digest anat online

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Digestive System

• Two groups of organs

1. Alimentary canal (gastrointestinal or GI tract)

• Digests and absorbs food

• Mouth, pharynx, esophagus, stomach, small intestine, and large intestine

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Digestive System

2. Accessory digestive organs

• Teeth, tongue, gallbladder

• Digestive glands

• Salivary glands

• Liver

• pancreas

Copyright © 2011 Pearson Education, Inc. Figure 22.1

Mouth (oral cavity)Tongue

Esophagus

LiverGallbladder

Anus

DuodenumJejunumIleum

Small intestine

Parotid glandSublingual glandSubmandibulargland

Salivaryglands

PharynxStomachPancreas(Spleen)

Transverse colonDescending colonAscending colonCecumSigmoid colonRectumVermiform appendixAnal canal

Largeintestine

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Digestive Processes

• Six essential activities

1. Ingestion

2. Propulsion

3. Mechanical digestion

4. Chemical digestion

5. Absorption

6. Defecation

Copyright © 2011 Pearson Education, Inc. Figure 22.2

FoodIngestion

PropulsionEsophagus

Stomach

PharynxMechanicaldigestion

Chemicaldigestion

• Chewing (mouth)• Churning (stomach)• Segmentation (small intestine)

Smallintestine Largeintestine

Defecation Anus

Feces

Bloodvessel

Lymphvessel

Absorption

• Swallowing (oropharynx)• Peristalsis (esophagus, stomach, small intestine, large intestine)

Mainly H2O

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Blood Supply: Splanchnic Circulation

• Arteries

• Hepatic, splenic, and left gastric

• Inferior and superior mesenteric

• Hepatic portal veins

• Drains nutrient-rich blood from digestive organs

• Delivers it to the liver

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TISSUES OF THE ALIMENTARY CANAL

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Histology of the Alimentary Canal

• Four basic layers (tunics)

1. Mucosa

2. Submucosa

3. Muscularis externa

4. Serosa

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MucosaInner layer of lumen

Three sublayers:

1. Epithelium – simple columnar and goblet cells

• Secrete mucus and enzymes

2. Lamina propria – areolar basement membrane

3. Muscularis mucosae– thin layer of smooth muscle

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Simple Columnar with Microvilli

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Submucosa, Muscularis Externa and SerosaSubmucosa

• Connective tissue

• Blood and lymphatic vessels

Muscularis externa

• Responsible for segmentation and peristalsis

• Smooth muscle

Serosa

• Fibrous covering (visceral peritoneum)

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ORAL CAVITY

Mouth, teeth, salivary glands and tongue

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Mouth• Oral (buccal) cavity

• Bounded by lips, cheeks, palate, and tongue

• Lined with stratified squamous epithelium

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Oral Cavity

• Lips form anterior border

• Cheeks form lateral border

• Palate forms superior border

• Hard palate: maxillae and palatine bones

• Ridges help create friction

• Soft palate: closes the nasopharynx for swallowing

• Uvula projects down from free edge

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Tongue

Oral cavity muscle• Assists in chewing

• forming bolus

• swallowing, speech, and taste

Contains taste buds

Frenulum attaches tongue to the floor of oral cavity

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Salivary Glands

Extrinsic salivary glands

•Secrete saliva, contains digestive enzymes

1.Parotid gland – buccal area• Duct opens near 2nd molar

2.Submandibular – medial mandible• Duct opens under tongue

3.Sublingual – anterior to submandibular, under tongue

Copyright © 2011 Pearson Education, Inc. Figure 22.9

Teeth

Ducts ofsublingualgland

Sublingualgland

Submandibularduct

Posterior bellyof digastric muscle

Parotid ductMasseter muscleBody ofmandible (cut)

Parotidgland

Tongue

Submandibulargland

(a)

Frenulumof tongue

Mylohyoidmuscle (cut)Anterior belly ofdigastric muscle Mucous

cells (b)

Serous cellsforming demilunes

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Teeth• 32 permanent teeth

• Covered by enamel – hardest substance in body

• Periodontal ligament• Forms fibrous joint called a gomphosis

• Incisors - chisel shaped for cutting

• Canine - fanglike

• Premolars (bicuspids) and molars • Have broad crowns for grinding or crushing

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Tooth Structure

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Pharynx and Esophagus

Muscular tubes allow passage of water and food

Esophagus uses peristalsis to move food

• Travels through diaphragm

• Esophageal sphincter

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STOMACH AND INTESTINES

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Stomach Regions

• Cardiac region• Connects to esophagus

• Fundus• Dome region below

diaphragm

• Body• midregion

• Pyloric region: • antrum, pyloric canal,

and pylorus

• Connects to duodenum via pyloric sphincter

• Greater curvature

• Lesser curvature

Copyright © 2011 Pearson Education, Inc. Figure 22.14a

CardiaEsophagus

Pyloric sphincter(valve) at pylorus

Pyloriccanal

Pyloricantrum

Body

Lumen

Fundus

Lessercurvature

Greatercurvature

(a)

Duodenum

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Stomach: Layers• Four tunics

• Three muscular layers and outer tunic (serosa)

• Muscularis externa

1.longitudinal

2.circular

3.oblique

• Covered by omentums

• Greater & lesser

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Stomach: Tissues • Mucosa

• Simple columnar epithelium with mucus covering

• Contain gastric pits• Produce gastric acid = HCl

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Digestive Processes so Far…

• Physical digestion (chewing)• Teeth and tongue

• Creates bolus• Enzymatic digestion • Enzymes in saliva

• Gastric acid

• Delivers chyme to the small intestine• Creamy food mass

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Small Intestine• Major organ of absorption

• Pyloric sphincter to ileocecal valve (2-4 m long)

• Subdivisions

1. Duodenum : beginning portion

• connects to stomach via pyloric sphincter

2. Jejunum : intermediate portion(~8ft)

3. Ileum : end portion (~12ft)

• Connects to large intestine via ileocecal valve

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Small Intestine

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Duodenum• Ducts for gallbladder and pancreases empty into

the hepatopancreatic ampulla• Bile duct

• Main pancreatic duct

• Enter at the duodenal papilla• Are controlled by the hepatopancreatic

sphincter

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Absorption of Small Intestine

• Modification help increase surface area (absorption):

1. Circular folds (plicae circulares)

2. Villi

3. Microvilli

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Villi and MicrovilliVilli

• fingerlike extensions of mucosa

• Simple columnar absorptive cells

• With microvilli – increase surface area

• Goblet cells – produce mucus

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Large Intestine• Compacts fecal mater (food waist) and

propels it out

• Regions

1. appendix

2. cecum

3. colon

4. rectum

5. anus

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Colon• Regions of colon

• Ascending colon

• Right (hepatic) flexure

• Transverse colon

• Left (splenic) flexure

• Descending colon

• Sigmoid colon (S – shaped)

• Contains pocketlike sacks haustrum

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Large Intestine

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Rectum and Anus• Rectum• Inferior holding chamber

• Anal canal• Last segment of the large intestine

• Sphincters• Internal anal sphincter —smooth muscle

• involuntary

• External anal sphincter —skeletal muscle

• voluntary

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Functions of the Large Intestine

• Major function: propulsion of feces toward the anus

• Reclaims : vitamins, water, and electrolytes

• Colon is not essential for life

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Motility of the Large Intestine

• Haustral contractions• Slow segmenting movements

• Haustra sequentially contract in response to distension

• Gastrocolic reflex• Initiated by presence of food in the stomach

• Three slow powerful peristaltic waves per day in the colon (mass movements)

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Defecation

• Mass movement of feces into rectum

• Distension initiates defecation reflex

• Parasympathetic signals• Stimulate contraction of the sigmoid colon and

rectum

• Relax internal anal sphincter

• Conscious control relaxation of external anal sphincter

Copyright © 2011 Pearson Education, Inc. Figure 22.29b

(b)

Rectal valveRectum

Anal canal

Levator animuscle

AnusAnal sinuses

Anal columns

Internal analsphincter

External analsphincter

Hemorrhoidalveins

Pectinate line