UNIT 1 PHYSIO

UNIT 1

Homeostasis

• Maintenance of relatively stable conditions within the internal environment regardless of what is happening in the external environment

  • Temperature, Blood pH, glucose levels, ions, oxygen and carbon dioxide levels. Blood pressure, water balance etc..

• Controlled by the nervous system and the endocrine system

  • Nervous system:Rapid adjustments in order to maintain homeostasis

  • Endocrine system: Gradual adjustments that are longer lasting.

• Internal vs External environment: Internal environment is constantly interacting with the external environment. Digestive system, lungs and kidneys are opened to the outside, which are considered part of the external environment. Unless a substance passes a cell membrane and is absorbed, it is considered outside the body. The circulatory system, including the heart and cardiovascular system, do not interact with the external environment.

Feedback mechanisms:

• Two major forms of Homeostatic control

  • Negative feedback: Maintains homeostasis

    • Set point: Parameter of the body; very specific. (temperature at 37 C)

    • Sensors: Constantly monitoring the internal environment and sending the information to the control centre (brain)

    • Control centre: Integrates information from the sensors and compares it to a set point. It then develops a plan to restore or maintain homeostasis. It sends the plan to the effectors.

    • Effector: Organ or organ systems that respond to the plan from the control centre. By responding to the plan, they are effective at changing the variable.

    • Variable: The internal condition that is being regulated through the negative feedback system.

    • This whole process is called a feedback loop, which will stop once the variable has returned to set point.

  • Positive feedback: Does not maintain homeostasis

    • Control center senses a particular variable

    • Acts on effectors

    • modify regulated variable

    • System feeds forward until the stimulus is gone.

    • Example; pregnancy and delivery. Baby pushes on the cervix -> releases oxytocin -> more uterine contraction -> more contact with the cervix

• Organizational Hierarchy of the body:

  • Atoms to Macromolecules: Atoms are the building blocks of the molecules, which then make macromolecules. Macromolecules include Lipids, Carbohydrates, Proteins, DNA.

  • Macromolecules to Organelles: Macromolecules work together to build an Organelle. For example, the membrane has a lipid bilayer and embedded glycoproteins (carbohydrates attached to proteins)

  • Cells, tissues and organs: Organelles then work together to make a cell. Similar cells combine together to make tissues, such as epithelial tissues, connective tissues, muscle tissues and neuronal tissues. These tissues work together to make organs

  • Organ Systems to Organisms: Organs then work together to form organ systems, such as the cardiovascular system.  Organ systems then work together to form an organism.

Fluids and ions

• Fluids are divided into two major categories:

  • Extracellular Fluid (ECF): All the fluid in the body that is found outside the cell

    • Blood plasma fluid: Fluid compartment inside the blood

    • Interstitial fluid: Fluids that are just outside of our cells

  • Intracellular fluid (ICF): All the fluid in the body that is found within the cell

• Ions

• Na+, Cl-, Ca++, K+.

  • Na+, Cl- and Ca++ are at higher concentrations in the extracellular fluid

  • K+ is at a higher concentration in the intracellular fluid 

  • Interior: Slightly negative

  • Outside:Slightly positive

• Ions want to move from an area of high concentration to an area of lower concentration

Cell Membrane, membrane transport, and the excitable cell

The structures in the cell:

Cells can alter where proteins are expressed on their cell surface, such as one side of the cell expresses pumps and the other side expresses channels, or the cell expresses receptors to respond to signals in the body.  This means that the cells of the heart are going to be organized differently than the cells of the kidney.

• Nucleus: Contains the cell’s genetic material (DNA) and controls its growth, metabolism and reproduction. It is often referred to as the control centre of the cell, as it regulates gene expression and mediates the replication of DNA during the cell cycle.Mature red blood cells do NOT have a nucleus.

• ER: network of membranous tubules and sacs involved in protein and lipid synthesis. It comes in two forms: rough ER, studded with ribosomes for protein synthesis, and smooth ER, which is involved in lipid synthesis and detoxification processes.

• Mitochondria: Mitochondria are membrane-bound organelles known as the powerhouses of the cell, as they generate ATP through cellular respiration. They also play crucial roles in energy production, regulation of the cell cycle, and apoptosis (programmed cell death).

• Cell membrane: surrounds the cell's cytoplasm and organelles, serving as a protective barrier. It regulates the passage of substances into and out of the cell through selective permeability, crucial for maintaining cellular homeostasis and communication with the external environment.

• Golgi body: stack of membrane-bound sacs responsible for processing, modifying, and packaging proteins and lipids synthesized in the cell. It sorts and directs these molecules to their appropriate destinations within the cell or for secretion outside the cell.

• Ribosomes: cellular structures composed of RNA and proteins that facilitate the synthesis of proteins by translating messenger RNA (mRNA) sequences into amino acid chains. They are found either floating freely in the cytoplasm or attached to the endoplasmic reticulum, forming rough ER.

Cell membrane and selective permeability

• Selective permeability: Able to keep things intracellular or extracellular

• The cell membrane is made of

  • Phospholipids: Has a hydrophobic tail made of lipids that interact with one another. It also has a phospholipid head that wants to interact with water

  • Non charged molecules like other fats or oxygen and carbon dioxide pass freely through the membrane

  • Macromolecules, proteins, cells, water and other charged particles dont pass freely.

Membrane potential and Equilibrium potential

• Membrane potential: Charge difference between the inside and the outside which allows the movement of ions to do and perform work within the cell.

• Equilibrium potential: Created by the electrical potential that exists inside of the cell vs the outside of the cell. Each ion has an equilibrium potential and its the electrical stimulus that exists inside the cell in order to stop the movement of an ion down its concentration gradient. This is the charge that would need to exist inside the cell to prevent an ion from moving down its concentration gradient. Equilibrium potential of an ion is what that ion wants the resting membrane potential to be

• The resting membrane potential for most cells is -70mV

• If the resting membrane potential and the equilibrium potential are the same (like with Cl) it going to be held outside the cell membrane

• Na+ wants to go inside the cell however the cell membrane is impermeable to sodium

• K+ wants to get out of the cell but the cell membrane is a bit permeable to potassium

• Crossing the membrane: 

  • Diffusion: Process by which a molecule spreads from an area of high concentration to an area of low concentration

    • Lipid soluble: pass freely

    • Water soluble: Need a protein or ion channel, aquaporin

  • Facilitated diffusion: Relies in carriers which are inside the cell membrane that allow the binding of the molecule from the outside or the inside of the cell. Molecules bind to the protein carrier, then that protein goes through some type of shape change that allows it to close to the outside of the cell or the inside and then open to the opposite side.

  • Active transport: Moving from a lower concentration to a higher concentration. Requires a protein carrier and ATP 

Osmosis

• Osmosis is the net movement of water down its concentration gradient

• Depends on:

  • Permeability of the membrane to solutes between intracellular and interstitial fluid

  • Concentration gradient between intracellular and interstitial fluid

  • Pressure gradient

    • Arises when differing concentrations of solutes are separated by a semipermeable membrane (Impermeable to the solute)

Osmolarity, Osmolality and tonicity

Tonicity: Water movement inside or out of the cell or no movement at all. so, how a solution affects movement of water across the membrane.It depends on the concentration of solutes that cannot pass through the membrane.

• Osmotically-active solutes are referred to osmoles (sodium, chloride, glucose, etc)

• There are two units to describe the concentration of a solution:

  • Osmolality: Number of osmoles per kg of water

  • Osmolarity: Number of osmoles per liter of solution

• Cells have an osmolarity/osmolality of 300 mOsm

• Tonicity of a solution:

  • Isotonic solution: Osmolarity of 300 mOsm. Water moves both outside and inside the cell at equal rates

  • Hypotonic solution: Inside of the cell has a higher osmolarity than the outside. Cell swells and bursts.

  • Hypertonic solution: Inside of the cell has lower osmolarity than the outside. Cell shrinks and dies

Homeostasis and the cell

Physiology: study of how systems (brain, heart, lungs, muscles, hormones) function in living organisms. It explores the mechanism by which organisms control their internal environment regardless of what happens in the outside environment. Physiology attempts to explain the physical and chemical factors responsible for both normal function and disease. The foundation of physiology lies in several key areas including genetics, anatomy, biochemistry, biophysics and cell biology.