Human Biology: Comprehensive Body Systems Review

Comprehensive review flashcards covering foundational human biology: the musculoskeletal, cardiovascular, respiratory, digestive, renal, and immune systems.

Neuromuscular Junction (NMJ)

A specialised synapse that links a motor neuron axon terminal to a skeletal muscle fibre, allowing a neural action potential to initiate muscle contraction.

Acetylcholine (ACh)

An excitatory neurotransmitter released from motor-neuron synaptic vesicles by exocytosis that diffuses across the synaptic cleft and binds receptors at the motor end plate.

Sarcomere

The repeating microscopic contractile unit of a myofibril bounded by Z discs, within which actin and myosin filaments slide past one another to generate tension.

Antagonistic Muscle Pair

A functional pairing of muscles where the agonist contracts and generates tension to pull a bone around a joint while the antagonist relaxes or yields opposing tension, reversing roles for the opposite movement.

Tendon

A tough connective tissue structure composed of tightly packed, parallel collagen fibres that connects muscle to bone and transmits muscular tension.

Ligament

A fibrous connective tissue containing collagen and elastin that connects bone to bone, supporting and stabilising a joint against excessive movement.

Myasthenia Gravis

An autoimmune disorder causing postsynaptic NMJ disruption through a reduction of functional acetylcholine receptors on the motor end plate, leading to muscle weakness.

Botulinum Toxin

A bacterial neurotoxin that causes presynaptic disruption at the NMJ by blocking acetylcholine vesicle release from the motor-neuron terminal, reducing muscle membrane depolarisation.

Synovial Joint

A freely movable joint comprising articulating bones, load-distributing articular cartilage, a joint capsule, and a synovial cavity filled with lubricating synovial fluid.

Periosteum

A vascular connective tissue covering the outer surface of a bone that participates in nourishment, tendon and ligament attachment, and bone repair.

Haematopoiesis

The formation and differentiation of blood cells from multipotent haematopoietic stem cells residing in the red bone marrow.

Perfusion

The flow of blood through a tissue's microscopic capillary network that delivers oxygen and nutrients while removing cellular metabolic wastes.

Double Circulation

A cardiovascular arrangement consisting of two linked circuits in series: the pulmonary circulation pumping deoxygenated blood to the lungs and the systemic circulation delivering oxygenated blood to the body.

Cardiomyocytes

Short, branched, fatigue-resistant muscle cells of the heart interconnected mechanically and electrically by intercalated discs containing gap junctions.

Sinoatrial (SA) Node

The primary physiological pacemaker located in the right atrial wall that spontaneously initiates electrical impulses to coordinate the heartbeat.

Cardiac Output (CO)

The total volume of blood ejected by a single ventricle each minute, determined by the formula: $\text{Cardiac Output} = \text{Heart Rate} \times \text{Stroke Volume}$.

Arterioles

Small, muscular arterial branches that adjust their diameter via smooth-muscle contraction or relaxation to control vascular resistance and regulate local tissue perfusion.

Formed Elements of Blood

The cellular components of whole blood, accounting for approximately $45\%$ of volume, consisting of erythrocytes (red blood cells), leukocytes (white blood cells), and platelets.

Haemostasis

The physiological process that prevents blood loss following vascular injury, involving endothelial collagen exposure, platelet adhesion, activation, plug aggregation, and insoluble fibrin stabilisation.

Agglutination

The clumping of donor red blood cells caused by recipient plasma antibodies binding complementary surface ABO antigens, which can trigger haemolysis and impair capillary perfusion.

Ventilation

The mechanical movement of air between the atmosphere and the lungs that continually renews gas concentrations at the alveolar respiratory exchange surface.

Inspiration Mechanics

An active process wherein the diaphragm contracts and flattens while external intercostals pull the ribs up and out, increasing thoracic volume and lowering intrapulmonary pressure below atmospheric pressure.

Alveoli

Microscopic, thin-walled, moist air sacs surrounded by a dense capillary network that serve as the primary site of rapid $O_2$ and $CO_2$ diffusion in the lungs.

Mucociliary Escalator

A respiratory defence mechanism where goblet-cell mucus traps inhaled particles and pathogens, and coordinated beating of ciliated epithelial cells propels the mucus toward the pharynx.

Tidal Volume (TV)

The volume of air inspired or expired during a single quiet, resting breath.

Vital Capacity (VC)

The maximum volume of air that can be exhaled following maximal inspiration, calculated as: $\text{Vital Capacity} = \text{Inspiratory Reserve Volume} + \text{Tidal Volume} + \text{Expiratory Reserve Volume}$.

Residual Volume (RV)

The volume of air remaining in the lungs following a maximal, forceful expiration, which cannot be measured directly by simple spirometry.

$\text{FEV}_1 / \text{FVC}$ Ratio

The ratio of forced expiratory volume in one second to total forced vital capacity, which falls during airway obstruction such as an asthma attack.

Bronchodilator

A therapeutic agent that relaxes airway smooth muscle in bronchi and bronchioles, widening the airway lumen, lowering resistance, and improving airflow.

Oxyhaemoglobin

The reversible complex ($\text{HbO}_2$) formed when molecular oxygen loads onto haemoglobin within erythrocytes in pulmonary capillaries.

Peristalsis

Rhythmic, coordinated waves of circular and longitudinal smooth-muscle contraction and relaxation that propel ingested material along the gastrointestinal tract.

Chemical Digestion

The enzymatic hydrolysis of large, complex dietary polymers into small, absorbable monomers capable of crossing the intestinal epithelium.

Pepsin

A protein-digesting gastric protease activated by acidic hydrochloric acid ($\text{pH}\sim 1\text{--}3$) that cleaves dietary proteins into smaller peptide chains in the stomach.

Bile Emulsification

The physical dispersion of large dietary fat globules into tiny lipid droplets by liver-produced bile salts, increasing the available surface area for pancreatic lipase activity.

Villi and Microvilli

Structural foldings and epithelial cellular projections of the small intestine that collectively amplify the luminal surface area to maximise nutrient absorption.

Lacteal

A specialised lymphatic capillary located in the core of an intestinal villus that absorbs reassembled triglycerides packaged into chylomicrons.

Hepatic Portal Vein

A major blood vessel that carries water-soluble nutrients, including glucose and amino acids, directly from intestinal capillary beds to the liver for metabolic processing.

Insulin

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

Glucagon

A peptide hormone released by pancreatic alpha cells during hypoglycemia that stimulates hepatic glycogen breakdown and glucose release into systemic blood.

Coeliac Disease

An autoimmune disorder triggered by gluten ingestion that causes chronic inflammation and flattening of small intestinal villi, resulting in nutrient malabsorption.

Urinary System Gross Anatomy

An organ system comprising two kidneys that filter blood, bilateral ureters transporting urine, a urinary bladder storing urine, and a urethra discharging urine from the body.

Nephron

The microscopic structural and functional working unit of the kidney, consisting of a renal corpuscle and an epithelial renal tubule system.

Glomerular Filtration

The pressure-driven movement of water and small solutes from the glomerular capillaries across a selective filtration barrier into Bowman's capsule to form filtrate.

Tubular Reabsorption (Recovery)

The selective transport of filtered water, glucose, amino acids, and essential ions from the tubule lumen across epithelial cells and interstitial fluid back into peritubular capillaries.

Tubular Secretion

The active or passive transport of select substances, such as hydrogen ions ($\text{H}^+$), excess potassium ($\text{K}^+$), and drugs, from peritubular blood into the tubule lumen for excretion.

Proximal Convoluted Tubule (PCT)

The initial convoluted portion of the renal tubule responsible for reabsorbing the majority of filtered water, sodium, and virtually all filtered glucose and amino acids.

Anti-Diuretic Hormone (ADH)

A hypothalamic neurohormone released by the posterior pituitary that promotes water conservation by triggering the insertion of aquaporin-2 water channels into collecting duct membranes.

Dialysis

An artificial blood-cleansing therapy in which patient blood flows past a dialysate solution across a semipermeable membrane, removing urea, excess ions, and fluid while retaining blood cells and large proteins.

Pathogen

A biological agent, such as a bacterium, virus, fungus, or parasite, capable of causing infectious disease within a host organism.

Antigen

A foreign or abnormal molecular structure, frequently a protein, that can be recognized by antibodies or specific lymphocyte antigen receptors.

Epitope

The specific localized molecular binding region on an antigen surface that is recognized by an antibody's variable region or a T-cell receptor.

Innate Immunity

Non-specific, rapid host defences present from birth that respond within hours to broad microbial patterns without generating immunological memory.

Adaptive Immunity

An antigen-specific immune response coordinated by B and T lymphocytes that develops over days upon initial exposure and produces long-lived immunological memory.

Phagocytosis

The cellular engulfment and lysosomal enzymatic degradation of particulate foreign matter, microorganisms, or cellular debris by cells such as neutrophils and macrophages.

Inflammation

An innate tissue response triggered by chemical mediators like histamine, characterised by vasodilation, increased capillary permeability, and recruitment of leukocytes resulting in heat, redness, swelling, and pain.

Natural Killer (NK) Cells

Innate cytotoxic lymphocytes that survey host cells for viral infection or abnormal transformation and trigger programmed cell death (apoptosis) without prior sensitisation.

Apoptosis

A controlled, programmed mechanism of cellular dismantling into membrane-bound vesicles that prevents the release of intracellular components and limits local tissue inflammation.

Antigen-Presenting Cells (APCs)

Immune cells, predominantly dendritic cells and macrophages, that internalise antigens, process them into peptide fragments, and display them bound to surface MHC molecules to activate naive T cells.

Major Histocompatibility Complex (MHC)

Cell-surface proteins that act as molecular display stands, binding intracellular or endocytosed peptide fragments to present them for recognition by specific T-cell receptors.

Helper T Cells ($\text{T}_\text{H}$)

Adaptive lymphocytes that recognise presented antigen fragments on MHC class II molecules and secrete cytokines that coordinate macrophage activity, cytotoxic T-cell expansion, and B-cell activation.

Cytotoxic T Cells ($\text{T}_\text{C}$)

Effector T lymphocytes that recognise matching viral or abnormal peptide fragments displayed on host cells and deliver lethal signals to trigger target cell apoptosis.

Plasma Cells

Terminally differentiated B-cell descendants specialised for the rapid synthesis and high-volume secretion of antigen-specific antibodies into blood and lymph.

Antibody Neutralisation

The binding of antibodies to viral surface proteins or microbial toxins, physically blocking their interaction with host receptors and preventing cellular invasion.

Secondary Immune Response

A rapid, robust, and prolonged adaptive immune reaction upon re-exposure to a previously encountered antigen, driven by pre-existing memory B and T cells.

Active Immunity vs. Passive Protection

Active immunity is protection generated by an individual's own adaptive response following antigen exposure or vaccination, forming memory cells; passive protection is temporary defence conferred by transferring ready-made antibodies without generating immune memory.

Autoimmunity

A pathological state arising when immunological self-tolerance fails, causing lymphocytes and autoantibodies to launch a targeted destructive response against the body's own tissues.

Allergy (Type I Hypersensitivity)

An inappropriate adaptive immune response against a harmless environmental allergen, mediated by allergen-specific IgE antibodies bound to mast cells that release histamine upon re-exposure.