BIO 142 Unit 1: Endocrine System and Blood – Structured Study Notes

Chapter 16 – The Endocrine System

Overview of the Endocrine System

The endocrine system is a major regulatory system in the human body, working alongside the nervous system to maintain homeostasis. It uses hormones to control and coordinate body functions over longer periods.

• Endocrine System: A network of glands that secrete hormones directly into the bloodstream.

• Hormones: Chemical messengers that regulate physiological processes.

• Main Functions: Growth, metabolism, reproduction, and stress response.

• Comparison with Nervous System: Nervous system acts rapidly via electrical impulses; endocrine system acts slowly via hormones.

Hormone Secretion and Regulation

Hormone secretion involves several steps and is tightly regulated to ensure proper physiological responses.

• Four Steps of Hormone Secretion:

  1. Synthesis

  2. Storage

  3. Release

  4. Transport

• General Functions: Hormones regulate metabolism, growth, development, and tissue function.

• Endocrine vs. Paracrine Secretion: Endocrine hormones travel through blood to distant targets; paracrine hormones act locally.

Endocrine Organs

Endocrine organs are classified as primary (main function is hormone secretion) or secondary (hormone secretion is a secondary function).

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

• Secondary Endocrine Organs: Heart, kidneys, intestines, thymus.

• Neuroendocrine Organs: Hypothalamus, which links nervous and endocrine systems.

Hormone Chemistry and Transport

Hormones can be classified based on their chemical structure and solubility, which affects their transport and receptor interactions.

• Hydrophobic Hormones: Steroid hormones, thyroid hormones; transported bound to plasma proteins.

• Hydrophilic Hormones: Peptide and protein hormones; transported freely in plasma.

• Protein-Bound Hormones: Hormones attached to carrier proteins for transport.

Hormone-Receptor Interactions

Hormones exert their effects by binding to specific receptors on target cells. The nature of the hormone (hydrophobic or hydrophilic) determines the location and type of receptor.

• Hydrophobic Hormones: Bind to intracellular receptors; often alter gene expression.

• Hydrophilic Hormones: Bind to cell surface receptors; activate second messenger systems.

• Types of Interactions: Cellular changes, formation of products, signal amplification.

Hormone Interactions

Hormones can interact in various ways to regulate physiological processes.

• Synergistic: Hormones work together to produce a greater effect.

• Antagonistic: Hormones have opposing effects.

Hormone Half-Life

The half-life of a hormone is the time required for its concentration to decrease by half in the bloodstream. Hydrophobic hormones generally have longer half-lives due to protein binding.

Hormone Regulation and Feedback

Hormone levels are regulated by feedback mechanisms, often involving negative feedback to maintain homeostasis.

• Negative Feedback: A process where the output of a system inhibits its own production.

• Example: Regulation of thyroid hormones by the hypothalamic-pituitary-thyroid axis.

Anatomy of the Hypothalamus and Pituitary Gland

The hypothalamus and pituitary gland are central to endocrine regulation, controlling many other glands through releasing and inhibiting hormones.

• Hypothalamus: Produces releasing and inhibiting hormones.

• Anterior Pituitary: Releases hormones in response to hypothalamic signals.

• Posterior Pituitary: Stores and releases hormones produced by the hypothalamus.

Major Hormones and Their Functions

Several key hormones are produced by the hypothalamus and pituitary gland, each with specific target organs and effects.

Hormone	Source	Main Function
TRH/TSH	Hypothalamus/Pituitary	Stimulates thyroid hormone release
ACTH	Pituitary	Stimulates adrenal cortex
GH	Pituitary	Promotes growth
LH/FSH	Pituitary	Regulates reproductive organs
Prolactin	Pituitary	Stimulates milk production

Growth Hormone (GH) and IGF

Growth hormone and insulin-like growth factor (IGF) are critical for growth and metabolism.

• GH Effects: Stimulates growth in muscle, bone, and adipose tissue.

• IGF Effects: Promotes cell growth and division.

• Disorders: Excess GH leads to gigantism; deficiency leads to dwarfism.

Thyroid and Parathyroid Glands

The thyroid gland regulates metabolism, while the parathyroid glands control calcium homeostasis.

• Thyroid Hormones: Thyroxine (T4), Triiodothyronine (T3); regulate metabolic rate.

• Parathyroid Hormone (PTH): Increases blood calcium levels.

• Disorders: Hyperthyroidism, hypothyroidism.

Adrenal Glands

The adrenal glands produce hormones involved in stress response and metabolism.

• Cortex: Produces corticosteroids (cortisol, aldosterone).

• Medulla: Produces catecholamines (epinephrine, norepinephrine).

• Cortisol: Known as the "stress hormone"; increases blood glucose.

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

Pancreas and Blood Glucose Regulation

The pancreas has both endocrine and exocrine functions, with key roles in blood glucose regulation.

• Endocrine Cells: Alpha cells (glucagon), beta cells (insulin).

• Glucagon: Raises blood glucose by stimulating glycogen breakdown.

• Insulin: Lowers blood glucose by promoting uptake into cells.

• Diabetes Mellitus: Type 1 (insulin deficiency), Type 2 (insulin resistance).

Pineal Gland

The pineal gland secretes melatonin, which regulates circadian rhythms and sleep cycles.

• Melatonin: Hormone involved in sleep-wake regulation.

Chapter 19 – Blood

Blood Composition and Functions

Blood is a connective tissue composed of plasma and formed elements, serving as the main transport medium in the body.

• Formed Elements: Erythrocytes (red blood cells), leukocytes (white blood cells), platelets.

• Plasma: Liquid component containing water, proteins, nutrients, and waste products.

• Main Functions: Transport, regulation, protection.

Blood Plasma

Plasma is the non-cellular part of blood, containing dissolved substances and proteins.

• Main Components: Water, albumin, globulins, fibrinogen.

• Functions: Maintains osmotic balance, transports substances.

Hematocrit and Blood Analysis

Hematocrit is the percentage of blood volume occupied by red blood cells.

• Higher in Males: Due to increased erythropoietin and testosterone.

• Measurement: Centrifugation separates plasma and formed elements.

Erythrocytes (Red Blood Cells)

Erythrocytes are specialized for oxygen transport and have unique structural features.

• Structure: Biconcave, anucleate, flexible.

• Hemoglobin: Oxygen-carrying protein; consists of globin and heme group.

• Benefits: Shape increases surface area for gas exchange.

• Life Cycle: Produced in bone marrow, destroyed in spleen/liver.

Hemoglobin and Oxygen Transport

Hemoglobin binds oxygen in the lungs and releases it in tissues.

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

• Hemoglobin Structure: Four polypeptide chains, each with a heme group.

• Equation: $\text{Hb} + \text{O}_2 \rightarrow \text{HbO}_2$

Leukocytes (White Blood Cells)

Leukocytes are immune cells classified as granulocytes or agranulocytes.

Type	Main Function
Neutrophils	Phagocytosis of bacteria
Eosinophils	Combat parasites, allergic reactions
Basophils	Release histamine, inflammation
Lymphocytes	Adaptive immunity (B and T cells)
Monocytes	Phagocytosis, become macrophages

Platelets and Hemostasis

Platelets are cell fragments essential for blood clotting and wound repair.

• Hemostasis: The process of stopping bleeding.

• Steps: Vascular spasm, platelet plug formation, coagulation.

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

• Equation: $\text{Fibrinogen} \xrightarrow{\text{Thrombin}} \text{Fibrin}$

• Thrombolysis: Breakdown of clots.

Blood Types and Transfusion

Blood types are determined by antigens on erythrocytes and antibodies in plasma.

• ABO System: Types A, B, AB, O; based on surface antigens.

• Antibodies: Present in plasma; react with foreign antigens.

• Universal Donor: Type O (no antigens).

• Universal Recipient: Type AB (no antibodies).

• Rh Factor: Rh positive (antigen present), Rh negative (absent).

• Transfusion Reactions: Occur if mismatched blood is given.

Summary Table: Blood Types

Blood Type	Surface Antigen	Plasma Antibody	Transfusion Compatibility
A	A	Anti-B	Can receive A, O
B	B	Anti-A	Can receive B, O
AB	A and B	None	Can receive A, B, AB, O
O	None	Anti-A, Anti-B	Can receive O only

Additional info: These notes expand upon the learning objectives by providing definitions, examples, and context for each major topic. Tables have been recreated to summarize hormone functions and blood types for easy comparison.