Human Anatomy & Physiology: The Endocrine and Cardiovascular Systems

Comprehensive vocabulary flashcards covering the Endocrine System, Heart Anatomy and Electrophysiology, Cardiac Cycle, and Vascular Mechanics from Human Anatomy & Physiology.

Exocrine Glands

Glands that feature ducts through which secretions are transported onto body surfaces, predominantly multicellular in nature with unicellular exceptions.

Endocrine Glands

Ductless glandular units that secrete chemical signaling molecules (hormones) directly into the blood for systemic transport.

Target Cells

Specific cells that express compatible receptors for a circulating hormone and alter their activity upon binding.

Up-regulation

The mechanism whereby target cells synthesize and display an increased number of receptors in response to low circulating levels of a hormone.

Down-regulation

The mechanism whereby target cells decrease their receptor density in response to persistently high hormone levels, desensitizing the cells to overreaction.

Permissiveness

A hormonal interaction wherein one hormone cannot fully exert its biological actions unless a second hormone is simultaneously present.

Synergism

A hormonal interaction in which more than one hormone exerts the same physiological effect on a target cell, resulting in an amplified combined response.

Antagonism

A hormonal interaction wherein one hormone opposes or reverses the action of another hormone on target tissues.

Oxytocin

A water-soluble posterior pituitary hormone that utilizes $PIP_2\text{-Calcium}$ signaling to stimulate uterine contractions during childbirth and trigger milk letdown during nursing.

Antidiuretic Hormone (ADH)

A water-soluble hormone released by the posterior pituitary when hypothalamic osmoreceptors detect elevated solute concentrations, targeting kidney tubules to reabsorb water.

Diabetes Insipidus

A homeostatic imbalance resulting from hyposecretion or deficiency of ADH caused by hypothalamic or posterior pituitary damage, marked by severe dehydration, intense thirst, and massive polyuria.

Thyroid-Stimulating Hormone (TSH)

A water-soluble anterior pituitary tropic hormone released under the influence of TRH that stimulates the normal growth and secretory activity of the thyroid gland.

Adrenocorticotropic Hormone (ACTH)

An anterior pituitary hormone stimulated by CRH with a morning circadian peak that prompts the adrenal cortex to secrete corticosteroids, particularly glucocorticoids.

Prolactin (PRL)

An anterior pituitary hormone regulated by prolactin-inhibiting hormone and estrogen levels that stimulates lactation and milk synthesis in female mammary tissue.

Isthmus

The central, median tissue mass connecting the right and left lateral lobes of the thyroid gland across the anterior trachea.

Follicular Cells

Epithelial cells forming the walls of thyroid follicles that synthesize and secrete thyroid hormone ($\text{TH}$).

Parafollicular Cells

Endocrine cells located in the loose connective tissue between thyroid follicles that synthesize and secrete calcitonin in response to hypercalcemia.

Graves' Disease

An autoimmune hyperthyroid condition wherein abnormal antibodies mimic TSH to overstimulate thyroid follicular cells, causing elevated metabolic rate, weight loss, and exophthalmos.

Calcitonin

A water-soluble polypeptide hormone released by parafollicular cells in response to high blood $Ca^{2+}$ levels that acts as an antagonist to PTH by inhibiting osteoclasts.

Parathyroid Hormone (PTH)

The primary water-soluble regulator of blood calcium homeostasis, released by parathyroid cells during hypocalcemia to stimulate bone osteoclasts, renal calcium reabsorption, and intestinal absorption.

Zona Glomerulosa

The outermost layer of the adrenal cortex containing spherical cell clusters that synthesizes mineralocorticoids, predominantly aldosterone.

Zona Fasciculata

The thick middle layer of the adrenal cortex arranged in linear cell cords that synthesizes glucocorticoids, primarily cortisol.

Zona Reticularis

The innermost layer of the adrenal cortex bordering the adrenal medulla that synthesizes gonadocorticoids (adrenal sex hormones).

Aldosterone

A lipid-soluble mineralocorticoid that acts for approximately $20\,\text{min}$ to enhance renal tubule reabsorption of $Na^+$ and water while stimulating the secretion of $K^+$.

Renin-Angiotensin-Aldosterone System (RAAS)

An endocrine cascade triggered by reduced renal perfusion wherein renin cleaves angiotensinogen into angiotensin I, which is converted to angiotensin II to promote aldosterone release, vasoconstriction, and fluid retention.

Melatonin

An amine hormone secreted by the pineal gland in the epithalamus that regulates sleep/wake cycles, peaking in concentration during the night and declining to a minimum around noon.

Acinar Cells

Exocrine secretory cells comprising the bulk of the pancreas that synthesize and secrete enzyme-rich digestive juices into ducts.

Pancreatic Islets (Islets of Langerhans)

Microscopic clusters of endocrine cells within the pancreas containing alpha cells (which produce glucagon) and beta cells (which produce insulin).

Glucagon

A hyperglycemic hormone released by pancreatic alpha cells in response to low blood glucose or sympathetic signals that stimulates liver glycogenolysis and gluconeogenesis.

Insulin

A hypoglycemic hormone secreted by pancreatic beta cells as proinsulin that promotes glucose uptake by mobilising GLUT 4 transporters into plasma membranes while suppressing glycogenolysis and gluconeogenesis.

Osteocalcin

A hormone secreted by bone osteoblasts that stimulates pancreatic beta cells to produce insulin, enhances insulin sensitivity, and restricts adipose storage.

Cardiac Skeleton

A network of dense connective tissue fibers that anchors heart valves, reinforces the myocardium, and electrically isolates the atria from the ventricles.

Fossa Ovalis

An oval depression located on the interatrial septum representing the adult remnant of the fetal foramen ovale.

Coronary Sinus

A wide venous vessel located on the posterior aspect of the heart that collects deoxygenated blood from the coronary cardiac veins and empties into the right atrium.

Pectinate Muscles

Parallel, comb-like muscular ridges lining the anterior internal wall of the right atrium and extending into the auricles.

Crista Terminalis

A C-shaped muscular ridge in the right atrium that demarcates the smooth-walled posterior section from the pectinate-lined anterior section.

Semilunar (SL) Valves

Three-cusp pocket-like valves situated at the bases of the pulmonary trunk and aorta that prevent blood backflow into the ventricles during diastole.

Angina Pectoris

Transient thoracic pain resulting from a temporary deficiency in myocardial blood supply and oxygenation without leading to immediate permanent infarction.

Myocardial Infarction

Ischemic necrosis and cellular death in myocardial tissue resulting from prolonged coronary arterial occlusion, repaired by noncontractile fibrous scar tissue.

Endomysium

The delicate connective tissue matrix filling intercellular spaces around cardiac myocytes, connecting them to the cardiac skeleton and supporting an extensive capillary bed.

Sinoatrial (SA) Node

The primary physiological pacemaker situated in the right atrial wall that generates action potentials at the fastest spontaneous intrinsic rate.

Purkinje Fibers

Specialized autorhythmic myocardial conduction fibers that distribute depolarizing impulses across the apex and outer ventricular walls to trigger ventricular contraction.

Cardioacceleratory Center

A medullary cardiovascular reflex center that transmits sympathetic impulses down the spinal cord to increase heart rate and myocardial contractility.

Cardioinhibitory Center

A medullary cardiovascular reflex center that transmits parasympathetic impulses via the vagus nerve to slow firing of the SA and AV nodes.

Electrocardiogram (ECG)

A graphic composite tracing of all electrical currents generated throughout the heart during a given period, detected using external recording electrodes.

Cardiac Cycle

The complete series of mechanical, pressure, and volume changes involving both atrial and ventricular systole and diastole during a single heartbeat.

Systole

The phase of the cardiac cycle during which heart chambers actively contract and pump blood into adjacent chambers or great vessels.

Diastole

The phase of the cardiac cycle during which heart chambers relax and fill with blood.

End Diastolic Volume (EDV)

The total volume of blood contained within each ventricle at the end of ventricular diastole, just before contraction commences.

End Systolic Volume (ESV)

The residual volume of blood remaining inside each ventricle at the end of ventricular systole, following the ejection phase.

Cardiac Output (CO)

The volume of blood pumped out by each ventricle every minute, defined by the product of heart rate and stroke volume ($\text{CO} = \text{HR} \times \text{SV}$).

Stroke Volume (SV)

The volume of blood ejected from a single ventricle with each contraction, calculated mathematically as $\text{SV} = \text{EDV} - \text{ESV}$.

Frank-Starling Law of the Heart

The physiological principle stating that increased venous return distends ventricular muscle fibers (increasing preload/EDV), resulting in an elevated stroke volume.

Afterload

The opposing arterial back pressure exerted against semilunar valves (approximately $80\,\text{mm Hg}$ in the aorta) that ventricles must overcome to eject blood.

Elastic Arteries

Large-diameter, thick-walled conducting vessels possessing abundant elastin in all tunics that expand and recoil to act as pressure reservoirs smoothing blood flow.

Muscular Arteries

Medium-sized distributing arteries possessing the thickest tunica media of smooth muscle that are actively involved in vasoconstriction to direct blood flow to organs.

Arterioles

The smallest arterial vessels that function as resistance vessels, controlling blood distribution into capillary beds via smooth muscle vasodilation and vasoconstriction.

Vascular Anastomoses

Interconnections between adjacent blood vessels providing collateral circulatory pathways to ensure uninterrupted tissue perfusion if a vessel becomes occluded.

Mean Arterial Pressure (MAP)

The average pressure driving blood into tissues throughout the cardiac cycle, calculated as diastolic pressure plus one-third of the pulse pressure ($\text{MAP} = \text{diastolic} + \frac{1}{3}\text{pulse pressure}$).

Atheroma

A fibrofatty plaque formed in the tunica intima following endothelial injury, marked by lipid accumulation, foam cell formation, smooth muscle migration, and calcification.

Circulatory Shock

A clinical state characterized by inadequate filling of blood vessels and impaired circulation, leading to severe cellular hypoxia, tissue damage, and organ failure.

Capillary Hydrostatic Pressure

The physical fluid pressure exerted by blood against the internal capillary wall, which drives fluid and solutes out of the capillary into the interstitial space.

Colloid Osmotic Pressure

The osmotic pulling force exerted by nondiffusible plasma proteins within capillary blood that draws interstitial fluid back into the vascular lumen.