Source: APK2105C Final Exam Review, University of Florida
Tags: physiology, homeostasis, cells, tissues, organs, body fluids, ECF, ICF, TBW, atoms, chemical bonds, ions, functional groups, APK2105C
Difficulty: Introductory Prerequisites: None. This is foundational material for the entire course.
Physiology is the study of how the body maintains a stable internal environment so it can survive. Everything in this course builds on that single idea: homeostasis. Before you can understand how organs and systems keep the body in balance, you need to know what the body is built from (cells, tissues, organs, systems), where its water lives (intracellular vs. extracellular compartments), and the chemical rules that govern how molecules interact. This section is the scaffolding for every later topic, from membrane transport to metabolism.
The body is organised from cells upward into tissues, organs and systems, all working to maintain homeostasis. Roughly 60% of body weight is water, split between intracellular and extracellular compartments. The chemistry of life depends on how atoms bond (covalent, ionic), the polarity of those bonds, and the functional groups attached to biomolecules.
Physiology
The study of how the body functions to maintain a constant internal environment so it can survive.
Homeostasis
The internal constancy needed to survive. In simple terms, it is the body's ongoing effort to keep its internal conditions (temperature, pH, glucose, etc.) within a narrow, liveable range.
Cells
The basic functional unit of the body. Think of them as the smallest living units capable of carrying out their own life functions.
Tissues
Two or more cells grouped together with specific functions in physiological control. Four main types exist: nervous, muscle, epithelial and connective.
Organs
Structures formed by combining two or more tissue types. They usually help support homeostasis.
Systems (organ systems)
When two or more organs work together to maintain homeostasis, they form an organ system.
Negative feedback
The process by which a change in a regulated variable (such as body temperature or blood glucose) is sensed by receptors that trigger responses to return the variable to its normal level. This is the body's primary control mechanism.
Homeotherms
Organisms whose body temperature must remain within a relatively narrow limit. Humans are homeotherms.
Water
The most abundant substance in the body, roughly 60% of body weight. It acts as a solvent for the large number of solutes found in body fluids.
Total Body Water (TBW)
The volume of water contained in all of the body's compartments. It is all the water enclosed by the external epithelial layer (skin).
Extracellular fluid (ECF)
Fluid outside cells, composed of interstitial fluid and plasma. It contains a slight excess of cations over anions, giving it a net positive charge.
Intracellular fluid (ICF)
Fluid inside cells. It has a high protein and potassium concentration and contains a slight excess of anions over cations, giving it a net negative charge.
Blood plasma
About 20% of the ECF. It is the water portion of the blood and has a high sodium and protein concentration.
Interstitial fluid (ISF)
The largest portion of the ECF (80%). It bathes most of the cells in the body.
Atoms
The fundamental units of biomolecules, made up of three elementary particles: protons, electrons and neutrons.
Electron shell
The chemical reactivity of an atom is determined by the number of electrons in its outermost shell.
Octet rule
The tendency to fill the outermost electron shell with eight electrons. Elements with filled outer shells are inert, meaning they cannot donate or receive electrons.
Chemical bond
An attractive force between atoms. Bond formation relies on the ability of atoms to share, donate or receive electrons.
Covalent bond
A bond that results when two atoms share electrons. If electrons are shared equally, the bond is nonpolar covalent. If shared unequally, the bond is polar covalent.
Electronegativity
The degree to which an atom attracts electrons. Differences in electronegativity between atoms create polar covalent bonds.
Ions
Atoms that have lost or acquired electrons. Positive ions are cations; negative ions are anions. They form ionic bonds by electrical attraction.
Hydrophilic
Polar molecules that dissolve in water. In simple terms, "water-loving."
Hydrophobic
Nonpolar molecules that do not dissolve in water. In simple terms, "water-fearing."
Biomolecules
Molecules synthesised by living organisms that contain carbon atoms, built by joining atoms through covalent bonds. The most common elements in biomolecules are carbon, hydrogen, nitrogen and oxygen.
Functional groups
Characteristic groups of atoms that determine the properties of biological molecules. They are the basis of individual function for almost all macromolecules.
Hydroxyl group
Readily forms hydrogen bonds. Found in alcohols and carbohydrates. Makes molecules polar.
Carbonyl group
A carbon-oxygen double bond. Contributes to making molecules water-soluble.
Carboxyl group
A weak organic acid: a carbon atom double-bonded to one oxygen and single-bonded to another. Found in amino acids and fatty acids.
Amino group
A nitrogen atom bonded to two hydrogens. Hydrophilic. These are building blocks of protein.
Sulfhydryl group (thiol group)
Sulfur bonded to hydrogen. Stabilises protein structure through disulfide bridges.
Phosphate group
Phosphorus bonded to four oxygen molecules. Found in DNA, RNA and certain lipids. Involved in the biological storage and release of energy (e.g. ATP).
Cells are the smallest unit of life. They group into tissues, tissues combine into organs, organs form organ systems.
The four primary tissue types are:
Nervous tissue: specialised for generating electrical signals.
Muscle tissue: specialised to contract (skeletal, cardiac, smooth).
Epithelial tissue: assembled in sheet-like arrays on a basement membrane; specialised in separating fluids. Forms glands.
Connective tissue: a broad category (blood, bone, fat, lymph) not defined as precisely as the other types.
Neurons: nerve cells specialised to transmit impulses. Motor neurons transmit outward from the brain and spinal cord. Sensory neurons receive impulses (light, smell, touch) and relay them inward.
Muscle cells (muscle fibres): overlapping proteins that contract. Skeletal muscle is voluntary. Cardiac and smooth muscle are involuntary.
Epithelial cells: form glands. Exocrine glands secrete products into ducts leading to the body exterior (sweat glands, salivary glands). Endocrine glands secrete hormones directly into the bloodstream.
Connective tissue cells: include the extracellular matrix, a dense meshwork of proteins such as elastin (for elasticity) and collagen (for strength).
Chemicals released into the blood for circulation to other tissues, with the purpose of controlling the function of those target cells.
Water makes up roughly 60% of body weight.
TBW is split between intracellular fluid (inside cells) and extracellular fluid (outside cells).
ECF is further divided into blood plasma (20% of ECF) and interstitial fluid (80% of ECF).
Blood plasma and ISF replenish the ECF by bathing and nourishing cells.
The lumen is the interior cavity of organs and vessels.
The body uses negative feedback as its main control loop: a sensor detects a deviation, and effectors act to bring the variable back to its set point.
Cardiopulmonary resuscitation (CPR) and hospital life support systems exist to maintain air exchange and blood circulation when the body's own mechanisms fail.
Atoms consist of protons, electrons and neutrons.
Chemical reactivity depends on the outermost electron shell.
The octet rule drives bond formation: atoms "want" eight electrons in their outer shell.
Covalent bonds involve sharing electrons. Ionic bonds involve transferring electrons, creating cations (+) and anions (−).
Polarity matters: polar molecules are hydrophilic; nonpolar molecules are hydrophobic.
Hydroxyl (−OH): found in carbohydrates and alcohols; makes molecules polar.
Carbonyl (C=O): contributes to water solubility.
Carboxyl (−COOH): weak acid; found in amino acids and fatty acids.
Amino (−NH₂): hydrophilic; building block of proteins.
Sulfhydryl (−SH): stabilises protein structure.
Phosphate (−PO₄): found in nucleic acids and ATP; involved in energy storage and release.
Negative feedback is the principle behind a household thermostat: the heater switches off once the room reaches the set temperature, and switches on again when it drops. Your body regulates temperature, blood sugar and blood pressure in essentially the same way.
Understanding body water compartments is clinically important. Intravenous saline solutions must be isotonic to avoid damaging cells, and fluid imbalances are a primary concern in emergency medicine.
Students often assume "negative feedback" means something bad. It does not. "Negative" refers to the direction of the response (opposing the change), not to any harmful outcome.
Covalent and ionic bonds are sometimes treated as totally separate. In reality, many bonds have partial ionic and partial covalent character, depending on the electronegativity difference.
"Hydrophobic" does not mean a molecule is repelled by water. It means water molecules preferentially hydrogen-bond with each other rather than interact with the nonpolar molecule.
Homeostasis does not mean conditions are perfectly constant. It means they are kept within a narrow, tolerable range through continuous adjustment.
⚠️ Know the difference between intracellular and extracellular fluid, and the subdivisions of ECF (plasma vs. ISF), including the percentage breakdown (20/80).
⚠️ Be able to identify each functional group and state where it is found and what property it confers.
⚠️ Understand that negative feedback returns a variable to normal, and be ready to give an example (temperature regulation, glucose control).
⚠️ Distinguish the four tissue types and the subcategories of muscle (skeletal, cardiac, smooth) and glands (exocrine, endocrine).
True or false: Interstitial fluid makes up about 20% of the ECF. (False, it is 80%.)
Fill in the blank: The tendency to fill the outermost electron shell with eight electrons is called the _______ _______. (Octet rule.)
True or false: Nonpolar molecules are hydrophilic. (False, they are hydrophobic.)
Fill in the blank: Chemicals released into the blood to control the function of distant cells are called _______. (Hormones.)
True or false: Negative feedback amplifies a change away from the set point. (False, it opposes the change and returns the variable toward normal.)
Q: What is homeostasis and what is its purpose?
A: Homeostasis is the internal constancy needed to survive. Its purpose is to maintain a constant internal environment (temperature, pH, solute concentrations, etc.) within a narrow, liveable range.
Q: Approximately what percentage of body weight is water, and how is total body water distributed?
A: Roughly 60%. It is divided into intracellular fluid (inside cells) and extracellular fluid (outside cells). ECF itself splits into blood plasma (20% of ECF) and interstitial fluid (80% of ECF).
Q: Distinguish between a nonpolar covalent bond and a polar covalent bond.
A: In a nonpolar covalent bond, electrons are shared equally between atoms. In a polar covalent bond, electrons are shared unequally due to a difference in electronegativity, creating partial charges on the atoms.
Q: Name three functional groups found in biomolecules and state one role of each.
A: Hydroxyl (−OH): makes molecules polar, found in carbohydrates. Amino (−NH₂): hydrophilic, building block of proteins. Phosphate (−PO₄): involved in energy storage and release, found in ATP and nucleic acids.
Q: What is the key difference between exocrine and endocrine glands?
A: Exocrine glands secrete products into ducts leading to the body exterior (e.g. sweat, saliva). Endocrine glands secrete hormones directly into the bloodstream.
This material connects directly to membrane transport (Part 4 of these notes), because the distribution of water and ions across compartments creates the concentration and electrical gradients that drive passive and active transport. It also underpins metabolism and ATP production (Part 3), since the functional groups you learn here (phosphate, carboxyl, amino) appear repeatedly in glycolysis, the Krebs cycle and oxidative phosphorylation.
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