Exam 3 biology- homeostasis and osmolarity

Biology exam 3 based on homeostasis and hormone control

Homeostasis

Stability of the internal environment and mechanisms that maintain it.

Maintains dynamic equilibrium in the body within a tolerable range around a set point.

Homeostasis regulates in the body

Blood glucose/water levels

pH, ion concentration

Core body temperature

Levels of metabolic waste products

Blood osmolarity and pressure

3 components for homeostasis

Sensor – Detects changes (e.g., temperature sensors in the body).

Integrator – Compares sensor input to set point (e.g., hypothalamus).

Effector – Structure/behavior that restores internal conditions (e.g., shivering, sweating).

Thermoregulation in animals

Endotherm, ectotherm, homeotherms, poikilotherms .

Endotherms

Generate body heat through metabolism.

Ectotherms

Rely on environmental heat sources.

Homeotherms

Maintain constant body temperature.

Poikilotherms

Body temperature fluctuates with the environment.

Thermoneutral zone (TNZ)

Range of external temperatures where metabolic rate is minimal.

Metabolic rate increases out of TNZ when

In homeotherms, metabolic rate rises as external temperature drops to generate heat.

In poikilotherms, metabolic rate rises with external temperature, speeding up biochemical processes.

Metabolic rate differences

Higher in homeotherms than poikilotherms, especially in cold environments.

Insects: Some are temporarily homeothermic (e.g., during flight when muscle contractions generate heat).

Cold environment adaptations in Homeotherms

1- Increase metabolic rate

2-insulation

3-evaporative cooling

1-Increase metabolic rate

Shivering: Skeletal muscles contract, using ATP to generate heat.

Nonshivering thermogenesis:

• - Brown adipose tissue (BAT) in mammals.

• - Oxidative phosphorylation is uncoupled from ATP production, producing heat.

2- Insulation

Fur, feathers, and specialized blood flow conserve heat.

3- Evaporative Cooling

Water absorbs heat energy from liquid to gas.

Sweating and panting enhance cooling by evaporation

Examples of thermoregulatory strategies

• African elephants: Allow body temperature to rise during hot parts of the day (some poikilothermic traits).

• Japanese honeybees: Generate heat endothermically when defending hives.

• Dormice: Reduce metabolic rate and body temperature (poikilothermy).

  • Torpor: Temporary body temperature drop.

  • Hibernation: Extended body temperature drop.

2 Control systems in thermoregulation

Positive feedback
Negative feedback

Negative feedback in temperature regulation

1. Sensors: Detect temperature changes.

2. Integrator (Hypothalamus): Compares input to set point (37°C in humans).

3. Effectors:

   • -If body temperature rises:

     • Blood vessels dilate, sweat glands activate, and respiratory centers stimulate panting.

   • - If body temperature drops:

     • Shivering and nonshivering thermogenesis activate to increase heat production.

Positive feedback in temperature regulation

Amplifies deviations from the set point (e.g., nerve impulses, childbirth contractions).

Phenotypic plasticity in animals

Reindeer: Exhibit seasonal metabolic plasticity.

Lower metabolic rate in winter compared to humans.

Regional hypothermia: Allows extremities to be cooler than the core, conserving heat.

Countercurrent heat exchange (thermoregulation)

Arctic foxes: (Maintain foot pad temperature just above freezing) Arteries transfer heat to adjacent veins, maintaining core temperature. (between arteries and veins)

Whales: Heat exchange in tongue vessels minimizes heat loss while feeding.

Hot environment adaptations

Small mammals: Burrow during the day to avoid heat.

Large animals: Tolerate core temperature rise to conserve water (avoid sweating).

Lizards & insects: Seek shade or burrow underground.

Osmoregulation

Maintains water and electrolyte balance during homeostasis

Electrolytes: Dissociate into ions in water (e.g., Na⁺, Cl⁻, K⁺)

Osmotic stress: Abnormal concentration of dissolved substances..

Osmolarity

Total solute concentration (osmoles/L).

• Hyperosmotic: Higher solute concentration.

• Hypoosmotic: Lower solute concentration.

• Isosmotic: Equal solute concentration.

Hyperosmotic

Higer solute concentration

Hypoosmotic

lower solute concentration

Osmoconformers

Maintain internal osmolarity similar to seawater (e.g., sharks).

Osmoregulator freshwater fish

(Hyperosmotic)

• Gain water via osmosis, Lose electrolytes(lose salt) via diffusion.

• Adaptations:

  • Do not drink water.

  • Excrete dilute urine.

  • Actively absorb ions via gills.

Osmoregulator marine fish

(Hypoosmotic)

• Lose water via osmosis, Gain electrolytes(salts) via diffusion.

• Adaptations:

  • Drink large amounts of seawater.

  • Excrete concentrated urine.

  • Actively secrete ions via gills

Nitrogenous waste and water balance

• Ammonia (NH₃): Toxic, requires lots of water for excretion.

  • Used by bony fish & amphibian larvae (diffuses across gills).

• Urea: Less toxic, requires moderate water and energy to synthesize.

  • Used by mammals, amphibians, sharks (excreted via urine).

• Uric Acid: Insoluble, excreted as a paste with minimal water loss.

  • Used by birds, reptiles, insects.

Ammonia nitrogenous waste

• Toxic, requires lots of water for excretion.

  • Used by bony fish & amphibian larvae (diffuses across gills).

Urea nitrogenous waste

• Less toxic, requires moderate water and energy to synthesize.

  • Used by mammals, amphibians, sharks (excreted via urine).

Uric acid nitrogenous waste

• Insoluble, excreted as a paste with minimal water loss.

  • Used by birds, reptiles, insects.

Urinary system function

• Eliminates nitrogenous waste.

• Maintains water and electrolyte balance.

ADH in water retention

Released in response to high blood osmolarity

Regulates water retention in response to increased blood osmolarity or low blood volume.

Increases water reabsorption in collecting ducts, concentrating urine.

Cell communication

Cells communicate to maintain homeostasis by responding to environmental changes.

Communication occurs via neurotransmitters (animals) and hormones (animals and plants).

Hormones

Circulate in low concentrations to relay information to distant cells.

Can be peptides, steroids, or gases.

Function in growth, development, and responses to internal/external stimuli.

Plant hormones

• Growth regulators produced by plant cells.

• Transport mechanisms:

  • Diffuse through cell walls.

  • Move via xylem or phloem sap.

  • Cell-to-cell transport by diffusion or transport proteins.

Signal receptors in plasma membranes detect stimuli.

Signal 4 steps

Stimulus: External factor triggers response.

Sensory Reception: Converts external stimulus into an internal signal.

Signal Transmission: Cell-to-cell signaling occurs throughout the body.

Response: Target cells detect the signal and modify activity accordingly.

Cell signaling

• Organisms and individual cells respond to environmental variables (temperature, light, sound, pH, etc.).

• Detection: Change in tertiary structure of a sensory receptor initiates response.

• Signaling: One cell produces a signal for another cell to receive.

Goal: Elicit a response in the target cell.

Signaling Juxtacrine

• Direct cell to cell contact

• Embryonic development (cell surface proteins regulate gene expression).

Signaling paracrine

• affects nearby cells by diffusion

• inflammatory response

Signaling autocrine

• Affects the same cell that releases the signal.

• immune cell signaling

signaling endocrine

• Hormones transported long distances via bulk flow.

• insulin regulating blood sugar

Ligand

• Chemical signal that binds to a receptor, triggering signal transduction.

• Specificity: Receptors only bind specific ligands.

Without a receptor, a signal cannot be detected.

Ligand receptor placement

• Intracellular receptors: Bind small, nonpolar ligands that diffuse across membranes.

• Membrane receptors: Bind large, polar ligands that cannot cross membranes.

The cytosolic region of membrane receptors initiates signal transduction.

this needs TRANSDUCTION

Membrane receptor- Ion channel

• Ligand binding alters receptor shape to open/close channels.

Example: Acetylcholine binds to skeletal muscle receptors, opening Na+ channels.

Membrane receptor- G protein coupled receptors

• Ligand binds to the extracellular domain, activating a protein inside the cell.

• Heterotrimeric G protein has three subunits (α, β, γ).

Activation of GDP

To GTP exchange on the α-subunit, triggering intracellular signaling.

• Second Messengers:

  • Small, non-protein molecules that amplify signals.

Example: cAMP (cyclic AMP) in epinephrine’s fight-or-flight response

Membrane receptor- Protein kinase receptors

Ligand binding activates protein activity, leading to phosphorylation of proteins.

Example: Insulin receptor, which phosphorylates proteins to regulate glucose uptake.

Signal transduction pathway

• Converts an extracellular signal into an intracellular response.

• Enzyme regulation (e.g., allosteric changes, phosphorylation).

• Short-Term Responses: Ion channel opening or enzyme activation.

• Long-Term Responses: Changes in gene expression.

Amplify signals

by signal transduciton pathway

• A single molecule (e.g., epinephrine) can lead to the release of 10,000 molecules of glucose.

Allows cells to generate large responses from small signals.

Negative feedback

• Reverses a physiological change to return to a set point.

Example: Hypothalamus regulates body temperature.

Positive feedback

• Amplifies a physiological response.

Example: Erythropoietin release in response to low oxygen levels.

Thermoregulation other 2 responses

• Behavioral Responses

  • Example: Lizards bask in the sun to raise body temperature.

• Evaporative Cooling

  • Example: Sweating or panting, though it increases ATP and water loss.

Water movement for osmoregulation

• Osmotic Pressure: Total solute concentration in a solution.

• Water Movement:

  • Moves via osmosis from low to high solute concentration.

Marine bony fish drink seawater to compensate for dehydration.

Osmoconformers

• Body fluid osmolarity matches the environment.

• marine invertebrates (corals and stuff)

• Maintain internal osmolarity similar to seawater (e.g., sharks).

Osmoregulators

• Maintain constant internal osmolarity.

• freshwater and marine bony fish

Special cases

• Salmon migrate between freshwater and saltwater, adjusting osmoregulatory mechanisms accordingly.

• Goldfish in freshwater → Water enters via osmosis, excretes dilute urine rapidly.

Bony fish avoid dehydration by → Drinking seawater & actively excreting ions.