TOPIC 8 Digestive System

1
TOPIC 8Digestive System
Biology 221 Anatomy Physiology II

• Chapter 18
• pp. 651-677

E. Lathrop-Davis / E. Gorski / S. Kabrhel
2
Digestive System Functions

• Provide nutrients in usable form
• Remove unusable wastes

3
Digestive System Overview

• Two main groups of organs
• Alimentary canal (a.k.a. Gastrointestinal tract)
• tube through which food passes
• responsible for digestion and absorption of food
• mouth, pharynx, esophagus, stomach, small
  intestines, large intestines
• Accessory organs
• organs, glands and structures which aid digestion
  but not part of GI tract itself
• teeth, tongue, salivary glands, pancreas, liver,
  gall bladder

Fig. 24.1, p. 888
4
Processes of Digestion

• Ingestion entrance of food and drink into mouth
• Mechanical digestion physical breakdown into
  smaller pieces
• Propulsion movement through gut
• Chemical digestion breakage of molecules into
  smaller compounds
• Absorption uptake of nutrients from lumen
• Defecation removal of indigestible material

Fig. 24.2, p. 889
5
Peritoneum

• Serous membrane
• parietal peritoneum lines abdominal cavity
• organs posterior to the parietal peritoneum are
  retroperitoneal
• visceral peritoneum (serosa) covers surfaces of
  most abdominal organs
• Mesenteries double layer of peritoneum
  extending from body wall to digestive organs
• intraperitoneal organs are those in mesentaries
• Peritoneal cavity fluid-filled space between
  visceral and parietal peritoneum
• Peritonitis inflammation of the peritoneum

See also Fig. 24.5, p. 891
Fig,. 24.30, p. 929
6
Splanchnic Circulation

• Arteries serving the digestive organs
• Celiac Trunk very short gives rise to
• hepatic artery liver gall bladder stomach
  duodenum
• left gastric artery stomach inferior esophagus
• splenic artery spleen stomach pancreas
• Superior Mesenteric Artery small intestines
  most of large intestine pancreas
• Inferior Mesenteric Artery large intestine

Fig. 20.22, p. 761
Fig. 20.22, p. 759
7
Hepatic Circulation Hepatic portal system

• Veins draining digestive organs and carrying
  nutrient-rich blood to liver
• gastric vein drains stomach
• superior mesenteric vein drains small intestine
• splenic vein drains spleen
• inferior mesenteric vein drains large intestine
• Venous blood from hepatic portal system mixes
  with arterial blood (hepatic artery) in liver

Fig. 20.27, p. 771
8
Hepatic Circulation Hepatic Veins

• drain venous blood from liver into inferior vena
  cava

Fig. 20.27, p. 771
9
Mucosa

• Mucous membrane lining gut
• Consists of
• epithelium lining
• lamina propria areolar connective tissue layer
• muscularis mucosae smooth muscle

http//www.usc.edu/hsc/dental/ghisto/gi/d_1.html
10
Mucosa Epithelium

• Type varies depending on location
• stratified squamous epithelium found in mouth,
  esophagus and anal canal
• simple columnar epithelium found in stomach and
  intestines
• Secretes mucus, digestive enzymes, hormones
• Provides intact barrier to protect against entry
  of bacteria

http//www.usc.edu/hsc/dental/ghisto/gi/c_2.html
http//www.usc.edu/hsc/dental/ghisto/gi/d_15.html
11
Mucosa Lamina Propria

• Layer of areolar connective tissue
• Blood capillaries nourish epithelium, absorb and
  transport digested nutrients
• Lymphatic capillaries provide drainage for
  interstitial fluid and transport fats to venous
  circulation

http//www.usc.edu/hsc/dental/ghisto/gi/d_60.html
12
Mucosa Muscularis Mucosae

• Smooth muscle used for local movement and to hold
  mucosa in folds (small intestine)

http//education.vetmed.vt.edu/Curriculum/VM8054/L
abs/Lab19/EXAMPLES/Exileum.htm
13
Submucosa

• Dense connective tissue superficial to mucosa
• Highly vascularized
• Many lymphatic vessels
• Lymph nodules
• MALT mucosa-associated lymphatic tissue
• especially in small (Peyers Patches) and large
  intestines

http//education.vetmed.vt.edu/Curriculum/VM8054/L
abs/Lab19/EXAMPLES/Exileum.htm
14
Muscularis Externa (Muscularis)

• Two layers in most organs (3 in stomach)
• circular layer
• longitudinal layer
• Peristalsis moves material through gut
• Segmentation helps mix material with digestive
  enzymes in small intestine

Fig. 24.3, p. 890
15
Serosa

• Visceral peritoneum simple squamous epithelium
  (mesothelium) with areolar CT
• Adventitia dense connective tissue covering
  without epithelium found around esophagus
• Retroperitoneal organs have both a serosa (of
  parietal peritoneum) and adventitia (on side
  abutting body wall)

16
Enteric Nervous System

• Intrinsic nerve plexuses
• Enteric neurons
• neurons able to act independently of central
  nervous system
• communicate with each other to control GI
  activity
• Two main enteric plexuses
• submucosal nerve plexus regulates glands in
  submucosa and smooth muscle of muscularis mucosae
• myenteric nerve plexus regulates activity of
  muscularis externa (with aide of submucosal nerve
  plexus)

17
Central Nervous System Control

• Enteric nerve plexuses linked to CNS by visceral
  afferent (sensory) fibers
• Digestive system receives motor input from
  sympathetic and parasympathetic divisions of
  autonomic nervous system
• parasympathetic outflow generally increases
  activity
• sympathetic outflow generally decreases activity

18
Mouth (Oral Cavity)

• Oral oriface is anterior opening
• Mouth is continuous with oropharynx
• Lips and cheeks keep food in oral cavity
• Three layers of tissue
• mucosa (stratified squamous epithelium)
• submucosa
• muscularis externa (skeletal muscle)

19
Mouth Palate

• Hard palate
• palatine process of maxilla
• palatine bones
• Soft palate
• muscle only
• prevents food from entering nasopharynx during
  swallowing
• uvula (part that hangs down in middle)

Fig. 24.7, p. 895
20
Mouth Arches

• Palatoglossal arch anchors soft palate to
  tongue
• Palatopharyngeal arch anchors soft palate to wall
  of oropharynx
• Fauces area between arches
• palatine tonsils located in fauces

Fig. 24.7, p. 895
21
Mouth Tongue

• Lingual tonsil sits at base of tongue protects
  against invasion by bacteria
• Taste buds
• contain receptors for taste
• found in some papillae

Fig. 24.8, p. 896
22
Mouth Tongue

• Tongue forms bolus
• ball of food
• makes food easier to swallow
• keeps food between teeth
• Muscles served by nerve XII
• intrinsic muscles within tongue (not attached
  to bone) allow tongue to change shape for
  swallowing and speech
• extrinsic muscles attach to bone or soft
  palate alter tongue position (protrusion,
  retraction, side-to-side)

Fig. 24.7, p. 895
23
Salivary Glands

• Produce saliva
• Two groups of salivary glands
• intrinsic glands (buccal glands) within oral
  cavity
• extrinsic glands 3 pairs (see AP I Unit VI for
  innervation)
• parotid glands (connected to oral cavity by
  parotid duct mumps is a viral infection of the
  parotid glands)
• sublingual glands
• submandibular glands

Fig. 24.9, p. 897
24
Saliva

• Mucus cells produce mucus (less common)
• Watery saliva produced by serous cells
  composition
• 97-99.5 water
• slightly acidic (pH 6.8)
• electrolytes (ions such as Na, K, Cl-, PO4,
  HCO3-)
• metabolic wastes (urea, uric acid)
• proteins

25
Salivary Proteins

• Mucin glycoprotein portion of mucus that
  lubricates oral cavity)
• Lysozyme antibacterial
• IgA antibodies that prevent antigens from
  attaching to mucus membrane
• Defensins secreted by neutrophils act as local
  antibiotic and chemotatic agent when mucosa is
  damaged
• Salivary amylase hydrolyzes starch

26
Control of Salivation

• Sympathetic division
• stimulates production of mucin-rich saliva, or
• inhibits salivation altogether at high levels

27
Control of Salivation

• Parasympathetic division of ANS stimulates
  activity
• chemoreceptors (excited most by acidic
  substances) and baroreceptors (excited by
  mechanical stimuli) send messages to salivatory
  nuclei in pons and medulla
• parasympathetic motor output results in
  salivation
• psychological control response to visual,
  olfactory stimuli, even thoughts of food
• salivary nuclei are stimulated by irritation to
  lower GI tract
• Parasympathetic nerves
• facial to submandibular, sublingual
• glossopharyngeal to parotids

28
Teeth

• Lie in alveoli of mandible and maxilla (see AP I
  axial skeleton lab)
• Primary dentition deciduous teeth (20 milk or
  baby teeth)
• roots are absorbed as permanent teeth grow in,
  causes baby teeth to fall out

Fig. 24.10, p. 899
29
Teeth

• Permanent dentition adult teeth (32)
• 8 Incisors (central and lateral)
• 4 Canines (eyeteeth)
• 8 Bicuspids premolars
• Molars
• 4 first molars
• 4 second molars
• 4 third molars
• wisdom teeth
• may become impacted as grow in

Fig. 24.10, p. 899
30
Tooth Structure

• Crown - covered by enamel (hardest substance in
  body) underlain with dentin
• Neck
• Root
• cementum calcified connective tissue covering
  dentin of root attaches root to periodontal
  ligament which anchors tooth to alveolus
• no enamel (dentin is under cementum)
• pulp cavity houses blood vessels and nerves
  that enter/leave via apical foramen in the root
  canal

Fig. 24.11, p. 900
31
Pharynx

• Only oropharynx and laryngopharynx are involved
  in digestion (nasopharynx is only respiratory)
• Lined with nonkeratinized stratified squamous
  epithelium
• Mucus-producing glands in submucosa produce mucus
  that lubricates food
• Skeletal muscle responds to somatic reflexes to
  move food quickly past laryngopharynx
• No serosa or adventitia

32
Esophagus

• Runs from laryngopharynx through mediastinum to
  stomach
• All 4 layers present in wall
• Mucosa consists of stratified squamous
  epithelium
• Submucosa mucus-secreting esophageal glands

http//www.usc.edu/hsc/dental/ghisto/gi/c_2.html
33
Esophagus

• Muscularis changes type as goes down
• top 1/3 skeletal muscle
• middle 1/3 mix
• bottom 1/3 smooth muscle
• Adventitia dense connective tissue covering

http//www.usc.edu/hsc/dental/ghisto/gi/d_8.html
http//www.usc.edu/hsc/dental/ghisto/gi/d_3.html
34
Structures Associated with the Esophagus

• Upper esophageal sphincter controls movement of
  material from pharynx into esophagus
• Esophageal hiatus opening in diaphragm that
  allows esophagus to pass from thoracic cavity
  into abdominal cavity
• Gastroesophageal (cardiac) sphincter
• thickening of smooth muscle of inferior esophagus
• aided by diaphragm to close bottom of esophagus
• helps prevent reflux of acidic gastric juice

35
Esophageal Disorders

• heartburn failure of lower esophageal sphincter
  to close completely allowing acidic gastric juice
  into esophagus
• hiatus hernia protrusion of the superior
  portion of stomach above diaphragm
• esophageal ulcer erosion of wall due to chronic
  reflux of stomach acid

36
Digestive Processes in Mouth, Pharynx and
Esophagus

• Ingestion
• Mechanical Digestion
• mastication by teeth (with aid of tongue)
• formation of bolus
• Chemical digestion by salivary amylase produced
  by salivary glands
• breaks starch and glycogen into smaller fragments
  (including maltose disaccharide if left long
  enough)
• continues activity until reaches acid stomach
• Absorption essentially none (except some drugs,
  e.g., nitroglycerine)

37
Digestive Processes in Mouth, Pharynx and
Esophagus

• Movement deglutition (swallowing)
• moves food from oral cavity to stomach
• voluntary in oral cavity (buccal phase)
• reflexive in pharynx
• involuntary peristalsis where smooth muscle is
  found

Fig. 24.13, p.904
38
Stomach Gross Anatomy

• Cardiac region (cardia)
• Fundus - temporary storage area
• Body
• greater curvature
• lesser curvature
• Pyloric region distal portion
• Pyloric sphincter controls movement of chyme
  into small intestine

http//medlib.med.utah.edu/WebPath/GIHTML/GI194.ht
ml
Fig. 24.14, p. 905
http//medlib.med.utah.edu/WebPath/GIHTML/GI194.ht
ml
39
Stomach Histology

• Mucosa
• simple columnar epithelium
• muscularis mucosae throws mucosa into folds
  called rugae
• Submucosa connective tissue
• Muscularis 3 layers create mixing waves in
  addition to peristalsis
• longitudinal layer
• circular layer
• oblique layer
• Serosa - covers stomach

http//www.gutfeelings.com/STOMACH.HTML
Fig. 24.14, p. 905
40
Microscopic Anatomy

• Surface composed mainly of goblet cells (secrete
  mucus)
• Gastric pits
• tight junctions between epithelial cells prevent
  acidic gastric juice from reaching underlying
  layers
• contain gastric glands which secrete gastric
  juice
• mucus neck cells
• parietal (oxyntic) cells
• chief (zymogenic) cells
• enteroendocrine cells

Fig. 24.15, p. 906
http//www.usc.edu/hsc/dental/ghisto/gi/d_15.html
41
Gastric Pit Cells

• Mucous neck cells secrete bicarbonate-rich mucus
• Parietal (oxyntic) cells secrete
• HCl (buffered by bicarbonate rich mucus)
• intrinsic factor (essential to absorption of Vit.
  B12 by small intestine)
• Chief (zymogenic) cells secrete
• pepsinogen (inactive form of the protease pepsin
  for protein hydrolysis)
• minor amounts of lipases (lipid hydrolysis)

42
Gastric Pit Cells

• Enteroendocrine cells release hormones and
  hormone-like products into the lamina propria
  where they are picked up by blood and carried to
  other digestive organs
• gastrin generally stimulatory
• histamine stimulates H secretion
• somatostatin generally inhibitory

43
Enteroendocrine Cells Gastrin

• most diverse action
• increases gastric cell activity, especially H
  secretion
• stimulates gastric emptying
• stimulates contraction of small intestine
• relaxes ileocecal valve
• stimulates mass movement (large intestine)

44
Enteroendocrine Cells Somatostatin

• also secreted by small intestine in larger
  amounts
• inhibits gastric secretion, motility and emptying
• inhibits pancreatic secretion
• inhibits activity in small intestine
• inhibits contraction of gall bladder

45
Digestive Processes in Stomach

• Mechanical digestion
• mixing waves help break food into smaller
  particles
• Chemical digestion produces chyme (pH 2)
• acid (HCl) secreted by parietal cells breaks some
  bonds and activates pepsinogen into pepsin
• pepsin
• produced as pepsinogen by chief cells
• hydrolyses proteins
• rennin protease secreted in children that acts
  on milk proteins

46
Digestive Processes in Stomach

• Movement
• mixing waves mix food with acid and enzymes
• peristalsis moves material through stomach and
  into small intestine
• Absorption limited to lipid soluble substances
• alcohol
• aspirin
• some other drugs

47
Regulation of Gastric Secretion

• Controlled by nervous system and hormones
• Hormonal control
• gastrin stimulates secretion
• somatostatin, gastric inhibitory protein (GIP),
  and cholecystokinin inhibit secretion
• Neural control
• autonomic control (CNS)
• parasympathetic division
• Vagus (X) nerve
• sympathetic division - thoracic spinal nerves
• local enteric nerve reflexes
• distension of stomach stimulates activity
• distension of duodenum inhibits activity

See Fig. 24.16, p. 910
48
Stimulation of Gastric Secretion

• Cephalic Phase (cerebral)
• Gastric Phase (stomach)
• Intestinal Phase (duodenum)

Fig. 24.16, p. 910
49
Inhibition of Gastric Secretion

• Cephalic Phase (cerebral)
• Gastric Phase (stomach)
• Intestinal Phase (duodenum)

Fig. 24.16, p. 910
50
Gastric Disorders

• Gastritis inflammation of underlying layers of
  wall
• Gastric ulcers erosions of stomach wall
• Helicobacter infections associated with 90 of
  all ulcers (uncertain as to whether it is
  causitive agent)
• non-infectious ulcers associated with persistent
  inflammation

51
Gastric Disorders (cont)

• Emesis vomiting
• usually caused by
• extreme stretching of stomach or small intestine,
  or
• presence of irritants in stomach (e.g., bacterial
  toxins, excessive alcohol, spicy foods, certain
  drugs)
• emetic center in medulla initiates impulses to
• contract abdominal muscles (increases
  intra-abdominal pressure)
• relax cardiac sphincter
• raise soft palate (closes off nasal passages)
• excessive vomiting results in dehydration and
  metabolic alkalosis (increased blood pH)

52
Small Intestine Gross Structure

• Diameter 2.5 cm
• Length 2-4 m (8-13) (in cadaver, 6-7 m
  20-21 because muscle is not contracted)
• Small intestine designed for secretion
  (especially proximal end) and absorption
• site of most chemical digestion
• site of most absorption
• pH 7-8
• Three areas
• duodenum (25 cm)
• jejunum
• ileum

Fig. 24.21, p. 916
53
Small Intestine Duodenum

• Receives chyme from stomach
• Hepatopancreatic ampulla
• union of common bile duct and pancreatic duct
• opens via major duodenal papilla
• hepatopancreatic sphincter (sphincter of Oddi)
  controls entry of fluid from ampulla
• Duodenal (Brunners) glands secrete alkaline
  mucus

Fig. 24.20, p. 915
http//www.usc.edu/hsc/dental/ghisto/gi/d_36.html
54
Small Intestine Jejunum Ileum

• Jejunum
• extends from duodenum to ileum
• Ileum
• extends from jejunum to large intestine
• ileocecal valve controls movement of material
  into large intestine

http//www.usc.edu/hsc/dental/ghisto/gi/d_43.html
http//www.usc.edu/hsc/dental/ghisto/gi/d_53.html
55
Small Intestine Innervation

• Parasympathetic impulses supplied by Vagus nerve
  stimulates activity
• Sympathetic impulses supplied by thoracic
  splanchnic nerves inhibit activity
• Enteric nerves act locally

Fig. 14.4, p. 517
Fig. 14.5, p. 519
56
Small Intestine Blood Supply

• Arteries
• common hepatic artery serves duodenum
• superior mesenteric artery serves most of small
  intestine
• Veins
• superior mesenteric vein drains entire small
  intestine

Fig. 20.22, p. 761
Fig. 20.27, p. 771
57
Small Intestine Overview ofSpecial Anatomical
Features

• Plicae circularis circular folds
• Villi fingerlike projections of intestinal wall
• Microvilli projections of cell membranes

http//remf.dartmouth.edu/images/humanMicrovilliTE
M/source/1.html
See Fig. 24.21, p. 916
http//www.usc.edu/hsc/dental/ghisto/gi/c_43.html
58
Small Intestine Plicae Circularis

• Circular folds
• Deep, permanent folds of mucosa and submucosa
• Force chyme to spiral through lumen
• mixes chyme with intestinal juice
• slows movement
• Why is this helpful?

http//www.shu.edu/ha/anirefs/8751.htm
http//www.udel.edu/Biology/Wags/histopage/colorpa
ge/csi/csiipcv.gif
Fig. 24.21, p. 916
59
Small Intestine Villi

• Finger-like projections of mucosa (over 1 mm
  tall)
• Each villus contains
• blood capillary bed
• lacteal
• smooth muscle - allows villus to shorten
• increases contact between villus and soup in
  lumen
• milks lacteal

http//www.udel.edu/Biology/Wags/histopage/colorpa
ge/csi/csivv.GIF
http//www.udel.edu/Biology/Wags/histopage/colorpa
ge/csi/csiivgc.GIF
See also Fig. 24.22, p. 917 Fig. 24.21, p. 916
60
Small Intestine Microvilli

• Extensions of cell membrane
• Called brush border
• Functions
• secrete brush border enzymes
• increase surface area for absorption

Fig. 24.21, p. 916
See also Fig. 24.22, p. 917
http//remf.dartmouth.edu/images/humanMicrovilliTE
M/source/1.html
61
Small Intestine Mucosa

• Renewed every 3-6 days
• Simple columnar epithelium
• goblet cells secrete mucus
• absorptive cells absorb nutrients
• bound by tight junctions
• microvilli
• Lamina propria
• blood vessels
• lacteals
• Intestinal crypts (crypts of Lieberkuhn)
  between villi
• most cells secrete intestinal juice
• Paneth cells secrete lysozyme (antibacterial)

See Fig. 24.21, p. 916
http//www.udel.edu/Biology/Wags/histopage/colorpa
ge/csi/csidmbg.GIF
http//www.usc.edu/hsc/dental/ghisto/gi/c_38.html
62
Small Intestine Submucosa

• Peyers patches lymphatic tissue for protection
  against disease
• Duodenal (Brunners) glands
• secrete alkaline mucus rich in bicarbonate to
  raise pH of chyme from lt3 to gt7
• only in duodenum

http//medicine.ucsd.edu/pathology/som213/Histolo
gyImageBank/chapter_4/slide_61_peyers/pages/a.4.61
.1.1.htm
http//www.udel.edu/Biology/Wags/histopage/colorpa
ge/csi/csidmbg.GIF
63
Small Intestine Muscularis Serosa

• Muscularis two layers of smooth muscle create
  two kinds of movement
• peristalsis moves chyme through intestine
• segmentation mixes chyme with intestinal juice
• moves between segments a few cm at a time
• intrinsic control in longitudinal muscle
  (intrinsic pacemaker cells)
• intensity altered by nervous system and hormones
• parasympathetic impulses increase strength of
  contraction
• sympathetic impulses decrease it

64
Small Intestine Muscularis Serosa

• Serosa (visceral peritoneum) outer covering
• Mesenteries
• visceral peritoneum
• attach small intestine to posterior body wall
• Intraperitoneal organs - surrounded and supported
  by mesenteries

65
Small Intestine Digestive Processes

• Mechanical digestion bile salts secreted by
  liver (stored in and released from gall bladder)
  emulsify fat globules (make them into smaller
  droplets) to increase surface area lipases have
  available to work on
• Chemical digestion hydrolysis of macromolecules
• lipid digestion
• protein digestion
• carbohydrate digestion
• nucleic acid digestion

See Fig. 24.33, p. 933
66
Small Intestine Lipid Digestion

• Pancreatic lipase
• Most common lipids are neutral fats
  (triglycerides)
• glycerol 1 fatty acid monoglyceride
• glycerol 2 fatty acids diglyceride
• glycerol 3 fatty acids triglyceride
• Triglycerides cleaved into glycerol and 3 fatty
  acids or monoglycerides and 2 fatty acids

Fig. 2.14, p. 48
67
Small Intestine Protein Digestion

• Pancreatic and intestinal proteases break
  proteins into amino acids
• Pancreatic proteases trypsin, chymotrypsin and
  carboxypolypeptidase
• secreted as inactive precoursers (trypsinogen,
  chymotrypsinogen, and procarboxypolypeptidase,
  respectively) to protect intestinal mucosa from
  being digested
• cleave large proteins into small peptides
• Intestinal proteases
• include aminopeptidase, carboxypeptidase,
  dipeptidase
• cleave small peptides into amino acids

See Fig. 2.17, p. 52
68
Small Intestine Carbohydrate Digestion

• Starches cleaved into short chains
  (oligosaccharides) and maltose (disaccharide) by
  pancreatic amylase secreted by pancreas
• Disaccharides hydrolyzed by intestinal (brush
  border) enzymes
• maltase cleaves maltose
• lactase cleaves lactose
• sucrase cleaves sucrose

Fig. 2.13, p. 46
69
Small Intestine Nucleic Acid Digestion

• Pancreatic nucleases cleave nucleic acids into
  nucleotides
• Nucleosidases and phosphatases cleave
  nucleotides into sugars, phosphates, bases

Fig. 2.22, p. 58
70
Small Intestine Absorption of Carbohydrates

• Absorption moves nutrients from lumen into cells,
  thence into interstitial fluid to blood or lymph
• Carbohydrates absorbed as monosaccharides by
• cotransport with Na (based on setting up Na
  gradient using active transport glucose and
  galactose)
• facilitated transport (fructose)

71
Small Intestine Absorption of Proteins and
Nucleic Acids

• Proteins absorbed as amino acids
• cotransport with Na (based on setting up Na
  gradient using active transport)
• proteins rarely taken up intact (absorbed
  peptides may cause food allergies)
• Nucleic acids actively absorbed as components
  sugar (ribose/deoxyribose), phosphate, nitrogen
  bases

72
Small Intestine Absorption of Lipids

• Lipids
• combine with bile salts to form micelles
• absorbed passively through lipid bilayer as
  glycerol and fatty acids or monoglycerides
• combine with proteins within cell to form
  chylomicrons which are then released into
  interstitial fluid
• chylomicrons enter lymph through lacteals
  (lymphatic capillaries) in villi and are
  transported to subclavian veins

73
Small Intestine Absorption of Vitamins

• Fat-soluble vitamins (DAKE) incorporated into
  micelles and absorbed in same manner as fats
  (passively through lipid bilayer)
• Water-soluble vitamins (C, B complex) mostly
  absorbed by diffusion
• exception is B12, which must bind to intrinsic
  factor produced in stomach to be actively
  absorbed in ileum (recognition of B12-intrinsic
  factor complex by receptors in plasma membrane of
  cells triggers active receptor-mediated
  endocytosis)

74
Small Intestine Absorption of Electrolytes

• Most actively absorbed throughout small intestine
• absorption based on how much is in food
• Na/K pump plays role (Na into/ K out)
• K passively absorbed based on gradient created
  by pump
• Iron (Fe) and calcium (Ca) only absorbed in
  duodenum
• depends on needs of body
• iron actively transported into cells where it
  becomes bound to ferritin
• calcium absorption regulated by vitamin D which
  serves as cofactor in Ca transport

75
Small Intestine Movement

• Peristalsis moves chyme through intestine
• Segmentation mixes chyme with intestinal juice

Fig. 24.3, p. 890
76
Hormonal Control of Small Intestine Activity

• Gastrin secreted by stomach
• stimulates contraction of intestinal smooth
  muscle
• stimulates relaxation of ileocecal valve
• Vasoactive intestinal peptide (VIP) from
  duodenum acts on duodenum
• stimulates secretion of bicarbonate-rich
  intestinal juice
• Somatostatin from stomach and duodenum
• inhibits blood flow and absorption from small
  intestine

77
Nervous System Control of Small Intestine Activity

• Sympathetic impulses decrease activity
• Gastroileal reflex initiated by increased
  activity in stomach
• long reflex involving brain and parasympathetic
  innervation
• parasympathetic impulses increase activity

78
Accessory Glands Liver Gross Anatomy

• Largest gland in body, approximately 1.4 kg
• Upper right hypochondriac and epigastric regions
• 4 primary lobes right, left, caudate, quadrate
• Covered by serosa except for uppermost region
  just under diaphragm

Fig. 24.1, p. 888 See Fig. 24.23, p. 919
http//telpath2.med.utah.edu/WebPath/LIVEHTML/LIVE
R002.html
79
Liver Hepatic Ducts

• Right hepatic duct serves right lobe
• Left hepatic duct serves other lobes
• Common hepatic duct
• formed from union of right and left hepatic ducts
• joins with cystic duct of gall bladder to form
  common bile duct, which joins with pancreatic
  duct to form hepato-pancreatic ampulla

Fig. 24.20, p. 915
80
Liver Ligaments

• Falciform ligament
• piece of mesentery that separates right and left
  lobes
• suspends liver from diaphragm and anterior
  abdominal wall
• Round ligament ( ligamentum teres) remnant of
  umbilical vein
• Ligamentum venosum
• remnant of ductus venosus

http//storm.aecom.yu.edu/virtualDissector/New_onl
ine_dissector/Abdomen/Abdomen5-6/photos/STEP3/PAGE
S/ligamentum20venosum_jpg.htm
http//www.shu.edu/ha/imgs/00000/8000/000/8052.jpg
See Fig. 24.23, p. 919
81
Liver Blood supply

• Hepatic artery arterial blood
• Hepatic portal vein receives nutrient-rich
  venous blood from stomach, intestines, pancreas,
  spleen (see lab for vessels)
• Hepatic vein drains venous blood into inferior
  vena cava

Fig. 20.27, p. 771
82
Liver Microscopic Anatomy

• Designed to filter and process nutrient-rich
  blood
• Composed of lobules with portal triad at each
  corner of hexagonal structure
• branch of hepatic artery (HA)
• branch of hepatic portal vein (HPV)
• bile duct (BD)

http//www.usc.edu/hsc/dental/ghisto/gi/d_88.html
Fig. 24.24, p. 921
83
Liver Microscopic Anatomy (cont)

• Sinusoids specialized capillaries in which
  venous and arterial blood mix
• hepatocytes (liver cells) just inside walls of
  sinusoid perform functions of liver
• Kupffer cells (macrophages) found along wall
  remove debris, bacteria, worn out RBCs

Fig. 24.24, p. 921
84
Liver Microscopic Anatomy (cont)

• Central vein drains lobule
• join to form hepatic veins
• Bile canaliculi channels between hepatocytes
• join to form bile ducts
• bile flow is counter to blood flow

http//www-edlib.med.utah.edu/WebPath/LIVEHTML/LIV
ER003.html
Fig. 24.24, p. 921
85
Liver Functions

• Process blood-borne nutrients
• Store glucose (as glycogen)
• Store fat-soluble vitamins
• Store iron (Fe)
• Detoxify poisons
• Produce plasma proteins (see Topic 1)
• Cleanse blood of debris, including bacteria and
  worn out RBCs
• Produce bile

86
Liver Functions Bile

• Consists of bile salts, bile pigments,
  cholesterol, neutral fats, phospholipids,
  electrolytes in water
• Aid digestion of fat
• emulsify (break up) fat globules into droplets
• form micelles (ferry fats to mucosal wall)
• Conserved by enterohepatic circulation (some is
  reabsorbed by ileum and returned to liver via
  hepatic portal system)
• Main bile pigment is bilirubin
• formed from breakdown of hemoglobin
• metabolized by bacteria in large intestine
  (becomes brown pigment)

87
Control of Bile Production

• Stimulated by bile salts returning via hepatic
  portal blood
• Stimulated by secretin (hormone secreted by small
  intestine in response to fats in chyme)

Fig. 24.25, p. 923
88
Liver Disorders/Disease

• Hepatitis inflammation of liver, often caused
  by viral infection
• transmitted enterically (HVA) or through blood
  (HVB, HVC, HVD)
• blood-borne viruses are linked to chronic
  hepatitis and cirrhosis
• Cirrhosis chronic disease characterized by
  growth of scar tissue
• Jaundice yellowing of skin due to build up of
  bilirubin from liver disease or excessive
  destruction of RBCs (e.g., neonatal jaundice)

89
Accessory Glands Gall Bladder

• Lies in depression on ventral surface of liver
• Thin-walled, muscular sac (holds about 50 ml)
• Stores and concentrates bile
• Releases bile via cystic duct
• Histology
• mucosa cells contain microvilli for
  reabsorption of water
• submucosa dense CT
• muscularis contracts to expel bile
• serosa over ventral portion only

http//www.usc.edu/hsc/dental/ghisto/gi/d_91.html
90
Control of Bile Release

• Bile produced by liver backs up into gall bladder
  when hepatopancreatic sphincter is closed
• Gall bladder releases bile into cystic duct when
  stimulated by cholecystokinin (secreted by
  duodenum) and/or parasympathetic impulses
• Release inhibited by somatostatin produced by
  stomach and duodenum

Fig. 24.25, p. 923
91
Disorders of the Gall Bladder

• Gallstones (biliary calculi) result from
  crystallization of cholesterol due to excess of
  cholesterol or too little bile salts
• Obstructive jaundice yellowish coloration of
  skin due to build up of bile pigments caused by
  blockage of bile ducts

92
Accessory Glands Pancreas

• Mostly retroperitoneal, head encircled by
  duodenum, tail abuts spleen
• Acinar cells (acini)
• secrete pancreatic juice rich in enzymes, which
  are stored in zymogen granules until release
• pancreatic juice excreted through pancreatic duct
• Islets of Langerhans endocrine cells
• secrete insulin, glucagon, somatostatin

http//www.usc.edu/hsc/dental/ghisto/gi/d_95.html
See Fig. 24.20, p. 915
93
Composition of Pancreatic Juice

• Watery, rich in bicarbonate (HCO3-)
• bicarbonate makes it alkaline and neutralizes
  acidity of chyme
• Digestive enzymes see Small Intestine
  Digestion
• proteases released as zymogens (inactive
  precursors)
• trypsin released as trypsinogen (activated by
  enterokinase enzyme in brush border cells)
• carboxypeptidase chymotrypsin activated from
  precursors by trypsin

94
Pancreatic Enzymes (cont)

• Digestive enzymes
• amylase hydrolyzes starch and glycogen (animal
  starch) into short carbohydrate chains and
  maltose
• lipases hydrolyze neutral fats into fatty acids
  and glycerol (or mono- and diglycerides)
• nucleases hydrolyze nucleic acids into
  nucleotides
• nucleosidases hydrolyze nucleotides into
  ribose, nitrogen bases and phosphate

95
Control of Pancreatic Secretion

• Secretin
• released from small intestine in response to
  acidic chyme entering duodenum
• stimulates acini to produce juice rich in
  bicarbonate
• Cholecystokinin
• released from duodenum in response to fatty or
  protein-rich chyme
• stimulates acini to secrete juice rich in enzymes
• Vagus nerve stimulates secretion during
  cephalic and gastric phases of digestion

Fig. 24.28, p. 925
96
Pancreas Endocrine Role Insulin

• Secreted when blood glucose increases
• Lowers blood sugar by
• stimulating uptake by body cells (except liver,
  kidney and brain)
• stimulates glycogen formation in liver and
  skeletal muscle
• inhibits gluconeogenesis (conversion of fats and
  protein to glucose) in liver
• stimulates carbohydrate metabolism in most cells

97
Pancreas Endocrine Role Glucagon

• Secreted in response to low blood glucose
• Increases blood sugar by
• Promotes breakdown of glycogen by liver
  (glycogenolysis)
• Stimulates synthesis of glucose from lactic acid
  and noncarbohydrate sources (gluconeogenesis) by
  liver
• Stimulates release of glucose into blood by liver
• Inhibits uptake and use of carbohydrates by
  skeletal muscle

98
Disorders of the Pancreas

• Pancreatitis inflammation of the pancreas
• may be caused by excessive fat in blood
• activation of enzymes within pancreas (pancreas
  digests itself)

99
Large Intestine

• Located primarily in abdominal cavity, distal end
  is in pelvic cavity
• Larger in diameter, but shorter (1.5 m) than
  small intestine
• Modifications
• teniae coli reduction of longitudinal layer of
  muscularis
• haustra pocket-like sacs formed by motor tone
  of teniae coli
• epiploic appendages small, fat-filled pouches
  of visceral peritoneum

Fig. 24.29, p. 928
100
Large Intestine Subdivisions

• Cecum
• vermiform appendix
• Colon
• ascending
• transverse
• descending
• sigmoid
• Rectum

Fig. 24.29, p. 928
101
Large Intestine Anal Canal

• Arranged as anal columns (long folds of anal
  mucosa)
• composed of stratified squamous epithelium
• anal sinuses secrete mucus when compressed by
  feces
• Sphincters control defecation
• internal anal sphincter smooth muscle
• external anal sphincter skeletal muscle

Fig. 24.29, p. 928
102
Large Intestine Histology

• Mucosa thicker than in small intestine
• crypts contain numerous goblet cells
• simple columnar epi. with lots of goblet cells
• stratified squamous in anal canal
• Submucosa thinner than in small intestine
• less lymphatic tissue
• Muscularis longitudinal layer is modified as
  teniae coli
• Serosa covers all but region in pelvic cavity

http//www.usc.edu/hsc/dental/ghisto/gi/d_60.html
See Fig. 24.31, p. 930
103
Intestinal Flora

• Resident bacteria dominated by Escherichia coli
  (E. coli)
• Ferment some indigestible carbohydrates
• results in mixture of irritating acids and gases
• Synthesize B vitamins and vit. K

104
Digestion in Large Intestine

• No additional breakdown of molecules except by
  bacteria
• Reabsorption of water and electrolytes (very
  important to water and electrolyte balance)
• Absorption of vitamins produced by bacteria

105
Movements in Large Intestine

• Formation of feces
• Haustral churning
• slow process in which distention of hastrum
  stimulates contraction which moves food into next
  haustrum
• mixes food residue and aids water reabsorption
• Mass peristalsis
• long, slow movements along length of large
  intestine force food toward rectum
• stimulated by gastrocolic reflexes based on
  stretching of stomach

106
Defecation

• Parasympathetic reflex relaxation of smooth
  muscle (internal) sphincter
• Voluntary relaxation of external sphincter
  (skeletal muscle)

Fig. 24.32, p. 931
107
Large Intestine Disorders

• Appendicitis inflammation of the appendix,
  usually caused by bacterial infection
• Diarrhea
• watery stools due to shortened residence time
• caused by irritants, bacterial or viral disease
• loss of water and electrolytes can lead to
  dehydration and electrolyte imbalances
• Constipation
• hard stools due to increased time for water
  reabsorption
• can also lead to electrolyte and pH imbalances

108
Large Intestine Disorders

• Hemorrhoids inflammation of the superficial
  anal veins
• Colitis inflammation of the colon
• Diverticulosis
• formation of small herniations in mucosa of large
  intestine
• common in elderly, especially those whose diets
  are low in bulk (fiber from fruits and vegetables
  provides bulk)
• Diverticulitis inflammation of diverticula
• Crohns disease chronic inflammation usually
  in ileum or large intestine