Unit 15: Digestive System Flashcards
Main Function
Breakdown of organic nutrients so that they can be absorbed into the body
Organic Nutrients
Carbohydrtaes Lipids Proteins Water Vitamins Minerals
Mouth
Food is broken up chewing and mixing with saliva to form a bolus
Salivary Glands
Produce Saliva to moisten and begin digesting some food particles
Esophagus
Straight muscular tube that connects the mouth and pharynx to the stomach
Stomach
Stores, mixes and disgests some food and delivers food to the small intestine
Liver
Many functions for digestion: secreting bile
Secretion from the Liver involves
The release of digestive fluids into the lumen of the digestive tract
Fluids from the Liver (6)
Water Mucous Acid electrolytes enzymes bile salts digestive enzymes
Digestion
Is the process whereby food is broken down into smaller molecules by the digestive enzymes so they can be taken up by the body
Absorption
Is the process whereby the small molecules are taken up by the circulatory system and distributed through the body
Saliva
Water + ions + protein
lubricates the bolus of food
digests carbohydrates (amylase)
3 Salivary Glands
Parotid
Sublingual
Submandibular
2L of saliva
Control of production and secretion of saliva
Under control of the ANS
Swallowing (1)
Bolus of food is lubricated by saliva and pushed to the back of the mouth by the tongue + swallowing reflex is initiated
Swallowing (2)
Uvula of the soft palate closes over the nasopharynx
larynx is lifted by the muscle in the neck
Swallowing (3)
Epiglottis bends back over the glottis covering the larynx
Swallowing (4)
The bolus moves down the esophagus through the cardiac orifice (lower esophageal sphincter) and into the stomach by a smooth wave of muscle contractions called peristalsis
Stomach Structure
Esophagus Fundus Body Antrum Pyloric Sphincter
Pyloric Sphincter
Located at the distal portion
Regulated the emptying of the stomach into the first part of the small intestine (duodenum)
Empty Stomach
Thrown into folds rugae
Increasing the surface area allowing for expansion of the stomach as it fills with food
Stomach function
Liquifies, mixes and stores each bolus of food from the meal, mixture is called the chyme.
Stomach regulates the amount of chyme entering the small intestine so that it can become fully digested and reabsorbed
Some digestion takes place in the stomach
Digestion in the Stomach
Proteins being to be digested in the stomach by the enzyme pepsin
very little absorption
Substances that can cross the lining of the stomach to be absorbed into the bloodstream
Alcohol
Aspirin
How is mixing of the chyme in the stomach achieved (begin and end at?)
Mixing of the chyme is acheived by peristalsis contraction of the stomach walls that begin at the fundus and end at the antrum
Stomach contractions also help
Move the chyme through the pyloric sphincter into the small intestine where most of the digestion and absorption takes place
Motility
Muscle activity causes the movement of substances through the digestive tract
Stomach Secretes
Mucus HCl Pepsinogen Gastrin Intrinsic factor
Mucus (stomach)
Which is secreted by cells in the body + antrum of the stomach from the extremely acidic environment that is produced by HCl
HCl
Secreted by cells in the stomach body
begins to denature and unfold the complex proteins
kills bacteria
converts pepsinogen to its active form pepsin
Pepsinogen
Secreted from cells in the stomach
converted to its active form by HCl
Gastrin (secreted by cells in the…)
Hormone secreted by cells in the antrum
Instrinsic Factor
Helps with the absorption of vitamin B12
Pancreas
Part of it drains into the small intestine
Below the stomach
consists of endocrine, exocrine and digestive functions
Exocrine products of the pancreas
Are secreted into the long pancreatic duct
Pancreas produces and secretes the carbohydrate digesting enzyme
Amylase
Protein digesting Enzymes (Pancreas)
Trypsin
Chymotrypsin
Protease
Lipid digesting enzymes
Lipase
Pancreas secretes (pH)
sodium bicarbonate into the duodenum to neutralize the acid from the stomach
Contents from the stomach empty
Through a pyloric sphincter into the small intestine
Small Intestine structure
Longest section of the digestive tract reaching 9m in length
ends at the ileocecal sphincter where it empties into the ascending colon of the large intestine
Small intestine sections
Duodenum (shortest segment) Jejenum Ileum (longest section; 50%)
Inner Structure of Small Intestine
Inner walls of the small intestine is thrown into folds
folds contain villi
the end result is a large surface area in which food comes into contact
Villi Contains
A capillary network and lymphatic lacteral to absorb the digestive material
Epithelial Intestinal Cells
Secrete digestive enzymes
All digestion and absorption in the small intestine (location)
All digestion and absorption takes place in the duodenum and jejunum
Digestion of the chyme
Occurs by the digestive enzymes from the pancreas and epithelial cells
Bile
From liver
digests fat although not a digestive enzyme
Process of Absorption is greatly enhanced by (3)
The large surface area produced by the villi lining the walls of the intestine
the large blood supply to the digestive tract
the motility/movement of the food in the intestine
Forms of Carbohydrates
Monosaccharide
Disaccharide
Polysaccharide
Monosaccharides
Glucose
Fructose
Galactose
Disaccharide
Maltose
Lactose
Sucrose
Polysaccharides
Glycogen
Starch
To be absorbed carbohydrates
Must be broken down into monosaccharides
they can be absorbed by the transport systems in the wall of the small intestine
Amylase
Digests carbohydrates in the mount
Salivary Enzyme
Small Intestine + Carbohydrates+Pancreas
Pancreas secretes amylase into the duodenum
Pancreas also secretes bicarbonate ions which neutralize the acids from the stomach
Each disaccharide requires a
specific enzyme to break it down its component monosaccharide
These enzymes are located in the
Brush border of the microvilli located on the intestinal epithelial cell
Lactose
Lactase
Maltose
Maltase
Sucrose
sucrase
Lactose intolerance
Lactose found in milk products
Gas, Cramps, Bloating, Diarrhea
Inability to digest lactose because of the inability to produce the enzyme lactase
Lactose cannot be broken down and absorbed into the body and will shut off the digestive tract
carbohydrates present in the large intestine are fed on by bacteria producing gas, bloating and cramps
Carbohydrate Absorption
Intestinal epithelial cells contain Na+/K+ pumps on their basal side to establish a concentration gradient for sodium
Gradient powers the Na+/glucose located on the luminal side of the cell
Transporter move glucose into the cell as Na+ moves down its concentration gradient
Once glucose is inside the cell it will then diffuse out through the basal side by facilitated diffusion
Proteins + AAs (structure/amount)
Consists of long chains of amino acids linked together
20 different AAs
11 non-essential AAs (produced by the body)
9 essential amino acids )that must be from the diet)
Different groups of amino acids require
different enzymes to break them apart
Proteins must be broken down into the AA building blocks
before they can be absorbed by the transport systems in the small intestine
Protein Digestion
Begins in the stomach
HCl converts inactive pepsinogen to the active enzyme pepsin
HCl also helps to denature the long twisted strands of proteins
Protein unfolding gives the pepsin access to the long protein chains in order to digest them into smaller chains called a polypeptide
Proteins leave the stomach as
Polypeptides passing through the pyloric sphincter
Pancreatic protein-digesting enzymes pH
Require a neutral pH
Chyme form the acidic stomach must be neutralized (HCO3)
Pepsin is inactivated
Pancreatic protein-digesting enzymes
Trypsin
Chymotrypsin
Protease location
Found along the brush border of intestinal epithelial cells
Two different classes of protease enzymes
Endopeptidases
Exopeptidases
Protein Absorption (AA + Small Polypeptides)
Secondary active transport requires the presence of a Na+ concentration gradient
As Na+ moves into the intestinal epithelial cell and down their concentration gradient they power a cotransporter that also moves amino acids into the cell
Small peptides are absorbed through endocytosis
Types of fats
Triglycerides + phospholipids + cholesterol + long fatty acids chains
not water-soluble + do not mix well with water
Stomach+Intestin fat digestion
Churning action of the stomach breaks up the large drops of fat into smaller ones
Emulsification
Is important because it allows fat-digesting enzymes to do their work on very small drops of fat
Fats tend to aggregate to form large droplets of fat
The difficulty is keeping these fats apart
Bile
Produced by the liver + transported to the gallbladder where it is stored and concentrated
not a digestive enzyme
Bile Composition
Water, bile salts, cholesterol, fatty acids + many ions
Gall bladder releases bile
Into the duodenum of the small intestine during a meal
Bile salts role
keep the lipids emulsified + prevent them from forming large aggregates
Colipase
Lipid droplets coated in bile salts can not be reached by lipase
The pancreas secretes colipase a protein that allows lipase to get access to the lipid interior of the fat droplets
Fat Droplets composition
Phospholipids
Cholesterol
Pancreatic Lipase function
Attacks the phospholipids + removes 2 fatty acid chains leaving monoglycerides behind
As lipase slowly digests the lipid interior of the fat droplets the droplets get smaller
Micelles
Single-layer of bile salts surrounding a very small lipid droplet
Help ferry the lipid droplets to the intestinal epithelial cells where lipids are absorbed
Fat Absorption
Fatty acids and monoglycerides can diffuse into the epithelial cells that line the intestine
Cholesterol molecules are
transported into the cell by a specific active transport system
Bile Salts after use
Left behind after the fats are absorbed
reabsorbed by a transport system in the cells in the ileum
bile salts return to the liver they are reused
Monoglycerides+fatty acids in the intestinal cell
enter the endoplasmic reticulum when they will combine w/ cholesterol + proteins to form chylomicrons
Chylomicrons are packaged up into
Secretory vesicles by the GA
they will leave the cell and enter the lacteals of the lymphatic system which eventually drains into the circulatory system
Vitamins
Absorbed in the small intestine
Lipid-soluble vitamins
ADEK
Diffuses through the membrane
Water-soluble vitamins, how are they absorbed?
B C Folic acid Niacin absorbed by carrier-mediated mechanisms require an Na+ concentration gradient+ transporter
Amount of water absorbed by the small intestine
9L
Where does this water come from?
Not always from eating and drinking
80% is reabsorbed from water contained in saliva+ digestive enzymes from the stomach + pancreas + bile and the secretion from intestine
The remaining water comes from (percentage)
20% comes from eating and drinking
Amount of Water absorbed in the intestine varies…
Varies along its length
Small intestine/large intestine water absorption
- duodenum + jejunum absorb 44%
- Ileum absorbs roughly 38%
- large intestine absorbs 1.5%
- 100ml is excreted in the feces
Water reabsorption mechanism
As the molecular glucose, amino acids, lipids are absorbed an osmotic gradient begins to build up across the intestinal epithelial cells
- water flows into the cells from the lumen of the intestine
- As ions move into circulation and water follows into circulation
Absorption of Na+
same as in the kidneys
occurs with the help of the Na+/K+ pump located on the basal lateral side of the intestinal cells
Na+ will move into the cell + down its concentration gradient from the lumen of the intestin
Colon begins at the
ileocecal valve
Length of Colon
1m
Structure
- Ascending
- Longitudinal/transverse
- descending limb
- Curved Sigmoid section
- Rectum + Anus
diameter of colon
Large
Colon has no
Folds or Villi
