Exam 3: Ch 18 Digestive System Flashcards
Digestive System Overview
- Inside gastrointestinal (GI) tract, food is
broken down (digestion) by hydrolysis into molecular monomers
Digestive System Overview
- Absorption of monomers
occurs in small intestine
Digestive System Overview
- Ingested food molecules
are used to make ATP or to make additional tissue
Digestive System Overview
- Enzymes are required to
- make polymers into monomers; usually only active in the lumen of the GI tract
Functions of GI Tract
- Motility
- Secretion
- Digestion
- Absorption
- Storage and Elimination
Motility
movement of food through GI tract by means of:
- ingestion
- mastication
- deglutition
- peristalsis
Ingestion-
-taking food into mouth
Mastication–
chewing food & mixing it with saliva
Deglutition–
swallowing food
Peristalsis
–rhythmic wave-like contractions that move food through GI tract
Secretion
Includes release of exocrine & endocrine products into GI tract
Exocrine secretions include
HCl, H20, HC03-, bile, lipase, pepsin, amylase, trypsin, elastase, & histamine
Endocrine includes
- hormones secreted into stomach & small intestine to help regulate GI system
- E.g. gastrin, secretin, CCK, GIP, GLP-1, guanylin, VIP, & somatostatin
Digestion
breakdown of food molecules into their smaller subunits
Absorption
= passage of digested end products into blood or lymph
Storage and elimination
= Includes temporary storage & subsequent elimination of indigestible components of food
Digestive System
is composed of
- GI tract (alimentary canal) & accessory digestive organs
- GI tract is 30 ft long; extends from mouth to anus
Digestive system Organs include
oral cavity, pharynx, esophagus, stomach, & small & large intestine
Digestive system Accessory organs include
include teeth, tongue, salivary glands, liver, gallbladder, & pancreas
Bile is mostly
bile pigment, bile salts, phospholipids, cholesterol, and inorganic ions
Bile production is between
250 ml/day – 1500 ml/day
Bile pigment (bilirubin) is produced in
spleen, bone marrow, & liver
Bile pigment (bilirubin) is derivative of
heme groups (minus iron) from Hb
Bile pigment (bilirubin) is carried in
blood attached to albumin
Free bilirubin combines with
with glucuronic acid to form conjugated bilirubin that is secreted into bile
conjugated bilirubin converted by
intestinal bacteria to urobilinogen (produces the brown color of feces)
30-50% of urobilinogen is absorbed by
by intestine & enters hepatic vein
urobilinogen enters enterohepatic circulation to
to be recycled or filtered by kidneys & excreted in urine (produces amber color of urine)
Bile acids are formed in
major breakdown pathway for cholesterol
2 major bile acids
- Cholic acid
- chenodeoxycholic acid
Bile acids form bile salts by
combining with glycine or taurine, which aggregate as micelles
combining with glycine or taurine, which aggregate as micelles
groups of molecules that are both hydrophobic and hydrophilic which allows them to surround hydrophobic molecules (emulsification)
Bile salts recirculate (via
enterohepatic circulation ~ 6Xs/day)
Liver - Detoxification of Blood
Liver can remove hormones, drugs, & other biologically active molecules from blood
Liver - Detoxification of Blood by
- excretion into bile
- phagocytosis by Kupffer cells that line sinusoids
- chemical alteration of molecules by hapatocytes
Liver - Detoxification of Blood:
ammonia is produced by
deamination of aa’s; liver converts it to the less toxic urea which is excreted in urine
Liver - Detoxification of Blood:
toxic purines
(Guanine and Adenine) are converted to uric acid
Liver - Detoxification of Blood:
Liver conjugates
steroid hormones & xenobiotics (foreign biologically active molecules) with groups that make them anionic and hydrophilic, which can be transported into bile or urine by multispecific organic anion transport carriers & excreted
Liver helps regulate
- blood glucose by removing it from blood or releasing it to blood via glycogenesis & lipogenesis
- Or produces it via glycogenolysis & gluconeogenesis
Liver can also convert
free fatty acids into ketone bodies (ketogenesis) that can be used for energy during fasting
Liver - Production of Plasma Proteins
-
Albumin & most of plasma globulins are produced by liver
Albumin makes up
70% of total plasma protein & contributes most to colloid osmotic pressure of blood
Globulins transport
cholesterol & hormones, inhibit trypsin (protease), & are involved in blood clotting
Clotting factors
(fibrinogen) are also made in liver
Hormone angiotensin
(causes vasoconstriction and has other affects)
Most carbohydrates are ingested
- asstarch
- a polymer of glucose mostly:
- sucrose = table sugar = glucose-fructose
- lactose = glucose-galactose
- a polymer of glucose mostly:
Salivary amylase
begins starch digestion
Pancreatic amylase converts starch to
- oligosaccharides
- Which are then hydrolyzed by SI brush border enzymes
Protein digestion begins in
in stomach when pepsin digests proteins to form polypeptides
In SI, endopeptidases (trypsin, chymotrypsin, elastase) cleave peptide bonds in
interior of polypeptides
In SI exopeptidases (carboxypeptidase, aminopeptidase) cleave peptide bonds from
ends of polypeptides
Protein digestion in SI results in
in free amino acids, dipeptides, & tripeptides, which are transported into SI cells where di- & tripeptides are broken down to amino acids, which are secreted into blood
Digestion & Absorption of Lipids Occurs in
SI; arrival of lipids in duodenum causes secretion of bile
Fat is emulsified by
- bile salt micelles
- Forms tiny droplets of fat isolated in bile salt micelles
- greatly increases surface area for fat digestion by lipases
Pancreatic lipase hydrolyzes
triglycerides to free fatty acids & monoglycerides
Phospholipase A breaks down
phospholipids into fatty acids & lysolecithin (remainder of lecithin after 2 FAs have been removed)
Free fatty acids, monoglycerides, & lysolecithin leave
- micelles & enter epithelial cells, where they are resynthesized into triglycerides & phospholipids
- not transported directly into blood like sugars and aa’s
Triglycerides, phospholipids, and cholesterol combine with
a protein to form small particles called chylomicrons
which are secreted into central lacteals of SI villi
