Digestive System Flashcards
Refers to the food we eat and the nutrients contained within
Nutrition
Refers to the use of the nutrients gained from food to build/maintain and provide energy
Also refers to interactive set of chemical pathways
Metabolism
While there, food is broken down into absorbable molecules in GI tract/lumen (still external)
Digestion
then transported out of the GI lumen and placed into the portal vascular system
Absorption (now internal)
when nutrient molecules enter cells and undergo many chemical changes
Assimilation
Before food can be used for energy, growth and maintenance, and regulation of bodily functions, the nutrients have to be ____
assimilated
a decomposition process
Catabolism
act of building nutrient molecules into large molecular compounds that requires the use of energy
Anabolism
The act of breaking food molecules down into smaller molecular compounds that, in-turn, releases energy
Catabolism
a synthesis process
Anabolism
Released in frequent, small bursts or otherwise it would “cook” the cell it is being released in
Thermal energy (heat)
Thermal energy is practically useless as an energy source for cells because it can’t be used to carry out work
Thermal energy (heat)
This heat that gets released from all cells collectively maintains the body temperature for homeostasis
Thermal energy (heat)
Cannot be used directly for biological reactions
It first has to be transferred into the high-energy molecule of adenosine triphosphate (ATP)
Chemical energy
Releases energy in two forms (catabolism)
thermal
chemical
readily absorbed in their original form
micronutrients
need to be small enough to be absorbed
macronutrients
Proteins need to be
Amino acids or small chains of amino acids (di/tripeptides)
Carbohydrates need to be
Monosaccharides such as
Glucose
Fructose
Galactose
Lipids need to be
Fatty acids (FAs) or monoglycerides (MGs)
Micronutrients
vits/mins
Needed in much smaller quantities in the body
** 28 of these are considered essential micronutrients – meaning required to live
**Do not provide calories of energy
Provides 4 calories of energy
protes
carbs
Provides 9 cals of energy
Lipids
Digestion requires enzymes called amylases
Carbohydrates
Sucrose
Lactose
Maltose
Unable to be absorbed as is
Byproduct of polysaccharide (starch) digestion
Found in excess in beer and some liquor (Barley)
Maltose
Only stored form of glucose in the body
glycogen
Found in the liver, muscle tissue, and some glial brain cells
cannot be absorbed or broken down
Cellulose
Monosaccharides and disaccharides
Fast source of energy
Simple carbohydrates
More difficult to digest because of longer chain sizes
Polysaccharides
Provides a more consistent amount of energy while being broken down (if able to be broken down)
Can be found in things like whole grains, legumes, starchy vegetables
Complex carbohydrates
are most common form of lipid found in the diet and in the body
Triglycerides (TAGs)
Consists of one glycerol subunit that is attached to three fatty acids
A high-energy nutrient synthesized and stored in adipocytes (adipose cells) as well as hepatocytes (liver cells)
Can be used by most cells in the body to power metabolism
Triglycerides (TAGs)
Can be used by most cells in the body to power metabolism
Not efficient in brain for sole source of energy
Still requires glucose
Triglycerides (TAGs)
Triglycerides are required for absorption of fat-soluble vitamins including
A, D, E, K
provides constituent molecules for cellular membranes
Triglycerides
all hydrogen bonds are used (solid at room temp)
Found in animal meats and dairy fats
Can also be found in coconut and palm oils
Saturated Fatty acids
Triacylglycerols (AKA triglycerides or “fat”)
1 glycerol cluster + 3 fatty acids = triglycerides
triglycerides combined with other components
Compound Lipids
Fatty acids + phosphorus + nitrogen
Lipid “bilayer” in cell membranes, part of the nerve sheath
Phospholipids
Fatty acids + carbohydrate + nitrogen
Part of cell membrane, helps to facilitate cellular recognition
Glycolipids
Chylomicrons
Very low-density lipoproteins (VLDL’s)
Low-density lipoproteins (LDL’s)
High-density lipoproteins (HDL’s)
Lipoproteins
simple + compound lipids together
Derived Lipids
Steroids (Cholesterol primary one)
Derived Lipids
Can be synthesized endogenously
Helps to build plasma membranes
Precursor in synthesis of Vitamin D
Requires for synthesis of androgens/sex hormones
Terpenes (various plant and animal oils; essential oils)
Fat-soluble vitamins
Ketone bodies
Derived Lipids
In order to be absorbed at the cellular level, triglycerides have to be hydrolyzed (broken down) into smaller components
Fatty acids (FAs) Monoglycerides (MGs)
Hydrolyzed by certain lipase enzymes
Lipid Digestion
Small fat droplets found in blood soon after absorption has occurred
During absorptive state blood may contain so many chylomicrons that it can appear turbid, or yellowish
In post-absorptive state (usually ~4 hours after meal) few chylomicrons exist in blood
Contents have moved mostly into adipose tissue
Chylomicrons (a lipoprotein)
lipid transport
Very low-density lipoproteins
Low-density lipoproteins
High-density lipoproteins
lipid transport
most active in post-absorptive state
Produced mostly in the liver from lipids and proteins
In post-absorptive state (usually ~4 hours after meal) few ___ exist in blood
chylomicrons
Entering blood from adipose tissue or other cells, fatty acids combine with albumin to form FFAs
When rate of fat-catabolism increases (i.e. starvation), FFAs levels in blood increase markedly
Free fatty acids (FFAs)
lipid transport
Lowest density
Largest
chylomicrons
Delivers triglycerides to cells throughout the body
Synthesized in enterocytes (intestinal cells) from fat and cholesterol absorbed in the small intestine
Because of large size, have to enter lacteals (lymphatic capillaries) which carries them to thoracic duct to be dumped into blood
Chylomicrons
Very triglyceride-rich
Very large particle
Delivers triglycerides to cells throughout the body
Synthesized in the liver from excess fats and cholesterol that have made it there from portal circulation
Very triglyceride rich
Large particle, smaller than chylomicron
Very low-density lipoproteins (VLDL’s)
Delivers cholesterol to cells throughout the body
As VLDL’s are stripped of their triglycerides, the “leftovers” get remodeled in the liver to form LDL’s
Smaller particles than VLDL’s
Low-density lipoproteins (LDL’s)
Reverse cholesterol transport for excess cholesterol
Returns excess cholesterol to the liver for recycling
Is made in both the liver and the small intestines
High-density lipoproteins (HDL’s)
Triglycerides are first hydrolyzed to yield fatty acids and a ___
glycerol
Fatty acids are broken down into two carbon pieces (acetyl-CoA) by a process called beta-oxidation
These then enter the ____
citric acid cycle
Glycerol is then converted to ____ which is then either Converted to glucose OR
Enters the glycolysis pathway
glyceraldehyde-3-phosphate
Lipid anabolism
lipogenesis
The synthesis of various types of lipids Triglycerides Phospholipids Cholesterol Prostaglandins
Absorption of proteins requires them to be broken down into any of the following:
Amino acid (single)
Dipeptide (two amino acids linked together)
Tripeptide (three amino acids linked together)
Anything larger than 3 amino acids together is too large for absorption therefore requiring something to break it down smaller
Broken down by proteases (pepsin, trypsin etc)
There are 20 amino acids
9 are essential (These have to be consumed as they cannot be made in the body)
7 are conditionally essential
4 are non-essential
Process by which amino acids are broken down for energy use
Catabolism Protein Metabolism
Process by which proteins are synthesized
Every cell synthesizes its own structural proteins
Anabolism Protein Metabolism
Constitutes the major process for growth, reproduction, tissue repair, and replacement of all cells destroyed by wear and tear
Both protein catabolism and anabolism are occurring continually, only their rates differ depending on the need of the body
Protein Metabolism
tubular system
Extends from the mouth to the anus
Forms extensive surface area in contact with the external environment
Closely associated with cardiovascular system because of the blood vessels involved in the digestive process
Digestive system
Six Basic Processes
of Digestive system
Ingestion
Secretion
Mixing/propulsion
Digestion
Absorption
Defecation
everyday, cells within the GI tract and accessory organs secrete ~7L of water, acid, buffers, enzymes into lumen of tract
Secretion
mix and movement of material along tract
Motility
teeth cut and grind food before swallowed, smooth muscles of stomach and small intestine churn food- this helps to mix with enzymes to dissolve food
Mechanical digestion-
large carbohydrate, lipid, protein, molecules are split into smaller molecules by hydrolysis- enzymes produced by salivary glands, tongue, stomach, pancreas, small intestine catalyze these catabolic reactions
Chemical digestion
entrance of ingested and secreted fluids, ions, and products of digestion into the epithelial cells lining the GI tract
Absorption
Absorbed substances pass into blood or lymph and circulate to various locations in the body
wastes, indigestible substances, bacteria, cells sloughed from lining of tract, digested materials not absorbed leave the body through the anus
Defecation
From outer layer to inner-most layer (contact with tract contents)
Serosa or adventitia (depends on the location)
Muscularis
Submucosa
Mucosa
Wall of GI tract from lower esophagus to anal canal has same basic four-layered arrangement of tissue
Serosa or adventitia (depends on the location)
Muscularis
Submucosa
Mucosa
Found on almost all parts of the GI tract (see adventitia)
Serous membrane composed of areolar connective tissue and simple squamous epithelium (mesothelium)
Also called the visceral peritoneum
Forms from a portion of the visceral peritoneum
Serosa
Single layer of connective tissue for the esophagus and proximal duodenum
Adventitia
Muscularis
Skeletal muscle- voluntary
Smooth muscle- involuntary
Contains myenteric plexus (plexus of Auerbach)
Skeletal muscle- voluntary only in?
Mouth, pharynx, superior aspect of esophagus
Also present in external anal sphincter, permits voluntary control of defecation
Smooth muscle- involuntary
Found in the rest of the tract
Involuntary contractions help break down food, mix it with secretions, and propel it forward
Inner sheet of circular fibers, outer sheet of longitudinal fibers
Network of neurons between the circular and longitudinal muscle layers
myenteric plexus (plexus of Auerbach)
Consists of areolar connective tissue that binds the mucosa to muscularis
Contains many blood and lymph vessels that receive absorbed food molecules
Contains submucosal plexus (plexus of Meissner)
Submucosa
Extensive network of neurons
submucosal plexus (plexus of Meissner)
Mucosa- inner lining of GI tract
composed of three layers
Muscularis mucosae (outer-most layer of mucosa)
Lamina propria (Middle layer of mucosa)
Epithelium
Thin layer of smooth muscle fibers
This layer is what causes the mucous membrane of the small intestine and stomach to have the folded appearance
These folds increase surface area for digestion and absorption
Movement of this layer ensures all absorptive cells are fully exposed to contents of GI tract
Muscularis mucosae (outer-most layer of mucosa)
Areolar connective tissue containing many blood and lymphatic vessels which allow nutrients to reach other tissues of the body
Supports the epithelium and binds to the muscularis mucosae
Contains majority of mucosa-associated lymphatic tissue (MALT)
Lamina propria (Middle layer of mucosa)
This lymphatic nodular tissue contains immune cells that protect against disease
present along GI tract especially tonsils, small intestine, appendix, and large intestine
MALT
in lamina propria
every 5-7 days these cells are replaced by new cells, old slough off and are excreted
Epithelium
Protective function Nonkeratinized stratified squamous found in mouth, pharynx, esophagus and anal canal
Epithelium
Simple columnar found in stomach and intestines
Secretion and absorption function
Tight junctions between cells here prevent leakage
Epithelium
secrete mucous/fluid/enzymes into lumen
Exocrine cells- epithelium of mucosa
secrete hormones into lumen
Enteroendocrine cells - epithelium of mucosa
Myenteric (or Auerbach) plexus located between longitudinal and circular smooth muscle layers of the muscularis
Submucosal plexus (plexus of Meissner) found within the submucosa
Enteric Nervous System
plexus located between longitudinal and circular smooth muscle layers of the muscularis
Myenteric (or Auerbach)
found within the submucosa
Submucosal plexus (plexus of Meissner)
Both plexuses consist of neurons, interneurons, and sensory neurons
tight
supply motor impulses to longitudinal and circular smooth muscle layers of muscularis
This leads to this plexus controlling the majority of GI tract motility
Particularly the frequency and strength of contraction of muscularis
Myenteric (Auerbach) plexus-
motor neurons supply the secretory cells of the mucosal epithelium
This leads to this plexus controlling secretions of the organs of the GI tract
Submucosal (Meissner) plexus-
connect the myenteric and submucosal plexuses
Interneurons
Sensory neurons- supply the mucosal epithelium. Some function as
chemoreceptors,
Activated by certain chemicals in food located in the lumen of GI organs
Other sensory functions of the mucosal epithelium function as ____
baroreceptors (stretch receptors)
Activated when food stretches/distends the wall of a GI organ
Helps to regulate the enteric nervous system (ENS)
Autonomic Nervous System
supply parasympathetic fibers to most parts of GI tract. These parasympathetic nerves form neural connections with the enteric nervous system
Vagus (X) nerves
Stimulation of the parasympathetic nerves that innervate the GI tract
Causes an increase in GI secretion and motility by increasing activity of the ENS
