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Martini’s Visual
Anatomy and Physiology
First Edition
Martini w Ober
Chapter 21 - Digestive System I, II
Lectures 7 & 8
1
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
2
Digestive System
Functions of Digestive System
• ingestion
• mechanical digestion
• chemical digestion
Digestion is the
mechanical and chemical
breakdown of food into a
form that cells can absorb
• propulsion
• absorption
• excretion
• defecation
3
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
4
The Greater and Lesser Omenta
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
5
The Mesentery
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
6
The Abdominal Cavity & Peritoneum
Notice that the
pancreas, duodenum,
and rectum are
retroperitoneal
Figure from: Martini,
Anatomy & Physiology,
Prentice Hall, 2001
7
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?
8
Alimentary Canal Wall
Know the 4 layers of the alimentary canal
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
9
Alimentary Canal Wall
10
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.)
11
Innervation of the Alimentary Canal
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
• 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
12
Mouth (Oral or Buccal cavity)
(Labium)
• ingestion
• mechanical
digestion
• prepares food for
further chemical
digestion
(Labium)
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
13
Tongue
Very muscular; muscles run in several directions
Covered by mucous membranes
Blast from the
past - Root of
tongue is
anchored to the
hyoid bone
1. Tastebuds
2. Friction for
food handling
3. Secretes
lingual lipase
14
Palate
• roof of oral cavity
(adenoids)
Important in
separating the
nasopharynx
from the
pharynx
during
swallowing
15
Secondary (Permanent) Teeth
Total of 32
secondary
(permanent)
teeth
1
16
32
17
Watch for incoming
ICBMs!!!
Know the
order of these
16
Primary (Deciduous, Baby, Milk) Teeth
(Mastication =
chewing)
• 8 incisors
• 4 cuspids
• 8 molars
• 20 total
All primary teeth are lost, generally between ages 6 and 12
17
Section of a Tooth
Oh no!
Not again!
What type of
articulation is
this?
Know this diagram for exam
18
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)
19
Salivary Glands
20
Secretions of Salivary Glands
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)
• 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
21
Pharynx
Pharynx aids swallowing by grasping food and
moving it toward the esophagus.
22
Three Phases of the Swallowing Reflex
Only voluntary phase is the buccal (oral) phase, i.e., the
initiation of swallowing, then…
• soft palate and uvula raise
• hyoid bone and larynx elevate
Pharyngeal phase
• epiglottis closes off top of trachea
• longitudinal muscles of pharynx contract
reflexive
• inferior constrictor muscles relax and
esophagus opens
Esophageal phase
• peristaltic waves push food through pharynx
23
Swallowing Mechanism
24
Esophagus
Veins drain
into hepatic
portal vein
(via gastric
veins)
Lower esophageal (cardiac)
sphincter prevents reflux
(backup) of stomach acid
into the esophagus.
Esophagus conveys food from pharynx to stomach by peristalsis
25
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
26
Blood Supply and Drainage of Stomach
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
27
Lining and Gastric Glands of Stomach
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
28
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
29
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
30
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)
31
Cephalic Phase of Gastric Secretion
Emotional states can exaggerate or inhibit this phase
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
32
Gastric Phase of Gastric Secretion
Proteins, alcohol, and caffeine can markedly increase
secretions by stimulating gastric chemoreceptors
Histamine stimulates acid secretion by parietal cells
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
33
Intestinal Phase of Gastric Secretion
Enterogastric reflex (inhibits gastric activity) –reduces gastric motility,
stimulates contraction of pyloric sphincter (pylorus)
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
34
Key
Overview of Gastric Control/Secretion
Emptying of
Stomach
Stomach Molility
(Segmentation/Peristalsis)
ECL Cells
+
+
+
+
(cephalic/gastric phases)
-
G cells
Fats in
Small
Intestine
+
+
pH > 3.0
(dilution of H+)
+
Stretch
of
stomach
Endocrine Factor
Exocrine Factor
B12
Parietal Cells
H+ + Cl-
Gastrin
(intestinal
phase)
Inhibition
Intrinsic
Factor
+
+
Somatostatin
Histamine
Stimulation
+
Both
pH < 3.0
Parasympathetic NS
+
D cells
-
Mucous
Cells
( [H+ ])
+
+
+
+
Peptides
HCO3- (alkaline tide)
Chief
Cells
Pepsinogen
Pepsin
Protein
Breakdown
Food in
Stomach
Fat
Breakdown
Lipases
35
Mixing and Emptying Actions
36
Gastric Absorption
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:
• some water
• certain salts
• certain lipid-soluble drugs, e.g., aspirin
• alcohol (slowed by presence of fats)
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…
40
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
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
44
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
45
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)
46
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
47
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
48
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
49
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
50
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)
51
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
52
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
53
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
54
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
55
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
56
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
57
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
58
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
59