MLT GlobePhysiology: Cell physiology & body fluids – page 2
44 Physiology MCQs on Cell physiology & body fluids with answers and explanations.
When core temperature rises during exercise, which response acts as negative feedback to cool the body?
Evaporation of sweat removes heat, bringing temperature back toward the set point. Shivering and skin vasoconstriction conserve or produce heat.
A neutrophil engulfs a bacterium, enclosing it in a membrane-bound vacuole. This form of bulk transport is:
Phagocytosis takes in large particles; pinocytosis takes in fluid droplets and exocytosis releases vesicle contents. Facilitated diffusion moves small solutes through carriers, not vesicles.
On a hot day when air temperature is higher than skin temperature, the body can lose heat only by:
When the environment is warmer than the skin, radiation, conduction and convection add heat. Evaporation of water from the skin is then the only way to lose heat.
Osteoid, the unmineralised bone matrix laid down by osteoblasts, consists mainly of:
Osteoid is mainly type I collagen with ground substance. It becomes bone when hydroxyapatite (calcium phosphate) is deposited, a step that fails in osteomalacia.
The sweat test for cystic fibrosis relies on the concentration of which ion, the main solute lost in eccrine sweat?
Eccrine sweat is mostly water with NaCl, plus some K+, urea and lactate. In CF, defective CFTR raises sweat chloride (at least 60 mmol/L is diagnostic).
A DEXA scan in a 60-year-old shows bone density below normal but above the osteoporosis threshold. This osteopenia results mainly from:
Osteopenia (T-score -1.0 to -2.5) reflects demineralisation that accompanies ageing and oestrogen loss. Below -2.5 is osteoporosis.
Which change would increase the net rate of simple diffusion of a solute across a membrane?
By Fick's law, net diffusion rises with concentration gradient and surface area and falls with membrane thickness and molecular size.
Which organelle uses oxidases to make hydrogen peroxide and catalase to break it down?
Peroxisomes hold oxidases that generate H2O2 while oxidising substrates such as fatty acids, plus catalase that breaks H2O2 into water and oxygen. Lysosomes hold acid hydrolases.
Which cytoskeletal element has the smallest diameter?
Actin microfilaments are about 7 nm wide, intermediate filaments about 10 nm, and microtubules about 25 nm. Myosin thick filaments in muscle are about 15 nm.
Lean (fat-free) body tissue contains roughly how much water?
Fat-free mass is about 70-73% water, whereas adipose tissue contains little water. That is why total body water is lower in people with more body fat.
The size of the extracellular fluid compartment depends mainly on the body's total content of which ion?
Sodium is the main ECF osmole, so water follows total body sodium and sets ECF volume. Potassium is mainly intracellular.
How does the osmolality of intracellular fluid compare with that of plasma and interstitial fluid in the steady state?
Water moves freely across cell membranes, so all compartments settle at about 290 mOsm/kg. Plasma is only marginally higher because of proteins.
A laboratory reports a healthy adult's measured serum osmolality. Which value is within the reference interval?
Normal serum osmolality is roughly 275-295 mOsm/kg, typically about 290. Values near 350 indicate marked hyperosmolality (e.g., hypernatraemia or hyperglycaemic states).
Which organelle, containing a pair of centrioles, organises the mitotic spindle during cell division?
The centrosome is the main microtubule-organising centre; it duplicates and forms the spindle poles that separate chromosomes. Hemidesmosomes anchor cells to basement membrane.
Hepatocytes of a patient on long-term phenobarbital show proliferation of which organelle, where drug-metabolising cytochrome P450 enzymes are located?
Cytochrome P450 enzymes are bound to smooth ER membranes; inducers such as phenobarbital enlarge the smooth ER to speed drug detoxification.
Kinesin and dynein motor proteins carry mitochondria and secretory vesicles through the cytoplasm along which structures?
Microtubules act as intracellular tracks for kinesin and dynein. Actin microfilaments support myosin-based movement and cell shape; intermediate filaments give mechanical strength.
What ensures that lymph flows in only one direction within lymphatic vessels?
Lymphatic vessels contain numerous valves that prevent backflow; contraction of vessel smooth muscle and skeletal muscle compression propel lymph forward.
Newborn mammals absorb intact colostral immunoglobulins from the gut by:
Neonatal enterocytes take up whole proteins in endocytic vesicles, giving passive immunity. Macromolecules cannot pass by diffusion or through small-solute carriers.
Why does a pure lipid bilayer block the passage of ions such as Na+ and K+?
Charged, hydrated ions cannot enter the non-polar interior, so they need channels or carriers. The bilayer has no fixed pores, and the glycocalyx does not determine ion permeability.
A membrane carrier moves three Na+ ions into the cell and one Ca2+ ion out in the same cycle. It is best described as a(n):
Antiporters move two solutes in opposite directions; the Na+/Ca2+ exchanger is a classic example. Symporters move both in the same direction; uniporters move one solute.