Study Notes: The Endocrine System, Blood, and The Heart

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Chapter 16: The Endocrine System

Overview of the Endocrine System

The endocrine system is a complex network of organs that synthesize and secrete chemical messengers called hormones. These hormones interact with specific target cells to regulate functions such as homeostasis, growth, and metabolism.

Hormones: Chemical messengers secreted by endocrine glands to regulate other cells.
Target Cells: Cells with specific receptors for hormones.
Homeostasis: Maintenance of fluid, electrolyte, and acid-base balance.

Comparison of Endocrine and Nervous Systems

The endocrine and nervous systems both regulate homeostasis but differ in their mechanisms and speed.

Nervous System: Uses neurons and neurotransmitters for immediate, short-lived effects.
Endocrine System: Uses hormones secreted into the bloodstream for slower, longer-lasting effects.

Types of Chemical Signals

Endocrine: Hormones travel through blood to distant targets.
Paracrine: Chemicals affect nearby cells.
Autocrine: Chemicals affect the same cell that secreted them.
Additional info: Neurotransmitters are a fourth type, acting across synapses.

Endocrine Organs

Anterior Pituitary: Located in the sphenoid bone.
Thyroid Gland: Anterior neck.
Parathyroid Glands: Posterior side of thyroid gland.
Adrenal Cortices: Superior to each kidney.
Pancreas: Left abdominal cavity, posterior to stomach.
Thymus: Superior mediastinum.

Classes of Hormones

Amino-acid hormones: Hydrophilic, bind to plasma membrane receptors.
Steroid hormones: Derived from cholesterol, hydrophobic, bind to cytosolic or nuclear receptors.

Hormone Transport and Action

Transport: Hormones can act quickly or slowly depending on their type.
Target Cells: Only cells with specific protein receptors are affected.
Hydrophilic Hormones: Use second messenger systems (e.g., cAMP).
Hydrophobic Hormones: Cross plasma membrane, bind to intracellular receptors, alter protein synthesis.

Hormone Effects and Interactions

Effects: Stimulate secretion, inhibit secretion, stimulate growth, activate enzymes, alter membrane permeability.
Synergists: Hormones with similar effects on the same cell.
Antagonists: Hormones with opposing effects.

Hormone Half-Life and Regulation

Hydrophobic hormones: Longest half-lives (week or more).
Hydrophilic hormones: Shorter half-lives.
Regulation: Initiated/inhibited by hormonal, humoral, or neural stimuli.
Feedback Loop: Stimulus → Receptor → Control Center → Effector/Response → Homeostatic Range.

Chapter 19: Blood

Overview of Blood

Blood is a fluid connective tissue, making up about 8% of body weight. It consists of plasma and formed elements.

Plasma: Liquid extracellular matrix (90% water).
Formed Elements: Erythrocytes (RBCs), Leukocytes (WBCs), Platelets.

Blood Layers (after centrifugation)

Layer	Component	% of Blood Volume
Top	Plasma	~55%
Middle	Buffy coat (leukocytes & platelets)	~1%
Bottom	Erythrocytes	~44%

Functions of Blood

Gas Exchange: Oxygen and carbon dioxide transport.
Solute Distribution: Nutrients, hormones, wastes.
Immune Functions: Leukocytes and antibodies.
Temperature Regulation: Heat distribution.
Clot Formation: Platelets and clotting proteins.
Acid-Base Homeostasis: Buffering capacity.
Blood Pressure Stabilization: Volume and viscosity.

Plasma Composition

Water: 90% of plasma, determines viscosity.
Plasma Proteins: 9% of plasma volume.

Protein	Source	Function
Albumin	Liver	Maintains osmotic pressure
Immune Proteins (γ-globulins)	Leukocytes	Antibodies
Transport Proteins	Various	Carry hydrophobic molecules
Clotting Proteins	Liver	Blood clot formation

Erythrocytes and Oxygen Transport

Structure: Biconcave, anucleate, filled with hemoglobin.
Hemoglobin: Four polypeptide chains (2α, 2β), each with a heme group containing iron.
Oxygen Transport: Iron binds O2 in lungs, releases in tissues.
CO2 Transport: Binds to hemoglobin in tissues.

Erythrocyte Life Cycle

Lifespan: 120 days.
Production: Hematopoiesis in red bone marrow.
Erythropoiesis: Stimulated by erythropoietin (EPO) from kidneys.
Destruction: Occurs in spleen; hemoglobin broken down.

Regulation of Erythropoiesis (Negative Feedback)

Stimulus: Low O2 levels
Receptor: Kidney detects hypoxia
Control Center: Kidney releases EPO
Effector: Increased RBC production
Homeostasis: Restored O2 levels

Anemia

Definition: Decreased oxygen-carrying capacity.
Causes: Decreased hemoglobin, decreased hematocrit, abnormal hemoglobin.
Symptoms: Fatigue, pallor, tachycardia.
Types: Iron-deficiency, pernicious, hemolytic, aplastic, sickle-cell.

Leukocytes and Immune Function

Leukocytes: White blood cells, larger than RBCs, prominent nucleus.
Granulocytes: Neutrophils (phagocytosis), Eosinophils (parasites/allergy), Basophils (inflammation).
Agranulocytes: Lymphocytes (B cells: antibodies, T cells: cell-mediated immunity), Monocytes (macrophages).

Leukopoiesis

Myeloid Line: Produces granulocytes and monocytes.
Lymphoid Line: Produces B and T lymphocytes.

Platelets

Function: Blood clotting.
Structure: Cell fragments, lack nucleus.
Formation: From megakaryocytes in bone marrow.
Lifespan: 7–10 days.

Hemostasis

Vascular Spasm: Immediate constriction after injury.
Platelet Plug Formation: Platelets adhere to injury site, aggregate.
Coagulation: Cascade of clotting factors, formation of fibrin.
Clot Retraction: Platelets contract, wound edges pulled together.
Thrombolysis: Clot breakdown via fibrinolysis.

Coagulation Pathways

Pathway	Trigger	Key Steps
Intrinsic	Contact with collagen	Activation of factor XII → cascade → factor Xa
Extrinsic	Tissue factor (outside blood)	Activation of factor VII → cascade → factor Xa
Common	Factor Xa	Prothrombin → thrombin → fibrinogen → fibrin

Regulation and Disorders

Anticoagulants: Antithrombin III, heparin sulfate, protein C.
Bleeding Disorders: Hemophilia.
Hypercoagulable States: Thrombosis, embolism, DVT, pulmonary embolism.

Blood Typing and Matching

ABO Group: A, B, AB, O antigens.
Rh Group: Rh+ or Rh-.
Universal Donor: O-
Universal Recipient: AB+
Agglutination: Antibodies cause clumping if blood types are incompatible.

Blood Type	Antigens Present	Antibodies Produced
A	A	Anti-B
B	B	Anti-A
AB	A, B	None
O	None	Anti-A, Anti-B

Chapter 17: The Cardiovascular System I: The Heart

Overview of the Heart

The heart is a muscular organ that pumps blood through two circuits: pulmonary (to lungs) and systemic (to body). It is located in the thoracic cavity, slightly left of center.

Four Chambers: Right/Left atria, Right/Left ventricles.
Blood Flow: Veins bring blood to atria; ventricles pump blood into arteries.

Circuits of the Heart

Pulmonary Circuit: Right side pumps deoxygenated blood to lungs.
Systemic Circuit: Left side pumps oxygenated blood to body.
Pressure: Pulmonary circuit is low-pressure; systemic is high-pressure.

Heart Anatomy

Pericardium: Fibrous and serous layers surround heart.
Myocardium: Cardiac muscle tissue and fibrous skeleton.
Endocardium: Inner lining of heart chambers.

Chambers, Valves, and Blood Flow

Atria: Receive blood from veins; separated by interatrial septum.
Ventricles: Pump blood into arteries; separated by interventricular septum.
Valves: Ensure one-way flow; AV valves (tricuspid, bicuspid/mitral), semilunar valves (pulmonary, aortic).

Coronary Circulation

Coronary Arteries: Supply myocardium with oxygen.
Coronary Veins: Drain blood into coronary sinus.
Coronary Artery Disease: Plaque buildup can cause myocardial infarction (heart attack).

Cardiac Muscle and Electrophysiology

Pacemaker Cells: Generate action potentials spontaneously (autorhythmicity).
Conduction System: SA node, AV node, Purkinje fibers.
Action Potentials: Pacemaker and contractile cell types; plateau phase unique to cardiac muscle.

Cardiac Conduction System

Component	Location	Intrinsic Rate
SA Node	Right atrium	~60-80 bpm
AV Node	Posterior to tricuspid valve	~40 bpm
Purkinje Fibers	Ventricles	~20 bpm

Electrocardiogram (ECG)

P Wave: Atrial depolarization.
QRS Complex: Ventricular depolarization.
T Wave: Ventricular repolarization.
Dysrhythmia: Abnormal electrical rhythm.

Mechanical Physiology: The Cardiac Cycle

One Heartbeat: One cycle of contraction (systole) and relaxation (diastole).
Pressure Gradients: Drive blood flow; valves open/close in response.
Heart Sounds: S1 (AV valves close), S2 (semilunar valves close).
Phases: Ventricular filling, isovolumetric contraction, ventricular ejection, isovolumetric relaxation.

Cardiac Output and Regulation

Cardiac Output (CO): Amount of blood pumped per minute.
Formula:
Stroke Volume (SV):
Ejection Fraction:
Factors Influencing SV: Preload, contractility, afterload.
Regulation: Autonomic nervous system (sympathetic: increases CO, parasympathetic: decreases CO), endocrine system, other factors (electrolytes, temperature, fitness).

Heart Failure

Definition: Reduced ability of heart to pump blood.
Treatment: Lifestyle, medications, surgery.

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