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Chapter 21 - Digestive System I, II

Lectures 7 & 8

Martini’s VisualAnatomy and Physiology

First Edition

Martini Ober

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Lecture Overview (Lectures 7 & 8)

• Introduction to the digestive system

• General characteristics of the alimentary canal

• The mouth and tongue

• Salivary glands

• Pharynx and esophagus

• Stomach

• Pancreas

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Digestive SystemFunctions of Digestive System

• ingestion

• mechanical digestion

• chemical digestion

• propulsion

• absorption

• excretion

• defecation

Digestion is the mechanical and chemical breakdown of food into a form that cells can absorb

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Major Organs of Digestive SystemFigure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

Organs can be divided into the:

-Digestive tract (primary) (alimentary canal); tube extending from mouth to anus (about 30 ft.)

-Accessory organs; teeth, tongue, salivary glands, liver, gallbladder, and pancreas

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The Greater and Lesser Omenta

Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

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The Mesentery

Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

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The Abdominal Cavity & Peritoneum

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Notice that the pancreas, duodenum, and rectum are retroperitoneal

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Alimentary Canal

Continuous tube modified along its length to carry out specialized, regional functions.

Mouth, pharynx, esophagus, and anal canal are lined by nonkeratinized stratified squamous epithelium

Stomach and intestines are lined by simple columnar epithelium.

Why?

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Alimentary Canal Wall

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Know the 4 layers of the alimentary canal

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Alimentary Canal Wall

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Movements Through the Alimentary Canal• mixing movements (segmentation)

• peristalsis - The wavelike muscular contractions of the alimentary canal or other tubular structures by which contents are forced onward toward the opening. (Triggered by pacesetter cells.)

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Innervation of the Alimentary Canal

• submucosal plexus – controls secretions/blood flow• myenteric plexus – controls gastrointestinal motility/sphincters• parasympathetic division of ANS – increases activities of digestive system and relaxes sphincters

• sympathetic division of ANS – generally inhibits digestive actions and contracts sphincters

The alimentary canal has extensive sympathetic and parasympathetic innervation - mainly in the muscularis externa - regulates its tone and the strength, rate, and velocity of muscular contractions

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Mouth (Oral or Buccal cavity)

• ingestion

• mechanical digestion

• prepares food for further chemical digestion

Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

(Labium)

(Labium)

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TongueVery muscular; muscles run in several directionsCovered by mucous membranes

1. Tastebuds

2. Friction for food handling

3. Secretes lingual lipase

Blast from the past - Root of tongue is anchored to the hyoid bone

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Palate• roof of oral cavity

Important in separating the nasopharynx from the pharynx during swallowing

(adenoids)

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Secondary (Permanent) Teeth

Total of 32 secondary (permanent) teeth

Watch for incoming ICBMs!!!

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32 17

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Know the order of these

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Primary (Deciduous, Baby, Milk) Teeth

• 8 incisors• 4 cuspids• 8 molars

• 20 total

All primary teeth are lost, generally between ages 6 and 12

(Mastication = chewing)

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Section of a Tooth

What type of articulation is this?

Know this diagram for exam

Oh no! Not again!

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Functions of Saliva

• Moistens food

• Binds food particles

• Dissolves food for tasting

• Begins chemical digestion of complex CHO (amylase)

• Cleans teeth and mouth (pH = 6.5 – 7.5)

• Anti-microbial (IgA and lysozyme)

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Salivary Glands

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Secretions of Salivary Glands

• Parotid glands • clear• primarily water, serous fluid• rich in amylase • mumps virus typically attacks here

• Submandibular glands• primarily serous fluid• some mucus, amylase

• Sublingual glands• primarily mucus• most viscous

Secretions are slightly acidic and continual due to basal parasympathetic stimulation, but increase after

- presence, or anticipation of, food; - parasympathetic stimulation (watery, large volume) - sympathetic stimulation (viscous, small volume)

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Pharynx

Pharynx aids swallowing by grasping food and moving it toward the esophagus.

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Three Phases of the Swallowing Reflex

• soft palate and uvula raise

• hyoid bone and larynx elevate

• epiglottis closes off top of trachea

• longitudinal muscles of pharynx contract

• inferior constrictor muscles relax and esophagus opens

• peristaltic waves push food through pharynx

Only voluntary phase is the buccal (oral) phase, i.e., the initiation of swallowing, then…

Pharyngeal phase

Esophageal phase

reflexive

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Swallowing Mechanism

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Esophagus

Lower esophageal (cardiac) sphincter prevents reflux (backup) of stomach acid into the esophagus.

Veins drain into hepatic portal vein (via gastric veins)

Esophagus conveys food from pharynx to stomach by peristalsis

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Stomach

Greater curvature

Stomach Functions: - Mixing - Reservoir - Secretion of gastric juice - Digestion, anti-bacterial action, facilitates absorption of vitamin B12

- Secretion of gastrin, somatostatin

Stomach can hold about 1-1.5 liters of material

M

Gastricglands

MG cellsD cells

Rugae flatten as stomach fills

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Blood Supply and Drainage of Stomach

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

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Lining and Gastric Glands of Stomach

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

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Gastric Secretions

• pepsinogen• from chief cells• inactive form of pepsin

• pepsin• from pepsinogen in presence of HCl• protein splitting enzyme

• hydrochloric acid• from parietal cells• needed to convert pepsinogen to pepsin• ‘p’ in parietal and ‘p’ in pH

• mucus (cardia)• from goblet cells and mucous glands• protective to stomach wall

• intrinsic factor• from parietal cells• required for vitamin B12 absorption

• INFANTS ONLY• rennin (chymosin)• gastric lipase

• mucus, gastrin, somatostatin• from pyloric glands• protective to stomach wall• gastrin and somatostatin are hormones

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Secretion of H+ by Parietal Cells

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Important functions of the stomach pH (1.5 – 2.0)

- kills microorganisms

- denatures proteins

- breaks down plant material and CT in meats

- activates pepsin

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Three Phases of Stomach Control

• Cephalic phase• triggered by smell, taste, sight, or thought of food• begin secretion and digestion

• Gastric phase• triggered by distension, presence of food, and rise in pH in stomach• enhances secretion and digestion

• Intestinal phase • triggered by distension of small intestine and pH change• controls rate of gastric emptying; may slow emptying

NOTE that all these phases control activity in the STOMACH

Know what each phase does (shown in red)

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Cephalic Phase of Gastric Secretion

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Emotional states can exaggerate or inhibit this phase

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Gastric Phase of Gastric Secretion

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Proteins, alcohol, and caffeine can markedly increase secretions by stimulating gastric chemoreceptors

Histamine stimulates acid secretion by parietal cells

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Intestinal Phase of Gastric Secretion

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Enterogastric reflex (inhibits gastric activity) –reduces gastric motility, stimulates contraction of pyloric sphincter (pylorus)

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+ +

Parasympathetic NS

G cells

Gastrin

+

+

Both

Mucous Cells

ECL Cells

Histamine

Parietal CellsH+ + Cl-

HCO3- (alkaline tide)

Intrinsic Factor

+

+

+

Chief Cells

Pepsinogen Pepsin

Protein Breakdown

Peptides

+

Stretch of

stomach

pH > 3.0(dilution of H+)

Food in Stomach

++ +

D cells

Somatostatin

pH < 3.0+

Emptying of Stomach

( [H+ ])

-

Overview of Gastric Control/Secretion

Fats in Small

Intestine

+

(cephalic/gastric phases)

(intestinal phase)

+

Key

Stimulation

-Inhibition

Endocrine Factor

Exocrine Factor

LipasesFat

Breakdown

B12

Stomach Molility (Segmentation/Peristalsis)

+

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Mixing and Emptying Actions

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Gastric Absorption

• some water• certain salts• certain lipid-soluble drugs, e.g., aspirin• alcohol (slowed by presence of fats)

Gastric absorption is very limited due to:

- blanket of mucus covering cells - epithelial cells lack specialized transport mechanisms - tight junctions between adjacent epithelial cells - gastric lining is relatively impermeable to water - chyme usually contains only partially digested material

Some substances can be absorbed by the stomach:

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Pancreas

Exocrine (digestive) and endocrine (metabolic) functions

Completes digestion of proteins that was started in the stomach

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Blood Supply and Drainage of Pancreas

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

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Pancreatic Juice

• pancreatic amylase – splits glycogen into disaccharides

• pancreatic lipases – break down triglycerides

• pancreatic nucleases – digest nucleic acids

• bicarbonate ions – make pancreatic juice alkaline (pH = 8) and neutralize acid coming from stomach

• Pancreatic proteolytic enzymes…

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Pancreatic Proteolytic Enzymes

Pancreas

ProelastaseProcarboxypeptidaseChymotrypsinogen

Trypsinogen Trypsin

Enteropeptidase (Enterokinase)

(brush border of sm. intestine)

ElastaseCarboxypeptidaseChymotrypsin

ProteinsDipeptides, tripeptides, amino acids

(Proenzymes, Zymogens)

Know this chart

Purpose of proteolytic enzymes is continued breakdown of proteins that began in the stomach

(Active enzymes)

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Regulation of Pancreatic Secretions

• acidic chyme stimulates release of secretin

• secretin stimulates release of watery pancreatic juice with bicarbonate and phosphate (= buffers; to pH)

CCK and parasympathetic NS stimulate production and secretion of pancreatic enzymes and zymogens

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Acidic Chyme Enters Duodenum

Secretin

+

Cholecystokinin(CCK)

Enterokinase

Trypsinogen

ChymotrypsinogenProcarboxypeptidaseProelastase

Trypsin

Pancreas TrypsinogenCarboxypeptidaseElastase

Gallbladder Contraction

Relaxation of hepatopancreatic

sphincter

Bile

TriglyceridesCholesterolFat Soluble Vitamins

Lipases

Bile and Pancreatic

ducts

Nucleases(DNA, RNA)

Amylase(glycogen, starches)

Monosaccharides

Nucleotides

Proteins

Fatty acids,monoglyceride

s

Di- and tripeptides

Amino acids

HCO3-, PO4

3-

pH to ≈ 8 (req. for enzyme

action)

Conversion to chylomicrons

+++

++

+

Action of brush border enzymes

Lacteals

Regulation of Pancreas/Intestinal Digestion+

Key

Stimulation

(brush border)

Mono-, di-, trisaccharides

(proenzymes, zymogens)

Subclavian vein

Portal Vein

(emulsification)

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Review • Alimentary canal (direct contact with food)

– Mouth, pharynx, esophagus, stomach, small and large intestines, anal canal

• Accessory structures (no direct contact with food, but provide secretions)– Salivary glands, liver, gall bladder, pancreas

• Four layers of the alimentary canal– Mucosa – absorption, secretion, protection– Submucosa – nutrition and transport– Muscularis – movement– Serosa – protection, lubrication

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Review • Wave-like movement of alimentary canal is

called peristalsis– Results from stretching– Bowel sounds

• Innervation of the alimentary canal (enteric nervous system)– Parasympathetic – increases activity– Sympathetic – decreases activity

• Mouth– Mastication – mechanical processing of food

and mixing with saliva

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Review • Tongue

– Lined by mucous membranes– Thick, skeletal muscle– Papillae function in food handling and taste– Lingual frenulum– Lingual tonsils– Lingual glands secrete lingual lipase

• Palate (roof of oral cavity)– Hard palate (Palatine proc. of maxillary bones)– Soft palate

• Uvula is suspended from this• Uvula closes opening to nasal cavity (nasopharynx)

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Review • Tonsils

– Lingual (back of tongue)– Palatine (lateral to tongue)– Pharyngeal (posterior wall of pharynx; adenoids)

• Teeth– Primary teeth (deciduous teeth; baby teeth)

• 6 months to 2-4 years

• 20 total

– Secondary (permanent teeth)• 6 yrs to 17-25 years

• 32 total

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Review • Teeth (continued)

– Incisors – sharp for biting– Cuspids (canine) – for grasping/tearing– Bicuspids and molars – grinding– Structure

• Crown – above gum line• Root – below gum line• Outer covering is enamel

– hardest substance in body– NOT replaceable

• Inner substance is dentin (alive)• Pulp cavity• Periodontal ligament

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Review • Alimentary canal (direct contact with food)

– Mouth, pharynx, esophagus, stomach, small and large intestines, anal canal

• Accessory structures (no direct contact with food)– Salivary glands, liver, gall bladder, pancreas

• Four layers of the alimentary canal– Mucosa – absorption, secretion, protection– Submucosa – nutrition and transport– Muscularis – movement– Serosa – protection, lubrication

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Review • Wave-like movement of alimentary canal is

called peristalsis– Results from stretching– Bowel sounds

• Innervation of the alimentary canal (enteric nervous system)– Parasympathetic – increases activity– Sympathetic – decreases activity

• Mouth– Mastication – mechanical processing of food

and mixing with saliva

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Review • Tongue

– Lined by mucous membranes– Thick, skeletal muscle– Papillae function in food handling and taste– Lingual frenulum– Lingual tonsils– Lingual glands secrete lingual lipase

• Palate (roof of oral cavity)– Hard palate (Palatine proc. of maxillary bones)– Soft palate

• Uvula is suspended from this• Uvula closes opening to nasal cavity (nasopharynx)

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Review • Tonsils

– Lingual (back of tongue)– Palatine (lateral to tongue)– Pharyngeal (posterior wall of pharynx; adenoids)

• Teeth– Primary teeth (deciduous teeth; baby teeth)

• 6 months to 2-4 years

• 20 total

– Secondary (permanent teeth)• 6 yrs to 17-25 years

• 32 total

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Review • Teeth (continued)

– Incisors – sharp for biting– Cuspids (canine) – for grasping/tearing– Bicuspids and molars – grinding– Structure

• Crown – above gum line• Root – below gum line• Outer covering is enamel

– hardest substance in body– NOT replaceable

• Inner substance is dentin (alive)• Pulp cavity• Periodontal ligament

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Review • Salivary glands produce saliva which

– Moistens food– Binds food particles– Begins chemical digestion of CHO– Dissolves food (for taste)– Cleanses mouth and teeth; antibacterial

• Three pairs of salivary glands– Parotid; front of ear, watery fluid rich in

amylase– Submandibular; floor of mouth, viscous fluid– Sublingual; below tongue, thick, stringy

secretion

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Review • Salivary glands

– Sympathetic stimulation – small quantity of viscous saliva

– Parasympathetic stimulation – large volume of watery saliva

• Pharynx– Cavity connecting mouth with esophagus– Nasopharynx, oropharynx, laryngopharynx– Muscles

• Inner circular – constriction

• Outer longitudinal – movement of food bolus

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Review • Swallowing

– Initiation is voluntary; act of swallowing is NOT – it’s a reflex

– Three stages• Chewing and rolling of food into oropharynx (voluntary, buccal)

• Swallowing reflex (pharyngeal)– Epiglottis closes over larynx

– Muscles in lower pharynx relax

– Esophagus opens and food moves in

• Peristalsis in esophagus transports food to stomach (esophageal)

• Esophagus– Muscular tube connects to cardiac region of stomach

– Esophageal hiatus

– Lower esophageal (cardiac) sphincter

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Review • Stomach

– Cardiac, fundus, body, pylorus

– Mixes food and begins digestion of protein

– Limited absorption (alcohol)

– Moves food into small intestine

– Pyloric sphincter (entrance to small intestine)

– Rugae and gastric pits

– Gastric glands• Mucous cells (goblet) – secrete mucous

• Chief cells (peptic) – secrete digestive enzymes, esp. pepsinogen

• Parietal cells (oxyntic) – secrete HCl (Parietal, pH)

• Infants only - Gastric lipase and rennin

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Review• Regulation of gastric activity

– Cephalic phase (primarily neural)• Prior to food entry into stomach

• Increased motility and production of gastric juice

– Gastric phase• Neural: Food entering stomach / pH rising

• Hormonal: gastrin release

• Local: histamine release (stimulates parietal cells)

– Intestinal phase• Neural: distension of duodenum (enterogastric reflex)

• Hormonal: CCK, GIP, and secretin, gastrin

• Reduction (slowing) of gastric emptying

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Review• Pancreas

– Both exocrine and endocrine functions– Main source of intestinal digestive enzymes

• Pancreatic amylase (starches)• Pancreatic lipase (fats)• Nucleases• Proteolytic proenzymes / enzymes

– Regulation of pancreatic activity• Acid chyme stimulates secretin• Secretin stimulates watery buffering secretion• Parasympathetic NS and CCK stimulate production

and secretion of digestive enzymes