INI CET Physiology Syllabus

Describe the synthesis and actions of thyroid hormones.

The thyroid uses iodine and tyrosine to make T4 (thyroxine) and T3 (more active), stored on thyroglobulin. They increase basal metabolic rate and heat production and are essential for growth and CNS development. Regulated by TSH and TRH with negative feedback. Calcitonin (parafollicular C cells) lowers blood calcium.

Compare the actions of parathyroid hormone and calcitonin on calcium.

PTH raises blood calcium: stimulates osteoclastic bone resorption, increases renal Ca2+ reabsorption and phosphate excretion, and activates vitamin D to enhance gut Ca2+ absorption. Calcitonin (thyroid C cells) lowers blood calcium by inhibiting osteoclasts. PTH is the dominant regulator.

Name the hormones of the adrenal cortex and medulla and their functions.

Cortex: zona glomerulosa - aldosterone (mineralocorticoid: Na+ retention, K+ excretion); zona fasciculata - cortisol (glucocorticoid: gluconeogenesis, anti-inflammatory); zona reticularis - androgens. Medulla: epinephrine and norepinephrine (catecholamines: fight-or-flight response).

Which pancreatic islet cells secrete which hormones and what are their effects?

Beta cells secrete insulin (lowers blood glucose: promotes glucose uptake, glycogenesis, lipogenesis). Alpha cells secrete glucagon (raises blood glucose: glycogenolysis, gluconeogenesis). Delta cells secrete somatostatin (inhibits insulin and glucagon). PP cells secrete pancreatic polypeptide.

Outline the hypothalamic-pituitary-gonadal axis in reproduction.

Hypothalamic GnRH stimulates the anterior pituitary to release FSH and LH. In males, LH stimulates testosterone from Leydig cells and FSH supports Sertoli cell spermatogenesis. In females, FSH/LH drive follicle development, estrogen/progesterone secretion, and ovulation, with feedback regulation.

How is hormone secretion regulated?

Mainly by negative feedback (rising hormone or its effect inhibits further release, e.g. cortisol on CRH/ACTH); occasionally positive feedback (the LH surge before ovulation; oxytocin in labor). Control inputs are humoral (blood metabolite levels), hormonal (tropic hormones), and neural.

Describe the flow of blood through the chambers and valves of the heart.

Systemic venous blood enters the right atrium -> tricuspid valve -> right ventricle -> pulmonary (semilunar) valve -> pulmonary artery -> lungs. Oxygenated blood returns to the left atrium -> mitral (bicuspid) valve -> left ventricle -> aortic (semilunar) valve -> aorta to the body.

Describe the cardiac conduction system and pacemaker.

Impulses originate in the SA node (natural pacemaker, ~60-100/min), spread through the atria, reach the AV node (which delays conduction), then the bundle of His, right and left bundle branches, and Purkinje fibers, causing ventricular contraction. The SA node sets heart rate via spontaneous depolarization.

Define cardiac output, give its formula, and state the Frank-Starling law.

Cardiac output (CO) = heart rate x stroke volume (~5 L/min at rest); stroke volume depends on preload, afterload, and contractility. The Frank-Starling law states that greater stretch (end-diastolic volume/preload) within limits increases the force of contraction and stroke volume, letting the heart match output to venous return.

How does the baroreceptor reflex regulate blood pressure?

Baroreceptors in the carotid sinus and aortic arch sense arterial stretch. A rise in BP increases their firing, prompting the medullary cardiovascular center to raise parasympathetic and lower sympathetic output - reducing heart rate, contractility, and vasoconstriction. A fall in BP does the opposite. It is a rapid short-term regulator.

Compare the structure and function of arteries, capillaries, and veins.

Arteries have thick elastic/muscular walls to withstand high pressure; arterioles are the main resistance vessels. Capillaries are single endothelial layers for exchange of gases and nutrients. Veins are thin-walled, high-capacitance vessels with valves that act as a blood reservoir and return blood to the heart.

State Poiseuille's law and the dominant determinant of vascular resistance.

Flow is proportional to (pressure difference x radius^4) / (viscosity x length). Because resistance varies with the fourth power of the radius, vessel radius (vasoconstriction/dilation) is by far the most important determinant of resistance and blood flow.

Trace the path of air through the conducting and respiratory portions of the lung.

Conducting zone (no gas exchange): nose/pharynx -> larynx -> trachea -> bronchi -> bronchioles -> terminal bronchioles. Respiratory zone (gas exchange): respiratory bronchioles -> alveolar ducts -> alveolar sacs -> alveoli, where gas exchange occurs with pulmonary capillaries.

Explain the mechanics of quiet inspiration and expiration.

Inspiration is active: the diaphragm and external intercostals contract, expanding the thorax, lowering intrapleural pressure, so air flows in (Boyle's law - volume up, pressure down). Quiet expiration is passive: muscles relax and elastic recoil of the lungs decreases volume, raising pressure and expelling air.

Define tidal volume, vital capacity, and residual volume.

Tidal volume (TV): air moved per normal breath (~500 mL). Vital capacity (VC): maximum exhaled after maximum inhalation (TV + IRV + ERV, ~4800 mL). Residual volume (RV): air remaining after maximal expiration (~1200 mL) that cannot be exhaled and keeps alveoli open.

How are oxygen and carbon dioxide transported in the blood?

Oxygen: ~98% bound to hemoglobin as oxyhemoglobin, ~2% dissolved in plasma. Carbon dioxide: ~70% as bicarbonate (HCO3-) via the chloride shift, ~23% bound to hemoglobin as carbaminohemoglobin, ~7% dissolved. Gas exchange occurs by diffusion down partial pressure gradients.

How is respiration regulated by neural and chemical mechanisms?

Neural: the medullary respiratory centers (dorsal and ventral groups) set the basic rhythm, modulated by the pontine centers. Chemical: central chemoreceptors (medulla) respond mainly to CSF CO2/H+, and peripheral chemoreceptors (carotid and aortic bodies) respond to low O2, high CO2, and low pH - a rise in CO2 is the most powerful stimulus to breathe.

Describe the functional structure of the nephron.

The nephron is the functional unit of the kidney: a renal corpuscle (glomerulus + Bowman's capsule) filters blood, followed by the proximal convoluted tubule, loop of Henle (descending and ascending limbs), distal convoluted tubule, and collecting duct, which process filtrate into urine.

What are the three basic processes of urine formation?

Glomerular filtration (plasma filtered into Bowman's capsule), tubular reabsorption (useful substances - glucose, water, ions - returned to blood, mainly in the proximal tubule), and tubular secretion (wastes and ions like H+, K+, and drugs actively moved from blood into the tubule).

Define glomerular filtration rate (GFR) and the forces that determine it.

GFR is the volume of filtrate formed by both kidneys per minute (~125 mL/min). Net filtration pressure = glomerular capillary hydrostatic pressure - (Bowman's capsule hydrostatic pressure + glomerular oncotic pressure). GFR depends on these Starling forces and the filtration coefficient.

How are renal blood flow and GFR autoregulated?

Autoregulation keeps GFR stable over a wide range of arterial pressures via the myogenic mechanism (the afferent arteriole constricts when stretched by high pressure) and tubuloglomerular feedback (the macula densa senses distal tubular NaCl and adjusts afferent arteriolar tone). The renin-angiotensin system also modulates it.

How do the kidneys and lungs regulate acid-base balance?

Lungs give rapid control by altering CO2 elimination (more ventilation lowers CO2 and raises pH). Kidneys give slower but powerful control by excreting H+ and reabsorbing/generating bicarbonate (HCO3-). With chemical buffers (bicarbonate, phosphate, proteins) they keep blood pH at 7.35-7.45.

What digestive enzymes break down carbohydrates, proteins, and fats?

Carbohydrates: salivary and pancreatic amylase, plus brush-border disaccharidases. Proteins: pepsin (stomach) and pancreatic proteases (trypsin, chymotrypsin), then peptidases. Fats: lingual/gastric lipase and pancreatic lipase, aided by bile salts that emulsify fat.

How are gastrointestinal functions regulated, including the key GI hormones?

By neural control (the enteric nervous system plus autonomic input; parasympathetic stimulates, sympathetic inhibits) and hormonal control: gastrin (stimulates gastric acid), secretin (stimulates pancreatic bicarbonate), cholecystokinin/CCK (stimulates enzymes, bile release, gallbladder contraction), and GIP.

List the major physiological functions of the liver.

Carbohydrate metabolism (glycogen storage, gluconeogenesis), protein metabolism (plasma proteins, urea from ammonia), lipid metabolism, bile production (fat emulsification), detoxification of drugs/toxins, storage of vitamins and iron, and clotting factor synthesis.

Compare skeletal, cardiac, and smooth muscle.

Skeletal: striated, multinucleated, voluntary, attached to bones. Cardiac: striated, branched, involuntary, with intercalated discs and gap junctions forming a functional syncytium with autorhythmicity. Smooth: non-striated, spindle-shaped, single nucleus, involuntary, in walls of viscera and vessels.

Describe the sliding filament theory and excitation-contraction coupling at the neuromuscular junction.

ACh from the motor neuron binds nicotinic receptors at the neuromuscular junction, depolarizing the fiber; the impulse travels down T-tubules and triggers Ca2+ release from the sarcoplasmic reticulum. Ca2+ binds troponin, shifting tropomyosin to expose actin sites. Myosin cross-bridges then bind actin and pivot, sliding thin filaments inward and shortening the sarcomere; ATP and Ca2+ drive the cross-bridge cycle.

Describe phototransduction and the visual pathway.

Light strikes photoreceptors (rods for dim/black-and-white vision, cones for color and acuity); it bleaches photopigment (rhodopsin), hyperpolarizing the cell. Signals pass to bipolar then ganglion cells, whose axons form the optic nerve -> optic chiasm (partial decussation) -> optic tract -> lateral geniculate nucleus -> visual cortex.

Explain how sound is transduced into a neural signal in the ear.

Sound waves vibrate the tympanic membrane; the ossicles (malleus, incus, stapes) amplify and transmit them to the oval window; fluid waves in the cochlea move the basilar membrane; hair cells of the organ of Corti bend against the tectorial membrane, opening ion channels and generating signals carried by the cochlear nerve (CN VIII) to the auditory cortex.

How does the vestibular apparatus maintain balance and equilibrium?

The vestibular apparatus of the inner ear detects head position and motion: the three semicircular canals sense rotational (angular) acceleration via hair cells in the cristae, while the otolith organs (utricle and saccule) sense linear acceleration and gravity via hair cells in the maculae. Signals travel through the vestibular branch of CN VIII.