L Flashcards
Lactation
Production and release of milk from the mammalian mammary gland.
Lagena
An extension of the saccule of the inner ear of vertebrates; small in reptiles and amphibians but extended to form the cochlear duct in birds and the cochlea in mammals.
Lamella
A general term referring to a morphology that resembles stacks of leaves.
Lamellipodia
Flat, sheet-like extensions of the cell, supported by the actin cytoskeleton.
Laminar Flow
A pattern in which the layers of fluid move in parallel, usually relative to the surface of an object.
Larva
A pre-adult developmental stage that bears little resemblance to the adult form.
Latch State
A condition in smooth muscle in which force is generated with less than expected ATP consumption; usually attributed to a more efficient mechanism of crossbridge cycling.
Lateral Inhibition
Process by which a sensory stimulus at one location inhibits the activity of adjacent neurons. Lateral inhibition enhances contrast and improves edge detection in sensory systems.
Lateral Line System
A mechanoreceptive organ in fishes and amphibians that senses vibrations in the water surrounding the animal. Contains hair cells grouped into structures called neuromasts.
Law of Bulk Flow
Physical principle that states that fluids flow down pressure gradients, and that this flow is opposed by the resistance of the system; flow = pressure gradient / resistance.
Leak Channel
A passive ion channel in the cell membrane that allows the movement of ions down their concentration gradients.
Leaky Epithelia
An epithelial layer with cell-cell connections that permit paracellular transport.
Length Constant (λ)
A mathematical constant that expresses the distance that electrotonic current can spread along the membrane of a neuron; the distance over which a change in membrane potential decreases to 37% of its original value.
Lengthening Contraction
A type of muscle contraction in which external forces cause the muscle to lengthen while force is being generated.
Length-Tension Relationship
Describes the influence of sarcomere length on force development in muscle; muscle generates optimal force when sarcomere length is about 2 μm (in most muscles), and tension declines at higher or lower sarcomere lengths.
Lens
A clear object that can refract light. In the eye, the lens bends incoming light rays, helping to form a focused image on the retina.
Leukocytes
Vertebrate white blood cells; cells in blood that are involved in the immune system.
Leydig Cell
A testosterone-producing cell interspersed in the interstitium of the testes.
Lift
An upward force creating changes in pressure associated with movement over surfaces of an aerofoil/hydrofoil.
Lift Coefficient
A property of a surface that expresses its ability to generate lift.
Ligament
A form of connective tissue that joins two bones.
Ligand
A chemical that specifically and reversibly binds to a receptor or enzyme.
Ligand-Gated Ion Channel
An ion channel that opens or closes in response to the binding of a specific chemical.
Limbic System
A group of structures in the vertebrate brain that is involved in processes
including emotions and memory.
Lineweaver-Burk Equation
A plot of the reciprocals of reaction velocity (1/V) and substrate concentration (1/[S]); generates a linear relationship for enzymes with hyperbolic kinetics.
Lipase
An enzyme that breaks down lipid; includes triglyceride lipases, lipoprotein lipase, and phospholipase.
Lipid
A class of organic molecules that share hydrophobicity; includes fatty acids, phospholipids, triglycerides, and steroids.
Lipid Bilayer
The model for a plasma membrane in which the hydrophobic faces of two monolayers of phospholipids are associated.
Lipid Raft
A thickened region of the plasma membrane; often accumulates cholesterol, phospholipids with long chain fatty acids, and proteins with long transmembrane domains.
Lipogenesis
Conversion of fatty acids and glycerol to acylglycerides including monoacylglycerides, diacylglycerides, triglycerides, and phospholipids.
Lipolysis
Breakdown of acylglycerides and phospholipids.
Lipophilic
Hydrophobic or nonpolar.
Lipoprotein
A complex of lipids and proteins; central to the transport of lipids between tissues.
Load
A force that opposes muscle contraction.
Locomotor Module
A set of musculoskeletal components that work together to perform a single function, such as flying.
Long-Term Potentiation
A long-lasting enhancement of the postsynaptic response as a result of high-frequency stimulation of the presynaptic neuron.
Loop of Henle
A region of a mammalian kidney tubule that connects the proximal and distal tubule; central to the production of hyperosmotic urine.
Lower Critical Temperature (LCT)
The lowest environmental temperature at which a homeotherm can survive for long periods; the lower limit of its thermoneutral zone.
Lumen
The internal cavity of a multicellular unit, such as a kidney tubule or gastrointestinal tract.
Lungs
Respiratory surfaces that originate as invaginations of the body surface. Generally used for gas exchange in air.
Luteal Phase
The portion of an ovulatory cycle after the follicle has expelled the ovum and before a second follicle matures.
Lymph
A fluid consisting of an ultrafiltrate of blood and immune cells that travels through the lymphatic system of vertebrates.
Lymph Hearts
The pumping structures of the lymphatic system, present only in some vertebrates (including fish, amphibians, and reptiles).
Lymph Nodes
Small bean-shaped organs found in various locations in the lymphatic system of tetrapods; they filter lymphatic fluid and produce lymphocytes.
Lymphatic System
In the vertebrates, a network of vessels or sinuses (depending upon the species) that carries lymph back to the primary circulatory system. In many species it also performs an immune function.
Lymphocytes
Leukocytes that are involved in adaptive immunity in vertebrates.
Lysosomes
Organelles responsible for the breakdown of damaged and unnecessary membranous compartments and membrane proteins.
