Endocrine System

Nervous System vs. Endocrine System

The nervous system and endocrine system are the body's main communication networks, but they differ in how they send signals, their speed, and their effects.

• Nervous System: Uses fast electrical signals along nerves; effects are immediate and short-lived; targets specific locations (e.g., a muscle or gland).

• Endocrine System: Uses chemical messengers called hormones transported in the blood; effects are slower and longer-lasting; targets any cell with the appropriate receptor, leading to widespread effects.

Types of Hormones

Hormones are classified based on their solubility and how they interact with cells.

• Water-Soluble Hormones: Includes proteins and peptides. Cannot cross the cell membrane; bind to surface receptors and use second messengers (e.g., cAMP) to relay signals inside the cell.

• Fat-Soluble Hormones: Includes steroids and thyroid hormones. Easily cross the cell membrane; bind to receptors inside the cell, often in the cytoplasm or nucleus, and directly influence gene expression.

Mechanism of Fat-Soluble Hormone Action

Fat-soluble hormones act by directly influencing gene expression within the cell.

1. Hormone enters the cell by passing through the membrane.

2. Binds to an intracellular receptor (cytoplasm or nucleus).

3. The hormone-receptor complex moves into the nucleus.

4. Attaches to DNA, activating or repressing specific genes.

5. Triggers synthesis of new proteins, altering cell function.

Triggers for Hormone Release

Hormone secretion is regulated by three main types of stimuli:

• Humoral Stimulus: Changes in blood levels of ions or nutrients (e.g., high blood glucose triggers insulin release).

• Neural Stimulus: Direct stimulation by nerve fibers (e.g., sympathetic nerves trigger adrenaline release).

• Hormonal Stimulus: Hormones from one gland stimulate another gland (e.g., pituitary hormones stimulate thyroid hormone release).

Main Endocrine Glands and Their Hormones

The endocrine system consists of several glands, each producing specific hormones with distinct effects.

• Pituitary Gland: The "master gland" controlling other glands.

  • Growth Hormone (GH): Stimulates growth; excess causes gigantism/acromegaly, deficiency causes dwarfism.

  • Thyroid-Stimulating Hormone (TSH): Stimulates thyroid activity.

  • Adrenocorticotropic Hormone (ACTH): Stimulates adrenal cortex to release stress hormones.

  • Antidiuretic Hormone (ADH): Promotes water retention in kidneys; imbalance leads to SIADH or diabetes insipidus.

  • Oxytocin: Causes uterine contractions and milk ejection.

• Thyroid Gland:

  • Thyroid Hormones (T3 & T4): Regulate metabolic rate; excess causes hyperthyroidism, deficiency causes hypothyroidism.

  • Calcitonin: Lowers blood calcium by promoting storage in bones.

• Parathyroid Glands:

  • Parathyroid Hormone (PTH): Raises blood calcium by releasing it from bones; imbalance affects bone strength and neuromuscular function.

• Adrenal Glands:

  • Aldosterone: Regulates sodium and water balance, affecting blood pressure.

  • Cortisol: Stress hormone; excess causes Cushing's syndrome, deficiency causes Addison's disease.

  • Epinephrine (Adrenaline): Initiates "fight-or-flight" response.

• Pancreas:

  • Insulin: Lowers blood glucose; deficiency or resistance leads to diabetes mellitus.

  • Glucagon: Raises blood glucose by promoting breakdown of glycogen in the liver.

Integumentary System (Skin)

Layers and Parts of the Skin

The skin is the body's largest organ, providing protection, sensation, and regulation.

• Epidermis: Outermost layer; protects against pathogens, UV radiation, and water loss.

• Dermis: Middle layer; contains blood vessels, nerves, hair follicles, and glands.

• Hypodermis: Deepest layer; composed of fat for insulation and shock absorption.

• Glands:

  • Sebaceous Glands: Produce sebum (oil) for skin lubrication and antibacterial action.

  • Sweat Glands: Produce sweat for cooling via evaporation.

Factors Affecting Metabolic Rate

Metabolic rate is the speed at which the body uses energy at rest.

• Thyroid Hormone: Increases metabolic rate.

• Age: Younger individuals have higher metabolic rates.

• Muscle Mass: More muscle increases metabolism.

• Body Temperature: Higher temperatures (e.g., fever) increase metabolic rate.

Thermoregulation: Body Temperature Control

The hypothalamus acts as the body's thermostat, maintaining a set point around 98.6°F.

• When Hot:

  • Blood vessels in skin dilate (vasodilation) to release heat.

  • Sweat glands produce sweat; evaporation cools the skin.

• When Cold:

  • Blood vessels constrict (vasoconstriction) to retain heat.

  • Muscles shiver to generate heat.

Heat Exhaustion vs. Heat Stroke

Both are heat-related illnesses, but differ in severity and symptoms.

• Heat Exhaustion: Dehydration and overheating; skin is cool and clammy, heavy sweating, dizziness, nausea.

• Heat Stroke: Medical emergency; body temperature >104°F, skin is hot and dry, confusion or unconsciousness, sweating stops.

Stages of Fever

A fever is a controlled increase in body temperature to fight infection.

1. Onset (Chills): Brain raises set point; shivering generates heat.

2. Stadium (Plateau): Body temperature stabilizes at higher level; metabolism increases.

3. Defervescence (Fever Breaks): Set point returns to normal; sweating and flushing release excess heat.

Burns & Rule of Nines

Burns are classified by depth and extent; the Rule of Nines estimates affected body surface area.

• 1st-Degree: Epidermis only; red, painful, no blisters.

• 2nd-Degree: Epidermis and part of dermis; red, painful, blistered.

• 3rd-Degree: Full thickness; skin is white, charred, or leathery; no pain at site due to nerve destruction.

Common Skin Disorders

Several conditions affect the skin's health and function.

• Basal Cell Carcinoma: Most common, least dangerous skin cancer.

• Melanoma: Most dangerous skin cancer; use ABCD rule for mole assessment:

  • Asymmetry: One half does not match the other.

  • Border: Edges are irregular or jagged.

  • Color: Multiple or uneven colors.

  • Diameter: Larger than 6 mm (pencil eraser).

• Albinism: Genetic lack of melanin pigment.

• Psoriasis: Autoimmune disorder causing rapid skin cell growth and red, scaly patches.

• Acne: Infection and inflammation of clogged oil glands and hair follicles.

• Bedsores (Decubitus Ulcers): Skin breakdown from prolonged pressure and reduced blood flow.

Example: A person with hypothyroidism may experience fatigue, weight gain, and sensitivity to cold due to reduced thyroid hormone levels affecting metabolism.

Additional info: The notes have been expanded to include definitions, mechanisms, and examples for clarity and completeness.