mcat biology

Endocrine System

  • Endocrine signaling uses hormones through the blood.

  • The pituitary gland controls many endocrine functions.

  • The posterior pituitary releases ADH and oxytocin.

  • ADH increases water reabsorption in the kidneys.

  • Oxytocin stimulates uterine contractions and milk ejection.

  • Insulin generally stores fuel and lowers blood glucose.

  • Pathways that increase with insulin:

    • Glycolysis

    • Glycogenesis

    • Fat synthesis

  • Glucagon generally raises blood glucose and mobilizes fuel.

  • Pathways that increase with glucagon:

    • Glycogenolysis

    • Gluconeogenesis

    • Beta-oxidation

Muscular System

  • The three muscle types are skeletal, cardiac, and smooth.

  • Skeletal muscle is voluntary.

  • Calcium triggers muscle contraction.

  • Troponin binds calcium in skeletal muscle.

  • Neither filament shortens; sarcomeres shorten during contraction.

  • The functional unit of muscle is the sarcomere.

Nervous System

  • The two major divisions of the nervous system are central and peripheral nervous systems.

  • The sympathetic nervous system is responsible for the fight-or-flight response.

  • The parasympathetic nervous system is responsible for the rest-and-digest response.

  • Norepinephrine is the neurotransmitter most associated with sympathetic activity.

  • Acetylcholine is used at neuromuscular junctions.

  • Oligodendrocytes form myelin in the CNS.

  • Schwann cells form myelin in the PNS.

Cardiovascular System

  • Blood pressure equation: BP = CO × TPR.

  • Cardiac output equation: CO = HR × SV.

  • Stroke volume (SV) is calculated as SV = EDV − ESV.

  • Arterioles have the greatest pressure drop.

  • Capillaries have the greatest cross-sectional area.

  • Red blood cells primarily transport oxygen.

  • Platelets primarily assist in blood clotting.

  • Veins return blood to the heart.

  • Veins have the highest compliance.

Renal System

  • Major functions of kidneys:

    • Waste removal

    • Blood pressure regulation

    • Electrolyte balance

    • Acid-base balance

    • EPO production

    • Vitamin D activation

  • Inulin is filtered but not reabsorbed.

  • PAH is filtered and secreted.

  • The first structure to filter blood in the nephron is the glomerulus.

  • Nephron flow order: Bowman’s capsule → PCT → Loop of Henle → DCT → Collecting duct.

  • In the descending loop of Henle, water reabsorption occurs.

  • In the ascending loop of Henle, salt reabsorption occurs.

  • Aldosterone increases sodium reabsorption.

Metabolism

  • Glycolysis occurs in the cytosol.

  • The TCA cycle occurs in the mitochondrial matrix.

  • The final electron acceptor in the ETC is oxygen.

  • Glycolysis produces 2 ATP and NADH.

  • Beta-oxidation breaks down fatty acids.

  • Ketogenesis produces ketone bodies.

  • The pentose phosphate pathway makes NADPH.

  • NADH enters Complex I of the ETC.

  • FADH2 enters Complex II of the ETC.