Chapter 9 - Digestive System Flashcards
What is digestion?
The breakdown of food into organic molecules:
Lipids into fatty acids and glycerol
Starch and carbs into monosaccharides
Proteins into amino acids
Mechanical digestion - what is it, and what ISNT it?
Physically breaking down large pieces of food - it is NOT chemical breakdown
Chemical digestion - what is it, and some examples
The enzymatic cleavage of chemical bonds
Ie, the peptide bonds of proteins, or the glycosidic bonds of starches
The order of what structures food travels through:
7
Mouth Pharynx Esophagus Stomach Small intestine Large intestine Rectum
What additional structures help provide enzymes and lubrication to aid in digestion?
(4)
Salivary glands
Pancreas
Liver
Ball bladder
What is the enteric nervous system?
Millions of neurons that govern the GI system
These are present in the walls of the digestive tracts and trigger PERISTALSIS (rhythmic contractions of the gut to help move food along)
What controls the enteric nervous system?
It is largely autonomic, but it can function independently of the brain and spinal cord.
PARASYMPATHETIC: stimulates digestion, increased secretions, promotes peristalsis
SYMPATHETIC: inhibits the above activities
What is intracelullar digestion?
What is extracellular digestion?
Intracelullar: the oxidation of glucose and fatty acids for energy
Extracellular: obtaining nutrients from food in the lumen of the alimentary canal
What role do ADH (aka vasopressin) and ALDOSTERONE play in feeding behavior?
They trigger the sensation of thirst, encouraging the behavior of fluid consumption.
What substances trigger the feeling of HUNGER?
Glucagon (secreted by the pancreas)
Ghrelin (secreted by the stomach and pancreas)
What substances trigger SATIETY?
Leptin
Cholecystokinin (peptide hormone secreted by GI tract)
What 3 substances account for chemical digestion in the oral cavity?
Salivary amylase “ptyalin” (starch into smaller sugars such as maltose and dextrin)
Lipase (breaks down lipids)
What are the 3 portions of the pharynx?
Nasopharynx
Oropharynx
Laryngopharynx (above vocal cords)
What structures does the esophagus connect?
The pharynx and the stomach
Different muscle composition of the esophagus:
3
Top third: skeletal muscle
Middle third: mix
Bottom third: smooth muscle
Aka top: somatic/voluntary
Bottom: autonomic/involuntary control
Where does peristalsis start?
At the smooth muscle (lower third) of the esophagus
What is emesis?
VOMITING
the reverse of peristalsis
Where is swallowing initiated?
In the muscles of the oropharynx (upper esophageal sphincter)
What is the cardiac sphincter?
The lower esophageal sphincter
(Empties into the cardia of the stomach)
**weakness in this sphincter leads to gastroesophageal reflux disease (GERD) = “heartburn”
What are the THREE main sources of energy?
Protein
Carbohydrates
Fats
Stomach as an organ (Size?) (What is it made of?) (Where is it?) (What substances does it use to digest food?)
Holds about 2 L’s
Made of muscle; thick mucosa
Upper left quadrant of the abdominal cavity, under the diaphragm
Uses hydrochloride acid and enzymes
Four main anatomical divisons of the stomach
Fundus - gastric glands
Body - gastric glands
Antrum - pyloric glands
Pylorus -pyloric glands
How does NSAIDs impact the stomach?
They MAY disrupt mucus production which leaves the mucosa unprotected and probe to irritation.
Gastritis, or gastric ulcers may result
How are gastric glands innervated?
What cell types do they have? (3)
Respond to signals from the vagus nerve (PARASYMPATHETIC nerve) which is activated by sight/smell/taste of food
Mucous cells
Chief cells
Parietal cells
What do mucous cells do?
bicarbonate-rich mucous that protects mucosa
What do chief cells and parietal cells do?
Chief cells make PEPSINOGEN (which is inactive - Pepsin is active)
And parietal cells make hydrochloric acid
These combine to make GASTRIC JUICE
What is special about PEPSIN?
An enzyme that breaks down proteins
It is activated by the ACIDIC environment - most active at a low pH
Other enzymes mostly active at physiological pH
What do the pyloric glands do?
They have G-cells that secrete GASTRIN
What is GASTRIN?
Peptide hormone
Induced parietal cells to secrete more HCl and stomach to contract and mix it’s contents.
What is CHYME:
(Unlike chyle - lymphatic fluid)
Chyme is the contents of the stomach - an acidic, semi fluid mixture
What 6 products does the stomach secrete?
- HCL
- PEPSINOGEN
- Mucus
- Bicarbonate
- Water
- Intrinsic factor
What are brush-border enzymes?
Activated by the presence of chyme in the duodenum
Disaccharidases and peptidases
Break down dimers and trimers into absorbable monomers
What other (3) things does the duodenum secrete?
- Enteropeptidase (activates other digestive enzymes)
- Secretin
- Cholecystokinin (CCK)
Disaccharidases
Digest the sugar close to their name (or maltase digests maltose)
Lack of a particular disaccharidase means inability to break down that corresponding disaccharide
Undigested disaccharides have an osmotic effect (pull water into the stool - cause DIARRHEA)
*lactose intolerance leads to bloating, flatulence, diarrhea etc
How do bacteria in the intestine hydro luxe disaccharides?
What is the byproduct?
Methane has as a byproduct
Peptidases
Aminopeptidase (removes the n-terminal amino acid)
Dipepridase (cleave the peptide bond to make free amino acids)
Di and even tripeptides CAN be absorbed into the small intestine, unlike polysaccharides
What is enteropeptidase?
Critical for the activation of TRYPSINOGEN into TRYPSIN
(Pancreatic protease)
Can also activate procarboxypeptidases A and B to their active forms
What is SECRETIN?
Peptide hormone
Causes pancreatic enzymes to be released into the duodenum
Regulates pH by reducing HCl secretions
It’s an ENTEROGASTRONE: slows down motility in the digestive tract to allow time to things to be digested, ie fats
What is CHOLECYSTOKININ?
Secreted in response to chyme entering the duodenum
Stimulated the release of bile and pancreatic juices
Promotes SATIETY in the brain
What is bile made of?
3
Bike salts
Pigments (ie bilirubin)
Cholesterol
What role does bile play?
Doesn’t chemically digest anything (it’s not an enzyme) but plays a role in mechanical digestion of FATS and ultimately help in the chemical digestion of lipids.
Mechanism of bile:
Hydrophobic and hydrophilic ends - act as detergents
- Emulsify fats and cholesterol into micelles (increased surface area)
- Increased surf area helps pancreatic LIPASE act on the lipids (breaks Esther bonds)
What are pancreatic juices composed of?
Several enzymes in a bicarbonate-rich alkaline solution.
Neutralizes acidic chyme - provides an ideal environment for the digestive enzymes (whose optimal pH are close to 8.5
What (3) peptide hormones does the pancreas release?
Insulin
Glucagon
Somatostatin
What is pancreatic lipase?
Breaks down fats into free fatty acids and glycerol
What structure allows pancreatic juices to enter the duodenum?
Pancreatic duct which runs inside the pancreas
Empties into the MAJOR and MINOR DUODENAL PAPILLAE
(Minor is ABOVE the major)
What do BILE DUCTS connect?
The liver with the gallbladder and the small intestine
What is the HEPATIC PORTAL VEIN?
The liver receives ALL blood draining from the abdominal portion of the digestive tract through this vein
NUTRIENT-RICH blood
The liver processes the blood, then drains into the INFERIOR VENA CAVA
How does the lives store nutrients?
Stores sugars as glycogen
Stores fats as triacylglycerols
Can also do the reverse: gluconeogenesis and mobilizing fats in lipoproteins
Examples of things that the liver detoxifies:
Ammonia (byproduct of amino acid breakdown) into urea
Alcohol
Medications
What is pancreatitis?
Inflammation of the pancreas
Results in pemature activation of pancreatic enzymes and autodigestion of the pancreatic tissue.
Outcomes of this are a lot of pain, potentially diabetes, and reduced digestion of proteins and fats.
How does jaundice occur?
What is it?
(3 poss causes)
When the liver is not able to process bilirubin
(The liver conjugated the bilirubin - attached it to a protein - and then secreted into bile)
May be caused by:
Liver damage
Excessive red blood cell destruction
Blockage of bike duct
Which PROTEINS does they we synthesize?
2
Albumin (maintains plasma oncotic pressure - carrier for many drugs and hormones)
Clotting factors (used during blood coagulation)
What is CIRRHOSIS OF THE LIVER?
Causes of CIRRHOSIS OF THE LIVER
4
Scarring of the liver - scar tissue builds up and creates resistance in the portal vein - leads to portal hypertension.
Alcohol consumption
Hepatitis C
Autoimmune hepatitis
Fatty liver disease
What are the results of CIRRHOSIS OF THE LIVER?
5
- swollen veins in the digestive system (due to a backup of fluid in the backup system)
- the swollen veins especially impact the ESOPHAGUS which may rupture (hematemesis)
- bleeding disorders (bc of disruption of clotting factors)
- increased ammonia in the blood (may affect mental functions)
- hepatocellular carcinoma
What does the gallbladder do?
Where is it located?
Stores and concentrates bile
Just below the liver (right upper quadrant)
How does the gallbladder work?
What activates is?
Upon release of CCK (from the duodenum) gallbladder contracts and pushes bile into the biliary tree.
Bile duct merges with the pancreatic duct and together they empty into the duodenum.
What are gall stones made of?
Meet do they happen here?
Cholesterol or bilirubin
They happen in he gallbladder because bile is concentrated here
How are amino acids and simple sugars absorbed into the epithelium?
Secondary active transport
Facilitated diffusion
What happens to large fatty acids (the can’t just go into the cell):
- Break down to move separately into the cell
- Chylomicrons (insoluble: made up of triglycerides and estherified cholesterol molecules)
- Chylomicrons enter the lymph via the lacteals
- Lacteals converge and enter the venous circulation via thoracic duct in the neck, and the lymph empties into the L subclavian vein.
Which (4) vitamins are fat-soluble?
A
D
E
K
What happens to fat-soluble vitamins?
Dissolve into chylomicrons and are absorbed into the body.
What happens if the body cannot digest fats properly?
Body’s inability to digest fats can lead to problems with gallbladder, pancreas, small intestine.
May lead to deficiencies in fat-soluble vitamins
What is the main role of the large intestine?
How does it physically compare to the small intestine?
Water absorption (although the small intestine actually absorbs more!)
Larger diameter but shorter length.
3 main parts of the large intestine
Cecum
Colon
Rectum
What does the cecum do?
A pocket that accepts fluid coming from the small intestine via the ILEOCECAL VALVE
This is the site of the APPENDIX
What is the appendix?
Small finger-like projection (long tube)
Likely plays a role in warding off bacteria and repopulating the large intestine with flora after episodes if diarrhea.
Located in LOWER RIGHT quadrant
What is the colon?
Divided into sections; Ascending Transverse Descending Sigmoid
Absorbs water and salts (ie sodium chloride) from indigenes material left over from the small intestine.
Concentrates the remaining material into feces
What does the rectum do?
Site of storage for feces
- indigestible material
- bacteria (ie, E Coli) - ABOUT 30%!
- digestive secretions that aren’t re absorbed (bile, enzymes)
What are he two sphincters of the anus?
Internal and external anal sphincters
Internal: autonomic
External: somatic
Good bacteria in the gut
Mostly anaerobes, but some aerobic bacteria
Some bacteria in the guy produce vitamin K (needed for clotting factor)
Some produce Biotin (Vit B7) which is an important coenzyme in metabolic processes
