Q & A Pathophysiology

Explain the relationship between potassium and insulin.

Insulin causes movement of potassium into the cell and is one of the treatments for hyperkalemia. Potassium balance is especially significant in the treatment of conditions requiring insulin administration, such as insulin-dependent diabetes mellitus (type 1). Potassium is the major intracellular electrolyte and maintains the osmotic balance of the intracellular fluid (ICF) space. During acidosis, potassium is shifted out of the cell in exchange for hydrogen ions. Aldosterone is secreted when potassium is elevated, resulting in the excretion of potassium by the kidneys.

How does plasma albumin cause edema?

Low plasma albumin causes edema as a result of a reduction in capillary oncotic pressure.

What facilitates the movement of potassium and sodium across plasma membranes?

Potassium and sodium are transported across plasma membranes by adenosine triphosphate enzyme (ATPase).

What results are triggered by an increase in plasma osmolality?

Secretion of antidiuretic hormone and the perception of thirst are stimulated by an increase in plasma osmolality

How does hypotonic extracellular fluid (ECF) causes intracellular water gain and swelling?

When the ECF is hypotonic, water moves from the intravascular space to the interstitial space, across the cell membrane, and into the cell. This action causes the cell to swell. An isotonic solution is equal to the plasma in concentration of solute molecules. Therefore no net water will move because equilibrium exists. The cell size is unchanged. A hypertonic fluid has excessive solute; therefore water will leave the cell and move into the vascular space to help balance this excess. Water leaving the cell results in cell shrinkage. Hypernatremia can occur with an acute gain in sodium or a loss of water, but generally it does not cause cellular swelling.

How do myocardial cells respond to increased workload demands on the heart?

When the heart's workload increases, myocardial cells increase in size.

Discuss why proteins and lipids in plasma membranes are dynamic and asymmetrically distributed.

Answer: According to the fluid mosaic model, biologic membranes are dynamic and change in response to cell needs. Lipids are very fluid and mobile in the plasma membrane. They are not only asymmetrically distributed but are also capable of fairly free lateral and rotational mobility. Asymmetric distribution of lipids changes plasma fluidity, which affects the flexibility and curvature of membranes. The type of fatty acid and the length of the fatty acid chains affect fluidity. For example, cholesterol, which is a small molecule with a small hydroxyl ion (OH) head group, occurs at the bilayer surface, decreasing fluidity and increasing the mechanical strength and stability of the membrane. Proteins define the specific function of the membrane because they are asymmetrically distributed. They can be either integral (intrinsic) or peripheral and float either singly or in an aggregate within the membrane. Integral proteins are associated directly with the lipid bilayer. Peripheral membrane proteins are associated ionically with hydrophilic lipid molecule heads or other proteins.

Explain how cells are connected to form tissues and organs.

Answer: Cells can be bound together via the extracellular matrix that the cells secrete around themselves. It is an intricate network of fibrous proteins embedded in a watery gel-like substance composed of complex carbohydrates. It is like glue, but it provides a pathway for diffusion of nutrient wastes and other water-soluble traffic between the blood and tissue cells. Interwoven within the matrix are three types of protein fibers: —Collagen: forms cable-like fibers or sheets that provide tensile strength or resistance to longitudinal stress —Elastin: a rubber-like protein fiber that is most abundant in tissues that are capable of stretching and recoiling —Fibronectin: promotes cell adhesion and cell anchorage The matrix is not just scaffolding for cellular attachment, it also helps regulate the functions of cells with which it interacts. The matrix helps regulate cell growth and differentiation.

How does the variety of cells differ in cell division?

Answer: Cells differ in a variety of ways. First, adult cells from the nerves, lens of the eye, and muscle cells cannot replicate and divide. However, epithelial cells found in the intestine, lung, and skin can divide. These types of cells rapidly divide and complete the cycle in less than 10 hours.

What is the difference between the absolute refractory period and the relative refractory period of the repolarization phase of impulse generation?

Answer: During the absolute refractory period the plasma membrane cannot respond to an excitatory stimulus, no matter how strong the stimulus is. The concentration of sodium ions is too high within the cell to permit generation of an action potential. During the relative refractory period the cell is considered to be hyperpolarized or less excitable. Potassium ions are returning into the cell, and sodium ions are leaving. A stronger than normal excitatory stimulus can result in generation of an action potential.

Explain the role of electrolytes and nonelectrolytes in body fluids

Answer: Electrolytes consist of polarity in which they gravitate to a positive or negative pole. They are electrically charged ions that make up 95% of the molecules of solute in body water. The concentrations of these anions and cations are responsible for how the electrical impulses transmit across the muscle and nerve cells.

Explain the four different types of tissues.

Answer: Epithelial tissue is found on most internal and external surfaces of the body. Because of their different locations, epithelial tissues have different functions. For example, the epidermis provides protection from outside trauma. Epithelial cells found in respiratory passages assist in moving particles such as dust out of the body. Connective tissue provides strength in binding different types of tissues and organs together. As opposed to the epithelial tissue, connective tissue contains an enormous amount of extracellular matrix and is classified as either dense or loose. Muscle tissue is made up of long, slim fibers that highly contract. There are different types of muscle tissue: skeletal, cardiac, and smooth. Neural tissue is composed of highly specialized cells that quickly receive and transmit nerve impulses across synapses. The total number of neurons is determined at birth.

Why is cellular communication important to the survival of cells?

Answer: In order to maintain a stable environment, cells must have communication with each other. They communicate by forming protein channels that assemble nearby cells activities, activate receptors that affect the cells, and secrete chemicals that alert other cells of a change. Any discourse in cell communication leads to the onset of disease and affects the progression.

Explain the difference between osmosis, osmolality, and osmolarity.

Answer: Osmosis is the ability of water to move across a concentration gradient (semipermeable membrane) from a higher concentration of water to a lower concentration of water. Osmolality is responsible for how the body compartments control the distribution and water movement. The measurement of osmolality is determined by the number of milliosmoles per kilogram of water. Body fluids have the normal osmolality of 280 to 294 mOsm/kg. Osmolarity is the concentration of the active particles in the solution.

If aqueous solution A and aqueous solution B are separated by a membrane that is impermeable to solutes, and solution A has a concentration of 300 mOsm/kg and solution B has a concentration of 500 mOsm/kg, the net movement of the water (solvent) will be in which direction?

Answer: Osmosis is the movement of water across a semipermeable membrane from a region of higher water concentration to a region of lower concentration. In this illustration, the net movement of water will be from solution A to solution B.

What is apoptosis?

Apoptosis is a programmed cell death of scattered, single cells.

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Hypoxia is a deficiency of oxygen, which causes cell injury by reducing aerobic oxidative respiration. Hypoxia is an extremely important and common cause of cell injury and cell death. Causes of hypoxia include all of the following: reduced blood flow (ischemia), inadequate oxygenation due to cardiopulmonary failure, and decrease oxygen carrying capacity, as in anemia, carbon monoxide poisoning and blood loss.

Discuss the types of necrosis.

Caseous necrosis is the type of necrosis found in the lung as result of tuberculosis. Tissues appear soft and granular and resemble clumped cheese (hence the name caseous) and are surrounded by a granulomatous inflammatory wall; this pulmonary infection is caused by Mycobacterium tuberculosis. It is a combination of liquefactive and coagulative necrosis. Coagulative necrosis occurs primarily in the kidneys, heart, and adrenal glands and is caused by protein degradation. Liquefactive necrosis commonly occurs in the neurons and glial cells. Fat necrosis occurs in the breast, pancreas, and other abdominal structures. It is cellular dissolution caused by powerful enzymes called lipases.

What is Chemotaxis?

Chemotaxis is cellular movement along a chemical gradient caused by chemical attraction. Auto-stimulation is when a cell releases a signal that actually affects the cell of origin. A pass-it-on signal is a description for a second messenger system. A second messenger system is a means by which a ligand binds with receptors of a membrane system and then triggers a second system or reaction.

Discuss the various passive forms of movement of solutes and water.

Diffusion is the movement of a solute from an area of high concentration to an area of low concentration. Osmosis is the movement of water down a concentration gradient from an area of higher water concentration to an area of lower water concentration. Filtration is the movement of water and solute through a membrane because of a greater pushing pressure on one side of the membrane than the other. Hydrostatic pressure is the mechanical force of water pushing against a cell membrane. The movement of fluid across the arterial end of a capillary membrane into the interstitial fluid surrounding the capillary is an example of Hydrostatic pressure. Hydrostatic pressure is the mechanical force of water pushing against a cell membrane.

During acidosis, how does the body compensate for the increase in hydrogen ions?

During acidosis, the body compensates for the increase in hydrogen ions in the blood by shifting hydrogen ions into the cells in exchange for potassium.

How does ischemia affect cells?

During ischemia the loss of ATP causes cells to swell because of the influx of sodium.

Explain how altitude can caus injuries. How do blast injuries cause injuries?

High altitude causes hypoxic injury. This hypoxia causes shunting of blood from the periphery to vital organs including the lungs and results in pulmonary hypertension. Caisson disease is often called the bends and occurs when divers ascend too quickly, resulting in a gas embolism. Gas emboli are formed when carbon dioxide and nitrogen, which are normally dissolved in blood, bubble out of solution. Blast injuries cause significant injury through the collapse of the thorax, the rupture of internal organs, and widespread hemorrhage.

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Metaplasia is a reversible change in which one differentiated cell type (epithelial or mesenchymal) is replaced by another cell type . It often represents an adaptive response in which one cell type that is sensitive to a particular stress is replaced by another cell type that is better able to withstand the adverse environment. Atrophy is a decreased cell and organ size, as a result of decreased nutrient supply or disuse; associated with decreased synthesis of cellular building blocks and increased breakdown of cellular organelles

Identify the roles of the Mitochondria, the Golgi Complex, and the Nucleolus, all cellular organelles found in eukaryotic cells.

Mitochondria play a role in cellular metabolism, cellular respiration, and energy production. The Golgi complex is responsible for processing and packaging proteins from the endoplasmic reticulum, where they are synthesized. The nucleolus is a small, dense structure that contains the ribonucleic acid (RNA), DNA, and DNA-binding proteins. Lysosomes are sacs that contain enzymes capable of cellular autodigestion when released during cell injury.

What is oxidative phosphorylation?

Oxidative phosphorylation occurs in the mitochondria. This is the mechanism by which the energy produced from carbohydrates, fats, and protein is transferred to ATP. Glycolysis is a process that breaks down glucose molecules; it produces a net of two ATP molecules. Oxidation is a process during which a pair of electrons are removed and transferred. Oxidative cellular metabolism involves 10 biochemical reactions. Anaerobic glycolysis occurs in the absence of oxygen. Aerobic means "in the presence of oxygen."

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Plasma membranes are more than just static lipid sheaths. Rather, they are fluid bilayers of amphipathic phospholipids with hydrophilic head groups that face the aqueous environment and hydrophobic lipid tails that interact with each other to form a barrier to passive diffusion of large or charged molecules. The plasma membrane is liberally studded with a variety of proteins and glycoproteins that are involved in all of the following: Ion and metabolite transport, Fluid-phase and receptor-mediated uptake of macromolecules, Cell-ligand, cell-matrix, and cell-cell interactions. Small, nonpolar molecules like O 2 and CO 2 readily dissolve in lipid bilayers and therefore rapidly diffuse across them; in addition, hydrophobic molecules also cross lipid bilayers with relative impunity. Similarly, polar molecules smaller than 75 daltons in mass readily cross membranes. Examples of these molecules include all of the following: water, ethanol, and urea. Channel proteins create hydrophilic pores, which, when open, permit rapid movement of solutes, which are usually restricted by size and charge.

Discuss the concepts of first and second messengers in cell signaling.

The binding of a ligand to a cell surface receptor triggers the activation of intracellular second messengers. Second messengers activate signal transduction pathways in the cell that can initiate different intracellular events. Cyclic adenosine monophosphate (cAMP) and calcium (Ca++) are the two major second-messenger pathways. First messengers are the extracellular ligands that bind to cell surface receptors. Binding of first messengers can result in the opening or closing of specific cell membrane channels or the activation of second messengers.

How does hypernatremia affect the brain?

The high sodium in the blood vessels pulls water out of the brain cells into the blood vessels causing the brain to shrink which results in the clinical manifestations of confusion, convulsions, cerebral hemorrhage, and coma in hypernatremia

Explain why oxygen (O2) can easily cross a plasma membrane, whereas sodium ions (Na+) are unable to cross a plasma membrane.

The lipid portion of the plasma membranes is composed of polar or amphipathic lipid molecules. The lipid molecules are arranged with their hydrophilic (water-loving) portions at the membrane inner and outer surfaces. The hydrophobic (water-hating) portions of the lipid molecule on the inside of the membrane face each other. This creates a "sandwich effect" with a hydrophobic oily core. These components are constructed into a lipid bilayer, forming a selectively permeable barrier. Oxygen is able to easily cross the plasma membrane because it is soluble in lipids. Sodium ions are unable to cross the plasma membrane because they are insoluble in the lipid core of the membrane and therefore are actively transported by a pump that uses ATP for energy.

What do natriuretic peptides do>

The natriuretic peptides decrease blood pressure and increase sodium and water excretion.

Explain the action potential.

The rapid change in the resting membrane potential that initiates an action potential is caused by sodium gates opening allowing sodium to rush into the cell changing the membrane potential from negative to positive.

Differentiate between various forms of injuries to the skin.

The term "laceration" describes a tear or rip of the skin with a jagged and irregular edge. Lacerations occur when the tensile strength of the skin is exceeded, resulting in ragged and irregular abraded edges; an extreme example is an avulsion, in which a wide area of tissue is pulled away. An abrasion results from the removal of the superficial layers of the skin caused by friction between the skin and the injuring object. An incision is a precise cut with an instrument that leaves regular clean edges. An incised wound is longer than it is deep and has distinct edges without abrasion.

A patient has a long history of smoking. He has blood studies done because he is tired and short of breath. His blood gases reveal the following: pH 7.3, HCO3 27mEq/L, CO2 58mmHg. What is the interpretation of these gases?

This is a Respiratory acidosis