Chapter 9: The Endocrine System

Overview of the Endocrine System

The endocrine system is a slow-acting control system that works in conjunction with the fast-acting nervous system to maintain homeostasis. Endocrine glands are ductless and release hormones directly into the bloodstream, targeting specific cells throughout the body.

• Endocrine glands: Ductless; secrete hormones into blood.

• Exocrine glands: Have ducts; secrete substances onto epithelial surfaces.

• Role of the endocrine system: Regulates metabolism, growth, reproduction, and homeostasis.

Key Point: Only cells with specific receptors for a hormone can respond to that hormone.

Hormone Mechanisms and Classes

• Lipophilic hormones (e.g., steroids): Can cross the plasma membrane and bind to intracellular receptors.

• Hydrophilic hormones (e.g., most amino acid-based hormones): Bind to surface receptors and use a second messenger system (e.g., cAMP).

• Chemical classes of hormones:

  • Amino acid-based hormones (majority)

  • Steroids (derived from cholesterol)

  • Prostaglandins (local hormones derived from lipids)

Second messenger: An intracellular molecule (e.g., cAMP) that mediates the effects of a hormone that cannot cross the plasma membrane.

Major Endocrine Glands and Hormones

Refer to Table 9.1 for the major endocrine glands and their hormones. Most hormones are amino acid-based; exceptions include steroid hormones (e.g., cortisol, aldosterone, sex hormones).

Table 9.2 lists hormones produced by organs other than the major endocrine organs (e.g., heart, kidneys, GI tract).

Stimuli for Hormone Release

• Hormonal stimuli: Hormones stimulate other endocrine glands.

• Humoral stimuli: Changes in blood levels of ions/nutrients trigger hormone release.

• Neural stimuli: Nerve fibers stimulate hormone release.

Most hormone systems operate via negative feedback to maintain homeostasis.

Pituitary Gland and Hypothalamus

• Pituitary gland: The "master gland"; divided into anterior and posterior lobes.

• Anterior pituitary: Produces and releases hormones (e.g., GH, TSH, ACTH, FSH, LH, PRL).

• Posterior pituitary: Stores and releases hormones made by the hypothalamus (e.g., ADH, oxytocin).

• Hypothalamus: Controls pituitary via releasing/inhibiting hormones and neural connections.

Hormonal Regulation of Homeostasis

• PTH (parathyroid hormone): Increases blood calcium by stimulating osteoclasts, increasing intestinal absorption, and reducing renal excretion.

• Calcitonin: Lowers blood calcium by inhibiting osteoclasts and increasing calcium deposition in bone.

• Aldosterone: Released in response to low blood sodium, high potassium, or angiotensin II; increases sodium reabsorption in kidneys.

• Insulin and glucagon: Insulin lowers blood glucose; glucagon raises blood glucose.

Stress Responses

• Short-term stress: Mediated by adrenal medulla (epinephrine/norepinephrine); "fight or flight" response.

• Long-term stress: Mediated by adrenal cortex (cortisol, aldosterone); affects metabolism and fluid balance.

Hormone Abbreviations

• GH: Growth Hormone

• TSH: Thyroid Stimulating Hormone

• ACTH: Adrenocorticotropic Hormone

• FSH: Follicle Stimulating Hormone

• LH: Luteinizing Hormone

• PRL: Prolactin

• ADH: Antidiuretic Hormone

Example: Insulin is released from the pancreas in response to high blood glucose and promotes glucose uptake by cells.

Chapter 10: Blood

Composition and Functions of Blood

Blood is a connective tissue with a liquid matrix (plasma) and formed elements (cells and cell fragments). It transports gases, nutrients, wastes, hormones, and helps regulate temperature and pH.

• Plasma: The liquid matrix; contains water, proteins (albumin, globulins, fibrinogen), nutrients, hormones, and waste products.

• Albumin: Most abundant plasma protein; maintains osmotic pressure; produced by the liver.

• Physical characteristics: pH 7.35–7.45; adult blood volume ~5 liters.

Formed Elements of Blood

• Erythrocytes (RBCs): Transport oxygen; biconcave, anucleate; most abundant.

• Leukocytes (WBCs): Defend against pathogens; classified as granulocytes or agranulocytes.

• Platelets (thrombocytes): Cell fragments; essential for clotting.

All formed elements derive from hematopoietic stem cells in the red bone marrow.

Granulocytes vs. Agranulocytes

• Granulocytes: Neutrophils, eosinophils, basophils (contain granules in cytoplasm).

• Agranulocytes: Lymphocytes, monocytes (lack visible granules).

Hemostasis

Hemostasis is the process of stopping bleeding, involving three steps:

1. Vascular spasm (vasoconstriction)

2. Platelet plug formation

3. Coagulation (blood clotting)

Blood Groups and Transfusions

• ABO blood groups: Determined by presence/absence of A and B antigens on RBCs.

• Agglutination: Clumping of RBCs due to antibody-antigen reaction.

• Hemolysis: Destruction of RBCs; can occur in incompatible transfusions.

Example: Type A blood has A antigens and anti-B antibodies.

Chapter 11: The Cardiovascular System

Anatomy of the Heart

• Heart chambers: Right/left atria (upper), right/left ventricles (lower).

• Valves: Atrioventricular (tricuspid, bicuspid/mitral), semilunar (pulmonary, aortic).

• Chordae tendineae: Tendinous cords anchoring AV valve flaps to papillary muscles.

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

• Pericardium: Double-layered sac covering the heart.

• Apex: Pointed end of the heart; base: broad superior region.

• PMI (Point of Maximal Impulse): Location where heart beat is most strongly felt.

Blood Flow Through the Heart and Circuits

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

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

Pathway of blood: Vena cavae → right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary arteries → lungs → pulmonary veins → left atrium → bicuspid/mitral valve → left ventricle → aortic valve → aorta → body.

Electrical Activity and Cardiac Cycle

• Conduction pathway: SA node → AV node → AV bundle (bundle of His) → bundle branches → Purkinje fibers.

• Purpose: Coordinates contraction for efficient pumping.

• Cardiac cycle: Sequence of events in one heartbeat (systole and diastole).

• Heart sounds: "Lub" (AV valves close), "dup" (semilunar valves close).

Cardiac output (CO) formula:

Where HR = heart rate, SV = stroke volume.

Factors Affecting Cardiac Output

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

• Contractility: Strength of contraction at a given preload.

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

• Heart rate: Influenced by autonomic nervous system, hormones, fitness, age.

Blood Vessels and Circulation

• Arteries: Carry blood away from heart; thick walls, high pressure.

• Veins: Carry blood toward heart; thinner walls, valves to prevent backflow.

• Capillaries: Microscopic vessels; thin walls for exchange of gases, nutrients, wastes.

Venous return: Assisted by skeletal muscle pump, respiratory pump, and valves.

Portal circuits: Vascular pathways connecting two capillary beds (e.g., hepatic portal system).

Blood Pressure and Capillary Exchange

• Blood pressure: Force of blood against vessel walls; measured in mmHg.

• Systolic pressure: During ventricular contraction.

• Diastolic pressure: During ventricular relaxation.

• Pulse: Rhythmic expansion of artery due to heartbeat.

• Pressure points: Arteries close to skin surface where pulse can be felt.

Capillary exchange: Movement of fluids and solutes across capillary walls via diffusion, filtration, and osmosis.

Developmental Aspects

The cardiovascular system develops early in embryogenesis and undergoes changes at birth and throughout life.

Chapter 12: The Lymphatic System and Body Defenses

Lymphatic System Structure and Function

• Lymphatic vessels: Return interstitial fluid (lymph) to the bloodstream; similar to veins (thin walls, valves).

• Lymph: Fluid collected from tissues; returned to circulation via lymphatic ducts.

• Lymph nodes: Filter lymph; contain immune cells; more afferent than efferent vessels to slow flow for filtration.

• Lymphoid organs: Spleen, thymus, tonsils, Peyer's patches, appendix.

Body Defenses: Innate vs. Adaptive Immunity

• Innate (nonspecific) immunity: First and second lines of defense; barriers (skin, mucous membranes), phagocytes, inflammation, fever, NK cells.

• Adaptive (specific) immunity: Third line of defense; lymphocytes (B and T cells), antibodies; specific to pathogens.

Pathogen: Disease-causing organism (e.g., bacteria, viruses, fungi, parasites).

Humoral and Cellular Immunity

• Humoral immunity: Mediated by B cells and antibodies; targets extracellular pathogens.

• Cellular immunity: Mediated by T cells; targets infected or abnormal cells.

Antigens, Haptens, and Antibodies

• Antigen: Substance that triggers an immune response.

• Hapten: Small molecule that becomes antigenic when attached to a larger carrier.

• Antibody: Protein produced by B cells; binds specific antigens.

• Antibody classes (MADGE):

  • IgM: First antibody produced; in blood and lymph.

  • IgA: In secretions (saliva, tears, mucus).

  • IgD: On B cell surface; function unclear.

  • IgG: Most abundant; crosses placenta; in blood and tissues.

  • IgE: Involved in allergies and parasitic infections.

Active vs. Passive Immunity

Lymphocyte Development and Immunocompetence

• B cells: Mature in bone marrow; responsible for humoral immunity.

• T cells: Mature in thymus; responsible for cellular immunity.

• Immunocompetence: Ability of lymphocytes to recognize a specific antigen.

Tissue Transplant Rejection and Immunity Disorders

• Transplant rejection: Immune response against transplanted tissue due to antigenic differences.

• Types of transplants: Autograft (self), isograft (identical twin), allograft (same species), xenograft (different species).

• Minimizing rejection: Tissue matching, immunosuppressive drugs.

• Disorders of immunity: Autoimmune diseases, immunodeficiencies, allergies (hypersensitivities).

Example: Type I diabetes is an autoimmune disorder where the immune system attacks pancreatic beta cells.

Additional info: For diagrams and tables referenced (e.g., Table 9.1, Table 9.2, Figures 11.3a/b, 11.13, 11.14, 11.19), consult your textbook for visual identification and further details.