Overview
This lecture explains the organization of the human body's cavities, their subdivisions, serous membranes, medical imaging techniques, and how knowledge of these can help with clinical diagnoses.
Body Cavities and Regions
- A body cavity is any fluid-filled space within the axial region of the body (head to pubic region, excluding limbs).
- Cavities protect internal organs and enable movement and expansion.
- Major body cavities: dorsal (posterior/back) and ventral (anterior/belly side).
- Dorsal cavity includes the cranial cavity (brain) and vertebral (spinal) cavity.
- Ventral cavity is divided into thoracic and abdominopelvic cavities, separated by the diaphragm.
- Thoracic cavity contains pleural cavities (lungs), mediastinum, and pericardial cavity (heart).
- Abdominopelvic cavity is further divided into the abdominal and pelvic portions.
Abdominopelvic Quadrants & Clinical Relevance
- The abdominopelvic cavity is divided into four quadrants: right upper (RUQ), right lower (RLQ), left upper (LUQ), left lower (LLQ).
- RUQ: liver, gallbladder, part of transverse colon.
- LUQ: stomach, spleen, pancreas (behind stomach), part of transverse colon.
- RLQ: appendix, ascending colon, right ovary (females), last part of small intestine.
- LLQ: descending colon, some small intestine, left ovary (females).
- Kidneys are retroperitoneal (behind the cavity), not included in the quadrants.
Serous Membranes
- Serous membranes are double-walled membranes with lubricating serous fluid between layers.
- Functions: reduce friction, hold organs in place, compartmentalize organs.
- Types: peritoneum (abdominopelvic), pleura (lungs), pericardium (heart).
- Inner (visceral) membrane touches the organ; outer (parietal) membrane is against the cavity wall.
- Mesenteries are folds of peritoneum that support intestines and provide pathways for vessels.
Medical Imaging Techniques
- X-rays use ionizing radiation to view hard, dense tissues (e.g., bones, teeth).
- CT scans use ionizing radiation to create detailed 3D images of bones, organs, and blood vessels.
- MRI uses magnetic fields for high-contrast images of soft tissues (no ionizing radiation).
- Ultrasound (sonography) uses sound waves, mainly for pregnancy and soft tissue imaging (no radiation).
Review Questions & Answers
- The heart is located in the thoracic cavity, mediastinum, and most specifically, the pericardial cavity.
- Gallbladder pain typically presents in the right upper quadrant (RUQ).
- X-rays are used to visualize broken bones.
- MRI is the safest imaging choice for pregnant patients with abdominal pain.
Key Terms & Definitions
- Body cavity — fluid-filled space protecting organs in the axial body.
- Dorsal cavity — houses brain and spinal cord (posterior side).
- Ventral cavity — houses thoracic and abdominopelvic regions (anterior side).
- Serous membrane — double-walled membrane with lubricating fluid.
- Visceral membrane — inner layer touching the organ.
- Parietal membrane — outer layer lining the cavity wall.
- Mesenteries — peritoneum extensions stabilizing intestines.
- Retroperitoneal — organs located behind the peritoneal cavity.
Action Items / Next Steps
- Review the differences between pericardium, pleura, and peritoneum membranes.
- Memorize which organs are found in each abdominopelvic quadrant.
- Understand the applications and limitations of each medical imaging technique.