Homeostasis, Feedback Mechanisms, and Biochemistry (Video Notes)
Regulated Physiological Variables (Mnemonic)
Big → Blood Pressure
Bad → Blood Volume
Bears → Blood Osmolarity
Crack → Calcium
Tiny → Temperature (body)
Pigeon → pH (hydrogen ions, H⁺)
Eggs → Glucose
Cook → Carbon Dioxide
Perfect → Potassium
Omelets → Oxygen
Learning Objectives
Recognize each component of a homeostatic system in representative systems.
Explain how homeostatic mechanisms regulated by negative feedback detect and respond to environmental changes.
Define negative feedback.
Describe the actions of a positive feedback loop and be able to recognize each of the components in representative systems.
Explain the general relationship of maintaining homeostasis to health and disease.
Homeostatic Control Mechanism and Components
Homeostasis: maintenance of stable internal conditions.
Components (3):
Receptor (sensor) – detects changes from the set point.
Control Center – processes the input and determines the response.
Effector – carries out the response to restore homeostasis.
Define homeostasis and the components of a homeostatic system.
Diagrammatic example (Figure references): Sensory receptor (e.g., in skin) → Control Center (e.g., Hypothalamus) → Effectors (e.g., Blood Vessels in skin, Skeletal Muscle, Brown Adipose Tissue).
Negative Feedback
Negative feedback: the resulting action is in the opposite direction of the stimulus (most common).
Regulated by the endocrine and nervous systems.
Key idea: stabilizes the system by counteracting the initial change.
Positive Feedback
Positive feedback: the resulting action amplifies or intensifies the original stimulus.
Unlike negative feedback, positive feedback drives the system further away from the set point.
Key idea: destabilizes the system by enhancing the initial change, often leading to a rapid completion of an event.
Examples of Positive Feedback Loops:
Childbirth (Uterine Contractions):
Stimulus: Baby's head pushes against the cervix.
Sensor: Stretch receptors in the cervix are activated.
Control Center: Oxytocin is released from the posterior pituitary.
Effector: Oxytocin stimulates stronger uterine contractions.
Outcome: Stronger contractions push the baby further, leading to more cervical stretching and further oxytocin release, amplifying the process until birth occurs.
Blood Clotting:
Stimulus: Damage to a blood vessel wall (initial platelets adhere).
Sensor: Platelets release chemicals (e.g., ADP, thromboxane).
Control Center: These chemicals attract more platelets to the site.
Effector: More platelets aggregate and release more chemicals, forming a platelet plug; this process is amplified until the vessel is sealed.
Quick Concept Checks (From iClicker/Slides)
Which component brings about a change to the stimulus? Answer: - D) Effector
Which component detects a change in the stimulus?
C) Receptor
Glucose Homeostasis (Example of Negative Feedback)
Stimulus: Blood glucose rises after a meal.
Sensor/Detector: Pancreas detects the rise in blood glucose.
Control Center: Pancreatic beta cells regulate hormone output.
Effector: Target tissues (skeletal muscle, liver, adipose tissue) respond to insulin by increasing glucose uptake.
Outcome: Blood glucose returns toward basal levels; system exhibits negative feedback.
Diagram expectations: Identify the stimulus, receptor, control center, and effector; indicate negative feedback in the center.
Restored homeostasis when glucose levels normalize.
Normal ranges (context): Blood glucose commonly cited as ~80\text{ mg/dL}\text{ to } 110\text{ mg/dL} in fasting/measured states (as per slides).
Pathology and Health Implications
Pathology: Failure to maintain homeostasis contributes to disease.
Example ranges:
Blood glucose: 80\text{ mg/dL}\rightarrow 110\text{ mg/dL} (normal fasting range cited in slides) → Diabetes when elevated.
Blood Pressure: ~120/70\text{ mmHg} (normal reference). Hypertension refers to elevated BP.
Relationship: Maintaining homeostasis is essential for health; disruption can lead to disease states such as diabetes and hypertension.
pH, Acids, Bases, and Buffers
Fundamental questions: What is pH? Why is it important?
Key terms to define: dissociate, anion, cation, solvent, solute, solution, acid, base.
Atom and chemical compound: definitions and behavior in water.
Strong vs. weak acids and bases; neutral solutions.
Buffers: substances that resist pH change by taking up or releasing H⁺.
Example buffers in blood: Carbonic acid (H₂CO₃) and bicarbonate (HCO₃⁻).
Buffers maintain blood pH between 7.35 and 7.45; small deviations can be fatal.
pH concept:
pH is the negative logarithm of hydrogen ion concentration: \text{pH} = -\log_{10}[\text{H}^+]
Scale ranges from 0 to 14.
Inverse relationship: lower pH = more acidic, higher pH = more basic.
Neutral pH = 7 (equal H⁺ and OH⁻).
Neutralization: acid + base → salt + water.
Medications like antacids (e.g., TUMS, Rolaids) provide base to neutralize stomach acid.
Ion – an atom or molecule that has gained or lost electrons, giving it a charge.
Anion – a negatively charged ion (gains electrons).
Cation – a positively charged ion (loses electrons).
Ionic Compound – a compound made of cations and anions held together by electrostatic attraction.
Solution – a uniform mixture of two or more substances.
Solvent – the substance that does the dissolving (present in the greatest amount, e.g. water).
Solute – the substance that gets dissolved (e.g. salt in water).
Dissociate – when an ionic compound separates into individual ions in solution (e.g. NaCl → Na⁺ + Cl⁻ in water).
Acid – a substance that increases the concentration of H⁺ (protons) in solution; often donates H⁺.
Base – a substance that increases the concentration of OH⁻ in solution; often accepts H⁺.
Acids = dissociate in H2O, forms H+ and Anion
Substance A (an acid in water) H+ + Anion
Proton donors:
Strong Acids: produce a lot of H+, Hydrochloric acid
(HCl), H+ and Cl-
Weak Acids: produce fewer H+, carbonic acid (H2CO3),
Bases = accept H+ when in H2O
Substance B (a base in water) + H+ B---H
Proton acceptor:
Strong Bases: dissociate and bind more H+, Sodium
hydroxide (NaOH)
Weak Base: bind less H+, Bicarbonate (HCO3-), weak
base doesn't mean unimportant, lactic acid is a weak acid
Biological Macromolecules and Chemistry Refresher
Four organic macromolecule classes: Carbohydrates, Proteins, Lipids, Nucleic Acids.
Common atoms:
Carbohydrates, Lipids, Proteins, Nucleic Acids all contain carbon (C) and hydrogen (H) and generally oxygen (O).
Proteins contain nitrogen (N) and often sulfur (S) as well.
Nucleic acids contain phosphorus (P).
Polymers and monomers:
Molecules built from repeating subunits (monomers) form polymers.
Monomer examples: Carbohydrates — sugar monomers; Proteins — amino acids; Nucleic Acids — nucleotides (DNA/RNA).
Lipids are not typically polymers in the same sense as the others.
Glycogen: storage form of carbohydrate in animals, stored in skeletal muscle and liver.
Simple carbohydrates vs glycogen storage context is illustrated in figures (e.g., Figure 2.20, simple carbohydrates).
Quick QA from slides:
Which macromolecule does not exist in the body as a polymer? Lipids.
Lactose is a disaccharide.
Storage form of carbohydrate in animal skeletal muscle? Glycogen.
Quick Summary: Key Concepts to Remember
Negative feedback is the dominant homeostatic mechanism, stabilizing the internal environment by opposing the initial change.
Positive feedback amplifies the initial change, pushing the system further from the set point to complete an event.
Homeostatic components: Receptor detects changes, Control Center processes information, Effector executes response.
Glucose regulation is a classic negative-feedback loop involving insulin signaling.
pH homeostasis is tightly regulated by buffers (e.g., carbonic acid/bicarbonate) and neutralization to keep blood pH tightly within a narrow range.
Four major biomolecule classes form the basis of structure and function in biology; all contain carbon and hydrogen and various other elements; monomers form polymers for carbs, proteins, and nucleic acids.
Carbohydrate storage in animals is primarily glycogen stored in liver and skeletal muscle.
Practice and Concept Checks (From Slides)
Q: A chemical compound that fully dissociates to anion and H⁺ in water is:
Answer: A strong acid (e.g., HCl) — fully dissociates to H⁺ and Cl⁻.
Q: Which acid listed is a strong acid? (Hydrochloric acid is strong; lactic acid and carbonic acid are weaker in comparison.)
Q: A solution with pH 2 vs pH 7: Which has higher [H⁺]? The pH 2 solution has a higher [H⁺], so the statement that pH 2 has lower [H⁺] than pH 7 is False.
Q: Which has the highest pH among: Stomach, Blood, Oral cavity, Skeletal Muscle? Answer: Blood (approximately around pH 7.4).
Q: Lactose is a disaccharide.
Q: Storage form of carbohydrate in animal skeletal muscle? Glycogen.
Important Normal Ranges (As Mentioned on Slides)
Blood glucose: 80\text{ mg/dL}\text{ to } 110\text{ mg/dL}
Blood pressure: around 120/70\text{ mmHg}
Blood pH: 7.35\text{ to } 7.45
Notes on Figures and Lecture Structure
Figure references (e.g., Figure 1.11, Figure 1.13a, 1.13b) illustrate the components of a homeostatic system and how receptors, control centers, and effectors interact.
Concept maps (e.g., Concept Mapping of Homeostatic Control Mechanism) emphasize connections among stimulus, sensors, integrating centers, and effectors.
Emphasize: Misconception that negative feedback is inherently bad and positive feedback is inherently good. Reality: Both are necessary for normal physiological function (e.g., some rapid amplifications in childbirth, blood clotting; negative feedback for stability).
Exit Poll / Reflective Prompts
Muddiest Point: What about today’s material remains unclear?
One physiology question you’