Nutrition Exam 3

Systems involved in digestion

→ digestion occurs under involuntary control - autonomic & enteric nervous systems

• PNS = controlled by vagus nerve

  • increases saliva production, gastric acid secretion, pancreatic enzymes, nike, peristalsis, nutrient absorption

• SNS = inhibits digestion activity during exercise

  • inhibits digestive secretions, GI motility, constricts blood vessels, reducing blood flow to GI tract, slows digestion, GI discomfort

• Enteric = gut brain

  • regulates peristalsis, enzyme secretion, blood flow, independent, but modulated by SNS & PNS

Digestive System Hormones

→ Ghrelin:

• hunger hormone released from stomach

• triggered before meals, fasting

• increase appetite, signaling brain to eat

→ Leptin:

• satiety hormone released from adipose tissue

• triggered after eating

• decreases appetite, signaling brain to stop eating

• eating slow and mindfully helps leptin work properly

Hormones that control digestion

→ Gastrin:

• secreted from stomach

• stimulates the secretion of HCL, which helps breakdown food, protects inner lining of stomach, and helps things move around to create bolus

• increases gastric motility

• triggered by detection of food or acid, stomach digestion

→ Secretin:

• secreted from Duodenum

• stimulates bicarbonate release from pancreas

• neutralizes acidic chyme

• decreases gastric acid secretion

• helps w/ stomach mobility

• triggered by low ph (acid)

→ Cholecystokinin (CCK):

• secreted from duodenum

• stimulates bile release from gallbladder

• stimulates secretion of pancreatic enzymes

• Slows gastric emptying

• triggered by detection of FAs & AAs

→ Gastric Inhibitory Peptide (GIP):

• secreted from duodenum & jejunum

• stimulates insulin release

• decreases gastric activity/ delays gastric emptying

• triggered by glucose, fats, AAs

• triggers the secretion of insulin to help w/ glucose regulation and promotes satiety

→ Glucagon-Like-Peptide-1 (GLP-1):

• secreted from small intestine (ileum)

• enhances insulin secretion

• slows gastric emptying

• promotes satiety

• decreases glucagon secretion, so glucose levels can’t rise

  • glucagon = hormone released by alpha cells in pancreases that trigger the breakdown of glycogen when glucose levels are low

• triggered by carbs and fats

→ Gastrin starts digestion in the stomach, Secretin protects the intestine from acid, CCK drives fat digestion, and both GIP and GLP-1 help regulate blood sugar—while GLP-1 also plays a major role in appetite and energy balance.

The Mouth

• Salivary Amylase = breaks down starch into simpler disaccharides

• Lingual lipase = lipid digestion begins w/ this

The Stomach

• mucous neck cells = produce mucus, gel layer that protects epithelial from HCL, prevents self digestion

• pepsinogen = HCL triggers to the conversion to pepsin to break down proteins

• parietal cells = produce HCL to break down food, activates pepsinogen

• chief cells = secrete pepsinogen, gastric lipase

The Stomach Cont.

→ Vagus nerve releases -

1. acetylcholine, which stimulates parietal cells to release H+

2. pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates ECL cells to release histamine, which stimulates parietal cells to release H+

3. gastrin-releasing peptide (GRP) stimulates G-cells to secrete gastrin, which stimulates parietal cells and ECL cells to release H+

• H+ + Cl = HCL in stomach lumen

Pancreas and digestion

→ Pancreas secretes -

• alkaline juice to buffer HCl

• enzymes:

  • pancreatic amylase → starch breakdown

  • trypsin, chymotrypsin, carboxypeptidase → protein breakdown

  • pancreatic lipase → TAG breakdown

• bicarbonate neutralizes acidic chyme, pH balance

• insulin, glucagon

Small Intestine

• most digestion takes place in the small intestine (jejunum), absorption takes place in villi of intestinal mucosa

Small Intestine Absorption

• Microvilli = brush boarder where digestion is finished and the nutrients are diffused into the blood stream through sorted mechanism

  • increase surface area for digestion and absorption

  • CHO: releases maltase, sucrase, lactase, which breakdown glucose, fructose, and galactose into absorbable forms facilitated by enzymes (GLUT transporters)

  • Peptides: peptidases breakdown AAs, dipeptides, tripeptides to then be transported into cells

  • Fats: packaged into chylomicrons, then diffused into cells, reassembled, and the enter the lymph

Small Intestine: Fate of Carbs

→ SLGT1 - moves glucose & galactose into the cell (fast process)

• GLUT2 - takes the two monosaccharides into the bloodstream

→ GLUT5 - passive, slower diffusion of fructose into the cell

• GLUT2 - takes fructose into the blood stream

Small Intestine: Fate of lipids

• lingual lipase begins lipid digestion in the mouth

• gastric lipase continues the breakdown in the stomach

• bile emulsifies the lipids

• pancreatic enzymes help digest the fatty acids

Small Intestine: Fate of proteins

• gastrin stimulates the secretion of HCl

• pepsin initiates protein digestion in the stomach

• pepsin breaks down AAs, which are absorbed into the blood stream to be used for structural proteins, or glucose for energy

Small Intestine: Fat Soluble Vitamin Absorption

Small Intestine: Water Soluble Absorption