Physiology Chapter: Membrane Structure & Function
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Questions and Answers

What is physiology the study of?

Physiology is the study of biological function—of how the body works, from cell to tissue, tissue to organ, organ to system, and of how the organism as a whole accomplishes particular tasks essential for life.

In the study of physiology, what is the emphasis on?

The emphasis is on mechanisms—with questions that begin with the word how and answers that involve cause-and-effect sequences.

What is human physiology?

Human physiology is the study of functions of various cells, organs and organ systems of the human body.

Explain the concept of medical physiology.

<p>Medical physiology is the application of knowledge of human physiology in the management of dysfunctions and diseases in human beings.</p> Signup and view all the answers

Why is physiology considered the key subject in medicine?

<p>Starting from the knowledge of body functions, physiology provides the concept of dysfunctions, the basis of understanding the disease processes and the insight into disease management and prevention. Physiology is the core of medical wisdom.</p> Signup and view all the answers

Physiology is the foundation of medical practice.

<p>True</p> Signup and view all the answers

In what year did S. Singer and G. Nicolson revise the model of the cell membrane?

<p>1972</p> Signup and view all the answers

What is the name of the model of the cell membrane that S. Singer and G. Nicolson proposed?

<p>Fluid mosaic model</p> Signup and view all the answers

What percentage of molecules in the membrane are lipids?

<p>98%</p> Signup and view all the answers

What percentage of lipids in the membrane are phospholipids?

<p>75%</p> Signup and view all the answers

What type of molecules are phospholipids?

<p>Amphiphilic</p> Signup and view all the answers

Where do the hydrophilic heads of phospholipids face?

<p>The water on each side of the membrane</p> Signup and view all the answers

Where do the hydrophobic tails of phospholipids face?

<p>The center of the membrane, avoiding the water</p> Signup and view all the answers

What are fatty acids?

<p>Monocarboxylic acids that usually contain an even number of carbon atoms</p> Signup and view all the answers

Fatty acid chains may contain what?

<p>One or more double bonds</p> Signup and view all the answers

What are glycolipids?

<p>Glycolipids are molecules that contain both carbohydrate and lipid components.</p> Signup and view all the answers

Glycolipids are derivatives of ceramides.

<p>True</p> Signup and view all the answers

What is the more precise name for glycolipids?

<p>Glycosphingolipids</p> Signup and view all the answers

Glycosphingolipids are essential components of all membranes in the body.

<p>True</p> Signup and view all the answers

Where are glycosphingolipids found in the greatest amounts?

<p>Nerve tissue.</p> Signup and view all the answers

Where are glycosphingolipids located in the cell?

<p>Outer leaflet of the plasma membrane</p> Signup and view all the answers

What role do glycosphingolipids play in the regulation of cellular interactions?

<p>They play a role in the regulation of cellular interactions, growth, and development.</p> Signup and view all the answers

Glycosphingolipids are antigenic.

<p>True</p> Signup and view all the answers

Glycosphingolipids have been identified as a source of blood group antigens.

<p>True</p> Signup and view all the answers

Glycosphingolipids have been identified as a source of embryonic antigens.

<p>True</p> Signup and view all the answers

Glycosphingolipids have been identified as a source of tumor antigens

<p>True</p> Signup and view all the answers

What is the antigenic determinant of a glycolipid?

<p>The carbohydrate portion</p> Signup and view all the answers

What do glycolipids serve as?

<p>Cell surface receptors for cholera and tetanus toxins, as well as for certain viruses and microbes</p> Signup and view all the answers

What are prostaglandins, thromboxanes, and leukotrienes collectively known as?

<p>Eicosanoids</p> Signup and view all the answers

What are eicosanoids derived from?

<p>Polyunsaturated fatty acids with 20 carbons</p> Signup and view all the answers

What type of compounds are eicosanoids?

<p>Extremely potent compounds that elicit a wide range of responses, both physiologic and pathologic.</p> Signup and view all the answers

Eicosanoids are produced in specialized glands.

<p>False</p> Signup and view all the answers

Eicosanoids act locally rather than after transport in the blood to distant sites.

<p>True</p> Signup and view all the answers

What is phosphatidylinositol a precursor of?

<p>Second messengers</p> Signup and view all the answers

When phosphatidylinositol is cleaved, what two products are produced?

<p>Diacylglycerol and inositol trisphosphate</p> Signup and view all the answers

What percentage of the molecules of the plasma membrane are proteins?

<p>2%</p> Signup and view all the answers

Proteins make up about 50% of the membrane weight.

<p>True</p> Signup and view all the answers

What are integral (transmembrane) proteins?

<p>Integral proteins, pass through the membrane.</p> Signup and view all the answers

What type of regions do integral proteins have in contact with the cytoplasm and extracellular fluid?

<p>Hydrophilic regions</p> Signup and view all the answers

What type of regions do integral proteins have that pass back and forth through the lipid of the membrane?

<p>Hydrophobic regions</p> Signup and view all the answers

Most integral proteins are glycoproteins.

<p>True</p> Signup and view all the answers

What are glycoproteins?

<p>Proteins that are conjugated with oligosaccharides on the extracellular side of the membrane</p> Signup and view all the answers

What are some integral proteins anchored to?

<p>The cytoskeleton, an intracellular system of tubules and filaments.</p> Signup and view all the answers

What are receptors?

<p>Receptors are the chemical signals by which cells communicate with each other.</p> Signup and view all the answers

Chemical signals that bind to receptors often cannot enter the target cell.

<p>True</p> Signup and view all the answers

What are second-messenger systems?

<p>Second-messenger systems are triggered when a messenger binds to a surface receptor.</p> Signup and view all the answers

Second-messenger systems trigger changes within the cell that produce a second messenger in the cytoplasm.

<p>True</p> Signup and view all the answers

Proteins can function as enzymes.

<p>True</p> Signup and view all the answers

Where do proteins that function as enzymes catalyze reactions?

<p>At the surfaces of the membrane.</p> Signup and view all the answers

Where do peripheral proteins adhere?

<p>Peripheral proteins do not protrude into the phospholipid layer but adhere to the intracellular face of the membrane.</p> Signup and view all the answers

Peripheral proteins are typically associated with an integral protein.

<p>True</p> Signup and view all the answers

Peripheral proteins are tethered to the cytoskeleton.

<p>True</p> Signup and view all the answers

What is an example of a peripheral protein?

<p>The anion exchanger, a major protein of the human erythrocyte membrane</p> Signup and view all the answers

To what is the anion exchanger bound?

<p>The spectrin network that undergirds the membrane</p> Signup and view all the answers

Through what protein is the anion exchanger bound to the spectrin network?

<p>Ankyrin</p> Signup and view all the answers

What is spectrin considered to be?

<p>The predominant protein of the skeletal protein lattice</p> Signup and view all the answers

What are channel proteins?

<p>Channel proteins are integral proteins with pores that allow passage of water and hydrophilic solutes through the membrane.</p> Signup and view all the answers

Some channels are always open.

<p>True</p> Signup and view all the answers

Some channels function as gates that open and close under different circumstances.

<p>True</p> Signup and view all the answers

What are the three types of stimuli that can cause these gates to open or close?

<p>Mechanically regulated gates</p> Signup and view all the answers

What do ligand-regulated gates respond to?

<p>Chemical messengers</p> Signup and view all the answers

What do voltage-regulated gates respond to?

<p>Changes in electrical potential</p> Signup and view all the answers

What do mechanically regulated gates respond to?

<p>Physical stress on a cell, such as stretch and pressure.</p> Signup and view all the answers

What are pumps?

<p>Pumps are proteins that actively transport ions across the membrane.</p> Signup and view all the answers

What are carriers?

<p>Carriers are proteins that transport substances down electrochemical gradients by facilitated diffusion</p> Signup and view all the answers

What makes membranes quite selective about which molecules can pass through them?

<p>The structure of membranes</p> Signup and view all the answers

What makes membranes highly impermeable to most polar molecules?

<p>The hydrophobic interior of the lipid bilayer</p> Signup and view all the answers

The hydrophobic interior of the lipid bilayer prevents water-soluble components of the cell from easily entering or escaping.

<p>True</p> Signup and view all the answers

What are the two basic processes by which transport across the cell membrane occurs?

<p>Diffusion or active transport</p> Signup and view all the answers

What is one of the most important factors that determines how rapidly a substance diffuses through the lipid bilayer?

<p>The lipid solubility of the substance</p> Signup and view all the answers

Oxygen, nitrogen, carbon dioxide, and alcohols are all highly lipid soluble.

<p>True</p> Signup and view all the answers

The permeability of the plasma membrane to different substances varies.

<p>True</p> Signup and view all the answers

What is the term for the property of membranes that permits some substances to pass more readily than others?

<p>Selective permeability</p> Signup and view all the answers

The lipid bilayer portion of the membrane is permeable to nonpolar, uncharged molecules.

<p>True</p> Signup and view all the answers

The lipid bilayer portion of the membrane is impermeable to ions.

<p>True</p> Signup and view all the answers

The lipid bilayer portion of the membrane is impermeable to large, uncharged polar molecules.

<p>True</p> Signup and view all the answers

The lipid bilayer portion of the membrane is slightly permeable to small, uncharged polar molecules such as water and urea.

<p>True</p> Signup and view all the answers

What is urea?

<p>A waste product from the breakdown of amino acids</p> Signup and view all the answers

What is simple diffusion?

<p>Simple diffusion is the only form of transport across cell membranes that is not carrier-mediated.</p> Signup and view all the answers

Study Notes

Physiology

  • Physiology is the study of biological function, focusing on how the body works from the cellular to organismal level.
  • The emphasis is on mechanisms, answering "how" questions and using cause-and-effect sequences.
  • Physiology studies body functions, mechanisms, and regulations in all living organisms.
  • Human physiology specifically studies functions in the human body, including cells, organs, and organ systems.
  • Medical physiology applies human physiological knowledge to manage dysfunctions and diseases.

Membrane Structure and Function

  • In 1972, Singer and Nicolson revised the fluid mosaic model.
  • Globular proteins are embedded in the lipid bilayer.
  • Nonpolar regions of proteins touch bilayer's interior; polar regions project outward.
  • This model portrays a dynamic, fluid membrane, with lateral movement of lipids and proteins.

Membrane Lipids

  • Lipids are the major component of cell membranes.
  • Phospholipids form a bilayer arrangement, oriented with hydrophilic heads facing water and hydrophobic tails facing inward.
  • Fatty acids are important components of lipids, typically containing even numbers of carbon atoms, potentially saturated or unsaturated.

Glycolipids

  • Glycolipids contain both carbohydrates and lipids, derived from ceramides.
  • Critical components of cell membranes, especially abundant in nerve tissue.
  • Play a role in cellular interactions, growth, and development, serving as antigens and receptors.
  • Prostaglandins, thromboxanes, and leukotrienes, collectively called eicosanoids, are derived from fatty acids with 20 carbons.
  • They act as potent regulators of various physiological and pathologic processes, unlike hormones which act systemically.
    • They act locally, unlike hormones.

Phosphatidylinositol

  • Phosphatidylinositol is a precursor to second messengers.
  • It's broken down to diacylglycerol and inositol triphosphate.
    • These molecules act as internal signals or second messengers.

Cholesterol

  • Cholesterol accounts for about 20% of membrane lipids, and sits among the fatty acid tails.
  • It regulates membrane fluidity, stiffening in some areas.

Membrane Proteins

  • Membrane proteins, though only about 2% of molecules, constitute 50% by weight.
  • Proteins like integral or transmembrane proteins permeate the membrane, with hydrophobic parts in the bilayer and hydrophilic parts interacting with the cytoplasm or extracellular environment.
    • Integral proteins often have oligosaccharide attachments on the extracellular surface.
  • Peripheral proteins, anchored to the cytoskeleton.
    • Some, like the anion exchange protein, are linked to a spectrin framework.

Membrane Proteins: Channel Proteins

  • Channel proteins are integral proteins with pores that allow water or hydrophilic solutes to pass through.
  • Can be opened or closed in response to:
    • Ligand-regulated gates (chemical messengers)
    • Voltage-regulated gates (electrical potential)
    • Mechanically-regulated gates (physical stress)

Membrane Proteins: Pumps and Carriers

  • Proteins act as pumps, actively transporting ions across the membrane.
  • Others function as carriers, moving substances down electrochemical gradients by facilitated diffusion.
    • These aid in the movement of molecules across the membrane.

Membrane permeability

  • Selectively permeable membranes pass some substances readily while blocking others.
  • The lipid bilayer is permeable to nonpolar, uncharged molecules (oxygen, carbon dioxide, steroids) but impermeable to most large molecules or ions.

Transport of Substances

  • Substances cross membranes by either:
    • diffusion
    • active transport
  • Lipid solubility correlates to the rate of diffusion across the lipid layer. Water-soluble compounds need specific channels/carriers.

Simple Diffusion

  • Simple diffusion is a passive process, moving substances down an electrochemical gradient without energy input.

Facilitated Diffusion

  • Facilitated diffusion is like simple diffusion, but uses a membrane carrier protein.
  • It's also passive and subject to saturation and competition for carrier proteins.

Active Transport

  • Active transport moves substances against an electrochemical gradient, requiring energy (typically ATP).
  • Primary active transport, using ATP directly, and
  • Secondary active transport, using electrochemical gradients established by primary active transport.

Na+/K+ Pump

  • The Na+/K+ pump, a primary active transport protein, maintains low intracellular sodium concentration.
    • It regulates cell volume, supports secondary active transport, produces heat, and maintains membrane potential.

Secondary Active Transport

  • Secondary active transport uses an electrochemical gradient, typically sodium, to move a second solute.
  • Cotransport (symport) or countertransport (antiport) are subtypes, based on the relative directions of movement.

Cotransport (Symport) / Countertransport (Antiport)

  • Examples include Na+ - glucose and Na+-amino acid transport in the intestines and kidneys.

SGLT2 Inhibitors

  • SGLT2 inhibitors lower blood sugar in adults with type 2 diabetes.

Osmolarity

  • The total solute concentration in a solution.
  • Expressed as osmoles per liter (Osm/L) or milliosmoles per liter (mOsm/L).

Osmotic Pressure

  • The pressure required to prevent the net movement of water across a semipermeable membrane.
  • Proportional to the total solute concentration.

Diffusion of Water Through Aquaporins

  • Most water movement across membranes uses aquaporins (pores that permit water passage).

Tonicity

  • How a solution affects cell volume:
    • Isotonic: No net water movement.
    • Hypotonic: Water enters the cell, causing swelling.
    • Hypertonic: Water exits the cell, causing shrinkage.

Vesicular Transport

  • Large molecules and particles move through the cell membrane in vesicles.
  • Endocytosis and exocytosis are prominent types.
  • Types of endocytosis include phagocytosis, pinocytosis, and receptor-mediated endocytosis.

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Description

This quiz explores key concepts in physiology, particularly focusing on membrane structure and function. It covers the fluid mosaic model and the role of lipids in cell membranes. Test your understanding of how these mechanisms impact biological functions in living organisms.

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