Chapter 16 – The Endocrine System

Main Differences Between Endocrine and Nervous Systems

The endocrine and nervous systems are two major control systems in the body. They differ in how they transmit signals and the speed and duration of their effects.

• Endocrine system: Uses hormones released into the bloodstream to target distant organs. Effects are slower but longer-lasting.

• Nervous system: Uses electrical and chemical signals for rapid, short-lived responses.

• Example: Adrenaline (epinephrine) can be released by both systems, but the nervous system acts faster.

What is a Hormone?

A hormone is a chemical messenger made by endocrine glands and released into the blood. Hormones bind to specific receptors on target cells, causing changes in cell activity.

• Example: Insulin lowers blood glucose by signaling cells to take up glucose.

Main Types of Hormones

Hormones are classified by their chemical structure:

• Amino acid-based hormones: Most common; includes proteins and peptides.

• Steroid hormones: Derived from cholesterol; includes sex hormones and corticosteroids.

• Additional info: Amino acid-based hormones are water-soluble and act quickly; steroid hormones are lipid-soluble and act more slowly.

Hormone Signaling Pathways

Hormones signal cells by binding to receptors, triggering a cascade of cellular events.

• Second messenger systems: Used by water-soluble hormones; involves molecules like cAMP.

• Direct gene activation: Used by lipid-soluble hormones; hormones enter the cell and bind to DNA to regulate gene expression.

Stimuli for Hormone Release

Hormones are released in response to:

• Hormonal stimulation: One hormone triggers another gland (e.g., TSH triggers thyroid hormones).

• Neural stimulation: Nerve signals from the nervous system (e.g., stress signals release epinephrine).

• Humoral stimulation: Changes in blood levels of ions or nutrients (e.g., calcium triggers parathyroid hormone).

Main Endocrine Glands and Their Hormones

Major glands include the pituitary, thyroid, adrenal, pancreas, and gonads. Each produces specific hormones with distinct functions.

• Pituitary gland: Releases GH, ACTH, TSH, PRL, ADH, oxytocin.

• Thyroid gland: Releases T3 and T4 for metabolism.

• Adrenal gland: Releases cortisol, aldosterone, epinephrine.

• Pancreas: Releases insulin and glucagon for blood sugar regulation.

Blood Glucose Regulation

Insulin and glucagon control blood sugar levels:

• Insulin: Lowers blood sugar by promoting glucose uptake.

• Glucagon: Raises blood sugar by stimulating glucose release from the liver.

Diabetes Mellitus

Diabetes is a disorder of blood sugar regulation:

• Type 1: Insulin production is impaired.

• Type 2: Cells become resistant to insulin.

Chapter 17 – The Cardiovascular System I: The Heart

General Structure and Location

The heart is a muscular organ located in the mediastinum, protected by the pericardium.

• Pericardium: Double-layered sac that surrounds and protects the heart.

• Wall layers: Epicardium (outer), myocardium (muscle), endocardium (inner).

Main Functions of the Heart

The heart pumps blood through two circuits:

• Pulmonary circuit: Right side pumps blood to lungs for oxygenation.

• Systemic circuit: Left side pumps oxygenated blood to the body.

Heart Valves and Blood Flow

Valves ensure one-way blood flow:

• Atrioventricular valves: Tricuspid (right), bicuspid/mitral (left).

• Semilunar valves: Pulmonary (right), aortic (left).

• Chordae tendineae and papillary muscles: Prevent valve prolapse.

Electrical Conduction System

The heart's rhythm is controlled by electrical impulses:

• Sinoatrial (SA) node: Natural pacemaker; initiates heartbeat.

• Atrioventricular (AV) node: Delays impulse before passing to ventricles.

• Bundle of His and Purkinje fibers: Spread impulse through ventricles.

Cardiac Cycle and Heart Sounds

The cardiac cycle includes systole (contraction) and diastole (relaxation).

• "Lub-dub" sounds: Caused by closing of heart valves.

• ECG: Measures electrical activity; P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization).

Chapter 18 – The Cardiovascular System II: Blood Vessels

Arteries vs. Veins

Arteries and veins differ in structure and function:

• Arteries: Thick, elastic walls; carry blood away from the heart under high pressure.

• Veins: Thinner walls; carry blood toward the heart; contain valves to prevent backflow.

Vasoconstriction and Vasodilation

Blood vessel diameter changes regulate blood pressure:

• Vasoconstriction: Smooth muscle contracts, narrowing the vessel.

• Vasodilation: Smooth muscle relaxes, widening the vessel.

Layers of Blood Vessel Walls

Blood vessels have three layers:

• Tunica intima: Inner layer; smooth endothelium.

• Tunica media: Middle layer; smooth muscle controls diameter.

• Tunica externa: Outer layer; connective tissue anchors vessel.

Blood Pressure

Blood pressure is the force blood exerts against vessel walls.

• Normal reading: mmHg (systolic/diastolic).

• Equation:

Mechanisms of Venous Return

Blood returns to the heart via:

• Skeletal muscle pump: Muscles squeeze veins during movement.

• Respiratory pump: Breathing changes pressure in chest and abdomen.

• Valves: Prevent backflow.

Capillaries and Exchange

Capillaries are the site of exchange between blood and tissues.

• Diffusion: Movement of molecules from high to low concentration.

• Filtration: Fluid moves out due to blood pressure.

• Osmosis: Fluid moves in due to proteins attracting water.

Chapter 19 – Blood

Components of Blood

Blood consists of plasma and formed elements:

• Plasma: Liquid portion; contains water, proteins, nutrients, hormones, wastes.

• Formed elements: Red blood cells (RBCs), white blood cells (WBCs), platelets.

Main Functions of Blood

• Transports oxygen, nutrients, hormones, and wastes.

• Regulates pH, body temperature, and fluid balance.

• Protects the body through clotting and immune defenses.

Major Plasma Proteins

Red Blood Cells (Erythrocytes)

• Main function: Transport oxygen using hemoglobin.

• Structure: Biconcave discs without nuclei.

Hemoglobin

• Structure: Four protein chains (globins), each with a heme group containing iron.

• Function: Binds oxygen for transport.

White Blood Cells (Leukocytes)

• Neutrophils: Most common; phagocytize bacteria.

• Lymphocytes: Include B and T cells; immune response.

• Monocytes: Become macrophages.

• Eosinophils: Fight parasites.

• Basophils: Release histamine.

Platelets (Thrombocytes)

• Main function: Blood clotting.

Hematopoiesis

Blood cell formation occurs in red bone marrow from hematopoietic stem cells.

• Erythropoietin (EPO): Hormone from kidneys that stimulates RBC production.

Anemia

Anemia is a condition of reduced oxygen-carrying capacity due to low RBCs or hemoglobin.

• Symptoms: Fatigue, weakness, pale skin.

Summary Table: Formed Elements of Blood

Additional info: These notes cover the main topics from the provided file, including definitions, examples, and tables for key concepts in Anatomy & Physiology related to the endocrine system, heart, blood vessels, and blood.