Human Anatomy and Physiology: Blood, Endocrine, Heart, and Vessels

Comprehensive vocabulary flashcards covering the blood, endocrine system, heart, and circulatory blood vessels based on Marieb Human Anatomy & Physiology (12th Edition).

Hematocrit

The percentage of total blood volume composed of red blood cells, normally $47\% \pm 5\%$ in males and $42\% \pm 5\%$ in females.

Albumin

The most abundant plasma protein (60%), produced by the liver, which acts as a blood buffer, transport carrier, and primary contributor to plasma osmotic pressure.

Erythrocyte Structure

Anucleate, biconcave discs measuring $7.5\,\mu m$ in diameter and $2.5\,\mu m$ in thickness, filled with hemoglobin and structurally optimized for rapid gas exchange.

Hemoglobin

A red, iron-bearing protein inside erythrocytes responsible for gas transport, consisting of four globin polypeptide chains each bound to a central heme group containing an iron ion.

Erythropoietin (EPO) Mechanism

A hormonal homeostatic feedback loop where hypoxia stimulates kidney cells to release erythropoietin, which acts on red bone marrow to accelerate erythrocyte maturation.

Neutrophil

The most abundant leukocyte (50–70%), characterized by a 3–6 lobed nucleus and granules containing hydrolytic enzymes and defensins, functioning as phagocytic bacteria slayers.

Eosinophil

A granulocyte (2–4% of WBCs) with a bilobed nucleus and coarse red cytoplasmic granules that release digestive enzymes to counteract parasitic worms.

Basophil

The rarest leukocyte (0.5–1%), featuring a U- or S-shaped nucleus and purplish-black granules loaded with histamine, an inflammatory vasodilator.

Lymphocyte

An agranulocyte (25% of WBCs) with a large circular dark-purple nucleus and thin rim of pale-blue cytoplasm, operating via T cells and B cells to execute adaptive immune responses.

Monocyte

The largest leukocyte (3–8% of WBCs), featuring a U- or kidney-shaped nucleus; leaves blood circulation to differentiate into a highly phagocytic macrophage.

Platelets

Discoid cytoplasmic fragments of megakaryocytes containing purple granules with clotting factors, serotonin, ADP, and $Ca^{2+}$, active in plug formation and blood clotting.

Hemostasis

A rapid, localized sequence of steps that halts bleeding after blood vessel injury, consisting of vascular spasm, platelet plug formation, and coagulation.

Coagulation Cascade (Phase 1)

The complex pathway involving intrinsic or extrinsic procoagulant activation that converges on activating factor $X_a$, which forms prothrombin activator with factor $V_a$, $Ca^{2+}$, and phospholipids.

ABO Blood Antigens

Specific surface glycoprotein agglutinogens (A and B) on erythrocyte membranes that determine blood type and trigger immune responses if transfused into an incompatible recipient.

Autocrines vs. Paracrines

Local chemical messengers not considered part of the endocrine system; autocrines affect the same cell that secretes them, whereas paracrines affect nearby cells within the same tissue.

Water-Soluble vs. Lipid-Soluble Hormones

Water-soluble hormones (amino acid-based except thyroid hormone) act on extracellular plasma membrane receptors using second messengers; lipid-soluble hormones (steroids and thyroid hormone) cross membranes to bind intracellular receptors and directly activate genes.

Cyclic AMP (cAMP) Signaling Mechanism

A second-messenger cascade where a hormone binds a membrane receptor, activates a G protein, stimulates adenylate cyclase to convert ATP to cAMP, and activates protein kinases.

Permissiveness

A type of hormonal interaction in which one hormone cannot exert its full physiological effect unless another specific hormone is concurrently present.

Hypophyseal Portal System

A specialized vascular connection between the hypothalamus and anterior pituitary consisting of primary capillaries, portal veins, and secondary capillaries that transports releasing and inhibiting hormones.

Growth Hormone (GH)

An anterior pituitary hormone that exerts direct anti-insulin metabolic effects (raising blood glucose and lipolysis) and indirect growth-promoting actions via liver-derived insulin-like growth factors (IGFs).

Thyroid Hormone ($T_4$ and $T_3$)

Iodine-containing metabolic amine hormones synthesized by thyroid follicular cells that enter target nuclei to increase basal metabolic rate, calorigenesis, and normal tissue growth.

Parathyroid Hormone (PTH)

The primary regulator of blood calcium homeostasis, secreted by parathyroid glands during hypocalcemia to stimulate osteoclast activity, renal $Ca^{2+}$ reabsorption, and activation of vitamin D.

Aldosterone

The principal mineralocorticoid from the adrenal cortex (zona glomerulosa) that acts on renal tubules to stimulate $Na^+$ reabsorption and $K^+$ secretion, elevating blood volume and pressure.

Cortisol

The primary glucocorticoid from the adrenal cortex (zona fasciculata) that facilitates energy mobilization during long-term stress by promoting gluconeogenesis, lipolysis, and protein breakdown.

Insulin

A hypoglycemic peptide hormone secreted by pancreatic beta cells in response to elevated blood glucose that promotes glucose uptake into tissue cells, glycolysis, and glycogen synthesis.

Diabetes Mellitus

A metabolic disorder caused by insulin deficiency (Type 1) or target cell resistance (Type 2), presenting with polyuria, polydipsia, and polyphagia.

Pulmonary Circuit vs. Systemic Circuit

The pulmonary circuit routes oxygen-poor blood from the right ventricle to the lungs for gas exchange; the systemic circuit pumps oxygenated blood from the left ventricle through the body.

Cardiac Skeleton

A dense fibrous network of collagen and elastic fibers within the myocardium that anchors cardiac muscle fibers, supports heart valves, and limits the direct spread of action potentials.

Ventricular Myocardial Thickness

Structural adaptation in which the left ventricle possesses a significantly thicker, rounder wall than the crescent-shaped right ventricle due to pumping against higher systemic vascular resistance.

Pacemaker Potential

The hyperpolarization-triggered, continuous depolarization of cardiac autorhythmic cells toward threshold, caused by slow $Na^+$ channel opening and $K^+$ channel closure.

Cardiac Output (CO)

The volume of blood pumped by each ventricle per minute, defined mathematically as heart rate multiplied by stroke volume ($\text{CO} = \text{HR} \times \text{SV}$).

Frank-Starling Law of the Heart

The physiological relationship stating that critical stretch of cardiac muscle cells prior to contraction (preload) increases ventricular contractile force and stroke volume.

Tetralogy of Fallot

A congenital heart condition comprising four defects: pulmonary trunk stenosis, right ventricular hypertrophy, ventricular septal defect, and an overriding aorta.

Tunica Media

The middle layer of blood vessel walls, composed of smooth muscle cells and elastic sheets under autonomic vasomotor control to regulate vessel diameter and blood pressure.

Continuous Capillary

The most common and least permeable capillary type, possessing an intact endothelial lining with tight junctions and intercellular clefts to allow limited passage of fluids and small solutes.

Capacitance Vessels

Veins and venules characterized by high distensibility and thin walls, accommodating up to $60\%$ to $65\%$ of the body's total blood volume as blood reservoirs.

Total Peripheral Resistance (TPR)

The overall resistance to blood flow encountered in systemic blood vessels, influenced primarily by blood viscosity, vessel length, and arteriolar diameter.

Mean Arterial Pressure (MAP)

The functional pressure driving blood through body tissues, calculated as diastolic pressure plus one-third of the pulse pressure ($\text{MAP} = \text{Diastolic BP} + \frac{1}{3}\text{Pulse Pressure}$).

Baroreceptor Reflex

An autonomic neural feedback pathway originating in the carotid sinuses and aortic arch that restores arterial blood pressure to homeostatic range by altering heart rate and vasomotor tone.

Bulk Flow across Capillaries

The passive fluid movement across capillary walls controlled by net filtration pressure, balancing outward capillary hydrostatic pressure against inward colloid osmotic pressure.

Cerebral Arterial Circle (Circle of Willis)

An arterial anastomosis located at the base of the brain that unites the internal carotid and basilar arteries to protect cerebral tissue from ischemia.

Nervous System Response Speed and Duration

Initiates responses rapidly (in milliseconds), resulting in short-duration responses.

Endocrine System Response Speed and Duration

Initiates responses slowly (seconds to days), resulting in long-duration responses.

Nervous System Signal Coding

Signal strength is coded by the frequency of action potentials.

Endocrine System Signal Coding

Signal strength is coded by the concentration of circulating hormone.

Exocrine Glands

Duct-containing glands that produce non-hormonal substances (e.g., sweat, saliva) delivered to membrane surfaces.

Endocrine Glands

Ductless glands that produce hormones, secreting them directly into surrounding extracellular fluid and blood vessels.

Pure Endocrine Glands

Pituitary gland, thyroid gland, parathyroid glands, adrenal glands, and pineal gland.

Neuroendocrine Organ

The hypothalamus, because it performs neural functions and secretes regulatory hormones.

Autocrines

Locally acting chemicals that exert their effects on the exact same cells that secreted them.

Paracrines

Locally acting chemicals that exert their effects on neighboring cell populations within the same tissue.

Amino Acid-Based Hormones

Water-soluble hormones (except thyroid hormone) including amino acid derivatives, peptides, and proteins that cannot cross the plasma membrane.

Steroid Hormones

Lipid-soluble hormones synthesized from cholesterol that can cross the plasma membrane; includes gonadal and adrenocortical hormones.

Cyclic AMP (cAMP) Signaling Steps

1. Hormone binds receptor. 2. Receptor activates G protein. 3. G protein alters adenylate cyclase. 4. Adenylate cyclase converts ATP to cAMP. 5. cAMP activates protein kinases.

PIP2-Calcium Signaling Pathway

Hormone activates G protein -> Phospholipase C cleaves PIP2 into DAG (activates protein kinases) and IP3 (releases Ca2+ from ER) -> Ca2+ acts as second messenger or binds calmodulin.

Direct Gene Activation Mechanism

Lipid-soluble hormone diffuses into cell -> binds intracellular receptor -> complex enters nucleus and binds DNA response element -> stimulates mRNA transcription -> protein translation.

Humoral Stimulus

Hormone secretion in direct response to changing blood levels of critical ions or nutrients (e.g., low blood Ca2+ stimulating PTH release).

Neural Stimulus

Direct nerve fiber stimulation of hormone release (e.g., sympathetic nerves stimulating adrenal medulla catecholamine release).

Hormonal Stimulus

Hormone secretion in response to other circulating hormones (tropic hormones).

Up-Regulation

Target cells display additional receptors in response to persistently low circulating hormone levels to increase sensitivity.

Down-Regulation

Target cells lose or desensitize receptors in response to persistently high hormone concentrations to prevent overstimulation.

Permissiveness

Hormone interaction where one hormone cannot exert full effect without the presence of another hormone (e.g., thyroid hormone required for reproductive tissue development).

Synergism

Hormone interaction where multiple hormones produce the same effect and their combined presence amplifies the response (e.g., glucagon and epinephrine releasing glucose).

Antagonism

Hormone interaction where one hormone opposes the action of another (e.g., insulin lowers blood glucose while glucagon raises it).

Hypothalamic-Hypophyseal Tract

Neural connection connecting the hypothalamus to the posterior pituitary, arising from cell bodies in paraventricular and supraoptic nuclei.

Hypophyseal Portal System

Vascular system connecting the hypothalamus to the anterior pituitary, consisting of primary capillary plexus, portal veins, and secondary capillary plexus.

Oxytocin

Synthesized in paraventricular nuclei; stimulates uterine smooth muscle contraction and milk ejection ('let-down' reflex) via PIP2-calcium system.

Antidiuretic Hormone (ADH / Vasopressin)

Synthesized in supraoptic nuclei; stimulates kidney collecting tubules to reabsorb water in response to high blood osmolarity or low blood pressure.

Diabetes Insipidus

Disorder caused by ADH deficiency resulting in intense thirst (polydipsia) and massive output of dilute urine (polyuria).

Syndrome of Inappropriate ADH Secretion (SIADH)

Hypersecretion of ADH leading to fluid retention, dilutional hyponatremia, and severe brain edema.

Growth Hormone (GH) Direct Effects

Decreases cellular glucose uptake (glucose-sparing), stimulates hepatic glycogenolysis, and promotes lipolysis in adipose tissue.

Growth Hormone (GH) Indirect Effects

Triggers production of insulin-like growth factors (IGFs) by liver, muscle, and bone to stimulate cell division, protein synthesis, and bone matrix deposition.

Gigantism vs. Acromegaly

Gigantism is caused by GH hypersecretion in children (open epiphyseal plates); acromegaly is caused by GH hypersecretion in adults (thickening of hands, feet, face).

Pituitary Dwarfism

Condition caused by GH hyposecretion in children, leading to delayed skeletal growth.

Thyroid-Stimulating Hormone (TSH)

Tropic hormone secreted by thyrotropic cells of anterior pituitary; stimulated by TRH and inhibited by thyroid hormones and GHIH.

Adrenocorticotropic Hormone (ACTH)

Tropic hormone derived from POMC precursor; stimulates adrenal cortex to release corticosteroids (chiefly glucocorticoids); stimulated by CRH.

Follicle-Stimulating Hormone (FSH)

Gonadotropin that stimulates gamete (egg or sperm) production; stimulated by GnRH and inhibited by gonadal steroids and inhibin.

Luteinizing Hormone (LH)

Gonadotropin that promotes gonadal sex hormone production, triggers ovulation in females, and stimulates Leydig cell testosterone production in males.

Prolactin (PRL)

Hormone that stimulates mammary gland development and milk production; continuously inhibited by Prolactin-Inhibiting Hormone (PIH/dopamine).

Thyroid Hormone Synthesis Steps

1. Thyroglobulin synthesis -> 2. Iodide trapping -> 3. Iodide oxidation -> 4. Tyrosine iodination (MIT/DIT) -> 5. Coupling (T3/T4) -> 6. Endocytosis -> 7. Lysosomal cleavage & diffusion.

T4 vs. T3

T4 (thyroxine) has 4 bound iodines and is the main form secreted; T3 (triiodothyronine) has 3 bound iodines and is 10 times more active at target receptors.

Myxedema and Goiter

Myxedema is adult hypothyroidism (low BMR, cold intolerance, lethargy, edema). Goiter is thyroid enlargement due to lack of dietary iodine causing uninhibited TSH accumulation.

Graves' Disease

Autoimmune hyperthyroidism where abnormal antibodies mimic TSH; leads to elevated BMR, sweating, rapid heartbeat, weight loss, and exophthalmos.

Calcitonin

Secreted by parafollicular (C) cells in response to high blood Ca2+ levels; at high doses inhibits osteoclasts and stimulates Ca2+ uptake into bone matrix.

Parathyroid Hormone (PTH) Effects

1. Stimulates osteoclasts to release Ca2+ into blood. 2. Enhances renal Ca2+ reabsorption and PO43- excretion. 3. Promotes renal activation of Vitamin D to calcitriol.

Hyperparathyroidism

Excess PTH causing osteitis fibrosa cystica (severe bone demineralization), hypercalcemia, depressed nervous system, and kidney stones.

Hypoparathyroidism

Deficient PTH leading to severe hypocalcemia, membrane hyperexcitability, muscle twitches, tetany, and potential fatal respiratory paralysis.

Adrenal Cortex Zones and Hormones

Zona Glomerulosa (outer): Mineralocorticoids (Aldosterone). Zona Fasciculata (middle): Glucocorticoids (Cortisol). Zona Reticularis (inner): Gonadocorticoids (Androgens).

Aldosterone Actions and Regulation

Promotes distal renal tubule Na+ reabsorption and K+ excretion. Stimulated by RAAS and elevated blood K+; inhibited by ANP.

Cortisol Physiological Functions

Promotes gluconeogenesis, mobilizes fatty acids, increases protein catabolism, preserves blood glucose for brain, and enhances vasoconstrictive reactivity.

Cushing's Syndrome vs. Addison's Disease

Cushing's: Cortisol excess -> hyperglycemia, muscle loss, hypertension, 'buffalo hump', 'moon face'. Addison's: Cortisol/Aldosterone deficit -> weight loss, hypotension, dehydration, skin bronzing.

Adrenal Medulla Catecholamines

Synthesizes epinephrine (80%) and norepinephrine (20%) from tyrosine; controlled by preganglionic sympathetic fibers during acute fight-or-flight stress.

Pheochromocytoma

Chromaffin cell tumor causing hypersecretion of catecholamines, resulting in severe hypertension, rapid heart rate, sweating, and extreme nervousness.

General Adaptation Syndrome Phases

1. Alarm Reaction (sympathetic fight-or-flight). 2. Resistance Reaction (cortisol & aldosterone long-term response). 3. Exhaustion (depletion of body reserves).

Melatonin

Synthesized from serotonin in pinealocytes; exhibits diurnal rhythm peaking at night; targets hypothalamic suprachiasmatic nucleus to regulate sleep/circadian rhythm.

Glucagon Mechanism

Secreted by pancreatic alpha cells during hypoglycemia; targets liver to induce glycogenolysis and gluconeogenesis, raising blood glucose.

Insulin Mechanism

Secreted by pancreatic beta cells during hyperglycemia; binds tyrosine kinase receptors to enhance glucose transport into muscle and fat cells for storage.

Three Cardinal Signs of Diabetes Mellitus

1. Polyuria (massive urine output). 2. Polydipsia (excessive thirst). 3. Polyphagia (excessive hunger).

Ketoacidosis in Diabetes Mellitus

Unregulated lipolysis produces excess ketone bodies, lowering blood pH and leading to hyperpnea, heart arrhythmias, coma, and death.

Hyperinsulinism

Excessive insulin secretion causing severe hypoglycemia, resulting in anxiety, tremors, confusion, convulsions, and unconsciousness.