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Brain Death: A state of prolonged irreversible cessation of all brain activity, including lower brain stem function with the complete absence of voluntary movements, responses to stimuli, brain stem reflexes, and spontaneous respirations. Reversible conditions which mimic this clinical state (e.g., sedative overdose, hypothermia, etc.) are excluded prior to making the determination of brain death. (From Adams et al., Principles of Neurology, 6th ed, pp348-9)

Urea Cycle

JoVE 10892

The urea cycle describes how liver cells convert ammonia to urea. Ammonia is a toxic waste product of protein catabolism. Land animals must convert ammonia into the less toxic urea which can be safely eliminated by the kidneys through urine. Marine animals excrete ammonia directly, and the surrounding water dilutes the ammonia to safe levels.

There are five basic steps in the urea cycle: the conversion of ammonia (NH3) to carbamoyl phosphate the introduction of ornithine in the transformation of carbamoyl phosphate to citrulline the transformation of citrulline into arginosuccinate involving aspartate and chemical energy (ATP) the conversion of arginosuccinate into arginine with fumarate as a by-product the formation of urea and ornithine from arginine Notice that ornithine is used in the second step and is regenerated in the last step. Since ornithine is recycled, the urea cycle is sometimes referred to as the ornithine cycle. Elevated levels of blood ammonia, or hyperammonemia, results from an interruption of the urea cycle. This can occur at the organ level where scar tissue blocks the blood supply to the liver. Scar tissue, or cirrhosis, can result from chronic alcohol abuse, hepatitis B, or hepatitis C infection. Within the liver cells, disruption of the urea c

 Core: Biology

Cell Division- Concept

JoVE 10571

Cell division is fundamental to all living organisms and required for growth and development. As an essential means of reproduction for all living things, cell division allows organisms to transfer their genetic material to their offspring. For a unicellular organism, cellular division generates a completely new organism. For multicellular organisms, cellular division produces new cells for…

 Lab Bio

Adult Stem Cells

JoVE 10810

Stem cells are undifferentiated cells that divide and produce more stem cells or progenitor cells that differentiate into mature, specialized cell types. All the cells in the body are generated from stem cells in the early embryo, but small populations of stem cells are also present in many adult tissues including the bone marrow, brain, skin, and gut. These adult stem cells typically produce the various cell types found in that tissue—to replace cells that are damaged or to continuously renew the tissue. The epithelium lining the small intestine is continuously renewed by adult stem cells. It is the most rapidly replaced tissue in the human body, with most cells being replaced within 3-5 days. The intestinal epithelium consists of thousands of villi that protrude into the interior of the small intestine—increasing its surface area to aid in the absorption of nutrients. Intestinal stem cells are located at the base of invaginations called crypts that lie between the villi. They divide to produce new stem cells, as well as daughter cells (called transit amplifying cells) that divide rapidly, move up the villi and differentiate into all the cell types in the intestinal epithelium, including absorptive, goblet, enteroendocrine, and Paneth cells. These mature cells continue to move up the villi as they carry out their functions, except Paneth cell

 Core: Biology


JoVE 10902

In response to tissue injury and infection, mast cells initiate inflammation. Mast cells release chemicals that increase the permeability of adjacent blood capillaries and attract additional immune cells to the wound or site of infection. Neutrophils are phagocytic leukocytes that exit the bloodstream and engulf invading microbes. Blood clotting platelets seal the wound and fibers create a scaffold for wound healing. Macrophages engulf aging neutrophils to end the acute inflammatory response. Tissue injury and infection are the primary causes of acute inflammation. Inflammation protects the body by eliminating the cause of tissue injury and initiating the removal of cell debris resulting from the initial damage and related immune cell activity. Inflammation involves mediators of both the innate and adaptive immune system. Proper regulation of inflammation is crucial to clear the pathogen and remove cell debris without overly damaging healthy tissue in the process. If inflammatory processes are not properly regulated, chronic inflammation can arise that is often fatal. Mast cells are the first to respond to tissue injury, as they are primarily located in areas that have contact with the exterior: the skin, gut, and airways. Mast cells have an arsenal of receptors on their cell surface and can hence be activated by a wide variety of stimuli, such as mi

 Core: Biology

Ionic Bonds

JoVE 10665

When atoms gain or lose electrons to achieve a more stable electron configuration they form ions. Ionic bonds are electrostatic attractions between ions with opposite charges. Ionic compounds are rigid and brittle when solid and may dissociate into their constituent ions in water. Covalent compounds, by contrast, remain intact unless a chemical reaction breaks them.

Ionic bonds are reversible electrostatic interactions between ions with opposing charges. Elements that are the most reactive (i.e., have a higher tendency to undergo chemical reactions) include those that only have one valence electron, (e.g., potassium) and those that need one more valence electron (e.g., chlorine). Ions that lose electrons have a positive charge and are referred to as cations. Ions that gain electrons have a negative charge and are called anions. Cations and anions combine in ratios that result in a net charge of 0 for the compound they form. For example, the compound potassium chloride (KCl) contains one chloride ion for each potassium ion, because the charge of potassium is +1 and the charge of chloride is -1. The compound magnesium chloride (MgCl2) contains two chloride ions for each magnesium ion because magnesium’s charge is +2. The electrostatic forces holding ionic compounds together are strong when the compounds are in solid form. Since t

 Core: Biology

The TUNEL Assay

JoVE 5651

One of the hallmarks of apoptosis is the nuclear DNA fragmentation by nucleases. These enzymes are activated by caspases, the family of proteins that execute the cell death program. TUNEL assay is a method that takes advantage of this feature to detect apoptotic cells. In this assay, an enzyme called terminal deoxynucleotidyl transferase catalyzes the addition of dUTP…

 Cell Biology

The Cochlea

JoVE 10855

The cochlea is a coiled structure in the inner ear that contains hair cells—the sensory receptors of the auditory system. Sound waves are transmitted to the cochlea by small bones attached to the eardrum called the ossicles, which vibrate the oval window that leads to the inner ear. This causes fluid in the chambers of the cochlea to move, vibrating the basilar membrane.

The basilar membrane extends from the basal end of the cochlea near the oval window to the apical end at its tip. Although the cochlea itself narrows towards the apical end, the basilar membrane has the opposite geometry—becoming wider and more flexible towards the apical end. Primarily because of these physical characteristics, the apical end of the basilar membrane maximally vibrates when exposed to low-frequency sounds, while the narrower, stiffer basal end maximally vibrates when exposed to high frequencies. This gradient of frequency response creates tonotopy—a topographic map of pitch—in the cochlea. The hair cells are stimulated by the shearing force created by the vibration of the basilar membrane below them, relative to the stiffer tectorial membrane above them. Because of the tonotopy of the basilar membrane, hair cells are maximally stimulated by different frequencies depending on where they are in the cochlea. Those at the basal end respond be

 Core: Biology

Anesthesia Induction and Maintenance

JoVE 10263

Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN

The Guide for the Care and Use of Laboratory Animals ("The Guide") states that pain assessment and alleviation are integral components of the veterinary care of laboratory animals.1 The definition of anesthesia is the loss …

 Lab Animal Research

An Introduction to Caenorhabditis elegans

JoVE 5103

Caenorhabditis elegans is a microscopic, soil-dwelling roundworm that has been powerfully used as a model organism since the early 1970’s. It was initially proposed as a model for developmental biology because of its invariant body plan, ease of genetic manipulation and low cost of maintenance. Since then C. elegans has rapidly grown in popularity and is now utilized…

 Biology I

Live Cell Imaging of Mitosis

JoVE 5642

Mitosis is a form of cell division in which a cell’s genetic material is divided equally between two daughter cells. Mitosis can be broken down into six phases, during each of which the cell’s components, such as its chromosomes, show visually distinct characteristics. Advances in fluorescence live cell imaging have allowed scientists to study this process in…

 Cell Biology
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