survey of anatomy & physiology chap 15

The Gastrointestinal System:

Fuel for the Trip

15

Gastrointestinal System

• Takes in (ingests) raw material

• Breaks it down (digests) both physically and chemically to usable elements

• Absorbs those elements• Eliminates what isn't

usable

Gastrointestinal System

Alimentary Canal

• Digestive tract, often called alimentary tract or canal, is muscular tube that contains organs of digestion

• Tube begins with mouth and ends at anus

Alimentary Canal

In Between:

Digestive System Functions

Digestive System Functions

Figure 15-1The digestive system.

Oral Cavity

• Mouth (oral cavity) is mucous-lined opening; also called buccal cavity

• Lips (labia) act as door to cavity

• Hard and soft palates create roof

Oral Cavity-Tongue is Border

• Tongue acts as floor

• Tongue's base and uvula act as boundary between oral cavity and pharynx

Oral Cavity-Uvula, Teeth & Tonsils

• Uvula aids in swallowing, directing food toward pharynx and blocking food from entering nose

• Tonsils help in fighting infection as part of lymphatic system

• Teeth for grinding food

Oral CavityOral Cavity

• Sides of cavity created by cheeks

• Mouth receives, tastes, mechanically breaks down, and begins process of chemical breakdown of food, adding saliva

Salivary Glands Begin Breakdown of FoodSalivary Glands Begin Breakdown of Food

Figure 15-2The mouth and oral cavity.

TongueTongue

• Tongue is muscle that provides taste stimuli to brain, determines temperature, manipulates food, aids in swallowing

• As tongue moves food around in oral cavity, saliva added to moisten and soften it, while teeth crush food

TongueTongue

• Tongue pushes food into ball-like mass, called bolus, so it may be swallowed, passed to pharynx

Tongue-The FrenulumTongue-The Frenulum

• Lingual frenulum, membrane under tongue, keeps you from swallowing your tongue and aids in speaking

Salivary Glands-3 Pairs

Salivary Glands-3 Pairs

• Controlled by autonomic nervous system• Found slightly inferior

and anterior to each ear; these swell when you get mumps

Large Parotid Salivary GlandLarge Parotid Salivary Gland

Salivary Glands-3 Pairs

• Sublingual salivary glands: located under tongue

• Submandibular salivary glands: on both sides along inner surfaces of mandible, or lower jaw

Sublingual and Submandibular Salivary GlandSublingual and Submandibular Salivary Gland

Salivary Glands

• Salivary glands produce 1–1.5 liters of saliva daily

• Saliva is 99.4% water; contains antibodies, buffers, ions, waste products, and enzymes

*Sight of food can stimulate secretion of saliva**Sight of food can stimulate secretion of saliva*

Salivary Glands-Enzymes

• Enzymes are biological catalysts to speed up chemical reactions• Salivary amylase:

speeds chemical activity of breaking down carbohydrates

Salivary Amylase breaks down CarbohydratesSalivary Amylase breaks down Carbohydrates

Salivary Glands-Enzymes

• Enzymes are biological catalysts to speed up chemical reactions• Ptyalin: specific

salivary amylase that converts starches to simple sugars

Ptyalin converts starches to simple sugarsPtyalin converts starches to simple sugars

Saliva Cleans Teeth

• After eating, saliva cleans oral surfaces, reducing amount of bacteria that grows in mouth

Less bacteria in the mouthLess bacteria in the mouth

Figure 15-3The salivary glands.

Pharynx-3 Parts

• Nasopharynx: primarily part of respiratory system,

• Oropharynx and laryngopharynx: act as passageway for food, water, and air

• Epiglottis: covers trachea to prevent food from entering lungs, forcing food into opening for esophagus

Esophagus

• Approximately ten inches long; connected to stomach

• Extends from pharynx, through thoracic cavity, and diaphragm, connecting to stomach in peritoneal cavity

Esophagus-Peristalsis

• Rhythmic contractions, called peristalsis, pushes food down esophagus

Esophagus

• Pharyngo esophageal sphincter, relaxes to open esophagus so food can enter

• Walls lined with stratified squamous epithelium that secrete mucus to make walls slippery

Esophagus

• At entrance to stomach is lower esophageal sphincter, or cardiac sphincter, opening door to stomach and closing to prevent acidic gastric juices from splashing into esophagus causing heartburn

Condition called GERD caused by incompetent sphincter

Condition called GERD caused by incompetent sphincter

Stomach

• Approximately ten inches long with diameter dependent on how much just eaten

• Can hold up to four liters when filled

• Rugae, or folds, help stomach expand and contract

Located under the diaphragm, mid to left upper quadrant

Located under the diaphragm, mid to left upper quadrant

Stomach-4 Functions

Stomach

• Liquids pass through fairly quickly

• Carbohydrates move through quickly

• Proteins take more time to pass through

• Fats take longest, usually between 4 to 6 hours

Movement of material through stomach

Movement of material through stomach

Stomach

• FOUR REGIONS• Near heart is cardiac

region, surrounding lower esophageal sphincter

• Fundus, lateral and slightly superior to cardiac region, temporarily holds food as it enters stomach

Stomach

• FOUR REGIONS• Body is mid portion of

stomach• Funnel-shaped, terminal

end of stomach called pylorus; most of work of stomach performed here; where food passes through pyloric sphincter into small intestine

Stomach

• Muscular action works like cement mixer, achieved by three layers of muscles: longitudinal layer, circular layer, and oblique layer

Food “churned up” by muscles of the stomachFood “churned up” by muscles of the stomach

Stomach

• Churns food as it mixes with gastric juices excreted by gastric glands in gastric pits of columnar epithelial lining of stomach

Stomach

• Works food toward pyloric sphincter through peristaltic activity of muscles

• Both chemical and physical digestion occurs here

Stomach-Gastric Juices

Stomach-Gastric Juices

• Pepsin, chief digestive enzyme

• Pepsin breaks down protein; HCl breaks down connective tissue

Stomach-Gastric Juices

• HCl has pH of 1.5 to 2; effective at killing pathogens

• Mucous cells generate thick layer of mucus shielding stomach from effects of HCl

Stomach-Vitamin 12 Absorbed

• Stomach also secretes intrinsic factor, allowing vitamin B12 to be absorbed

Table 15-1 Gastric Glands and Their Functions

Stomach

• Activity controlled by parasympathetic nervous system, particularly vagus nerve

• Vagus nerve stimulation increases motility and secretory rates of gastric glands

Gastric Juice Production

Three Phases

Gastric Juice Production

Cephalic phase

Sensory stimulation (sight or smell of food) stimulates parasympathetic nervous system via medulla oblongata, stimulating release of gastrin which travels through bloodstream and reaches stomach, stimulating gastric gland activity

Gastric Juice Production

Gastric phase

•Two-thirds of gastric juices secreted as food enters stomach and distends, signaling stomach to secrete more gastric fluid

Gastric Juice Production

Intestinal phase

•Food enters duodenum, distending and sensing acidity, causing intestinal hormones to be released, slowing gastric gland secretions; lasts until bolus leaves duodenum

Figure 15-9Mechanisms of peptic ulcers and GERD

Small Intestine

• Located in central and lower abdomen

• Functions as major organ of digestion; where most of food digested

Small Intestine

• Small in diameter, not length; longest section of alimentary canal; length up to 20 feet and diameter ranging from 4 cm where it connects to stomach and 2.5 cm where it meets large intestine

Figure 15-10The small intestine.

Walls secrete digestive enzymes, important for final stages of chemical digestion, and two hormones that stimulate pancreas and gallbladder to act, and control stomach activity

Small Intestine-Villi

• 80% of absorption of usable nutrients occurs when chyme comes in contact with mucosal walls; amino acids, fatty acids, simple sugars, vitamins, and water are all absorbed here into bloodstream and cells

Villi in small intestine increase surface area for absorption

Villi in small intestine increase surface area for absorption

Small Intestine

• Remaining 20% absorbed in stomach

• Any residue not utilized in small intestine sent to large intestine for removal from body

Small Intestine-3 Sections

Duodenum:, located near head of pancreas; Jejunum: middle section, 2.5 m longIleum: terminal end, 6–12 feet long; attaches to large intestine at ileocecal valve

Small Intestine-Pancreas & Gallbladder

• Pancreas and gallbladder add secretions: bile from gallbladder

• Pancreatic juice from pancreas

• Bile emulsifies fat, making fat disperse in water

Small Intestine

• Mechanical and• Chemical irritation

of acidic chyme, plus• Distention of

intestinal walls, creates localized reflex action that causes release of enzymes and two hormones

Small Intestine-2 Hormones

• Secretin from duodenum stimulates secretion of enzymes and sodium bicarbonate from pancreas, which neutralizes acidic chyme

• Cholecystokinin (CCK) secreted by duodenum stimulates gallbladder activity

Table 15-2 Hormones in the Digestive Process

Small Intestine

• Muscular action occurs in two ways• Segmentation causes mixing

of chyme and digestive juices like cement mixer

• Peristalsis moves food toward large intestine

Chyme

Small Intestine

• Digestive enzymes needed to complete chemical digestion are produced by exocrine cells

Acinar cells secrete digestive enzymes in the small intestineAcinar cells secrete digestive enzymes in the small intestine

Small Intestine

• Capillaries absorb and transport sugars (result of carbohydrate digestion) and amino acids (result of protein digestion) to liver for further processing before being sent throughout body

Nutrients travel to Liver before going to the bodyNutrients travel to Liver before going to the body

Small Intestine

• Glycerol and fatty acids (obtained from fat digestion) are now a white, milky substance called chyle

• Chyle goes directly into lymphatic system for distribution into bloodstream

Take a Break

Large Intestine

• Beginning at junction of small intestine, ileocecal orifice, and extending to anus is large intestine, bordering small intestine

Large Intestine

Figure 15-12The large intestine.

Approximately five feet long and 2.5 inches in diameter; divided into three main regions: cecum, colon, and rectumPouch-shaped structure, cecum, receives undigested food and water from ileum

Large Intestine

• Some of water used in digestion and electrolytes reabsorbed in cecum and ascending colon; water absorbed is small amount, but crucial to maintaining proper fluid balance

Appendix

• Attached to

cecum• Three inches

long, slender, hollow, dead-end tube lined with lymphatic tissue

Appendix

• Reservoir for

useful bacteria to replace bacteria lost in intestines as result of diseases

Appendix

• If becomes

blocked or inflamed, causes appendicitis and must be treated with either antibiotics or surgical removal

Large Intestine

• Four sections of colon:

• Ascending, • Transverse, • Descending, and • Sigmoid• Ascending colon travels

up right side to level of liver

Large Intestine

• Transverse colon travels across abdomen just below liver and stomach

• Descending colon bends downward near spleen and travels to left side becoming sigmoid colon

Large Intestine

• Sigmoid colon extends to rectum

• Rectum opens to anal canal that leads to anus

• Anus relaxes and opens to allow passage of solid waste (feces)

Large Intestine

• Peristalsis continues in large intestine, but at slower rate

• As slower intermittent waves move fecal matter toward rectum, water is removed, turning it from watery soup to semisolid mass

Rectum

• As rectum fills with feces, defecation reflex occurs, which causes rectal muscles to contract and anal sphincters to relax

Diarrhea/ConstipationDiarrhea/Constipation

• If fecal matter moves through too rapidly, not enough water is removed and diarrhea occurs

• Conversely, if fecal matter remains too long in large intestine, too much water is removed and constipation occurs

Large Intestine

• Bacteria in bowel play two important roles:• Help break down

indigestible materials• Produce B complex

vitamins and most of vitamin K needed for proper blood clotting

Accessory OrgansAccessory Organs

• Besides salivary glands found in mouth, other accessory organs needed for digestion:• Liver• Gallbladder• Pancreas

Liver

• Weighs 1.5 kg, located below diaphragm; largest glandular organ in body, and largest organ in abdomino pelvic cavity

• Organ performs many functions vital to life

Liver

• Divided into large right lobe and smaller left lobe; right side has anterior lobe and two smaller, inferior lobes

Liver-Portal Vein

• Receives about 1.5 quarts of blood every minute from portal vein (carrying blood full of end products of digestion) and hepatic artery (providing oxygen-rich blood)

Figure 15-15The liver.

Liver-Functions

Liver-Functions

Liver-Functions

Liver and Bile Production

• Secretion of hormone secretin stimulates bile production, critical liver digestive function

Liver and Bile Production

• Salts found in bile act like detergent, breaking fat up into tiny droplets; process called emulsification, making work of digestive enzymes easier

Liver and Bile Production

• Bile helps absorb fat from small intestine and transports bilirubin and excess cholesterol to intestine for elimination

Gallbladder Stores Bile

• Bile leaves liver via hepatic duct, travels through cystic duct to gallbladder, and is stored there until needed by small intestine

Gallbladder

• Sac-shaped organ, 3 to 4 inches long, located under liver's right lobe

Gallbladder and Gallstones

• While storing bile absorbs much of its water content, making it 6 to 10 times more concentrated; if too much water reabsorbed, bile salts may solidify into gallstones

Gallbladder and Bile

• Fatty foods in duodenum cause release of CCK

• Release causes smooth muscle walls of gallbladder to contract, squeezing bile into cystic duct, through common bile duct, and into the duodenum

Pancreas

• Plays role in digestion, as well as being endocrine gland

• 6 to 9 inches long, located posterior to stomach, and extends laterally from duodenum to spleen

Secretes insulin from cells in Islets of LangerhansSecretes insulin from cells in Islets of Langerhans

Pancreas

• Exocrine portion secretes buffers and digestive enzymes through pancreatic duct to duodenum

Pancreas

• Buffers needed to neutralize acidity of chyme, to pH ranging from 7.5 to 8.8, saving intestinal walls from damage

Pancreas-Digestive Enzymes

Common Symptoms of Digestive System Disorders

• Generally include one or more of the following:• Vomiting• Diarrhea• Constipation• Abdominal pain

Common Symptoms of Common Symptoms of Digestive System DisordersDigestive System Disorders

• Vomiting• Protective

mechanism, ridding digestive tract of irritant or overload of food that stimulates sensory fibers, sending signal to vomiting center in brain

Common Symptoms of Common Symptoms of Digestive System DisordersDigestive System Disorders

• Vomiting• Motor impulses sent

to diaphragm and abdominal muscles to contract, squeezing sphincter at esophageal opening, and contents are regurgitated

Common Symptoms of Common Symptoms of Digestive System DisordersDigestive System Disorders

• Diarrhea• Fluid contents in small

intestine rushed through large intestine without reabsorbing enough water

• Proper absorption of electrolytes and nutrients prevented; can cause serious problems

Common Symptoms of Common Symptoms of Digestive System DisordersDigestive System Disorders

• Diarrhea• Frequent loose and

watery bowel movements

• Caused by infection, poor diet, toxins, food allergies or irritants, and stress

Common Symptoms of Digestive System Disorders

• Constipation• Opposite of

diarrhea; feces pass too slowly through colon and too much water is reabsorbed; stool becomes hard, dry, difficult to pass

Common Symptoms of Common Symptoms of Digestive System DisordersDigestive System Disorders

• Constipation• May be over

stimulation of musculature of intestine creating more narrow passage for material

Common Symptoms of Digestive System Disorders

• Constipation• May be musculature has

become flaccid or slow as often found in bedridden geriatric patients

Typical “FOS” XrayTypical “FOS” Xray

Common Symptoms of Digestive System Disorders

• Constipation• Dietary changes with

more liquid, more roughage, reestablishment of regular bowel habits, avoidance of stress/tension, moderate exercise can contribute to improving condition

Common Symptoms of Digestive System Disorders

• Constipation• Chronic use of

laxatives and enemas should be avoided; may aggravate existing conditions or create new ones

Common Symptoms of Digestive System Disorders

• Pain• Can be sharp, dull,

localized, diffuse, radiating, occasional, or constant

• Severity of pain does not always indicate severity of disease

Large amount of gas can cause temporary pain until released

Large amount of gas can cause temporary pain until released

Common Symptoms of Digestive System Disorders

• Pain• Stomach cancer may initially present with relatively mild

form of indigestion• Any pain from GI tract should be investigated

Case Study

Review SOAP Note on Gastrointestinal

Disease

Watch video in class (not

available online)