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Flashcards in Principles Of Cellular Function Deck (23):

How is water distributed through the body compartments? How do age and gender affect total body water?

1. Total body water (TBW) is 60% body weight
- 2/3 (40%) ICF
- 1/3 (20%) ECF -> 1/4 Plasma, 3/4 Interstitial

2. Age
- Body water decreases with age

3. Gender
- Body water higher in males


What are the buffer systems in the BLOOD?

1. Carbonic acid/Bicarbonate system
- Main buffer

2. Plasma proteins
- Free carboxyl and amino groups

3. Haemoglobin
- Imidazole groups of histidine residues
- Deoxygenated Hb better than oxygenated Hb


Explain the carbonic acid/bicarbonate system

1. H2CO3 H + HCO3
- Reaction sped up in the presence of carbonic anhydrase found intracellularly
- Increase acid/H in blood will shift the equilibrium to the left -> Forms more carbonic acid
- Increase OH in blood will shift the equilibrium to the right -> To replace H used up with OH to form H20

2. Buffering system linked to
- Renal system -> Removes HCO3
- Respiratory system -> Removes CO2


What are the major buffers in CELLS and how do they work?

1. Hprotein H + Protein

2. H2PO4 H + HPO4


Describe the Henderson-Hasselbach equation

pH = pKa + log [A-]/[HA]
- Most effective when [A-]/[HA] = 1, so pH = pKa


Outline the different ways in which a substance can cross a cell membrane.

1. Passive
- Diffusion
- Facilitated diffusion

2. Active
- Endocytosis -> Phagocytosis by leukocytes
- Exocytosis -> Golgi apparatus to extracellular
- Ion channels
- Active transport via transport protein
> Primary active transport - Na/K ATPase pump
> Secondary active transport - Na/glucose transporter


Can you please explain the process of secondary active transport?

- The movement of an ion down its electrochemical gradient provides energy to another substrate/ion to move against its electrochemical gradient
- Eg. Na/glucose transporters, Na/amino acids transporters


Describe the Na/K pump

- Energy-dependant pump requiring ATP to ADP as energy source
- Transports 3Na out of cell + 2K into cell against its electrochemical gradient for each ATP molecule


Describe the synthesis and metabolism of cAMP. Discuss the function of cAMP.

1. Cyclic adenosine monophosphate
- Intracellular secondary messenger
- Formed from ATP by adenyl cyclase into cAMP
- Metabolised by Phosphodiesterase

2. Functions
- Intracellular secondary messenger
- Stimulates protein synthesis
- Activates cAMP-related element-binding protein (CREB) to alter transcription of genes


What are the major factors determining plasma glucose level? List the hormones which affect plasma glucose levels.

1. Overall determined by intake/glucose entering blood stream vs output/glucose leaving blood stream
- Dietary carbohydrate intake
- Cells uptake of glucose
- Liver glycogenolysis, gluconeogenesis, glycogenesis
- Renal filtration and reabsorption of glucose
- Hormonal effects -> insulin, glucagon, cortisol, thyroid hormone

2. Hormones affecting glucose level
- Reduce BSL -> Insulin, Insulin-like growth factor 1 and 2
- Increase BSL -> Glucagon, Cortisol, Catecholamines


What are the potential pathways for glucose metabolism in the body.

- Aerobic
- Anaerobic
- Glycogen
- Pentoses


What are the types of immunoglobulin and clinical significance of each

1. Immunoglobulin A
- Found in mucous membranes
- Important in mucous secretions

2. Immunoglobulin D
- Antigen recognition by B cells

3. Immunoglobulin E
- Anaphylaxis
- Histamine release by mast cells and basophils

4. Immunoglobulin G
- Infection causing complement activation
- Crosses the placenta and breast milk

5. Immunoglobulin M
- Infection causing complement activation
- First to be produced
- Largest immunoglobulin


Draw a typical immunoglobulin molecule and label the parts

- Fab = Antigen-binding portion
- Antigen-binding site
- Fc = Effector portion
- Hinge
- Variable region


What are the features of innate vs acquired immunity?

1. Innate immunity
- Defence mechanism present even before infection
- E.g: Phagocytes, NK cells, complements
- Important in early phases of infection
- Triggered by cellular receptors -> Toll-like receptors

2. Acquired immunity
- Defence mechanism against infection
- Cellular mediated -> T cells -> Recognizes antigen on antigen-presenting cells (APC), major histocompatibility complex (MHC), human leukocyte antigen (HLA) -> Protects against intracellular microbes
- Humoral mediated -> B cells -> Protects against extracellular microbes -> Releasing antibodies


How do cells communicate with one another?

1. Cell-to-cell
- Gap junctions

2. Chemical mediators in the ECF
- Neural -> Neurotransmitters in synapses
- Autocrine -> Cell produces messenger that acts on itself
- Paracrine -> Cell produces messenger that acts on neighbouring cells
- Endocrine -> Hormone and growth factor secreted from another site and circulating in blood or lymph
- Juxtacrine -> Molecules attached to receptor of membrane that attaches to another cell


How do receptors respond to variations in messenger?

1. Upregulation of receptors
- Deficient messenger causes increase in receptors

2. Downregulation of receptors
- Excess messenger causes decrease in receptors


How do messengers act? What are the actions of second messengers?

1. Open or close ion channels
2. Produce cAMP
3. Produce cGMP
4. Increase activity of tyrosine kinase
5. Activates phospholipase-C to produce intracellular IP3, DAG
6. Increase serine, threonine


Name the principal ketone bodies. How are ketone bodies produced and metabolised? In which clinical situation do they accumulate in the body?

1. Principal ketone bodies are
- Acetoacetate
- Acetone
- B-hydroxybutyrate

2. Metabolism of ketone bodies
- Produced in mitochondria of liver and all tissues
- Substrate -> Fatty acids, AcetylCoA
- Fatty acids undergo B-oxidation to form AcetylCoA -> Enters citric acid cycle -> Yields 11 ATP, 1 GTP

3. Ketones accumulate in ketosis metabolic acidosis during
- Starving/fasting
- Diabetes (T1DM)
- High fat low carbohydrate diet


Describe the structure, mechanism of action and function of the Na/K pump

1. Structure
- Antiport
- 2a + 2b subunits
- a-subunit binds Na + ATP intracellularly and K extracellularly
- b-subunit does not have Na or K binding site

2. Mechanism of action
- Na binds to a-subunit intracellularly
- ATP also binds to a-subunit intracellularly
- ATP converted to ADP
- Causes change in protein configuration
- Na expelled out of cell
- K then binds to a-subunit extracellularly
- Dephosphorylates a-subunit to return protein to original configuration
- K released into cell

3. Function of pump
- Maintains electrochemical gradient -> Pumping 3 Na out, 2 K in
- Co-transport of other molecules -> Glucose in small intestine


What is normal serum osmolality? What substances contribute to serum osmolality? How does plasma differ in composition intracellularly vs extracellularly?

1. Normal serum osmolality is 290mOsm/L

2. Substances
- Mainly ions (270mOsm) -> Na, K, Cl, HCO3
- Rest (20mOsm) -> Other cations, anions, urea, glucose, protein

3. Difference in plasma composition
- Intracellularly -> High K, PO4, proteins
- Extracellularly -> High Na, Cl


What is the difference between diffusion and osmosis? Define tonicity.

1. Diffusion is
- Movement of solutes through semi-permeable membrane down its concentration gradient
- Governed by Fick’s Law

2. Osmosis is
- Movement of SOLVENT/water molecules through membrane impermeable to solutes
- Down its concentration gradient to area of high concentration of SOLUTES

3. Tonicity is osmolality of a solution relative to plasma osmolality
- Isotonic -> Same osmolality as plasma
- Hypotonic -> Lower osmolality than plasma
- Hypertonic -> Higher osmolality than plasma


What is the genesis of the membrane potential?

- Due to difference in concentration and electrochemical gradient of Na + K intracellularly and extracellularly
- Maintained by Na/K pump
- Pumps 3 Na out and 2 K in


What are the phases of protein synthesis? Describe the process of protein secretion from cells.

1. Protein synthesis has 2 phase
- Transcription of DNA into mRNA in nucleus
- Translation of mRNA into amino acid chain by ribosome with help of tRNA in cytoplasm

2. Protein secretion has 2 pathways
- Amino acid/polypeptide produced are cleaved and secreted out of cell by ATP-dependent membrane transporters
- Amino acid/polypeptides are transporters into endoplasmic reticulum to be modified, packaged and secreted by exocytosis