Lecture 3 Flashcards
Absoprtion
Small molecules move frim walls of GI into circulation
Digestion
Food is broken down into small molecules
- barrier and immune function
Transport
In circulation and to cells
Metabolism
In the cell, the chemical reactions that occur to molecules so they can be utilized
Why do we eat?
- hunger
- appetite
Hunger
A physiological process that prompts us to find and eat food
Appetite
A psychological desire to eat specific foods, from environmental stimulu
- smell, sight, sound ( marketing and presentation of food)
- social cues: certain location/activities, feelings
Satiety
The feeling of being full
What prompts hunger and satiety?
- signal to the hypothalamus
• nerve cells/stretch receptors
• hormones - food bulk: bulk (fiber and water), protein and fat, and eating slowly can promote satiety
Hormones that promote hunger and satiety
- low blood glucose levels trigger glucagon (signals hunger)
- ghrelin (signals hunger)
- Cholecystokinin (signals satiety)
Ancillary organs
- pancreas
- liver
- gallbladder
Mechanical digestion
Muscle action and movement
Chemical digestion
Reaction and secretion
- hydrolysis: break down of compounds with the addition of water
- enzymes: proteins that speed up chemical reaction, unchanging in the process (-ase)
- hormones: chemical messengers that travel to target cells, which then carry out a targeted response
Saliva contains…
- mucus: that lubricates and moistens food
- antibodies and lysozyme (enzyme): defend against bacteria
- chemicsl digestion: amylase to break down starch
Esophagus
- anatomy
• connects mouth and stomach: 10 inches long
• epiglottis: prevents food from getting lodged in trachea
-muscle action: peristalsis and gravity - passes lower esophageal sphincter into the stomach
Stomach anatomy
- empty is about 3/4 of a cup large
- reservoir that can hold up to about 4 cups
Stomach: muscle action
-peristalsis
-mechanical digestion by miscle layers: grinds, churns, mixes
-chyme: semiliquid mass mixed with gastric secretions
• chyme leaves stomach via phyloric sphincter 1-4 hrs after eating
Stomach secretion: gastic juice
- HCl
- pepsinogen/pepsin
- gastric lipase
- intrinsic factor
HCl
- release stimulated by the hormone gastrin
- denatures protein- chemical digestion
- kills bacteria
- activates enzymes
Pepsinogen
- inactive protein enzyme
- activated to pepsin (active pepsin enzyme) by HCl
- starts protein digestion -chemical digestion
Gastric lipase
- fat digestion begins, small amount occurs - chemical digestion
Intrinsic factor (IF)
Protein needed for absorbtion of vitamin B12
GI Problems: gastro-esophageal reflux disease (GERD)
- weakened LES
- some contributors: smoking, overweight large high fat meals, spicy, and acidic foods, caffeine, chocolate, alcohol, lying down after a meal
- treatment: diet, antacids, other drugs to reduce HCl production
Segmentation
A muscle movement action that helps movement of food in the small intestine
- churning and mixing and moving the food up and down as well so its well mixed
Small intestine: anatomy
- food stays 3-10 hrs in SI
- duodenum: 1’
• connected to stomach via pyloric sphincter - jejunum: 4-5’
- Ileum: 4-5’
• connected to large intestine via ileocecal valve - very folded interior
Small intestine: muscle action
Peristalsis and segmentation
Where is nutrients absorbed the most in thr small intestine??
Duodenum and jejunum
Small intestine secretions
- secretions received from:
• pancreas, gallbladder and liver, intestinal cells - hormones secretred from small intestine to target organs
Pancreas makes ______ for digestion
- bicarbonate: nuetralize contents, enzymes can function
- enzymes: amylase, protease, lipase
Liver makes _____ for digestion.
Produces bile, an emulsifier for fat ansorption
- other major nutrient related jobs too
The gallbladder stores ____ for digestion
Stores and secretes bile
Intestinal cell enzyme secretions
- cells of the SI produce brush border enzymes
• specific protease
• lipase
• specific sugar enzymes (sucrase, maltase, lactase)
Secretin signals….
- the stomach to slow gastric emptying
- the pancreas to secrete panceatic bucarbonate
Chilecystokinin (CCK) signals…
- the gallbladder to release bile
- the pancrease to release pancreatic enzymes
- the stomach to slow gastric emptying
- satiety
Gastric inhibitory peptide(GIP) signals…
- the stomach ti slow gastric emptying
- the pancreas to increase insulin release
Large intestine/ colon
- undigested/ unabsorbed matter passes through ileocecal valve to the large intestine
• water, undigested/ unabsorbed residues - fibers, sloughed cells, bacteria, non-food items
Bacteria in the large intestine/colon
- 90 trillion bacterial cells
- finish digestion and make
• short chain fatty acids- used by colon cells
• vitamin K
• B12 that the bacteria use- not absorbed
• gas - prebiotics: feed the bateria
- probiotics: replace the bacteria
Large intestine: muscle action and movement
Peristalsis
- food may stay in LI FOR 12-24 hrs
Absorption
- absorption: passing of nutrients from thr GI tract into circulation
- most absorption occurs in thr SI
• stomach: some water, alcohol, fluoride
• large intestine: water, short chain fatty acid, vit K - SI: heavily folded tissue called mucosal membrane
• 500x increase surface area = increase absoption
• within folds fingerlike projections called villi
• villi contains absoprtive cells called enterocytes
• each enterocytes contain microvilli (brush border)
Passive/simple diffusion
Solutes travel from a high to a low concentration
Facilitated diffusion
Carrier protein facilitates, high to low
Active transport
Carrier protein and energy, solutes can travel from a low to a high concentration
Endocytosis (pinocytosis)
Active transport by which a small amount of intestinal contents is engulfed by the cell membrane into the cell
SI into circulation: nutrieny transport
- nutrients travel to the blood or lymph for distribution to other cells
- each villus contains capillaries (smallest blood vessel) and lacteal (lymph vessel)
- nutrients cross over into these system
Nutrient transport: Cardiovascular system
- nutrients cross over into capillaries in villa —> hepatic portal vein —> to the liver for storage, utilization or back into curculation
- water-soluble nutrients (protein, carb, some vits, small fatty acids)
Nutrient transport: lymphatic system
- nutrients cross into lacteals in villi —> transported to larger lymph vessels —> drains into circulation by the heart —> the curculation and liver
- larger fat soluble nutrients
Metabolism
- the sum of all chemical processes involved in maintaining life
Anabolism
Build up molecules and use energy
Catabolism
Break down molecules and release energy
