Anatomy and Physiology: Musculoskeletal, Reproductive, Nervous, and Gastrointestinal Systems

Comprehensive practice flashcards featuring key vocabulary, structural features, anatomical divisions, histology, and clinical concepts from musculoskeletal, reproductive, central and peripheral nervous, and gastrointestinal lectures.

Hyaline Cartilage

A glassy-looking cartilage providing firm support with some pliability, containing large numbers of invisible collagen fibers and 1% to 10% chondrocytes; located at the articular ends of long bones, costal cartilages, respiratory pathways, nose, and the embryonic skeleton.

Fibrocartilage

A highly compressible cartilage with thick collagen fibers and no perichondrium; optimized for tensile strength and shock absorption in intervertebral discs, the pubic symphysis, and menisci of the knee.

Elastic Cartilage

Cartilage nearly identical to hyaline cartilage but containing significantly more elastic fibers, found where strength and exceptional stretching and bending are required, such as the external ear and epiglottis.

Osteon (Haversian System)

The structural and functional unit of compact bone, consisting of concentric, weight-bearing lamellar rings of matrix surrounding a central Haversian canal that carries blood vessels and nerves.

Perforating (Volkmann's) Canals

Channels lying at right angles to the long axis of the bone that connect the vascular and nerve supplies of the periosteum to those of the central canals and medullary cavity.

Hydroxyapatite

The inorganic mineral component of bone matrix, mainly calcium phosphates $\text{Ca}_5(\text{PO}_4)_3(\text{OH})$, constituting roughly $65\%$ of bone mass and providing hardness and resistance to compression.

Osteoid

The organic component of the bone matrix consisting of proteoglycans, glycoproteins, and collagen fibers secreted by osteoblasts.

Intramembranous Ossification

The process of bone development directly from fibrous connective tissue membranes formed by mesenchymal cells; forms the clavicles and cranial flat bones of the skull starting at week 8 of embryonic development.

Endochondral Ossification

The formation of bone by breaking down and replacing a pre-existing hyaline cartilage model; begins in the second month of embryonic development for most bones below the base of the skull.

Appositional Bone Growth

The growth process by which bones increase in width or girth through the addition of new bone tissue beneath the periosteum accompanied by resorption at the endosteal surface.

Interstitial Bone Growth

The longitudinal lengthening of long bones occurring at the epiphyseal plates via cartilage cell division, hypertrophy, calcification, and ossification as long as hyaline cartilage remains.

Greenstick Fracture

An incomplete bone fracture in which one side of the shaft breaks while the other side bends; common in children due to their higher proportion of flexible organic matrix.

Disuse Atrophy

The rapid loss of muscle mass and function occurring immediately after immobilization or loss of neural stimulation, progressing at a rate of approximately $5\%$ per day.

Dartos Muscle

A layer of smooth muscle in the superficial fascia of the scrotum that contracts in response to cold temperatures, wrinkling the scrotal skin to reduce surface area and minimize heat loss.

Cremaster Muscle

Bands of skeletal muscle arising from the internal oblique muscles of the trunk that elevate the testes closer to the pelvic floor when exposed to cold.

Seminiferous Tubules

Tightly coiled tubular structures within testicular lobules composed of thick stratified epithelium containing spermatogenic cells, sustentocytes, and outer myoid cells; the actual sites of sperm production.

Interstitial Endocrine (Leydig) Cells

Cells located in the soft connective tissue surrounding seminiferous tubules that produce androgens, predominantly testosterone.

Pampiniform Venous Plexus

An extensive network of veins arising from the testicular veins that surrounds the testicular artery within the spermatic cord, acting as a countercurrent heat exchanger to cool arterial blood entering the testes.

Corpora Cavernosa

Paired dorsal cylinders of erectile tissue bound by fibrous tunica albuginea that make up the bulk of the penis and whose proximal ends form the crura.

Corpus Spongiosum

A mid-ventral erectile body surrounding the spongy urethra that expands distally to form the glans penis and proximally to form the bulb of the penis.

Epididymis

A cup-shaped organ consisting of a head, body, and roughly $6\,\text{m}$ coiled duct lined with stereocilia-bearing pseudostratified epithelium, where immature sperm undergo a $\approx 20$-day transit to mature, gain motility, and be stored.

Seminal Glands (Seminal Vesicles)

Paired accessory glands on the posterior surface of the urinary bladder that secrete a yellowish, viscous alkaline fluid containing fructose that enhances sperm motility and makes up approximately $70\%$ of semen volume.

Bulbo-urethral Glands

Pea-sized glands located inferior to the prostate in the urogenital diaphragm that secrete a thick, clear mucus prior to ejaculation to neutralize acidic urine traces and lubricate the spongy urethra.

Corpus Luteum

The glandular endocrine structure formed from a ruptured ovarian follicle following ovulation that secretes progesterone and estrogens before eventually degenerating.

Stratum Functionalis

The superficial, dynamic stratum of the endometrium that undergoes cyclic changes in response to ovarian hormones and is shed during menstruation.

Stratum Basalis

The deeper, thinner endometrial layer containing stem cells that is unresponsive to ovarian hormones and remains intact after menstruation to regenerate a new stratum functionalis.

Greater Vestibular Glands

Pea-sized glands flanking the vaginal orifice, homologous to male bulbo-urethral glands, that secrete lubricating mucus into the vestibule during sexual arousal.

Primary Brain Vesicles

The three initial embryonic expansions of the anterior neural tube: the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain).

Primary Motor Cortex

The motor area located in the precentral gyrus of the frontal lobe containing pyramidal cells whose axons form the corticospinal tracts, controlling skilled voluntary muscle contractions in a contralateral, somatotopic fashion.

Primary Somatosensory Cortex

The sensory cortex located in the postcentral gyrus of the parietal lobe that receives and localizes somatic sensory input from skin receptors, proprioceptors, joints, and tendons.

Basal Nuclei

Subcortical gray matter structures deep within cerebral white matter—comprising the caudate nucleus, putamen, and globus pallidus—that help control and coordinate skeletal muscle movements.

Thalamus

A bilobed diencephalic structure connected by the interthalamic adhesion that serves as the major sensory relay station and gateway to the cerebral cortex, sorting and editing ascending impulses.

Hypothalamus

The main visceral control center of the body located below the thalamus; regulates the autonomic nervous system, body temperature, food intake, water balance, sleep-wake cycles, and pituitary hormone output.

Epithalamus

The most dorsal portion of the diencephalon forming the roof of the third ventricle; contains the pineal gland, which secretes melatonin to regulate sleep-wake cycles.

Arbor Vitae

The distinctive tree-like branching pattern of internal white matter within the cerebellum.

Arachnoid Granulations

Knob-like projections of the arachnoid mater that protrude superiorly through the dura mater into the superior sagittal sinus to reabsorb cerebrospinal fluid into venous blood.

Conus Medullaris

The cone-shaped, tapering terminal end of the spinal cord situated at the level of the first or second lumbar vertebra ($\text{L}_1$ or $\text{L}_2$).

Cauda Equina

The collection of nerve roots resembling a horse's tail that descends through the inferior vertebral canal below the conus medullaris.

Lumbar Puncture

A clinical procedure in which a needle is inserted into the subarachnoid space between $\text{L}_3$ and $\text{L}_4$ or $\text{L}_4$ and $\text{L}_5$ to safely sample cerebrospinal fluid without damaging the spinal cord.

Astrocytes

The most abundant and versatile CNS glial cells; they anchor neurons to capillaries, determine blood vessel permeability, recapture potassium ions and neurotransmitters, and guide neuronal migration.

Microglial Cells

Small, ovoid CNS neuroglia with thorny processes that monitor neuronal health and differentiate into specialized macrophages to phagocytose dead neurons and invading microorganisms.

Ependymal Cells

Squamous to columnar ciliated neuroglial cells lining the central cavities of the brain and spinal cord, forming a permeable barrier between CSF and brain interstitial fluid and assisting in CSF circulation.

Oligodendrocytes

Branching CNS glial cells whose multiple flattened processes wrap around thick axons of multiple neurons (up to 60 simultaneously) to form insulating myelin sheaths.

Schwann Cells (Neurolemmocytes)

PNS neuroglia that form myelin sheaths around individual thick peripheral nerve fibers, featuring an outer collar of perinuclear cytoplasm (neurilemma) and aiding in peripheral nerve fiber regeneration.

Trigger Zone (Neuron)

The junction between the axon hillock and the initial segment of the axon where the nerve impulse (action potential) is generated in motor neurons.

Nodes of Ranvier

Gaps in the myelin sheath occurring at regular intervals along an axon between adjacent Schwann cells or oligodendrocyte extensions, facilitating rapid impulse propagation.

Multipolar Neurons

Neurons having three or more processes (one axon and multiple dendrites); the most common structural type in the human body, accounting for over $99\%$ of neurons.

Bipolar Neurons

Rare structural class of neurons with exactly two processes extending from opposite sides of the cell body (one axon, one dendrite); found in special sense organs such as the retina and olfactory mucosa.

Unipolar (Pseudounipolar) Neurons

Neurons featuring a single short process emerging from the cell body that divides into a peripheral process associated with sensory receptors and a central process entering the CNS; typically located in dorsal root ganglia.

Interneurons

Multipolar nerve cells situated entirely within the CNS between sensory and motor neurons that process, shuttle, and integrate signals; constitute more than $99\%$ of all neurons.

Peritoneal Cavity

The potential slit-like space between the parietal and visceral peritoneum containing slippery serous fluid that lubricates abdominal organs to prevent friction during movement.

Mesentery

A double layer of fused peritoneum extending from the body wall to digestive organs that conducts blood vessels, lymphatics, and nerves, holds viscera in position, and stores fat.

Abdominal Wall Regions

A nine-region anatomical division of the anterior abdomen formed by two midclavicular planes, a subcostal plane, and an intertubercular plane; encompasses hypochondriac, lumbar/flank, iliac/groin, epigastric, umbilical, and pubic/hypogastric regions.

Parietal Cells

Gastric gland cells that secrete hydrochloric acid ($\text{HCl}$), which creates an acidic environment to activate pepsin and kill microbes, and intrinsic factor, which is required for vitamin $\text{B}_{12}$ absorption.

Chief Cells

Gastric gland cells located predominantly in the basal regions of the glands that secrete pepsinogen (the inactive precursor to pepsin) and lipases.

Enteroendocrine Cells

Specialized endocrine cells scattered in the mucosa of the stomach and small intestine that release chemical messengers directly into the interstitial fluid, such as gastrin, histamine, and secretin.

Portal Triad

A microscopic grouping situated at each corner of a liver lobule, consisting of a portal arteriole, a portal venule, and a bile duct.

Peyer's Patches

Aggregated lymphoid nodules located in the lamina propria and submucosa of the distal ileum that prevent bacteria from crossing into the bloodstream.

Teniae Coli and Haustra

Distinctive gross features of the large intestine: teniae coli are three ribbons of longitudinal smooth muscle whose muscle tone puckers the intestinal wall into pocket-like sacs called haustra.

Hepatic Portal System

A specialized venous circulation that collects nutrient-rich venous blood from the stomach, intestines, pancreas, and spleen via the splenic and superior mesenteric veins, delivering it to the liver sinusoids before entering the inferior vena cava.