Anatomy and Physiology: Tissues, Cellular Metabolism, Energy Balance, and Cell Signaling

Comprehensive practice flashcards in vocabulary style covering epithelial and connective tissues, cellular respiration and ATP production, metabolic rate, energy balance and obesity regulation, cell signaling mechanisms, and the immune system.

Epithelial Tissue

A primary tissue type composed of cells that cover body surfaces, line internal cavities, and rest on a basement membrane composed of fibers and glycoproteins that anchor cells and act as a barrier.

Simple Squamous Epithelium

A single layer of flattened epithelial cells designed for rapid diffusion, filtration, and gas exchange; located in the kidney filtration membranes, blood vessel linings, and lung alveoli.

Simple Cuboidal Epithelium

A single layer of cube-like cells that resemble blocks lined up, facilitating controlled secretion, absorption, and active transport; located in glands such as the thyroid, ovaries, and parathyroid.

Simple Columnar Epithelium

A single layer of tall, column-shaped cells providing protection and absorption; often possesses microvilli in the small and large intestines or cilia in the fallopian tubes.

Pseudostratified Columnar Epithelium

An epithelial tissue that appears stratified but consists of a single layer where all cells contact the basement membrane; contains goblet cells to secrete mucus and cilia to propel debris, located in the larynx and trachea.

Transitional Epithelium

A specialized stratified epithelium capable of transitioning between shapes to allow organ stretching and relaxation; appears cuboidal or columnar when relaxed and simple squamous when distended, located in the ureters and urinary bladder.

Stratified Squamous Epithelium

A multilayered epithelial tissue where superficial dead cells are sloughed off while basal cells remain attached to the basement membrane, providing protection in high-stress areas such as the mouth, tongue, skin, and vagina.

Connective Tissue Components

The three universal structural elements found across all connective tissue types: specialized cells, ground substance, and extracellular protein fibers (collagen, reticular, or elastic).

Dense Regular Collagenous Connective Tissue

A connective tissue composed of a tight, unidirectional arrangement of collagen fibers produced by fibroblasts, conferring high tensile strength in structures like tendons (muscle to bone) and ligaments (bone to bone).

Dense Irregular Elastic Connective Tissue

A connective tissue composed of bundles and sheaths of collagen and elastic fibers oriented in multiple directions to allow multi-directional stretch and recoil; found in large elastic arteries such as the aorta.

Areolar Connective Tissue

A loose connective tissue with open spaces among collagen and elastic fibers housing fibroblasts, macrophages, and lymphocytes; provides support, loose packing, and nourishment beneath epithelial basement membranes.

Reticular Tissue

A loose connective tissue composed of an irregular network of reticular fibers that forms the supportive framework for lymphatic and hemopoietic organs, including lymph nodes, the spleen, and bone marrow.

Adipose Tissue

A specialized loose connective tissue containing fat cells that store lipids within vacuoles, pushing the nucleus and cytoplasm to the periphery; functions in energy storage, thermal insulation, and organ protection.

Hyaline Cartilage

A supportive connective tissue with abundant collagen fibers that decreases friction at bone ends, forms the embryonic skeleton prior to bone replacement, and occurs in the nose, trachea, larynx, and costal cartilages.

Fibrocartilage

A tough supportive connective tissue containing a dense collagen matrix designed to withstand high pressure; located in the pubic symphysis, intervertebral discs, and knee menisci.

Elastic Cartilage

A flexible cartilage enriched with elastic fibers that enables structures to stretch and return to their original conformation; located in the external ears.

Skeletal Muscle

A striated, multinucleated, voluntary muscle tissue under somatic control (accounting for $40\%$ of body weight in men and $34\%$ in women) that contracts via sliding protein filaments to generate movement.

Cardiac Muscle

A striated, involuntarily controlled muscle tissue located in the heart featuring single nuclei and intercalated discs that electrically couple cells for synchronized contraction.

Smooth Muscle

An involuntary, non-striated, single-nucleated muscle tissue found within the walls of the gastrointestinal tract, surrounding bronchioles, and lining arteries.

Neurons

The electrically excitable cells of the nervous system consisting of dendrites that receive incoming electrical signals, axons that transmit impulses, and often myelin sheaths that accelerate transmission speed.

Energy Consumption Phase of Glycolysis

The initial preparatory stage of glycolysis where $2\text{ ATP}$ are invested to convert glucose ($\text{C-C-C-C-C-C}$) into fructose-1,6-bisphosphate, which subsequently splits into two molecules of PGAL (PGAL #1 and dihydroxyacetone phosphate / PGAL #2).

Energy Production Phase of Glycolysis

The downstream phase of glycolysis where two PGAL molecules undergo oxidation, reduction of $\text{NAD}^+$ to $\text{NADH}$, and substrate-level phosphorylation to generate a gross of $4\text{ ATP}$ (yielding a net of $2\text{ ATP}$ ready for use), $2\text{ NADH}$, and $2\text{ pyruvate}$ molecules.

Intermediate Steps (Pyruvate Oxidation)

The metabolic reactions occurring when oxygen is present, where each pyruvate from glycolysis is imported into the mitochondrial matrix and converted into acetyl CoA, yielding $\text{NADH}$ for the ETC and releasing $\text{CO}_2$ as waste.

Mitochondrial Respiration and Compartments

The eukaryotic compartmental arrangement where pyruvate produced by cytoplasmic glycolysis enters the mitochondrial matrix (if $\text{O}_2$ is present) for the intermediate step, Krebs cycle, and inner membrane electron transport chain.

Krebs Cycle (Citric Acid Cycle)

A cyclic series of reactions in the mitochondrial matrix utilizing acetyl CoA that generates $1\text{ ATP}$, $2\text{ CO}_2$, $3\text{ NADH}$, and $1\text{ FADH}_2$ per single complete turn.

Mitochondrial Electron Transport Chain and ATP Synthase

The inner mitochondrial membrane protein complexes (1, 3, 5) that harness electron energy from $\text{NADH}$ and $\text{FADH}_2$ to actively pump $\text{H}^+$ into the intermembrane compartment, reduce $\frac{1}{2}\text{O}_2$ into metabolic $\text{H}_2\text{O}$, and power ATP synthase through facilitated diffusion.

Beta-Oxidation

The mitochondrial pathway that breaks down free fatty acids ($14\text{--}18$ carbons) into 2-carbon acetyl CoA units in the presence of oxygen; consumes $2\text{ ATP}$ initially and yields a net of $146\text{ ATP}$ for an 18-carbon fatty acid or $438\text{ ATP}$ per triglyceride.

Transamination

The enzymatic transfer of an amino group from an amino acid to a keto acid, generating metabolic intermediates that enter the Krebs cycle or can be converted to glucose for glycolysis.

Oxidative Deamination

The metabolic removal of an amino group from an amino acid to produce toxic ammonia ($\text{NH}_3$), which is subsequently converted into urea in the liver and excreted by the kidneys.

Basal Metabolic Rate (BMR)

The rate of energy expenditure needed to maintain basic physiological functions measured under resting conditions: at rest for at least $30\text{ minutes}$, mentally calm, in a comfortable room temperature, and fasted for at least $12\text{ hours}$.

Body Mass Index (BMI) Classifications

A standard clinical index where a value under $18.5$ is underweight, $18.5\text{--}24.5$ is normal, $25\text{--}29$ ($11\text{--}19\%$ above desirable weight) is overweight, $\ge 30$ ($\ge 20\%$ above desirable) is obese, $> 35$ is morbidly obese, and $> 40$ is super obese.

Neuropeptide Y (NPY)

A potent neurotransmitter synthesized in the arcuate nucleus of the hypothalamus that acts as a strong appetite stimulator.

Melanocortins

Neuropeptides produced in the arcuate nucleus of the hypothalamus that act as satiety signals to decrease food intake.

Leptin

An appetite-suppressing hormone synthesized by adipocytes (in the presence of insulin) that targets the hypothalamus to downregulate Neuropeptide Y, upregulate melanocortins, decrease hunger, and elevate metabolic rate.

Insulin

A peptide hormone secreted by pancreatic beta cells in response to elevated blood glucose; stimulates cellular glucose uptake, signals adipocytes to secrete leptin, and suppresses hypothalamic Neuropeptide Y.

Ghrelin

The 'hunger hormone' produced by the stomach and secreted into the bloodstream prior to meals, which stimulates hypothalamic Neuropeptide Y to trigger appetite.

PYY 3-36

A peptide hormone produced by the small and large intestines in response to food ingestion that travels to the hypothalamus to act as a satiety signal.

Cholecystokinin (CCK)

A digestive hormone released by the small intestine when filled with food that acts directly on the hypothalamus to promote satiety awareness.

Peripheral Digestive Hormones Summary

The peripheral signaling network governing energy intake, comprising leptin from adipocytes, insulin from the pancreas, PYY 3-36 from the intestines, CCK from the small intestine, and ghrelin from the stomach modulating hypothalamic NPY and melanocortin pathways.

Mechanisms of Cell Communication

The biological classifications of cell signaling, which include direct intercellular (gap junctions), contact-dependent signaling, autocrine ('self') signaling, paracrine (local) signaling, and endocrine (bloodstream transport) signaling.

Autocrine Signaling

A mode of contact-independent cell signaling where a cell secretes a chemical messenger that binds to and stimulates receptors on the identical cell that produced it.

Paracrine Signaling

A localized cell signaling mechanism in which chemical messengers diffuse through extracellular fluid to act on neighboring target cells within the immediate microenvironment.

Endocrine Signaling

A long-distance mode of cell communication where chemical messengers (hormones) are secreted into the bloodstream by endocrine glands to reach distant target tissues.

G-Protein Activation Cycle

The multi-step process wherein water-soluble hormone binding stimulates a receptor conformational change, prompting GTP to displace GDP on the $\alpha$ subunit; the activated $\alpha$ subunit dissociates until its intrinsic GTPase removes phosphate ($\text{P}_i$) to restore the inactive GDP-bound state.

Adenylate Cyclase Second Messenger Pathway

The signal transduction pathway wherein a GTP-bound G-protein $\alpha$ subunit activates adenylate cyclase to convert ATP into cyclic AMP (cAMP); cAMP activates protein kinases to trigger cellular responses until phosphodiesterase hydrolyzes cAMP into inactive AMP.

Lipid-Soluble Hormone Action

A slow-acting and slow-resolving signaling mechanism where lipid-soluble hormones diffuse freely through the plasma membrane, bind cytoplasmic or nuclear receptors, and bind hormone-response elements on DNA to alter gene transcription and protein synthesis.

Negative Feedback

A primary homeostatic regulatory mechanism in which the output or product of a physiological pathway feeds back to inhibit or shut down the upstream components of the pathway.

Positive Feedback

A self-amplifying regulatory cycle where the end product of a physiological cascade further accelerates its own production until a definitive physiological endpoint is reached (e.g., labor delivery, blood clotting, or breastfeeding).

Innate Immunity

The non-specific branch of the immune system that provides rapid, immediate defense against pathogens without forming immunological memory; utilizes anatomical barriers (skin, tears, stomach acid), granulocytes, and phagocytes.

Adaptive Immunity

The specific division of the immune system mediated by B lymphocytes and T lymphocytes that requires antigen presentation and contact-dependent activation to build tailored pathogen defenses and establish immunological memory.

Adaptive Immune Activation Pathways

The integrated adaptive immune response showing humoral immunity (where B cells encounter antigen, receive helper T cell paracrine signals, and differentiate into plasma cells producing antibodies) and cell-mediated immunity (where APCs present on MHC II to T helper cells and infected cells present on MHC I to cytotoxic T lymphocytes).

Mast Cell Activation and Signaling

The activation of mast cells by stimuli such as complement (C5a), IgE, IgG, neuropeptides, and cytokines, resulting in the release of histamine and TNF via autocrine, paracrine, or endocrine signaling to induce inflammation.