Lab 10
Anatomy & Physiology Part 1: The Digestive System

Learning Objectives
In this lab students will
- Be able to define anatomy and physiology
- Be able to label external and internal anatomical structures using proper scientific terminology.
- Explore and identify the major internal organs of the digestive system of the fetal pig.
- Describe the relative positions of the major digestive tract organs and the accessory organs of the digestive system.
- Be able to list the parts of the digestive tract in the order of their use during digestion.
- Identify the similarities and differences to human and pig anatomy and physiology.

Organization in Multicellular Organisms

Image shows the word Cells written at the bottom with and arrow pointing above to the word Tissues. There is an arrow pointing from tissues to Organs, then an arrow pointing up to Organ systems and another arrow pointing up to the word organisms.

• All living things are composed of one or more cells.
• As we have seen during the semester, some organisms consist of a single cell like bacteria and most protists.
• Other organisms are composed of many cells that function together.
• These last three labs will focus on multicellular organisms. More specifically these labs will focus on animals in the class Mammalia.
• There are different levels of complexity that we can arrange the components of a multicellular organism into.
• Cells – are the basic structural and functional unit of life.
Tissues - are groups of similar cells that perform the same function for an organ.
There are four types of tissue: epithelial tissue, connective tissue, nervous tissue and muscle. These are discussed in more detail in the lecture.
Organs - Contain two or more types of tissue that work together to perform a specific function. Examples of organs in humans include the stomach, heart, lungs and liver.
Organ Systems - are a group of organs that work closely together to perform a complex, integrated process.
• It is not uncommon for an organ to belong to more than one organ system (Example - the pancreas has functions in both the digestive system and the endocrine system).

• Pigs are a commonly dissected organism in biology labs for many reasons.
• Pigs, like humans, are mammals having hair on their bodies and mammary glands to nourish their young.
• The fetal pig is used because of the similarities between pig and human organ systems.
• The pig, like the human, is adapted for processing a variety of foods.
• The digestive system consists of the same set of organs and accessory organs responsible for moving food in a continuous process from mouth to anus.
• However, there are some anatomical differences, the pig lacks an appendix. In pigs the large intestine (or colon) is arranged differently than it is in humans.
• In this exercise you will  become familiar with anatomical terms, the external anatomy of a fetal pig and the digestive system.

Anatomical Terms and Directions

These are terms used to precisely describe the positions of structures relative to other structures or locations in the body.
When being told where to locate a structure these terms will be used.

Anterior  - means coming first or toward the front end; in the pig (or any animal that walks on all 4 legs) this means closer to the head or cranial area. In humans (or any animal that walks on 2 legs) means the ventral or belly surface, since this comes first.
Posterior - means coming last or toward the hind end; in the pig this refers to nearer the caudal or tail end, in humans this refers to the dorsal, or back side.
Dorsal – toward the back.
Ventral – toward the belly or underside.
Superior – toward the upper surface; in pigs this is also the dorsal or back, in humans it is towards the head.
Inferior – toward the lower surface; in pigs this will be towards the belly or ventral surface, in humans it is away from the head.
Medial – toward the midline or center of the body.
Lateral – toward the sides; away from the center of the body.
The next two terms are only used for appendages (arms, legs or tail)
Proximal – closer to the trunk.
Distal – farther from the trunk.
• It is also important to note that when we discuss LEFT and RIGHT we are discussing the subjects left or right. this is most often the reverse of your left or right. This may seem confusing at first. However, it is important that we have a standard for left and right. If I am standing at the head of a patient and you are standing at their feet and we need to amputate their left foot - we better both be amputating the same foot!

External Anatomy of the Fetal Pig

Figure 10.1 shows four pictures of the external anatomy of the fetal pig. The first panel in a female. Highlighted is the umbilical cord, the mammary papilla and the anus. The second panel is a male. Highlighted in this image is the umbilical cord, the male urogenital opening, the and the scrotum. The next panel shows a close up of the female genital papilla anterior to the anus. The final panel shows the close up of the male scrotum anterior to the anus.

• To determine the sex of the fetal pig, first locate the anus which is located ventral to the tail.
• If the fetal pig has a small opening just ventral to the anus, and a fleshy protuberance just above the opening, then the pig is a female.
• If the fetal pig has an opening just posterior to the umbilical cord and a sac-like scrotum near the anus, the pig is a male.
• Use Figure 10.1 to help you distinguish the sex of a pig.
• Note that both male and female pigs have  one urogenital opening and one anal opening.
• The urogenital opening is a common opening for the urinary system and the reproductive system.
• Also note that both male and male pigs have mammary papilla.

Figure 10.2 is a lateral view of a fetal pig. Highlighted on the head of the pig there are external ears or pinnae. On the pig’s snout there are external nostrils or nares. In the middle of the head are the eyelids. On the pig’s ventral surface is the umbilical cord.  Anterior of the body is the shoulder and elbows. Distal to the elbow is the wrist. Distal to the wrist are the digits. Posteriorly on the body is the hip. Distal to the hip is the knee. Distal to the knee is the ankle. Posterior to the hip is the scrotal sac and the tail.

• On the head of the pig there are external ears or pinnae. These help the pig hear by focusing sound into the middle ear.
• On the pigs snout there are external nostrils or nares. The snout is specially designed with a round disk of cartilage on its end to help the pig dig in the ground in search of food like roots and truffles.
• On the chin there is a small tuft of sensory hairs called vibrissae. These help them feel around in the dark.
• On the pigs ventral surface is the umbilical cord. These are fetal pigs so they still have this fetal structure.
• Within the umbilical cord there are 3 blood vessels; 2 small umbilical arteries that carry blood containing waste from the fetus to the placenta and one large umbilical vein, which carries oxygen and nutrients from the placenta to the fetus.
• Use Figure 10.2 to help you locate the external anatomical structures including the elbow, wrist, knee and ankle.

Digestive System

Image reads
Organs of the Digestive Tract: 
The Mouth or oral cavity
The Pharynx or throat
The Esophagus, a muscular tube between the pharynx and stomach
The Stomach, surrounded on both ends by valves, or sphincters.
The Small Intestine, which has three subdivisions: the duodenum, the jejunum and ileum.
The Large Intestine, aka the colon.
The Rectum.
The Anus.

Accessory Organs of the digestive system
A set of Salivary glands, secrete saliva into the oral cavity.
The Liver which has many functions in many organ systems. In digestion it produces bile. 
The Gall bladder stores the bile made by the liver and releases it into the duodenum as needed.
The Pancreas which secretes enzymes that breakdown fates into the duodenum. It also functions as part of the endocrine system.

• The digestive system can be subdivided into two sets of organs; the organs forming the digestive tract (aka the gastrointestinal tract or GI tract) and the accessory organs.
• The digestive tract is a continuous tube from the mouth to the anus. Food passes through these hollow organs.
• The accessory organs secrete substances into the digestive tract to aid in digestion. Food does not pass through these solid organs.
• During the process of digestion there is a coordinated series of mechanical and chemical steps that break food down before nutrients are absorb and utilized by individual cells of the body for energy.

Image shows the components of the digestive system. Highlighted are the mouth containing salivary glands above and below, the pharynx at the back of the mouth, the muscular tube called the esophagus and into the sac like stomach. Above the stomach is the large liver. Poking out below the liver and green in color is the gallbladder. Below the stomach is the pancreas. We see the small intestine coiled up and occupying most of the abdominal cavity.  The large intestine is large in diameter, but shorter in length than the small intestine and wraps around the lateral and superior parts of the small intestine. and the anus at the end of the large intestine.

Quick overview of the Digestive Tract
• Food first enters the digestive tract through the oral cavity (mouth). As the food is swallowed in passes into the pharynx (throat) and then down the muscular esophagus and into the stomach. After the stomach it enters into the small intestine (small in diameter but very long). The small intestine has 3 regions: the duodenum, jejunum and the ileum. What has not been absorbed into the body by this point will enter into the large intestine (large in diameter, but shorter in length). Another name for the large intestine is the colon. The remaining undigested material then enters into the rectum and then exits the body via the anus.
• Now lets look at what happens to the food as it passes through each of these structures in more detail.

Digestion from the Mouth to the Stomach

Image show the cat oral cavity. Highlighted is the bony hard palate on the roof of the mouth just behind the incisors; the soft palate located on the roof of the mouth posterior to the hard palate; the flap of cartilage called the epiglottis that covers the opening to the trachea when you swallow. The trachea can be seen posterior to the epiglottis and the muscular tongue.

• Digestion begins with the mechanical grinding of food by teeth in the mouth and the chemical breakdown of starch in foods by enzymes in saliva secreted by salivary glands.
• With the help of the tongue the bolus (the soft mass of food) is moved to the pharynx and then to the to the stomach via the esophagus.
• In the stomach food is mechanically churned and chemically broken down further by the action of acids and enzymes.
• The acids and enzymes here start the digestion of proteins.
• The acid in the stomach also protects the body against bacterial invasion.
• The main function of the stomach is to store food for a brief time and move it into the intestines in small amounts after it is liquefied.

Figure 10.4 shows the sac-like stomach. Above the stomach is the tube-like esophagus. Between the stomach and the esophagus is the ring is muscle called the cardiac sphincter. Inside the stomach is filled with liquid called chyme. Below the stomach is the duodenum. Between the duodenum and the stomach is the ring of muscle called the pyloric sphincter.

• Peristalsis is the waves of smooth muscle contraction that move food through the digestive tract. In the stomach it is used to mix the enzymes and acid with the food and move a small amount of chyme (the liquified, acidified mass of food) into the small intestine.
• Movement of food out of the stomach is regulated by the pyloric valve (located between the stomach and the duodenum).
• Food is prevented from moving back up into the esophagus by another valve called the cardiac sphincter (located between the esophagus and the stomach).
• When the cardiac sphincter fails we say we have 'heartburn". This is the acids burning the lining of our esophagus, not our heart.
• Figure 10.4 shows the stomach filled with chyme.

Digestion from Stomach to Small Intestine

• Before passing into the small intestine the chyme is neutralized by secretions from the pancreas.
• Most digestion occurs in the small intestine with the help of secretions from accessory organs including the liver, gall bladder and pancreas, which aid in breakdown of proteins, fats and carbohydrates.

Figure 10.5 the wall of the small intestine. (a) A portion of the small intestine cut open and a small section enlarged in (b) The wall of the small intestine with many finger-like projections called villi. Within the villi is a lacteal surrounded by red and blue capillaries. The cells lining the villus are mostly absorptive cells with a few goblet cells. (c) a single magnified villus. (d) a diagram of a single absorptive cell from the surface of the villi containing many small microvilli.

• The small intestine is also the major site of nutrient absorption and it is the longest part of the digestive tract.
• The small intestine contains a large surface area, including fingerlike projections called villi, and even smaller microvilli on its cells. The increased surface area allows more nutrients to be absorbed.
• The absorbed nutrients diffuse across the cells of the small intestines into the blood stream and travel to cells of the body.
• Figure 10.5 shows a cross section of the small intestine with the villi and microvilli.

The Pancreas, Liver and Gallbladder

• The liver produces bile which is stored in the gallbladder.
• Bile is a mixture of bile salts and bicarbonate.
• Bile salts emulsify fat (that means they break fat down into smaller globules).
The pancreas secretes bicarbonate, to neutralize the acid from the stomach, and enzymes that aid in the digestion of fats.
• Both pancreatic secretions and bile enter the small intestines through the bile duct.

Digestion from Large Intestine to the Anus

• The large intestine, also called the colon, is about 5 feet of tubing in an adult human.
• All that remains of the chyme is indigestible material, water, bacteria, and a few other things that could not be absorbed.
• The large intestine's primary role is to store fecal material, absorb water from it and propel it to the rectum.

The Liver is the the large, dark colored organ just below the diaphragm.The gallbladder is the small sac-like organ on the underside of the liver.The stomach is the sac like organ in the abdominal cavity below the liver.The large intestine is the thick, coiled short mass in the abdominal cavity.The pancreas is the granular organ below the stomach.The small intestine is the coiled mass that takes up most of the abdominal cavity. The rectum is the tube connecting the small intestine to the anus.Also show, but not part of the digestive system are the following:The diagram is the thin muscle that separates the thoracic and abdominal cavities. The spleen is the ribbon-shaped organ to the left of the pig’s stomach. The kidney is the bean-shaped organ dorsal to the abdominal organs.The ureter is the tube connecting the kidney to the urinary bladder.The urinary bladder which located between the two umbilical arteries.

Figure 10.6 highlights the organs found in the abdominal cavity.
The Liver is the the large, dark colored organ just below the diaphragm.
The gallbladder is the small sac-like organ on the underside of the liver.
The stomach is the sac like organ in the abdominal cavity below the liver.
The large intestine is the thick, coiled short mass in the abdominal cavity.
The pancreas is the granular organ below the stomach.
The small intestine is the coiled mass that takes up most of the abdominal cavity.
The rectum is the tube connecting the small intestine to the anus.
Also show, but not part of the digestive system are the following:
The diagram is the thin muscle that separates the thoracic and abdominal cavities.
The spleen is the ribbon-shaped organ to the left of the pig’s stomach.
The kidney is the bean-shaped organ dorsal to the abdominal organs.
The ureter is the tube connecting the kidney to the urinary bladder.
The urinary bladder which located between the two umbilical arteries.

Click on this image to trace the path of food through the digestive tract

At start of the animation, we see the major comments of the digestive system. A small bit of food enters from the left side and enters the Oral cavity. The word Oral cavity enlarges and shrinks. The food then enters the pharynx as the word pharynx enlarges and shrinks. The food then enters the esophagus as the word esophagus enlarges and shrinks. The food then does loops in the stomach as the word stomach enlarges and shrinks. The food then enters the Duodenum as the word duodenums enlarges and shrinks. The food then enters the jejunum as the word jejunum enlarges and shrinks. The food then enters the ileum as the word ileum enlarges and shrinks. The food then enters the colon as the word colon enlarges and shrinks. The food then enters the rectum as the word rectum enlarges and shrinks. Finally, the undigested food leaves the body through the anus as the word anus enlarges and shrinks.
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Non-majors College Biology Lab Manual © 2021 by Marie McGovern Ph.D. is licensed under CC BY-NC 4.0