Chapter 26 The Digestive System

Mouth

(oral cavity, buccal cavity) takes in food, where digestion begins (the cephalic phase of digestion).

Villi

Absorption of approximately 85% of nutrients used by the body occurs across the ________, small finger-like projections on the mucosa of the small intestine, into the capillary network.

liver, gallbladder, pancreas, and peritoneum

Accessory organs of the digestive system:

To break food into smaller particles, accomplished through mastication, chewing.

Chief function of teeth

•Physical breakdown (mastication) •Churning •Diluting •Chemical breakdown •Dissolving

Digestion is accomplished by:

•Activates the gallbladder to release bile. •Stimulates pancreas to secrete pancreatic juice. •Assists in inhibition of digestive processes in the stomach when appropriate.

Functions of Cholecystokinin

Provides absorption of nutrients, mainly from small intestine into capillaries

Functions of the Digestive System on Absorption

Breaks down food into smaller particles (mechanical digestion) Converts food into substances that can be absorbed (chemical digestion) Moves food materials through the gastrointestinal tract (peristalsis) Stores nutrients until needed

Functions of the Digestive System on Food Processing and Storage

Manufactures enzymes, hydrochloric acid, intrinsic factor, mucus, and other materials to assist in digestion Manufactures regulatory hormones in stomach Manufactures vitamin K and some B-complex vitamins in large intestine

Functions of the Digestive System on Manufacture

Reabsorbs water for reuse by the body Reabsorbs minerals and vitamins Forms feces from remaining waste products Produces defecation

Functions of the Digestive System on Reabsorption and Elimination

In addition to speech, it senses the temperature and texture of food, mixes food with saliva, and moves food into position to be chewed.

Functions of tongue

4 to 6 hours

How many hours after food has been in the small intestine before it passes into the large intestine?

Deciduous ("falling out," "baby teeth") Permanent or adult set

Humans have two sets of teeth:

This reverse peristalsis, combined with contraction of abdominal muscles and the diaphragm, forces food back through the esophagus and out through the mouth, vomiting (emesis).

If the stomach is irritated or too full, the direction of peristalsis waves may reverse and force material back into the lower end of the esophagus.

Pyloric stenosis (narrowing of the pyloric sphincter) and can be life threatening.

In infants, projectile vomiting can be a sign of?

The person is said to be "tongue-tied," a situation that can easily be surgically corrected.

In some cases, the frenulum is short or too tightly attached, making speech difficult;

Chyme

In stomach, foods mix with mucus and gastric acid, as well as pepsin and other digestive enzymes (about 3 quarts--2.8 L a day). These substances churn until they are in a semi-liquid, milky, form called _______________.

Contractions of the pharynx push food into the muscular esophagus. The smooth muscles pass food through the entire GI tube by waves of contractions, peristalsis.

Initial swallowing of food is voluntary, but when the food bolus enters the pharynx, swallowing becomes involuntary, as the medulla's swallowing center takes over.

cecum, colon, rectum, anus

Large intestine does not coil, but lies in folds, and is divided into areas:

Serous membrane (outer wall) Muscles - longitudinal, horizontal, oblique Submucosa - containing nerves, blood/lymph vessels Mucosa ( mucous membrane) - with gastric glands that secrete mucus, HCl, hormones, and precursors to digestive enzymes.

Layers of the stomach wall:

Storage and release of bile, as needed in the small intestine for fat emulsification. It also concentrates bile by absorbing water and salts.

Major function of the gallbladder

crown, neck and root

Parts of tooth

Soft palate and uvula

Prevent foods from entering nasal cavities above the mouth.

Digestion, absorption, elimination

Primary function of the digestive system

➢The wave-like contractions of circular muscles narrow the lumen of the intestine, squeezing food onward. ➢When the longitudinal muscles contract, the circular muscles relax (antagonistic), increasing the size of the lumen allowing food to pass. These rythmic waves constitute intestinal peristalsis and segmentation , which helps break up food particles.

Process of digestion in small intestine

➢Peristalsis of stomach muscles moves food toward the pyloric outlet. ➢The pyloric sphincter at the lower opening of the stomach contracts to keep food in the stomach until it is thoroughly mixed. ➢It then relaxes so peristalsis waves can squirt food in small amounts into the small intestine.

Process of digestion in stomach

speech and taste

Saliva also assists with?

Ptyalin (salivary amylase), water, mucous, and salts.

Saliva contains?

Pancreatic amylase: starch/carbohydrates Trypsin: protein Pancreatic lipase: fats--lipids (into triglycerides)

The acinar cells secrete three main enzymes which assist in digestion of specific nutrients:

duodenum, jejunum (midsection), ileum (terminal section)

The areas of the small intestine

mechanical and chemical

The body performs two types of digestion:

Alimentary canal

The efficient food-processing machine responsible for digestion and absorption, the digestive tract, is also called_______________, gastrointestinal (GI) tract, or GI system.

Small intestine

The intestinal phase of digestion begins with the __________________, the longest portion of the digestive tract. it is approximately 20 ft (6.1 m) long and 1.5 in (3.81 cm) in diameter (about 18ft longer than the large intestine)

•Secretion of bile •Absorption of bilirubin after destruction of old RBCs •Detoxification of blood (removal of toxins or poisons) •Storage of fat-soluble vitamins (A, D, E, K) •Formation of vitamin A and some nonessential amino acids; storage of vitamin B complex and iron •Formation of plasma proteins (albumin, prothrombin, globulins) •Synthesis of urea, a waste product from protein anabolism •Storage of glucose as glycogen (helps regulate glucose levels) •Sythesis of clotting factors (fibrinogen; prothrombin; factors V, VII, IX, X) •Formation of triglycerides and cholesterol Secretion of heparin (anticoagulant) •Synthesis of immunoglobulins •Breaking down of fats (lipids) •Metabolism of carbohydrates; storage of fats and carbohydrates •Regulation of amino acids •Production of body heat •Storage of minerals •Production of lymph

The liver plays such an important part in overall bodily function that severe disease or injury is life-threatening. Only the brain is capable of more functions than the liver. Some of the liver's major functions include:

To receive food via ingestion ( "to take in") Prepare food for digestion Begin digestion of starch/carbohydrates

The mouth's chief digestive functions:

The action of ptyalin, saliva begins to break down starch into smaller sugar molecules and helps reduce friction when chewing.

The nervous system controls the secretion of saliva (salivation) through?

mouth → pharynx → esophagus → (cardiac sphincter) → stomach → (pyloric sphincter) → small intestine (duodenum) → jejunum → (ileocecal valve) → large intestine (cecum) → colon: ascending, transverse, descending, sigmoid) → rectum → anus

The pathway of food through the body:

•Ingestion - taking in of food •Breakdown - mechanical and chemical conversion of food into usable molecules •Absorption - transfer of nutrients into circulatory/lymphatic systems for use by the body •Egestion - elimination of waste products by defecation

The stages of digestion are:

Intrinsic factor

The stomach's parietal cells also secrete this, essential for life, because it is required for vitamin B12 absorption, needed to develop RBCs in bone marrow.

Incisors (sharp, flat) - front teeth → cut and tear food Canines or cuspids (pointed) - side teeth → hold, pierce and tear food Premolars or bicuspids and Molars or tricuspids → crush and grind food Third molars or "wisdom teeth" - located far back in the mouth

The teeth are named and located as follows:

Catabolism (destruction, catabolic phase) Anabolism (construction, anabolic phase)

The two major categories of metabolism:

Ascending (going up) colon, Transverse (going across) colon, Descending (going down) colon

Three areas of the large intestine:

•Carbohydrate to monosaccharides (simple sugars): glucose, galactose, fructose •Protein to amino acids (and some dipeptides) •Fat to fatty acids (lipids) and glycerol

To be absorbed, foods must be broken into their simplest form:

The outer layer - runs up and down (longitudinal) The inner layer - lies in concentric circles provides alternating contraction and relaxation, resulting in peristalsis.

Two layers of smooth muscles facilitate peristalsis:

One is thin and watery - it wet food to facilitate swallowing A thicker, mucous secretion containing mucin - lubricates and causes food particles to stick together to form a bolus (ball or lump) of food

Two types of saliva

Esophageal or gastric ulcer and, in more serious cases, bleeding, stricture, or precancerous conditions. GERD may be successfully treated with medications and lifestyle changes (including weight loss and smoking cessation).

Untreated gastroesophageal reflux disease (GERD) can lead to?

Pernicious anemia

Vitamin B12 deficiency

Lifting and pushing the bolus of food, mixed with saliva, into the pharynx.

Voluntary movement of the tongue begins the swallowing process (deglutition), by?

carbon dioxide, water, and energy

What are the end products of catabolism resulting from cellular respiration?

synthesis of glycogen, triglycerides, or proteins

What are the examples of anabolism?

The stomach contents can re-enter the esophagus, causing a severe burning sensation, heartburn or acid reflux, due to the acidic stomach contents.

What happened if the LES does not close adequately?

Food can be prevented from entering the stomach, a condition known as achalasia.

What happened if the LES does not not relax appropriately?

The impulse tends to die and constipation often occurs. (This can become life-threatening if it results in bowel obstruction.)

What happens if the defecation reflex is ignored routinely?

A root canal procedure or removal of tooth (extraction)

What is required when tooth decay is so advanced that it permanently damages the pulp?

To produce pancreatic juice, which is necessary for life, because it is vital in digestion. It is produced by the acinar cells.

What is the exocrine function of pancreas?

bile production, which aids in fat digestion and absorption of fat and fat-soluble vitamins from the small intestine.

What is the liver's major digestive function?

To serve only as a passageway; no digestion takes place here--food passes through in 5 to 10 seconds.

What is the role of the esophagus in digestion?

Because it contains lysozyme (bacteriocidal enzymes) and immunoglobulins (IgA).

Why saliva helps prevent oral infections?

Because fecal material cannot always drain out.

Why the appendix frequently becomes infected?

Colon

a continuous tube, the next and longest portion of the large intestine.

Bile

a greenish brown liquid manufactured by the liver and stored in gallbladder, pours in through the bile duct to emulsify fats in preparation for further digestive action.

Cholecystokinin (CCK)

a hormone, stimulates the pancreas to secrete pancreatic juice and the gallbladder to contract, resulting in the release of bile, which is secreted in the liver and acts to digest fats--lipids. It is secreted by the duodenum and jejunum in response to the presence of fat in the duodenum.

Appendix

a small finger-like projection of the cecum is the vermiform known as ______________.

Ileocecal valve

a sphincter-like muscle, located where the large and small intestines meet, acts to prevent back flow of material to the small intestine and also regulates forward flow.

The fundus and body of the stomach

act mostly for storage

Peristalsis

an alternating muscular relaxation and contraction, without which digestion cannot occur. It entails progressive movements that move food onward in the digestive tract in a wavelike motion.

Segmentation

assists in breaking up food particles.

Peritoneal peritoneum

attaches the jejunum and ileum to the posterior abdominal wall, to prevent twisting.

defecation

bowel movement, egestion.

Gastric lipase

breaks down triglycerides in butterfat (found in milk and dairy products)

Micelles

colloid particles which transport digested fat to intestinal villi of absorption.

Transverse colon

crosses to the left side in the upper part of the cavity and the largest and most mobile portion of the colon. Absorb fluid, salts, and vitamins.

Lacteals

dead-end lymph capillaries within each villus that absorb fat-soluble nutrients.

Stomach acid

does not break down food particles. it provides the proper acid-base environment, allowing digestive enzymes to act on food. It prepares proteins for digestion and also kills unwanted microorganisms ingested with food.

Descending colon

goes down the left side into the pelvis. Holds resulting wastes.

Frenulum

helps attach the tongue to the floor of the mouth.

Peritoneum

is a large sheet of serous membrane covering and protecting many abdominal organs. It also secretes the thin peritoneal fluid, providing lubrication between its visceral and parietal layers.

Gallbladder

is a muscular pear-shaped sac 3 to 4 in long located under the liver. It is considered to be an enlargement of the cystic duct through which it drains.

Pepsinogen

is a precursor of pepsin, the enzyme needed to breakdown proteins.

Cellular respiration

is a series of catabolic reactions.

Tongue (lingua)

is a tough skeletal muscle, covered with smooth mucous membrane attached to four bones: the mandible, two temporal bones, and the hyoid, believed to be the only muscle in the body only attached at one end.

Metabolism

is defined as "biotransformation," the total of all physical/chemical changes occurring within the body to maintain life.

Spleen

is the body's largest lymphoid organ, lying near the liver. It produces antibodies and filters out damaged RBCs.

Chemical digestion

is the breakdown of chemical bonds in food, with the addition of enzymes, acids, and water. Some digestive processes begin in the mouth, pharynx, and stomach, but most digestion occurs in the duodenum.

Catabolism

is the breakdown of larger molecules into smaller ones, releasing energy.

Mechanical digestion

is the physical breakdown of food caused by chewing and the movement of food in the digestive tract. Breaking food into smaller pieces exposes more food surface area to the effects of enzymes, acids, and other chemicals.

pylorus

is the primary site of stomach digestion

Anabolism

is the synthesis of simpler substances into new, organized substances to be used by body cells.

Physiologic inferior esophageal sphincter

just above the Z-Line, food and liquid may be stopped here momentarily, to allow the stomach to prepare for the influx of food substances.

Lower Esophageal Sphincter (LES)

lies between the esophagus and stomach that prevents food from backing up into the esophagus.

Stomach (gaster)

located in the upper left side of the abdominal cavity, functions as a reservoir and "food blender."

Mucus, secreted by Brunner's glands

lubricates and protects the intestinal lining from the highly acidic chyme and digestive enzymes.

Jejunum

middle portion of the small intestine derived from Latin word meaning "fasting intestine", because it is almost always empty.

Basal metabolism

refers to the minimum amount of energy (calories) the body requires to maintain baseline vegetative vital functions, such as breathing, body temperature, and circulation.

Cholecystectomy

removal of the gallbladder, is a common surgical procedure, after which, other structures, particularly the liver, assume its functions.

Intestinal glands

secrete enzymes, proteins that act as catalysis, promoting and speeding up chemical reactions.

Parietal cells

secrete hydrochloric acid (HCl), which functions to activate pepsinogen and kill most stomach microorganisms. When activated, pepsinogen changes into the enzymes pepsin, which begins to break down proteins.

Chief cells

secrete pepsinogen and gastric lipase.

Pancreas

secretes hormones insulin, glucagon, and somatostatin into the bloodstream.

ATP

stores energy and uses it to drive all related cellular processes, including transport of ions and molecules across cell membranes, contraction of muscle fibers, and synthesis of many other compounds.

Liver

the body's largest glandular organ, lies just below the diaphragm in the URQ of the abdominal cavity, behind the lesser momentum, a fold of the peritoneum. Vital for metabolism.

Duodenum

the first portion of the small intestine in C-shaped. It contains specialized cells and glands to secrete mucus, to protect the small intestine from chyme.

Sigmoid colon

the last portion of the colon, follows the curve of the sacrum and coccyx and ends at the rectum. It stores feces until defamation occurs via the anus.

Dysphagia

the medical term for difficulty in swallowing.

biliary apparatus

the system of passageway for bile transport from the liver to the gallbladder to the intestine is complex.

Ascending colon

travels up the right side of the abdominal cavity and is narrower than the cecum. Absorb fluid, salts, and vitamins.

Rectal examination

yields information about the prostate and seminal glands in males, cervix in females, and other lower pelvic internal structures.