One question at a time. Build your PA-CAT understanding.
First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.
Continue in the practice tool above to load more questions, 50 at a time.
In the standard anatomical position, the body is upright with the face forward, upper limbs at the sides, and palms facing anteriorly. This posture provides a consistent reference for describing direction and location in anatomy.
The acetabulum is the hip socket formed by the ilium, ischium, and pubis, and it receives the head of the femur. The tibia and fibula form the knee and ankle regions, while the sacrum articulates with the ilium at the sacroiliac joint.
The right lung normally has superior, middle, and inferior lobes separated by the oblique and horizontal fissures. The left lung typically has two lobes because the cardiac notch reduces its anterior volume.
The brachialis inserts on the ulna and flexes the elbow regardless of forearm pronation or supination. The triceps brachii extends the elbow, while the deltoid and latissimus dorsi act mainly at the shoulder.
The calcaneus is the largest tarsal bone and forms the heel, transmitting body weight to the ground. The talus sits above it and articulates with the tibia to form the ankle joint.
The optic nerve, cranial nerve II, carries special sensory fibers from the retina to the brain for vision. The oculomotor nerve is mainly motor to extraocular muscles, while the trigeminal and facial nerves serve other sensory and motor functions.
The diaphragm is a dome-shaped muscle that forms the floor of the thoracic cavity and the roof of the abdominal cavity. The pleura surrounds the lungs, the pericardium surrounds the heart, and the mesentery supports abdominal organs.
The supraspinatus initiates the first 15 degrees of shoulder abduction before the deltoid becomes the dominant abductor. The other rotator cuff muscles mainly stabilize the humeral head and contribute to rotation.
The median nerve supplies the thenar muscles, including opponens pollicis, through its recurrent branch, so lesions at the wrist impair thumb opposition. Finger and wrist extension are radial nerve functions, and little finger abduction is ulnar nerve function.
The mitral valve is best heard at the cardiac apex, which lies near the left fifth intercostal space at the midclavicular line. The right second space is the aortic area, the left second space is the pulmonic area, and the lower left sternal border is the tricuspid area.
The portal triad consists of the portal vein, proper hepatic artery, and bile duct traveling together within portal tracts. The central vein lies at the center of a hepatic lobule, and hepatic veins drain blood toward the inferior vena cava.
The proximal tubule reabsorbs roughly two-thirds of filtered sodium and water and is the major site of reabsorption. The descending limb is mainly water permeable, while the distal tubule and collecting duct fine-tune sodium and water balance under hormonal control.
The anterior cruciate ligament prevents anterior displacement of the tibia relative to the femur and limits hyperextension. The posterior cruciate ligament resists posterior translation, while the collateral ligaments resist varus and valgus stresses.
The masseter is a major elevator of the mandible and works with the temporalis and medial pterygoid during jaw closure. The digastric depresses the mandible, while the platysma and orbicularis oris act on the neck and lips.
The radial nerve runs in the spiral groove of the humerus and supplies the wrist extensors; injury therefore causes wrist drop. The median and ulnar nerves mainly affect hand function, and the axillary nerve supplies the deltoid.
The foramen ovale transmits the mandibular division of the trigeminal nerve, along with the accessory meningeal artery and lesser petrosal nerve. The optic nerve passes through the optic canal, the facial nerve runs in the facial canal, and the maxillary division exits through the foramen rotundum.
The left lung has a cardiac notch on its anterior border that accommodates the heart. The right lung lacks this notch and is divided into three lobes by the oblique and horizontal fissures.
Each brachiocephalic vein forms behind the sternoclavicular joint from the internal jugular vein and the subclavian vein. The external jugular vein typically drains into the subclavian vein, and the axillary vein continues as the subclavian vein.
In most people, the atrioventricular node is supplied by a nodal branch from the right coronary artery, reflecting right coronary dominance. The left anterior descending artery mainly supplies the anterior ventricles and septum, while the circumflex supplies lateral and left atrial regions.
The superior gluteal nerve supplies the gluteus medius and gluteus minimus, which stabilize the pelvis during single-leg stance. Injury produces a Trendelenburg sign with pelvic drop on the unsupported side.
The phrenic nerve arises mainly from cervical roots C3, C4, and C5 and provides motor innervation to the diaphragm. This cervical origin explains why diaphragm function can be affected by neck or upper cervical spinal cord injury.
Broca's area lies in the inferior frontal gyrus of the dominant hemisphere and is usually supplied by branches of the middle cerebral artery. The anterior cerebral artery supplies medial frontal and parietal regions, while the posterior cerebral artery supplies occipital and inferior temporal regions.
The femoral triangle is bounded by the inguinal ligament superiorly, the sartorius muscle laterally, and the adductor longus muscle medially. The iliopsoas and pectineus form part of the floor rather than the medial border.
The resting membrane potential is dominated by the potassium concentration gradient and the high resting permeability of potassium leak channels. The Na+/K+ ATPase maintains the sodium and potassium gradients that underlie this potential. Voltage-gated calcium channels and ligand-gated sodium channels are largely closed at rest.
Motor neurons release acetylcholine at the neuromuscular junction, where it binds nicotinic receptors on the motor end plate. This produces an end-plate potential that initiates muscle excitation. Norepinephrine, dopamine, and GABA serve different signaling roles.
Surfactant reduces surface tension at the air-liquid interface, which increases lung compliance and helps prevent small alveoli from collapsing at end expiration. Without sufficient surfactant, alveoli become unstable and ventilation becomes inefficient. Surfactant does not primarily alter airway resistance or promote alveolar fluid secretion.
Insulin promotes translocation of GLUT4 transporters to the membranes of skeletal muscle and adipose cells, increasing glucose uptake. It also stimulates glycogen synthesis and inhibits hepatic glucose production. These actions together lower blood glucose after a meal.
Sinoatrial nodal cells undergo spontaneous phase 4 depolarization, driven largely by the funny current and calcium currents, which brings them to threshold automatically. This intrinsic automaticity sets the heart rate under normal conditions. A prolonged plateau phase is characteristic of ventricular contractile cells, not the SA node.
The proximal convoluted tubule reabsorbs about two-thirds of filtered sodium and water, making it the dominant site of renal reabsorption. This bulk reabsorption is coupled to active sodium transport and is relatively unregulated compared with later segments. The loop of Henle, distal tubule, and collecting duct handle smaller and more finely regulated fractions.
Chief cells in the gastric glands secrete pepsinogen, which is converted to active pepsin in the acidic environment of the stomach. Parietal cells secrete hydrochloric acid and intrinsic factor, while G cells secrete gastrin. Mucous neck cells secrete mucus that helps protect the gastric lining.
Plasma albumin is the main determinant of plasma oncotic pressure, which opposes glomerular filtration. When albumin is low, this opposing force decreases, so net filtration pressure and glomerular filtration rate tend to rise. Changes in capsular hydrostatic pressure are not caused directly by hypoalbuminemia.
The ventricular plateau reflects a balance between slow inward calcium current through L-type channels and outward potassium current. This prolonged depolarization extends the refractory period and supports coordinated contraction. The rapid inward sodium current is responsible for the initial upstroke, not the plateau.
Hyperventilation increases alveolar ventilation and removes carbon dioxide faster than it is produced, lowering arterial PCO2. Because CO2 forms carbonic acid, a fall in PCO2 reduces hydrogen ion concentration and raises pH, producing respiratory alkalosis. The expected pattern is therefore low PCO2 with high pH.
Sympathetic stimulation increases heart rate through beta-adrenergic effects on the SA node and conducting system. It also relaxes airway smooth muscle through beta-2 receptors, producing bronchodilation and reducing airway resistance. This combination supports greater oxygen delivery during exercise.
Chronic hypoxemia increases red blood cell 2,3-BPG, which shifts the oxyhemoglobin dissociation curve to the right. A rightward shift lowers hemoglobin oxygen affinity and enhances oxygen unloading at tissues. Leftward shifts and reduced erythropoietin would impair adaptation to altitude.
Aldosterone increases sodium reabsorption in the distal convoluted tubule and collecting duct while promoting potassium secretion into the tubular lumen. It achieves this by increasing expression and activity of epithelial sodium channels and the Na+/K+ ATPase. The net effect expands extracellular fluid volume and increases potassium excretion.
Alveolar ventilation equals the difference between tidal volume and dead space multiplied by respiratory rate. Here, (500 mL - 150 mL) × 12 breaths/min = 350 mL × 12 = 4,200 mL/min. This represents the volume of fresh air reaching alveoli each minute.
Constriction of the afferent arteriole reduces renal blood flow into the glomerulus and lowers glomerular capillary hydrostatic pressure. Because glomerular capillary pressure is the main driving force for filtration, GFR decreases. Efferent arteriolar constriction can help maintain pressure, but it is not the immediate effect of afferent constriction.
Thyroid hormones normally exert negative feedback on the hypothalamus and anterior pituitary, reducing TRH and TSH secretion. Exogenous thyroid hormone raises circulating levels and suppresses TSH through this same mechanism. Positive feedback and direct TSH stimulation would increase rather than suppress TSH.
ATP is needed for myosin heads to detach from actin during cross-bridge cycling and for the sarcoplasmic reticulum calcium pump to resequest calcium during relaxation. Without ATP, cross-bridges remain attached and muscle enters rigor. Calcium binding to troponin itself does not directly consume ATP.
Net filtration pressure equals capillary hydrostatic pressure minus interstitial hydrostatic pressure minus plasma oncotic pressure. With the given values, 35 - 0 - 25 = 10 mmHg. The positive value favors movement of fluid out of the capillary.
The loop of Henle creates a steep medullary osmotic gradient through countercurrent multiplication, and the vasa recta help preserve it. ADH then allows water reabsorption from the collecting duct along this gradient, concentrating the urine. Cortical blood flow and proximal NaCl secretion do not establish the medullary gradient.
Stretch of the carotid sinus increases baroreceptor firing and signals the medullary cardiovascular centers. The reflex increases parasympathetic vagal outflow to the heart and reduces sympathetic outflow to vessels. This lowers heart rate and promotes vasodilation, helping restore blood pressure toward normal.
In primary adrenal insufficiency, the adrenal cortex cannot produce enough cortisol, so cortisol negative feedback on the hypothalamus and anterior pituitary is lost. CRH and ACTH secretion therefore increase as the axis attempts to stimulate the adrenal glands. ACTH is produced by the anterior pituitary, not the adrenal cortex.
A rightward shift means hemoglobin releases oxygen more readily at a given PO2, which enhances unloading at tissues. The shift changes affinity, not the maximum amount of oxygen that hemoglobin can carry. Maximum carrying capacity depends mainly on hemoglobin concentration and saturation.
In metabolic acidosis, increased ventilation lowers arterial PCO2 and reduces the fall in pH. Appropriate compensation therefore shows low bicarbonate with low PCO2 and a pH moving back toward normal. A high PCO2 would worsen the acidosis rather than compensate for it.
Cysteine has a -CH2SH side chain, and two cysteine residues can oxidize to form a cystine disulfide bridge. This covalent link helps stabilize tertiary and quaternary protein structure. Serine and threonine contain hydroxyl groups, whereas methionine contains a thioether.
Primary structure is the sequence of amino acids joined by peptide bonds. Secondary structure refers to local patterns such as alpha helices and beta sheets, tertiary structure is the overall three-dimensional fold, and quaternary structure involves assembly of multiple polypeptide subunits.
Km is the substrate concentration at which the reaction velocity is half of Vmax. It is an inverse indicator of enzyme affinity for substrate under standard assumptions. Vmax itself is the maximal velocity at saturating substrate.
Phosphofructokinase-1 catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate, the committed and rate-limiting step of glycolysis. It is allosterically regulated by ATP, citrate, AMP, and fructose-2,6-bisphosphate.