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

Homeostasis and Body Fluid Compartments

Homeostasis: Definition and Importance

Homeostasis refers to the maintenance of a stable internal environment despite external changes. It is essential for the proper functioning of cells and organs.

• Dynamic, not static: Homeostasis involves constant adjustments to maintain equilibrium.

• Key variables: Temperature, pH, ion concentrations, and fluid balance.

Types of Equilibrium

• Electrical disequilibrium: Imbalance of ions (Na+, K+, Cl-) across cell membranes creates electrical gradients.

• Chemical disequilibrium: Unequal distribution of solutes (e.g., more K+ inside cells, more Na+ outside).

• Osmotic equilibrium: Water moves to balance solute concentrations; number of particles is equal on both sides of the membrane.

Body Fluid Compartments

• Intracellular fluid (ICF): Fluid inside cells; high in K+ and proteins.

• Extracellular fluid (ECF): Fluid outside cells; high in Na+ and Cl-.

• Plasma: The liquid component of blood, part of the ECF.

• Interstitial fluid: Fluid between cells, also part of the ECF.

Buffer zones: Interstitial fluid acts as a buffer between the outside world and most cells of the body.

Body Cavities

• Cranial cavity: Contains the brain.

• Thoracic cavity: Contains the heart (pericardial sac) and lungs (pleural sacs).

• Abdominal cavity: Contains digestive organs.

• Pelvic cavity: Contains reproductive organs and bladder.

Organ Systems and Their Functions

Overview of Organ Systems

The human body is organized into organ systems, each with specific functions essential for survival.

• Nervous: Controls and coordinates body functions through electrical signals; responsible for sensory ability.

• Digestive: Breaks down food, absorbs nutrients, eliminates waste.

• Respiratory: Facilitates CO2 and O2 exchange.

• Reproductive: Produces gametes and hormones.

• Cardiovascular: Transports nutrients, blood, and other products.

• Integumentary: Protects from environmental agents, regulates temperature, and prevents water loss.

• Urinary/Excretory: Removes waste, maintains water and electrolyte balance.

• Muscular: Enables movement and force exertion.

• Endocrine: Regulates bodily processes through hormones.

• Lymphatic: Defends against pathogens, transports fats, and filters fluids.

• Skeletal: Provides structure, protection, and produces blood cells.

Cell Structure and Function

Major Cell Components and Their Functions

• Plasma membrane: Controls movement of substances in and out of the cell; selectively permeable.

• Nucleus: Contains genetic material (DNA); controls cell activities.

• Endoplasmic reticulum (ER):

  • Rough ER: Site of protein synthesis.

  • Smooth ER: Synthesizes lipids, stores Ca2+.

• Golgi apparatus: Modifies and packages proteins into vesicles for transport.

• Mitochondria: Produces ATP via cellular respiration.

• Lysosomes: Contain digestive enzymes; break down waste and cellular debris.

Tissues of the Human Body

Main Tissue Types

• Epithelial tissue: Covers surfaces, lines cavities, and forms glands. Functions in secretion, absorption, and protection. Structure: tightly packed cells, may be simple (one layer) or stratified (multiple layers).

• Connective tissue: Supports, connects, and protects other tissues. Includes bone, cartilage, blood, adipose, and lymph.

• Muscle tissue: Responsible for movement. Contains actin and myosin filaments.

• Nervous tissue: Receives, processes, and transmits electrical signals. Composed of neurons and glial cells.

Membrane Transport Mechanisms

Types of Membrane Transport

• Simple diffusion: Passive movement of molecules from high to low concentration without energy input.

• Facilitated diffusion: Passive transport using carrier proteins or channels; no energy required.

• Active transport: Movement of molecules against their concentration gradient; requires energy (usually ATP).

Concentration gradient: The difference in concentration of a substance across a space or membrane.

Types of Membrane Proteins

• Channels: Allow specific ions or water to pass through membranes (e.g., Na+, K+ channels).

• Carriers: Bind and transport specific molecules across membranes.

• Receptors: Bind signaling molecules and initiate cellular responses.

• Enzymes: Catalyze metabolic reactions at the membrane surface.

Carrier-Mediated Transport

• Uniport: Transports one type of molecule.

• Symport: Transports two or more molecules in the same direction.

• Antiport: Transports two or more molecules in opposite directions.

Saturation, Specificity, and Competition

• Saturation: All available carriers or receptors are occupied by signaling molecules.

• Specificity: Ability of a receptor or carrier to bind only a specific ligand or family of ligands.

• Competition: Different molecules may compete for the same binding site.

Cell Signaling and Feedback Mechanisms

Agonists and Antagonists

• Agonist: Molecule that binds to a receptor and triggers a response.

• Antagonist: Molecule that binds to a receptor but does not trigger a response; blocks the action of agonists.

Feedback Mechanisms

• Negative feedback: Response counteracts the stimulus, shutting down the pathway (e.g., regulation of blood glucose).

• Positive feedback: Response reinforces the stimulus, driving the system further from equilibrium (e.g., childbirth contractions).

Endocrine System and Hormonal Regulation

Major Endocrine Glands and Hormones

• Thyroid hormones: T3, T4, Calcitonin

• TSH (Thyroid Stimulating Hormone): Stimulates thyroid hormone release

• Adrenal gland hormones: Cortisol (glucocorticoid), epinephrine, norepinephrine

• Growth hormone (GH): Stimulates growth and metabolism

• Insulin and glucagon: Regulate blood glucose levels

Hypothalamic-Pituitary Axis

• Hypothalamic-pituitary portal system: Direct vascular connection for rapid hormone signaling.

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

• Posterior pituitary: Releases vasopressin (ADH) and oxytocin.

Hormone Regulation and Feedback

• CRH (Corticotropin-releasing hormone): Stimulates ACTH release from anterior pituitary.

• ACTH: Stimulates cortisol release from adrenal cortex.

• Negative feedback: High cortisol inhibits CRH and ACTH release.

Calcium Homeostasis

• Parathyroid hormone (PTH): Increases blood Ca2+ by stimulating bone resorption and kidney reabsorption.

• Calcitonin: Lowers blood Ca2+ by inhibiting bone resorption.

• Vitamin D: Increases Ca2+ absorption from the gut.

Growth Hormone and IGF

• GH: Stimulates growth via IGF (insulin-like growth factors) from the liver.

• IGF: Promotes cell growth and division, especially in bones and muscles.

Thyroid Disorders

• Hypothyroidism: Low T3/T4, symptoms include fatigue, weight gain, cold intolerance.

• Hyperthyroidism: High T3/T4, symptoms include weight loss, heat intolerance, irritability.

• Iodine deficiency: Can cause hypothyroidism due to lack of T3/T4 synthesis.

Other Key Physiological Concepts

Osmolarity and Osmosis

• Osmolarity: Measure of solute concentration in a solution.

• Osmosis: Movement of water across a semipermeable membrane from low to high solute concentration.

Key Equations

• Osmolarity equation:

$\text{Osmolarity} = \text{Molarity} \times \text{number of particles per molecule}$

• Diffusion rate (Fick's Law):

$\text{Rate of diffusion} = \frac{(\text{surface area}) \times (\text{concentration gradient})}{\text{membrane thickness}}$

Sample Table: Comparison of Transport Mechanisms

Transport Type	Energy Required?	Direction	Example
Simple Diffusion	No	High to Low	O2, CO2
Facilitated Diffusion	No	High to Low	Glucose via GLUT transporter
Active Transport	Yes (ATP)	Low to High	Na+/K+ pump

Additional info:

• Some explanations and examples have been expanded for clarity and completeness.

• Table content inferred and summarized from standard physiology knowledge.