In today’s standard anatomy classes- among other science classes- pigs are the most commonly dissected mammal because they have the most similar anatomy to a human. They have the same organs and many of the same muscles pertaining to similar human functions. When dissecting pigs it is important to remember the basic directional points. For example, median means to the middle, lateral means to the sides, dorsal is the belly-side, etc. It is also important to have lab safety plans involved, such as wearing goggles, always cutting away from the body, wearing gloves, and cleaning up perfectly.
The first system I will cover is the muscular and skeletal system- this system allows our body to move and protects our organs. Pigs have the same exact muscles as humans with the exception of small variation in size and the location- keeping in mind that pigs are quadrupedal and humans are bipedal. In the hind limb, the pig has the same muscles as humans in the major thigh muscle groups, quadriceps, femoris, and the hamstrings. Both pigs and humans have a mandible that is directly hinged to the skull, while other vertebrates have a separate bone connecting the mandible to the skull.
Both the pig and human have an extended nasal chamber. The nasal passages have complex convolutions providing a greater surface area for odor protection. They each have seven cervical bones to aid in movement of the head region. An obvious difference is that pigs have a tail. Humans lack the bones needed to have a tail and have no use for a tail. The next system to go over is the integumentary system-the skin. As in humans, the integumentary system of the pig includes the skin, hair, fingernails, and toenails. The pig is surrounded by a layer of skin for the same reason humans’ are o support and protect bones and organs. Pigs also have hair, like humans, but it is called bristles. Because pigs do not sweat, that have little hairs to help regulate temperature and it is one reason that they roll in the mud so often. Humans have hair to protect different parts of our body. In both humans and pigs eyelashes protect our eyes by attempting to keep harmful particles out. Both humans and pigs also have nails, but pigs have larger nails called hoofs for stronger protection. Next is the circulatory system, sometimes known as the cardiovascular system in mammals.
The circulatory system in both pigs and humans is made up of the heart, veins, capillaries, and arteries which circulate blood throughout the body. The blood carries oxygen from the lungs to every living cell in the body, while also removing waste from the lungs and kidneys. Pigs and humans also share a very similar pulmonary system which is a part of the circulatory system where the blood is carried from the lungs where the heart has pumped blood, so it can gather oxygen. The blood then returns to the start- the heart. The heart is a two pump system.
The right side is where the deoxygenated blood is pumped to the lungs and the left side takes the oxygen filled blood and pumps it to the rest of the body. The human and pig heart both contain the vena cava, right and left atrium, right and left ventricle, and the aorta. Another function of the circulatory system is to fight off infections. Blood contains red blood cells, white blood cells, and platelets. Red blood cells carry oxygen to and from the heart, white blood cells are a sign of infection, and platelets help to reduce blood clotting.
Arteries in both humans and pigs carry blood away from the heart and veins carry blood back to the heart. Fetal pigs receive oxygen from the mother through the umbilical vein in the placenta. Another system in the thoracic body cavity includes the respiratory system which lies laterally to the heart. The only difference in the respiratory system of the pig and human are the sizes, otherwise the functions are the exact same. Both inhale oxygen through the oral cavity or the nares. Then, oxygen travels to the bronchi and alveoli for gas exchange through the larynx and trachea.
Gas exchange occurs across the membranes of capillaries in the capillary beds of the alveoli in the various lobes of the lung. The maximized surface area of these bronchioles and alveoli allow for highly efficient and rapid extraction of oxygen from the air. After the respiratory system, comes the digestive system. Pigs and humans have a very similar digestive system; because they are both mono-gastric- meaning they have one stomach. Digestion of the intake of food, in pigs and humans, occurs along the digestive tract. The digestive tract is made up of five main parts including: mouth, esophagus, stomach, small intestine, and large intestine.
The food consumed by the human or pig is first taken in the mouth where chemical and physical breakdown occurs. The teeth chew the food (physical) and saliva in the mouth (chemical) softens and begins to break down the food. The tongue then pushes food to the esophagus which is a muscular tube leading to the stomach. In the stomach, chemicals break down the food particles where some nutrition is absorbed. Then the food enters the small intestine which breaks down the food further with the help of the liver and pancreas.
This is where most of the nutrition is absorbed. Lastly, the food enters the large intestine where waste materials make up feces and water is taken out. The leftover food then enters the excretory system by exiting through the anus in both pigs and humans. The digestive system is as important as other organ systems because it provides the energy needed to survive. The urinary system comes after the digestive system. The urinary system is not only important for excreting urine from our body, it is also important for filtering our blood.
The urinary system is made up of the kidneys, ureters, urethra, and urinary bladder. The kidneys regulate the volume, composition, and pH levels of bodily fluids. They remove metabolic waste from the blood and eventually the body and help control the rate of red blood cell’s levels and reproduction rates. The ureters are a pair of tubes that carry the urine from the kidneys to the bladder. They are about 10 to 12 inches long, run parallel to the vertebral column, and the ends have valves that prevent backflow. The urethra is a tube that conveys urine from the urinary bladder.
The male urethra is about 8 inches long and the female urethra is about 1-2 inches long. The urinary bladder is a hollow-sac like organ and is located along the body’s mid-line and the inferior end of the pelvis. The urinary bladder contains the urine and can hold anywhere from 600 to 800 milliliters of urine. There are no differences between the functions of the human and pig urinary systems other than the thickness and lengths of the ureters and urethra. The next system to cover is the nervous system- the system that controls all the other systems.
The nervous system for both pigs and humans includes: brain, spinal cord, peripheral nervous system, and the autonomic nervous system. The brain for both humans and pigs is encased by the skull and is surrounded by nervous tissue. The spinal cord extends from the brain to the narrow canal to the tail, very similar to humans. The peripheral nervous system consists of nerves leaving the brain and the spinal cord to transmit the electrical pulses throughout the body, just like humans. The autonomic nervous system is the involuntary nervous system that controls the heart, lungs, movement of the muscular wall during digestion.
The nervous system is what helps to control movement and functions of the body. The function of the brain is the reception of stimuli, which is contributed by sensory cells. The system transfers information throughout the body through impulses known as nerve impulses, which are sent and received by neurons. The nervous system is known as the most important organ system because it tells the other systems what to do and when to do it. The endocrine system is largely connected to the nervous system because the brain tells the endocrine system what to roduce and when.
In the typical endocrine system, the larynx is located at the base of the throat in an ovular shape. The larynx is located anteriorly to the thyroid which then proceeds into the thymus. The thyroid glands serve the same purpose in a pig as they do in a human: metabolism regulation. The pituitary gland is located near the center and the bottom of the brain. It produces a number of critical hormones that control many parts of the body. The adrenal glands, located in front of the kidneys, have three layers set for secreting different hormones.
The pancreas, located in the abdominal cavity, produces hormones regulating blood sugar and digestive enzymes. The thyroid gland produces hormones regulating your metabolism and levels of triiodothyronine and thyroxine. The thyroid gland cannot function without proper levels of iodine which can only be obtained through iodine rich foods, such as strawberries, cranberries, potatoes, yogurt, and much more. The parathyroid gland, which extends down the sides of the necks, helps regulate the body’s level of calcium and phosphorus in the blood.
The endocrine system is much slower acting than the other body systems. It regulates bodily processes that occur over the course of days and even months! The next organ system is what keeps life sustained- the reproductive system. Male humans and pigs reproductive system is supported by the pelvis. The testes, in both, produce sperm. Their reproductive system is made up of the prostate gland, sperm duct, epididymis, scrotal sac, testis, and penis. Female pigs and female humans also have very similar reproductive systems such as the ovaries, oviduct, cervix, urethra, and vagina.
When humans conceive, they remain pregnant for 9 months, compared to female pigs which stay pregnant for 4-5 months. Humans typically only have 1 child at a time- occasionally more-, but pigs can have between 1 and 14 piglets born in one litter. The main function to the reproductive system is to sustain life, so we do not become extinct. In conclusion, the average American anatomy class chooses pigs to dissect due to their similarities to humans. The main differences are proportionate sizing, but the functions are all relatively the same.
