Digestion 2: Mouth through Stomach

Chapter 20; pages 570 - 581

Salivary Glands: Fig 20.9

Salivary Glands

• Parotid

– amylase (ptyalin)

– 1 - 4 hexose linkages

• Submaxillary & Sublingual

–mucin (protein for lubrication)

Fig 5.3: Review of Sugar Structure

– linkage

Starch: 1 – 4 & 1 – 6 linkages

Cellulose: 1 – 4 linkages

Salivary Glands

Acinus type glands:

Primary secretion by secretory cells and then modified by duct cells as saliva passes through on the way to the oral cavity

Accessory Gland Structure: Fig 20.8

Na+

K+ <--

Cl-

<-- HCO3-

Saliva

• As saliva flows down duct:

–[Na+] and [Cl-] decrease

–[HCO3-] and [K+] increase

– also decreases - hypotonic• As flow rates increase, this exchange is

less complete

Salivary pH

• Saliva pH is basic (vs. plasma pH)

• WHY?? (i.e., for what purpose?)

Excitatory Signal Molecules

• ACh from Parasympathetic NS onto muscarinic receptors

• VIP from enteric NS

• Increased blood flow in response to kininogen activation

Kininogen Activation

• Glands release Kallikrein when activated – acts on a kininogen, a plasma globulin

• Results cleavage forming a peptide --> bradykinin

• Bradykinin ---> local vasodilation (10X increase in BF)

Other Components of Saliva

• Muramidase --> cleave muramic acid in bacterial cell walls

• Lactoferrin --> binds Fe++

• Epidermal growth factor --> stimulates mucosal cell growth

• IgA• Lingual lipase (small amounts)• ABO antigens (secreters)

Salivary Secretion

• Cephalic Phase–Thought or sensory input

• Gastric Phase–Distention

–Secretagogues

–Vagal - Vagal reflex

Fig 20.29Fig 20.29

Stomach; Figure 20.4

Stomach Mucosal Surface:

Folds are called

Rugae gastricae

Achalasia: failure to open esophageal sphincter

History Lesson:

Alexis St. Martin

and

William Beaumont

http://www.james.com/beaumont/dr_life.htm

http://www.guineapigzero.com/AlexisStMartin.html

Dr. William Beaumont

Beaumont & St. Martin

Stomach; Figure 20.4

Oxyntic Glands

• Surface Epithelium - insoluble mucous

• Neck Cells - soluble mucous

• G cells - gastrin

• Parietal (or oxyntic) Cells - HCl & Intrinsic Factor

• Chief Cells - pepsinogen

Gastric Acid Secretion: Fig 20.22

Postprandial

Alkaline Tide

http://en.wikipedia.org/wiki/File:Control-of-stomach-acid-sec.png

Histamine

• From enterochromafin-like cells (ECL cells) in the gastric mucosa

• produce, store, & release histamine

• activated by ACh, gastrin, & secretagogues

Treatment of Hyperacidity

• Atropine

•Antihistamine (H2 antagonists)–Cimetidine

•Proton pump inhibitors–Nexium

Pepsin

• Pepsinogen ---> pepsin in acidic conditions of stomach

• It is a family of endopeptidases

• pH optima 1.8 - 3.5

Activation of Pepsin; Fig 20.14Activation of Pepsin; Fig 20.14

Three Different Pepsins

Vitamin B12

• aka, cyanocobalamin• required for nucleic

acid synthesis • is very labile in acid

Haptocorrin & Intrinsic Factor

• Haptocorrin (transcobalamin) made in salivary glands

• binds Vitamin B12 very tightly

• protects it from gastric acid digestion

Haptocorrin

http://en.wikipedia.org/wiki/Haptocorrin

Haptocorrin

• Haptocorrin is digested by pancreatic proteolytic enzymes in the duodenum

• Vit B12 now binds to Intrinsic Factor (IF)

• The B12 – IF complex is taken up by endocytosis in the duodenum

Intrinsic Factor

Secretagogues

• caffeine and theophylline

• peptides

• spices

• Alcohol

• aspirin

Digestion Review:

• ANS and enteric nervous system

• Smooth muscle structure - function

• Saliva and regulation of flow

• Stomach secretions

• On to regulation of gastric secretion and motility (emptying)…….

Table 20.2 Gastrointestinal Hormones

Hormones: GastrinHormone Site of secretion Stimuli Actions

Gastrin Stomach Protein digestion products in stomach, distention, and parasympathetic input

Stimulates gastric secretion & motility, relaxes ileocecal sphincter, stimulates mass movement of colon

Hormones: Cholecystokinin (CCK)

Hormone Site of secretion Stimuli Actions

CCK Duodenum and jejunum

Fat or protein digestion products in Duodenum

Inhibits gastric secretion & motility, potentiates secretin action, stimulates pancreatic enzyme secretion, stimulates bile secretion, and contracts bile duct and gall bladder

Hormones: SecretinHormone Site of secretion Stimuli Actions

Secretin Duodenum and jejunum

Acid in duodenum

Inhibits gastric secretion & motility, stimulates pancreatic HCO3

- secretion, potentiates actions of CCK, and stimulates bile secretion by liver

Hormones: GIP(glucose-dependent insulinotropic peptide)

Hormone Site of secretion Stimuli Actions

GIP Duodenum and jejunum

Glucose, fats or acid in duodenum and distention of the duodenum

Inhibits gastric secretion & motility, stimulates insulin secretion by the pancreas

Contol of G.I. Function: Fig. 21.21

GASTRIN

• Peptide hormone

• From G cells (stomach)

• Increases HCL & pepsinogen secretion

• Increases gastric motility and emptying into duodenum

Gastric Acid Secretion:Cephalic Phase Fig 20.23a

• Thought of food, smell, chewing, swallowing

• Vagus nerve to parietal cells (ACh)

• Vagus nerve (ACh) onto G cells & thus causes gastrin release

• See TABLE 20.2 !!!!!

Fig 20.23aCephalic Phaseof GastricSecretion

Fig 20.23bGastric Phaseof GastricSecretion

Gastric Acid Secretion:Intestinal Phase

• Stimulus - digested peptides, peptides in duodenum, distention

• G cells (gastrin)

• distention -->Intestinal endocrine cells release CCK, Secretin, & GIP

• see Table 20-2

Inhibition of Gastric Secretion

• Important for protection of duodenum

• Acid in duodenum ---> secretin & CCK---> inhibits gastric secretion and motility

See Table 20.2 for sure !!!

Inhibition of Gastric Secretion

• Acid, fats, hyper-osmotic solutions in the duodenum ---> release of enterogastrones ---> inhibit gastric motility and secretion

• Gastric Inhibitory Peptide or Glucose-dependent Insulinogenic Peptide (GIP) from duodenum ---> inhibits parietal cell function– Decreases release of acid, motility, & secretion– Increases release of insulin from pancreas

• Ulcers - page 576

–Peptic & Duodenal–Role of Helicobacter pylori

• Vomit reflex - page 599

–Note sympathetic symptoms