Module 9, Lecture 18 - Digestive System II PDF

Preview

Summary

Donna Fekete, Anatomy and physiology II, Digestive system II...

Description

Digestive System II

Contractile response of food in stomach: 1. Swallowing center of medulla oblongata a. Signal stomach to relax b. Vagus nerve i. ii.

Relays message Activate receptive relaxation response

c. Resists stretching for a little and then relaxes to hold food 2. The stomach will have a rhythm of peristaltic contractions a. It is controlled by i. ii.

Enteric pacemaker cells In longitudinal layer of muscularis externa

b. Constriction every 20 seconds c. Contractions get strong after 30 minutes d. This mixes the food with gastric juice i.

Promoting the physical breakup and chemical digestion

3. Muscularis of antrus a. Strong pump b. Breaks semi digested food to prepare for intestine 4. Chyme into duodenum a. Neutralize acid b. Digest nutrients slowly 5. A meal is typically emptied in four hours

Vomiting: 1. Forceful ejection of stomach and chyme 2. Emetic center in medulla oblongata a. Many muscle actions b. Retching i.

Thoracic expansion

ii.

Abdominal contraction

iii.

Pressure difference - dilate esophagus

c. Vomiting i.

When abdominal contraction and the rising thoracic pressure forces the upper esophageal sphincter open

3. It will be dangerous if chronic a. Bulimia, aspiration

Digestion and absorption: 1. Salivary and gastric enzymes a. Digest protein b. Less starch and fat c. Stomach doesn’t absorb lots of nutrients, aspirin, lipid soluble drugs 2. Absorption occurs mostly in small intestine 3. Stomach is protected a. Mucous coat b. Tight junctions i.

Prevent gastric juice from going into tissue

c. Epithelial cell replacement i.

3-6 life span

ii.

Sloughed off

iii.

Replaced rapidly with cell division

Regulation of Gastric Function: 1. Use nervous and endocrine systems 2. Three phases a. Cephalic phase i.

Control by brain

ii.

Response to senses or thought of food

iii.

Input on hypothalamus to medulla oblongata

iv.

Vagus nerves stimulate enteric nervous system of stomach

v. vi.

Stimulate gastric secretion 40% of acid secretion during this phase

b. Gastric phase i.

Control itself

ii.

Positive feedback loop

iii.

During semi digested protein

iv.

Either by 1. Stretching stomach 2. Increasing pH

v.

Three chemicals stimulate gastric secretion 1. ACh a. From parasympathetic nerve fibers 2. Histamine a. Paracrine secretion b. Enteroendocrine cells in gastric glands 3. Gastrin a. Hormone made by enteroendocrine G cells in pyloric glands b. Stimulate parietal cell secretions

c. Intestinal phase i.

Control by small intestine

ii.

Negative feedback loop

iii.

Duodenum responds to chyme

iv.

Moderate activity with hormones and nervous reflexes

v. vi.

Soon inhibit Steps 1. The duodenum will signal the medulla to inhibit vagal nuclei + stimulate sympathetic neurons 2. Acids and fats will trigger enterogastric reflex 3. Chyme will stimulate duodenal enteroendocrine cells a. Release secretin and cholecystokinin

4. Stimulate pancreas and gallbladder but suppress gastric secretion

Anatomy of liver, gallbladder, bile duct system, and pancreas: 1. Small intensive a. Get chyme from stomach and secretion from liver and pancreas b. Enter DT near junction 2. Liver a. Many func. Not related to digestion b. Make bile c. Gallbladder stores bile 3. Sinusoid of liver a. Irregular blood filled space b. Lined with fenestrated endothelium c. The blood that is filtered comes from the stomach and intestines 4. Hepatocytes a. Absorb from blood i.

Glucose

ii.

Amino acids

iii.

Iron

iv.

Vitamins

v.

Nutrients

b. Break down stored glycogen c. Release glucose into blood d. Remove and degrade i.

Hormones

ii.

Toxins

iii.

Bile pigments

iv.

Drugs

e. Secrete into blood i. ii.

Albumin Lipoproteins

iii.

Clotting factors

iv.

Angiotensinogen

v.

Other products

5. After filtration in sinusoids, blood collected into central vein a. Flows into hepatic veins b. Leaves liver c. Drains in inferior vena cava

Gallbladder and Bile: 1. Bile goes to gallbladder by overflowing the bile duct 2. 500-1000 mL of secretion from liver 3. 80% of bile acids are reabsorbed in ileum and returned to liver a. Hepatocytes absorb and secrete 4. 20% of bile acids excreted in feces a. We need to eliminate any extra cholesterol

Pancreas: 1. Endocrine a. Insulin b. Glucagon 2. Exocrine a. 99% of pancreas b. 1200-1500 mL of pancreatic juice i. ii.

Alkaline mixture Water, enzymes, zymogens, sodium, bicarbonate, electrolytes

c. Acini i.

Secrete the enzymes, zymogens

d. Ducts i.

Secrete the bicarbonate 1. Buffer HCL from stomach

3. Pancreatic zygoments

a. Trypsinogen b. Chymotrypsinogen c. Procarboxypeptidase 4. Other enzymes a. Pancreatic amylase - digest starch b. Pancreatic lipase - digest fat c. Ribonuclease & deoxyribonuclease - digest RNA and DNA 5. Regulation of secretion a. 3 stimuli i.

Acetylcholine 1. From vagus and enteric nerves 2. Stimulate acini a. Secrete enzymes before food is swallowed

ii.

Cholecystokinin 1. From mucosa of duodenum 2. Responding to fats in small intestine 3. Strong stimulation to gallbladder 4. Contraction and relaxation to discharge bile into duodenum

iii.

Secretin 1. Released from duodenum to acidic chyme from stomach 2. Stimulate liver and pancreas to secrete sodium bicarbonate 3. Raise pH to level a. Activity of enzymes

Small Intestine: 1. Duodenum a. Receive i.

Stomach content, pancreatic juice, bile

b. Neutralize stomach acid c. Fats broken up with bile acids d. Pepsin inactivated with high pH

e. Pancreatic enzymes do chemical digestion 2. Jejunum a. Most digestion here 3. Illeum a. Lymphoid nodules b. Regulate passage of food residue in large intestine 4. Anatomy of tissue a. Circular folds b. Villus (2 type of epithelial cells) i.

Absoprive cells

ii.

Goblet cells

iii.

Microvilli - brush border

c. Intestinal crypts i.

Goblet cells

ii.

Paneth cells

iii.

Secrete 1-2 L of intestinal juice per day

iv.

Responding to acid, hypertonic chyme, distension of intestines

v. vi.

pH: 7.4-7.8 Water, mucus, little enzyme

5. Duodenal glands a. In submucosa b. Bicarbonate rich mucus c. Neutralize stomach acid and shield mucosa d. Many lymphocytes e. Intercept pathogens

Large intestine: 1. 500 mL of residue per day 2. Microbes a. Gut i.

800 species of bacteria

ii.

Digest cellulose, pectin, carbohydrates (that our cells lack enzymes for)

iii.

Synthesize vitamin B and K

b. Flatus i. ii.

Gas 500 mL

3. Absorption a. Reabsorbs water and electrolytes b. Transverse colon c. 36-48 hours to reduce d. 75% water, 25% solids 4. Haustral contractions (every 30 mins) a. Stimulate to contract b. Promote water and salt absorption 5. Mass movements (1-3x a day) a. By gastrocolic and duodenocolic reflex 6. Defecation a. Neural control b. 2 involuntary defecation reflexes i. ii.

Intrinsic defecation reflex Parasympathetic defecation reflex 1. Uses spinal cord

c. Occurs with external anal sphincter and puborectalis muscles are voluntarily relaxed...