Fetal Pig, Sheep, and Human Comparative Anatomy Dissection

Fetal Pig Dissection: Introduction

Fetal pigs are commonly used for anatomical study due to their easily visible organs and anatomical similarity to humans.
They are often a byproduct of the farming industry (from pregnant sows slaughtered for food), making their use for dissection an ethical consideration as they are not exclusively taken for this purpose. This is also true for many other dissected organs.
**Organs to be examined (initial list):** Esophagus, Stomach, Small Intestine, Colon (Large Intestine), Liver, Gallbladder, Pancreas, Spleen, Kidneys, Adrenal Glands, Ureters, Urinary Bladder, Ovaries, Uterus, Testes.

Fetal Pig Thoracic Cavity Anatomy

**Diaphragm:** A muscular wall separating the thoracic and abdominal cavities, unique to mammals. Its up and down movements are responsible for inflating and deflating the lungs.
**Larynx (1):** The hardest and highest cartilage, located at the top.
**Trachea (2):** Comes from the larynx, characterized by C-shaped cartilage rings, giving it a ribbed or textured appearance.
**Esophagus:** A muscular tube located directly behind the trachea, lacking ring-like texture.
**Thyroid Gland:** Tissue sitting on top of the trachea.
**Thymus Gland:** Tissue overlying the center of the heart. Both thyroid and thymus glands have a spongy texture.
**Lungs (3):** Located on either side of the heart.
**Heart (5):** A large, four-chambered organ situated between the lungs. The pericardium (cardial sac) surrounds the heart.

Fetal Pig Abdominal Cavity Anatomy

**Liver:** The first and largest organ encountered below the diaphragm. It is dark, multi-lobed, and primarily responsible for producing bile, which is involved in fat breakdown.
**Gallbladder:** A small sac located underneath the liver (requires flipping the liver to view), which stores the bile produced by the liver. In preserved specimens, it may appear as a dried-out bag; in fresh specimens, it is filled with material and has a distinct color/texture from the liver.
**Stomach:** A C-shaped, bag-like organ situated below and slightly to the pig's left of the liver. Food enters the stomach from the esophagus.
**Spleen:** A tongue-shaped or horizontal organ found next to (not attached to) the stomach. It plays a role in red blood cell production, breakdown, and storage.
**Pancreas:** Mushy or spongy glandular tissue located typically between the stomach and the first coil of the small intestine. It can be hard to pick out without specific highlighting.
**Greater Omentum:** Fatty tissue that holds the stomach and spleen together. It is thin in fetal pigs but would be more substantial in grown individuals.
**Small Intestine:** Composed of many coils, appearing very long when stretched out. The term "small" refers to its diameter, not its length. It is the primary site of nutrient absorption.
**Mesentery:** A highly vascularized membrane that holds the small intestine coils together. It contains blood vessels that supply oxygen to the intestines and absorb nutrients from the small intestine wall.
**Large Intestine (Colon):** Has a distinct spiral shape in fetal pigs, unlike the ascending, transverse, and descending sections found in humans. It leads to the rectum and ultimately the anus.
**Kidneys:** Bean-shaped organs found retroperitoneally (against the dorsal body wall), one on each side. Internal structures like the cortex, medulla, and pyramids are visible to some extent.
**Adrenal Gland:** A small, unimpressive, bean-shaped structure situated slightly superior or just to the inside of the kidney.
**Ureters:** Small tubes connecting each kidney to the urinary bladder.
**Urinary Bladder:** In pigs, it is an elongated, balloon-shaped organ (more rounded in humans) located in the pelvic area, connected to umbilical arteries. The deepest part of the bladder, if traced further down, would be the urethra.

Fetal Pig Urogenital System Anatomy

**Male Reproductive Structures:**
- **Testes:** Located in the scrotal/groin area. Their presence is a clear indication of a male animal.
- The penis and the opening for the urethra (and where sperm would exit) are located more anteriorly.
- The anus is at the base of the tail, with no other genital opening below or above it.
**Female Reproductive Structures:**
- **External Genitalia:** An opening for the vaginal canal is clearly visible above the anus.
- **Ovaries:** Smaller and less conspicuous than the testes, found at the top of the uterine horns.
- **Uterus:** A V-shaped structure with a main body at the base of the bladder, branching into two coiled "horns" on either side.

Sheep Heart and Lung Anatomy

The anatomy of the sheep heart is remarkably similar to the human heart.
**Sheep Heart Structures:**
- Right auricle of the right atrium (1)
- Right ventricle (2)
- Pulmonary trunk (3)
- Anterior interventricular artery (4)
- Left ventricle (5)
**Sheep Lungs:** Freshly dissected lungs can be inflated in the lab to demonstrate pulmonary ventilation. The trachea is at the top, leading to deflated or inflated lung lobes.

Human Cadaver Dissection: Insights and Anomalies

**Gratitude for Body Donation:** Donated bodies are invaluable for teaching human anatomy, as "nothing replaces actually seeing the real thing." Medical schools typically cover cremation costs and return ashes to families (often after approximate 1 year of study), though arrangements for perpetuity are possible.
**Long-Term Preservation:** One cadaver was remarkably preserved for nearly 10 years, educating millions. This body was considered both the oldest (in terms of lab time) and youngest (died in mid-60s, whereas most others died in their late 70s or early 80s).
**Expected vs. Surprising Findings:** While cause of death and age provide expected abnormalities, full health history is unknown, leading to unexpected findings.
**Abdominal Cavity Observations:**
- **Greater Omentum (Anomalous):** Unlike a normal, thick, fatty apron that usually covers the small intestine and acts as a fat storage facility and infection fighter (containing lymph nodes and white blood cells), this cadaver had a very thin, frail, and holed omentum, shifted to the left side and not covering the small intestine. This thinness could be explained by weight loss due to cancer treatment.
- **Gallbladder (Absent):** The individual had undergone a cholecystectomy (surgical removal of the gallbladder) during life. While the gallbladder stores bile for fat emulsification, the liver still produces bile, allowing one to live without it, albeit with less bile storage for very fatty meals.
- **Cause of Death: Colorectal Cancer with Liver Metastasis:**
  - Cancer originated in the rectum and sigmoid colon.
  - Cancer cells metastasized (spread via bloodstream) to the liver, causing significant problems due to the liver's vital functions.
  - **Importance of Digestive Health Screenings:** Colon cancer is highly treatable if caught early (e.g., via colonoscopy), preventing metastasis.
  - **Factors for Digestive Health:** Diet (especially fiber) and the health of the gut microbiome are crucial.
- **Liver (Diseased):** Appears enlarged and has a nodular surface due to metastatic cancer cells. A healthy liver is smaller with a smooth, uniform surface.
- **Diverticula:** Outpouchings observed in the sigmoid colon wall. These are small, fatty appendages that are normal for many people and often asymptomatic. However, if feces or debris get clogged and infected, they can cause symptoms like lower abdominal pain, fever, and chills. Treatment can range from observation and antibiotics to surgical resection in severe cases. Diverticula are not necessarily linked to colon cancer.
**Lower Leg Observation (Mystery Finding):**
- **Partially Torn Achilles Tendon (Medial Belly):** The medial belly of the gastrocnemius muscle (in the calf/crus) was scrunched upward, indicating an old, partially torn Achilles tendon disguised by scar tissue.
- **Fascia Fusion:** The fascia, which normally wraps muscle groups and allows for sliding and gliding during contraction, was completely fused to the tendon in this area (myofascial adhesions). This would have caused a sensation of tightness and possibly decreased range of motion, as contraction would tug on the fascia instead of allowing smooth movement.

Additional Dissection Resources

Various tutorial videos (e.g., YouTube channels) provide different views and detailed dissections of fetal pigs, covering external, thoracic, abdominal, and urogenital anatomy.
Online learning tools like Quizlet and "Knowt" (a free alternative that can import Quizlet content) are valuable for studying anatomical structures.