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Questions and Answers
What is the main function of human physiology?
What is the main function of human physiology?
Which statement about Total Body Water (TBW) is correct?
Which statement about Total Body Water (TBW) is correct?
Which compartment contains the majority of Total Body Water (TBW)?
Which compartment contains the majority of Total Body Water (TBW)?
Which of the following components predominantly exists in the extracellular fluid compartment?
Which of the following components predominantly exists in the extracellular fluid compartment?
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What is homeostasis best defined as?
What is homeostasis best defined as?
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Which of the following is NOT a component of the cell membrane?
Which of the following is NOT a component of the cell membrane?
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What is the shape of a phospholipid molecule in the cell membrane?
What is the shape of a phospholipid molecule in the cell membrane?
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Which percentage of the cell membrane is made up of carbohydrates?
Which percentage of the cell membrane is made up of carbohydrates?
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What type of active transport carrier moves one substance in one direction?
What type of active transport carrier moves one substance in one direction?
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What happens to receptors during down regulation when a ligand is present in excess?
What happens to receptors during down regulation when a ligand is present in excess?
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Which type of junction connects cells by allowing the rapid passage of ions?
Which type of junction connects cells by allowing the rapid passage of ions?
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Which of the following statements about carriers in active transport is true?
Which of the following statements about carriers in active transport is true?
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What is the primary role of identity proteins in cells?
What is the primary role of identity proteins in cells?
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What characterizes symport carriers in active transport?
What characterizes symport carriers in active transport?
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What is the main function of enzymes associated with the cell membrane?
What is the main function of enzymes associated with the cell membrane?
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What occurs during up regulation of receptors?
What occurs during up regulation of receptors?
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What is the nature of the head portion of a phospholipid?
What is the nature of the head portion of a phospholipid?
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Which part of the phospholipid is characterized as hydrophobic?
Which part of the phospholipid is characterized as hydrophobic?
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What is the primary role of cholesterol in the cell membrane?
What is the primary role of cholesterol in the cell membrane?
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How are integral proteins characterized in relation to the cell membrane?
How are integral proteins characterized in relation to the cell membrane?
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What distinguishes gated channels from non-gated channels in the cell membrane?
What distinguishes gated channels from non-gated channels in the cell membrane?
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Which of the following is NOT a function of cell membrane proteins?
Which of the following is NOT a function of cell membrane proteins?
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What characteristic does a hydrophilic portion of cell membrane proteins exhibit?
What characteristic does a hydrophilic portion of cell membrane proteins exhibit?
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In facilitated diffusion, what role do carrier proteins play?
In facilitated diffusion, what role do carrier proteins play?
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What is the primary function of cell adhesion molecules?
What is the primary function of cell adhesion molecules?
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Which type of diffusion requires a carrier protein?
Which type of diffusion requires a carrier protein?
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What regulates the diameter of the channels in connexons?
What regulates the diameter of the channels in connexons?
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Which of the following statements is true regarding osmosis?
Which of the following statements is true regarding osmosis?
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What are connexons primarily composed of?
What are connexons primarily composed of?
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What is the role of the cytoskeleton within a cell?
What is the role of the cytoskeleton within a cell?
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What initiates voltage gating in protein channels?
What initiates voltage gating in protein channels?
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Which of the following transports substances across the membrane without the requirement for a carrier protein?
Which of the following transports substances across the membrane without the requirement for a carrier protein?
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Study Notes
Physiology Basics
- The study of the functions of living things.
- The human body is made up of 75 - 100 trillion cells.
- Cells with similar properties form tissues.
- Different tissues combine to form organs.
- Organs with complementary functions constitute the different systems.
Body Compartments
- The body of a normal adult male is composed of 18% protein, 15% fat, 7% minerals, and 60% water (Total Body Water - TBW).
- TBW is 75% in infants and less than 60% in adult females and obese individuals due to high fat content.
- TBW is present in two compartments:
- Intracellular Fluid Compartment (ICF):
- Constitutes 2/3 of TBW.
- Presents inside the cells.
- Equals 40% of Total Body Weight.
- Contains more K+ and less Na+, Cl-, and HCO3-.
- Extracellular Fluid Compartment (ECF):
- Constitutes 1/3 of TBW.
- Presents outside the cells.
- Equals 20% of Total Body Weight.
- Contains less K+ and more Na+, Cl-, and HCO3-.
- Intracellular Fluid Compartment (ICF):
- ECF is distributed as follows:
- 5% inside the blood vessels as intravascular fluid (IVF) which is plasma.
- 15% outside the blood vessels as interstitial fluid (ISF).
Homeostasis
- Maintaining constant conditions in the internal environment.
- Examples of regulated conditions include O2, CO2, glucose, different ions, amino acids, and fatty acid concentrations.
- Most bodily systems work directly or indirectly to maintain homeostasis.
The Cell
- The structural unit of various tissues and organs in the human body.
- Composed of a mass of protoplasm surrounded by the cell membrane.
- Protoplasm comprises:
- Cytoplasm
- Cell organelles
- Nucleus
The Cell Membrane
- Thickness of the cell membrane: 7.5nm (10-9 meter).
- Composition:
- Proteins: 55%
- Lipids: 29% (phospholipids & glycolipids)
- Cholesterol: 13%
- Carbohydrates: 3%
- Under an electron microscope, it is formed of a lipid bilayer with globular proteins interspersed in the thin lipid film.
- Structure:
- Phospholipids:
- Amphipathic: one hydrophilic (water-loving) and one hydrophobic (water-hating) part.
- Polar head: formed of phosphate charged group.
- Non-polar tails: formed of 2 fatty acid chains.
- The hydrophilic ends of the molecule are exposed to the aqueous environment, while the hydrophobic ends meet in the water-poor interior of the membrane.
- Phospholipids:
- The lipid bilayer is important for the flexibility and selective permeability of the cell membrane.
Structure and Function of Cell Membrane Proteins
- Present as globular masses floating in the lipid bilayer.
- Two parts:
- Hydrophobic uncharged portion: present in the interior of the membrane.
- Hydrophilic charged portion: directed to the surface.
- Types of cell membrane proteins:
- Integral proteins: pass all the way through the membrane.
- Peripheral proteins: attached only to one surface of the membrane and do not penetrate it.
- Cell membrane proteins form complexes with glycolipids that are important as recognition sites and act as antigens for cell self-recognition, immune system, and differentiation.
- Cholesterol molecules are completely hydrophobic and embedded in the phospholipid bilayer.
- Cholesterol affects the permeability of the membrane and gives it toughness.
Functions of Cell Membrane Proteins
- Structural proteins: maintain the integrity and strength of the membrane.
- Form passive channels:
- Protein channels with various diameters, shapes, and electric charges along their surfaces.
- Classified by the presence or absence of gates:
- Gated channels: closed during rest by a part of the protein molecule.
- Non-gated channels: open all the time.
- Gated channels are further classified as:
- Voltage gated: open or close when the membrane potential is changed.
- Ligand gated: open or close when a ligand binds to a specific receptor on the cell membrane.
- Carriers in facilitated diffusion: for large molecules passively e.g., facilitated diffusion of glucose.
- Bind the molecule and change their configuration, moving the bound molecule from one side of the cell membrane to the other.
- Carriers in active transport (= Pumps): transport substances against their electrical and chemical gradients.
- Require energy.
- Three types:
- Uniport: transports one substance in one direction e.g., Ca++.
- Symport: transports two substances simultaneously in the same direction, e.g., carriers of glucose and Na+ from the intestinal lumen to inside of the cell.
- Antiport: transports one substance in one direction and another substance in the opposite direction e.g., Na+ - K+ pump.
- Symport and Antiport are called Cotransport carriers.
- Receptors: present mainly on the outer cell membrane.
- Inactive during rest but become activated when they combine with their specific ligand (neurotransmitter, drug, or hormone).
- Activated receptors initiate a series of cellular reactions to stimulate or inhibit a certain cellular function.
- The number and sensitivity of the receptors can change:
- Down regulation: when a ligand is present in excess, the number of receptors for this ligand decreases, reducing sensitivity.
- Up regulation: when a ligand is deficient, the number of receptors for this ligand increases.
- Enzymes: present mainly on the inner surface of the cell membrane to catalyze certain reactions.
- Identity proteins: mostly glycoproteins, give cells individual identity labels.
- They prevent the cells from being attacked by the immune system.
Intercellular Connections
- Cells are connected by two types of junctions:
- Binding junctions: bind cells together to make strong tissues. These include:
- Tight junctions: ridges projecting from certain cells adhere strongly to similar ridges from neighboring cells, obliterating the intercellular space.
- Desmosomes: thickening of the membranes on two opposite cells connected with fibrils bridging the intercellular space.
- Channel junctions (=Gap junctions):
- Channels running across the intercellular space connecting one cell to another.
- Allow the rapid passage of ions and other substances with a molecular weight up to 1000 between cells without entering the intercellular space.
- Permit the rapid propagation of electrical activity from one cell membrane to another.
- At these junctions, hexagonal arrangements of protein units form what is called "connexon" surrounding a channel that will be in line with the channel in a corresponding connexon in the adjacent cell.
- Intracellular Ca++, pH, hormones, and drugs regulate the diameter of the channel.
- Binding junctions: bind cells together to make strong tissues. These include:
Functions of Cell Membrane Proteins
- Cell adhesion molecules: proteins responsible for the adhesions of the cells to basal lamina and to each other.
- Important in embryonic development of the nervous system, inflammation, wound healing, and metastasis of tumors.
- Fixation of parts of the cytoskeleton of the cell:
- The cytoskeleton is a system of fibers that maintains the structure of the cell and permits it to change shape and move.
- It is made up of microtubules, intermediate filaments, and microfilaments.
Three Types of Cellular Transport
- The mechanisms that control transport through cell membranes are vital to maintain the differences between ECF & ICF, which are essential for the life of the cell.
I. Diffusion
- Continuous movement of molecules in liquids or gases from regions of higher concentration to regions of lower concentration.
Types of Diffusion
- Simple diffusion: molecules or ions diffuse through the membrane according to the concentration gradient, passively without binding with carrier proteins.
- Occurs through two pathways:
- The lipid bilayer (allows the passage of lipid-soluble substances like O2 & N2 and water & lipid-insoluble substances like urea).
- Gating of protein channels.
- The opening and closure of the gates is controlled by:
- Voltage gating: open by a change in electric membrane potential.
- Ligand gating: open by binding to a specific ligand.
- Occurs through two pathways:
- Facilitated diffusion: passive mechanism but requires a carrier with a receptor for the substance to be transported.
- The substance then is transported through the channel of the carrier molecule, part of the way but not all the way.
- This is followed by conformational changes in the carrier protein to allow passage of the substance to the opposite side.
- Osmosis: diffusion of water molecules down their concentration gradient.
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Description
Explore the fundamental concepts of physiology, focusing on the functions of living organisms and the composition of the human body. This quiz covers the body compartments, including intracellular and extracellular fluids, and their significance in overall health.
