Homeostasis and Feedback Loops

Lab 1: Homeostasis

• Homeostasis stabilizes the body's set point
• Homeostatic feedback loops maintain balance

Negative Feedback

• Negative feedback produces an opposite result
• Examples include the regulation of blood sugar, blood pressure, and body temperature

Positive Feedback

• Positive feedback enhances or increases the initial result
• Examples include labor, blood clotting, and lactation

Homeostatic Reflexes

• Neural reflexes have a control center in the nervous system
• Hormonal (endocrine) reflexes have a control center in an endocrine gland
• Some reflexes involve both neural and hormonal components

Neural Reflex Arc

• Stimulus: A change or stress that triggers the reflex
• Receptors (sensors): Detect the stimulus
• Afferent pathway: Carries sensory input to the control center
• Control center (CNS):
  • The set point is in the medulla oblongata for hypotension.
  • The set point is in the hypothalamus for hypothermia.
• Efferent pathway: Carries motor output from the control center
  • Motor output, autonomic related to hypotension.
  • Motor output, somatic related to hypothermia.
• Effectors (organs):
  • SA node, myocardium, and blood vessels for hypotension.
  • Muscles (shivering) and blood vessels for hypothermia.
• Response (results):
  • Increased blood pressure for hypotension.
  • Increased body temperature for hypothermia.

Hormonal Reflex Arc

• Stimulus: A change or stress that triggers the reflex
• Receptors (sensors): Detect the stimulus
• Afferent pathway: Carries sensory input to the control center
• Control center (endocrine glands):
  • The set point is in the Pancreas for hyperglycemia.
  • The set point is in the Thyroid for hypercalcemia.
  • The set point is in the Parathyroid for hypocalcemia.
• Efferent pathway: Carries hormones from the control center
• Effectors (organs):
  • Liver and other tissues (hepatocytes) for hyperglycemia.
  • Bone matrix (osteoblast), kidneys, and small intestine for hypercalcemia
  • Bone matrix (osteoclast), kidneys, and small intestine for hypocalcemia
• Response (results):
  • Decreased blood glucose levels for hyperglycemia
  • Decreased blood calcium levels for hypercalcemia
  • Increased blood calcium for hypocalcemia

Both Neural and Hormonal Reflex Arcs

• Has both sensory and hormonal aspects

Conversion

• 1 mL = 1 g = 1 cc (cm³)

Practice Conversions

• 1 g = µg (microgram)
• 5 cm = m
• 3 cc = mg = uL (microliter)
• 50 g = kg
• 10 mL = g
• 2 g = ug

Graphs

• Independent variable (x-axis) vs. Dependent variable (y-axis)
• Bar graphs compare groups
• Line graphs show changes over time

Lab 2: Solutions, Diffusion, and Osmosis

• Solutions are made of solute and solvent

Solute

• The substance that is dissolved in a solution

Solvent

• The liquid in which the solute is dissolved
• Water is polar, while oil is nonpolar

Solubility and Polarity

• Like dissolves like
• Polar solutes dissolve in polar solvents
  • Food coloring dissolves in water
• Ions dissolve in polar solvents
• Nonpolar solutes dissolve in nonpolar solvents
  • Sudan black dissolves in oil

pH Scale

• Measures acidity and alkalinity
• Ranges from 0 to 14
• Acidic solutions have a pH below 7 (H+ > OH-)
• Alkaline solutions have a pH above 7 (H+ < OH-)
• Neutral solutions have a pH of 7
• pH is the negative logarithm of the hydrogen ion concentration: pH = -log [H+]

pH Scale Example

• Adding 100x more H+ to a solution with pH 6 results in pH 4

Normal pH Levels

• Normal pH is between 7.35 and 7.45
• Di water typically has a pH of 5, but lab water is more acidic.
• Prolonged vomiting can make the blood more basic because of losing stomach acid

Solutions

• Acidic solutions like HCl dissociate into H+ and Cl-
• Basic solutions like NaOH dissociate into Na+ and OH-
• Buffers and antacids are used to neutralize strong acids or bases

Neutralization

• Adding a buffer (AZ) to DI water neutralizes it + HCl or NaOH

Indicators

• Used to test for specific substances

I2KI

• Tests for starch (polysaccharides)
• Positive result: Dark purple or indigo blue
• Negative result: Amber yellow

Benedict Reagent w/Heat

• Tests for glucose (monosaccharides or reducing sugars)
• Positive result: Orange
• Negative result: Light blue

AgNO3

• Tests for chloride
• Positive result: White precipitation
• Negative result: Clear

Diffusion, Osmosis, and Tonicity

• indicates concentration

Diffusion

• Movement of molecules from high to low concentration

Factors affecting Diffusion

• Solute concentration
• Molecular weight
• Molecule size
• Temperature
• pH level

Osmosis

• Diffusion of water across a semipermeable membrane
• Water follows solute

Osmotic Pressure (OP)

• High solute concentration causes higher osmotic pressure

Hydrostatic Pressure (HP)

• High amount of water causes higher hydrostatic pressure

Tonicity

• Isotonic solutions have equal OP and HP, no net water movement
• Hypotonic solutions have high OP inside the cell and high HP outside, water moves in
• Hypertonic solutions have high OP outside the cell and high HP inside, water moves out

Solutions and Cell Behavior

• 5% starch - No diffusion because starch is too large
• 5% glucose - Yes diffusion, glucose moves out.
• 5% NaCl - Yes diffusion, NaCl moves out
• 5% NaCl & 5% NaCl - No net movement
• 0% NaCl & 1% Starch - No diffusion because starch is too large

Lab 3: Enzymes

Chemical Reactions

• Anabolism is synthesis, endergonic, and requires energy; A + B → AB
• Catabolism is degradation, exergonic, and releases energy; AB → A + B
• Catalysts are shortcuts to products, using less energy

Enzymes

• Organic catalysts
• Substrates are reactants
• Active sites are substrate binding sites
• Coenzymes are organic helper molecules
• Cofactors are inorganic helper molecules

Catalysts

• Organic catalysts are enzymes like catalase, found in liver and blood
• Inorganic catalysts include ferric oxide (Fe2O3, nail)
• Substrates react with hydrogen peroxide (H2O2)
• Products include water and oxygen (H2O + O2)

Enzyme Properties

• Specificity: bind to specific reactants
• Enzymes are recycled, used until saturated
• Saturation: enzymes at max efficiency, reaction rate plateaus, total rate depends on enzyme and substrate concentration
• Inhibition slows/stops reaction rate
• Competitive: binds to active site
• Non-competitive: binds elsewhere
• Denaturation can occur with extreme heat, pH changes, or specific chemicals

Experiments on pH Effects

• Acidity denatures enzymes/alkaline inhibits enzyme and slows down reaction

Enzyme Activity and Temperature

• Extreme heat denatures enzymes
• Cold temperatures inhibit and slow down reactions

Lab 4: Blood Properties

Blood components

• Formed elements:
  • Hematocrit: ratio of erythrocytes to total blood volume
  • Buffy coat: leukocytes and platelets
• Blood plasma:
  • Water, proteins and other solutes (hormones, nutrients…)

Hematocrit Calculation

• Hematocrit = (Length of RBC layer (mm) / Total blood length (mm)) x 100 = % hematocrit

Normal Hematocrit Values

• Male: 42-52%
• Female: 37-47%
• Newborn: 49-61%

Abnormalities based on Hematocrit Values

• Decreased hematocrit indicates Anemia, decreased oxygen, and RBC
• Elevated hematocrit indicates Polycythemia, caused by dehydration or high altitude

Red Blood Cells (RBCs)

• RBC → 250 million Hb × 4 𝑂2 per Hb = 1 billion 𝑂2 per RBC

Blood Typing

• Antigens coat every RBC
• Antibodies recognize antigens, protect against antigens, found in plasma
• Rh factor is inherited, found on the surface of RBC
  • Rh+ has Rh+ antigen, no antibodies
  • Rh- has no Rh antigen, has antibodies to Rh+ antigen
• Transfusions, Rh+ can receive Rh+ or Rh- blood
• Rh- can only receive Rh- blood because their Rh+ antibodies will destroy any Rh+ RBC
• Rh incompatibility occurs in mother with Rh- and fetus with Rh+

Osmosis of Red Blood Cells (RBCs)

• RBC + 0.9% NaCl = Isotonic, normal cell appearance
• RBC + 0.1% NaCl = Hypotonic, cells lysed
• RBC + 5% NaCl = Hypertonic, cells crenated

Clinical Applications

• Sickle cell anemia: Mutation, sickle-shaped cells, decreased O2, RBC, Hb
• Parasitic infections: Changes in structure/function, destroyed, increased eosinophils
• Parasitic anemia: Changes in structure/function, destroyed, increased eosinophils, decreased RBC and Hb
• Aplastic anemia: Caused by drugs/toxins/radiation/chemo, decreased RBC and Hb
• Cancer in bone marrow: Damages bone marrow, decreased lymphocytes, RBC, and Hb
• Iron deficiency anemia: Caused by low iron, decreased RBC and Hb
• B12 deficiency (pernicious anemia): results in abnormal large RBC, decreased RBC and Hb
• Folic acid deficiency: results in abnormal large RBC, decreased RBC and Hb
• Allergic reaction: rash, hard time breathing, increased eosinophils and basophils
• HIV: decreased lymphocytes