Gastrointestinal System - PowerPoint PPT Presentation

Loading...

PPT – Gastrointestinal System PowerPoint presentation | free to download - id: 3cf78b-NzRjN



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Gastrointestinal System

Description:

Gastrointestinal System Chapter 23 Rugae Rugae Absorption: Small Intestine (Fats) Monoglycerides (cont) Triglycerides are then packaged with cholesterol ... – PowerPoint PPT presentation

Number of Views:62
Avg rating:3.0/5.0
Slides: 105
Provided by: facultyMw9
Learn more at: http://faculty.mwsu.edu
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Gastrointestinal System


1
Gastrointestinal System
  • Chapter 23

2
GI Overview Organ systems
  • Gastrointestinal (GI) tract Alimentary canal a
    continuous muscular digestive tube
  • Digests
  • breaks food into smaller fragments
  • Absorbs
  • digested material is moved through mucosa into
    the blood
  • Eliminates
  • unabsorbed secreted wastes.

3
Organ systems
  • Includes
  • Mouth, pharynx esophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Accessory digestive organs teeth, tongue, gall
    bladder, salivary glands, liver pancreas

Figure 23.1
4
Processes
  • Ingestion
  • Propulsion
  • Mechanical digestion
  • Chemical digestion
  • Absorption
  • Defecation

5
Processes
  • Ingestion obtaining food
  • Propulsion moves food along the GI tract by
    peristalsis (wave-like muscular contraction)
  • Mechanical digestion
  • chewing mixing with saliva
  • mixing in stomach
  • segmentation (local constriction in intestine to
    mix food digestive juices)

6
Processes
  • Chemical digestion breaks down food to molecular
    fragments (monomers) (Hydrolysis).
  • Begins in the mouth with saliva continues into
    the small intestine.
  • Absorption movement of nutrients across the
    mucosal membrane into blood/lymph
  • Defecation eliminates unused/indigestible
    secreted substances from the body

7
Functional Considerations
  • Substances in the GI tract lumen are outside of
    the body.
  • Multiple sensors receptors line the GI tract to
    monitor contents respond to conditions.
  • Controls intrinsic (local control) extrinsic
    (CNS)

8
Peritoneum serous membrane
  • Visceral peritoneum covers the external surfaces
    of most digestive organs
  • Parietal Peritoneum lines the body wall
  • Peritoneal Space potential space containing
    fluid that separates the visceral parietal
    peritoneum

Figure 23.5a
9
Peritoneum
  • Mesentery double layer of peritoneum fused
    together that extends to the organs from the
    posterior body wall.
  • Provides support for the organs
  • Provides support for vessels nerves supplying
    the organs

Figure 23.5a
10
Peritoneum
  • Retroperitoneal organs
  • Organs that adhere to the posterior abdominal
    wall lose their peritoneum by resorption
  • Parts of the large small intestine most of
    the pancreas (also kidneys)

Figure 23.5b
11
GI blood supply
  • Blood supply about 25 of cardiac output
  • Arterial Abdominal aorta g celiac trunk
  • Celiac trunk g Hepatic, splenic gastric
    branches which serve the liver, spleen stomach
  • Celiac trunk g superior inferior mesenteric
    branches serve small large intestine

12
Histology
  • GI tract wall has 4 layers
  • Mucosa
  • Submucosa
  • Muscularis Externa
  • Serosa or Adventitia

13
Histology of the Alimentary Canal
Figure 23.6
14
Histology
  • Mucosa The epithelial membrane that lines the GI
    tract from mouth g anus.
  • Secretes mucous, digestive enzymes hormones
  • Absorbs nutrients
  • Protects from disease from the GI contents

15
Histology
  • Mucosa 3 layers
  • Epidermis
  • Lamina propria (loose ct contain capillaries
    some elements of MALT)
  • Muscularis mucosa

16
Histology
  • Submucosa moderately dense CT with blood, nerve,
    lymph vessels lymphoid follicles rich in
    elastic fibers
  • Muscularis externa smooth muscle
  • Responsible for peristalsis segmentation
  • Circular layer
  • Longitudinal layer
  • Sphincters in some areasthe circular layer
    thickens act as valves

17
Histology
  • Serosa of intraperitoneal organs visceral
    peritoneum
  • Esophagus has an outer covering of fibrous
    connective tissue adventitia
  • Retroperitoneal organs visceral serosa on the
    surface facing the peritoneal cavity adventitia
    on the surface facing the body wall.

18
Nerves
  • Intrinsic (Local) Short reflex
  • Submucosal nerve plexusregulates glands
    mucosal muscle
  • Myenteric plexus controls GI wall GI motility
  • Extrinsic (CNS) Long reflex
  • Parasympathetic NS enhances gut motility
    secretion
  • SNS inhibits gut motility secretion

19
Nerves
Figure 23.4
  • Intrinsic (Local) Short reflex
  • Submucosal nerve plexus regulates glands
    mucosal muscle
  • Myenteric plexus controls GI wall GI motility
  • Extrinsic (CNS) Long reflex
  • Parasympathetic NS enhances gut motility
    secretion
  • SNS inhibits gut motility secretion

20
Functional Anatomy Mouth
  • Mouth lips, palate, tongue
  • Mouth cavity Buccal cavity

21
Functional Anatomy Mouth
  • Lips extend from inferior margin of the nose to
    the superior margin of the chin. Red area red
    margin, is poorly keratinized lacks sweat or
    sebaceous glands.
  • Palate
  • Hard palate rigid surface against which food is
    forced in chewing
  • Soft palate muscular structure that rises
    blocks off the nasopharynx during swallowing

22
Functional Anatomy Mouth
  • Tongue muscular tentacle composed of interlaced
    muscle fibers that grips repositions food,
    mixes food with saliva compresses food to form
    a food bolus, prior to swallowing.

23
Functional Anatomy Mouth
  • Filiform papillae rough surface
  • Fungiform papillae house taste buds
  • Circumvallate papillae house taste buds,
  • Foliate papillae posterolateral taste buds

24
Functional Anatomy Mouth
  • Salivary Glands intrinsic extrinsic
  • Intrinsic glands scattered throughout the buccal
    cavity mucosa
  • Extrinsic glands supply most of the saliva
    outside buccal cavity supply secretions via
    ducts
  • Parotid
  • Submandibular
  • Sublingual

25
Functional Anatomy Mouth
  • Composition of saliva
  • 97-99.5 H2O
  • Electrolytes
  • pH 6.75-7.0
  • Amylase (digestive enzyme)
  • Proteins mucin, lysozyme, IgA
  • Protection from microbes by saliva
  • IgA immunglobulins in secretions
  • Lysozyme bacteriostatic (inhibits bacterial
    growth)
  • Cyanide
  • Defensins local antibiotic activity when
    activated promote chemotaxis by WBCs
  • Normal flora convert salivary components to
    nitrates then to NO. NO is toxic bacteriocidal

26
Functional Anatomy Mouth
  • Control of Salivation
  • Continuous baseline secretory activity
  • With food ingestion, salivation increases
    dramatically
  • Parasympathetic NS chemoreceptors
    pressoreceptors stimulate salivatory nuclei to
    increase salivation

27
Functional Anatomy Mouth, Pharynx
Figure 23.07
Figure 23.11
  • Teeth
  • Primary 2I 1C 2M x 2 20 2I
    1C 2M
  • Permanent 2I 1C 2PM 3M x 2 32
    2I 1C 2PM 3M
  • Structures
  • Crown exposed above gingiva (gum)
  • Root anchored by periodontal ligament to the
    bone by a fibrous joint (gomphosis)

28
Functional Anatomy Throat Esophagus
  • Pharynx oropharynx laryngopharynx muscular
    wall propels food to the esophagus
  • Esophagus
  • Muscular 25cm tube from laryngopharynx to stomach
  • Passes through the diaphragm at the esophageal
    hiatus
  • Gastroesophageal (cardiac) sphincter A
    physiologic sphincter that helps keep esophagus
    closed when empty

29
Functional Anatomy Esophagus
  • Esophagus (continued)
  • Wall has all 4 GI tract tunics
  • Epithelial layer changes at the junction with the
    stomach from stratified squamous epithelium to
    simple columnar epithelium
  • Esophageal mucous glands lubricate food bolus
  • Muscularis externa
  • Superior 1/3 of muscularis externa is skeletal
    muscle
  • Middle 1/3 is mixed skeletal smooth
  • Lower 1/3 is smooth muscle
  • Adventitia external covering

30
Digestive Processes Mouth, Pharynx Esophagus
  • Ingestion
  • Mechanical digestion chewing
  • Chemical digestion mixing food with saliva
  • Propulsion swallowing initiating peristalsis

31
Functional Anatomy Stomach
  • Cardiac region narrow, receives food bolus
  • Fundus bulge that extends supero-laterally to
    the cardia, reaches the diaphragm
  • Body mid-portion
  • Pyloric antrum funnel shaped portion narrows to
    form the
  • Pyloric canal?
  • Pylorous ?
  • Pyloric sphincter ?
  • small intestine
  • Rugae
  • longitudinal mucosalfolds
  • volume about 4L

Figure 23.14a
32
Rugae
33
Microscopic Anatomy Stomach
  • Stomach has the 4 tunics of the GI tract.
  • Epithelium Simple columnar epithelium (goblet
    cells-mucous)
  • Muscularis externa has an additional oblique
    layer of muscle (allows another dimension of
    contraction).

34
MicroscopicAnatomy Stomach
  • Gastric glands secrete gastric juices

Figure 23.15
35
Microscopic Anatomy Stomach
  • Mucous neck cells in the duct portion

Figure 23.15
36
Microscopic Anatomy Stomach
  • Gastric glands secrete gastric juices
  • Mucous neck cells in the duct portion
  • Parietal cells mid portion secrete HCl
    intrinsic factor for B12 absorption

Figure 23.15
37
Microscopic Anatomy Stomach
  • Gastric glands secrete gastric juices
  • Mucous neck cells in the duct portion
  • Parietal cells mid portion of glands secrete HCl
    intrinsic factor
  • Chief cells base of gland secretes pepsinogen a
    precursor molecule to pepsin (an enzyme that
    digests protein)

Figure 23.15
38
Microscopic Anatomy Stomach
  • Enteroendocrine cells secrete multiple hormonal
    products
  • Gastrin, histamine, endorphins, serotonin,
    cholecystokinin, somatostatin, which influence
    several digestive system organs

Figure 23.15
39
Microscopic Anatomy Stomach
  • Mucosal barrier protects the stomach from its
    own secretions
  • Viscous mucous overlies a thick coating of HCO3-
    rich mucous
  • Tight junctions between epithelial cellPM of
    glandular cells are impermeable to HCl
  • Epithelium is replaced every 3-6 days

40
Digestive Processes (Stomach)
  • Acts as a holding vessel for ingested food
  • Participates in mechanical chemical digestion
  • Propulsion Delivers its product (chyme) to the
    small intestine

41
Digestive Processes (Stomach)
  • Protein digestion HCl denatures protein
  • HCl activates pepsinogen to pepsin
  • Pepsin breaks peptide bonds of proteins
  • Rennin an enzyme that breaks down casein (milk
    protein) secreted in infants
  • Intrinsic factor required for Vit. B12
    absorption (needed to mature RBC)
  • Absence of B12 results in pernicious anemia

42
Regulation of gastric secretion (3 phases)
  • Cephalic Phase
  • Gastric Phase
  • Intestinal Phase

43
Cephalic phase Stimulation
  • Cephalic phase CNS response to presentation of
    food enhances gastric gland secretion
  • Loss of appetite satiety / depression

Cephalic phase Inhibition
44
Gastric phase Stimulation
  • Gastric phase food entering stomach
  • Stretch
  • Change in pH (increase)
  • Peptides
  • All cause increased gastric gland secretion

45
Gastric phase Stimulation
  • Stretch reflex arc causes increased
    Acetylcholine release which then causes increased
    gastric gland secretions
  • Increased pH / polypeptides / caffeine
  • All enhance Gastrin secretion by enteroendocrine
    G cells

46
Gastric phase Stimulation
  • 3 chemicals cause enhanced HCl secretion through
    2nd messenger systems
  • Gastrin
  • Acetylcholine
  • Histamine

47
Gastric phase Inhibition
  • pH lt2.0 inhibits Gastrin secretion
  • SNS inhibits Gastrin (G cell) activity

48
Intestinal phase Stimulation
  • Excitatory As chyme enters the duodenum the
    mucosa secretes enteric gastrin which stimulates
    secretion by gastric glands

49
Intestinal phase Inhibition
  • Inhibitory As more chyme fills the small
    intestine, the enterogastric reflex is triggered
  • Inhibits CNS stimulation
  • Inhibits local reflexes
  • Controls gastric emptying
  • Activates sympathetic fibers that tighten the
    pyloric sphincter

50
Regulation of Gastric Activity
Figure 23.16
51
Small Intestine Gross Anatomy
  • 6-7m long from pyloric sphincter to the
    ileocecal valve
  • 3 subdivisions
  • Duodenum
  • Jejunum
  • Ileum

52
Small Intestine Gross Anatomy
Fig 23.20
  • Duodenum
  • Curves around the pancreatic head (25cm long)
  • Contains the hepatopancreatic ampulla formed by
    the merger of the bile duct the pancreatic
    duct.
  • Hepatopancreatic sphincter controls admission of
    bile pancreatic enzymes to the duodenum
  • Duodenum is retroperitoneal

53
Small Intestine Regulatory Function
  • Duodenenal regulation of gastric emptying
    Feedback mechanisms monitor the contents being
    delivered from the stomach
  • High fat content
  • Low pH (high acidity)
  • Hypertonicity (high osmolality)
  • All result in decreased stomach emptying.

54
Regulation of Gastric Emptying
Figure 23.19
55
Small Intestine Gross Anatomy
  • Jejunum extends from duodenum to ileum (2.5m
    long)
  • Ileum from jejunum to ileocecal valve (3.6m
    long)

Figure 23.1
56
Small Intestine Gross Anatomy
  • Jejunum Ileum function in absorption
  • Intraperitoneal
  • Suspended from mesentery whose veins lymph
    vessels carry nutrients away from small intestine

57
Small Intestine Microanatomy
Microvilli PM projections forming brush
border Hold enzymes that complete protein
carbohydrate digestion
  • Plicae circularis mucosal folds cause chyme to
    spiral slowly through the lumen

Villi
Villi velvety mucosa of absorptive epithelium
containing capillaries lymph lacteals
Figure 23.21
58
Small intestine Wall
  • Cell types
  • Mostly absorptive cells
  • Goblet (mucous) cells increase in number as the
    small intestine progresses
  • Enteroendocrine cells
  • T-Lymphocytes

59
Small intestine Wall
  • Intestinal crypts with cells that secrete
    intestinal juice contain Paneth cells that
    secrete protective lysozyme (antibacterial)
  • Peyers Patches lymphoid follicle in submucosa

60
Small intestine Wall
  • Brunners glands (duodenum) secrete HCO3- rich
    mucous to increase the pH of chyme
  • Villus epithelium is replaced every 3-6 days
  • Intestinal Juice isotonic with blood plasma,
    slightly alkaline, low enzyme content

61
Liver Gall Bladder
  • Liver produces bile (fat emulsifier) that is
    stored in concentrated by the gall bladder.
    (metabolic role of the liver Ch. 24)

62
Liver Gross Anatomy
  • Largest gland
  • 4 Lobes
  • Falciform ligament
  • mesentery supports liver from diaphragm
    anterior body wall
  • separates R L lobes
  • Round ligament fibrous remnant of umbilical vein

Fig 23.23
63
Liver Gross Anatomy
  • Blood supply
  • hepatic artery hepatic portal vein
  • Bile
  • drains from biliary ducts to common hepatic duct
    which fuses with cystic duct from gallbladder to
    form the bile duct

Fig 23.23
64
Liver Microscopic Anatomy
  • Liver lobule hexagonal (Fig 23.24)
  • Central vein drains the lobule
  • Hepatocytes form plates that radiate from the
    central vein

65
Microanatomy of the Liver
Figure 23.24c, d
66
Liver Anatomy
  • Portal triad at each corner of the hexagonal
    system. Consists of branches of
  • Hepatic Artery ? delivers O2
  • Hepatic portal vein ? delivers nutrients from
    small intestine
  • Bile duct ? receives bile from the bile
    canaliculi that lie between layers of hepatocytes

Figure 23.24c, d
67
Liver Anatomy
  • Liver (cont)
  • Liver sinusoids ? Large leaky capillaries conduct
    blood from the artery portal vein to the
    central vein
  • Hepatic macrophages ? Kupffer cells lie in
    sinusoid walls
  • Central veins flow into hepatic veins then to the
    inferior vena cava

Figure 23.24c, d
68
Liver Gall Bladder
  • Composition of bile Alkaline solution Bile
    salts, bile pigments, cholesterol, fats
    phospholipids
  • Bile salts phospholipids participate in fat
    absorption

69
Liver Gall Bladder
  • Bile salts are conserved by enterohepatic
    circulation
  • Reabsorbed in the ileum
  • Return to Liver in hepatic portal blood
  • Re-secreted by the Liver
  • Bile pigments bilirubin break down to urobilin
    then stercobilin

70
Gall Bladder
  • Gall Bladder a muscular pouch that stores bile
    expels bile when needed via the cystic duct
    the bile duct.

Figure 23.20
71
Regulation of Bile Release
  • Cholecystokinin (CCK) secretin released by the
    small intestine in response to increased fats in
    chyme
  • CCK
  • Stimulates both Gall bladder pancreatic
    secretion
  • Relaxes hepatopancreatic sphincter
  • Secretin stimulates bile secretion

Figure 23.25
72
Pancreas Gross Anatomy
  • Head encircled by duodenum
  • Tail abuts the spleen
  • Mostly retroperitoneal

73
Pancreatic Acini
  • Large numbers of Acinar cells in clusters around
    ducts exocrine (Acini)
  • Acinar cells Secrete pancreatic digestive
    enzymes
  • Endocrine cell clusters form the pancreatic
    islets that produce insulin glucagon

74
Pancreatic Juice
  • Pancreatic Juice Alkaline, watery, contains
    enzymes electrolytes

75
Pancreatic Juice
  • Proteolytic enzymes are released as inactive
    forms then are activated in the duodenum
  • Trypsinogen g Trypsin by the brush border enzyme
    enterokinase
  • Trypsin activates precursors to form
    carboxypeptidase chymotrypsin
  • Amylase, lipase, nuclease are released in their
    active forms

76
Regulation of pancreatic secretion
  • Neural via PSNS
  • Hormonal Intestinal Hormones
  • CCK released in response to fats protein.
    Stimulates pancreatic secretion of enzymes
  • Secretin released in response to HCl. Stimulates
    pancreatic duct cells to release HCO3-

Figure 23.28
77
Digestive Processes Small Intestine
  • Optimal digestion requires adequate motility
    control of chemical composition

78
Digestive Processes Small Intestine
  • pH acidic chyme must be buffered to allow proper
    enzyme activity
  • Osmolality chyme is hypertonic would pull H2O
    out of circulation thus chyme is released in
    small amounts
  • Liver pancreatic function are required for
    appropriate delivery of bile salts enzymes to
    the small intestine

79
Digestive Processes Small Intestine
  • Segmentation moves intestinal contents back
    forth to mix
  • Duodenal rhythm for segmentation is greater than
    the rhythm in the ileum.
  • Contents move toward the ileum.

80
Digestive Processes Small Intestine
  • After most digestion has occurred,
  • Peristalsis begins sweeping from duodenum
    distally
  • Occurs in series with each peristaltic wave,
    originating more distally (migrating mobility
    complex)
  • Ileocecal valve (sphincter) is relaxed by neural
    (gastroileal reflex) impulses from the stomach
    hormonal (gastrin) secretion by the stomach

81
Large Intestine Gross Anatomy
  • Ileocecal valve to anus (1.5m)
  • Teniae coli 3 ribbons of longitudinal smooth
    muscle
  • Haustra pocket-like segments of large intestine
  • Epiploic appendages fat filled pouches of
    visceral peritoneum

Figure 23.29a
82
Large Intestine Gross Anatomy
  • Cecum blind pouch (below ileocecal valve)
  • Appendix attached to cecum (lymphoid)
  • Colon ascending, transverse, descending, sigmoid
  • Transverse colon sigmoid colon are
    intraperitoneal anchored by mesentery. The rest
    of the colon is retroperitoneal
  • Rectum
  • Anal canal

Figure 23.29a
83
Large Intestine Microscopic Anatomy
  • All 4 layers present
  • Mucosa simple columnar epithelium until anal
    canal (stratified squamous)
  • No folds or villi. No significant enzyme
    secretions
  • Crypts invaginations of mucosa contain large
    numbers of goblet cells that secrete mucous for
    protection lubrication

84
Large Intestine Microscopic Anatomy
  • Bacterial flora
  • Ferment indigestible CHO produces about 500ml of
    gas per day
  • Synthesize B complex vitamins most vitamin K

85
Large Intestine Digestive Processes
  • Propulsion
  • Haustra contractions stretch stimulate haustra
    to contract moving ( mixing) contents to next
    haustra
  • Mass peristalsis long, slow contractile waves
    moving contents toward rectum (3-4 per day)
  • Gastrocolic reflex food intake causes mass
    peristalsis

86
Large Intestine Digestive Processes
  • H2O reabsorption vitamin absorption
  • Defecation
  • Empty rectum receives waste, causing stretch
  • Stretch initiates reflex contraction of the
    rectum relaxation of both anal sphincters
  • Voluntary control of the external anal sphincter
    can postpone defecation
  • If suppressed the contraction stops is
    reinitiated later
  • With defecation rectal muscle contractions are
    aided by increased abdominal pressure (valsalva
    maneuver)

87
Structure of the Anal Canal
Figure 23.29b
Figure 23.32
88
Chemical Digestion of Specific Food Groups
  • Chemical Digestion Mechanism
  • Catabolic process break down of food molecules
    to monomeric form that can be absorbed
  • Enzymes break molecules by hydrolysis (Adding H2O
    into a molecular bond)

89
Chemical Digestion Carbohydrates
  • Carbohydrates (CHO) complex sugars are broken
    down to simple sugars (monomers)
  • Simple sugars (monosaccharides) glucose,
    fructose, galactose can be absorbed
  • Disaccharides (not absorbed) sucrose, maltose,
    lactose are hydrolyzed by sucrase, maltase,
    lactase (brush border enzymes) into
    monosaccharides

90
Chemical Digestion Carbohydrates
  • Polysaccharides broken down to smaller smaller
    oligosaccharides
  • Salivary amylase breaks starch into 2-8 linked
    monosaccharide
  • Salivary amylase is denatured by HCl in the
    stomach

91
Chemical Digestion Carbohydrates
  • Polysaccharides (cont)
  • Pancreatic amylase continues breakdown (mostly
    to maltose)
  • Brush border enzymes act on oligosaccharides of
    more than 3 simple sugars (brush border)
  • Sucrose, maltose lactose are broken down by
    specific brush border enzymes (sucrase, maltase,
    lactase)
  • Monosaccharides are absorbed.

92
Chemical Digestion Proteins
  • Proteins broken down to amino acid monomers.
    Begins in the stomach.
  • Pepsinogen is activated to pepsin by HCL
  • Pepsin cleaves peptide bonds associated with
    tyrosine phenylalanine forming polypeptides (
    a few amino acids).
  • Pepsin is inactivated by increased pH in the
    duodenum
  • Trypsin chymotrypsin pancreatic enzymes that
    further breakdown polypeptides.

93
Chemical Digestion Proteins
  • Proteins (cont)
  • Carboxypeptidase (pancreatic brush border
    enzyme)
  • Splits off single amino acid from the end of
    polypeptide chain that contains the carboxyl
    group
  • Aminopeptidase dipeptidase (brush border
    enzymes) release final amino acid monomers
  • Figure 23.34

Figure 23.34
94
Chemical Digestion Lipids
  • Lipids require emulsification to disperse fats
    into microdroplets which enhances enzyme activity
  • Bile salts surround fat droplets keep them in
    suspension in the aqueous digestive juices
  • Pancreatic lipase cleaves off two fatty acid
    chains from triglyceride molecules
  • Yields a monoglyceride 2 free fatty acids

Figure 23.35
95
Chemical Digestion Nucleic acids
  • Nucleic acids small amounts occur in the diet
  • Pancreatic nucleases Hydrolyze nucleic acids to
    nucleotide monomers
  • Nucleosidases phosphatases (brush border) break
    down nucleotides

96
Absorption Small Intestine
  • Most nutrients are absorbed from chyme prior to
    the ileum (ileum primarily reabsorbs bile salts)
  • Most nutrients cross the mucosa by active
    transport.
  • Some products of lipid digestion are absorbed by
    diffusion.
  • CHO, amino acids nucleic acid remnants are
    actively transported into mucosal cells then
    enter capillary blood

97
Absorption Small Intestine (Fats)
  • Monoglycerides free fatty acids are associated
    with bile salts lecithin (a phospholipid) to
    form micelles
  • Micelles diffuse between microvilli
  • The lipid substances leave the micelles diffuse
    across the PM of microvilli
  • Inside the intestinal epithelial cell, the
    components are reassembled into triglycerides

98
Absorption Small Intestine (Fats)
  • Monoglycerides (cont)
  • Triglycerides are then packaged with cholesterol
    phospholipids into chylomicrons
  • Chylomicrons are exocytosed diffuse to
    lymphatic lacteals to eventually be placed into
    blood by the lymphatic system
  • Chylomicrons in the blood are hydrolyzed by
    lipoprotein lipase to free fatty acids glycerol
    prior to tissue absorption
  • Fig. 23.36

99
Fatty Acid Absorption
Figure 23.36
100
Absorption Small Intestine
  • Vitamins
  • Some Vit. K B complex vitamins are absorbed in
    the large intestine
  • Dietary vitamins are absorbed in the small
    intestine
  • Fat soluble vitamins (A, D, E, K) dissolve in
    dietary fats are absorbed after being
    incorporated into micelles

101
Absorption Small Intestine
  • Electrolytes most ions are actively absorbed
    throughout small intestine
  • Na is coupled to absorption of glucose amino
    acids (cotransport)
  • Cl- actively transported into cells exchange for
    HCO3-

102
Absorption Small Intestine
  • K diffuses into the cells
  • Iron is transported into cells bound to
    ferritin
  • Ca2 absorption regulated by blood Ca2 levels
    Vit D
  • ( Vit D is a required cofactor for Ca2
    absorption)

103
Absorption Small Intestine
  • Water moves freely in both directions across the
    mucosa
  • Active transport of solutes create an osmotic
    gradient H2O follows
  • H2O movement changes solute concentrations
    effects absorption of substances that move by
    diffusion

104
Absorption Small Intestine
  • Malabsorption can result from
  • Disruption of secretion
  • Mucosal damage
  • Reduction of absorptive surface area
About PowerShow.com