Chapter 18: Digestive System - Glucose Regulation

Question 1

Digestive System Parts

Answer 1

Mouth, Pharynx, Esophagus, Stomach, Small Intestine, Large Intestine, Rectum/Anus

Question 2

Accessory Organ Parts

Answer 2

Teeth, Tongue, Liver, Gallbladder, Pancreas, Salivary Glands

Question 3

1. Cephalic Phase

Answer 3

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)

Question 4

Food is mixed with Saliva

Answer 4

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.

Question 5

Swallowing (Deglutition)

Answer 5

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),

Question 6

2. Gastric Phase – Digestion of Proteins

Answer 6

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.

Question 7

Food is mixed with Stomach secretions

Answer 7

Bolus is now called chyme (white fluid substance)

Innervation and Circulation of Stomach: Receives (mostly parasympathetic) and sympathetic innervation

Question 8

Stomach Wall

Answer 8

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

Question 9

Mucous Cells

Answer 9

Secrete mucous for lubrication and gastric mucosa protection from HCl,

Question 10

Regenerative Cells

Answer 10

Duplicate fast to replace cells of gastric mucosa that die.

Question 11

Parietal Cells

Answer 11

Secrete HCl, and intrinsic factor.

Question 12

Chief Cells

Answer 12

Most numerous, secrete:
In infants - rennin and gastric lipase

In adults pepsinogen (inactive) which is converted to pepsin (active) by HCl acid.

Question 13

Enteroendocrine Cells

Answer 13

Secrete hormones and paracrine messages that regulate digestion.

Question 14

Gastric Secretions

Answer 14

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.

Question 15

Parietal Cells secrete HCl

Answer 15

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

Question 16

3. Intestinal Phase – Absorption of Nutrients

Answer 16

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.

Question 17

Small Intestine Secretion and Motility

Answer 17

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.

Question 18

Liver

Answer 18

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.

Question 19

Gallbladder

Answer 19

stores bile to be secreted into duodenum (first portion of small intestine).

Question 20

Exocrine - Acini part of pancreas

Answer 20

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

Question 21

Exocrine - Pancreatic ducts

Answer 21

Secrete sodium bicarbonate, alkaline fluid that neutralizes acid in chyme.

Question 22

Endocrine - Pancreatic ducts

Answer 22

Islets of Langerhan’s cells secrete insulin and glucagon (discussed with endocrines)

Question 23

Nutrient Absorption in Small Intestine

Answer 23

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,

Question 24

Synergistic Effect on Blood [Glucose]

Answer 24

Glucagon, cortisol, epinephrine, growth hormone and thyroid hormone are glucogenic hormones (hyperglycemic) ↑[glucose] in blood.

Question 25

Glucagon Secretion and Function

Answer 25

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).

Question 26

Insulin Secretion and Function

Answer 26

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).

Question 27

Defecation

Answer 27

Is a somatic voluntary reflex. Everything is parasympathetic before Anal canal