Integ Physiol Comm

What is the structural organization of the Peripheral Nervous System (PNS) efferent division?

The efferent division is split into the Somatic Nervous System (innervates skeletal muscle via a single neuron) and the Autonomic Nervous System (innervates cardiac muscle, smooth muscle, and glands via a two-neuron chain).

What is the basic two-neuron efferent pathway of the Autonomic Nervous System?

It consists of a Preganglionic Neuron with its cell body in the CNS brainstem or spinal cord, which synapses in an autonomic ganglion onto a Postganglionic Neuron that innervates the effector organ.

What was the key significance of Otto Loewi's 1936 Nobel Prize-winning frog heart experiment?

It proved chemical neurotransmission by showing that stimulating the vagus nerve of a donor heart released a soluble substance ('Vagusstoff', later identified as acetylcholine) that slowed a second perfused heart.

What neurotransmitter and receptor type are used at ALL autonomic ganglia (both sympathetic and parasympathetic)?

Acetylcholine (ACh) acting on Nicotinic (nAChR) receptors.

What are the neurotransmitters and receptor types at parasympathetic postganglionic neuroeffector junctions?

Acetylcholine (ACh) acting on Muscarinic (mAChR) receptors.

What are the neurotransmitters and receptor types at most sympathetic postganglionic neuroeffector junctions?

Noradrenaline / Norepinephrine (NA/NE) acting on alpha (α1, α2) or beta (β1, β2, β3) adrenergic receptors.

What are two major anatomical exceptions to standard sympathetic postganglionic noradrenergic transmission?

1. Sweat glands (postganglionic sympathetic fibers release ACh onto Muscarinic receptors). 2. Adrenal Medulla (preganglionic fibers release ACh directly onto chromaffin cells, which secrete Epinephrine/Norepinephrine into the blood).

What are the central anatomical sites of origin for the Sympathetic vs. Parasympathetic divisions?

Sympathetic: Thoracolumbar region of the spinal cord (T1-L2). Parasympathetic: Craniosacral regions (Brainstem cranial nerves III, VII, IX, X and Sacral spinal cord S2-S4).

How do sympathetic and parasympathetic ganglion locations and axon lengths compare?

Sympathetic: Ganglia lie close to the spinal cord (paravertebral/prevertebral); short preganglionic, long postganglionic fibers. Parasympathetic: Ganglia lie near or within the target organ; long preganglionic, short postganglionic fibers.

What are the dual innervation effects of Sympathetic vs. Parasympathetic stimulation on the Eye?

Sympathetic: Contracts pupillary dilator muscle (radial muscle) via α1 receptors causing mydriasis (dilation). Parasympathetic: Contracts pupillary sphincter muscle via M3 receptors causing miosis (constriction).

What are the dual innervation effects on the Heart rate and conduction?

Sympathetic: Increases heart rate and force of contraction via β1 receptors. Parasympathetic: Decreases heart rate and slowing of AV conduction via M2 receptors.

How do the Autonomic divisions control Blood Vessels and Vascular Tone?

Vascular tone is primarily regulated by the Sympathetic division via α1 receptors (causing vasoconstriction) and β2 receptors (causing vasodilation in skeletal muscle). Parasympathetic innervation to most systemic blood vessels is minimal or absent.

What is the role of co-transmitters in autonomic neurotransmission (e.g., Neuropeptide Y)?

Co-transmitters like Neuropeptide Y (NPY) are co-released with primary transmitters (like NA) at higher stimulation frequencies to reinforce, prolong, or modulate the postsynaptic response.

What is the difference between Homotropic and Heterotropic presynaptic interactions?

Homotropic: The neurotransmitter binds to presynaptic autoreceptors on its own terminal to inhibit further release (e.g., NA on presynaptic α2 receptors). Heterotropic: A neurotransmitter binds to heteroreceptors on a different terminal to inhibit another transmitter's release (e.g., ACh inhibiting NA release).

What are the steps involved in a Visceral Reflex Arc?

1. Sensory receptor in viscera detects stimulus -> 2. Visceral afferent (sensory) fiber transmits signal to CNS -> 3. Integration center in spinal cord or brainstem -> 4. Efferent two-neuron autonomic pathway -> 5. Visceral effector response.

How does the Baroreceptor Reflex compensate for a sudden drop in blood pressure?

Decreased blood pressure reduces stretch on carotid sinus/aortic arch baroreceptors -> decreased sensory afferent firing to CNS -> reflex INCREASE in sympathetic outflow (increases HR, contractility, vasoconstriction) and DECREASE in parasympathetic outflow -> restoration of normal BP.

What is the Enteric Nervous System (ENS) and how is it integrated with the ANS?

The ENS is an intrinsic, semi-independent neuronal network within the gastrointestinal tract wall (myenteric and submucosal plexuses) that regulates motility and secretion. It functions autonomously but is modulated by sympathetic and parasympathetic inputs.

What are the four main normal characteristics of cell proliferation in multicellular animals?

1. Growth factor dependence. 2. Anchorage dependence (via integrins and ECM). 3. Contact inhibition of proliferation. 4. Limited proliferation capacity (Hayflick limit).

What is the Hayflick Limit?

The inherent built-in limit to somatic cell proliferation, where normal cells divide a finite number of times (approx. 50–70 divisions in humans) before entering a permanent non-dividing state called replicative senescence.

What are the seven protein classes that participate in controlling normal cell growth?

1. Growth factors (I). 2. Growth factor receptors (II). 3. Signal-transduction proteins (III). 4. Transcription factors (IV). 5. Pro- or anti-apoptotic proteins (V). 6. Cell-cycle control proteins (VI). 7. DNA repair proteins (VII).

What happens at the Restriction Point during the cell cycle, and when does it occur?

Occurs in late G1 phase; it is the critical point where the cell assesses environmental signals (growth factor availability). Once passed, the cell is committed to DNA replication (S phase) and cell division, independent of further growth factor signals.

What state do cells enter if growth factors are absent during late G1 phase?

They exit the cell cycle and enter a quiescent, non-dividing state known as G0.

What are the primary differences between Benign and Malignant tumors?

Benign tumors remain localized, are encapsulated, and do not invade surrounding tissue or metastasize (e.g., adenoma). Malignant tumors invade adjacent tissues, lack distinct borders, and metastasize via blood/lymphatics (e.g., adenocarcinoma).

What are the three main tissue-based categories of human cancers?

1. Carcinomas (malignancies of epithelial cells, ~90% of cases). 2. Sarcomas (solid tumors of connective tissues like muscle, bone, cartilage). 3. Leukemias/Lymphomas (cancers arising from blood-forming cells and immune system cells, ~8%).

What are the six key hallmark properties of cancer cells?

1. Insensitivity to density-dependent / contact inhibition. 2. Reduced requirement for extracellular growth factors (autocrine stimulation). 3. Reduced cell-cell and cell-matrix adhesion. 4. Secretion of proteases that degrade ECM (enabling invasion/metastasis). 5. Secretion of angiogenic growth factors. 6. Evasion of apoptosis / infinite proliferative lifespan.

How does the incidence of cancer change with age, and why?

Cancer incidence increases exponentially with advancing age because cancer development is a multi-step process requiring the cumulative accumulation of multiple somatic mutations over time.

What is the functional difference between a Proto-oncogene and an Oncogene?

A Proto-oncogene is a normal gene promoting cell growth and proliferation. An Oncogene is a mutated, hyperactive, or overexpressed form of a proto-oncogene that drives excessive, unregulated cell proliferation (gain-of-function mutation).

What is a Tumor-Suppressor Gene?

A gene encoding an anti-proliferation or pro-apoptotic protein that normally acts as a brake on cell division. Inactivation or loss of both alleles (loss-of-function mutation) allows unchecked cancerous growth.

What role does the Myc protein play in response to growth factor stimulation?

Growth factors induce rapid transcription and elevated concentrations of Myc transcription factor, driving the cell to exit G0 and enter S phase to begin proliferation.

What is the function of the p53 protein in normal cells, and why is it called the "guardian of the genome"?

In response to DNA damage or cell stress, p53 levels rise, inducing G1 cell-cycle arrest to allow DNA repair, or triggering apoptosis if repair is impossible.

Why are p53 mutations found in up to 50% of all human cancers?

Inactivation of p53 prevents damaged or mutated cells from undergoing G1 arrest or apoptosis, allowing abnormal cells carrying severe genetic lesions to survive and proliferate rapidly.

What is the concept of Tumor Clonality and Clonal Selection?

Cancers originate from a single mutated founding cell (monoclonal). As the tumor population grows, sequential secondary mutations create genetic variants; natural selection favors clones with higher growth rates, invasiveness, or survival capabilities.

What are the major drawbacks of traditional cancer therapies (surgery, radiation, chemotherapy)?

Surgery cannot eliminate disseminated metastases; radiation damages surrounding normal tissue; standard chemotherapies target all rapidly dividing cells, causing toxicity in gut epithelium and hair follicles (diarrhea, alopecia).

What is the mechanism of action of Alkylating Agents in cancer chemotherapy?

They cause cross-linking and miscoding of DNA strands, leading to strand breakage and inhibition of replication.

What is the mechanism of action of Antimetabolites (e.g., 5-Fluorouracil, Methotrexate)?

They act as structural analogs of purines or pyrimidines to subvert metabolic pathways, directly inhibiting essential DNA synthesis enzymes.

How does 5-Fluorouracil (5-FU) inhibit tumor cell growth?

5-FU converts into fluorodeoxyuridylate, a suicide inhibitor that blocks Thymidylate Synthase, depleting dTMP required for DNA synthesis.

How do Methotrexate and Aminopterin function as anti-cancer drugs?

They act as competitive inhibitors of Dihydrofolate Reductase (DHFR), blocking the synthesis of tetrahydrofolate needed for purine and thymidylate generation.

What is the mechanism of action of Mitotic Inhibitors (e.g., Taxol, Vinca alkaloids)?

They interfere with microtubule dynamics (assembly/disassembly), preventing proper mitotic spindle formation and arresting cells in metaphase.

What is the mechanism of action of Avastin (Bevacizumab)?

It is a monoclonal antibody against Vascular Endothelial Growth Factor (VEGF) that inhibits tumor angiogenesis (new blood vessel formation).

What is the mechanism of action of Erbitux (Cetuximab)?

It is a monoclonal antibody targeting the extracellular domain of the Epidermal Growth Factor Receptor (EGFR), blocking receptor activation and downstream proliferative signaling.

What is the rationale behind using Cyclin-Dependent Kinase (CDK) inhibitors (e.g., Flavopiridol)?

CDK inhibitors block the activity of cyclin-CDK complexes that drive cell cycle progression through G1, S, and G2 checkpoints, restoring cell cycle control.

Why are cancer cells described as being closer in properties to stem cells than mature differentiated cells?

Cancer cells exhibit self-renewal capabilities, loss of terminal differentiation markers, indefinite proliferative capacity, and the ability to survive in undifferentiated states like stem cells.

What are the four primary modes of intercellular signaling in endocrinology?

1. Endocrine (secreted into bloodstream to distant target cells). 2. Paracrine (diffuses through extracellular fluid to local neighboring cells). 3. Neuronal / Neuroendocrine (released from axon terminals into synapses or blood). 4. Contact-dependent / Juxtacrine (requires direct cell-to-cell membrane contact).

What are the four chemical classes of hormones and representative examples of each?

1. Steroids (Cortisol, Aldosterone, Estrogen, Testosterone). 2. Biogenic Amines (Thyroxine, Catecholamines). 3. Proteins & Peptides (Insulin, Oxytocin, Growth Hormone). 4. Eicosanoids (Prostaglandins, Leukotrienes).

How do Group I (Lipophilic) and Group II (Hydrophilic) hormones differ in transport and half-life?

Group I (Steroids/Thyroid): Lipophilic, require carrier proteins in plasma, long half-life (hours-days), intracellular receptors. Group II (Peptides/Catecholamines): Hydrophilic, soluble in plasma, short half-life (minutes), plasma membrane receptors.

What are the key physiological actions of Glucocorticoids (Cortisol) on metabolism?

Stimulates gluconeogenesis in liver, increases blood glucose, facilitates lipolysis in adipose tissue, blocks inflammatory responses, and suppresses the immune system.

What are the precursors and cleavage pathway of Adrenocorticotropic Hormone (ACTH)?

ACTH is synthesized as part of a large precursor polypeptide called Pro-Opiomelanocortin (POMC), which is cleaved in the anterior pituitary to yield ACTH, MSH, Lipotropin, and Endorphins.

What are the anatomical developmental origins of the Anterior vs. Posterior Pituitary Gland?

Anterior Pituitary (Adenohypophysis): Arises from ectodermal tissue in the roof of the mouth (Rathke's pouch). Posterior Pituitary (Neurohypophysis): Derived from embryonic brain tissue outgrowth of the hypothalamus.

How does the Hypothalamus communicate with the Anterior vs. Posterior Pituitary Gland?

Anterior Pituitary: Via the Hypothalamo-Pituitary Portal Venous system (hypophysiotropic releasing/inhibiting hormones). Posterior Pituitary: Via direct neural axons (neurohypophyseal tract) extending into the posterior lobe.

What are the two hormones stored and secreted by the Posterior Pituitary Gland, and their functions?

1. Antidiuretic Hormone (ADH / Vasopressin): Regulates kidney water retention and blood pressure. 2. Oxytocin: Stimulates uterine contractions during birth and milk ejection (let-down) during lactation.

What are the six key anterior pituitary hormones and their corresponding pituitary cell types?

1. Corticotrophs -> ACTH. 2. Thyrotrophs -> TSH. 3. Somatotrophs -> GH. 4. Mammotrophs -> Prolactin. 5. Gonadotrophs -> FSH and LH.

How do Prolactin and Oxytocin differ in their roles during lactation?

Prolactin (stimulated by suckling and decreased dopamine) promotes milk SYNTHESIS in gland cells. Oxytocin promotes milk EJECTION by contracting myoepithelial cells.

What is unique about the hypothalamic regulation of Prolactin compared to other pituitary hormones?

Prolactin secretion is under tonic INHIBITION by hypothalamic Dopamine (also called Prolactin-Inhibiting Hormone / PIH).

How are thyroid hormones (T3 and T4) synthesized within the thyroid follicle?

1. Active transport of Iodide into follicular cells -> 2. Oxidation by Thyroid Peroxidase (TPO) -> 3. Iodination of tyrosine residues on Thyroglobulin (organification) -> 4. Coupling of iodotyrosines (MIT/DIT) to form T3 and T4 -> 5. Endocytosis and proteolytic cleavage to release T3/T4 into blood.

What is the structural difference between Thyroxine (T4) and Triiodothyronine (T3)?

T4 contains 4 iodine atoms and is the primary secreted prohormone; T3 contains 3 iodine atoms and is the physiologically active form at nuclear receptors (T4 deiodinates to T3 in target tissues).

What causes Goiter formation in conditions of iodine deficiency?

Insufficient iodine leads to low circulating T3/T4 -> loss of negative feedback to hypothalamus and pituitary -> elevated TSH levels -> hyperstimulation and hypertrophy/hyperplasia of thyroid follicles (goiter).

What three primary effector organs regulate Calcium Homeostasis, and how?

1. Bone: Reservoirs for calcium deposition and resorption. 2. Kidneys: Renal calcium reabsorption and excretion. 3. GI Tract: Intestinal absorption of dietary calcium (dependent on active Vitamin D).

What are the opposing functions of Parathyroid Hormone (PTH) and Calcitonin in blood calcium regulation?

PTH (from parathyroid glands): Increases blood calcium (activates osteoclasts, increases renal Ca2+ reabsorption, stimulates active Vitamin D formation). Calcitonin (from thyroid C-cells): Lowers blood calcium (inhibits osteoclasts, increases urinary Ca2+ excretion).

How is Active Vitamin D (1,25-(OH)2D3) synthesized, and what is its main function?

Skin synthesis/dietary Vitamin D -> converted to 25-OH D in Liver (via 25-hydroxylase) -> converted to active 1,25-(OH)2D3 in Kidneys (via 1-hydroxylase, stimulated by PTH) -> promotes intestinal absorption of dietary Ca2+ and phosphate.

What is the pathophysiological cause of Parturient Hypocalcemia ("Milk Fever") in dairy cows?

A sudden, dramatic shift of calcium into colostrum/milk at onset of lactation that exceeds acute homeostatic capacity, often compounded by sluggish PTH receptor responsiveness.

What is the definition of Pharmacodynamics (PD) vs. Pharmacokinetics (PK)?

Pharmacokinetics: What the body does to the drug (Absorption, Distribution, Metabolism, Excretion). Pharmacodynamics: What the drug does to the body (relationship between drug concentration and pharmacological effect).

What is the core principle of Paul Ehrlich's Receptor Theory (1909)?

"Corpora non agunt nisi fixata" — A drug will not act unless it is bound to its specific target/receptor.

What is the difference between Agonist Potency (ED50) and Efficacy (Emax)?

Efficacy (Emax): The maximal response achievable by a drug, regardless of dose. Potency (ED50): The concentration/dose required to produce 50% of the maximum achievable effect.

What is the Therapeutic Index (TI) and how is it calculated?

The ratio comparing the dose causing toxicity to the dose causing desired therapeutic effect: TI = TD50 / ED50 (or LD50 / ED50). A high TI indicates a wide safety margin.

What is the concept of "Spare Receptors"?

A phenomenon where maximal biological response (Emax) is elicited at a drug concentration lower than that required to occupy 100% of available receptors (EC50 < Kd).

What is the operational definition of a Full Agonist vs. a Partial Agonist?

Full Agonist: Binds to receptor and induces maximal biological response (high efficacy). Partial Agonist: Binds to same receptor but produces a submaximal response even at 100% receptor saturation.

What is an Inverse Agonist?

A ligand that binds to a constitutively active receptor and shifts the equilibrium toward the inactive state, reducing baseline/spontaneous receptor activity below normal.

What is the shift observed on a dose-response curve in Reversible Competitive Antagonism vs. Irreversible Antagonism?

Reversible Competitive: Parallel rightward shift of dose-response curve without change in Emax (can be overcome by higher agonist concentration). Irreversible: Downward crushing shift of Emax (cannot be overcome by increasing agonist concentration).

What are the four major types of non-receptor/receptor Antagonism?

1. Chemical (direct chemical interaction neutralizing drug). 2. Pharmacokinetic (antagonist alters metabolic degradation or excretion). 3. Physiological (two drugs act on separate systems/receptors producing opposing net effects). 4. Receptor/Pharmacological (competitive or non-competitive site binding).

What is the phenomenon of Receptor Desensitization / Tachyphylaxis?

The progressive loss or decrease in cellular response to a drug following repeated or continuous administration over time.

What are the four primary Receptor Superfamilies (Types 1-4) and their signal transduction timescales?

Type 1: Ligand-gated ion channels (Milliseconds). Type 2: G-protein coupled receptors (Seconds). Type 3: Kinase-linked receptors (Hours). Type 4: Nuclear receptors (Hours/Days).

What are Voltage-Operated Channels (VOC) and how does Tetrodotoxin (TTX) affect them?

VOCs (like NaV1.7) open/close in response to membrane potential changes; Tetrodotoxin (from pufferfish) physically blocks the extracellular pore of voltage-gated Na+ channels, preventing action potential propagation.

What is the mechanism of action of Ziconotide (Prialt) in pain management?

It selective blocks N-type voltage-gated calcium channels (CaV2.2) on primary nociceptors, preventing release of pro-nociceptive neurotransmitters (glutamate, CGRP) in the spinal cord.

What is the structural composition and subunit arrangement of Cys-loop Ligand-Gated Ion Channels (ROC)?

They are pentameric receptor complexes (5 subunits surrounding a central ion pore), such as Nicotinic ACh receptors, GABAA receptors, and 5-HT3 receptors.

What structural motif characterizes all Type 2 G-Protein-Coupled Receptors (GPCRs)?

A single polypeptide chain with seven hydrophobic transmembrane-spanning α-helices ("The Magnificent Seven").

How does heterotrimeric G-protein activation work upon agonist binding to a GPCR?

Agonist binding causes conformational change -> GDP on Gα subunit is exchanged for GTP -> Gα-GTP dissociates from Gβγ -> both Gα and Gβγ modulate effector enzymes/channels.

What are the primary downstream effector pathways for Gs, Gi, and Gq proteins?

Gs: Stimulates Adenylate Cyclase -> increases cAMP -> activates PKA. Gi: Inhibits Adenylate Cyclase -> decreases cAMP. Gq: Activates Phospholipase C (PLC) -> cleaves PIP2 into IP3 (releases Ca2+) and DAG (activates PKC).

How does Cholera Toxin alter G-protein function in intestinal epithelial cells?

It ADP-ribosylates the Gsα subunit, locking it in a permanently active state -> constitutive activation of Adenylate Cyclase -> massive cAMP elevation -> uncontrollable Cl- and water secretion into gut lumen (diarrhea).

What molecular machinery regulates GPCR desensitization and internalization?

GPCR Kinase (GRK) phosphorylates activated receptor -> Arrestin (ARR) binds phosphorylated receptor (blocking G-protein coupling) -> Dynamin/Clathrin-coated pit formation drives receptor endocytosis.

How do Kinase-Linked Receptors (Type 3, e.g., Receptor Tyrosine Kinases) activate intracellular pathways?

Ligand binding induces receptor dimerization -> cross-autophosphorylation of tyrosine residues on cytoplasmic catalytic domains -> recruitment and activation of intracellular signaling proteins.

What is the mechanism of action of Sildenafil (Viagra) on vascular smooth muscle modulation?

Inhibits Phosphodiesterase-5 (PDE5), preventing breakdown of cyclic GMP (cGMP) downstream of Nitric Oxide (NO) release -> sustained cGMP level -> smooth muscle relaxation and vasodilation.

Where are Type 4 Nuclear Receptors located, and how do they alter cell function?

Located in cytoplasm or nucleus; upon lipophilic ligand binding (e.g., Cortisol), receptor-hormone complex homodimerizes, translocates to nucleus, binds DNA Response Elements (GREs), and alters gene transcription.

How does the GABAA receptor act as an allosteric target for Benzodiazepines and Barbiturates?

GABAA is a pentameric ligand-gated Cl- channel. Benzodiazepines and Barbiturates bind to distinct allosteric sites (separate from orthosteric GABA site) to enhance Cl- influx and hyperpolarize the cell.

What is Biased Agonism (Functional Selectivity)?

When different agonists binding to the same receptor stabilize distinct receptor conformations, selectively activating one intracellular pathway (e.g., G-protein) over another (e.g., β-Arrestin).

What is the intracellular cascade following β1-adrenoceptor stimulation in cardiac muscle myocytes?

β1 activation -> Gs protein activation -> Adenylate Cyclase stimulation -> cAMP increase -> PKA activation -> phosphorylation of L-type voltage-operated Ca2+ channels -> increased Ca2+ influx -> increased cardiac rate and force of contraction.

What structural type of neuron represents sensory interneurons vs. motor neurons?

Bipolar/Unipolar neurons typically function as sensory neurons or interneurons; Multipolar neurons typically function as motor neurons or postganglionic autonomic efferents.

What is the principal difference between afferent and efferent neuronal signaling?

Afferent neurons carry sensory input from peripheral tissues toward the CNS; Efferent neurons carry motor/autonomic commands away from the CNS to peripheral tissues.

What are the principal exceptions to noradrenergic postganglionic sympathetic transmission in mammals?

1. Sweat glands (cholinergic via muscarinic receptors). 2. Renal vascular smooth muscle (dopaminergic via D1 receptors). 3. Adrenal medulla (direct cholinergic innervation via nicotinic receptors).

What anatomical structures are innervated by the paravertebral sympathetic chain vs. prevertebral ganglia?

Paravertebral chain ganglia innervate thoracic organs (heart, lungs) and body wall (blood vessels, sweat glands); Prevertebral (midline) ganglia innervate abdominal/pelvic viscera (GI tract, liver, bladder, genitalia).

What is the function of the Nervi Erigentes in parasympathetic outflow?

They are sacral parasympathetic preganglionic fibers (S2-S4) that innervate pelvic ganglia to control lower GI tract, bladder constriction, and genital erection.

What is the physiological role of sympathetic vasomotor tone in blood pressure regulation?

Basal sympathetic tone maintains partial contraction of vascular smooth muscle; increasing sympathetic frequency causes vasoconstriction, while decreasing frequency causes passive vasodilation.

What are the dual autonomic responses controlling bronchial diameter and respiratory secretions?

Sympathetic: Beta-2 (β2) adrenoceptor activation causes bronchodilation. Parasympathetic: Muscarinic (M3) activation causes bronchoconstriction and increases mucus secretion.

What is the physiological effect of sympathetic vs. parasympathetic innervation on gastrointestinal motility and sphincters?

Sympathetic: Relaxes intestinal smooth muscle (inhibits peristalsis) and contracts sphincters. Parasympathetic: Contracts intestinal smooth muscle (increases peristalsis) and relaxes sphincters.

How does the sympathetic system regulate renal blood vessel resistance and renin release?

Renal blood vessels vasoconstrict via α1 adrenoceptors and dilate via D1 dopaminergic receptors; Juxtaglomerular cells release Renin via β1 adrenoceptor activation.

What is the autonomic feedback loop involved in long-term blood pressure control via the kidneys?

Decreased mean arterial pressure reduces renal perfusion -> kidneys release Renin -> angiotensinogen converted to Angiotensin I/II -> stimulates Aldosterone release -> increases renal Na+ and water retention to expand blood volume.

What are IPANs and EPANs in the Enteric Nervous System?

IPANs (Intrinsic Primary Afferent Neurons) mediate local mucosal reflexes within the gut wall; EPANs (Extrinsic Primary Afferent Neurons) transmit visceral sensory signals back to the CNS.

What neurotransmitter mediates inhibitory non-adrenergic non-cholinergic (NANC) neurotransmission in the gut wall?

Nitric Oxide (NO) and VIP (Vasoactive Intestinal Peptide), which cause smooth muscle relaxation.

What are the four phases of the eukaryotic cell cycle and their primary functions?

G1 (cell growth & preparation), S (DNA replication), G2 (post-replication growth & audit), and M (mitosis and cell division).

What is the role of integrins in cell proliferation?

Integrins are transmembrane proteins that anchor cells to the Extracellular Matrix (ECM); integrin binding provides anchorage dependence required for cells to pass cell cycle checkpoints.

What molecular event marks the inactivation of proto-oncogenes to cause malignant conversion?

Gain-of-function mutations (such as point mutations, gene amplifications, or chromosomal translocations) causing constitutive hyperactivity or overexpression.