CH. 24 - DIGESTIVE SYSTEM
I. INTRODUCTION & OVERVIEW
A. FUNCTIONS
1. INGESTèDIGESTèEGEST
MOUTHèG.I. TRACTèANUS
2. ABSORPTION OF:
a. Nutrients for energy & building blocks
b. Electrolytes
c. Water
B. ANATOMY (Fig. 24.1, p. 868)
ORAL CAVITYèPHARYNXèESOPHAGUSèSTOMACHè
SMALL INTESTINE (LIVER, GALLBLADDER & PANCREAS) è
LARGE INTESTINE (APPENDIX) èANUS
C. HISTOLOGY - ***KNOW 4 TUNICS in G.I. tract (Fig. 24.4, p. 871)
1. MUCOSA - innermost
a. Mucous epith.
i. Strat sq. - Mouthèesophagus & anus
ii. Simple columnar - stomach & intestine
b. Lamina Propria - loose C.T.
c. Muscularis mucosae - thin smooth muscle
2. SUBMUCOSA - C.T.
a. Nerves, vessels & glands
b. Submucosal plexus - Parasymp. nervous tissue
3. MUSCULARIS - smooth muscle
a. Inner - circular
b. Outer - longitudinal
c. * Stomach has 3 layers - oblique
d. Myenteric plexus - Parasymp.
Myenteric + submucosal = Intramural/enteric plexus
(controls movement & secretion)
4. SEROSA/ADVENTITIA
a. SEROSA = C.T. + Visceral peritoneum
b. ADVENTITIA = C.T. w/out visc. peritoneum
i. retroperiton. org. & esophagus
5. ACCESSORY STRUCTURES = GLANDS
a. Unicellular - in mucosa
b. Multicellular - in mucosa or submucosa
c. Multicellular - outside tunics
- Liver, gallbladder, pancreas, salivary glands
D. PHYSIOLOGY (Tab. 24.1, p. 869)
INGESTIONèMASTICATIONèPROPULSION (Deglutition &
Peristalsis) èMIXINGèSECRETION (Mucus, H2O, bile &
enzymes) èDIGESTION (Mechanical & Chemical) èABSORPTION
èTRANSPORTATIONèELIMINATION (Defecation) èREGULATION
(Local, nervous & hormonal)
II. ANATOMY & HISTOLOGY OF DIGESTIVE ORGANS
A. ORAL CAVITY – MOUTH (Fig. 24.6, p. 875)
1. BOUNDRIES
a. Lips - anterior
b. Fauces - posterior
c. Cheeks - lateral
d. Palate - roof
e. Muscular floor & tongue - inferior
2. TONGUE
a. Intrinsic muscles - 3 directions, D shape
b. Extrinsic muscles, move tongue, attach post.
c. Speech, moving food & taste
3. TEETH (Fig. 24.7, p. 877)
a. 20 10, Deciduous, milk teeth
b. 32 20, Permanent
c. Dental Formula - 4 quadrants w/ 8 @
i. I2 - Incisors
ii. C1 - Canine
iii. P2 - Premolars
iv. M3 - Molars
d. Anatomy (Fig. 24.8, p. 877)
i. Crown - enamel, Ca hydroxyapatite w/ OH replaced w/ fluoride, hard, acid-resistant
ii. Neck - Dentin - calcified tissue
iii. Root - Anchor, w/ apical foramen
e. Other:
i. Periodontal ligaments
ii. Cementum
iii. Gingiva - gums = Dense C.T. + Strat Sq. Epith
iv. Pulp - Nerves & vessels
v. Alveoli = sockets in Mandible & Maxilla for teeth
4. TONSILS - Immunity
5. SOFT PALATE & UVULA - prevent food from getting into Nasopharynx
6. SALIVARY GLANDS (Fig. 24.9, p. 878)
a. PAROTID - by ear, serous, Mumps = viral infection
b. SUBMANDIBULAR - serous & mucus
c. SUBLINGUAL - mucus
d. Other small
B. PHARYNX
C. ESOPHAGUS
1. 4 Tunics
2. Upper 1/3 Skeletal, voluntary swallowing
3. Middle 1/3, mixed skeletal & smooth
4. Lower 1/3, smooth muscle
D. STOMACH - (Fig. 24.11, p. 883)
1. Parts
2. Openings - 2
3. 4 Tunics - 3 muscle layers in muscularis
4. Rugae - “ROOGEE”, folds, distensible
5. Gastric pits
E. SMALL INTESTINE - 6 m (Fig. 24.15, p. 890)
1. DUODENUM - “12 finger width’s length”
a. Hepatopancreatic duct
2. JEJUNUM - 2.5 m
3. ILEUM - 3.5 m
4. Plicae “PLYSEE” Circularis (Fig. 24.16, p. 891)
a. Circular folds which é surface area
b. Villi = composed of cells
i. lacteals
ii. capillaries
c. Microvilli = Brush Border, on cells
F. LARGE INTESTINE 1.8 m (Fig. 24.25 & 24.26, p. 902 & 904)
1. CECUM - blind ended w/ APPENDIX--Ascending colonè
Hepatic flexureèTransverse colonèSplenic flexureè
Descending colonèSigmoid colonèRectumèAnus
2. Teniae Coli - “TEENY-E COLEE bands of longitud. smooth mus
a. Haustra - pouches
b. Crypts - mostly mucous cells
3. Anal Sphincters - 2
a. Inner - smooth, invol., controls voiding up to 18 mos.
b. Outer - skeletal, vol., controls voiding by choice
G. LIVER - 3 lbs, largest internal organ (Fig. 24.17, p. 894)
1. Lobes
a. 2 Major - L & R
b. 2 Minor - Caudate & Quadrate
2. Porta - 3
a. Hepatic artery
b. Hepatic portal vein
c. Common Hepatic duct
3. Lobules - functional units of liver (Fig. 24.19 & 24.20, p. 895 & 896)
a. Blood flows from TriadèCentral vein
b. Bile flows from CenterèTriad
H. GALLBLADDER - sac
1. Missing submucosa - 3 tunics
2. Stores bile - from liver
3. Cystic Duct - releases bile, gallstones (chol & fatty acids)
I. PANCREAS (Fig. 24.22, p. 900)
1. Exocrine
2. Acinar cells è Digestive enzymes & HCO3-
3. Duct pathway = (Fig. 24.18, p. 895)
HepaticsèCommon HepaticèCommon Bile ductèHepatopancreatic duct
(Liver) ì ì ê
Cystic duct í Pancreatic ductì Duodenum
(Gallbladder) (Pancreas)
J. PERITONEUM - lines abdominal cavity & many organs (Fig. 24.5, p. 874)
1. Mesenteries - C.T. sheets
a. Vessels & nerves to/from organs
b. Hi fat storage
c. Omentum - fatty apron
2. Retroperitoneal - duodenum, pancreas, parts of colon,
rectum, kidneys, adrenals, bladder
III. FUNCTIONS OF DIGESTIVE SYSTEM (Tab. 24.1, p. 869 & Tab. 24.2, p. 879)
Regulation: 1. Nervous system
2. Hormonal
3. Local - intramural plexus - NO C.N.S. involvement
A. ORAL CAVITY
1. Mastication - é surface area
2. Salivary amylase - starchèdisacc., 3-5% digested here
3. Mucin - lubrication
B. DEGLUTITION - swallowing (Fig. 24.10, p. 881)
1. Voluntary phase - Bolus (food) to oropharynx
2. Pharyngeal phase
a. ReflexèEsophagus opens
b. Soft palate closes nasopharynx
c. Epiglottis closes larynx
d. Lips close
3. Esophageal phase - Peristalsis, squeezing wave, to stomach
C. STOMACH (Fig. 24.11, p. 883)
1. Secretions = GASTRIC JUICES, 2-3 L/Day, 700 ml/meal!
a. Mucous cells - mucus, protection, lubrication
b. Parietal cells
i. HCl, activates pepsin, stops carbo. dig., pH 1-3
ii. Intrinsic factor - é B12 absorption
c. Chief cellsèPepsinogenèPepsinèprotein digestion
d. Endocrine cells - Gastrin - local hormone
2. Regulation (Fig. 24.13, p. 886)
a. Cephalic (A) - thoughts/smell of foodèVagus n. è
stomachègastrinècirculationèstomachè
Parietal & Chief cell stim.
b. Gastric (B) - greatest volume of gastric juices
Food in stomachèdistentionèstretch receptorsè
é gastric juices
c. Gastrointestinal (C)
i. Acidic CHYME into duodenumè
IF pH > 3èGastrinècirc. èstomachèégastric juices
IF pH < 2èSecretinècirc. èstomachèê “ juices, ébile
ii. Fats/lipids into duodenum è
Gastric Inhibitory Polypeptide èê juices
Cholecystokinin èê juices, ébile
3. Movement in Stomach (Fig. 24.14, p. 889)
Mixing, storage, chyme
D. SMALL INTESTINE - Digestion & Absorption of Nutrients
1. Secretions
a. Goblet cells èmucus, H2O & electrolytes
b. Disaccharidases & Peptidases, SURFACE-BOUND enz.
- Attached to walls
c. Liver èbile; Pancreas èEnzymes & HCO3-
i. Digest Carbos, fats, proteins & Nucleic acids
ii. Stim. by Secretin & cholecysto. (Fig. 24.21, 897)
d. Also stim. by Vagus n. (parasympathetic)
e. Secretion in duodenum, secretion & absorp in duo, jej. & ileum
2. Movement
a. Chyme 3-5 hours
b. Segmentation - mixing
c. Peristalsis - movement through
E. LARGE INTESTINE - Colon
1. Secretions - mucus from goblet cells = major secretion
2. Movement - 18-24 hours
a. Chyme èFeces (held together by mucus)
b. H2O, vitamins, electrolytes and some A.A. absorbed
i. CONSTIPATION - too much H2O absorbed
ii. DIARRHEA - not enough H2O absorbed
c. Segmentation - mixes
d. Mass Movements - 3-4X daily
3. Endosymbionts - E. coli, etc.
a. Bulk (30%) dry weight of feces
b. Flatus - gas
c. Vitamin K synthesis
F. LIVER
1. Bile - emulsify fats
2. Storage - glycogen, vitamins, fat & minerals
3. Nutrient interconversion
4. Detoxification, i.e. ammonia è urea, alcohol
5. Phagocytosis - old RBC’s, WBC’s, bacteria, debris
6. Synthesis of plasma proteins