Human Anatomy and Physiology: Nervous, Cardiovascular, Respiratory, and Reproductive Systems

Comprehensive practice flashcards defining core physiological and anatomical vocabulary covering the nervous system, blood, cardiovascular system, respiratory mechanics, and reproductive physiology.

Sensory input

The function of detecting changes occurring inside or outside the body through sensory receptors.

Integration

The processing and interpretation of incoming sensory information and coordinating an appropriate response within the central nervous system.

Motor output

The transmission of instructions from the central nervous system to peripheral effectors, such as muscles or glands, to elicit a response.

Homeostasis

The physiological maintenance of relatively stable internal conditions despite disturbances or fluctuations in the internal or external environment.

Central nervous system (CNS)

The anatomical division of the nervous system consisting of the brain and spinal cord that serves as the main integration and control centre.

Peripheral nervous system (PNS)

The division of the nervous system comprising all nervous tissue outside the brain and spinal cord, including cranial nerves, spinal nerves, and peripheral ganglia.

Somatic nervous system

The subdivision of the motor division that provides voluntary and involuntary skeletal reflex control over skeletal muscle.

Autonomic nervous system (ANS)

The involuntary branch of the motor division that innervates cardiac muscle, smooth muscle, and glands to regulate internal organ function.

Astrocytes

Neuroglial cells of the CNS that physically support neurons, anchor them to nutrient supplies, and regulate the surrounding extracellular chemical environment.

Microglia

CNS neuroglial cells that provide immune defence by engulfing microorganisms and clearing cellular debris via phagocytosis.

Ependymal cells

Neuroglial cells that line the brain ventricles and the central canal of the spinal cord, contributing to cerebrospinal fluid (CSF) circulation and regulation.

Oligodendrocytes

Specialised glial cells that form insulating myelin sheaths around multiple neuronal axons within the central nervous system.

Schwann cells

Glial cells of the peripheral nervous system responsible for producing the myelin sheath around peripheral nerve fibres.

Myelin

A lipid-rich insulating sheath wrapping sections of neuronal axons to reduce current leak and substantially increase nerve impulse conduction velocity.

Dendrites

Branching cellular processes extending from the neuronal soma that receive electrical and chemical inputs from neighbouring cells.

Axon

A long, slender neuronal projection that propagates action potentials away from the soma toward target cells via terminal arborisations.

Interneuron

A neuron situated entirely within the central nervous system that integrates and routes signals between sensory and motor neurons.

Resting membrane potential

The baseline electrical potential difference across an inactive neuronal membrane, typically measured at approximately $-70\,\text{mV}$.

Sodium-potassium pump

An ATP-dependent active transport carrier that pumps $3\,\text{Na}^+$ out of the cell for every $2\,\text{K}^+$ imported, maintaining transmembrane electrochemical gradients.

Graded potential

A localised, variable-amplitude change in membrane voltage that spreads passively and decays with distance from the site of stimulation.

Threshold

The specific membrane potential, typically around $-55\,\text{mV}$, required to activate voltage-gated sodium channels and trigger an all-or-none action potential.

Depolarisation

A shift in membrane potential toward a less negative value (rising toward $+30\,\text{mV}$ in an action potential) caused by inward current through open voltage-gated $\text{Na}^+$ channels.

Repolarisation

The restoration of a negative internal membrane potential driven by the closure/inactivation of $\text{Na}^+$ channels and the efflux of $\text{K}^+$ through open voltage-gated channels.

Saltatory conduction

The rapid jumping propagation of action potentials from one node of Ranvier to the next along myelinated axons.

Chemical synapse

A junction between two cells where an action potential in the presynaptic terminal triggers neurotransmitter exocytosis across the synaptic cleft to bind postsynaptic receptors.

Cerebrum

The largest brain region, consisting of two hemispheres responsible for conscious thought, intellectual functions, sensory perception, memory, and voluntary motor output.

Diencephalon

A central brain core enclosing the third ventricle, containing the thalamus, hypothalamus, and epithalamus to manage sensory relay, autonomic drives, and homeostasis.

Cerebellum

The hindbrain structure responsible for the unconscious coordination, precision timing, and balance of skeletal muscle movements.

Brainstem

The inferior brain region comprising the midbrain, pons, and medulla oblongata that governs essential vegetative reflexes and carries ascending and descending tracts.

Meninges

A triple-layered protective connective tissue sheath enclosing the brain and spinal cord, consisting of the dura mater, arachnoid mater, and pia mater.

Reflex arc

The neural wiring of a single reflex, consisting of five components: sensory receptor, sensory neuron, integration centre, motor neuron, and effector organ.

Phrenic nerve

A peripheral nerve arising from cervical spinal cord segments C3–C5 that delivers vital motor innervation to the diaphragm.

Neuromuscular junction (NMJ)

The specialized synapse formed between the axon terminal of a somatic motor neuron and the motor end-plate of a skeletal muscle fibre.

Autonomic tone

The continuous, basal background rate of sympathetic and parasympathetic nerve firing that allows autonomic systems to increase or decrease organ activity on demand.

Plasma

The noncellular, liquid extracellular matrix of blood comprising approximately $55\%$ of whole blood, containing about $90\%$ water, plasma proteins, electrolytes, and nutrients.

Albumin

The most abundant plasma protein, synthesised by the liver, which generates the majority of plasma colloid osmotic pressure and transports lipophilic substances.

Haematocrit

The clinical measurement of the percentage of total blood volume made up of packed red blood cells, normally about $45\%$.

Erythrocyte

A biconcave, anucleate formed element filled with haemoglobin dedicated to the transport of oxygen and carbon dioxide throughout the circulation.

Haemoglobin

A tetrameric erythrocyte protein composed of four polypeptide globin chains and four iron-containing haem groups, each capable of reversibly binding one $\text{O}_2$ molecule.

Erythropoiesis

The regulated process of new erythrocyte formation occurring in red bone marrow under the influence of the renal hormone erythropoietin.

Erythropoietin (EPO)

A glycoprotein hormone produced primarily by peritubular cells in the kidneys in response to cellular hypoxia that stimulates red blood cell maturation in bone marrow.

Leukocytes

Complete nucleated white blood cells that defend the body against microbial pathogens, toxins, and cellular debris.

Neutrophil

The most numerous circulating granulocyte, characterised by a multilobed nucleus and pale cytoplasmic granules, functioning as an active phagocyte during acute bacterial infection.

Haemostasis

The fast, localized series of defensive physiological events that stops blood loss from injured vessels, consisting of vascular spasm, platelet plug formation, and coagulation.

Coagulation

The complex enzymatic cascade of clotting factors culminating in the production of thrombin, which cleaves soluble fibrinogen into an insoluble cross-linked fibrin clot.

ABO blood groups

An erythrocyte classification system based on the inherited presence or absence of type A and type B glycoprotein antigens on red cell membranes and preformed agglutinins in plasma.

Rh blood group

A red blood cell typing system based on the presence ($\text{Rh}^+$) or absence ($\text{Rh}^-$) of the RhD cell surface antigen.

Heart chambers

The four internal muscular compartments of the heart: the right atrium, left atrium, right ventricle, and left ventricle.

Myocardium

The thick, contractile middle layer of the heart wall composed of branching, striated cardiac muscle cells joined by intercalated discs.

Atrioventricular (AV) valves

Heart valves positioned between atria and ventricles (tricuspid on the right, mitral on the left) that prevent the backflow of blood into the atria during ventricular systole.

Semilunar valves

Pocket-like heart valves located at the exits of the ventricles (pulmonary and aortic) that prevent the backward flow of ejected blood into the ventricles during diastole.

Sinoatrial (SA) node

The primary intrinsic pacemaker of the heart, located in the right atrium, which spontaneously depolarises to generate action potentials that establish sinus rhythm.

Electrocardiogram (ECG)

A graphic clinical record of the electrical voltage variations generated by cardiac muscle depolarisation and repolarisation over time.

P wave

The initial deflection on an electrocardiogram tracing representing electrical depolarisation of the atrial myocardium.

QRS complex

The prominent wave sequence on an ECG tracing resulting from rapid electrical depolarisation throughout the ventricular myocardium.

T wave

The dome-shaped deflection on an ECG tracing representing ventricular repolarisation and electrical recovery.

Systole

The contractile phase of the cardiac cycle during which high chamber pressures develop to drive blood ejection.

Diastole

The relaxation phase of the cardiac cycle characterised by falling chamber pressures and passive or active chamber filling.

Isovolumetric contraction

The early phase of ventricular systole where intraventricular pressure rises while all four cardiac valves remain closed, maintaining constant ventricular volume.

Cardiac output (CO)

The volume of blood pumped out by each ventricle in one minute, determined by multiplying heart rate by stroke volume ($\text{CO} = \text{HR} \times \text{SV}$).

Stroke volume (SV)

The volume of blood ejected by a ventricle per heartbeat, defined as end-diastolic volume minus end-systolic volume ($\text{SV} = \text{EDV} - \text{ESV}$).

Preload

The extent of stretch placed upon ventricular cardiac myocytes immediately prior to contraction, largely governed by end-diastolic volume and venous return.

Frank–Starling mechanism

The intrinsic law of the heart stating that within physiological limits, increased ventricular stretch (preload) causes myocytes to contract with greater force, increasing stroke volume.

Afterload

The resistance or pressure that ventricles must overcome in systemic or pulmonary arteries to open the semilunar valves and eject blood.

Arterioles

Small diameter blood vessels upstream of capillary beds that serve as primary resistance vessels by constricting or dilating to regulate arterial pressure and capillary flow.

Mean arterial pressure (MAP)

The estimated average pressure driving blood through the systemic arterial circulation during a complete cardiac cycle, estimated as $\text{MAP} \approx \text{Diastolic BP} + \frac{1}{3}(\text{Pulse Pressure})$.

Baroreceptor reflex

A rapid autonomic neural negative feedback loop initiated by stretch receptors in the carotid sinuses and aortic arch to buffer acute fluctuations in arterial blood pressure.

Renin–angiotensin–aldosterone system (RAAS)

A renal hormonal cascade initiated by the release of renin that produces angiotensin II and aldosterone to stimulate systemic vasoconstriction and renal sodium retention.

Pulmonary ventilation

The physical process of moving air mechanically into and out of the lungs to renew alveolar gases (breathing).

External respiration

The physical exchange of oxygen and carbon dioxide between the air spaces of the pulmonary alveoli and the blood flowing through pulmonary capillaries.

Internal respiration

The exchange of respiratory gases between oxygenated systemic capillary blood and metabolising tissue cells.

Larynx

A complex cartilaginous structure situated between the pharynx and trachea that maintains patent airway passage, prevents food aspiration via the epiglottis, and produces phonation.

Conducting zone

The anatomical passages of the respiratory tract (nose to terminal bronchioles) that filter, warm, and humidify air without performing gas exchange.

Respiratory zone

The distal anatomical structures of the lungs (respiratory bronchioles, alveolar ducts, and alveoli) where pulmonary gas exchange occurs across the respiratory membrane.

Alveoli

Thin-walled, microscopic microscopic air sacs clustered at the termini of respiratory bronchioles that form the main exchange surface for oxygen and carbon dioxide.

Pulmonary surfactant

A lipid-protein detergent complex produced by type II alveolar cells that lowers surface tension at the alveolar air-liquid interface to prevent alveolar atelectasis.

Boyle's law

The gas law stating that at a constant temperature, the pressure of a given gas mass is inversely proportional to its volume ($P \propto \frac{1}{V}$).

Tidal volume (TV)

The volume of air inspired or expired with each effortless breath during normal, quiet breathing (approximately $500\,\text{mL}$ in resting adults).

Vital capacity (VC)

The maximum volume of air that can be forcibly expired following a maximal inspiration ($\text{VC} = \text{IRV} + \text{TV} + \text{ERV}$).

Residual volume (RV)

The volume of gas remaining in the lungs following a maximal, forceful exhalation that keeps alveoli patent and prevents lung collapse.

Bohr effect

The reduction in haemoglobin's oxygen-binding affinity caused by increases in carbon dioxide, temperature, and hydrogen ion concentration (decreased pH), facilitating oxygen release to active tissues.

Carbonic anhydrase

An erythrocyte enzyme that reversibly accelerates the hydration of carbon dioxide into carbonic acid ($\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3$).

Chloride shift

The ionic exchange of bicarbonate ($\text{HCO}_3^-$) for chloride ($\text{Cl}^-$) across the erythrocyte membrane via carrier proteins to maintain electrical neutrality during gas transport.

Central chemoreceptors

Brainstem sensory neurons on the ventrolateral medulla that detect fluctuations in cerebrospinal fluid pH caused by changes in arterial $\text{PCO}_2$ to regulate respiratory rate.

Gametes

Haploid sex cells containing 23 chromosomes (spermatozoa in males and secondary oocytes in females) that fuse during fertilisation to re-establish the diploid chromosome number.

Gonads

The primary reproductive organs (testes in males and ovaries in females) responsible for producing gametes and secreting reproductive steroid hormones.

Male reproductive system

The system of reproductive organs responsible for producing sperm, synthesizing testosterone, and delivering semen into the female reproductive tract.

Epididymis

A tightly coiled tubular structure resting on the superior and posterior margins of each testis where developing spermatozoa mature, acquire motility, and are stored.

Ductus deferens

A muscular conduit that conveys mature sperm from the epididymis through the inguinal canal to the ejaculatory duct via peristalsis.

Spermatogenesis

The sequential process of sperm cell development in the seminiferous tubules of the testes from diploid spermatogonia to mature haploid spermatozoa.

Sertoli cells

Sustentacular supporting cells within the seminiferous tubules that protect and nurture developing spermatogenic cells and secrete the hormone inhibin.

Leydig cells

Interstitial endocrine cells located in the connective tissue spaces between seminiferous tubules that synthesize and secrete testosterone under the influence of luteinising hormone (LH).

Female reproductive system

The system of internal and external female reproductive organs that produces oocytes, secretes oestrogens and progesterone, supports fetal development, and enables parturition.

Uterine tubes

Fallopian tubes that extend laterally from the uterus toward the ovaries, capturing ovulated secondary oocytes and serving as the typical site for fertilisation.

Endometrium

The inner mucosal lining of the uterus, consisting of an inner functional layer (stratum functionalis) shed during menstruation and an underlying basal layer (stratum basalis).

Ovulation

The mid-cycle rupture of a mature tertiary follicle and release of a secondary oocyte into the peritoneal cavity, triggered by an anterior pituitary surge of LH.

Corpus luteum

A transient endocrine structure developed from the ruptured ovarian follicle after ovulation that secretes abundant progesterone and oestrogen to support the secretory endometrium.

Blastocyst

The hollow developmental embryonic stage featuring an inner cell mass and an outer epithelial trophoblast that implants into the receptive uterine wall.

Implantation

The biological process beginning approximately 6–7 days post-fertilisation wherein the blastocyst adheres to and burrows into the receptive functional layer of the endometrium.

Human chorionic gonadotropin (hCG)

A pregnancy hormone secreted by developing trophoblast tissue that prevents corpus luteum degeneration, preserving progesterone production during early gestation.