Download Figure from: Martini, Anatomy & Physiology

Marieb’s Human
Anatomy and Physiology
Ninth Edition
Marieb w Hoehn
Chapter 23
** Digestive System **
Stomach
Small/Large Intestine
Salivary Glands
Liver
Overview….Where have you been?
Figures from: Marieb, Human Anatomy &Physiology, Pearson, 2013
2
Stomach
M
Gastric
glands
M
G cells
D cells
Stomach can hold
about 1-1.5 liters
of material
Greater curvature
Stomach Functions:
- Mixing
- Reservoir
- Secretion of gastric juice
- Digestion, anti-bacterial action,
facilitates absorption of vitamin B12
- Secretion of gastrin, somatostatin
Rugae flatten as stomach fills
3
Blood Supply and Drainage of Stomach
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
4
Lining and Gastric Glands of Stomach
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
5
Gastric Secretions
• mucus (cardia)
• from goblet cells and mucous
glands
• protective to stomach wall
• pepsinogen
• from chief cells
• inactive form of pepsin
• pepsin
• from pepsinogen in presence of
HCl
• protein splitting enzyme
• INFANTS ONLY
• rennin (chymosin)
• gastric lipase
• hydrochloric acid
• from parietal cells
• needed to convert
pepsinogen to pepsin
• ‘p’ in parietal and ‘p’ in pH
• intrinsic factor
• from parietal cells
• required for vitamin B12
absorption
• mucus, gastrin, somatostatin
• from pyloric glands
• protective to stomach wall
• gastrin and somatostatin are
hormones
6
Secretion of H+ by Parietal Cells
Important functions
of the stomach pH
(1.5 – 2.0)
- kills
microorganisms
- denatures proteins
- breaks down plant
material and CT in
meats
- activates pepsin
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
7
Liver, Bile ducts, Pancreas and Small Intestine
Figures from: Marieb, Human Anatomy &Physiology, Pearson, 2013
8
Three Parts of Small Intestine
Figure from: Hole’s Human A&P, 12th edition, 2010
“Mixing bowl”; acid
neutralization
Bulk of
chemical
digestion
and
nutrient
absorption
occurs here
The ‘bowel’
consists of the
small and large
intestines.
Vitamin B12 absorption
Main functions of small intestine: 1) chemical digestion 2) absorption of
nutrients (90%) from chyme
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Blood Supply and Drainage of Small Intestine
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
10
Wall of Small Intestine
Figure from: Hole’s Human A&P, 12th edition, 2010
Plicae circulares –
permanent circular
folds of mucosa that
further increase
surface area for
absorption – do not
flatten out with
distention like rugae of
stomach.
Especially prominent
in lower duodenum
and upper jejunum
Submucosa of duodenum contains mucus-secreting glands
(Brunner’s glands) that protect the small intestine
11
Intestinal Villi & Glands
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
Enterocyte = Intestinal Cell
Intestinal glands secrete an abundant watery fluid that helps absorb
products of digestion. They also contain enteroendocrine cells
(enterokinase, gastrin, secretin, CCK)
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Intestinal Epithelium
Figure from: Hole’s Human A&P, 12th edition, 2010
Microvilli further increase
the surface area available
for absorption in the small
intestine
Form a ‘brush border’ on
the intestine
Digestive enzymes are
embedded in the
membrane of microvilli
Main function of plicae, villi, and microvilli is to increase the
surface area for absorption (from about 3.6 ft2 to about 2200 ft2!)
13
Secretions of Small Intestine
• peptidase – breaks down peptides into amino acids
• sucrase, maltase, lactase – break down disaccharides into
monosaccharides
Brush
border
• intestinal lipase – breaks down fats into fatty acids and glycerol
• enterokinase – converts trypsinogen to trypsin
• gastrin/somatostatin – hormones that stimulate/inhibit acid secretion by
stomach
• cholecystokinin (CCK) – hormone that inhibits gastric glands, stimulates
pancreas to release enzymes in pancreatic juice, stimulates gallbladder to
release bile, and relaxes hepatopancreatic sphincter (of Oddi)
• secretin – stimulates pancreas to release bicarbonate ions in pancreatic
juice; stimulates gall bladder to release bicarbonate-rich bile
See Table 23.32 in Marieb for a great summary of digestive enzymes
14
Movements of the Small Intestine
Movements in local segments can occur without
stimulation by parasympathetic NS. However, nervous
stimulation accelerates segmentation and peristalsis.
• peristalsis – pushing movements
• segmentation – ringlike contractions that aid in mixing and
slowing peristalsis
• overdistended or irritated wall triggers “peristaltic rush”
resulting in diarrhea
“Long distance” movements are triggered by stomach
filling:
- gastroenteric reflex (↑ motility and secretion along length of
small intestine)
- gastroileal reflex (relaxation of ileocecal sphincter)
15
Absorption in the Small Intestine
• monosaccharides and
amino acids
• through facilitated
diffusion and active
transport
• absorbed into blood
• electrolytes and water
• through diffusion,
osmosis, and active
transport
• absorbed into blood
• vitamins
• fat-soluble dissolve in dietary fats (vit A,D,E,K)
•Water-soluble through diffusion, except B12
(active transport)
• Vitamin K (large intestine) – with other lipids
• absorbed into blood
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Absorption of Fats in the Small Intestine
Figure from: Hole’s Human A&P, 12th edition, 2010
• fatty acids and
glycerol
• several steps
• absorbed into
lymph into
blood
Chylomicrons contain TG, cholesterol, and phospholipids
17
Large Intestine
Figure from:
Martini, Anatomy
& Physiology,
Prentice Hall,
2001
*
18
Histology of the Large Intestine
Figures from: Hole’s Human A&P, 12th edition, 2010
Walls of large intestine
are much thinner than
the small intestine,
however, the lumen is
larger
Note lack of villi and
presence of numerous
goblet cells (mucus)
No enzymes produced;
any digestion is from
previously introduced
enzymes or bacteria
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Functions of Large Intestine
• little or no digestive function
• absorbs water, bile salts, and electrolytes
• secretes mucus (lubrication, binding, protection, pH)
• conversion of bilirubin (uro- and stercobilinogen)
• houses intestinal flora (~800 species of bacteria) and
absorbs vitamins liberated by bacterial action (K, B5,
and Biotin); produces intestinal gas (flatus)
• forms and stores feces
• carries out defecation
20
The Rectum, Anal Canal, and Anus
Figure from: Hole’s Human A&P, 12th edition, 2010
Rectal
valves
Temporary storage of
fecal material in
rectum triggers the
urge to defecate
Internal anal
sphincter is usually
contracted but relaxes
in response to
distension. External
sphincter must be
tensed reflexively to
retain feces
Procto- = anus or rectum
(Keratinzed strat. squamous epithelium)
21
Movements of Large Intestine
• slower and less frequent than those of small intestine
• mixing movements (haustral churning every 30 min)
• mass movements - usually follow meals (stimulated
by distension of stomach and duodenum)
- gastrocolic reflex
- duodenocolic reflex
- peristaltic wave from transverse colon through
rest of large intestine
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All You Need to Know???
23
Parasympathetic Defecation Reflex
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
Note that this reflex
opens the internal
sphincter and closes the
external sphincter
Need voluntary
relaxation of the external
sphincter for defecation 24
Feces
• water (75%), solids (25%)
• electrolytes
• mucus
• bacteria (30% of solids) and sloughed epithelial cells
• bile pigments altered by bacteria provide color (mainly
urobilins and stercobilins)
• odor produced by bacterial compounds (indoles and
skatoles, phenols, H2S, ammonia)
• indigestible materials
25
Major Organs of Digestive System
Figure 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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Salivary Glands
Figure from: Saladin, Anatomy &
Physiology, McGraw Hill, 2007
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Secretions of Salivary Glands
Secretions are about neutral pH 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)
• 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
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Liver [ Hepat(o)- ]
Round ligament is part of the
falciform ligament that divides
the lobes; remnant of fetal
umbilical vein.
Note that the vena cava
does not enter the liver;
it passes by
Figure from: Martini, Anatomy & Physiology, Pearson Education, 2004
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Arterial Supply and Venous Drainage of Liver
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
30
Hepatic Lobule
Hepatic lobules are the functional units of the liver (>100,000)
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
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Paths of Blood and Bile in Hepatic Lobule
Figure from: Hole’s Human A&P, 12th edition, 2010
Liver’s role as an
accessory organ
in digestion is
production of
bile
Sinusoid
Hepatic portal vein → sinusoids → central vein → hepatic veins → inferior vena cava
Hepatic artery
32
Liver Functions (over 200!)
• Three general categories of function
1) Metabolic regulation
•
•
•
•
•
Interconversion of carbohydrates, lipids, amino acids
Removal of wastes
Vitamin and mineral metabolism
Drug inactivation
Know items
Storage of fats, glycogen, iron, vit A/B12/D/E/K
2) Hematological regulation
•
•
•
•
•
in red
Phagocytosis and antigen presentation; ab removal
Synthesis of plasma proteins
Removal of circulating hormones
Removal of worn-out RBCs (Kupffer cells)
Removal or storage of toxins
3) Synthesis and secretion of bile (role in digestion)
33
Gallbladder [Cyst(o)-]
Figure from: Martini, Anatomy &
Physiology, Prentice Hall, 2001
Main function is to store and concentrate bile between
meals, and release bile under the influence of CCK
34
Composition of Bile (Chole-)
Yellowish-green liquid continually secreted by hepatocytes
• water
• bile salts (bile acids)
• derived from cholesterol
• emulsification of fats (increases surface area for digestive enzymes)
• helps absorption of fatty acids, cholesterol, and fat-soluble vitamins
• 80% are recycled (reabsorbed and reused) – enterohepatic
circulation of bile
• 20% excreted in feces (disposes of excess cholesterol)
• bile pigments (bilirubin and biliverdin from breakdown of
RBCs)
• electrolytes
35
Regulation of Bile Release from GB
Figure from: Hole’s Human A&P, 12th edition, 2010
• fatty chyme
entering duodenum
stimulates the GB to
release bile (via
CCK)
Secretin causes the bile ducts (and pancreatic ducts) to
secrete bile rich in HCO3-
36
Actions of Cholecystokinin (CCK) on Digestion
Figure adapted from: Barrett, K.,
Gastrointestinal Physiology, Lange,
2006
CCK
Contraction of
Gallbladder
Secretion of
pancreatic
enzymes
Reduced
emptying of
stomach
Relaxation of
hepatopancreatic
sphincter
Protein, CHO, lipid absorption and digestion
Matching of nutrient delivery to digestive and absorptive capability
37
Pancreas
Exocrine
(digestive)
and
endocrine
(metabolic)
functions
Completes
digestion of
proteins that
was started
in the
stomach
38
Blood Supply and Drainage of Pancreas
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
39
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
Enteropeptidase
(Enterokinase)
(brush border of sm. intestine)
Trypsinogen
Pancreas
Know this chart
Trypsin
Chymotrypsinogen
Procarboxypeptidase
Proelastase
(Proenzymes, Zymogens)
Dipeptides, tripeptides, amino acids
Chymotrypsin
Carboxypeptidase
Elastase
(Active enzymes)
Proteins
Purpose of proteolytic enzymes is continued
breakdown of proteins that began in the stomach
41
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
42
Key
Regulation of Pancreas/Intestinal Digestion
+
Stimulation
Acidic Chyme Enters Duodenum
(brush border)
+
+
Secretin
+
+
Cholecystokinin
(CCK)
+
+
Bile and
Pancreatic
ducts
Gallbladder
Contraction
Bile
Trypsin
Chymotrypsinogen
Procarboxypeptidase
Proelastase
Trypsinogen
Carboxypeptidase
Elastase
Proteins
Lipases
(emulsification)
Triglycerides
Cholesterol
Fat Soluble Vitamins
Lacteals
Subclavian
vein
Pancreas
Trypsinogen
(proenzymes, zymogens)
HCO3-, PO43-
 pH to ≈ 8
(req. for enzyme
action)
Relaxation of
hepatopancreatic
sphincter
+
Enterokinase
Fatty acids,
monoglycerides
Conversion to
chylomicrons
Nucleases
(DNA, RNA)
Nucleotides
Portal
Vein
Amylase
(glycogen,
starches)
Mono-, di-,
trisaccharides
Di- and
tripeptides
Action of
brush
border
enzymes
Monosaccharides
Amino acids
43
Life-Span Changes
• gums recede
• teeth become sensitive
• teeth may loosen or fall out
• heartburn more frequent
• constipation more frequent
• nutrient absorption decreases
• accessory organs age but the effects are less
noticeable
44