Anatomy & Physiology Study Guide: Homeostasis, Cell Physiology, Tissues, and Endocrine System

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Homeostasis and Body Fluid Compartments

Definitions and Concepts

Homeostasis refers to the maintenance of a stable internal environment despite changes in the external environment. It is essential for proper physiological function and survival.

Homeostasis: The process by which the body maintains internal stability (e.g., temperature, pH, fluid balance).
Electrical equilibrium: A state where the net charge is balanced across cell membranes.
Chemical equilibrium: A state where the concentration of ions and molecules is balanced across compartments.
Osmotic equilibrium: A state where the total number of solute particles is equal across compartments.

Body fluid compartments:

Intracellular fluid (ICF): Fluid inside cells, high in potassium (K+).
Extracellular fluid (ECF): Fluid outside cells, high in sodium (Na+).
Blood plasma: The liquid component of blood, part of the ECF.
Interstitial fluid: Fluid between cells, also part of the ECF.

Buffer zones: Blood plasma acts as a buffer zone between the outside world and most cells of the body.

Body Cavities

Body cavities are spaces that hold organs in the body.

Cranial cavity: Contains the brain.
Thoracic cavity: Contains the heart and lungs (pleural and pericardial sacs).
Abdominal cavity: Contains digestive organs.
Pelvic cavity: Contains reproductive organs.

Cell Structure and Function

Major Organelles and Their Functions

Cells contain specialized structures called organelles, each with distinct functions.

Plasma membrane: Controls movement of substances in and out of the cell.
Nucleus: Contains genetic material (DNA) and controls cell activities.
Endoplasmic reticulum (ER):
- Rough ER: Site for protein synthesis.
- Smooth ER: Synthesizes lipids and detoxifies chemicals.
Golgi apparatus: Modifies and packages proteins into vesicles for transport.
Mitochondria: Produces ATP through cellular respiration.
Lysosomes: Contain digestive enzymes for breaking down waste and pathogens.

Tissues of the Human Body

Main Tissue Types

The human body is composed of four main tissue types, each with specific functions and structures.

Epithelial tissue: Covers body surfaces, lines cavities and organs. Functions in secretion, absorption, and protection. Can be simple (one layer) or stratified (multiple layers).
Connective tissue: Supports, connects, and protects other tissues. Includes blood, bone, cartilage, adipose, and tendons.
Muscle tissue: Responsible for movement. Types include skeletal, cardiac, and smooth muscle.
Nervous tissue: Processes and transmits electrical signals for communication and control.

Membrane Transport Mechanisms

Types of Transport

Cells exchange substances with their environment through various transport mechanisms.

Simple diffusion: Passive movement of molecules down their concentration gradient, no energy required.
Facilitated diffusion: Passive movement using membrane proteins (channels or carriers), no energy required.
Active transport: Movement against the concentration gradient, requires energy (usually ATP).
Osmosis: Diffusion of water across a selectively permeable membrane.

Types of membrane proteins:

Channels: Allow specific ions or water to pass through.
Carriers: Transport molecules by changing shape.
Pumps: Use energy to move substances against their gradient.

Concentration Gradient

A concentration gradient is the difference in concentration of a substance across a space or membrane.

Passive transport: Molecules move down the gradient (from high to low concentration).
Active transport: Molecules move against the gradient (from low to high concentration), requires energy.

Types of Carrier-Mediated Transport

Uniport: Transports only one kind of substrate.
Symport: Moves two or more substrates in the same direction.
Antiport: Moves substrates in opposite directions.

Cell Signaling and Receptors

Signal Transduction

Signal transduction is the process by which a cell converts an extracellular signal into a functional response.

First messenger: The extracellular signal molecule (e.g., hormone).
Membrane receptor: Protein that receives the signal.
Transducer: Converts the signal from one form to another (often a G protein).
Second messenger: Intracellular signaling molecules (e.g., cAMP).

Receptor Types and Functions

Agonist: A molecule that binds to a receptor and triggers a cellular response.
Antagonist: A molecule that binds to a receptor but does not elicit a response, blocking the action of agonists.
Saturation: Occurs when all available receptors are occupied by signaling molecules.
Specificity: The ability of a receptor to bind only to a specific ligand or family of related ligands.

Feedback Mechanisms

Negative feedback: The response counteracts the stimulus, shutting down the pathway. Example: High blood glucose triggers insulin release, lowering glucose levels.
Positive feedback: The response reinforces the stimulus, driving the system further away from equilibrium. Example: Childbirth contractions stimulate more contractions until delivery.

Endocrine System and Hormones

Major Endocrine Glands and Hormones

The endocrine system regulates body functions through hormones secreted by glands.

Thyroid hormones: T3, T4, and calcitonin regulate metabolism and calcium balance.
TSH (Thyroid Stimulating Hormone): Released by the anterior pituitary, stimulates thyroid hormone production.
Adrenal gland hormones: Glucocorticoids (e.g., cortisol), catecholamines (e.g., adrenaline, noradrenaline).
Growth hormone: Stimulates growth and metabolism.
Vasopressin (ADH) and oxytocin: Released through the posterior pituitary, regulate water balance and reproductive functions.

Hormone Pathways

Hypothalamic-pituitary axis: The hypothalamus controls the pituitary gland, which in turn regulates other endocrine glands.
Negative feedback: Hormone levels are regulated by feedback mechanisms to maintain homeostasis.

Hormone Functions and Disorders

Cortisol: Promotes gluconeogenesis, increases blood glucose, and suppresses the immune system.
Growth hormone: Stimulates growth of tissues, especially bone and cartilage.
Thyroid disorders: Hypothyroidism (low thyroid hormone), hyperthyroidism (high thyroid hormone).
Symptoms of hypothyroidism: Fatigue, weakness, weight gain, sensitivity to cold.
Symptoms of hyperthyroidism: High blood glucose, increased metabolism.

Calcium Homeostasis

Parathyroid hormone (PTH): Increases blood calcium by stimulating bone resorption.
Calcitonin: Lowers blood calcium by inhibiting bone resorption.
Vitamin D: Increases calcium absorption from the gut.

Other Terms in Physiology

Key Concepts

Molality and Osmolality: Measures of solute concentration in body fluids.
Osmotic pressure: The pressure required to prevent water movement across a semipermeable membrane.
Osmolarity: The concentration of solute particles per liter of solution.

HTML Table: Comparison of Body Fluid Compartments

Compartment	Main Ions	Location	Function
Intracellular Fluid (ICF)	K+, Mg2+, PO43-	Inside cells	Cell metabolism, signaling
Extracellular Fluid (ECF)	Na+, Cl-, Ca2+	Outside cells (blood plasma, interstitial fluid)	Transport, nutrient delivery, waste removal
Blood Plasma	Na+, Cl-, proteins	Vascular system	Buffer zone, transport of nutrients and waste
Interstitial Fluid	Na+, Cl-	Between cells	Medium for exchange between blood and cells

Key Equations

Osmolarity:
Fick's Law of Diffusion:

Additional info: Some explanations and examples have been expanded for clarity and completeness.