Digestive System (6/19)

Digestive system definition

• absorbs materials for building & replacing body tissues

our only source of chemical energy

Food

Gastrointestinal tract definition & pathway

• continuous tube from mouth to anus

  • Oral cavity—> pharynx—>esophagus—>small intestine—→ large intestine

Accessory organs function in digestive system

• produce secretions that chemically breakdown food

The accessory organs in the digestive system

1. Teeth

2. Tongue

3. Salivary glands

4. Liver

5. Gallbladder

6. Pancreas

6 functions of digestive system

1. Ingestion

2. Secretion

3. Motility (mixing/ propulsion)

4. Digestion

5. Absorption

6. Defecation

Ingestion

• taking in food & liquid

Secretion

• 7L of water, acid, buffers, enzymes

Motility (mixing/ propulsion)

• altering contractions

Digestion

• mechanical grinding & chemical

Absorption

• GI tract (blood or lymph

• Stomach absorbs:

  • Water

  • Ions

  • Fatty acids

  • Alcohol

  • Some drugs

Defecation

• elimination of material

Layers of GI tract

1. Mucosa

2. Submucosa

3. Muscularis

4. Serosa

Mucosa

• inner lining of GI tract

Epithelium of mucosa

• inner most layer, protective function

Lamina propia of mucosa

• connective tissue, contains blood & lymph vessels

  • Contains MALT

Muscularis mucosae

• thin muscle layer that causes folds for increase of surface area

Submucosa

• irregular connective tissue, contains blood & lymph vessels, neurons

Muscularis

• mostly smooth muscle, mixes & propels food thru tract

Serosa

• outer most layer, is serous membrane (adventitia), forms peritoneum

Peritoneum

• serous membrane of abdomen

Peritoneum layers in order

• Parietal peritoneum—>peritoneal cavity—> visceral peritoneum—> retroperitoneal

What are the 5 peritoneal folds?

1. Greater omentum

2. Lesser omentum

3. Falciform ligament

4. Mesentery

5. Mesocolon

Greater omentum

• fatty apron that covers transverse colon & small intestine

  • BEER BELLY

Lesser omentum

• suspends stomach & duodenum from liver, contains lymph nodes

Falciform ligament

• attaches liver to anterior abdominal wall

Mesentery

• connects SMALL intestine to posterior abdominal wall

Mesocolon

• connects LARGE intestine to posterior abdominal wall

Makes up the oral cavity

1. Cheeks

2. Lips

3. Hard palate

4. Soft palate

5. Uvula

major salivary glands

1. Parotid

2. Submandibular

3. Sublingual

Parotid gland & ducts

• inferior & anterior to ears

Submandibular glands & ducts

• beneath base of tongue, posterior to floor of mouth

Sublingual glands & ducts

• superior to submandibular gland

Mastication

• chewing

What saliva is made of

1. Water

2. Ions

3. Salivary amylase

4. Lingual lipase

   • saliva is slightly acidic= 1-1.5L/day

Salivary amylase

• breaks down starch

Lingual lipase

• breaks down triglycerides

Extrinsic tongue muscles function

• in & out motion

Intrinsic tongue muscle function

• speech & swallowing

• Alter shape & support

Modified papillae

• taste buds

  • Sweet, sour, bitter, umami

Teeth

• accessory digestive organs on mandible & maxillae

Crown (of teeth)

• visible portion above gums

Enamel (of teeth)

• outer surface, hardest substance in the body

Dentin (of teeth)

• under enamel, calcified connective tissue

• Gives shape & support

Pulp cavity (of teeth)

• cavity underneath dentin

Pulp (of teeth)

• connective tissue in pulp cavity, contains nerves, blood & lymph vessels

Neck (of tooth)

• narrowed junction between crown & root

Ginvigva (of teeth)

• gums

Root (of teeth)

• embedded in socket

Root canal (of teeth)

• channel for nerves & vessels

Periodontal ligament (of teeth)

• anchors teeth in positions, acts as a shock absorber

Cementum (of teeth)

• bone-like substance that attaches tooth to periodontal ligament

Apical foramen (of tooth)

• opening at base of root canal

Baby teeth overview

• after 6 months

• 20 teeth

Permanent teeth overview:

• after 6-12 years

• Total of 32

Pharynx

• throat

3 stages of swallowing (deglutition)

1. Voluntary

2. Pharyngeal

3. Esophageal

Voluntary stage of swallowing

• food passes from mouth to oropharynx

Pharyngeal stage

• INVOLUNTARY

  • From pharynx to esophagus, epiglottis keeps material out of trachea

Esophageal stage

• INVOLUNTARY

• A constricting progression toward stomach

Esophagus

• collapsible muscular tube

• Posterior to trachea

• Connects laryngopharynx to stomach

Peristalsis

• alternating muscle contractions (circular & longitudinal) to push BOLUS onward

Stomach definition

• connects the esophagus to the duodenum, acts as a mixing chamber (chyme) & holding reservoir

Stomach functions

1. Secretes gastric juice

   • HCL, pepsin, intrinsic factor, gastric lipase

2. Digestion of starch, proteins, & triglycerides

3. Secretes gastrin INTO BLOOD

4. HCL kills bacteria

Cardia of stomach

• surrounds superior opening of stomach

Fundus of stomach

• upper left, rounded part

Body of stomach

• large central portion

Rugae of stomach

• large folds of mucosa

Pylorus of stomach

• region that connects to duodenum

Pyloric sphincter of stomach

• limits emptying of stomach into duodenum

Lesser curvature of stomach

• CONCAVE medial border

Greater curvature of stomach

• CONVEX lateral border

Muscularis layers

• longitudinal, circular, oblique

Gastric pits

• narrow channels that hold gastric glands

Mucous neck cells

• secrete thick layer of mucus to protect stomach lining

Parietal cells

• produce HCL, produce intrinsic factor to absorb vitamin B12

Chief cells

• secrete pepsinogen—> pepsin & gastric lipase

G cells

• secrete gastrin into blood stream

2 phases of digestion

1. Cephalic

2. Gastric

Cephalic phase of digestion

• sight, smell, taste, or thought of food initiates neural stimulation of gastric glands

  • Pepsinogen, HCL, mucus

  • Gastrin into blood, increase in stomach motility (peristalsis)

Gastric phase of digestion

• neural & hormonal

• Stretch receptors monitor for distended stomach walls

• Chemoreceptors monitor for increase in pH

  • Both cause gastric juice secretion & motility (peristalsis)

Parasympathetic

• gastrin (G cells)

• Increase motility, relaxes pyloric & ileocecal sphincters

  • Gastric emptying

Enterogastric reflex

• Cholecystokinin (CCK)

  • Inhibits gastric emptying

  • Sympathetic

Intestinal phase

• slow exit of chime from stomach to duodenum

• Triggers release of CCK (inhibits gastric emptying) & secretin (decreases gastric juices)

CCK function

• Cholecystokinin

• inhibits gastric emptying

• Increases release of pancreatic juice

• Causes contraction of gallbladder

Secretin function

• decreases gastric juice

• Increases release of pancreatic juice (bicarb ions)

• causes liver to produce more bile

Diet

• chemical digestion in small intestine depends on activities of pancreas, liver, & gallbladder

Pancreas anatomy/ overview:

• head, body, tail, pancreatic duct, duodenal ampulla/papilla

  • About 99% of cells (acini) produce digestive enzymes called pancreatic juice

Pancreatic juice function

• buffers against low pH

• Contains enzymes to digest carbs (amylase), proteins (trypsin), triglycerides (lipase), & nucleic acid (DNAse)

Enzyme that digests carbs

Amylase

Enzymes that digests proteins

• trypsin

Enzyme that digests triglycerides

• lipase

Enzyme that digests nucleic acid

• DNAse

Gallbladder

• pear-shaped sac located posterior to liver

  • Store & concentrates bile until needed

Liver consists of

• largest gland in the body (after skin)

  • L, R, & caudate lobes

  • Lobules

  • Hepatocytes

  • Central vein

  • Falciform ligament

  • Sinusoids

Kupfler cells

• fixed phagocytes

  • Destroys worn out RBCs, WBCs, & some bacteria

Role of bile

• emulsification of fats

  • Break down large lipids & assists in their absorption

    • Cholesterol is made soluble because of bile salts

Old RBCs are secreted into

Bile

Blood supply to liver

1. Hepatic artery

   • Oxygenated blood

2. Hepatic portal vein

   • Deoxygenated blood w/ newly absorbed nutrients, drugs, microbes, toxins from GI tract

3. Hepatic vein

   • From central vein, out of liver to inferior vena cava

9 functions of liver

1. Carbohydrate metabolism

2. Lipid metabolism

3. Protein metabolism

4. Processing drugs & hormones

5. Excretion of bilirubin

6. Produce bile salts

7. Storage for vitamins A, B12, D, E, K, iron, copper, & glycogen

8. Phagocytosis

9. Activate vitamin D