Comprehensive Study Notes: Endocrine, Blood, and Lymphatic Systems in Anatomy & Physiology

Endocrine System

Definition and Function of Hormones

The endocrine system regulates body functions through the release of hormones, which are chemical messengers secreted by glands and transported by the bloodstream to target organs.

• Hormone: A chemical messenger produced by endocrine glands, affecting distant target cells.

• Types of Hormones:

  • Bound hormones: Attached to carrier proteins in the blood.

  • Free hormones: Circulate without carriers; usually act quickly.

  • Second messengers: Intracellular signaling molecules (e.g., cAMP) activated by hormone-receptor interaction.

• Importance: Hormones regulate growth, metabolism, reproduction, and homeostasis.

Hormone Interactions

• Synergistic: Two hormones produce a greater effect together.

• Antagonistic: One hormone opposes the action of another.

• Permissive: One hormone enables another to act.

Major Endocrine Glands and Hormones

Each hormone has a specific gland of origin, target site, and physiological effect. Some disorders are associated with abnormal hormone levels.

• ADH (antidiuretic hormone): Produced by hypothalamus, stored in posterior pituitary; targets kidneys to regulate water balance.

• Oxytocin: Posterior pituitary; stimulates uterine contractions and milk ejection.

• Thyroxine (T4): Thyroid gland; increases metabolic rate.

• Cortisol: Adrenal cortex; stress response, increases blood glucose.

• Aldosterone: Adrenal cortex; regulates sodium and potassium balance.

• LH (luteinizing hormone): Anterior pituitary; stimulates ovulation/testosterone production.

• FSH (follicle-stimulating hormone): Anterior pituitary; stimulates gamete production.

• GH (growth hormone): Anterior pituitary; stimulates growth and cell reproduction.

• Thymopoietin: Thymus; involved in T-cell maturation.

• ACTH (adrenocorticotropic hormone): Anterior pituitary; stimulates cortisol release.

• Insulin: Pancreas; lowers blood glucose.

• TSH (thyroid-stimulating hormone): Anterior pituitary; stimulates thyroid hormone release.

• Epinephrine/Norepinephrine: Adrenal medulla; fight-or-flight response.

• PTH (parathyroid hormone): Parathyroid; increases blood calcium.

• Glucagon: Pancreas; raises blood glucose.

• Calcitonin: Thyroid; lowers blood calcium.

• Melatonin: Pineal gland; regulates circadian rhythms.

• Prolactin: Anterior pituitary; stimulates milk production.

• Triiodothyronine (T3): Thyroid; increases metabolic rate.

• Androgens: Adrenal cortex/gonads; male sex characteristics.

• Norepinephrine: Adrenal medulla; stress response.

• Progesterone/Testosterone: Gonads; reproductive functions.

• Serotonin: CNS; mood regulation.

Up-Regulation vs. Down-Regulation

Cells can adjust their sensitivity to hormones by changing the number of receptors.

• Up-regulation: Increase in receptor number, enhancing sensitivity.

• Down-regulation: Decrease in receptor number, reducing sensitivity.

Anterior vs. Posterior Pituitary

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

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

• Portal system: Blood vessel network connecting hypothalamus to anterior pituitary for hormone transport.

Blood and Hematology

Composition and Functions of Blood

Blood is a connective tissue with multiple functions, including transport, regulation, and protection.

• Components: Plasma (55%), formed elements (45%: erythrocytes, leukocytes, platelets).

• Functions: Transport gases, nutrients, hormones; regulate pH and temperature; protect against pathogens.

Measurement and Analysis

• Hematocrit: Percentage of blood volume occupied by red blood cells.

• Hemoglobin: Oxygen-carrying protein in erythrocytes.

• Blood volume: Total amount of blood in the body; varies by age, sex, and body size.

Albumin

• Albumin: Most abundant plasma protein; maintains osmotic pressure and transports substances.

• Clinical importance: Low albumin can lead to edema and impaired transport of drugs/hormones.

Blood Cell Formation (Hematopoiesis)

• Hematopoiesis: Formation of blood cells in bone marrow.

• Stem cells: Hematopoietic stem cells differentiate into erythrocytes, leukocytes, and platelets.

• Factors: Growth factors (e.g., erythropoietin) regulate production.

Erythrocytes (Red Blood Cells)

• Structure: Biconcave, no nucleus; optimized for gas exchange.

• Function: Transport oxygen and carbon dioxide.

• Disorders: Anemia (low RBCs), Thalassemia, Sickle cell disease.

Leukocytes (White Blood Cells)

• Types: Neutrophils, lymphocytes, monocytes, eosinophils, basophils.

• Function: Immune defense against pathogens.

• Abundance: Neutrophils > lymphocytes > monocytes > eosinophils > basophils.

Platelets and Hemostasis

• Platelets: Cell fragments involved in clotting.

• Hemostasis: Process to stop bleeding; involves vascular spasm, platelet plug formation, and coagulation.

Blood Groups and Transfusion

• Blood types: Determined by antigens (A, B, AB, O) and Rh factor.

• Transfusion compatibility: Matching donor and recipient blood types prevents reactions.

• Universal donor: Type O negative; Universal recipient: Type AB positive.

Coagulation and Fibrinolysis

• Coagulation: Cascade of clotting factors leading to fibrin formation.

• Fibrinolysis: Breakdown of clots after healing.

Blood Table: Formed Elements

Type	Main Function	Relative Abundance
Erythrocytes	Oxygen transport	Most abundant
Leukocytes	Immune defense	Less abundant
Platelets	Clotting	Least abundant

Lymphatic System and Immunity

Functions of the Lymphatic System

The lymphatic system maintains fluid balance, absorbs dietary fats, and provides immune defense.

• Fluid recovery: Returns excess interstitial fluid to the bloodstream.

• Fat absorption: Lacteals in intestines absorb fats.

• Immunity: Lymph nodes filter pathogens; lymphocytes respond to infection.

Lymphoid Tissues and Organs

• Lymph nodes: Filter lymph; site of immune activation.

• Spleen: Filters blood, removes old RBCs, immune surveillance.

• Tonsils: Protect against inhaled/ingested pathogens.

• Thymus: T-cell maturation.

Lymphatic Circulation and Blockage

• Lymph transport: One-way system from tissues to veins.

• Blockage: Causes swelling (lymphedema); can result from infection or surgery.

Types of Lymphoid Tissue

• Diffuse lymphatic tissue: Scattered lymphocytes in mucous membranes.

• Lymphatic nodules: Dense clusters (e.g., tonsils).

• Lymphoid organs: Encapsulated structures (nodes, spleen, thymus).

Innate vs. Adaptive Immunity

• Innate (nonspecific) defenses: Physical barriers, phagocytes, inflammation, fever.

• Adaptive (specific) defenses: Lymphocytes (B and T cells), antibodies, memory response.

Cells of the Immune System

• B cells: Produce antibodies; humoral immunity.

• T cells: Cell-mediated immunity; helper, cytotoxic, regulatory types.

• Macrophages: Phagocytosis and antigen presentation.

• Natural killer (NK) cells: Destroy infected or abnormal cells.

Inflammatory Response

• Signs: Redness, heat, swelling, pain.

• Purpose: Isolate and eliminate pathogens, promote healing.

Immunological Concepts

• Interferon: Proteins that inhibit viral replication.

• Complement: Proteins that enhance immune response.

• Antigen: Substance that triggers immune response.

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

• Epitope: Specific part of antigen recognized by antibodies.

• MHC (major histocompatibility complex): Proteins presenting antigens to T cells.

Immunity Types

• Active immunity: Body produces its own antibodies (infection or vaccination).

• Passive immunity: Antibodies received from another source (e.g., maternal antibodies).

Hypersensitivities and Anaphylactic Shock

• Hypersensitivity: Excessive or inappropriate immune response (e.g., allergies).

• Anaphylactic shock: Severe, systemic allergic reaction; rapid drop in blood pressure, airway constriction.

HIV and Immune Function

• HIV: Virus that infects and destroys helper T cells, leading to immunodeficiency.

• Consequences: Increased susceptibility to infections and certain cancers.

Table: Comparison of Innate and Adaptive Immunity

Feature	Innate Immunity	Adaptive Immunity
Specificity	Non-specific	Highly specific
Memory	None	Long-lasting
Cells involved	Phagocytes, NK cells	B and T lymphocytes
Response time	Immediate	Delayed (days)

Additional info:

• Some content inferred from standard Anatomy & Physiology curriculum to provide complete context.

• Tables and lists expanded for clarity and exam preparation.