Ch25: Digestive SystemCh25: Digestive System

Objectives:

Discuss the general functions and anatomy of the digestive tract

Describe the individual organs of the system, including a discussion of the gross and microscopic anatomy.

DigestivDigestive Systeme SystemDigestivDigestive Systeme System

Muscular, hollow tube (= “digestive tract”)+Various accessory organs

consists of:

FunctionFunctionFunctionFunction

ingestion

mechanical digestion

chemical and enzymatic digestion

secretion

absorption

compaction

excretion and elimination

The function of the system as a whole is processing food in such a

way that high energy molecules can be absorbed and residues

eliminated.

Individual parts function in:

Muscularis externa

Histological Histological OrganizationOrganizationHistological Histological OrganizationOrganization

Tube made up of four layers.

Modifications along its length as needed.

12

3

4

The 4 Layers of the GutThe 4 Layers of the Gut1) Mucosa Epithelium – usually simple columnar with goblets; may be stratified squamous

if protection needed

Lamina propria - connective tissue deep to epithelium Muscularis mucosae -produces folds - plicae (small intestine) or rugae (stomach)

2) Submucosa – made up of loose connective tissue contains submucosal plexus and blood vessels

3) Muscularis externa – smooth muscle, usually two layers (controlled by the myenteric plexus ) -

outer layer: longitudinal inner layer: circular

4) Serosa visceral layer of mesentery or adventitia depending on location

Fig 25.2

MembranesMembranesMembranesMembranesPeritoneum - generic serous membrane in abdominal cavity

Mesenteries - double sheets of peritoneum, surrounding and suspending portions of the digestive organs

Greater omentum - "fatty apron", hangs anteriorly from stomach, double layer encloses fat

Lesser omentum - between stomach and liver Mesentery proper - suspends and wraps the small intestine Mesocolon - suspends and wraps the colon, parts are

i. transverse mesocolonii. sigmoid mesocolon

Fig. 25.4

Oral CavityOral Cavity

Also called buccal cavity - lined with oral mucosa (type of epithelium ?)

Hard and soft palates - form roof of mouth

Tongue - skeletal muscle

Salivary glands - three pairs

Teeth

Three pairs of Three pairs of Salivary Salivary GlandsGlandsThree pairs of Three pairs of Salivary Salivary GlandsGlands

Parotid – lateral side of face, anterior to ear, drain by parotid duct to vestibule near 2nd upper molar– mumps

Submandibular – medial surface of mandible – drain near lingual frenulum drain posterior to lower molars

Sublingual – in floor of mouth - drain near frenulum

1-1.5 l / day for digestion (?)lubrication (swallowing) moistening (tasting)

Structure of TeethStructure of Teeth

Crown - exposed surface of tooth Neck - boundary between root and crown

Enamel - outer surfaceDentin – bone-like, but noncellularPulp cavity - hollow with blood vessels and

nervesRoot canal - canal length of root gingival sulcus - where gum and tooth meet

Fig 25.7

Types and Numbers of TeethTypes and Numbers of Teeth

Dental successionDeciduous (baby, milk) teeth - 20, replaced byPermanent teeth - 32 teeth

Lesser curvature

Greater curvature

Cardia - end under the heart

Fundus - bulge above the esophageal opening

Body - largest region

Pylorus - J curve, inferior end, terminates in

Cardiac and Pyloric sphincters (importance?)

Rugae – highly extendable interior folds

Figs 25-10/11

Gross Anatomy of the StomachGross Anatomy of the Stomach

Histology of Histology of StomachStomach

Histology of Histology of StomachStomach

Type of epithelium lining stomach?

Gastric pits – shallow pits, external half rapidly reproduces for replacement

Gastric glands – deep in lamina propria, 3 types of cells

1. Parietal cells (produce HCl and intrinsic factor)

2. Chief cells (produce pepsinogen)

3. Enteroendocrine cells – G cells (several hormones including gastrin which stimulates both parietal and chief cells)

Fig 25.13

Regions of Small Regions of Small IntestineIntestineRegions of Small Regions of Small IntestineIntestine

SI is longest part of dig. tube

Duodenum (short, 12 inches)– fixed shape & position– Mixing bowl for chyme & ?

Jejunum (2.5 m long) – Most of digestion

Ileum (longest at 3.5 m) – Most of absorption, ends in

Ileocecal valve – slit valve into large intestine (colon)

Plicae circulares – circular pleats around the interior of the small intestine

Villi – minute finger-like projections, contain capillaries & lacteals

Microvilli – sub-microscopic size, projections on single cells Function of all three?

Intestinal glands (crypts) – intestinal juice production

– Cell regeneration

Histology in lab

Structure of Small Intestinal WallStructure of Small Intestinal Wall Fig 25.15

Cecum Cecum –– pocket at proximal end with Appendix

ColonColonAscending colon - on right, between cecum and right colic flexure

Transverse colon - horizontal portion

Descending colon - left side, between left colic flexure and

Sigmoid colon - S bend near terminal end

Regions of Large IntestineRegions of Large Intestine

Fig 25-17

Rectum Rectum –– terminal end is anal canal - ending at the anus - which has internal involuntary sphincter and external voluntary sphincter

1. Mucosa - abundant goblet cells, stratified squamous epithelium near anal canal

2. No villi

3. Longitudinal muscle layer incomplete, forms three bands or taenia coli

4. Circular muscle - forms pockets or haustra between bands

Histology of Large IntestineHistology of Large Intestine

Fig 25.19

LiverLiverOn right under diaphragm, largest

organ made up of 4 lobes (left and right, caudate, and quadrate)

Hilus (porta hepatis) – underside "entry" point

Extremely versatile: Know a few functions?

Gall bladder

Blood supply to liverFig 25.20

Microscopic anatomy: Liver lobules and triads Fig 25.21

Retroperitoneal

Endocrine or exocrine gland?

Common bile duct and pancreatic duct lead to duodenal ampulla and papilla

PancreasPancreas

Compare to Figs 25-22 / 23