Chapter 18: Digestive System - Glucose Regulation Flashcards
Digestive System Parts
Mouth, Pharynx, Esophagus, Stomach, Small Intestine, Large Intestine, Rectum/Anus
Accessory Organ Parts
Teeth, Tongue, Liver, Gallbladder, Pancreas, Salivary Glands
- Cephalic Phase
Parasympathetic stimulation (CN X) begins salivation, HCl acid secretion from parietal cells in stomach and increased motility (peristalsis).
Salivation, Lacrimation, Urination, Digestion and Defecation (SLUDD)
Food is mixed with Saliva
pH of 6.8 to 7.0
Salivary Amylase: Begins starch digestion in the mouth (inactivated by low pH of stomach).
Lingual Lipase: Activated by stomach acid, digests fats when it arrives in stomach (requires low pH).
Mucous: Binds and lubricates food for swallowing.
Lysozyme: Enzyme that kills bacteria.
Electrolytes: Na+, K+, Cl-, phosphate and bicarbonate ions, etc.
Swallowing (Deglutition)
Swallowing center: in medulla oblongata.
Coordinates muscle movements to push food bolus into esophagus (voluntary, somatic)
Once bolus passes to oropharynx:
Parasympathetic system ‘takes over’
Bolus moves through peristalsis; a wave of longitudinal muscular contractions (that continue until materials reach colon),
- Gastric Phase – Digestion of Proteins
Gastrin (hormone):
Produced by enteroendocrine G cells in pyloric glands (travels though blood).
As food is digested:
pH lowers <2.0 which inhibits parietal cells and G cells (negative feedback loop)
Low pH Terminates gastric secretions when stomach is empty.
Food is mixed with Stomach secretions
Bolus is now called chyme (white fluid substance)
Innervation and Circulation of Stomach: Receives (mostly parasympathetic) and sympathetic innervation
Stomach Wall
Stomach Wall:
Composed of same 4 layers of tissue as rest of GI tract,
Gastric mucosa has depressions called gastric pits into which gastric tubular glands empty
Mucous Cells
Secrete mucous for lubrication and gastric mucosa protection from HCl,
Regenerative Cells
Duplicate fast to replace cells of gastric mucosa that die.
Parietal Cells
Secrete HCl, and intrinsic factor.
Chief Cells
Most numerous, secrete:
In infants - rennin and gastric lipase
In adults pepsinogen (inactive) which is converted to pepsin (active) by HCl acid.
Enteroendocrine Cells
Secrete hormones and paracrine messages that regulate digestion.
Gastric Secretions
Hydrochloric Acid (HCl): pH of 0.8, secreted by Parietal cells that have carbonic anhydrase (CAH) enzymes,
Pepsin: secreted by Chief cells as pepsinogen to digest proteins,
Intrinsic Factor: Secreted by parietal cells, essential for absorption of B12 in the intestine.
Chemical Massagers: ~ 20 known molecules that act as hormones or neurotransmitters.
Parietal Cells secrete HCl
Parietal cells have carbonic anhydrase (CAH)
H+ is exchanged for K+ through an antiport (proton-potassium ATPase)
Cl- diffuses out of the parietal cells.
HCl is formed
Blood leaving stomach has high pH.
HCl activates pepsin
- Intestinal Phase – Absorption of Nutrients
Gastrin: Secreted by stomach and duodenum
Stimulates pancreatic juice secretion.
Cholecystokinin (CCK): Secreted by duodenum in response to fats and acid arriving from stomach.
Stimulates bile and pancreatic juice into duodenum.
Secretin: Secreted by duodenum in response to acid from chyme,
Stimulates secretion of bicarbonate to increase pH of chyme in intestine.
Small Intestine Secretion and Motility
Secretion: Intestinal juice (1-2 L/day), contains mostly water, mucus, sodium bicarbonate (pH=7.4-7.8).
Intestinal Motility
Peristaltic movements continue and work to move chyme toward large intestine.
Segmentation: ring-like contractions and relaxations that churn and mix food with digestive enzymes only in small intestine.
Liver
manufactures bile, filters blood to detoxify toxins in blood coming from small intestine
Bile: Functions to emulsify fats (physical breakdown), 80% is reabsorbed in ileum, 20% lost in feces. Contains Yellowish-green fluid containing minerals, cholesterol, neutral fats, phospholipids, pigments (bilirubin-hemoglobin decomposition), bile acids
Hepatocytes (cells of liver) contain cytochromes that chemically breakdown toxins.
Gallbladder
stores bile to be secreted into duodenum (first portion of small intestine).
Exocrine - Acini part of pancreas
secretes zymogens.
Trypsionogen: Activated by enterokinase trypsin (digests proteins) by activating other enzymes:
Chymotrypsinogen chemotrypsin (digest proteins) Procarboxypeptidase carboxypeptidase (digest proteins)
Pancreatic Amylase: Digests starch.
Pancreatic Lipase: Digests lipids
Exocrine - Pancreatic ducts
Secrete sodium bicarbonate, alkaline fluid that neutralizes acid in chyme.
Endocrine - Pancreatic ducts
Islets of Langerhan’s cells secrete insulin and glucagon (discussed with endocrines)
Nutrient Absorption in Small Intestine
Nutrients are absorbed as monomers of each macromolecule. Carbohydrates = monosaccharides, Proteins = amino acids, Fats = fatty acids and monoglycerides Nucleic acids = nucleotides
Hydrophilic nutrients are absorbed into small intestine and into the blood stream,
Lipids are absorbed into the lymphatic system and routed to the liver,
Synergistic Effect on Blood [Glucose]
Glucagon, cortisol, epinephrine, growth hormone and thyroid hormone are glucogenic hormones (hyperglycemic) ↑[glucose] in blood.
Glucagon Secretion and Function
Synthesized by A-cells (alpha cells) of Islets of Langerhan’s (pancreas),
Stimulus for release from A-cells of Pancreas:
Decreased [glucose] in blood < 70 mg/dL,
Decreased [amino acids] in blood,
Effects of glucagon on body cells, muscle and adipocytes:
Breakdown of glycogen in liver to release glucose into blood,
Shifts to fat catabolism (use fat as energy source)
Functions to increase glucose in blood plasma (hyperglycemic).
Insulin Secretion and Function
Synthesized by B-cells (Beta-cells) of Islets of Langerhan’s (pancreas),
Stimulus for release from B-cells of Pancreas:
Increased [glucose] in blood > 100 mg/dL,
Increased [amino acids] in blood,
Parasympathetic activity
Effects of insulin on body cells, muscle and adipocytes:
↑glucose uptake by cells by body cells,
↑glycogen, protein and triglyceride synthesis,
Shifts to carbohydrate catabolism (use glucose as energy source).
Defecation
Is a somatic voluntary reflex. Everything is parasympathetic before Anal canal
