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Kaplan Biology
MCAT Biology Flashcards
| Term | Definition |
|---|---|
| Respiratory Rate | Expressed as breaths per minute. Raising the respiratory rate can decrease the amount of carbon dioxide in the blood, thus increasing the pH. Likewise, decreasing the respiratory rate increases the concentration of carbon dioxide in the blood, resulting in a lower pH. |
| Pathway of the Respiratory Tract | Air travels through the nasal or oral cavity, pharynx, larynx, trachea, bronchi, bronchioles, and finally the alveoli (site of gas exchange). |
| Negative Pressure Breathing | The contraction of the diaphragm and the intercostal muscles increases the volume of the thoracic cavity, reducing the pressure in the intrapleural space. This decrease in pressure creates a vacuum that causes the lungs to suck in air. |
| Hyperventilation | An increase in the rate of respiration or tidal volume. Lack of oxygen or a decrease in blood pH promotes hyperventilation. |
| Thermoregulation | Maintenance of a constant internal body temperature. |
| Surfactant | A liquid substance produced by the lung that reduces surface tension in the alveoli. Surfactant prevents lung collapse and decreases the effort needed to expand the lungs (inhale). |
| Intrapleural Space | The space between the two membranes (visceral pleura and parietal pleura) that cover the lungs. |
| Epiglottis | A flap of cartilage that covers the glottis when swallowing food in order to prevent food particles from entering the larynx. |
| Capillaries | Blood vessels composed of a single layer of endothelial cells, facilitating exchange of gases, nutrients, and waste products between the blood and interstitial fluid. |
| Vagus Nerve | One of the twelve cranial nerves; the vagus nerve provides parasympathetic signaling to the thoracic and abdominal cavities. |
| Threshold Voltage | The minimal voltage that must be reached in order for an action potential to be fired at the axon hillock. |
| Synaptic Terminals | Ends of axons that form one side of the synaptic cleft; the location where vesicles of neurotransmitters are stored. |
| Efferent Neurons | Neurons that carry information from the central nervous system to other parts of the body. Also called motor neurons. |
| Depolarization | A process that occurs when the voltage-gated Na⁺ channels open, allowing Na⁺ to rush into the cell and depolarize it |
| Dendrite | An extension of the neuron that transmits impulses toward the cell body |
| Afferent Neurons | Neurons that carry information to the central nervous system from the periphery. Also called sensory neurons. |
| Synapse | The space between the axon terminal of one neuron and the dendrite of another neuron (or membrane of an effector organ) where neurotransmitters are released |
| Somatic Nervous System | Division of the peripheral nervous system that is responsible for voluntary movement. |
| Saltatory Conduction | A means by which action potentials jump from node to node along an axon. |
| Resting Potential | The charge difference across the cell membrane of a neuron or a muscle cell while at rest. Most often maintained by the sodium-potassium pump. |
| Nodes of Ranvier | Gaps between segments of myelin sheath where action potentials can take place, allowing for saltatory conduction. |
| Neurotransmitters | Chemical messengers released from synaptic terminals of a neuron that can bind to and stimulate a postsynaptic cell. |
| Axon Hillock | The portion of the neuron that connects the cell body (soma) to the axon. The impulses the neuron receives from all the dendrites are summed up at the axon hillock to determine whether or not an action potential will be initiated. |
| Action Potential | A sharp change in the membrane potential of neurons or muscle cells caused by a change in the selective permeability to Na⁺ and K⁺ using voltage-gated ion channels. Action potentials are all-or-nothing events. |
| Epiphysis | Dilated ends of long bones in the appendicular skeleton. |
| Diaphysis | Cylindrical shaft of a long bone. Filled with bone marrow for the production of blood cells. |
| White Fibers | Fast-twitch muscle fibers. They are primarily anaerobic and fatigue more easily than red fibers. |
| Transverse Tubules | A system of tubules that provides channels for ion flow throughout skeletal and cardiac muscle fibers to facilitate the propagation of an action potential. |
| Spongy Bone | Lighter and less dense than compact bone, it consists of an interconnecting lattice of bony spicules (trabeculae). The cavities between the spicules contain bone marrow. |
| Smooth Muscle | Nonstriated muscle, responsible for involuntary action. Controlled by the autonomic nervous system. |
| Skeletal Muscle | Type of muscle responsible for voluntary movement, consisting of multinucleated, striated (striped) muscle fibers |
| Sarcoplasmic Reticulum | A modified form of endoplasmic reticulum; stores calcium that is used to trigger contraction when muscle is stimulated. |
| Sarcomere | The structural unit of striated muscle. It is composed of thin (mostly actin) and thick (mostly myosin) filaments. |
| Red Fibers | Slow-twitch muscle fibers. They are primarily aerobic and contain many mitochondria and high levels of myoglobin. |
| Osteons | The structural unit of compact bone that consists of a central canal (either a Haversian or Volkmann's canal) surrounded by a number of concentric rings of bony matrix called lamellae. |
| Osteoclasts | Cells in the bone matrix that are involved in bone degradation. |
| Osteoblasts | Cells in the bone tissue that secrete the organic constituents of the bone matrix. Osteoblasts develop into osteocytes. |
| Compact Bone | Much more dense than spongy bone, compact bone consists of Haversian systems (osteons). |
| Cartilage | A firm, elastic, translucent connective tissue consisting of collagenous fibers embedded in chondrin. Produced by cells called chondrocytes. Cartilage is the principal component of embryonic skeletons and can harden and calcify into bone (ossify). |
| Cardiac Muscle | Type of muscle found within the heart; may contain one or two nuclei. Involuntary, like smooth muscle, but appears striated, like skeletal muscle. Able to depolarize independent of the nervous system. |
| Axial Skeletal System | The skull, vertebral column, ribcage, and hyoid bone. |
| Appendicular Skeletal System | The bones of the pelvis, the pectoral girdles, and the limbs. |
| Innate Immunity | Nonspecific immunity provided by structures and cells. Structures, such as the skin, and cells, such as macrophages, are able to recognize invaders and kill them. Some cells of the innate immune system, such as macrophages and dendritic cells, are able to signal the presence of an invader to the adaptive immune system. Contrast with adaptive immunity. |
| Immunoglobulin | Synonymous with antibody; produced in response to a specific foreign substance that recognizes and binds to that antigen and triggers an immune response. |
| Cell Mediated (Cytotoxic) Immunity | Branch of the immune system in which intracellular pathogens are eliminated by killing their host cells. T-cells are the primary mediators of cytotoxic immunity. |
| Antigen | A substance that is bound by an antibody, causing an immune reaction. |
| Secondary Response | Subsequent infections by pathogens that trigger a more immediate response from the memory cells produced during the primary immune response. |
| Primary Response | The initial response to a specific antigen. During a primary response, T- and B-cells are activated and specific antibodies and memory cells for the antigen are produced. |
| Lymphatic System | A system of vessels and lymph nodes that collect interstitial fluids and return them to the circulatory system, thereby maintaining fluid balance. The lymphatic system is also involved in lipid absorption and lymphocyte activation. |
| Humoral Immunity | The synthesis of specific antibodies by activated B-cells in response to an antigen. These antibodies bind to the antigen and either clump together to become insoluble, neutralize the antigen, or attract other cells that engulf and digest the pathogen. |
| Thyroid Stimulating Hormone (TSH) | Synthesized and released by the anterior pituitary, TSH stimulates the thyroid gland to absorb iodine and to synthesize and secrete thyroid hormones. TSH is regulated by thyroid releasing hormone (TRH), which is released by the hypothalamus |
| Growth Hormone (GH) | Synthesized and released by the anterior pituitary, GH stimulates bone and muscle growth as well as glucose conservation. GH is inhibited by somatostatin and stimulated by growth hormone releasing hormone (secreted by the hypothalamus). |
| Exocrine Glands | Glands that synthesize and secrete substances through ducts. The mammary glands and sweat glands are examples of exocrine glands. |
| Endocrine Glands | Glands that synthesize and secrete hormones into the circulatory system. Examples include the hypothalamus, pituitary gland, pineal gland, pancreas, testes, ovaries, adrenal glands, thyroid gland, and parathyroid glands. |
| Antidiuretic Hormone (ADH) | A peptide hormone, also known as vasopressin, that acts on the collecting duct to increase water reabsorption. ADH is produced by the hypothalamus and stored in the posterior pituitary. |
| Adrenocorticotropic Hormone (ACTH) | Synthesized and released by the anterior pituitary, ACTH stimulates the adrenal cortex to synthesize and secrete glucocorticoids. ACTH is regulated by corticotropin releasing factor (CRF), which is released by the hypothalamus. |
| Tropic Hormones | Hormones that travel to a target tissue and cause the release of another hormone. A hormone downstream will cause the physiological effect. |
| Thyroid Hormones | Synthesized and released by the thyroid gland, thyroid hormones triiodothyronine (T₃) and thyroxine (T₄) stimulate cellular respiration as well as protein and fatty acid synthesis and degradation. |
| Steroid Hormones | Nonpolar hormones that cross the cell membrane and act by binding intracellular receptors. |
| Somatostatin | Produced and secreted by the δ-cells of the pancreas, somatostatin inhibits the release of glucagon and insulin. |
| Signaling Cascade | Series of events, starting with the binding of a peptide hormone to a surface receptor. This sequence of events ultimately results in a change in cellular behavior. |
| Second Messenger | A small molecule that transduces a hormonal signal from the exterior of the cell to the interior. Usually released when a peptide hormone binds to its receptor; cAMP is a common example. |
| Prolactin | A hormone synthesized and released by the anterior pituitary that stimulates milk production and secretion in female mammary glands. |
| Posterior Pituitary | Stores and releases hormones (oxytocin and ADH) synthesized by the hypothalamus. The release of these hormones is triggered by an action potential that originates in the hypothalamus. |
| Peptide Hormones | Polar hormones incapable of permeating the cell membrane that bind to surface receptors and act through secondary messengers. |
| Parathyroid Hormone (PTH) | Synthesized and released by the parathyroid gland, PTH increases blood Ca²⁺ concentration by increasing Ca²⁺ reabsorption in the kidneys and by stimulating calcium release from bone. |
| Insulin | Produced and secreted by the β-cells of the pancreas, insulin decreases blood glucose concentrations by facilitating the uptake of glucose by muscle and adipose cells and the conversion of glucose to glycogen in muscle and liver cells. |
| Glucocorticoids | Synthesized and released by the adrenal cortex, glucocorticoids raise blood glucose levels while decreasing protein synthesis. |
| Glucagon | Produced and secreted by the α-cells of the pancreas, glucagon increases blood glucose concentration by promoting gluconeogenesis and the conversion of glycogen to glucose in the liver. |
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