A&P - Unit E: The Digestive System

Study Set for Anatomy and Physiology 12.

Digestion

Digestion

The mechanical and chemical breaking down of ingested food into particles, then into molecules small enough to move through epithelial cells and into the internal environment.

Absorption

The passage of digested nutrients from the gut lumen into the blood or lymph, which distributes them throughout the body.

Elimination

The expulsion of indigestible residues from the body.

Amino Acids

What Proteins are broken down into during the process of digestion.

Glucose

What Carbohydrates are broken down into during the process of digestion.

Glycerol and Fatty Acids

What Fats (Lipids) are broken down into during the process of digestion.

Nucleotides

What Nucleic Acids are broken down into during the process of digestion.

Extracellular Process

Digestion is an _______, meaning it occurs outside of the body. It is achieved through the cooperation of a number of body parts and organ systems. This coordination requires and depends on the actions of several key hormones.

Mouth

Where digestion begins. This organ receives food, chews it up, moistens it (with saliva), and starts to digest any starch in the food.

Hard Palate

The anterior (near the front) palate. It gets its name because it contains several bones.

Soft Palate

The posterior (further to the back) palate. It get its name because it is mainly composed of muscle tissue.

Uvula

The thing that hangs in the end of our throat. It forms the end of the soft palate.

Tonsils

Found on the side of the throat; they function in filtering out bacteria and other germs that can otherwise cause infections in the body.

Teeth

These function in mechanically breaking down (or chewing) food into pieces that can be swallowed easily. A normal adult mouth has 32 of them.

Enamel

A tough, extremely hard layer that shrouds the teeth; composed largely of calcium salts.

Dentine

A thicker, brownish bone-like material.

Pulp

An inner layer of nerves and blood vessels.

Incisors

Type of teeth that aid in biting. A normal adult mouth has 8.

Canines

Type of teeth that aid in tearing. A normal adult mouth has 4.

Flat Premolars

Type of teeth that aid in grinding. A normal adult mouth has 8.

Molars

Type of teeth that aid in crushing. A normal adult mouth has 12.

Wisdom Teeth

Final molars which may not erupt properly. If not, they must be removed surgically.

Cavities

Caused by bacteria in the mouth that feed on foods (like sugars) and give off acids that corrode the tooth.

Plaque

The living and dead bodies of millions of bacteria.

Fluoride

Makes the tooth enamel stronger and more resistant to decay.

Gum Disease / Gingivitis

Inflammation of the gums. The most common disease in the world!

Periodontal Membrane

The lining of the tooth socket.

Periodontitis

Bone loss in the socket and loosening of the teeth; caused if gingivitis spreads to the Periodontal Membrane.

Salivary Glands

Glands that produce saliva. Three sets.

Saliva

Moistens and lubricates food when we chew; contains water, mucus, and the enzyme salivary amylase.

Parotid Glands

Set of salivary glands located below the ears.

Sublingual Glands

Set of salivary glands located below the tongue.

Submandibular Glands

Set of salivary glands located under the lower jaw.

Salivary Amylase

A hydrolytic enzyme that breaks down starch in the presence of water. Found in saliva.

Maltose

Salivary Amylase breaks down starch into _____ (a disaccharide of glucose), which is then later broken down into glucose in the intestines.

Pharynx

The first region food enters. The region between the mouth and the esophagus where swallowing takes place.

Bolus

What food becomes when it has been chewed.

Nasopharyngeal Openings

The openings of the nose; in the process of swallowing, the soft palate moves back to cover them.

Trachea (Windpipe)

The airway that leads from the larynx (voice box) to the bronchi (large airways that lead to the lungs); in the process of swallowing, it moves up under a flap of tissue called the epiglottis.

Larynx

A hollow tube that lets air pass from the pharynx to the trachea on the way to the lungs; in the process of swallowing, the glottis (its opening) is covered when the trachea moves up. It gets covered by the epiglottis.

Glottis

The opening of the larynx. It gets covered when the trachea moves up by the epiglottis.

Esophagus

A long muscular tube that extends from the pharynx to the stomach.

Mucuous Membranes

Mucosa and Submucosa are ______

Mucosa

The innermost membrane of the esophagus.

Submucosa

The second innermost membrane of the esophagus.

Muscularis Propria

A layer of smooth muscle that the mucuous membranes are attached to by connective tissue. It contains both circular and longitudinal muscle.

Adventitia

The outer layer of the esophagus (and other organs).

Peristalsis

Rhythmical contractions of the esophageal muscles through which food moves down the esophagus.

Cardiac Sphincter

Made up of muscles that encircle tubes, and function like valves. When they relax, they open, and when they contract, they close. Normally, this organ prevents food from moving up and out of the stomach, and is located between the Stomach and Esophagus.

Vomiting

When this event occurs, a reverse peristaltic wave causes the sphincter to relax and the contents of the stomach are propelled forward.

Stomach

A thick walled, J-shaped organ that lies on the left side of the body beneath the diaphragm. It can stretch to hold about half a gallon (~2 liters) of solids and/or liquids in an average adult. Three layers of muscle contract to churn and mix its contents.

Inner Gastric Glands

Contained in the inner lining of the stomach; produce gastric juice.

Gastric Juice

Produced by the Inner Gastric Glands; contains pepsinogen and hydrochloric acid.

Pepsin

When combined, pepsinogen forms this; it is a hydrolytic enzyme that breaks down proteins into peptides.

Hydrochloric Acid

A component of Gastric Juice; gives the stomach a pH of ~3, which makes it highly corrosive. This kills bacteria in the food and helps break it down.

Pepsinogen

A component of Gastric Juice; when combined, forms Pepsin.

Acid Chyme

A semi-liquid food mass, formed out of anything that enters the stomach. Food will be turned into it after 2-6 hours, the length of time depending on the type of food.

Inner Wall

Produces a thick layer of mucus, secreted by mucosal cells; prevents the stomach from digesting itself.

Mucosal Cells

The cells that secrete the thick layer of mucus that the Inner Wall produces.

Ulcer

An open sore on the wall of the stomach; formed if hydrochloric acid penetrates through the Inner Wall’s layer of mucus, causing Pepsin to digest the stomach lining.

They can be caused by many factors (too much gastric juice, or too much nervous exertion or stimulation which can cause an over-secretion of gastric juices), but their number one cause are bacterial infections (I.e., Helicobacter pylori), which impair the cell’s ability to produce mucus. Most of these can be cured with antibiotics.

Pyloric Sphincter

Controls the emptying of the stomach into the first part of the Small Intestine; located at the bottom of the Stomach.

Small Intestine

Organ about 6 meters long (20 feet), compared to it’s counterpart which is only 1.5 meters long (around 5 feet). It is where most digestion and absorption of nutrients takes place, and it is divided into three zones: the Duodenum, Jejunum, and Ilium.

Duodenum

Makes up the first 25 cm of the small intestine, and plays a major role in digestion. It is here where the secretions sent from the Liver and the Pancreas break down Fats and Peptides. Meanwhile, secretions from this part itself also break down other nutrients.

Bile

Produced by the liver, and is sent to the Duodenum via the Common Bile Duct from the Gallbladder (where this is stored); a thick green liquid, which contains emulsifying agents called Bile Salts, which break down Fat into Fat Droplets.

Common Bile Duct

Sends bile to the Duodenum from the Gallbladder, where it is initially stored.

Gallbladder

Where Bile is stored.

Bile Salts

An emulsifying agent found in Bile; breaks down Fat into Fat Droplets.

Pancreas

Secretes Pancreatic Juice, and sends it to the Duodenum through the Pancreatic Duct.

Pancreatic Duct

How the Pancreas sends Pancreatic Juice into the Duodenum.

Pancreatic Juice

The secretion of the Pancreas. Contains Sodium Bicarbonate, which makes it highly alkaline (pH ~8.5). This neutralizes Acid Chyme and makes the Small Intestine basic. Contains many hydrolytic enzymes, including Pancreatic Amylase, Trypsin, and Lipase.

Pancreatic Amylase

Contained in the Pancreatic Juice; digests Starch to Maltose.

Trypsin

Contained in the Pancreatic Juice; digests Protein to Peptides.

Lipase

Contained in the Pancreatic Juice; digests Fat Droplets into Glycerol and Fatty Acids.

Interstitial Glands

Line the walls of the Duodenum and Small Intestine; produce juices containing enzymes that finish the digestion of Protein and Starch.

Villi (Villus)

Finger-like projections that line the small intestine, making it’s lining long and convoluted. The lining of each is made of columnar epithelial cells, which have microvilli across which nutrients are absorbed.

Microvilli

Folds of cell membrane across which nutrients are absorbed.

Lacteal

Blood vessels and lymph vessels contained in each Microvilli. This structure increases the surface area of the Small Intestine, which allows for absorption to take place across the wall of each villus. This can happen through both Passive and Active Transport; Active requires ATP.

Capillary Network

Sugars and Amino Acids enter the blood through the ___________.

Hepatic Portal Vein

The merged form of the blood vessels from the Villi in the Small Intestine; leads to the Liver.

Liver

A critically important organ in digestion and homeostasis, and has many functions.

Colon

The longest part of the Large Intestine, connected to the Small Intestine on on end and the Anus on the other.

Rectum

The last 20 CM of the Colon; the Anus forms its opening.

Anus

The opening of the Rectum.

Feces

Indigestible food matter; also contains bile pigments, heavy metals, and billions of E.coli bacteria. These bacteria can break down some indigestible food, and in the process, produce some vitamins, Amino Acids, and other growth factors.

Hormones of the Digestive System

The presence of food in the digestive system triggers the digestive glands to secrete their enzymes. Hormones control the secretion of specific digestive juices. They are: Gastrin, Secretin, CCK, and GIP.

Gastrin

A hormone released by the upper part of the Stomach, in response to Protein in the stomach. Acts on the secreting cells at the top of the stomach, causes the secretion of Gastric Juices.

Secretin

A hormone released by the Small Intestine, in response to the influx of Acid Chyme into the Small Intestine from the Stomach. Acts on the Pancreas, causes the Pancreas to release Sodium Bicarbonate and Pancreatic Enzymes.

Cholecystokinin (CCK)

A hormone released by the Small Intestine, in response to the influx of Acid Chyme into the Small Intestine from the Stomach. Acts on the Pancreas and Liver, causes the Liver to secrete Bile and the Pancreas to secrete Pancreatic Juices.

Enterogastrone / Gastric Inhibitory Peptide (GIP)

A hormone released by the Small Intestine, in response to the influx of Acid Chyme into the Duodenum that is rich in Fats. Acts on the Stomach, inhibits Stomach Peristalsis and Acid Secretion (opposes Gastrin).

The Steps of Control of Digestive Gland Secretion

1. When food is eaten, Sensory Cells in the stomach detect the presence of Peptides. Other sensory receptors detect that the Stomach is distending (I.e., stretching). This causes other Stomach cells to release Gastrin into the blood.

2. Gastrin travels the blood and finally reaches other cells in the Stomach that produce Gastric Juices (which takes about 1 minute), and stimulates the release of Gastric Juices.

3. Most digestion of food occurs in the Duodenum. The Acid Chyme seeps in from the Stomach and is first neutralized. Secretin mediates the neutralization by stimulating the release of Sodium Bicarbonate by the Pancreas.

4. The presence of Amino Acids or Fatty Acids in the Duodenum also triggers the release of Cholecystokinin (CCK) which stimulates the release of digestive enzymes by the Pancreas and Bile by the Gallbladder.

5. A fourth hormone, Enterogastrone / Gastric Inhibitory Peptide (GIP), slows the process of digestion by inhibiting Stomach peristalsis and acid secretion when Acid Chyme that is rich in Fats (which require additional digestion time) enters the Duodenum.

Nutrition

The study of food and its relationship to good health. An essential component of maintaining one’s health is ensuring that the proper amounts of the right foods are eaten.

Vitamins

Organic compounds that the body cannot produce. They must be present in the diet (although only required in very small amounts). The best source of them is fresh fruits and vegetables in a well-balanced diet.

Vitamin Supplements

In moderation, these have not been clearly established as being either harmful or significantly beneficial to the body.

Fat-Soluble Vitamins

Mega-doses of these should never be taken, as they can build up in the body.

Vitamin D

Usually manufactured naturally by the skin upon exposure to sunlight. A deficiency in this Vitamin leads to Rickets (bowing of the Legs).

Vitamin C

Found in various fruits and vegetables, especially citrus fruits. A deficiency in this Vitamin leads to Scurvy.

Riboflavin (Vitamin B2)

Found in plant and animal based foods, including meat, eggs, and milk. A deficiency in this Vitamin causes fissures of the lips (Cheilosis).

Niacin (Vitamin B3)

Commonly found in various meats and grains, including red meat, poultry, fish, and brown rice. A deficiency of this vitamin causes Dermatitis on areas of skin exposed to light (Pellagra).

Minerals

These are also needed for the body. There are two types: Macronutrients and Micronutrients.

Macronutrients

Gram amounts are needed daily. Examples include Sodium, Magnesium, Phosphorous, Chlorine, Potassium, Calcium.