Foundations of Anatomy & Physiology: Organization, Membranes, Tissues, and Digestive System

Systemic Physiology & Homeostasis

Levels of Organization

The human body is organized into hierarchical levels, each contributing to overall function and homeostasis.

• Molecular → Cellular → Tissue → Organ → System → Organism

Homeostasis

Homeostasis refers to the maintenance of stable internal conditions such as temperature and pH, essential for survival.

• Feedback mechanisms:

  • Negative feedback: Reverses deviation (e.g., receptor → control center → effector)

  • Positive feedback: Amplifies deviation

Anatomical Terms & Membranes

Directional Terms

Standard anatomical terms describe locations and directions in the body.

• Ventral: Anterior, front

• Posterior: Back

Serous Membranes

Serous membranes line and protect organs within body cavities.

• Peritoneum: Surrounds abdominal organs

• Pericardium: Surrounds the heart

• Pleura: Surrounds the lungs

Membrane Protein Functions

Membrane proteins play key roles in cell communication and function.

• Anchoring

• Receptors

• Recognition

Cell Biology & Transport

Cytosol & Red Blood Cells

The cytosol is the fluid component of the cell, with distinct properties.

• Cytosol: High potassium, low protein, some glycogen

• Red blood cells: No nucleus, cannot synthesize proteins, limited lifespan

Membrane Transport Mechanisms

Cells exchange substances with their environment through various transport mechanisms.

• Diffusion: Passive; influenced by membrane channels, ion charge

• Osmosis: Water moves from high to low concentration; affected by tonicity

• Hypotonic: Cells swell (hemolyze)

• Hypertonic: Cells shrink (crenate)

• Facilitated diffusion: Carrier proteins; no ATP; limited rate

• Active transport: Requires ATP; moves substances against gradient

• Vesicular transport: Endocytosis (phagocytosis/pinocytosis), exocytosis

Key Equation:

$\text{Rate of diffusion} = k \times [\text{Concentration gradient}]$

Epithelial Tissue

Characteristics & Types

Epithelial tissue lines body surfaces and cavities, providing protection and facilitating absorption and secretion.

• Polarity: Apical vs. basal surfaces

• Avascular: Lacks blood vessels

• Regenerates: High capacity for renewal

Cell Junctions & Specializations

• Gap junctions: Exchange small molecules

• Tight junctions: Prevent passage

• Desmosomes: Mechanical support

• Microvilli: Increase absorption

• Cilia: Enable movement

Examples of Epithelia

• Simple squamous: Alveoli, blood vessels

• Simple columnar: Intestine

• Transitional: Urinary bladder

Glands & Secretions

Types of Glands

Glands produce and secrete substances necessary for bodily functions.

• Salivary glands: Produce amylase; parotid and submandibular (parotid = mostly serous)

Secretion Types

• Merocrine: Exocytosis (watery sweat)

• Apocrine: Cell apex pinches off

• Holocrine: Whole cell bursts

Connective Tissue

Types & Functions

Connective tissue supports, protects, and binds other tissues.

• Types: Proper, fluid, supporting

• Protein fibers: Collagen, reticular, elastic

• Loose connective tissue: Support, cushion

• Dense connective tissue: Tendons, ligaments, aponeuroses

• Blood: Fluid connective tissue

Digestive System

Wall Layers of the Digestive Tract

The digestive tract consists of several layers, each with specific functions.

• Mucosa: Innermost layer; includes digestive epithelium and lamina propria

• Muscularis mucosae

• Submucosa

• Muscularis externa: Responsible for peristalsis

• Serosa: Outermost layer

Stomach Structure & Function

• Parietal cells: Secrete HCl

• Chief cells: Secrete pepsinogen

• G cells: Secrete gastrin

• Rugae: Folds in stomach lining

• Three muscle layers in muscularis externa

Gastric Phases

• Cephalic: Prepares stomach

• Gastric: Secretes juice, mixes food

• Intestinal: Empties stomach, reduces secretions

Small Intestine Functions

• Duodenal ampulla: Receives bile and pancreatic juice

• Secretin: Stimulates bicarbonate-rich pancreatic juice

• GIP: Stimulates insulin release

• CCK: Stimulates enzyme release

Pancreas & Bile

• Pancreas: Trypsinogen (proenzyme), amylase (digests starch)

• Bile: Cystic + hepatic = common bile duct

Large Intestine & Digestion

• Large intestine: Absorbs water, compacts feces; haustra = pouches

• Salivary & Starch Digestion: Parotid gland is main source of salivary amylase

Summary Table: Epithelial Cell Junctions

Junction Type	Main Function	Example Location
Gap Junction	Exchange small molecules	Cardiac muscle
Tight Junction	Prevent passage	Intestinal epithelium
Desmosome	Mechanical support	Skin epidermis

Additional info:

• Some content was expanded for clarity and completeness, such as the functions of membrane proteins and the summary table of cell junctions.

• Scientific names and terms were italicized where appropriate.