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30 cardsMedical University Entrance Examination (Bulgaria)

Human Biology and Medical Physiology

30 study flashcards covering core human physiology, organ systems, cell biology, and genetics for Bulgarian medical entrance examinations.

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Sodium-potassium pump stoichiometry (Na+/K+-ATPase)
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1
Sodium-potassium pump stoichiometry (Na+/K+-ATPase)
3 Na+ ions pumped out of the cell, 2 K+ ions pumped into the cell, consuming 1 ATP molecule.
2
Resting membrane potential of human neurons
Approximately -70 mV, established primarily by outward K+ flux through background non-gated leak channels.
3
Action potential threshold and depolarization mechanism
Threshold is ~ -55 mV; rapid opening of voltage-gated Na+ channels drives phase 0 depolarization toward +60 mV.
4
First heart sound (S1) cause
Closure of the atrioventricular (mitral and tricuspid) valves at the onset of ventricular isovolumetric contraction.
5
Second heart sound (S2) cause
Closure of the semilunar (aortic and pulmonary) valves at the onset of ventricular isovolumetric relaxation.
6
Frank-Starling law of the heart
Increased ventricular end-diastolic volume (preload) stretches myocardial sarcomeres, increasing contraction force and stroke volume.
7
Primary pacemaker of the human heart
Sinoatrial (SA) node located in the right atrium (inherent pacing rate of 60-100 impulses per minute).
8
Bohr effect on hemoglobin
Increased PCO2, decreased pH (elevated [H+]), elevated temperature, and 2,3-BPG shift the oxygen dissociation curve rightward, promoting O2 unloading.
9
Primary form of CO2 transport in venous blood
Bicarbonate ions (HCO3-) dissolved in plasma (~70%), generated by erythrocyte carbonic anhydrase.
10
Pulmonary surfactant composition and function
Secreted by Type II pneumocytes (primarily dipalmitoylphosphatidylcholine); reduces alveolar surface tension to prevent collapse.
11
Gastric parietal cell secretions
Hydrochloric acid (HCl via H+/K+-ATPase) to denature proteins, and intrinsic factor essential for vitamin B12 absorption.
12
Cholecystokinin (CCK) physiological actions
Stimulates gallbladder contraction and pancreatic acinar enzyme secretion while relaxing the sphincter of Oddi.
13
Obligatory nephron water and solute reabsorption site
Proximal convoluted tubule (reabsorbs ~65-70% of filtered water and sodium, and ~100% of glucose and amino acids).
14
Loop of Henle countercurrent multiplier transporter
NKCC2 cotransporter (Na+-K+-2Cl-) in the thick ascending limb, which is impermeable to water.
15
Antidiuretic hormone (ADH / vasopressin) mechanism
Binds V2 receptors on principal cells, promoting insertion of aquaporin-2 channels into apical membranes to reabsorb water.
16
Renin secretion site and stimulus
Secreted by juxtaglomerular granular cells in response to decreased renal perfusion pressure or sympathetic stimulation.
17
Aldosterone site of action and effect
Acts on renal principal cells to upregulate ENaC channels and Na+/K+-ATPase, promoting Na+ retention and K+/H+ excretion.
18
Parathyroid hormone (PTH) physiological actions
Increases blood calcium by stimulating osteoclast bone resorption, enhancing renal Ca2+ reabsorption, and activating 1-alpha-hydroxylase.
19
Calcitonin origin and biological function
Produced by thyroid parafollicular C cells; inhibits osteoclastic bone resorption to lower serum calcium.
20
Insulin-dependent glucose transporter and target tissues
GLUT4, expressed primarily in skeletal muscle, cardiac muscle, and adipose tissue.
21
Hormones of the posterior pituitary (neurohypophysis)
Oxytocin and antidiuretic hormone (vasopressin), synthesized in hypothalamic supraoptic and paraventricular nuclei.
22
Trigger for human ovulation
Luteinizing hormone (LH) surge triggered by sustained high estradiol positive feedback from the mature follicle.
23
Primary inhibitory neurotransmitter of the brain
GABA (gamma-aminobutyric acid), acting via GABAA chloride channels (IPSP) and GABAB metabotropic receptors.
24
Phototransduction cascade in photoreceptor rods
Light isomerizes 11-cis-retinal to all-trans-retinal -> transducin activation -> PDE activation -> cGMP decrease -> CNG channel closure and hyperpolarization.
25
Endolymph ionic composition in the cochlea
Exceptionally high K+ concentration (~150 mM) with an endocochlear potential of +80 mV, causing K+ influx upon hair cell stereocilia deflection.
26
Only maternal antibody isotype that crosses the human placenta
Immunoglobulin G (IgG), via neonatal Fc receptors (FcRn) in the syncytiotrophoblast.
27
Secretory antibody protecting mucosal epithelia
Dimeric Immunoglobulin A (sIgA) joined by a J chain and secretory component.
28
MHC class I versus MHC class II antigen presentation
MHC class I presents endogenous cytosolic peptides to CD8+ cytotoxic T cells; MHC class II presents exogenous peptides to CD4+ helper T cells.
29
Universal start codon and amino acid specified
AUG, specifying methionine in eukaryotes (N-formylmethionine in prokaryotes).
30
Three stop (nonsense) codons in standard genetic code
UAA (ochre), UAG (amber), and UGA (opal); recognized by release factors rather than tRNAs.

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