Osmoregulation and Osmotic Balance

• Osmoconformers match their internal osmolarity to their environment, while osmoregulators maintain a constant internal osmolarity regardless of their surroundings.
  • Example of osmoconformer: Marine invertebrates.
  • Example of osmoregulator: Freshwater fish.

Osmotic Challenges and Adaptations

• Freshwater animals face water influx and solute loss, countered by excreting large amounts of dilute urine and actively transporting ions in through the gills.
• Marine animals face water loss and solute gain, addressed by drinking seawater, excreting excess salts through gills or salt glands, and producing small amounts of concentrated urine.
• Terrestrial animals face water loss, combatted by adaptations like waterproof skin, efficient kidneys, and behavioral modifications like nocturnal activity.

Nitrogenous Waste

• Ammonia is highly toxic and very soluble, excreted by aquatic animals.
• Urea is less toxic and soluble, excreted by mammals, amphibians, and sharks.
• Uric acid is non-toxic and insoluble, excreted by birds, reptiles, and insects.

Osmoregulatory Organs

• Flatworms use protonephridia with flame bulbs for filtration, releasing dilute urine.
• Earthworms utilize metanephridia, where filtration, reabsorption, and excretion occur along the nephridial tubule.
• Insects have Malpighian tubules that secrete waste into the gut; water and ions are reabsorbed in the hindgut.

Loop of Henle Significance

• The loop of Henle is essential for producing concentrated urine in mammalian and avian kidneys, allowing for water conservation in terrestrial environments.

Mammalian Kidney Components

• Filtration occurs in the glomerulus, where water and small solutes are forced into Bowman's capsule.
• Reabsorption happens in the proximal tubule, loop of Henle, and distal tubule, reclaiming water, ions, and nutrients.
• Secretion involves the transport of toxins and excess ions from the blood into the nephron.
• Excretion is the elimination of urine from the collecting duct.

Mammalian Nephron Diagram

• Artery: Supplies blood to the kidney -Renal artery
• Vein: Drains blood from the kidney - Renal vein
• Capillaries: Involved in reabsorption and secretion (peritubular capillaries and vasa recta).
• Loop of Henle: Concentrates the urine through countercurrent exchange - descending and ascending limb
• Glomerulus: Site of filtration.
• Bowman’s capsule: Receives filtrate from the glomerulus.
• Vasa recta: Blood vessels parallel to the Loop of Henle that help maintain the concentration gradient.
• Distal tubule: Further reabsorption and secretion occur here.
• Proximal tubules: Initial reabsorption of water, ions, and nutrients.
• Collecting duct: Carries urine to the renal pelvis.
• The kidney carries out osmoregulation by filtering blood, reabsorbing essential substances, and secreting waste, regulating water and solute balance.

Homeostatic Kidney Functions and ADH

• ADH (antidiuretic hormone) increases water reabsorption in the collecting ducts, reducing urine volume and conserving water, demonstrating how kidney functions are hormonally coordinated.

Innate Immune System of Vertebrates

• Barrier defenses include skin and mucous membranes.
• Internal defenses include phagocytic cells, natural killer cells, antimicrobial proteins, and inflammatory response.
• Innate defenses are non-adaptive because they respond in the same way to all threats, without prior exposure.

Adaptive Immunity Characteristics

• Adaptive immunity exhibits specificity, diversity, self-tolerance, and memory.
• Brough about by B cells and T cells.

Adaptive Immunity Molecules

• Epitope: Specific part of an antigen that is recognized by an antibody or T-cell receptor and originates from pathogens or foreign substances.
• Antigen: Substance that triggers an immune response and originates from pathogens or foreign substances.
• MHC (Major Histocompatibility Complex): Proteins on cell surfaces that present antigens to T cells and originate from all nucleated cells.
• Antibody: Protein produced by B cells that binds to specific antigens and originates from plasma cells.
• Cytokines: Signaling molecules that mediate and regulate immune responses and originate from immune cells.

Adaptive Immunity Cells

• Macrophages: Originate from monocytes and phagocytose pathogens, presenting antigens to T cells.
• Natural killer cells: Originate from lymphoid stem cells and kill infected or cancerous cells.
• Mast cells: Originate from bone marrow and release histamine during inflammation and allergic reactions.
• B-cells: Originate from bone marrow and differentiate into plasma cells that produce antibodies.
• T-cells: Originate from the thymus and include helper T cells (activate other immune cells) and cytotoxic T cells (kill infected cells).

Immune Cells

• Antigen-presenting cells (APCs) present antigens to T cells, initiating adaptive immune responses.
• B-cells produce antibodies and differentiate into plasma cells.
• Plasma cells secrete large quantities of antibodies.
• Helper T-cells activate B-cells and cytotoxic T-cells by secreting cytokines.
• Cytotoxic T-cells kill infected or cancerous cells by recognizing antigens presented on MHC I molecules.

Humoral vs. Cell-Mediated Immunity

• Humoral immunity involves B-cells and antibodies, targeting pathogens in body fluids.
• Cell-mediated immunity involves T-cells, targeting infected cells.

Passive vs. Active Immunity

• Passive immunity is the transfer of antibodies from one individual to another, providing immediate but temporary protection.
• Active immunity develops after exposure to antigens, resulting in long-lasting protection.
• Immunization works by introducing weakened or inactive pathogens to stimulate active immunity.

Allergies and Autoimmune Diseases

• Allergies are exaggerated immune responses to harmless substances (allergens).
• Autoimmune diseases occur when the immune system attacks the body's own cells.

HIV/AIDS and the Immune System

• HIV infects and destroys helper T-cells, crippling the immune system.
• AIDS (acquired immunodeficiency syndrome) is the final stage of HIV infection, characterized by severe immune deficiency.
• An effective HIV vaccine is difficult to produce because of the virus's high mutation rate and ability to hide within host cells.

Ion Channels, Pumps, and Membrane Potential

• Pumps: Maintain ion gradients across the membrane
• Channels: Facilitate diffusion of ions down their electrochemical gradients
• Membrane potential: established by the unequal distribution of ions across the membrane

Nervous System Subdivisions and Neurons

• Central Nervous System: Brain and spinal cord.
• Peripheral Nervous System: Nerves outside the brain and spinal cord.
• Sensory neurons: Transmit information from sensors to the CNS.
• Motor neurons: Transmit signals from the CNS to muscles or glands.
• Interneurons: Connect sensory and motor neurons within the CNS.

Neuron Structure

• Dendrites receive signals.
• The cell body (soma) contains the nucleus and organelles.
• The axon transmits signals away from the cell body.
• The axon hillock is where the action potential is initiated.
• Synaptic terminals release neurotransmitters.

Neuroglial Cells Functions

• Astrocytes: Support neurons and maintain the blood-brain barrier.
• Oligodendrocytes & Schwann cells: Myelinate axons.
• Microglia: Immune cells of the CNS.
• Ependymal cells: Line brain ventricles and produce cerebrospinal fluid.

Membrane, Resting, and Graded Potentials

• Membrane potential is the voltage difference across a cell membrane.
• Resting potential is the membrane potential of a neuron at rest (typically -70mV), established by Na+/K+ pumps and ion leak channels.
• Graded potentials are small changes in membrane potential that vary in size and occur in response to stimuli.
• Graded potentials vary in magnitude with the strength of the stimulus.

Resting and Graded Potentials on a Membrane

• Resting potential is maintained by Na+/K+ pumps and K+ leak channels.
• Graded potentials are caused by the opening or closing of ion channels in response to a stimulus.

Action Potentials

• Action potentials are rapid, all-or-nothing changes in membrane potential that transmit signals over long distances.
• Graded potentials are variable in magnitude and decay with distance.

Action Potential Phases

• Resting state: Na+ and K+ channels are closed.
• Depolarization: Na+ channels open, and Na+ rushes into the cell, making the inside more positive.
• Rising phase: Further Na+ influx rapidly depolarizes the membrane.
• Falling phase: Na+ channels inactivate, K+ channels open, and K+ flows out of the cell, repolarizing the membrane.
• Undershoot: K+ permeability is higher than at rest, causing a brief hyperpolarization.

Action Potential Propagation

• Action potentials are propagated along axons by local currents that depolarize adjacent regions of the membrane.
• Myelination speeds up propagation through saltatory conduction.
• Action potentials are unidirectional because of the refractory period following depolarization.
• Maintained without loss of signal

Electrical vs. Chemical Synapses

• Electrical synapses: ions flow directly between cells through gap junctions.
• Chemical synapses: neurotransmitters released from one neuron bind to receptors on another neuron.

Neurotransmitter Transmission

• Acetylcholine is released into the synaptic cleft.
• It binds to receptors on the postsynaptic membrane, causing ion channels to open.
• Acetylcholine is then broken down by enzymes or reabsorbed by the presynaptic neuron.

Excitatory vs. Inhibitory Postsynaptic Potentials

• Excitatory postsynaptic potentials (EPSPs) depolarize the membrane, making it more likely to fire an action potential.
• Inhibitory postsynaptic potentials (IPSPs) hyperpolarize the membrane, making it less likely to fire an action potential.

Spatial and Temporal Summation

• Spatial summation occurs when multiple presynaptic neurons release neurotransmitters simultaneously at different locations on the postsynaptic neuron.
• Temporal summation occurs when a single presynaptic neuron releases neurotransmitters in rapid succession.

Nicotine Effects on the Nervous System

• Nicotine mimics acetylcholine, binding to acetylcholine receptors and causing increased neuronal activity.

Animal Brain Organization

• The animal brain organization has become more complex in vertebrates over time, with increased specialization of brain regions.

Human Cerebrum

• Frontal lobe: Involved in motor control, decision-making, and planning.
• Parietal lobe: Processes sensory information.
• Temporal lobe: Involved in auditory processing, memory, and language.
• Occipital lobe: Processes visual information.

Short-Term vs. Long-Term Memory

• Short-term memory: Temporary storage of information.
• Long-term memory: Permanent storage of information.
• Long-term potentiation (LTP): Possible mechanism of long-term memory, involving the strengthening of synaptic connections.

Reflex Arc

• Sensory receptor detects a stimulus.
• Sensory neuron transmits the signal to the spinal cord.
• Interneuron processes the signal.
• Motor neuron transmits the signal to the effector.
• Effector produces a response.

Peripheral Nervous System Organization

• Motor nervous system: Controls voluntary movements through the use of skeletal muscles.
• Autonomic nervous system: Regulates involuntary functions (e.g., heart rate, digestion).

Sympathetic vs. Parasympathetic Divisions

• Sympathetic division: "Fight or flight" response.
• Parasympathetic division: "Rest and digest" response.

Sensory Receptors

• Exteroceptors: Detect external stimuli.
• Interoceptors: Detect internal stimuli.
• Mechanoreceptors: Respond to mechanical forces.
• Chemoreceptors: Respond to chemicals.
• Electromagnetic receptors: Respond to light, electricity, and magnetism.

Sensory Information Transmission

• Sensory neurons transduce stimuli into electrical signals.
• Gated ion channels open or close in response to stimuli, changing the membrane potential.
• If the receptor potential reaches threshold, an action potential is generated.

Sensory Receptor Categories

• Nociceptors: Pain receptors.
• Thermoreceptors: Temperature receptors.
• Proprioceptors: Detect body position and movement.
• Baroreceptors: Detect pressure changes.

Sound Detection in Terrestrial Vertebrates

• Sound waves cause the tympanic membrane (eardrum) to vibrate.
• Vibrations are transmitted through the ossicles to the oval window.
• Pressure waves in the cochlea cause hair cells to bend, generating action potentials.
• Different frequencies stimulate different regions of the basilar membrane.

Hearing in Aquatic vs. Terrestrial Animals

• Aquatic animals: Can detect sound through vibrations in the water and lateral line systems.
• Terrestrial animals: Use ears to detect airborne sound waves.

Body Position and Movement Detection

• Terrestrial animals: Rely on proprioceptors in muscles and joints, and the vestibular system in the inner ear.
• Aquatic animals: Use lateral line systems to detect water currents and vibrations.

Taste Buds

• Taste buds contain taste receptor cells that detect different tastes (sweet, sour, salty, bitter, umami).
• Taste molecules bind to receptors, triggering a signal transduction pathway that leads to action potentials.

Olfactory Neurons

• Olfactory neurons in the nasal cavity detect odor molecules.
• Odor molecules bind to receptors, triggering a signal transduction pathway that leads to action potentials.

Vertebrate vs. Invertebrate Eyes

• Vertebrate eyes: Single-lens eye with a retina.
• Invertebrate eyes: Compound eyes (insects) or single-lens eyes (squid).
• Vertebrate eyes focus by changing the shape of the lens.

Vertebrate Retina

• Photoreceptors (rods and cones): Detect light.
• Rods: Sensitive to dim light.
• Cones: Detect color.
• Bipolar cells: Transmit signals from photoreceptors to ganglion cells.
• Ganglion cells: Transmit signals to the brain via the optic nerve.
• Photons activate rhodopsin, a light-sensitive pigment in rods, triggering a signal transduction pathway that leads to a change in membrane potential.

Hydrostatic Skeletons, Exoskeletons, and Endoskeletons

• Hydrostatic skeletons: Fluid-filled cavities surrounded by muscles (e.g., earthworms).
  • Animals with hydrostatic skeletons move by contracting muscles to change the shape of the fluid-filled cavity.
• Exoskeletons: Hard external coverings (e.g., insects).
• Endoskeletons: Internal skeletons (e.g., vertebrates).

Sliding Filament Mechanism

• Myosin filaments bind to actin filaments, forming cross-bridges.
• Myosin heads pull the actin filaments towards the center of the sarcomere, shortening the muscle fiber.

Calcium's Role in Muscle Contraction

• Calcium ions bind to troponin, causing it to shift tropomyosin away from the myosin-binding sites on actin.
• This allows myosin to bind to actin and initiate muscle contraction.

Motor Units

• Motor units: A motor neuron and all the muscle fibers it innervates.
• Precise coordinated movement is produced by activating different motor units.

Tetanus vs. Twitches

• Twitches: Single muscle fiber contractions
• Tetanus: A sustained muscle contraction caused by high-frequency stimulation.

Slow-Twitch vs. Fast-Twitch Muscle Fibers

• Slow-twitch fibers: Contract slowly but have high endurance (fatigue resistant).
• Fast-twitch fibers: Contract rapidly but fatigue quickly.