PHGY Midterm Exam Notes: Key Concepts in
Physiology
, MIDTERM NOTES
PHGY Module 1 Notes
Section 1
Introduction
-Physiology is the scientific study of the functions of our body.
-Human body is made up of cells that can either work individually or as part of a larger network.
-Cells --> Tissues --> Organs --> Organ systems
Homeostasis and Set Point
-Physiology studies how an organism is affected when a tissue or system is acted upon by influences
(internal or external), and how the organism responds.
-Homeostasis: The ability of a cell or organism to regulate and maintain its internal environment
regardless of the influences of the external environment.
-Set Point: The range or point at which a variable physiological state (ex. Body temp) tends to stabilize. -
It is very difficult to achieve a set point since everything in the body is dynamic, so the set point can be
considered a range.
Homeostatic Control Systems
-In order to maintain a set point, we need a homeostatic control mechanism.
-Most homeostatic control systems have 3 components; the sensor, integrator, and effector.
-Sensor: Responsible for detecting an environmental variable.
-Integrator: Compares the variable being detected to its set point.
-Effector: Responsible for initiating the changes to restore the variable back to its set point.
Intrinsic and Extrinsic Control
-The 2 types of homeostatic regulation are intrinsic regulation/local regulation/autoregulation and
extrinsic regulation.
-Intrinsic control: The sensor, integrator, and effector are all located within a tissue so that the tissue
can regulate its own internal environment.
• Ex. An exercising muscle that needs oxygen to produce ATP. When local oxygen concentration
drops, blood vessels within the muscle dilate to increase oxygen that can be delivered.
-Extrinsic control: Regulatory mechanisms are outside of the tissue or organ.
• Ex. Regulation of body temperature.
• Majority of homeostatic control systems are extrinsic.
Feedback Loops
Negative Feedback
-Majority of homeostatic mechanisms use negative feedback.
-Refers to a change in an environmental parameter that causes the effector to initiate a response in the
opposite direction, restoring the parameter to set point.
-Once set point is achieved again, the system stops signalling.
,-Ex. Blood glucose regulation:
1. After ingesting a meal, blood glucose levels rise (away from homeostasis/set point).
2. Insulin is released by pancreas in response
3. Insulin lowers blood glucose by increasing the ability of body cells to uptake glucose from the
blood.
4. Insulin also upregulates the liver's ability to convert glucose and store it as glycogen.
Positive Feedback
-Occurs when the effector causes changes that amplify the initial signal.
-Positive feedback is not homeostatic.
-Ex. Positive feedback in childbirth:
1. Brain stimulates pituitary gland to secrete oxytocin
2. Oxytocin is carried in the bloodstream to the uterus
3. Oxytocin stimulates uterine contractions which push baby towards the cervix
4. Head of the baby pushes against cervix
5. The nerve impulses from the cervix are transmitted to the brain.
Section 2
The Plasma Membrane
-Physical barrier is both a protective barrier for the cell and allows cells to maintain an internal fluid
composition that is different from the external fluid composition.
-Plasma membrane plays a role in regulating the internal fluid composition since it can control what can
enter/exit.
-Allows nutrients to enter cells and waste to leave.
-Permits chemical signals released from other cells in the body to influence a cell (cell to cell
communication).
-Membrane participates in joining cells together to form tissues.
Membrane Physiology
-Plasma membrane has 3 primary functions:
• Ensure the cell's survival
• Maintain homeostasis
• Function cooperatively and in coordination with surrounding cells.
Structure and Function of the Plasma Membrane
-Phospholipids: Make up the lipid bilayer. Composed of a polar head with a negatively charged
phosphate group and 2 non-polar fatty acid tails.
Head is hydrophilic and tail is hydrophobic.
-Cholesterol: Found in the plasma membrane tucked between phospholipids. Prevent the fatty acid
chains from packing too tightly together and forming rigid structures; keep the membrane fluid. -
Membrane proteins: Inserted into the phospholipid membrane. Function to maintain cell structure,
regulate cell function, allow transport across the membrane, and facilitate signalling.
-Ion channels: Specialized membrane proteins that span the entire lipid membrane and permit entry
and exit of ions.
, -Carbohydrate chains: Short chains of carbohydrates attached to their proteins (glycoproteins) or to the
bilayer (glycolipids). Involved in stabilizing membrane structure, act as cell surface receptors, participate
in transportation, and more.
The Fluid Mosaic Model
-The membrane is fluid due to the fact that the phospholipid bilayer is viscous and that the individual
phospholipids can move.
-It is the lipid bilayer that gives the membrane its fluidity and elasticity.
-The membrane is a mosaic since it is embedded with other proteins and molecules that perform many
functions for proper cell functioning.
Cell-to-Cell Adhesions
-In order for the cells to come together to form tissues, they must first physically adhere to each other. -
The 3 ways cells are held together are by the extracellular matrix, cell adhesion molecules, and cell
junctions.
-Extracellular Matrix: A network of fibrous proteins embedded in a gel-like mixture of complex
carbohydrates.
• Surrounds all cells in tissues and keeps them in place.
• Watery gel allows for diffusion of nutrients from the blood and removal of waste from cells.
o This is often referred to as interstitial fluid and is made of 3 major protein fibres.
• The 3 main proteins involved:
o Collagen: Forms the cable-like fibres that give ECM its tensile strength.
o Elastin: Rubber-like protein that allows tissues to be stretched and then recoil once force is
removed.
o Fibronectin: Promotes cell adhesion.
• The majority of the ECM is secreted by fibroblasts in the interstitial space.
-Cell Adhesion Molecules: Usually transmembrane proteins. The intracellular side of the protein
interacts with the cytoskeleton, and the extracellular side interacts with the ECM CAMs from other cells.
• CAMs are involved in protein-protein interactions because they bind with other cells or the ECM.
• They stick to each other and their surroundings.
• The 4 main families of CAMs are Cadherins, Selectins, NCAMs, and Integrins.
-Cell Junctions: The 3 main types are desmosomes, tight junctions, and gap junctions.
• Desmosomes (Adherens junctions): Used to anchor together two adjacent cells that aren't
otherwise in direct contact. o Composed of dense intracellular thickenings called plaques that
are connected to glycoprotein filaments containing cadherins to attach neighbouring plaques
together. o Within a cell, other cytoskeletal anchoring proteins can also attach to plaque area.
This creates a network of strong fibres extending through tissues and cells. This also gives
desmosome containing cells (ex. Skin cells) a considerable amount of stretch.
• Tight Junctions (Impermeable junction): Creates a very tight seal between cells, preventing
movement of molecules from cell to cell.
o Long strings of junctional proteins in the plasma membrane align and adhere to form a tight
junction.
o The area where opposing junctional proteins from neighbour cells meet is a kiss site. o This
type of junction is mainly found in epithelial tissues (ex. Digestive tract).
Physiology
, MIDTERM NOTES
PHGY Module 1 Notes
Section 1
Introduction
-Physiology is the scientific study of the functions of our body.
-Human body is made up of cells that can either work individually or as part of a larger network.
-Cells --> Tissues --> Organs --> Organ systems
Homeostasis and Set Point
-Physiology studies how an organism is affected when a tissue or system is acted upon by influences
(internal or external), and how the organism responds.
-Homeostasis: The ability of a cell or organism to regulate and maintain its internal environment
regardless of the influences of the external environment.
-Set Point: The range or point at which a variable physiological state (ex. Body temp) tends to stabilize. -
It is very difficult to achieve a set point since everything in the body is dynamic, so the set point can be
considered a range.
Homeostatic Control Systems
-In order to maintain a set point, we need a homeostatic control mechanism.
-Most homeostatic control systems have 3 components; the sensor, integrator, and effector.
-Sensor: Responsible for detecting an environmental variable.
-Integrator: Compares the variable being detected to its set point.
-Effector: Responsible for initiating the changes to restore the variable back to its set point.
Intrinsic and Extrinsic Control
-The 2 types of homeostatic regulation are intrinsic regulation/local regulation/autoregulation and
extrinsic regulation.
-Intrinsic control: The sensor, integrator, and effector are all located within a tissue so that the tissue
can regulate its own internal environment.
• Ex. An exercising muscle that needs oxygen to produce ATP. When local oxygen concentration
drops, blood vessels within the muscle dilate to increase oxygen that can be delivered.
-Extrinsic control: Regulatory mechanisms are outside of the tissue or organ.
• Ex. Regulation of body temperature.
• Majority of homeostatic control systems are extrinsic.
Feedback Loops
Negative Feedback
-Majority of homeostatic mechanisms use negative feedback.
-Refers to a change in an environmental parameter that causes the effector to initiate a response in the
opposite direction, restoring the parameter to set point.
-Once set point is achieved again, the system stops signalling.
,-Ex. Blood glucose regulation:
1. After ingesting a meal, blood glucose levels rise (away from homeostasis/set point).
2. Insulin is released by pancreas in response
3. Insulin lowers blood glucose by increasing the ability of body cells to uptake glucose from the
blood.
4. Insulin also upregulates the liver's ability to convert glucose and store it as glycogen.
Positive Feedback
-Occurs when the effector causes changes that amplify the initial signal.
-Positive feedback is not homeostatic.
-Ex. Positive feedback in childbirth:
1. Brain stimulates pituitary gland to secrete oxytocin
2. Oxytocin is carried in the bloodstream to the uterus
3. Oxytocin stimulates uterine contractions which push baby towards the cervix
4. Head of the baby pushes against cervix
5. The nerve impulses from the cervix are transmitted to the brain.
Section 2
The Plasma Membrane
-Physical barrier is both a protective barrier for the cell and allows cells to maintain an internal fluid
composition that is different from the external fluid composition.
-Plasma membrane plays a role in regulating the internal fluid composition since it can control what can
enter/exit.
-Allows nutrients to enter cells and waste to leave.
-Permits chemical signals released from other cells in the body to influence a cell (cell to cell
communication).
-Membrane participates in joining cells together to form tissues.
Membrane Physiology
-Plasma membrane has 3 primary functions:
• Ensure the cell's survival
• Maintain homeostasis
• Function cooperatively and in coordination with surrounding cells.
Structure and Function of the Plasma Membrane
-Phospholipids: Make up the lipid bilayer. Composed of a polar head with a negatively charged
phosphate group and 2 non-polar fatty acid tails.
Head is hydrophilic and tail is hydrophobic.
-Cholesterol: Found in the plasma membrane tucked between phospholipids. Prevent the fatty acid
chains from packing too tightly together and forming rigid structures; keep the membrane fluid. -
Membrane proteins: Inserted into the phospholipid membrane. Function to maintain cell structure,
regulate cell function, allow transport across the membrane, and facilitate signalling.
-Ion channels: Specialized membrane proteins that span the entire lipid membrane and permit entry
and exit of ions.
, -Carbohydrate chains: Short chains of carbohydrates attached to their proteins (glycoproteins) or to the
bilayer (glycolipids). Involved in stabilizing membrane structure, act as cell surface receptors, participate
in transportation, and more.
The Fluid Mosaic Model
-The membrane is fluid due to the fact that the phospholipid bilayer is viscous and that the individual
phospholipids can move.
-It is the lipid bilayer that gives the membrane its fluidity and elasticity.
-The membrane is a mosaic since it is embedded with other proteins and molecules that perform many
functions for proper cell functioning.
Cell-to-Cell Adhesions
-In order for the cells to come together to form tissues, they must first physically adhere to each other. -
The 3 ways cells are held together are by the extracellular matrix, cell adhesion molecules, and cell
junctions.
-Extracellular Matrix: A network of fibrous proteins embedded in a gel-like mixture of complex
carbohydrates.
• Surrounds all cells in tissues and keeps them in place.
• Watery gel allows for diffusion of nutrients from the blood and removal of waste from cells.
o This is often referred to as interstitial fluid and is made of 3 major protein fibres.
• The 3 main proteins involved:
o Collagen: Forms the cable-like fibres that give ECM its tensile strength.
o Elastin: Rubber-like protein that allows tissues to be stretched and then recoil once force is
removed.
o Fibronectin: Promotes cell adhesion.
• The majority of the ECM is secreted by fibroblasts in the interstitial space.
-Cell Adhesion Molecules: Usually transmembrane proteins. The intracellular side of the protein
interacts with the cytoskeleton, and the extracellular side interacts with the ECM CAMs from other cells.
• CAMs are involved in protein-protein interactions because they bind with other cells or the ECM.
• They stick to each other and their surroundings.
• The 4 main families of CAMs are Cadherins, Selectins, NCAMs, and Integrins.
-Cell Junctions: The 3 main types are desmosomes, tight junctions, and gap junctions.
• Desmosomes (Adherens junctions): Used to anchor together two adjacent cells that aren't
otherwise in direct contact. o Composed of dense intracellular thickenings called plaques that
are connected to glycoprotein filaments containing cadherins to attach neighbouring plaques
together. o Within a cell, other cytoskeletal anchoring proteins can also attach to plaque area.
This creates a network of strong fibres extending through tissues and cells. This also gives
desmosome containing cells (ex. Skin cells) a considerable amount of stretch.
• Tight Junctions (Impermeable junction): Creates a very tight seal between cells, preventing
movement of molecules from cell to cell.
o Long strings of junctional proteins in the plasma membrane align and adhere to form a tight
junction.
o The area where opposing junctional proteins from neighbour cells meet is a kiss site. o This
type of junction is mainly found in epithelial tissues (ex. Digestive tract).
