BIO 142 Unit 1: The Endocrine System and Blood – Study Guide

The Endocrine System

Overview of the Endocrine System

The endocrine system is a network of glands that secrete hormones to regulate various bodily functions. It works closely with the nervous system to maintain homeostasis.

• Endocrine vs. Nervous System: The nervous system uses electrical impulses for rapid, short-term responses, while the endocrine system uses hormones for slower, long-lasting effects.

• Hormones: Chemical messengers secreted into the bloodstream, affecting distant target organs.

• General Functions: Regulation of metabolism, growth, reproduction, and stress responses.

Hormone Secretion and Regulation

• Steps of Hormone Secretion:

  1. Synthesis

  2. Storage

  3. Release

  4. Transport

  5. Target interaction

  6. Degradation

• Endocrine vs. Paracrine Secretion: Endocrine hormones travel through the blood to distant targets; paracrine signals affect nearby cells.

• Primary vs. Secondary Endocrine Organs: Primary organs (e.g., pituitary, thyroid) have hormone secretion as their main function; secondary organs (e.g., heart, kidneys) secrete hormones as a secondary function.

Major Endocrine Glands and Hormones

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

• Secondary Endocrine Organs: Pancreas, gonads, heart, kidneys, thymus.

• Neuroendocrine Organs: Hypothalamus, adrenal medulla, pineal gland.

Hormone Chemistry and Transport

• Amino Acid-Based Hormones: Water-soluble, bind to cell surface receptors.

• Steroid Hormones: Lipid-soluble, derived from cholesterol, bind to intracellular receptors.

• Hormone Transport: Hydrophilic hormones travel freely in blood; hydrophobic hormones require carrier proteins.

• Hormone Complexes: Bound hormones are attached to carrier proteins; free hormones are unbound and active.

Hormone-Receptor Interactions

• Hydrophobic Hormones: Cross cell membranes, bind to intracellular receptors, alter gene expression.

• Hydrophilic Hormones: Bind to membrane receptors, activate second messenger systems.

• Types of Hormone Interactions:

  • Synergistic: Hormones amplify each other's effects.

  • Antagonistic: Hormones have opposing effects.

  • Permissive: One hormone enables another to act.

Hormone Half-Life and Feedback

• Half-Life: The time required for half the hormone to be removed from the blood.

• Negative Feedback: A process where the end product inhibits its own production, maintaining homeostasis.

Hypothalamus and Pituitary Gland

• Anatomical Relationship: The hypothalamus is connected to the pituitary gland via the infundibulum.

• Releasing and Inhibiting Hormones: Hypothalamic hormones regulate anterior pituitary hormone secretion.

• Major Pituitary Hormones:

  1. Thyroid-Stimulating Hormone (TSH)

  2. Adrenocorticotropic Hormone (ACTH)

  3. Growth Hormone (GH)

  4. Prolactin (PRL)

  5. Follicle-Stimulating Hormone (FSH)

  6. Luteinizing Hormone (LH)

  7. Antidiuretic Hormone (ADH)

  8. Oxytocin

Growth Hormone (GH)

• Short-Term Effects: Increases blood glucose, stimulates lipolysis.

• Long-Term Effects: Promotes growth in bones and tissues via Insulin-like Growth Factor (IGF).

• Disorders: Excess GH causes gigantism (children) or acromegaly (adults); deficiency causes dwarfism.

Thyroid and Parathyroid Glands

• Thyroid Gland: Located in the neck, produces T3, T4, and calcitonin.

• Functions: Regulates metabolism, growth, and thermoregulation.

• Disorders: Hyperthyroidism (excess hormone), hypothyroidism (deficiency).

• Parathyroid Glands: Located on the posterior thyroid, secrete parathyroid hormone (PTH) to regulate calcium.

Adrenal Glands

• Adrenal Cortex: Produces corticosteroids (aldosterone, cortisol, androgens).

• Adrenal Medulla: Produces catecholamines (epinephrine, norepinephrine).

• Cortisol: Known as the "stress hormone," increases blood glucose and suppresses inflammation.

• Disorders: Cushing's syndrome (excess cortisol), Addison's disease (deficiency).

Pancreas and Hormone Regulation of Blood Glucose

• Pancreas: Both an endocrine and exocrine gland.

• Islets of Langerhans: Contain alpha cells (glucagon), beta cells (insulin), delta cells (somatostatin).

• Glucagon: Raises blood glucose by stimulating glycogen breakdown.

• Insulin: Lowers blood glucose by promoting cellular uptake.

• Disorders: Diabetes mellitus (Type 1: insulin deficiency; Type 2: insulin resistance), hypoglycemia.

Pineal Gland

• Location: Deep in the brain.

• Hormone: Melatonin, regulates circadian rhythms.

Blood

Blood Composition and Functions

• Main Elements: Red blood cells (erythrocytes), white blood cells (leukocytes), platelets (thrombocytes), plasma.

• Functions: Transport of gases, nutrients, waste; immune defense; clotting; regulation of pH and temperature.

Blood Plasma

• Components: Water, proteins (albumin, globulins, fibrinogen), electrolytes, nutrients, hormones, waste products.

• Plasma vs. Serum: Serum is plasma without clotting factors.

Erythrocytes (Red Blood Cells)

• Structure: Biconcave, anucleate, flexible for capillary passage.

• Function: Transport oxygen (via hemoglobin) and carbon dioxide.

• Hemoglobin: Protein with four heme groups, each binding one O2 molecule.

• Oxygenated vs. Deoxygenated Blood: Oxygenated blood is bright red; deoxygenated is dark red.

• Destruction: Old erythrocytes are broken down in the spleen and liver.

Leukocytes (White Blood Cells)

• Types:

  • Granulocytes: Neutrophils, eosinophils, basophils.

  • Agranulocytes: Lymphocytes, monocytes.

• Functions: Immune defense, phagocytosis, antibody production.

Platelets (Thrombocytes)

• Function: Blood clotting (hemostasis).

Hemostasis and Coagulation

• Hemostasis: The process of stopping bleeding, involving vascular spasm, platelet plug formation, and coagulation.

• Coagulation Factors: Vitamin K, fibrinogen, calcium, clotting factors, thrombin.

• Fibrin: The protein that forms the mesh of a blood clot.

• Thrombolysis: The breakdown and removal of a blood clot.

Blood Typing and Transfusion

• Blood Types: Determined by surface antigens (A, B, AB, O) and plasma antibodies.

• Rh Factor: Presence (+) or absence (−) of D antigen.

• Universal Donor: Type O (no A/B antigens).

• Universal Recipient: Type AB (no anti-A/B antibodies).

• Mismatched Transfusion: Can cause agglutination and hemolysis.

Key Tables

Table: Comparison of Hydrophilic and Hydrophobic Hormones

Property	Hydrophilic Hormones	Hydrophobic Hormones
Chemical Nature	Amino acid-based	Steroid-based
Transport in Blood	Free (unbound)	Bound to carrier proteins
Receptor Location	Cell membrane	Intracellular (cytoplasm/nucleus)
Mechanism of Action	Second messenger systems	Direct gene activation
Examples	Insulin, epinephrine	Cortisol, estrogen

Table: Major Blood Cell Types and Functions

Cell Type	Main Function
Erythrocytes	Transport oxygen and carbon dioxide
Leukocytes	Immune defense
Platelets	Blood clotting

Key Equations

• Oxygen Carrying Capacity: $\text{O}_2 \text{ capacity} = \text{Hemoglobin concentration} \times 1.34 \text{ mL O}_2/\text{g Hb}$

• Hematocrit Calculation: $\text{Hematocrit} = \frac{\text{Volume of RBCs}}{\text{Total blood volume}} \times 100$

Additional info: Some explanations and tables were expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.