Human Anatomy 1: Body Cavities and Body Membranes

Body Cavities

• The body has five cavities: cranial, vertebral, thoracic, abdominal, and pelvic cavities
• These cavities contain and protect internal organs

Cranial Cavity

• Formed by the cranium (cranial bones) and houses the brain
• The bones forming the cranial cavity are:
  • 2 parietal bones
  • 2 temporal bones
  • 1 frontal bone
  • 1 occipital bone
  • 1 sphenoid bone
  • 1 ethmoid bone

Vertebral/Spinal/Neural Cavity

• Formed by the 26 individual bones of the vertebral column
• Contains and protects the spinal cord

Thoracic Cavity

• Formed by the sternum, 24 ribs, and 12 thoracic vertebrae
• Contains and protects the heart, lungs, oesophagus, trachea, thymus gland, etc.
• Has three sub-cavities:
  • Pleural cavity
  • Mediastinum
  • Pericardial cavity

Abdominal Cavity

• Formed by the anterior and posterior abdominal muscles
• Contains and protects the stomach, liver, gallbladder, kidneys, spleen, intestines, etc.
• Can be subdivided into 4 quadrants or 9 regions

Abdominopelvic Region

• Divided into either four quadrants or nine regions
• The nine regions are delineated by four planes
• The quadrants are used to locate the site of an abdominopelvic abnormality in clinical studies

Pelvic Cavity

• Lies within the pelvis and is formed by 2 hip bones, sacrum, coccyx, and pelvic muscles
• Contains and protects the urinary bladder, rectum, uterus, ovaries, fallopian tubes, prostate gland, seminal vesicles, ejaculatory ducts, etc.

Body Membranes

• Thin sheets of tissues that cover the body, line body cavities, and cover hollow organs within the cavities
• Include:
  • Mucous membrane
  • Serous membrane
  • Cutaneous membrane
  • Synovial membrane
  • Meninges

Cutaneous Membrane

• Refers to the skin covering the whole body
• Has two layers:
  • Epidermis: outer layer
  • Dermis: inner layer
• Provides protection

Synovial Membrane

• Lines the cavities of the freely movable joints (synovial joints) such as the shoulder, elbow, and knee
• Lines cavities that do not open to the outside
• Secrete synovial fluid into the joint cavity for lubrication
• Prevents friction and injury

Meninges

• The connective tissue covering the brain and spinal cord, within the dorsal cavity
• Consists of three layers:
  • Outer layer: Dura mater/layer
  • Middle layer: Arachnoid mater/layer
  • Inner layer: Pia mater/layer
• The space between dura matter and arachnoid matter is called subdural space
• The space between the arachnoid matter and pia matter is known as subarachnoid space
• The subarachnoid space contains cerebrospinal fluid (CSF)

Mucous Membrane

• Epithelial membrane
• Has goblet cells that secrete mucus which lubricate the surfaces they line, protecting them from drying, mechanical and chemical injury
• Lines the body cavities/tracts that open to the outside such as digestive, respiratory, excretory/URINARY, and reproductive tracts

Serous Membranes

• Thin, slippery membrane lines body cavities not open to the outside
• Has two layers:
  • Parietal layer: outer layer that lines walls of cavities
  • Visceral layer: inner layer that covers viscera within the cavities
• The space between the two layers contains serous fluid which reduces friction between the two layers
• Examples of serous membranes are:
  • Pleura: covers the lungs and has pleural cavity
  • Pericardium: covers the heart and has pericardial cavity
  • Peritoneum: lines the abdominal cavity and covers the abdominal organs, and has peritoneal cavity