q
Tight Junctions
A
- Claudins and Occludins
22
Q
Paracellular Transport
A
- Transport via tight junctions
- In a leaky epithelium paracellular dominates
- Proximal
23
Q
Transcellular Transport
A
- Tight epithelium transcellular dominates
- Distal
- Secretion or absorption
24
Q
Proximal
A
- Leaky epithelium
- Low electrical resistance
- Low number of tight junction strands
- Paracellular transport
- E.g. duodenes, proximal tube
25
Distal
- Tight epithelium
- High electrical resistance
- High number of tight junction strands
- Transcellular transport
- E.g. coelum
26
Types of epithelium
1. Covering and lining epithelium
| 2. Glandular Epithelium
27
Glandular Secretion
- Acinar cells create the primary secretions
| - Duct cells modify composition of primary secretion by absorbing or secreting molecules
28
Steps to Glucose absorption
1. Tight Junctions divide the cell into apical and basolateral membranes
2. Na+/K+ Pump sets up ion gradients
3. Na+/Glucose Symporter uses energy of Na+ gradient to transport glucose into the cell against concentration gradient
4. Facilitative Glucose Transport mediates glucose exit across the basolateral membrane via passive diffusion
5. Na+ taken up by symporter exits though the basolateral membrane
6. This induces paracellular transport of Cl- and H2O
29
Oral Rehydration Therapy
The use of Glucose and Na+ (NaCl) to stimulate fluid uptake
- Given to dehydrated babies suffering from diarrhoea
- Via steps of glucose absorption
30
Glucose/Galactose Malabsorption Syndrome
- Mutation in Na+/Glucose Symporter SGLT
- Accumulation of Glucose and Galactose in the lumen of Small Intestine
- Osmotic imbalance attacking water resulting in severe diarrhoea
- Facilitative glucose transporter is capable of taking up glucose from the blood
31
Treatment of Glucose/Galactose Malabsorption Syndrome
- Remove Glucose/Galactose from the diet and replace with Fructose
32
Glucose Reabsorption in Kidney (Glycosuria)
- In the kidney glucose in the plasma is filtered and needs to be reabsorbed or it will appear in urine
- If SGLT has exceeded capacity glucose will appear in urine - renal threshold
- Cause is diabetes as insulin activity is deficient and cannot stimulate SGLT
33
Steps to Chloride Secretion
1. Tight junctions separate cell into apical and basolateral membranes
2. Na+/K+ Pump sets up ion gradients
3. NaKCl2 Symporter uses the energy of the Na+ gradient to actively accumulate Chlorine above its concentration gradient
4. Cl- leaves the cell at apical membrane through highly regulated ion change (passive)
5. Na+ exits at the basolateral membrane through the Na+/K+ Pump, K+ exits via channel
6. Induces paracellular transport of Na+ and H2O
34
Cystic Fibrosis (CF)
- Cystic Fibrosis Transmembrane Conductance Regulator (CFTR)
- Over stimulation results in secretory diarrhoea, disfunction results in CF
- Autosomal recessive
35
Sweat formation of CF
- Primary isotonic secretions of fluid by acing cells
- In normal people there would be a secondary absorption of NaCl to produce a hypotonic solution
- In case of CF there is not reabsorption producing the salty sweat
- Apical membrane of duct cells have a low permeability to H2O
36
Clinical Management of CF
- Antibiotics
- Pancreatic enzyme replacement
- Attention to nutrition
- Chest percussions to improve clearance of infected secretions
37
Defect in Cl- Secretion
- In a normal lung there is balance between secretion and absorption to kept the lung surface moist
- In CF the defection Cl- channels prevent isotonic fluid secretion and enhances Na+ absorption giving a dry lung surface
- Mucus becomes thick and hard to remove
- Bacteria proliferate and attract immune cells damaging healthy tissue
- DNA released from bacteria and lung cells adds to stickiness
- Airways become plugged
38
CFTR Protein
- CFTR is a Cl channel regulated by protein Kinase A dependant phosphorylation of the R domain and binding of ATP then binding to the Nucleotide Binding Domain
39
Secretory Diarrhoea
- Enterotoxins secreted by bacteria irreversibly activate adenylate cyclase (over production of cAMP) causing a maximum stimulation of CFTR leading to secretion of Cl- and this H2O that overwhelms absorptive capacity of colon
- Happens with Cholera
- Keep hydrated and crypt cells in the gut will move past the secretion area in 5 days
40
Transcellular Transport - Secretion
1. Entry and exit steps
- Entry in the basolateral membrane
- Exit in the apical membrane
2. Electrochemical gradient
- Is the entry/exit step passive or active
- Typically a Primary Active Transporter setting up ion gradients for the Secondary Active Transporters to use
3. Electroneutrality
- The movement of a positive ion will attract a negative ion
- How can we preserve electroneutrality?
4. Osmosis
- Net movement of ions will establish a difference in osmolarity and cause water to move
41
Transcellular Transport - Absorption
1. Entry and exit steps
- Entry in the apical membrane
- Exit in the basolateral membrane
2. Electrochemical gradient
- Is the entry/exit step passive or active
- Typically a Primary Active Transporter setting up ion gradients for the Secondary Active Transporters to use
3. Electroneutrality
- The movement of a positive ion will attract a negative ion
- How can we preserve electroneutrality?
4. Osmosis
- Net movement of ions will establish a difference in osmolarity and cause water to move
Biology 107
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