Biology 151 Lecture Learning Objectives PDF

Fall 2024 - Exam 3 Biology 151 Lecture Learning Objectives Dr. Madison Updated 12/9/24 Fri. Nov. 8 Structure and Function: Homeostasis 1. Know the definition of physiology and the levels of...

Fall 2024 - Exam 3 Biology 151 Lecture Learning Objectives Dr. Madison Updated 12/9/24 Fri. Nov. 8 Structure and Function: Homeostasis 1. Know the definition of physiology and the levels of organization in the body. Physiology: the study of functions of living things; focuses on the underlying mechanisms of body processes; understanding function is crucial to understand dysfunction Closely related to anatomy (structure) because structure and function are inseparable Levels of organization 1. Chemical a. Atoms and molecules of life 2. Cellular a. Basic and specialized functions i. Specialized cell functions: secrete digestive enzymes that break down ingested food (gastric cells); retain and eliminate substances accordingly (kidney cells); produce intracellular movement (muscle cells); generate and transmit electrical impulses that relay information (nerve cells) b. Single-celled or multicellular organisms 3. Tissues a. 4 types 4. Organs a. Consists of two or more types of primary tissues organized to perform particular functions 5. Body systems a. Group of organs that perform related functions b. Elevel systems 6. Organism a. Many complex body processes depend on the interplay among mutliple systems Cephalization: nervous system tissue concentrated at one end Evolved independently several times (convergenet evolution) ○ Forward locomotion ○ Predatory adaptation Evolutionary arms race, between predator and prey to better perceive and respond to environmental cues ○ Eg. springbok video Segmentation: organization of the body into segments 2. Know the four types of tissue in the human body and what each tissue does in general. Tissues are groups of cells with a similar structure and specializaiton ○ Epithelial tissue: exchange materials between the cell and environment ○ Connective tissue: connects, supports, and anchors various body parts ○ Muscle tissue: skeletal, cardiac, and smooth muscle ○ Nervous tissue: initiates and transmits electrical impulses ○ All present in the stomach 3. Understand the concept of homeostasis and how negative feedback helps multicellular organisms maintain homeostasis. Homeostasis: balance cells in a multicellualr organism Cannot live and function without other cells Most are not in direct contact with the surrounding external environment in which an organism lives Life-sustaining exchanges are made through the internal environment—the fluid that surroudnst the cells Negative feedback Opposes an initial change and is widely used to maintain homeostasis ○ A change in a controlled variable triggers a response that drives the variable in the opposite direction of the initial change, thus opposing the change ○ E.g. cold → hypothalamus → muscles (shivering) → heat; high blood pressure/low blood pressure and pancreas Positive feedback Output enhances or amplifies a change so that the controlled variable continues to move in the direction of the initial change ○ Less common than negative feedback, but is important in some instances ○ Less about returning to homeostasis and more about a CHANGE in body status ○ Eg. childbirth Homeostatic disruptions Can lead to illness and death Pathophysiology: abnormal functioning of the body associated with diease When a homeostatic disruption becomes so severe that it is no longer compatible with survival, death results 4. Apply the concept of form and function to predict the function of an organ/tissue/system by considering its form/shape. Neuron organization Alveoli and microvilli increase SA to maximize oxygen exchange, nutrient absorption, respectively Mon. Nov. 11 Nervous System I 1. Know that an animal’s nervous system (NS) allows it to sense and respond to the environment, coordinate movement, and regulate internal functions of the body. Sensory input (PNS, afferent) → integration in CNS → motor output in effector (PNS, efferent) 2. Know where on a neuron it receives information and transmits information. Afferent neurons (sensory neuron) have cell body in axon; remember, APs accumulate before cell body rather than at it (axon hillock) like in interneurons and efferent neurons Interneurons have a lot more dendrites because lots of sensory info Signal transmission: 1. Stimuli received by the dendrites and cell body 2. Synaptic stimuli are summed at the axon hillock, where an AP is triggered if the sum of the arriving signals is high enough 3. APs are conducted to the axon terminal, where they cause the release of neurotransmitters. These bind to receptors on the postsynaptic cell membrane, creating a new signal in the postsynaptic neuron… and triggers APs in the adjacent neurons 3. Understand how the charge difference between the inside and the outside of a neuron due to differences in charged ions determine the neuron's membrane potential. There are ions of all types on both sides of the cell, however: Outside has higher concentration of Na+, Ca++, Cl- ○ More positive on the outside of the cell and resting potential on the inside is negative Inside has higher concentrations of K+ and organic anions - Equilibrium potential “Reversal potential” —when the net movement of ions across membrane is balanced due to  competing electrical and chemical (gradient) forces ○ Na+ = 60mV ○ K+ = -90mV 4. Understand how the membrane potential is maintained at rest and how it changes during an action potential, why, and what proteins and ions are responsible. How is the membrane potential maintained at rest? The Na+-K+ pump moves Na+ ions out out of the cell K+ ions into the cell to maintain a negative resting potential (3 Na+ out, 2 K+ in) K+ channels allow K+ ions to “leak” out of the cell, resulting in a negative resting potential on the inside relative to the outside of the cell Na+ channels exist too! Sodium Potassium Pump-Primary Active Transport ○ 3 Na+ out and 2 K+ in ○ When 3 Na+ from ICF bind to pump, it splits ADP into ATP and phosphate ○ Phosphate binds to pump → phosphorylation causes the pump to change transformation, Na{ sites are exposed to ECF ○ Change in the shape also exposes bidning sites for K+ to ECF ○ When 2 K+ from ECF binds to the pump, it releases the phosphate group → phosphorylation leading to conformation change ○ Two 2+ are released into the ICF, releasing phosphate group; affinity to Na+ increases Action potential 1. Threshold a. Summed input depolarizes the cell membrane at the axon hillock above the threshold potential (~-55mV) 2. Depolarization a. Voltage-gated Na+ channels open and Na+ rapidly enters the cell, causing a positive spike in the membrane potential (positive relative to outside). K+ channels open more slowly, allowing fewer K+ ions to leave the cell (peak = +40mV) 3. Repolarization a. As the voltage rises to +40mV, Na+ channels close and voltage-gated K+ channels open, allowing K+ ions to leave the cell and causing the membrane potential to become more negative 4. Refractory a. An overshoot in the amount of K+ ions that leave the cell causes the cell membrane to be hyperpolarized (-90mV). This results in a refractory period during which the nerve cannot fire another AP b. Gradually the membrane returns to resting, as excess K+ ions are returned to teh cell, assisted by Na+-K+ pumps 5. Describe how neurotransmitters are stored & released. Synaptic transmission: APs opens voltage gated calcium channels→ Ca++ channels are essential for exocytosis (the release of NTs) 1. Synaptic transmission begins with the AP conduction to the axon terminal 2. Depolarization of the axon terminal opens voltage-gated Ca2+ channels on pre-synaptic terminal 3. Vesiclse respond by fusing with the presynaptic membrane, releasing neurotranmssiters into the synaptic cleft 4. NTs bind with receptors on the postsynaptic cell that are ligand-gated ion channels, causing a change in membrane potential 5. After inactivaiton, NTs are re-absorbed into the pre-synaptic terminal and stores in vesicles until the next AP arrives Neurotransmitter release  Ca++ binds to Calmodulin, activating it and starting a signal transduction pathway Calmodulin activates protein kinase II (PK2) PK2 phosphoryaltes syapsin causing actin proteins to release their vesicles Vesicles are “docked” adjacent to the membrane where snare proeins await their release Once liberated, vesicles are fused, snared, and “recycled” to store NTs again 6. Know the role of glial cells and why they are necessary for proper neuron function. Saltatory propagation: Layers of myelin insulate the axon. As a result, action potentials “jump” from node to node, increasing the speed of conduction At nodes of Ranvier, there is a buildup of + charges inside and - charges outside the axon How action potentials move from hillock to terminal The depolariztion of one region of axon stimulates the depolarization of the next region Why doesn’t the AP move backward? ○ Na+ channels become inactivated (repolarizing) Synapses and Neuronal Integration Synapse: junction between neurons ○ Electrical synapses: neurons connected irectly by gap junctions (cardiac muscle) ○ Chemical synapses: chemical messenger (neurotransmitter) transmits information one way across a space separating the two neurons MOST synapses in the human nervous system are chemical synapses Wed. Nov. 13 Nervous System II 1. Neurons can receive and respond to both excitatory and inhibitory signals. Understand the difference between an EPSP and IPSP with respect to the ions involved and the change in membrane potential of the postsynaptic cell. Integrating information Neurons synapse with 100s of other neurons Neurons make only one NT Each dendrite has many different ligand receptors Thus, each neuron can receive unqiue chemical signals, some excitatory and some inhibitory 3 Excitatory Synaptic Inputs (EPSPs): No summation No summation: Multiple EPSPs widely spaced in time do not set off an AP Cancellation: An EPSP and an IPSP may cancel each other out so no AP is set off ○ Eg. glutamate and GABA (IPSP) Temporal summation: Multiple EPSPs arrive quickly at a single synapse and set off an AP Spatial summation: EPSPs at 2 or more different synapses set off an AP 2. Know that the CNS and PNS work together to sense and respond to the environment, coordinate movement, and regulate internal functions of the body. Peripheral nervous system Voluntary = somatic ○ Conscious reactions ○ Sensing and responding to the environment ○ Sight, smell, sound, etc. ○ Motor neurons that excite muscles causing contraction Autonomic ○ Unconscious reactions ○ Regulate internal body functions that maintain homeostasis  Sympathetic Fight or flight… dilates pupils, inhibits salivary gland secretion, accelerates heart, relaxes bronchi in heart (vasodilation) Stimulates adrenal medulla… Parasympathetic Rest and digest…constricts pupil, slows heart, cosntricts bronchi (vasoconstriciton) ○ Dual innervation Sympathetic and parasympathetic NS dually innervate most visceral organs (both branches present) Times of sympathetic dominance → fight or flight response Times of parasympathetic dominance → rest and digest response ○ Eg, cold response, negative feedback and shivering 3. Know the Sympathetic and Parasympathetic control of internal functions within the body and often have antagonistic effects on each other. 4. Understand how simple reflex circuits make fast responses possible and underpin a mouse’s ability (or inability) to escape from a cat. Motor neurons initiate muscle contractions (motor endplate, motor neuron axon, muscle cell → muscle unit) Acetylcholine binds to muscle membrane receptors, causing a depolarization of the muscle cell and contraction Rapid response in reflex circuits A physician strikes the patellar tendon with a reflex hammer A stretch receptor in an extensor msucle responds by sending a signal along the sensory nerve The sensory neuron synapses with a motor neuron in the spinal cord The motor neuron sends an excitatory signal to the same extensor muscle, which responds by contracting An inhibitory internaturon inhibits the contraction of the opposing flexor muscle Fri. Nov. 15 Sensory Systems I 1. Describe the fundamental difference between chemo- mechano- and photoreception and the specialized proteins responsible for receiving the different environmental signals. Receptor physiology: Stimulus: change detectable by the body ○ Exist in various energy forms or modalities Afferent neurons: have sensory receptors at their peripheral endings ○ Respond to stimuli in both the external world and the internal environment ○ Sensory receptors: extra special proteins, in sensory cells, embedded in sensory organs Chemoreceptors → signal opens ion channel → cell depolarized Smell and taste Mechanorecptors → pressure open ion channel → cell is depolarized Hair cells in inner ear Photorecptors → signal CLOSES ion channel → cell is hyperpolarized Stimuli bring about receptor potentials in the sensory receptor → sensory transduction Receptors have differential sensitivities to various stimuli Types of receptors according to their adequate stimulus ○ Photorecptors, mechanorecptors, thermoreceptors, osmoreceptors, chemoreceptors, and nocioreceptors (pain) Information detected by receptors is conveyed via afferent neurons to the CNS, where it is used for various purposes (integrated, receptor adaptation, efferent neuron response) Chemical senses: Smell and taste:  Generate neural signals on binding with particular chemicals in their environment Sensations of smell and taste in association with food intake ○ Influence flow of digestive juices and affect appetite ○ Induces pleasurable or objectionable sensations: seek or avoid (evolutionary) 2. Know the process of sensory transduction in general from detection to signal transmission to the brain. 3. Understand how an action potential conveys information about intensity, location, duration, and enhances edge and border detection. Tactile receptors on the skin Mechanorecpetors, ○ Merkel’s disc, Pacinian corpuscle, ruffuni endings, and Meissner’s corpuscle 4 types providing information about touch, pressure, vibration, and tension HIGH sensitivity (low threshold of activation) Innervated by large heavily myelinated neurons Lateral inhibition Lateral inhibition of sensory receptor cells enhances edge and border detection by reducing excitation of adjacent interneurons Send IPSPs to surrounding neurons just so it can send specific internuron so brain knows where touch is Filterns out surroudning noise AP Firing Rate Physiological Morse Code Strength of signal ○ Low and high firing rate (stronger touch) Source of singal Filter out noise Spatial vs. temporal summation Firing Rate due to continuous or novel stimuli Adaptiation to continuous stimuli reduces the firing rate over time ○ Why you don’t notice clothes on ur skin after a while 4. Draw an example of GPCRs ability to amplify a signal. And know which of our senses rely on them for signal transduction. GPCRs essential for smell and taste/chemoreception Activation of a second messenger pathway via binding of a first messenger to a G protein couple receptor Amplifies signal 5. Describe signal transduction for smell and taste from stimuli detection to nerve transmission. Chemical sense: Smell 1. Olfactory sensory neurons sense odorants that bind to specific receptors on chemosensitve hairs that project into the nares 2. Action potentials produced in response to the binding of odorants to membrane receptors are sent to the olfactory interneurons 3. Interneurons integrate the odorant information received by the olfactory receptors before sending it to the brain Olfaction and gustation Your sense of taste is linked to your sense of smell Oral referral, causes us to perceive what’s happening in the nose as if it’s inside the mouth Trigeminal nerve ○ spicy/hot, carbonation, menthol/cool sensation Chemical sense: Taste Taste receptor cells are located primarily within tongue taste buds ○ Bud consists of about 50 long, spindle shaped taste receptor cells Packaged with supporting cells in an arrangement like slices of an orange ○ Taste discrimination is coded by patterns of activity in various taste bud receptors Salty, sour (not GPCR) Salty: Na+ depolarizes the cell opening voltage gated Ca2+ channels Sour: acitdity; via H+ ion channels to depolarize but also inhibit K+ channels Sweet, bitter, umami (GPCR) Mon. Nov. 18 Sensory Systems II 1. Know which of our senses rely on mechanotransduction, chemotransduction, and phototransduction. Sensory Transd Stimulus Recepto Cell Type Effect on Membrane Potential Cortex of System uction r Type (sensory cell or Brain Type sensory neuron) Pressure Touch, mechan Tactile receptors: Depolarization; membrane Somatosens (touch) mecha pressure, orecept Merkel’s disc (light, potential increases with high ory sustained), Pacinian no vibration, ors corpuscle firing rate due to strength of (parietal) tension (vibrations,deep signal/touch pressure) Ruffini endings (deep Lateral inhibition of sensory pressure), cells by reducing excitation of Meissner’s corpuscle (light, adjacent interneurons fluttering touch) Olfaction odorants/s chemor Olfactory Depolarization; GPCR Primary olfactory cortex chemo mells eceptor receptors in the inferior portion of the temporal lobe (makes sense bc near the nose) Gustation Any salty, chemor 50 Taste sensory Depolarization; GPCR Gustatory cortex; one part chemo sour, sweet, eceptor cells within 1 in anterior bitter, or taste buds insula, one part umami in the frontal operculum in taste the frontal lobe Hearing Sound mechan Hair cells within Depolarization Auditory mecha waves → orecept cochlea cortex no pressure ors Sound vibrations push the basilar waves membrane upward. The hair cells stereocilia bend against the tectorial membrane (upper membrane), triggering the release of NTs. Sight Light Photore Rods and cones Hyperpolarization of rods Visual photo ceptors (different from the rest)... cortex which leads to the depolarization of on-center bipolar cells since no glutamate is released and hyperpolarization of off-center bipolar cells Through lateral inhibition (IPSPs), horizontal cells sharpen an image and amacrine cells adjust motion and brightness 2. Understand how hair cells convey information about gravity, movement, and sound by physically opening ion channels when activated. Sound vibrations push the basilar membrane upward. The hair cells stereocilia bend against the tectorial membrane (upper membrane), triggering the release of NTs. 3. Describe the role of the outer, middle, and inner ear and what forces are being generated in each portion. Pinna: frequency dependent amplification; impedance matching Wavelengths similar to or smaller than the size of the opening = high-frequency detection So an elephant is attuned to lower frequencies because its ear is so big (structure and function) Sound waves (traveling vibrations of air with regions of compression and rarefaction of air molecules) Middle ear: tympanic membrane (eardrum and 3 bones) Amplification: eardrum → 3 bones (30x) Sound vibrations → fluid pressure waves Inner ear: semicricular canals, utricle, oval window for vestibular sense; cochlea for pitch detection Mechanoreception by hair cells of cochlea Hair cell activation  ○ 1. No sound vibrations present. That basilar membrane is immobile ○ 2. Sound vibrations push the basilar membrane upward. The hair cell stereocilia bend agaisnt the tectorial membrane, triggering the release of NTs ○ 3. The downward motion of the basilar membrane relative to the tectorial membrane bends stereocilia in the opposite direction, causing the hair cells to repolarize Vestibular system ○ Motion and gravity ○ stereoilia of hair cells are moved, and this causes depolarization when moving head or moving forward in ultricle 4. Recognize how sound perceived by an ear conveys information about pitch by stimulating different portions of the cochlea and volume by stimulating the hair cells w/in the cochlea more or less intensely. Apex: high pitch, high frequency Base of cochlea: low pitch, low frequency 5. Recall how light activates the retinal, changing opsin’s confirmation and initiating the phototransduction cascade (sensory transduction for vision). Light → retinal changes to all-trans form, activating photopigment rhodopsin from opsin → cascade of events → Na+ in outer segment close → Hyperpolarization of photoreceptors → spreads to synaptic terminal → Closes Ca2+ channels in synaptic terminal → Decreased release of NT → depolarization (+) of on-center bipolar and then ganglion cells → hyperpolarization (-) of off-center bipolar (and subsequently ganglion cells) ○ APs fire in one-center ganglion cells ○ No APs fire in off-center ganglion cells ○ Then, propagation to visual cortex via the optic nerve 6. Describe the phototransduction cascade in general, starting with rods/cones and finishing with action potentials sent to the visual cortex.  Direction of light and direction of visual processing are opposite Cones: color vision; high acuity for color; low sensitivity to light ○ Sharp color vision during the day ○ Each cone type if most effectively activated by a particular wavelength of light in the range of color indicated by its name (red, green, blue) Rods: shades of gray; low acuity for color; high sensitivity to light ○ Indistinct gray vision at night Phototransduction ○ Converts light stimuli into neural signals ○ Rods and cones send “graded potentials” in response to absorbing different wavelengths of light more or less intensely ○ Horizontal cells clarify graded potentials to bipolar cells to sharpen signal 2 types of Bipolar cells (interneurons) Amacrine: motion and brightness Horizontal: sharpen image Lateral inhibition (IPSPs) mediated by bipolar cells “Off” center bipolar cells follow faithfully rod and cone cells (ie. hyperpolarized if rod/cone is hyperpolarized) “On” bipolar cells depolarize when rods/cones are hyperpolarized ○ Ganglion cells behave more like typical neurons; depolarize in response to neurotransmitters and send APs through optic nerve to the brain 7. Know the cellular organization of the retina and each cell's role in phototransduction (sensory transduction for vision). Focusing an image When focusing on close objects, the ciliary muscles contract, making the lens more round and increasing the bending of light rays When focusing on distant objects, the ciliary muscles relax, allowing the lens to flatten and reducing the bending of light rays Wed. Nov. 20 completed on Nov. 22 Sensory Systems III 1. Know how the brain processes and integrates information from multiple sensory systems, to different areas in the brain responsible for each. Forebrain: cerebral cortex, thalamus, hypothalamus Cerebrum: ○ Cerebral cortex: outer layer “grey matter” neuronal soma ○ Inner layer white matter neuronal axons Thalamus relays info to coretx but also regulates consciousness ○ Preliminary processing of sensory input Hypothalamus links NS and endocrine system via the pituitary gland ○ Collection of specific nuclei and associated vibers that lie beneath the thalamus ○ Integrating center for many homeostatic functions (4Fs) Basal nuclei ○ Basal ganglia, several layers of gray matter located deep within the cerebral white matter ○ Important inhibitory role in motor control (inhibiting muscle tone, maintaining purposeful motor activity, suppressing useless or unwanted movement, and monitoring and coordinating slow and sustained contractions) Pituitary gland: endocrine powerhouse ○ Posterior pit ○ Anterior put Pineal gland: ○ Melatonin and circadian rhythm Midbrain: Midbrain (part of brainstem) Hindbrain: Pons (neural pathway from cortex to medulla w reticular formation to regulate degree of activation/sleep of the brain) and medulla oblongata (center for respiration and circulation) (Part of brainstem), cerebellum (integrates motor and sensory information) 2. Understand the two cortices responsible for coordinating a physical response via our muscles. Primary motor cortex (PMC): frontal lobe Basic skeletal muscle movement in response to PSC Primary Somatosensory cortex (PSC): “Human body sensory” —takes in tactile info (vibrations, pain, temp, position); parietal lobe 3. Understand how your brain rewards pleasurable experiences via a complex pathway that reinforces that pathway. Limbic system: amygdala and hippocampus Behavior! Instincts, emotions and motivations Spatial orientation and navigation (hippocampus) Learning and LTM formation (hippocampus) Neurogenesis 4. Know that cognition is the brain's ability to process and integrate complex information, remember and interpret past events, solve problems, reason, and form ideas. 5. Apply your understanding of learning to understand positive feedback. Learning is the acquisition of knowledge as a result of experience ○ Rewards and punishments integral  ○ STM, LTM, working memory ○ STM: transient notifications in preexisting synapse function Eg. amount of NT released ○ LTM: relatively permanent structural or functional changes between existing neurons in the brain E.g. increase in glutamate receptors, strengthening connections between neurons, synthesis of new proteins Long term potentiation Repeated stimulation also induces new dendritic synapses to grow further strengthening the signal connections between the two cells and thereby reinforcing a particular memory Repeated release of NT glutamate stimulates production of new glutamate receptors, increasing strength of signals received by the cell The more we learn the easier it becomes (positive feedback) 6. Understand how sleep and learning are linked. Brain stem and consciousness Consciousness: awareness of one’s existence, thoughts, and surroundings ○ Wakefulness and sleep ○ Different EEG wavelengths associated with different states of consciousness Beta: alert Alpha: light meditation Theta: drowsy Delta: deep sleep Why do we dream or sleep anyways? ○ sleep restores energy ○ Neurons terrible at storing energy (brain uses 20-25% of body’s energy) Stage 1 ○ Betwen being awake and falling asleep, light sleep Stage 2 ○ Onset of sleep, becoming disengaged from surroundings, body temp drops Stage 3 ○ Deepest and most restorative sleep BP drops, breathing slows, muscles relaxed, blood supply to muscles increase Tissue growth and repair occurs Energy is restored REM ○ First occurs about 90 minutes after falling asleep and recurs about every 90 minutes, getting longer later in the night Provides energy to brain and body Restores brain chemistry Solidifes new memories (learning) Synaptic consolidation Dreams occur Mon. Nov. 25: Muscles 1. Know the basic structure of muscles and how they are organized from the sarcomere through the muscle. From largest unit to smallest unit, it goes muscle → muscle bundle → muscle fibers → myofibrils → sarcomeres with actin and myosin  Surrounding the muscle is connective tissue (epimysium and perimysium); other than muscle bundles within muscles, there are also nerves and blood vessels Muscle cells/fibers are grouped together in a bundle which group to form said muscle Muscles are composed of elongated cells called muscle fibers that are embedded in surrounding connective tissue (endomysium) Individual fibers (cells) have many myofibrils with a striated appearance due to the filaments within sarcomeres Sarcomeres: The longitudinal sarcomere is the basic contractile unit Filaments are the molecular basis of contraction ○ Thin, actin filament (with tropomyosin and troponin) ○ Thick, myosin filament ○ 6 actin filaments : 1 myosin filament Bands/striations ○ A-band: myosin and Actin overlap, DARK, contains the H-band in the middle (just myosin), length remains unchanged during contraction ○ I-band: only Actin, LIGHT, cross in the middle = Z-line (protein backbone, dark), length contracts or shortens during muscle contraction 2. Understand how actin and myosin interact via the cross-bridge cycle to generate force and produce movement. Big picture: actin filaments move toward the H Zone, while myosin thick filaments don’t move 1. The myosin head (globular head) binds ATP, leading to detachment from actin 2. The myosin head catalyzes the hydrolysis of ATP, forming ADP and Pi and cocking the myosin head back 3. The myosin head binds actin, forming a cross bridge 4. ADP and Pi are released, producing a POWER STROKE that causes the thin filament to slide relative to the thick filament, causing the sarcomere to shorten (contract) 3. Know how smooth and striated (cardiac & skeletal) muscle types differ and are controlled by different branches of the nervous system. Smooth muscle is controlled by the autonomic peripheral nervous system (involuntary), while striated muscle is controlled by the somatic peripheral nervous system (voluntary). Smooth muscle lacks troponin and tropomyosin, less Sarcoplasmic reticulum, less Ca2+ pumps, and overall slower contraction Smooth muscles contain dense bodies on the actin which allow the contractile unit to contract in unison, with the dense bodies on separate actin strands being pulled when thin filaments slide past thick filaments. It looks  scrunched up. 4. Understand how muscle contraction starts via motor neurons depolarizing muscle cells resulting in calcium release initiating sarcomere contraction via the cross-bridge cycle. Muscle excitation–getting tropomyosin out of the way (a cascade event!) 1. An action potential from a motor neuron leads to release of acetylcholine and depolarization of the muscle cell 2. The depolarization is conducted into the interior of the fiber by the T-tubules 3. Depolarization leads to the release of calcium from the sarcoplasmic reticulum (the highway for Ca2+) 4. Ca2+ binds to troponin (circular molecule) which causes movement of tropomyosin (rope molecule), exposure of myosin-binding sites on actin, and formation of cross-bridges to produce shortening of the muscle. Wed. Nov. 29: Endocrine Systems (Note we started this lecture Wednesday, but will complete it Monday Dec. 2nd) 1. Understand how the endocrine system (ES) works in tandem with the nervous system (NS) to better respond to an animal’s environment. The ES and NS are the main regulatory systems of the body The nervous system swiftly transmits electrical impulses to the skeletal muscles and exocrine glands that it innervates The Endocrine system secretes hormones into the blood for delivery to distant sites of action The NS is “wired” whereas the endocrine system is “wireless” ○ NS: Neurotransmitters released into the synaptic cleft, rapid ○ ES: Hormones released into blood, slow Neuroendocrine communication A neuron synapses onto a neuroendocrine cell (mediator); the AP propagates down the axon and instead of releasing NTs, it releases hormones, which diffuse into the bloodstream, eventually reaching target cells 2. Understand the difference between hydrophilic and hydrophobic hormones based on where their receptors are on/in the cell and the type of response invoked. Hydrophilic Peptide hormones (oxytocin, antidiuretic hormone (ADH)) ○ Oxytocin and ADH are peptide hormones that are 9 amino acids long and share a similar  structure Amine hormones ○ Derived from aromatic amino acids. All four examples are derived from phenylalanine ○ L-dopa, dopamine, norepinephrine, epinephrine By far most abundant Do not cross lipid bilayer Activate signal transduction pathways ○ Cell surface/membrane receptors on target cell necessary for hydrophilic hormones ○ Second messenger pathways change the metabolic state or can affect gene expression of the target cell Responses occur more quickly (within minutes) ○ Eg. fight or flight Effects last for hours Hydrophobic The steroid hormones all share a similar structure and are derived from cholesterol Progesterone & testosterone = sex steroids Cortisol = corticosteroid 2 classes: corticosteriods & sex steroids Cross lipid bilayer (bc like attracts like) Alter gene expression and thus proteins produced (can act as transcription factors) ○ Steroid hormones are hydrophobic and diffuse into the target cell, where they bind a cytoplasmic or nuclear receptor that allows them to act as transcription factors to alter the gene expression of the cell (bind to DNA) Response is slower (hours) Effects last for days/months 3. Know the difference between tropic and direct hormones released by the anterior pituitary. Hypothalamus secretes releasing factors which either go to the anterior pituitary gland or the posterior pituitary gland Anterior pituitary gland has a capillary bed portal system connecting hypothalamus neurosecretory cells to it (releases TSH, FSH, LH, ACTH, GH, prolactin), whereas neurosecretory cells in the hypothalamus directly extend their axons all the way to the posterior pituitary gland, weather they release their hormones into the bloodstream (oxytocin and ADH) Tropic vs. Direct Hormones Tropic targets other endocrine glands, stimulating them to produce and release their own hormones  (ex. F.L.A.T) ○ Follicle Stimulating Hormone (FSH) ○ Luteinizing Hormone (LH) ○ Adrenocorticotropic Hormone (ACTH) ○ Thyroid Stimulating Hormone Direct act directly on non-endocrine target tissues or cells, causing an immediate effect (eg. PEG) ○ Prolactin stimulates lactation ○ Endorphins (made in the pituitary gland but also everywhere) ○ Growth hormone 4. Describe examples of how our ES utilizes negative and positive feedback. Autocrine mediation: autocrine substances feed back to influence the same cells that secreted them (can regulate one's own cell’s function!) Cancer cells, cytokines Paracrine mediation: paracrine cells secrete chemicals that affect nearby/adjacent cells, unlike endocrine cells that affect distant target cells Nitric oxide, histamines We haven’t learned much about this yet… slides say that negative feedback occurs: Kidneys–filter blood Liver–convert to bile Positive feedback = amplification of stress response 5. Describe how your body maintains blood sugar levels homeostatically when they get too high or too low. High blood glucose (right after meal) Pancreas releases insulin Insulin causes body cells to take up glucose and muscle and liver take up glucose and store it as glycogen Leads to a decrease in blood glucose Low blood glucose (several hours after meal) Pancreas releases glucagon Glucagon causes muscle and liver to break down glycogen and release glucose This leads to an increase in blood glucose 6. Know how the sympathetic NS interacts with the ES, amplifying the signal and fully engaging an animal’s fight  or flight response. Still have yet to learn in lecture; here’s what the slides say: HPA & Stress: Sympathetic NS and Endocrine System Amplification Stress → hypothalamus → corticotropin releasing factor (0.1 microgram) → Anterior pituitary → ACTH hormone secreted (1 microgram)) → Adrenal cortex → cortisol (40 microgram) → liver → secretes 5600 micrograms of glycogen !!!! At each step, the hormonal signal is amplified, so that a small amount of corticotropin releasing factor leads to a large effect (in this case, the production of glucose by the liver) This is an example of positive feedback Mon (12/2): Respiration 1. Understand anatomically, where multicellular organisms utilize diffusion over short distances and bulk flow over long distances. Bulk flow: long distances Ventilation: breathing moves air (containing O2) into the lungs and air (containing CO2) out of the lungs Circulation: Oxygen and carbon dioxide are transported by the circulatory system to and from cells Diffusion: short distances Across respiratory surfaces: oxygen diffuses from the lungs into the blood and carbon dioxide diffuses out of the blood into the lungs Between blood and cells: oxygen diffuses from the blood into the cells and carbon dioxide diffuses out of the cells into the blood 2. Know that any organ in the body where gas exchange occurs will maximize surface area and work hard to maintain a gradient to facilitate diffusion. Eg. the alveoli–large SA but take up little space to maximize O2 diffusion into capillaries ○ Hemoglobin carries oxygen in RBCs 3. Describe how differences in partial pressure drive diffusion in/out of alveoli, capillaries, and tissues/cells. High pressure goes to low pressure ○ Eg. when O2 parietal pressure is higher in the alveoli than the capillaries, O2 will go towards the capillaries until an equilibrium is reached ○ Same thing happens with capillaries → cells/tissues Highest PO2 in pulmonary veins, mouth, trachea; lowest O2 in pulmonary arteries 4. Know the structure of Hemoglobin and how it facilitates the loading/unloading of O2 via cooperative binding. Large molecule found in RBCs ○ Globin portion: protein with 4 subunits: 2 alpha and 2 beta polypeptide chains ○ Heme portion: 4 iron containing groups bound to alpha and beta subunits ○ Red when bound to O2 ○ Blue when deoxygenated 5. Understand how Oxygen dissociation curves help illustrate how oxygen is loaded or unloaded and shifts in different environments. Sigmoidal due to cooperative binding of oxygen by hemoglobin. In the middle, small  increases/decrease in PO2 result in large increases/decreases in hemoglobin saturation ○ % hemoglobin saturation refers to the average amount of oxygen carried on each hemoglobin ○ Hemoglobin unloads oxygen as Po2 decreases Effect of PH ○ A decrease in pH (from increased cell activity, exercise), causes a right shift in hemoglobin’s O2 dissociation curve. Hemoglobin then releases more O2 to these active cells ○ At same PO2, percent of O2 saturation decreases ○ Exercise → H+ concentration increases, along with CO2 Myoglobin dissociation curve ○ At any given PO2, myoglobin binds oxygen more readily than hemoglobin. So, hemoglobin delivers oxygen to myoglobin in muscle tissues, when needed most ○ Myoglobin makes sure O2 gets to skeletal muscle by having higher O2 sat at any given PO2 ○ Myoglobin curve shifts left Fetal vs. adult hemoglobin ○ Fetal hemoglobin curve is left shifted relative to maternal, allowing the fetus to take up O2 from the mother’s circulation Terms: Gas exchange, bulk flow vs diffusion, ventilation, circulation, blood (RBC), tidal ventilation, intercostal muscles and diaphragm, trachea, lungs, Bronchi, bronchiole, alveoli, pulmonary capillaries, Hemoglobin vs Myoglobin, Heme group (Fe), 02 dissociation curve, cooperative binding Wed (12/4): Circulation and the Heart 1. Explain how vessels of different sizes facilitate bulk flow and diffusion. Smaller vessels (capillaries) → diffusion ○ Lined with epithelial tissue to prompt exchange of materials ○ Greatest surface area, slowets rate of blood flow Larger vessels (aorta, vena cava) → bulk flow 2. Understand how the differences in the structure of veins and arteries underlie their different functions. Arteries are more oxygenated than veins, travel AWAY from the heart, low volume (10-15%) and high pressure Veins travel towards the heart, high volume (60-70%) and low pressure arteries are thicker and have 2 elastic layers to accommodate the force of blood ○ Veins have valves to prevent back flow since gravity works against them 3. Recognize how pressures facilitate things leaving and returning into capillary beds. Pressure required to override resistance due to narrow capillary radius ○ Resistance to blood flow dependent on: viscosity (constant) Distance traveled (length) Longer the vessel > R Vessel radius, r ○ Smaller radius, greater resistance Rate of flow = P/R ○ The cross-sectional area for the blood to go to increases as you go from aorta → capillaries; this leads to a decrease in the velocity of the flow Vessel area and flow velocity are inversely proportional Arterial end of capillary: Blood pressure (32) - osmotic pressure (22) = net pressure out for interstitial fluid (10 mmHg) ○ Osmotic pressure pulls fluids in, blood pressure pushed fluids out ○ Promotes filtration Venous end of capillary: Blood pressure (15) - osmotic pressure (24) = net pressure in (9 mmHg)  ○ Nutrients, fluids 20 L of fluid and “stuff” exits your capillaries/day and 17 L is returned; what happens to the rest? ○ Goes to the lymphatic system and drains ○ Many lymphs that attach to capillaries ○ Whatever squeezes out between the cells in your capillaries Water, proteins (small), minerals, lymphocytes ○ Vessels: similar in structure to veins ○ Ducts: drain vessels ○ Nodes: collection points filled with immune cells 4. Explain the path of blood from the body, through the heart to the lungs, back to the heart, and out to the body again. Goals: Increase O2 to active tissues Increase O2 uptake in lungs Pathway: 1. Deoxygenated blood enters the right atrium from the inferior and superior vena cava 2. Deoxygenated blood passes thru the right AV valve and enters the right ventricle 3. Deoxygenated blood pumped into the pulmonary arteries through the pulmonary (semilunar) valve 4. Oxygenated blood returns from the lungs to the L atrium 5. Oxygenated blood enters the L ventricle through the left AV valve 6. Oxygenated blood is pumped by the L ventricle through the aortic valve into systemic circulation Systole: a contracting chamber will eject blood (ventricles to arteries thru semilunar valves) The ventricles contract, pumping blood out of the heart Diastole: a relaxed chamber will fill with blood (AV valves open, atria to ventricles) Atria contract, filling ventricles with blood 5. Examine the connectivity of the specialized cardiac muscle cells and how they generate action potentials to synchronously pump blood through the chambers. Heartbeat is coordinated with action potentials via Gap junctions between intercalated discs of cardiac muscle ○ Electrically important gap junctions link the cells of each chamber into a functional syncytium Heartbeat depolarization process 1. The pacemaker (SA node near upper R atrium) generates AP that spreads through both atria. They contract in unison 2. The signals from the pacemaker reach the AV node (top of septum), which activates and fires 3. Two steps: a. The APs are transmitted through a set of modified muscle fibers (Purkinje fibers) b. The depolarization spreads from the modified muscle fibers through the entire ventricle. The ventricles contract. 6. Understand how the nervous and endocrine systems control heart rate as needed and how under different circumstances blood flow to different organs will change. Sympathetic stimulation speeds up heart rate ○ Norepinephrine excites the SA, AV, and purkinje fibers ○ Vasoconstriction, increased unloading of O2 in capillary beds, and HR increases up to 100 bpm (80 bpm = normal) Parasympathetic stimulation slows HR ○ Acetylcholine released via vagus nerve onto the SA and AV nodes ○ Heart rate decreases and vasodilation (down to 60 bpm) Maintaining blood pressure ○ Aortic bodies constantly monitor blood pressure Low blood pressure → blood vessels constrict (vasoconstriction) High blood pressure → blood vessels relax (vasodilation) From rest to stress/exercise ○ Blood Flow to skeletal muscles increases a ton due to vasodialtion Exercise Terms: Artery & arteriole vs vein & venule, capillary, pressure vs resistance, blood pressure vs. osmotic pressure, lymph, vasoconstriction vs vasodilation, pulmonary vs systemic circulation, Every term on the heart diagram (I’m sorry there are so many…), systole vs diastole, SA node, AV node, modified muscle fibers, electrocardiogram (EKG) Fri (12/6): Ingestion, Digestion, & Absorption 1. Know the foregut, midgut, and hindgut’s roles in digestion. Foregut = mouth to stomach MOUTH ○ Chemical digestion of carbs with salivary amylase Saliva: 99.5% water, also electrolytes, mucus, salivary amylase, and lysozyme (antibacterial enzyme); helps with motility, taste, cleansing the mouth, and speaking Increases the surface area for absorption Salivary lipase → lipids ○ Mechanical digestion  Teeth: rips cuts, crushes and grinds good Incisors: cut and tear Canines: tear Premolars/molars: chew and grind Mastication: chewing of food by teeth and mix food with salvia into a soft pulp that is easy to swallow, stimulate taste buds to encourage ingestion of food Tongue: moves the food in your mouth to help you swallow STOMACH Stomach pH ○ Stomach enzymes act at low pH of 1.5-3 Antimicrobial Denatures proteins ○ Cells lining the stomach secrete HCl to maintain low pH (and activate pepsinogen → pepsin) ○ Gastrin, secreted when food arrives, stimulates the production of more HCl and pepsinogen (precursor to pepsin) Stomach digestive enzymes (chemical) ○ Pepsin: breaks fown proteins into amino acids ○ Lipases: break down lipids ○ Notice NO NEW chemical breakdown of carbs in stomach ○ The stomach stores food as well as digests it Midgut = small intestine ○ Where mostly chemical digestion and absorption occurs--using enzymes to break bonds of large molecules (polymers) into small molecules (monomers) ○ 3 regions Duodenum Jejunum Illeum ○ 2 muscle layers Longitudinal and circular muscle to assist in movement of food—innervated by ANS which is why “rest and digest” can occur (parasympathetic) Segmentation: a series of ring like contractions using circular muscle that propels chyme in the small intestine 9-12 cycles per minute 3-5 hours to move food completely through ○ 20 feet of villi and microvilli to help with absorption of nutrients Glucose absorption Na+—glucose cotransporter (symporter): Glucose enters intestinal cells along with Na+ driven by the Na+ concentration difference between the lumen the lumen of the intestine (outside) and the cytoplasm of the cell (inside) Na+ concentration is kept low inside the cell by the action of the Na+–K+ pump Glucose exits the intestinal cell passively by a glucose transport protein and into the blood vessels  Positive feedback in duodenum: ○ Stomach acid in the duodenum stimualtes cells lining the duodenum to release secretin that in turn stimulates the pancreas to release bicarbonate ions to neurtralize the acid ○ Fats in the duodenum stimulate cells lining the duodenum to secrete CCK that in turn stimulatesthe gallbladder to contract and release stored bile that helps break down fats Liver produces the bile Hindgut = large intestine → anus ○ Digestion and absorption processes are mostly complete by the time the chyme reaches the large intestine ○ What’s left is indigestible, insoluble waste, unabsorbed bile, and fluid 95% of bile salts are reabsobred by terminal ileum (small intestine) via the hepatic portal vein 5% of bile salts are lose in feces ○ Colon absorbs water and salt, and propels waste forward for removal 2. Know where and how the three macromolecules break down (both chemically and mechanically) in the foregut and midgut and how they are absorbed into the body. Amino acids: ○ proteins broken down in stomach by pepsin ○ Also in small intestine: Pancreas Exocrine function: Via the pancreatic duct cells Trypsin and chymotrypsin released to digest protein Carbs: ○ Dietary carbs broken down into starch and glycogen in mouth and digestive tract ○ Carbs broke down in small intestine epithelial cells Via amylase secreted by pancreas duct cells Lipids ○ Stomach with lipases ○ Primarily in small intestine, with the help of bile salts released from gallbladder and produced by liver Also lipase from pancreas → small intestine ○ Also in mouth with salivary lipase  Autonomic NS & The movement of food Rythmic muscular contraction (smooth) and relaxation (peristalsis) moves food downward. Peristalsis occurrs throughout the GI tract Food leaving the stomach passes through the pyloric sphincter, a band of muscle at the base of the stomach that opens and closes to regulate the rate at which the stomach empties Chruning of the food in the stomach and small interesting ensures mixing and increases chemical digestion via increasing SA 3. Understand the necessity of a strongly acidic stomach and how protein digestion occurs within the stomach. HCl functions ○ HCl in the gastric juice has 4 main functions (produced by parietal cells) Activates pepsin Pepsinogen → pepsin 1. Pepsinogen and HCl are secreted by chief cells and parietal cells, respectively 2. HCl converts pepsinogen to pepsin 3. Pepsin activates more pepsinogen Breaks down tough, fibrous foods Denatures proteins Kills bacteria and other microorganisms 4. Describe how the stomach creates and maintains an acidic stomach. Gatric Juices ○ The stomach secrets about 2L of gastric juice per day ○ Within the gastric pits, 3 types of exocrine cells are found that contribute to gastric juices Mucus cells: thin, watery mucus Chief cells: pepsinogen, precursor to pepsin, an enzyme that digests proteins Parietal cells: hydrochloric acid (HCl) 5. Describe how the small Intestine works with the pancreas and liver to finish digestion and start/complete absorption. Pancreas and liver The pancreas and liver are both accessory organs to the digestive system Both have ducts that enter the duodenum Secrete necessary digestive products  Not part of digestive tract Have many non-digestive functions Liver Performs many functions but also contributes to digestion by secreting bile ○ Bile salts–fat digestion When bile is not actively being secrteted, it is stored in the gallbladder Pancreas Has acinar cells that secrete pancreatic juice (digestive enzymes) into the duodenum Endocrine: Islets of Langerhans ○ Alpha cells—glucagon ○ Beta cells—insulin Exocrine: ○ Via the pancreatic duct cells Trypsin and chymotrypsin to digest protein Amylase digests carbs Lipase digests fats ○ Alkaline fluid is secreted to neurtralize acidic chyme from the stomach Bicarbonate ions Glycogen is an efficient form of stored glucose: negative feedback loop ○ Insulin released via beta cells of pancreas ○ Glucagon released via alpha cells of pancreas ○ Mnemonic: AgBi (agriculture business) 6. Know that the large intestine retains digesta long enough to absorb water and nutrients before expulsion. ○ Digestion and absorption processes are mostly complete by the time the chyme reaches the large intestine ○ What’s left is indigestible, insoluble waste, unabsorbed bile, and fluid 95% of bile salts are reabsobred by terminal ileum (small intestine) via the hepatic portal vein 5% of bile salts are lose in feces  ○ Colon absorbs water and salt, and propels waste forward for removal Large intestine: “Good Bacteria” ○ Bacteria accumulate in the large instensine because the motility is slow enough ○ 500-1000 species of bacteria estimated in colon, some beneficial functions Prevent pathogenic bacterial growth Breakdown dietary fiber (produces gas) Promote motility Maintain mucosa Synthesize vitamin K Large intestine: Defecation ○ Defecation reflex: rectum wall stretched; internal anal sphincter relaxed Involuntary control ○ Voluntary control of external anal spinchter to release contents 7. Compare and contrast hindgut vs. foregut fermentation strategies. Know where fermentation happens for each and what strategies are employed to maximize energy and nutrient acquisition. Didn’t cover in lecture Mon. Dec. 9 Digestion II (no new learning objectives) Wed. Dec. 11 Osmoregulation 1. Know why renal organs eliminate nitrogenous wastes and regulate water and electrolyte levels. Osmosis: a selectively permeable membrane allows movement of water but not solutes; water moves from region of lower solute concentration to higher solute concentration (so solute concentration decreases); net movement of water stops when osmotic pressure = hydrostatic pressure due to gravity (hydrostatic is the pressure pushing against the walls of the container on the higher solute side) Osmoregulation: water homeostasis Normal cell volume of RBC intracellular fluid = 300 mOsm/L non penetrating solutes ○ 300 mOsm/L non penetrating solutes solution → isotonic solution → no net movement of water; no change in cell volume ○ 200 mOsm/L nonpenetrating solutes solution → hypotonic solution → water diffuses into cells; RBCs swell ○ 400 mOsm/L nonpenetrating solutes solution → hypertonic solution → water diffuses out of the cell → RBC shrinks Osmoregulation in animals  ○ Fluid Intake: water or other fluid; water has fluid! Loss: cellular respiration; sweat/urine ○ Electrolytes (NaCl, other ions) Intake: foods, some drinks Loss: sweat/urination, defecation Why renal organs eliminate nitrogenous wastes Animals exrete three forms of nitrogenous waste from proteins and nucleic acids ○ Ammonia (most aquatic animals) ○ Urea (mammals, amphibians, sharks, etc) ○ Uric acid (birds, insects, many reptiles, land snails) Ammonia is the most toxic but it released easily in water. Uric acid is least toxic, but is energetically costly to produce Kineys osmoregulate and eliminate water soluble waste ○ Primary organs of the urinary system ○ At less than 1% of body weight, they receive 20-25% of total cardiac output ○ Functions Maintain blood volume/blood pressure Maintain fluid and electrolyte composition Water, ions Maitain acid/base balance (pH) Eliminate metabolic wastes, toxic substances, vitamin D activation Hormone production renin-water/salt conservation 2. Understand the role of the Glomerulus, how it filters, and what comes through. General process of filtration Filtration produces a filtrate of the blood Reabsorption removes useful solutes from the filtrate and returns them to the blood Secretion adds solutes to the filtration ○ Metabolic wastes Mammalian Glomerulus and Bowman’s Capsule Blood is filtered under pressure into the extracellular space formed by Bowman’s capsule through a filtration barrier ○ Fenestra = windows/slits that go to filtration slit ○ Podocyte= food; make up external area of glomeruli Blood enters the glomerulus first at the top of the nephron 3. Explain the role of the convoluted tubules, what comes out, and what stays in the filtrate. In the proximal convoluted tubule, microvilli function to increase SA so they can efficiently reabsorb important nutrients; functions to get important nutrients back into bloodstream and water reabsorption Drugs and poisons are actively transported into the tubule HCO3-, H2O, K+ passively transported out of the tubule NaCl, nutrients (glucose, amino acids, ions) are actively transported out of the tubule ○ Glucose/Na+ symporter ○ Ion uniporter This leaves the filtrte with a low salt concentration 4. Analyze the loop of Henle in the nephron and understand how water & NaCl are retained via the countercurrent structure. Loop of Henle Functions Reabsorb water ○ Descending limb (water limb) only permeable to water (water limb) and urea → back into systemic circulation ○ Water cannot be actively pumped out Makes the medulla hypertonic ○ Ascending limb actively pumps salts (Na, K, Cl), creating a concentration gradient Salty limb of the loop is not permeable to water so it actively transports electrolytes into the interstituial fluid ○ Medulla is hypertonic to the filtrate facilitating water reabsorption (goes into the filtrate) 5. Know where urea recycling occurs and why it is necessary. Urea recycling Urea is conserved because it plays a critical role in the kidney’s ability to concentrate urine and conserve water by contributing to the osmotic gradient in the renal meddula ○ To increase water absorption in the medulla (collecting duct) Urea is water-soluble (Hydrophillic and small) Can diffuse across a lipid bilayer…barely Urea transport proteins, facilitated diffusion, upregulated in response to ADH Urea can also cross some aquaporins Descending limb (water limb) IS permeable to to urea Ascending limb (salty limb) is NOT permeable Collecting duct is always permeable, but even more so when ADH is present 6. Know when/how antidiuretic hormone and aquaporins are employed to save water and create concentrated urine. Hormonal control of urine concentration ADH/vasopressin released from the posterior pituitary gland increases the collecting ducts’ permeability to water, allowing water to diffuse out of the filtrate with the gradient created by the loop of henle ○ Basically ADH says “increase water reabsorption to increase hydration!” In the absence of ADH, the collectiving duct is less permeable to water, resulting in dilute urine ○ Such is the case when alcohol is in your blood, leading to dehydration because a lot of water is released as urine and not reambsorbed in the presence of ADH Aquaporins (AQP): When osmosis alone just won’t do Transmembrane protein Impermeable to ion flow…sometimes 13 unique AQPs discovered in humans so far AQ 1, 3, 4, 7 have been found in nephron 3, 4, and 7 allow urea to pass Vasopressin binding activates second messenger pathway nad cAMP increases the luminal membrane permeability to water by inserting new AQP 2 water channels ○ Water exits through either AQP 3 or AQP 4 to the peritubular capillary (blood)