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October, 2006
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Homeostasis: The processes whereby the internal environment of an organism tends to remain balanced and stable.

Assessment of Dopaminergic Homeostasis in Mice by Use of High-performance Liquid Chromatography Analysis and Synaptosomal Dopamine Uptake

1Molecular Neuropharmacology and Genetics Laboratory, Lundbeck Foundation Center for Biomembranes in Nanomedicine, Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2Laboratory of Neuropsychiatry, Psychiatric Center Copenhagen and Department of Neuroscience and Pharmacology, University of Copenhagen

JoVE 56093


Physiology of the Circulatory System- Concept

JoVE 10625


Conditions in the external environment of an organism can change rapidly and drastically. To survive, organisms must maintain a fairly constant internal environment, which involves continuous regulation of temperature, pH, and other factors. This balanced state is known as homeostasis, which describes the processes by which organisms maintain their optimal internal…

 Lab Bio

What is Biology?

JoVE 10647

Biology is the natural science that focuses on the study of life and living organisms, including their structure, function, development, interactions, evolution, distribution, and taxonomy. The scope of the field is extensive and is divided into several specialized disciplines, such as anatomy, physiology, ethology, genetics, and many more.

All living things share a few key traits: cellular organization, heritable genetic material and the ability to adapt/evolve, metabolism to regulate energy needs, the ability to interact with the environment, maintain homeostasis, reproduce, and the ability to grow and change. Despite its complexity, life is organized and structured. The cell theory in biology states that all living organisms are composed of one or more cells. The cell is the basic unit of life, and all cells arise from previously existing cells. Even single-celled organisms, such as bacteria, have structures that allow them to carry out essential functions, such as interacting with the environment and carry out chemical reactions that maintain life, or metabolism. In multicellular organisms, cells work together to form tissues, organs, organ systems, and finally, entire organisms. This hierarchical organization can extend further into populations, communities, ecosystems, and the biosphere. An organism’s genetic material, the biologi

 Core: Biology

Key Elements for Plant Nutrition

JoVE 11103

Like all living organisms, plants require organic and inorganic nutrients to survive, reproduce, grow and maintain homeostasis. To identify nutrients that are essential for plant functioning, researchers have leveraged a technique called hydroponics. In hydroponic culture systems, plants are grown—without soil—in water-based solutions containing nutrients. At least 17 nutrients have been identified as essential elements required by plants. Plants acquire these elements from the atmosphere, the soil in which they are rooted, and water. Nine of these essential nutrients—collectively called macronutrients—are needed by plants in more significant amounts. The macronutrients include carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, calcium, magnesium, and potassium. Critical plant compounds, such as water, proteins, nucleic acids, and carbohydrates, contain macronutrients. Macronutrients also regulate cellular processes. For example, potassium regulates the opening and closing of stomata for gas exchange. Plants need micronutrients in smaller amounts. These include chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum. Many micronutrients function as cofactors, which enable the activity of enzymes. Therefore, without micronutrients, plants are unable to perform critical functions. A plant experiencing an

 Core: Biology

Responses to Heat and Cold Stress

JoVE 11119

Every organism has an optimum temperature range within which healthy growth and physiological functioning can occur. At the ends of this range, there will be a minimum and maximum temperature that interrupt biological processes.

When the environmental dynamics fall out of the optimal limit for a given species, changes in metabolism and functioning occur – and this is defined as stress. Plants respond to stress by initiating changes in gene expression - leading to adjustments in plant metabolism and development aimed at attaining a state of homeostasis. Plants maintain membrane fluidity during temperature fluctuations Cell membranes in plants are generally one of the first structures that are affected by a change in ambient temperature. These membranes primarily constitute phospholipids, cholesterol, and proteins, with the lipid portion comprising long chains of unsaturated or saturated fatty acids. One of the primary strategies plants can adopt under temperature change is to alter the lipid component of their membranes. Typically, plants will decrease the degree of unsaturation of membrane lipids under high temperature, and increase it under low temperature, maintaining the fluidity of the membrane. Heat Shock Proteins The exposure of plant tissue or cells to sudden high-temperature stress res

 Core: Biology

The Parasympathetic Nervous System

JoVE 10839

The parasympathetic nervous system is one of the two major divisions of the autonomic nervous system. This parasympathetic system is responsible for regulating many unconscious functions, such as heart rate and digestion. It is composed of neurons located in both the brain and the peripheral nervous system that send their axons to target muscles, organs, and glands.

Activation of the parasympathetic system tends to have a relaxing effect on the body, promoting functions that replenish resources and restore homeostasis. It is therefore sometimes referred to as the “rest and digest” system. The parasympathetic system predominates during calm times when it is safe to devote resources to basic “housekeeping” functions without a threat of attack or harm. The parasympathetic nervous system can be activated by various parts of the brain, including the hypothalamus. Preganglionic neurons in the brainstem and sacral part of the spinal cord first send their axons out to ganglia—clusters of neuronal cell bodies—in the peripheral nervous system. These ganglia contain the connections between pre- and postganglionic neurons and are located near the organs or glands that they control. From here, postganglionic neurons send their axons onto target tissues—generally smooth muscle, cardiac muscle, or glands. Typic

 Core: Biology

Thyroid Exam

JoVE 10098

Source: Richard Glickman-Simon, MD, Assistant Professor, Department of Public Health and Community Medicine, Tufts University School of Medicine, MA

The thyroid gland is located in the neck anterior trachea between the cricoid cartilage (above) and the suprasternal notch (below) (Figure 1). It consists of a right and left…

 Physical Examinations II

Autocrine Signaling

JoVE 10973

Secreted signals can act on a variety of target cells. In some cases, the cell that secretes a signal also detects and responds to the signaling molecule it produces; this is called Autocrine Signaling.

Under normal physiological conditions, autocrine signaling is important for homeostasis. This process is well characterized in the macrophages of the immune system. Macrophages secrete a variety of signals including the cytokine Interleukin-1, IL-1. The secreting macrophages also possess membrane receptors for IL-1 that, when bound, can activate an intracellular signaling cascade. The resulting intracellular signals trigger the secretion of additional cytokines including more IL-1 from the target cell. Though IL-1 secreted by these macrophages can also bind to receptors on other cells and cell types, binding to the signaling cell is important in the regulation of signal production. Autocrine signaling is also a major mechanism of cancer cell proliferation. Cancerous cells secrete a variety of growth signals to themselves, through autocrine signaling, and to nearby tissues. For example, progesterone appears to act in an autocrine manner in breast cancer, whereby progesterone binds to progesterone receptors on the signaling cell, stimulating the action of growth-promoting genes. Autocrine signaling can also play a role in the development of skin cancer by stim

 Core: Biology
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