Physiology Exam 2: Endocrine and Nervous System Study Guide

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Long Distance Signaling: Endocrine and Nervous Systems

Overview of Signaling Types

Long-distance signaling in the body is primarily mediated by the endocrine and nervous systems. These systems coordinate physiological processes through chemical messengers and electrical signals.

Speed and Duration: Nervous system signals are rapid and short-lived; endocrine signals are slower but longer-lasting.
Voluntary vs. Involuntary Control: Nervous system can be voluntary (somatic) or involuntary (autonomic); endocrine control is generally involuntary.
Hormones vs. Neurotransmitters: Hormones are secreted into the bloodstream and act on distant targets; neurotransmitters are released at synapses and act locally.
Location of Receptors: Hormone receptors may be on the cell surface or inside the cell; neurotransmitter receptors are typically on the postsynaptic membrane.

Types of Chemical Signaling

Autocrine: Signals act on the same cell that secreted them.
Paracrine: Signals act on nearby cells.
Endocrine: Signals (hormones) travel through the bloodstream to distant targets.
Exocrine: Secretions released onto epithelial surfaces (not typically involved in signaling).

Endocrine System

Glands, Hormones, and Functions

The endocrine system consists of glands that secrete hormones to regulate various physiological processes.

Gland Locations: Hypothalamus, pituitary, pineal, thyroid, parathyroid, adrenal, pancreas, gonads.
Hormone Functions: Regulation of metabolism, growth, reproduction, stress response, and homeostasis.
Hormone Targets: Cells with specific receptors for the hormone.
Chemical Properties: Hormones can be amino acid-based (peptides/proteins) or steroids (lipid-soluble).
Regulation: Feedback mechanisms (negative and positive), tropic hormones, neural and humoral stimuli.
Imbalances: Too much (hypersecretion) or too little (hyposecretion) can cause disease.

Hormones: Chemical Properties

Amino Acid-Based Hormones: Include peptides, proteins, and amines; generally water-soluble and act on cell surface receptors.
Steroid Hormones: Derived from cholesterol; lipid-soluble, act on intracellular receptors. Six major steroid hormones include cortisol, aldosterone, estrogen, progesterone, testosterone, and androgens.
Transport: Water-soluble hormones travel freely in blood; lipid-soluble hormones require carrier proteins.
Receptor Location: Surface (G-protein coupled) for peptides; cytosolic or nuclear for steroids.
Removal: Hormones are removed by metabolism, excretion, or enzymatic breakdown.

Control of Hormone Release

Humoral: Changes in blood levels of ions/nutrients trigger hormone release.
Neural: Nerve fibers stimulate hormone release.
Hormonal (Tropic): Hormones stimulate other glands to release hormones.
Cell Sensitivity: A cell must have the appropriate receptor to respond to a hormone.
Pathology: Primary (problem in the gland itself) vs. Secondary (problem in regulatory input).

Hypothalamus and Pituitary Gland

Hypothalamic Hormones: GHRH, GHIH, TRH, CRH, GnRH, PIH (dopamine).
Function: Regulate anterior pituitary hormone secretion via the hypophyseal portal system.
Anterior Pituitary Hormones: FSH, LH, ACTH, TSH, PRL, GH.
Posterior Pituitary Hormones: Oxytocin, Antidiuretic hormone (ADH/vasopressin); produced in hypothalamus, released from posterior pituitary.

Anterior Pituitary Hormones

FSH & LH: Regulate gonadal function (ovaries/testes), feedback via sex steroids.
ACTH: Stimulates adrenal cortex; imbalances cause Cushing's or Addison's disease.
TSH: Stimulates thyroid hormone production; regulated by TRH and negative feedback.
PRL: Stimulates milk production; inhibits GnRH.
GH: Stimulates growth, metabolism; acts via IGF-1; imbalances cause gigantism, acromegaly, dwarfism.

Posterior Pituitary Hormones

Oxytocin: Stimulates uterine contractions, milk ejection; positive feedback.
ADH: Regulates water reabsorption in kidneys and vasoconstriction; imbalances cause diabetes insipidus.

Pineal Gland

Melatonin: Regulates circadian rhythms; secretion regulated by light exposure.

Thyroid and Parathyroid Glands

Thyroid Hormones (T3, T4): Regulate metabolism; synthesized from iodine; transported in blood bound to proteins; act on nuclear receptors.
Regulation: TRH (hypothalamus) → TSH (pituitary) → T3/T4 (thyroid); negative feedback.
Imbalances: Iodine deficiency (hypothyroidism, goiter), Graves' disease (hyperthyroidism).
Calcitonin: Lowers blood calcium; used to treat hypercalcemia.
Parathyroid Hormone (PTH): Raises blood calcium; imbalances affect neuromuscular function.

Adrenal Gland

Cortex: Produces corticosteroids.
Mineralocorticoids (Aldosterone): Regulate sodium and potassium balance.
Glucocorticoids (Cortisol): Regulate metabolism, stress response; excess causes Cushing's, deficiency causes Addison's.
Gonadocorticoids (Androgens): Contribute to secondary sex characteristics.
Medulla: Produces epinephrine and norepinephrine; mediate fight-or-flight response.

Pancreas

Acinar Cells: Exocrine function (digestive enzymes).
Alpha Cells: Secrete glucagon (raises blood glucose).
Beta Cells: Secrete insulin (lowers blood glucose).
Glucose Homeostasis: Involves glycogenolysis, gluconeogenesis, glycogen/fat synthesis.
Insulin Secretion: Triggered by increased blood glucose, ATP/ADP ratio, Ca2+ influx.
Diabetes Mellitus: Type I (autoimmune, insulin deficiency), Type II (insulin resistance); symptoms include hyperglycemia, polyuria, glucose in urine.

Nerve Cell Function

Membrane Potential

Neurons maintain a voltage difference across their membrane, essential for signal transmission.

Nernst Equation: Calculates equilibrium potential for a single ion:
Goldman-Hodgkin-Katz Equation: Calculates membrane potential considering multiple ions:
Resting Membrane Potential: Primarily determined by K+ conductance; Na+/K+ pump maintains gradients.

Ion Conductance and Transport

Simple Diffusion: Movement down concentration gradient.
Facilitated Diffusion: Via channels or carriers.
Primary Active Transport: Direct use of ATP (e.g., Na+/K+ pump).
Secondary Active Transport: Uses gradient established by primary transport.

Neuronal Histology

Neuron Types: Multipolar, bipolar, unipolar.
Glial Cells: CNS (astrocytes, microglia, oligodendrocytes, ependymal cells); PNS (Schwann cells, satellite cells).
Myelination: Increases conduction velocity; nodes of Ranvier concentrate voltage-gated channels.

Nervous System Functions

Sensory Input: Detection of stimuli by sensory receptors.
Integration: Processing of sensory input in CNS.
Motor Output: Activation of muscles or glands.
Sensory Receptors: Mechanoreceptors, proprioceptors, photoreceptors, thermoreceptors, chemoreceptors, nociceptors.
Somatic vs. Autonomic: Somatic controls voluntary muscles; autonomic controls involuntary functions (sympathetic and parasympathetic branches).

Neurotransmitters and Receptors

Receptor Location: Postsynaptic membrane; can be ionotropic (ligand-gated ion channels) or metabotropic (G-protein coupled).
Acetylcholine: Nicotinic (ionotropic, skeletal muscle), muscarinic (metabotropic, cardiac/smooth muscle, glands).
Catecholamines: Dopamine, epinephrine, norepinephrine.
Amino Acid Neurotransmitters: Glutamate (excitatory), GABA, glycine (inhibitory).
Other: Serotonin, ATP.

Graded Potentials and Action Potentials

Graded Potentials: Local changes in membrane potential; can be depolarizing (EPSP) or hyperpolarizing (IPSP); summate temporally and spatially.
Action Potentials: All-or-none, propagated along axon; involve voltage-gated Na+ and K+ channels.
Phases: Resting, threshold, depolarization, repolarization, hyperpolarization.
Refractory Periods: Absolute (no AP possible), relative (AP possible with strong stimulus).
Recovery: Na+/K+ pump restores gradients.
Disorders: Hyperkalemia, hypernatremia, hyponatremia affect excitability.

Synaptic Transmission

Synapse: Junction between neurons; neurotransmitter release and binding.
Neurotransmitter Removal: Reuptake, enzymatic degradation, diffusion.
Toxins: Botulinum and tetanus toxins disrupt synaptic transmission.

Conduction Velocity

Axon Diameter: Larger diameter increases speed.
Myelination: Increases speed; demyelination (e.g., multiple sclerosis) slows conduction.

Sensory Physiology: Vision, Hearing, Balance, Smell, and Taste

Vision

Eye Structure: Sclera, cornea, choroid, ciliary body, aqueous humor, iris, retina, photoreceptors, bipolar cells, ganglion cells.
Light Focusing: Cornea and lens refract light; lens shape adjusted by ciliary muscles.
Photoreceptors: Rods (low light, no color), cones (color, high acuity).
Phototransduction: Light activates rhodopsin, leading to changes in cGMP and ion channel activity; results in hyperpolarization in light.
Adaptation: Light and dark adaptation adjust sensitivity.
Clinical Tests: Snellen's test (visual acuity), ophthalmoscope (retinal exam).

Hearing and Balance

Ear Structure: External, middle, internal ear; cochlea (hearing), vestibular apparatus (balance).
Cochlea: Scala vestibuli, scala tympani, cochlear duct, basilar membrane, organ of Corti.
Sound Transmission: Vibration of oval window transmits sound; basilar membrane movement activates hair cells.
Frequency Coding: Different regions of basilar membrane respond to different frequencies.
Clinical Tests: Otoscope (ear exam), Weber's and Rinne's tests (hearing loss type).
Balance: Saccule, utricle (linear acceleration), semicircular canals (rotational movement); motion sickness from conflicting signals.

Smell (Olfaction)

Olfactory Epithelium: Contains diverse G-protein coupled receptors for odorants.
Signal Transduction: Odorant binding leads to depolarization and action potential generation.

Taste (Gustation)

Taste Receptors: Five basic tastes: salt, sour, sweet, bitter, umami.
Activation: Different mechanisms for each taste; all lead to depolarization of taste cells.

Hormone	Source	Main Function	Receptor Location
Insulin	Pancreas (beta cells)	Lowers blood glucose	Cell surface
Glucagon	Pancreas (alpha cells)	Raises blood glucose	Cell surface
Cortisol	Adrenal cortex	Stress response, metabolism	Intracellular
Thyroxine (T4)	Thyroid	Regulates metabolism	Intracellular
ADH	Posterior pituitary	Water reabsorption	Kidney, blood vessels
FSH/LH	Anterior pituitary	Gonadal function	Ovaries/testes

Example: In diabetes mellitus, insufficient insulin (Type I) or insulin resistance (Type II) leads to elevated blood glucose, increased urine output (polyuria), and glucose in urine (glycosuria).

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