Chapter 14 – Autonomic Nervous System

Main Divisions and Functions of the ANS

The Autonomic Nervous System (ANS) regulates involuntary physiological processes, including heart rate, blood pressure, respiration, digestion, and sexual arousal. It is divided into two main branches: the sympathetic and parasympathetic divisions.

• Sympathetic Division: Prepares the body for 'fight or flight' responses; increases heart rate, dilates pupils, inhibits digestion.

• Parasympathetic Division: Promotes 'rest and digest' activities; slows heart rate, stimulates digestion, constricts pupils.

• Neurotransmitters: Sympathetic uses norepinephrine (postganglionic), parasympathetic uses acetylcholine (both pre- and postganglionic).

• Origin in CNS: Sympathetic neurons originate in thoracolumbar spinal cord; parasympathetic in craniosacral regions.

• Ganglia: Sympathetic ganglia are close to the spinal cord; parasympathetic ganglia are near or within target organs.

• Axon Lengths: Sympathetic: short preganglionic, long postganglionic; Parasympathetic: long preganglionic, short postganglionic.

Anatomical Pathways of Sympathetic and Parasympathetic Neurons

Sympathetic and parasympathetic neurons follow distinct anatomical routes to reach their target effectors.

• Sympathetic Pathways: Preganglionic neurons synapse in sympathetic chain ganglia or collateral ganglia; postganglionic fibers extend to organs.

• Parasympathetic Pathways: Preganglionic neurons travel long distances to ganglia near or within target organs; short postganglionic fibers complete the pathway.

Effects of Sympathetic vs. Parasympathetic Innervation

These divisions often have opposing effects on target organs.

• Sympathetic: Increases heart rate, dilates bronchioles, inhibits gastrointestinal activity.

• Parasympathetic: Decreases heart rate, constricts bronchioles, stimulates gastrointestinal activity.

Adrenal Medulla and Sympathetic Division

The adrenal medulla acts as a modified sympathetic ganglion, releasing hormones directly into the bloodstream.

• Adrenal Medulla: Secretes epinephrine and norepinephrine during sympathetic activation.

• Relationship: Enhances and prolongs sympathetic effects throughout the body.

Cholinergic and Adrenergic Receptors

ANS neurotransmitters bind to specific receptors, producing varied effects.

• Cholinergic Receptors: Bind acetylcholine; include nicotinic (excitatory, found in ganglia) and muscarinic (excitatory or inhibitory, found in target organs).

• Adrenergic Receptors: Bind norepinephrine/epinephrine; include alpha and beta subtypes, each with distinct effects.

Dual Innervation

Most organs receive input from both sympathetic and parasympathetic divisions, allowing precise regulation.

• Example: Heart rate is increased by sympathetic stimulation and decreased by parasympathetic stimulation.

Chapter 16 – Endocrine System

Functions and Organization of the Endocrine System

The endocrine system consists of glands that secrete hormones to regulate body functions such as growth, metabolism, and homeostasis.

• Primary Endocrine Organs: Pituitary, thyroid, parathyroid, adrenal glands, pancreas.

• Secondary Endocrine Organs: Heart, kidneys, intestines (produce hormones but have other primary functions).

Key Terms

• Hormone: Chemical messenger secreted into the blood, affecting distant target cells.

• Endocrine Organ: Structure that produces and releases hormones.

• Receptor: Protein on/in target cells that binds a specific hormone.

Nervous vs. Endocrine Control

The nervous system provides rapid, short-term control via electrical impulses; the endocrine system provides slower, long-term regulation via hormones.

• Nervous: Fast, localized, neurotransmitters.

• Endocrine: Slow, widespread, hormones.

Hormone Secretion: Hypersecretion and Hyposecretion

• Hypersecretion: Excess hormone production; can cause disorders like hyperthyroidism.

• Hyposecretion: Insufficient hormone production; can cause disorders like hypothyroidism.

Chemical Classes of Hormones

• Steroid Hormones: Derived from cholesterol; lipid-soluble (e.g., cortisol, estrogen).

• Peptide Hormones: Chains of amino acids; water-soluble (e.g., insulin, growth hormone).

Production and Action of Steroid vs. Peptide Hormones

• Steroid Hormones: Synthesized in smooth ER; diffuse through cell membranes; bind intracellular receptors.

• Peptide Hormones: Synthesized in rough ER; stored in vesicles; bind membrane receptors.

Mechanisms of Hormone Action

• Plasma Membrane Receptors: Peptide hormones bind to receptors on cell surface, activating second messenger systems.

• Intracellular Receptors: Steroid hormones cross cell membrane and bind to receptors inside the cell, affecting gene transcription.

Hormone Regulation and Feedback

• Negative Feedback: Most common; hormone levels are regulated by feedback inhibition.

• Example: High blood glucose stimulates insulin release; insulin lowers glucose, reducing stimulus.

Major Endocrine Glands and Hormones

• Pituitary Gland: Anterior pituitary secretes growth hormone, TSH, ACTH, etc.; posterior pituitary releases ADH and oxytocin.

• Thyroid Gland: Produces thyroid hormones (T3, T4) regulating metabolism.

• Parathyroid Glands: Secrete parathyroid hormone (PTH) regulating calcium.

• Adrenal Glands: Cortex produces corticosteroids; medulla produces catecholamines.

• Pancreas: Produces insulin and glucagon for blood glucose regulation.

Chapters 17 & 18 – Cardiovascular System

Heart Anatomy and Position

The heart is a muscular organ located in the thoracic cavity, slightly left of the midline, within the mediastinum.

• Pericardium: Double-walled sac enclosing the heart; includes fibrous and serous layers.

• Chambers: Right and left atria (receive blood); right and left ventricles (pump blood).

• Valves: Atrioventricular (tricuspid, bicuspid/mitral) and semilunar (pulmonary, aortic) valves ensure unidirectional flow.

Major Blood Vessels

• Arteries: Carry blood away from the heart (usually oxygen-rich).

• Veins: Carry blood toward the heart (usually oxygen-poor).

Microscopic Anatomy of the Myocardium

• Intercalated Discs: Specialized connections between cardiac muscle cells for synchronized contraction.

Cardiac Conduction System

The heart's electrical system coordinates contraction.

• SA Node: Pacemaker; initiates action potentials.

• AV Node, Bundle of His, Purkinje Fibers: Conduct impulses through the heart.

Action Potentials and Contraction

• Phases: Depolarization, plateau, repolarization.

• Plateau Phase: Maintained by calcium influx; unique to cardiac muscle.

• Refractory Period: Longer in cardiac muscle, preventing tetanus.

Electrocardiogram (ECG/EKG)

• P Wave: Atrial depolarization.

• QRS Complex: Ventricular depolarization.

• T Wave: Ventricular repolarization.

Cardiac Cycle and Heart Sounds

• Systole: Contraction phase; blood is ejected.

• Diastole: Relaxation phase; chambers fill with blood.

• Heart Sounds: "Lub" (AV valves close), "Dub" (semilunar valves close).

Pressure and Volume Changes

• End-Diastolic Volume (EDV): Volume in ventricle at end of filling.

• End-Systolic Volume (ESV): Volume in ventricle after contraction.

• Stroke Volume (SV): Amount of blood ejected per beat.

Formula:

Cardiac Output (CO):

Regulation of Cardiac Output

• Preload: Degree of stretch of cardiac muscle before contraction.

• Afterload: Pressure the heart must overcome to eject blood.

• Contractility: Strength of contraction at a given preload.

• Frank-Starling Law: Increased preload increases stroke volume.

Blood Vessels and Circulation

• Tunics: Layers of blood vessel walls: tunica intima, tunica media, tunica externa.

• Arteries vs. Veins: Arteries have thicker walls and smaller lumens; veins have valves and larger lumens.

• Capillaries: Sites of exchange; thin walls for diffusion.

Anastomoses and Blood Flow

• Anastomosis: Connection between blood vessels, providing alternate routes for blood flow.

• Blood Flow: Volume of blood moving through a vessel per unit time.

• Blood Pressure: Force exerted by blood on vessel walls.

• Peripheral Resistance: Opposition to flow, mainly in arterioles.

Mean Arterial Pressure (MAP):

Capillary Exchange and Filtration

• Hydrostatic Pressure: Pushes fluid out of capillaries.

• Osmotic Pressure: Pulls fluid into capillaries.

• Net Filtration Pressure (NFP): Determines direction of fluid movement.

Formula:

Regulation of Blood Pressure

• Short-term: Neural and hormonal mechanisms (baroreceptors, chemoreceptors).

• Long-term: Renal regulation of blood volume.

Baroreceptor Reflex

• Baroreceptors: Detect changes in blood pressure and initiate compensatory mechanisms.

Types of Capillaries

Summary Table: Key Cardiovascular Formulas

Additional info: These study notes expand upon the question-based structure of the original file, providing definitions, examples, and key formulas for exam preparation in Anatomy & Physiology.