olinmhvgtcd3 Flashcards
Objective:
Review anatomy, function and regulation of gastro-intestinal system (GIT)
Objective:
Understand the digestion and absorption of nutrients in different parts of the GIT
Objective:
Describe the absorption pathways of hydrophilic (water-soluble) and hydrophobic (fat soluble) nutrients and how they are transported via the vascular and lymphatic systems
Role of mouth in digestion?
Ingesting food
Chewing food
Saliva released has amylase; breaks down starches
Role esophagus in digestion?
Esophageal sphincter:
1) Allows passes from mouth to esophagus and from esophagus to stomach
2) Prevents back flow from stomach up the esophagus
Role of stomach
- Acids and enzymes mix with food
- Turns the food into a paste for easier digestion (liquid mass called “the chime”
- The chime then goes into small intestine (duodenum first)
Phyloric sphincter
Allows the chime to go from stomach –> duodenum
- prevents back flow from duodenum –> stomach
Role of small intestine
Enzymes are secreted from pancreas that break down energy-yielding macronutrients and macronutrients into their singular form (primed for digestion)
Role of Pancreas
Makes the enzymes that help break down the energy-yeilding nutrients in small intestine.
Role of Bile
produced in Liver
stored in galbladder
released in small intestine for liquid digestion
Role of Large Intestine
reabsorption of minerals, nutrients and water
Role of Rectum
Elimination!
Role of intestinal folds and villi
in small intestine
has peaks and valleys
help absorb nutrients
Has lacteal (tip of lymphatic vessel)
Arteries move blood towards the tip (capillaries) and veins move blood away
Also has lymphatic vessel going in and out to the tip of the capilaries
Role of small intestine Microvilli
For absorption; they have “transporters” for nutrients
Also have digestive enzymes to break down any remaining molecules into their simplest form (for absorption)
Peanut Butter Sandwich example: What’s the role of each organ for digestion?
Mouth:
- chewing and swallowing of “bolus” (little digestion)
- CHO/Starch: salivary amylase
- Fibre: seed coat crushed by teeth
Stomach:
- collecting and churning (some digestion)
- CHO/Starch: bolus mixed with gastric juice, inactivation of amylase
- Protein: denaturation (uncoil) b/c of acid + gastric protease (breaks down proteins –> peptides)
- Lipid: mixed with gastric juice and separates into water / lipid phase
-lipid phase stays longer (floats to the top); water goes straight into duodenum
Small intestine
- Digesting and absorbing
- Sugars: absoption
- Starch: pancreatic and intestinal sell surface (Brush-boarder membrane;BBM) enzymes = simple sugars (monosaccharides)
- Lipid (TG) - bile (emulsifies fat) + pancreatic lipase breaks lipid –> glycerol + fatty acids (absorbed)
- Protein: pancreatic proteases = amino acids absorbed
- Vitamins/Minerals: absorbtion
Large intestine:
- reabsorbing and eliminating
- Fluid/Minerals: absorbed
- Fibre: bacterial fermentation products absorbed / unfermented fibres –> decal bulk; binds cholesterol and minerals to poo and excreted
- Lipids: Bile and cholesterol excreted
How are nutrients absorbed in the intestine?
(3 ways)
Water & simple lipids: simple diffusion (high –> low conc. via phospholipid bi-layer)
Water-soluble, hydrophilic vitamins: facilitated diffusion (carrier flips from lumen to intrasite)
Glucose & Amino Acids: active transport (requires energy, carrier flips from lumen to intrasite)
*“Lumen” is outside the cell
Describe how: water-soluble (hydrophilic) nutrients enter the body?
From the small intestine –> Capiliaries (tips of villi) –> Hepatic Portal Vein –> Liver –> rest of the body
Describe how: fat-soluble (lipophilic) nutrients enter the body?
i.e. cholesterol, phospholipids, fatty-acids, and glycerol
Packaged into “chylomicrons (CM)” in enterocyte –> CM enters lymphatic vessels –> lymph circulation (thoracic duct collects lymph and enter circulation via left subclavian vein; just above the heart) –> directly to vascular circulation (supplies tissues); bypasses the liver (may uptake by liver post bypass
)
Describe Endocrine Regulation of Digestion and Absorption.
(6 ways)
under self-regulating or negative-feedback mechanisms
When food bolus enters stomach:
Gastrin – G-gastrin cells maintain pH 1.5 –> HCl release from parental cells in stomach
When chyme enters duodenum:
Secretin – S-cells in Cryps of Lieberkuhn –> Targets pancreas to release neutralizing HCO3 + digestive enzymes (don’t want to burn duodenum)
When lipids enter duodenum:
CCK – Cholecystokinin; I-cells in duodenum –> Targets gall bladder to release bile, and the liver to synthesize bile
When lipids or protein enters duodenum:
CCK – Targets pancreas to release HCO3 + digestive enzymes, and slows GI mobility (good for digestion)
When glucose enters duodenum:
**Gastric-inhibitory peptide – GI-Peptide, K-cells in duodenum/jejunum –> Targets Beta-cells pancreas –> insulin secretion (important for glucose transport and absorption)
When nutrients enter ileum:
Glucagon-like peptide 1 – GL-Peptide-1, L-cells in ileum –> Targets Beta-cells pancreas –> insulin secretion (increase glucose uptake) –> surpasses glucagon secretion from Alpha-cells pancreas
