Digestive System PPT – function and histology

June 17, 2012 | By | Reply More

Digestive System PPT -  function and histology
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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.

 

consists of:

Picture4 Digestive System PPT    function and histology

Muscular, hollow tube (= “digestive tract”)

+

Various accessory organs

 

Function

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:

ingestion
mechanical digestion
chemical and enzymatic digestion
secretion
absorption
compaction
excretion and elimination

Histological Organization 

Picture5 Digestive System PPT    function and histology

Tube made up of  four layers.

Modifications along its length as needed.

The 4 Layers of the Gut

1) 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

 

Membranes

Peritoneum – 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  mesocolon

ii. sigmoid mesocolon

 

Oral 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 Salivary Glands

1-1.5 l / day for

digestion (?)

lubrication (swallowing) moistening (tasting)

 

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
Mumps

Swollen, painful salivary glands on one or both sides of the face

Fever and sometimes orchitis, pancreatitis etc.

About 1/3 of infected people do not show symptoms

Effective vaccine since 1967

 

Structure of Teeth

Crown – exposed surface of tooth

Neck – boundary between root and crown

Enamel – outer surface

Dentin – bone-like, but noncellular

Pulp cavity – hollow with blood vessels and nerves

Root canal – canal length of root

gingival sulcus – where gum and tooth meet

 

Types and Numbers of Teeth

Dental succession

Deciduous (baby, milk) teeth – 20, replaced by

Permanent teeth – 32 teeth

Gross Anatomy of the Stomach

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

 

Histology of Stomach

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)
Regions of Small Intestine

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)

Structure of Small Intestinal  Wall

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

 

Regions of Large Intestine

Cecum – pocket at proximal end with Appendix

Colon

Ascending 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

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

Histology of Large Intestine

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

Liver

On 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 liver

Microscopic anatomy: Liver lobules and triads

 

Pancreas

Retroperitoneal
Endocrine or exocrine gland?
Common bile duct and pancreatic duct lead to duodenal ampulla and papilla

 

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