Lecture 1: Intro to Physiology/Background Terms

What is physiology?

The study of interactions between molecules, cells, tissues, organs, and organ systems to understand the structure and function of an organism and its interaction with the environment

At what levels can physiology be studied?

cell + molecular physiology → systems physiology → organismal physiology → ecological physiology

Comparative physiology

studies and explores the diversity of functional characteristics of various kinds of organisms

Integrative physiology

investigates the broader aspects of physiology that involve the integration of mechanisms and regulatory functions at all biological levels

Structure vs. function (with examples)

* Differences between related animals living in different extreme environments (ex: arctic vs. temperate forest vs. desert foxes)


* Similarities between unrelated animals living in the same environment (ex: we see this primarily with color)


* Common solutions to physiological problems in unrelated organisms (ex: breathing and gas exchange)
* Causes of pathological conditions
* Pathophysiological conditions + disease states can provide insight to physiological regulatory mechanisms (ex: Goiter)

Goiter

thyroid hyperplasia that can be prevented by the use of idolized salt

Physiological regulation

a. Conformers vs. Regulators

b. Homeostasis

c. Positive vs. Negative Feedback

Conformers (+ ex)

Allow internal conditions to change when subjected to variation in external conditions

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(ex: temperature regulation in fish, amphibians, reptiles, most insects)

Regulators (+ ex)

Maintain relatively constant internal conditions regardless of external conditions (ex: temperature regulation in birds and mammals)

Can an animal be a conformer for one physiological condition and a regulator for another? What is an example of this?

Yes; fish are conformers for body temperature but are regulators for salt balance in body fluids

Homeostasis

The process of maintaining a stable internal environment in the face of changing external conditions

_______ about a variable is used to control processes in cells, tissues, and organs that influence the internal level of the variable

Sensory information

What is the generalized feedback control system cycle

Disturbance → Sensory → Reponse

Negative feedback loop

* The sampling of a controlled variable with immediate corrective action
* Common in physiological systems because they maintain homeostasis

Negative feedback loop cycle

Disturbance → Sensor → Correction

The set point

The desired point of homeostasis

Negative feedback loops will always do what to the set point?

Bring the system back to the set point

Negative feedback loop examples

* BP
* Hormone levels
* Salt concentrations

Positive feedback loop

the sampling of a controlled variable leading to the amplification of the disturbance

Positive feedback loop cycle

Disturbance → Sensor → Amplification

What do positive feedback loops do to the set point?

They lead the system away from the set point

Are positive feedback loops stable or unstable?

Highly unstable; due to this, they are rarely encountered in healthy states

Positive feedback loop examples

* Birth of a baby
* Milk production

Adaptation

* A trait that arose via an evolutionary process such as natural selection and improves an animal’s fitness (survival and reproductivity success)
* As a result of adaptation, the physiology of an animal is usually very well suited to its environment
* Gradual changes over many generations
* Hereditary
* Not reversible

What makes acclimatization and acclimation different from adaptation?

* They are adjustments of physiological processes in response to environmental change
* They are changes that occur during an animal’s lifetime and are usually reversible
* Result from chronic exposure to a new environment

Acclimatization

Refers to changes in a natural environment

Acclimation

Changes are induced experimentally in the lab, not in a natural environment

Polarity

degree to which positive and negative charges are separated at different ends of the molecule

Is water polar?

Yes, because it forms H bonds

\-philic

To have an affinity for

\-phobic

To have an aversion to

Amphipathic

Contains both hydrophobic and hydrophilic components

Hydrophobic

Doesn’t mix with water

Hydrophilic

Mixes with or dissolves in water

Lipophobic

Having no affinity for fats or organic solvents

Lipophilic

Tending to combine with or dissolve in lipids or fats

Acid

Any molecule that can donate a proton (H+) // ex: hydrochloric acid, HCl

Base

Any molecule that can accept a proton (H+) // ex: ammonia, NH3

pH scale

a measure of acidity ranging from 0-14 (0=extremely acid, 7=neutral, 14=extremely basic)

pH = -log10\[H+\]

Do cells and tissues have wide or narrow pH tolerances/ranges?

narrow

How is this narrow pH range achieved?

Buffers! The body generates bicarbonate ions (HCO3-) to bind to the protons generated during metabolism

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HCO3- + H+ → H2CO3

Carbohydrates

molecules consisting of C, H, O containing many alcohol ground (-OH)

Monosaccharides (+ ex)

Small carbohydrates, often in a ring structure (ex: glucose)

Disaccharides (+ ex)

Two monosaccharides attached by a covalent bond (ex: lactose)

Polysaccharides (+ ex)

* aka complex carbohydrates
* Long polymers of monosaccharides
* Can function in energy storage (e.g. starch + glycogen) or can be structural (e.g. cellulose + chitin)
* Hydrophilic due to polar -OH groups

Proteins

* Molecules consisting of linear chains of amino acids
* Can be structural (i.e. muscle) or can be enzymes

Amino acids

* Have both an amino group (-NH2) and a carboxylic acid group (-COOH)
* The side chain varies depending on the specific amino acid (side chains can be hydrophilic or hydrophobic)

Draw an amino acid chain

Peptides

Small chains of amino acids joined by peptide bonds

Enzymes

Molecules that catalyze or increase the rate of chemical reactions (i.e. Carbonic Anhydrase)

Protein structure

Primary structure, secondary structure, tertiary structure, quaternary structure

Protein primary structure

Amino acid sequence

Protein secondary structure

Highly regular sub-structures (i.e. alpha helix, beta sheets)

Protein tertiary structure

3D structure of single protein molecule

Protein quaternary structure

3D structure of multi-subunit protein (i.e. hemoglobin)

Are proteins hydrophilic or hydrophobic? Why?

* Hydrophilic due to their 3D structure
* Hydrophobic amino acids contained on the inside; hydrophilic amino acids found on the exterior – this allows for interaction with water

Lipids (+ ex)

Hydrophobic molecules containing mostly C and H atoms (ex: fats, phospholipids, and steroids)

Fatty acids

* Hydrocarbon chains with a carboxylic acid group (-COOH) at one end.


* Saturated = no double bonds between Cs
* Unsaturated = at least one double bond

Triglyceride

* A glycerol molecule bonded to three fatty acid chains.
* Functions in energy storage

Phospholipids

* Lipids containing a polar head with phosphate group (hydrophilic) and fatty acids (hydrophobic) à amphipathic


* Important structural molecules in cell membranes

Steroids

Lipid molecules composed of four hydrocarbon rings (ex: Cholesterol, many hormones like estrogen and testosterone)

Energy transfer in cells

Some chemical reactions occur spontaneously and release energy (**exergonic**) whereas others require energy to proceed (**endergonic**)

Exergonic

Release energy/occur spontaneously

Endergonic

Require energy to proceed

ATP

Adenosine triphosphate; most common molecule used for energy transfer in cells

Metabolism

* All the reactions that occur in living organisms to maintain life


* Involves reactions that harvest energy from food and use energy for life processes

What are cell (plasma) membranes composed of?

A phospholipid bilayer

Draw the phospholipid bilayer and explain

Cholesterol

Reduces membrane permeability by strengthening interactions between polar head groups

How does temperature influence fluidity in how it pertains to cholesterol?

Higher temps → decrease fluidity

Lower temps → increase fluidity

Lipid rafts

membrane microdomains containing elevated levels of cholesterol and phospholipids with saturated fatty acid chains. These play an important role in membrane protein localization.

Membrane function

* Selective permeability
* Ion gradients across lipid bilayers (ex: there is a large, around 20,000 fold, calcium gradient across the cell membrane)

Types of transport mechanisms across the membrane

1. Passive diffusion
2. Facilitated diffusion (either channel or permease)
3. Active transport
4. Concentration gradient

Which types of transport do not require energy?

Passive diffusion and facilitated diffusion

Which types of transport require energy?

Active transport

What are the two types of active transport?

Primary active transport and secondary active transport

Primary active transport

Uses energy stored in ATP to move molecule/ion against concentration gradient

Secondary active transport

Uses energy associated with gradient of one molecule/ion to move another molecule/ion against its concentration gradient

Example of primary active transport

Na+K+ATPase

* Pumps 3 Na+ out of the cell for every 2 K+ it pumps into the cell. This requires energy provided by the hydrolysis of ATP.
* This contributes to several electrochemical gradients
* \[Na+\] greater outside than inside the cell
* \[K+\] greater inside than outside the cell
* Inside of cell is negatively charged relative to outside

Example of secondary active transport

The Glucose-Na+ cotransporter

* Na+ concentration high outside cell, glucose concentration high inside cell
* Movement of glucose into cells against its concentration gradient using the energy supplied by the concentration gradient of Na+

G-protein-coupled receptors (GPCRs) (+ ex)

* Signal across the membrane
* Located in the cytoplasm
* Ex: some hormone receptors (e.g. adrenalin) and some neurotransmitter receptors

How do GPCRs work

1. Ligand binds to a G-protein-coupled receptor, causing a conformational change
2. The activated receptor signals to an associated G protein, causing the alpa subunit to release GDP and bind GTP
3. The activated alpha or beta gamma subunits move through the membrane and interacts with an amplifier enzyme
4. The activated amplifier enzyme converts and inactive second messenger to its active form
5. The activated second messenger activates or inhibits cellular pathways

Mitochondria

* Produce ATP through aerobic processes


* Powerhouse of the cell

Nucleus

Contains DNA, the genetic material that encodes proteins

Endoplasmic reticulum (two types)

Smooth endoplasmic reticulum

* does not bind ribosomes
* site of Ca2+ storage

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Rough endoplasmic reticulum

* has ribosomes bound to outer surface (“rough”)
* Involved in packaging proteins fro secretion

Golgi apparatus

Aka Golgi complex or Golgi network

Involved in protein processing and modification

Endosomes

* transport
* contain proteins, etc. from outside of the cell via endocytosis (pinocytosis or phagocytosis) or from inside the cell (ER or Golgi)
* Recycle proteins or deliver them to the lysosome for protein breakdown

Lysosomes

* breakdown
* have acidic interior
* break down proteins and other molecules

Cytoskeleton

* Made up of microtubules, microfilaments, and intermediate filaments


* Determine the cell shape and intracellular transport of molecules

MTOC

Microtubule Organizing Center

Microtubule Organization

Cell cargo transport in microtubules

Kinesin and Dynein

Kinesin

Motor protein that transports its cargo vesicles along microtubules in a “plus-end” direction

Dynein

Motor protein that transports it cargo vesicles along microtubules in a “minus-end” direction

What is found in the space between cells

* The extracellular matrix (ECM), which is a network of extracellular molecules secreted by cells
* It contains collagen, fibronectin, and integrin

Collagen

Protein that forms fibers and sheets for structural support

Fibronectin

Glycoprotein that can bind to integrin and fibers in the ECM, contributing to cell adhesion

Integrin

Membrane receptors for ECM proteins, help attach cells to their external environment

Plasma membrane

Also called the cell membrane, it’s the membrane found in all cells that separates the interior of the cell from the outside environment

Ribosomes

Involved in making proteins