IPHY 3430 1-27-11

Control of saliva secretion

Pressure and chemoreceptors in mouth-->and/or input from cerebral cortex (thoughts, smell, sight, sound)--->

Salivary center inMedulla PNS

Salivary glands

SNS output from other centers (a. diminish blood supply, b) change composition

Swallowing1. Voluntary stage--tongue moves bolus back to

back of tongue2. Involuntary stage-- pressure receptors on

tongue send signal to swallowing centers in pons and medulla-->

Output of swallowing centers: 1. motor output--a) tongue moves up to hard palate to prevent food return to mouthb) uvula elevated to seal off nasal passages

c.Larnyx is elevated and laryngeal muscles contract vocal folds to seal off trachea.d. Epiglottis tilted over glottis helps seal off trachea.e. After all these motor outputs occur, pharyngeal muscles contract to force bolus into esophagus.

2. Swallowing center inhibits inhalation stimulus from medulla respiratory centers

Accomplishments in the mouth

1. Increase surface area of food2. Moisten and lubricate food3. Some carbohydrate digestion4. Some pathogens killed

Stomach1. Store food2. Continue carbohydrate digestion3. Begin protein digestion4. Moisten and mechanical breakdown5. No absorption of food6. Some absorption of lipid-soluble things like alcohol, aspirin, etc.

In oxyntic mucosa

Gastricpit

Gastricgland

Surface epithelial cells

Mucosa cells

Chief cells

Parietal cells

Enterochomaffin-like (ECL) cells

In pyloric gland area

G cells

D cells

Table 16-3, p. 596

Stomach secretions1. More mucus from mucus glands2. Parietal cell a. intrinsic factor b. HCl3. Chief cell a. pepsinogen4. More water

Secretions and stomach contractions caused by A. Pre-meal and during eating: vagus nerve B. During eating and post meal a. Local distension,

b. intrinsic nerve plexic. Vagus (to some extent)

d. G-cell (enteroendocrine cell) secretes gastrin

Fig. 16-9, p. 607

Benefits of acidification of stomach contents:1. Mechanical breakdown of food2. Activation of pepsinogen3. Low pH necessary for pepsin activity4. Low pH kills many pathogens

MOVEMENT OF CHYME FROM STOMACH INTO SMALL INTESTINEFactors that stimulate stomach emptying:1. Degree of stomach distension (volume of chyme)2. Hypotonic chyme3. High gastrin concentration

Factors in duodenum that inhibit stomach emptying(signaled to stomach by intrinsic nerve plexus andsecretin and cholecystokinin) 1. High acidity of chyme2. High fat content of chyme3. Hypertonic chyme4. High distension of small intestine5. High concentration of amino acids and/or fatty acids

ACCOMPLISHMENTS IN THE STOMACH1. Some carbohydrate breakdown2. Some protein breakdown3. Most if not all pathogens killed4. Chyme highly liquified

SMALL INTESTINE

1. Complete enzymatic breakdown2. Almost complete absorption of nutrients

The presence of chyme on intestinal wall causes secretion of the following hormones:

1. Secretin2. Cholecystokinin

SECRETIN

Target glands:1. Stomach--inhibits emptying and secretions2. Pancreas-- causes release of aqueous NaHCO3

In small intestine NaHCO3 + HCl --> NaCl + H2CO3 --> NaCl + CO2 + H20

CHOLESYSTOKININ

Target organs: a. Gall bladder--causes it to contract and release bile b. Pancreas--causes release of aqueous solution containing: 1. amylase (carbohydrate) 2. Trypsinogen (protein) 3. Chymotrypsinogen (protein) 4. Procarboxypolypeptidase (protein) 5. Lipase (fats) c. Stomach-inhibits gastric motility and secretion d. Brain--regulation of food intake

WHEN PANCREATIC SECRETIONS REACH SMALL INTESTINE VIA BILE DUCT:

1. Enterokinase secreted by small intestine wall activates trypsin from trypsinogen2. Trypsin activates chymotrypsin from chymotrypsinogen3. Trypsin activates carboxypolypeptidase from procarboxypolypeptidase

BILE

Synthesized by liver, stored in gall bladder

1. Water2. Bilirubin3. Cholesterol4. Ions (Na, K, Cl)5. Bile salts6. Lecithin