Digestive SystemChapter 17

• Undernourished – diet deficient in calories• Malnourished – diet is missing one or more

essential nutrients

• 4 classes of essential nutrients: 1. Essential amino acids 2. Essential fatty

acids

3. Vitamins 4. Minerals

Obesity in the US

• % of obese people has doubled in 20 years

30% in US• Another 35% are overweight• 15% of children and adolescents are overweight • Obesity is a factor in over 300,000 deaths/year

Food Processing

• Ingestion – act of eating (1st stage)• Digestion – process of breaking down into

molecules small enough for the body to absorb (2nd stage)

Enzymatic Hydrolysis• Absorption – take-up of small molecules by cells

(3rd stage)• Elimination – of undigested material (4th stage)

Alimentary Canals• Tubular part of the digestive tract from the mouth to the anus

- mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anal canal

- accessory organs of the digestive system; salivary glands, liver, gall bladder, pancreas (these are not a part of the

alimentary canal)

Movements through the alimentary canal

1. Segmentation – alternating contraction and relaxing of smooth muscle

ex: muscular contraction of muscle every 20 secondshttp://www.youtube.com/watch?v=URHBBE3RKEs

2. Peristalsis – a wavelike motion in which a ring of contraction occurs in the wall of the tube

ex: pushes food down the esophagushttp://www.youtube.com/watch?v=l5qacwLIToo

http://www.youtube.com/watch?v=Ri8bBhw9msQ

Layers of the Wall of the Alimentary Canal

1. Mucosa – epithelium, connective tissue, smooth muscle

protection, secretion, absorption

2. Submucosa – loose connective tissue, blood and lymph vessels, nerves

Nourishment of tissues, transports absorbed material

3. Muscular Layer – smooth muscle fibers

Movements of the tube and its contents

4. Serosa – epithelium, connective tissue

Protection, lubrication

Mouth, pharynx and esophagus initiate food processing

Oral Cavity – saliva (mucin, buffers, antibacterial agents)

Digestion of carbohydrates

Bolus

Pharynx – the throat, leads to esophagus

Glottis and epiglottis

Esophagus – peristalsis pushes bolus

Salivary amylase continues digestion of starch

Salivary GlandsSerous cells produce watery fluid with salivary amylase

Mucous cells produce thick liquid called mucus

1. Parotid Glands: largest salivary glands, secrete clear, watery fluid with salivary amylase (Stenson’s duct)

2.Submandibular Glands: floor of mouth, ducts open near lingual frenulum, secrete serous and mucus fluids (Wharton’s duct)

3.Sublingual Glands: inferior to tongue, produce thick, stringy mucus (Rivinus’s duct)

The Teeth

• 20 primary (deciduous)

• 32 secondary (permanent)

• Hardest structures in body

• 2 portions – crown and root

• Enamel covers crown

• Cementum (bone-like material) and periodontal ligament surrounds root

The Mouth

Tongue

Lingual frenulum

Uvula

Palate

Pharynx

• Connects nasal and oral cavity with larynx and esophagus

• 3 parts:– Nasopharynx– Oropharynx– Laryngopharynx

Esophagus

• Passageway for food from the pharynx to the stomach

• Penetrates the diaphragm through the esophageal hiatus

• Esophageal sphincter (cardiac sphincter)• Hiatal Hernia – stomach protruding through

weakened area in diaphragm and the esophageal sphincter

The Stomach

Parts: Cardia, Fundus, Body, Pyloric AntrumContents mixed every 20 seconds – an acid chyme is formed.

Hunger pains result when an empty stomach churns• Openings at both ends - Cardiac sphincter (esophagus to

stomach) and pyloric sphincter (stomach to small intestine)• Acid chyme is produced• Stomach wall not adapted for absorption

Gastric Secretions

Mucous Membrane – inner lining with many gastric glands

3 cell types:

mucous cell

mucous

chief cell

digestive enzymes

parietal cell

HCl

Gastric Juice – pepsinogen, pepsin,

HCl, mucus, intrinsic factor

Gastric Secretion1. Cephalic Phase (30% - 50%)

sight, smell, taste, and thought of food triggers gastric

juice secretion

2. Gastric Phase (40% - 50%)

Food in stomach

Gastrin released gastric juice released

pH approaches 1.5 gastrin secretion stops

HCl is released

3. Intestinal Phase (5%)Begins when food leaves stomach

Intestinal gastrin released increases gastric juice secretion

Fats and proteins in intestine stimulate cholecystokinin decreases gastric motility. Fats also increase intestinal somatostatin inhibits gastric juice

• ALKALINE TIDE

1. Stomach secretes HCl

2. Gets H+ from blood

3. Bicarbonate released into blood

4. Blood conc. of bicarbonate increases

5. Urine excretes excess bicarbonate

• ENTEROGASTRIC REFLEX

Entero = small intestine

Gastric = stomach

- Food in duodenum stretches walls

Reflex:

- decreased peristalsis in stomach

- intestinal filling slows

Regulates rate at which chyme leaves the stomach

Small Intestine

• Major organ of digestion and absorption• 20 feet in length (5.5 – 6.0 meters)• 3 regions:

1. Duodenum – shortest section

2. Jejunum – 2/5 of intestine

3. Ileum

Mesentery – fold of the peritoneum

Greater Omentum – a drap over the stomach and small intestine

3 Main Functions of Small Intestine

1. Completes digestion

2. Absorbs digestive products

3. Transports remaining residue to Large Intestine

Structure of the Small Intestine

• Intestinal villi – most numerous in duodenum and proximal jejunum

• Microvilli – brush border

• Goblet cells and Brunner’s Glands secrete mucous

• Cell lining is replaced every 3-6 days through mitosis – Cellular Turnover

- Feces is 25% dead intestinal cells

• Plicae Circulares – circular folds of the mucosa (helps increase surface area)

Structure of Intestinal Wall

•

Intestinal Enzymes

• Peptidases

• Sucrase, Maltase, Lactase

• Intestinal Lipase

• Enterokinase

Large Intestine

• Reabsorption of water – 90% of water that enters alimentary canal (along with small intestine), preparation of feces, and bacteria that produce Vitamin K, biotin, folic acid, and methane

• 12 – 24 hours to travel length• Rich flora of mostly harmless bacteria (E. coli)• Ileocecal valve prevents movement back into

small intestine• Terminal portion is the rectum – waste exits the

anal sphincter through voluntary control

Parts of Large Intestine

1. Cecum – beginning, pouchlike structure, hangs inferior to ileocecal valve

appendix – no digestive function2. Colon: - ascending, Transverse, Descending, Sigmoid colon

3. Rectum

4. Anal Canal

• Wall lacks villi and plicae circularis

• Teniae coli – 3 distinct bands of muscle fibers which exert tension and create a series of pouches (haustra)

• No digestive functions

• Has Goblet cells – mucous secretions

• Absorption is limited to water and electrolytes

• Intestinal flora – break down some cellulose, and help produce vitamins such as K, B12, thiamine and riboflavin

• Feces – water, electrolytes, mucus, and bacteria. Bile gives its color

The Pancreas

• Pancreatic acinar cells form clusters called acini – produce pancreatic juice

• Pancreatic duct – extends length of pancreas into duodenum

• Hepatopancreatic ampulla (ampulla of Vater) – pancreatic and bile ducts

• Hepatopancreatic sphincter (sphincter of Oddi) – band of smooth muscle that surrounds the ampulla

Pancreatic Juice

• Enzymes that digest carbs, fats, proteins, and nucleic acids• Pancreatic amylase• Pancreatic Lipase• Trypsin• Chymotrypsin• Carboxypeptidase• Nucleases

• A peptide hormone – SECRETIN – stimulates pancreas to secrete bicarbonate when acid chyme enters the stomach. Secretin is released from duodenal mucous membrane

• Cholecystokinin stimulates pancreas to release pancreatic juice

The Liver• Largest internal organ• 4 lobes• Falciform Ligament – separates right

and left lobes• Lobes are separated into hepatic

lobules – the functional unit of the liver

- hepatic cells around a central vein

- hepatic sinusoids surround cells

- hepatic portal vein - carries blood from digestive tract to liver

- hepatic artery carries oxygenated blood to liver

• Kupffer cells – line hepatic sinusoids and phagocytize

Liver Functions

• Carbohydrate metabolism – responds to insulin and glucagon

• Lipid metabolism – oxidizes fatty acids

• Synthesizes lipoproteins, phospholipds, and cholesterol

• Protein metabolism – deaminate amino acids, forming urea

• Storage of glycogen, iron, vitamins A,D, B12

• Destruction of damages RBC’s

• Removal of toxic substances from blood

Gall Bladder

• Connected to cystic duct which joins the common hepatic duct to form bile duct

• Stores bile between meals, concentrates bile by reabsorbing water, and releases bile into duodenum

• Bile duct – forms from union of common hepatic duct and cystic duct

• Bile salts break fat globules into droplets – emulsification

• Lipases are then able to digest fats more effectively

• Bile also helps in the absorption of fat soluble vitamins

Digestion in Herbivores

• Must digest cellulose, but mammals don’t produce cellulase.

• Large teeth grind the cellulose

• 4-chambered stomach that contains protozoans and bacteria that breakdown cellulose

• Ruminants – mammals (order Artiodactyla) that digest plant-based food. Cattle, goats, sheep, giraffes, deer, etc.

Energy Content of Food

• Fat = 9 kcal/gram

• Protein = 4 kcal/gram

• Carbohydrates = 4 kcal/gram