Biology Flashcards
Sarcoplasmic Reticulum
A modified form of endoplasmic reticulum; stores calcium that is used to trigger contraction when muscle is stimulated.
Acrosome
The large vesicle at the head of a sperm cell containing enzymes that degrade the ovum cell membrane to allow fertilization.
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 violated-gated ion channels. Action Potentials are all-or-nothing events.
Schwann Cells
Cells that produce myelin in the peripheral nervous system.
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.
Secondary Response
Subsequent infections be pathogens that trigger a more immediate response from the memory cells produced during the primary immune response.
Semen
The fluid discharged during ejaculation. Semen consists of sperm cells and seminal fluid (fluid from the prostate and bulbourethral glands).
Semilunar Valves
Valves (the aortic valve and the pulmonic valve) that prevent backflow of blood from the arteries into the ventricles.
Seminiferous Tubules
Located in the testes, the seminiferous tubules are the site of sperm production.
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.
Sister Chromatids
The relationship between the strands of DNA after replication. Each chromosome consists of two identical chromatids held together at a central region called the centromere. After the mitotic spindle pulls the sister chromatids apart, each chromatid is referred to as a chromosome on its own.
Skeletal Muscle
Type of muscle responsible for voluntary movement, consisting of multi nucleated, striated (striped) muscle fibers.
Small Intestine
Section of the digestive tract that can be divided into three sections: Duodenum, jejunum, and ileum. Most digestion takes pace in the duodenum and most absorption takes place in the jejunum and the ileum.
Smooth Muscle
Nonstriated muscle, responsible for involuntary action. Controlled by the autonomic nervous system.
Sodium-Potassium Pump
A protein that hydrolyzes one ATP to transport three NA+ out of the cell for every two K+ it transports into the cell.
Somatic Cells
All cells excluding the germ (reproductive) cells.
Somatic Nervous System
Division of the peripheral nervous system that is responsible for voluntary movement.
Somatostatin
Produced and secreted by the O-cells of the pancreas, somatostatin inhibits the release of glucagon and insulin.
Spermatozoa
Mature sperm specialized for transporting the genetic information from the male to the ovum.
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.
Stabilizing Selection
Type of natural selection where the average phenotype is favored while those outside the norm are eliminated.
Starling Forces
A balance between hydrostatic and oncotic pressures on both side of a membrane essential for maintaining proper fluid volumes and soluate concentrations inside and outside the vasculature.
Steroid Hormones
Nonpolar hormones that cross the cell membrane and act by binding intracellular receptors.
Superior Vena Cava
A large vein that returns deoxygenated blood from the head and neck regions, as well as the upper extremities, to the right atrium of the heart.