The Ultimate Guide to the Autonomic and Endocrine Systems

Posted on Jun 22, 2024 in Biology

Similarities and Differences Between the Somatic and Autonomic Nervous Systems

Similarities:

  • Both are part of the peripheral nervous system (PNS).
  • Both involve efferent (motor) pathways that control muscles.
  • Both have sensory input to the CNS.

Differences:

Somatic Nervous System

  • Controls voluntary movements.
  • Uses a single neuron pathway (lower motor neuron from CNS to effector).
  • Innervates skeletal muscles.

Autonomic Nervous System

  • Controls involuntary movements and visceral functions.
  • Uses a 2-neuron pathway (preganglionic neuron from CNS to ganglion, postganglionic neuron from ganglion to effector).
  • Innervates smooth and cardiac muscle and glands.

General Structure and Function of Sympathetic and Parasympathetic Divisions

Sympathetic Division

Structure:

Originates from thoracolumbar regions (T1-L2 segments) of the spinal cord.

Function:

Prepares the body for stressful situations (“fight or flight”), increases heart rate, dilates airways, inhibits digestion.

Parasympathetic Division

Structure:

Originates from craniosacral regions (cranial nerves & S2-S4 segments of the spinal cord).

Function:

Promotes “rest and digest” activities, decreases heart rate, constricts airways, stimulates digestion.

Origin of Sympathetic vs. Parasympathetic Nerves

  • Sympathetic Nerves: Originate from thoracolumbar regions (T1-L2 segments) of the spinal cord.
  • Parasympathetic Nerves: Originate from craniosacral regions (brainstem & S2-S4 segments of the spinal cord).

Location of Ganglia in Sympathetic & Parasympathetic Nervous Systems

  • Sympathetic Nervous System: Ganglia are located close to the spinal cord (sympathetic chain ganglia and collateral ganglia such as celiac and superior mesenteric ganglia).
  • Parasympathetic Nervous System: Ganglia are located near or within the target organs (terminal ganglia).

Neurotransmitters & Receptors of Sympathetic & Parasympathetic Nervous Systems

Sympathetic Nervous System:

  • Neurotransmitter: Primarily norepinephrine at postganglionic synapses.
  • Receptors: Adrenergic receptors (alpha and beta).

Parasympathetic Nervous System:

  • Neurotransmitter: Acetylcholine at both pre- and postganglionic synapses.
  • Receptors: Nicotinic receptors at ganglia and muscarinic receptors at target organs.

Nature of Autonomic Tone & its Effects

  • Autonomic Tone: Continuous, baseline level of activity in both sympathetic & parasympathetic divisions.
  • Effects: Maintains physiological functions (heart rate, GI motility) within normal ranges.

Explanation of Dual Innervation

  • Dual Innervation: Most organs receive input from both sympathetic & parasympathetic divisions.
  • Effect: Allows for precise control & balance of organ function based on physiological needs.

Effects of ANS on Selected Body Systems

  • Cardiovascular: Sympathetic activation increases heart rate & contractility; parasympathetic activation decreases heart rate.
  • Respiratory: Sympathetic activation dilates airways; parasympathetic activation constricts airways.
  • Digestive: Sympathetic activation inhibits digestion; parasympathetic activation stimulates digestion.

How Autonomic Reflexes Help Maintain Homeostasis

  • Autonomic Reflexes: Reflex arcs that maintain homeostasis through rapid adjustments in organ functions.
  • Examples: Baroreceptor reflex (regulates BP), pupillary light reflex (controls pupil size in response to light).

Major Types of Autonomic Reflexes

  • Baroreceptor: Regulates blood pressure.
  • Pupillary Light: Controls pupil size in response to light.
  • Gastrocolic: Stimulates motility & secretion in the digestive tract after a meal.

How the CNS Controls the ANS

  • Hypothalamus: Major integration center for autonomic regulation, coordinating responses to internal & external stimuli.
  • Brainstem & Spinal Cord: Control centers for reflex activities & basic autonomic functions.

Definition of Homeostasis & Its Use in Physiology

  • Homeostasis: Maintenance of stable internal conditions despite external changes.
  • Use in Physiology: Ensures optimal conditions for cellular function & survival.

Nature of Negative Feedback Loops & How They Maintain Homeostasis

  • Negative Feedback: Mechanism where deviations from set points are detected & corrected.
  • Maintenance: Acts to stabilize physiological variables (body temperature, blood glucose levels) within narrow ranges.

Nature of Positive Feedback Loops & Their Function in the Body

  • Positive Feedback: Mechanism where a physiological change leads to further amplification of that change.
  • Function: Important in processes that require rapid completion (childbirth, blood clotting).

Explanation of Negative Feedback Inhibition in Regulating Hormone Secretion, Using Insulin as an Example

  • Negative Feedback Inhibition: Mechanism where rising levels of a hormone inhibit its own further release.
  • Insulin Example: High blood glucose stimulates insulin release; insulin promotes glucose uptake by cells, lowering blood glucose levels & inhibiting further insulin secretion.

Comparison & Contrast of Actions of Endocrine System & Nervous System to Control Body Function

  • Endocrine System: Uses hormones released into the bloodstream to regulate physiological processes over longer timescales.
  • Nervous System: Uses electrical signals & neurotransmitters for rapid, short-term control of body functions.

Characteristics of Endocrine Glands and Endocrine Tissues

  • Endocrine Glands: Ductless organs that secrete hormones directly into the bloodstream (pituitary and adrenal glands).
  • Endocrine Tissues: Individual cells or clusters of cells that secrete hormones (pancreatic islets).

3 Mechanisms for Regulation Secretion of Hormones

  • Humoral: Hormone release in response to blood levels of ions or nutrients (parathyroid hormone).
  • Neural: Hormone release in response to neural inputs (adrenal medulla).
  • Hormonal: Hormone release in response to other hormones (hypothalamic-pituitary axis).

3 Structural Categories of Hormones

  • Peptides/Proteins: Chains of amino acids (insulin, growth hormone).
  • Amines: Derived from amino acids (epinephrine, thyroid hormones).
  • Steroids: Derived from cholesterol (cortisol, testosterone).

Comparison Between Lipid-Soluble & Water-Soluble Hormones

  • Lipid Soluble: Can diffuse through cell membranes, bind to intracellular receptors, & directly affect gene expression (steroid hormones).
  • Water Soluble: Bind to receptors on the cell surface, activate second messenger systems (cyclic AMP) & induce rapid cellular responses (peptide hormones).

Mechanisms of Transport of Hormones Within the Blood

  • Lipid Soluble: Typically bind to carrier proteins for transport in the blood (thyroid hormones, steroid hormones).
  • Water Soluble: Circulate freely in the blood (peptide hormones) or bind to plasma proteins temporarily.

Major Factors Affecting Concentration of Circulating Hormones

  • Rate of Secretion: Controlled by feedback mechanisms.
  • Rate of Metabolic Activation & Inactivation: Influence the duration of hormone action.
  • Changes in Plasma Volume: Affect hormone concentration without a change in secretion rate.

How Lipid Soluble Hormones Reach Target Cell Receptors & Cellular Changes They Initiate

  • Transport: Diffuse across the cell membrane due to lipid solubility.
  • Effect: Bind to intracellular receptors, form a hormone-receptor complex, & directly influence gene expression (synthesis of new proteins).

How Water Soluble Hormones Induce Cellular Changes in Their Target Cells

  • Binding to Receptors: Bind to specific receptors on the cell surface.
  • Activation of 2nd Messenger Systems: Trigger intracellular signaling pathways (cyclic AMP, IP3/DAG), leading to rapid cellular responses (enzyme activation, ion channel opening).

Definition of Up-Regulation & Down-Regulation

  • Up-Regulation: Increase in the number of receptors on target cells in response to low hormone levels (increased sensitivity).
  • Down-Regulation: Decrease in the number of receptors on target cells in response to high hormone levels (decreased sensitivity).

Enzymatic Control of Nutrient Levels in the Blood

  • Role of Hormones: Hormones like insulin & glucagon regulate blood glucose levels.
  • Insulin: Stimulates glucose uptake by cells & promotes glycogen synthesis in the liver.
  • Glucagon: Stimulates glycogen breakdown in the liver & release of glucose into the blood.

Structure of the Pituitary Gland

  • Location: Below the hypothalamus, connected by the pituitary stalk.
  • Division: Anterior pituitary (adenohypophysis) & posterior pituitary (neurohypophysis).

Relationship of Pituitary Gland & Hypothalamus

  • Hypothalamic-Pituitary Axis: Hypothalamus controls the anterior pituitary via releasing & inhibiting hormones transported via the portal system.
  • Posterior Pituitary: Stores & releases hormones (oxytocin, vasopressin) synthesized in the hypothalamus.

Two Major Hormones Released by the Posterior Pituitary & Their Control by the Hypothalamus

  • Oxytocin: Stimulates uterine contractions during childbirth, milk ejection during breastfeeding.
  • Vasopressin (Antidiuretic Hormone, ADH): Promotes water retention in kidneys to maintain blood pressure & osmolarity.

6 Tropic Hormones Produced by the Anterior Pituitary & Their Functions

  • Growth Hormone (GH): Stimulates growth of bones & tissues.
  • Thyroid-Stimulating Hormone (TSH): Stimulates the thyroid gland to release thyroid hormones.
  • Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal cortex to release cortisol.
  • Follicle-Stimulating Hormone (FSH): Stimulates gamete production (sperm in males, eggs in females).
  • Luteinizing Hormone (LH): Stimulates ovulation in females, testosterone production in males.
  • Prolactin (PRL): Stimulates milk production in mammary glands.

Thyroid Gland Location, Anatomy & Control of Thyroid Hormone Secretion

  • Location: Anterior neck, below the larynx.
  • Anatomy: Composed of follicles containing colloid (thyroglobulin matrix).
  • Control: TSH from the anterior pituitary stimulates the synthesis & release of thyroid hormones (T3 & T4).

Functions of Thyroid Hormones on Target Tissues

  • Metabolic Rate: Increase basal metabolic rate (BMR) in most tissues.
  • Growth & Development: Essential for normal growth & development, especially in children.

Structure & Location of the Adrenal Gland

  • Location: Atop kidneys (suprarenal glands).
  • Structure: Adrenal cortex (outer layer) & adrenal medulla (inner core).

Hormones Secreted by the Adrenal Cortex & Their Effects on Target Tissues

  • Mineralocorticoids (Aldosterone): Regulate electrolyte balance, particularly sodium & potassium levels.
  • Glucocorticoids (Cortisol): Regulate glucose metabolism, suppress immune responses.
  • Androgens: Weak male sex hormones, contribute to libido in females.

Hormones Secreted by the Adrenal Medulla & Their Effects on Target Tissues

  • Epinephrine (Adrenaline) & Norepinephrine (Noradrenaline): Enhance “fight or flight” responses, increase heart rate, dilate airways, mobilize energy reserves.

Gross Anatomy & Cellular Structure of the Pancreas

  • Location: Behind the stomach, near the duodenum.
  • Structure: Composed of exocrine acini (produce digestive enzymes) & endocrine pancreatic islets (islets of Langerhans).

Types of Pancreatic Islet Cells & Hormones They Produce

  • Alpha: Produce glucagon, increase blood glucose levels.
  • Beta: Produce insulin, lowers blood glucose levels.
  • Delta: Produce somatostatin, inhibits the release of insulin & glucagon.

Effects of Insulin & Glucagon on Blood Glucose Concentration

  • Insulin: Stimulates the uptake of glucose by cells, promotes glycogen synthesis & storage in the liver, lowers blood glucose levels.
  • Glucagon: Stimulates the breakdown of glycogen (glycogenolysis) & release of glucose into the blood, raises blood glucose levels.