Digestive System

How is the Digestive system divided?

1\. Digestive organs: collectively make up the gastrointestinal (GI) tract (alimentary canal).

2\. Accessory digestive: food does not pass through their lumens, but they assist digestion

What are the Accessory organs

Teeth

Tongue

Salivary glands

Liver

Gall bladder

Pancreas

What are the GI tract organs

Oral cavity

Pharynx

Esophagus

Stomach

Small intestine

Large intestine

Digestive system functions

Ingestion

Propulsion

Secretion

Digestion

Absorption

Elimination

Peristalsis

ripple-like wave of muscular contraction that forces material to move further along the GI tract.

or Waves of contraction propel food along the GI tract

Segmentation

churning and mixing of material helping to disperse the material and mix it with digestive organ secretions.

or Process of moving food back & forth along the SI

Gingiva

Alveolar processes of the teeth are covered by the gums

Labial frenulum

Internal surface of the upper and lower lips are attached to the gingivae by a thin, midline mucosal fold

Soft palate

Posterior 1/3 palate (dense CT & muscle).

Hard palate

Anterior 2/3 palate (maxilla & palatines)

Uvula

elevates during swallowing and closes off entrance to nasopharynx

Tongue

manipulates and mixes food with saliva during chewing, and compresses partially digested materials into a bolus.

Bolus

chewed up food

Lingual frenulum

Inferior surface of tongue attaches to oral cavity floor

Saliva functions

• Moistens ingested materials to become a slick bolus.

• Moistens, cleans, lubricates oral cavity structures.

• Chemical digestion of food.

• Antibacterial action

• Dissolves food to enable taste receptor stimulation

Parotid glands

• Largest salivary gland.

• Near the ear.

• More serous cells

Submandibular glands

• Under mandible.

• Produces 70 % saliva volume.

• More serous cells.

Sublingual glands

• Under tongue.

• Produces 3-5% saliva volume.

• More mucous cells.

What is the difference b/w serous cells vs. mucous cells

Serous cells produce saliva that is 97-99% water & enzymes (salivary amylase, lingual lipase), ions.

Mucous cells secrete mucin, a stringy viscous mucous solution.

Dentition

what teeth are collectively known as

Tooth- crown, root, neck, dental alveoli, pulp

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enamel

of the crown it a thin, brittle ceramic material (hardest substance in the body)

Dentin

forms the primary mass of the tooth (harder than bone, shock absorber)

surrounds the pulp cavity (CT, blood vessels, nerves = pulp).

cementum

a hard, calcified layer of tissue that covers the root of the tooth

Deciduous vs. permanent teeth

20 milk/baby teeth, erupt 6-30 months

32 Permanent teeth replaced by the end of adolescence. Third molars (wisdom teeth) emerge 17-25

Incisors

mostly anterior, shaped like chisels, single root. Adapted for biting or nipping off food

Canines

(cuspids or eye-teeth) have pointed tips for puncturing and tearing.

Premolars

(bicuspids) have two cusps (ridges) on the crown for crushing or grinding.

Molars

largest and thickest posterior teeth, have 4-5 cusps for crushing and grinding food. Upper and lower molars lock together to create tremendous crushing force

Pharyngeal constrictors- superior, middle, inferior

muscles form the wall of the pharynx and participate in swallowing

\- Superior 1/3 is skeletal muscle- voluntary

\- Middle 1/3 is mixed skeletal & smooth muscle

\- Inferior 1/3 is smooth muscle- involuntary

Stages of deglutition explain

oral, pharyngeal, esophageal

Buccal phase

Tongue presses against hard palate, bolus moves to oropharynx

Pharyngeal-esophageal phase

Pharyngeal constrictors contract, bolus moves into esophagus

Tunics of the GI tract

Mucosa, Submucosa, Muscularis, Adventitia

Mucosa

closest to the lumen; epithelium, areolar CT, smooth muscle

Epithelium + lamina propria + muscularis mucosa

Lamina propria

**a complex mesh of extracellular proteins and structural molecules**

Muscularis mucosae

**lamina muscularis mucosae (or muscularis mucosae) is a thin layer ( lamina) of muscle of the gastrointestinal tract**

Submucosa

lymphatics, mucin glands, blood vessels, nerves

GI tunic under the mucosa with loose CT and vessels

Meissner’s nerve plexus

Submucosal nerve plexus (inner plexus)

between submucosa and muscularis

Muscularis externa

inner circular muscle and outer longitudinal smooth muscle

Auerbach’s nerve plexus

Myenteric nerve plexus (outer plexus)

between smooth muscle layers

Serosa/adventitia

loose CT with blood & lymph vessels

Esophagus

tube that bolus goes from oropharynx to stomach, posterior to trachea.

Approx. 25 cm long, collapsible,

Connects to stomach at gastro-esophageal junction

Esophageal hiatus

an opening in the diaphragm

Stomach

• Upper left quadrant of abdomen.

• It continues the mechanical and chemical digestion of the bolus.

• The bolus eventually is processed into a paste-like soup called chyme.

• Possesses three layers of muscle to aid in the mechanical processing of ingested materials

Chyme

what the bolus turns into in the stomach

Cardia

toppish region of the stomach where the cardiac sphincter is

Fundus

top of the stomach

Body

the body of the stomach aka middle

Pylorus

bottomish region of the stomach where the pylorus sphincter is

Greater & lesser curvature

big curve and small curve of stomach shape

Rugae

Longitudinal folds of the stomach mucosa & submucosa

Oblique muscle layer

Additional inner muscle layer of the stomach

what prevents food from coming up from your throat?

Upper esophageal sphincter

Cardiac (lower esophageal) sphincter

Sphincter regulating bolus passage from esophagus to stomach

Pyloric sphincter

Sphincter regulating chyme passage from stomach to duodenum

Appendix

Worm-like organ with lymphocytes & bacterial reserves

Ascending colon

Section of large intestine between the cecum & transverse colon

Bile

Green-yellow alkaline solution, bile salts & phospholipids

Descending colon

Large intestine region between the transverse & sigmoid colons

Travels inferiorly from splenic flexure on the left abdomen. • Adjacent to the ileum and terminates in the sigmoid colon.

Duodenum

Proximal small intestine, has most plicae & villi

• C- shaped, URQ. • Entry- Pyloric sphincter of the stomach. • Exit- duodenojejunal junction. • Pancreas → major duodenal papilla permits pancreatic secretions and bile to enter. • Kick starts chemical digestion of chyme.

Epiploic appendages

Small fat deposits attached to haustra & taenia coli

Gall bladder

Small sac that holds and concentrates bile until needed

Haustra

Pocket-like bumps of the wall of the large intestine

Hemorrhoids

Dilated veins in the anus and rectum, may lead to complications

Hepatopancreatic ampulla

Junction point of the bile duct & pancreatic duct

Ileocecal valve

Sphincter regulating chyme passage from small to large intestine

Ileum

Distal part of small intestine with fewest villi & microvilli

distal segment • Longest portion, smallest lumen • Terminates at ileocecal valve → large intestine

Jejunum

Middle part of small intestine, most absorption occurs here

Both chemical digestion and nutrient absorption.

Left colic flexure

Splenic flexure; 90º bend between transverse & descending colons; under spleen

Mesentery

Series of peritioneal folds attaches organs to abdominal wall

Pancreas

Digestive secretions include digestive juices & bicarbonate

Pharyngeal constrictors

Three sets of muscle, contain both skeletal & smooth muscle

Rectal valve

Folds in the rectal wall that hold feces during flatulence

Right colic flexure

aka hepatic flexure; 90º bend between ascending & transverse colons; under liver

Sigmoid colon

S-shaped region of the colon leading to the rectum

Tenia coli

Unique 3-banded arrangement of colon muscularis externa

Transverse colon

Section of the large intestine that runs horizontally

Adventitia

Outer serosa tissue layer of the GI system organs

Emulsification

Bile acts on lipids to permit digestion and absorption

Endocrine pancreas

Islets of Langerhans secrete insulin & glucagon (5%)

Exocrine pancreas

Pancreatic acinar cells secrete digestive juices (90%)

Hepatic portal system

Deoxygenated blood & nutrients from SI processed in liver

Lacteals

Lymphatic vessels in each villus for fat absorption

Microvilli

Cell membrane & cytoplasm folding’s for absorption

Plicae (circularis)

Large folds of the small intestine mucosa and submucosa

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The mucosal and submucosal tunics are thrown into folds called the circular folds

Villi

Finger-like projections of the mucosa to increase surface area

Small intestine region

Duodenum

Jejunum

Ileum

major duodenal papilla

permits pancreatic secretions and bile to enter

Ileocecal valve

valve that connects small intestine with large intestine

Large intestine

Diameter is 6.5 cm vs 2.5 cm lumen of small intestine. • Absorbs fluids and ions, compacts indigestible wastes and solidifies fecal material. • Stores and expels feces

Cecum

Proximal segment of the large intestine. • Blind-end sac located in LRQ. • Ileocecal valve represents junction of small & large intestines.

Transverse mesocolon

ligament that holds the transverse colon up

Sigmoid mesocolon

ligament that holds the sigmoid colon up

Rectum

• Muscular tube that expands to store feces prior to defecation • Rectum terminates at the anal canal.

Rectal valves

3 thick transverse folds of rectal wall that allow gas to pass while retaining fecal material (\~ 500 ml/day).

Anal canal

Distal end of large intestine

Anal columns

line internal surface

Anal sinuses

secrete mucin for lubrication during defecation

Internal & external anal sphincters

anal sphincters open and close the anal canal during defecation

no control over internal one but some control over external one