movement of food through GI tract by means of: - ingestion - mastication - deglutition - peristalsis

- hormones secreted into stomach & small intestine to help regulate GI system - E.g. gastrin, secretin, CCK, GIP, GLP-1, guanylin, VIP, & somatostatin

Exam 3: Ch 18 Digestive System Flashcards by jill celaje

Digestive System Overview

- Inside gastrointestinal (GI) tract, food is

broken down (digestion) by hydrolysis into molecular monomers

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Digestive System Overview

- Absorption of monomers

occurs in small intestine

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Digestive System Overview

- Ingested food molecules

are used to make ATP or to make additional tissue

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Digestive System Overview

- Enzymes are required to

make polymers into monomers; usually only active in the lumen of the GI tract

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Functions of GI Tract

Motility
Secretion
Digestion
Absorption
Storage and Elimination

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Motility

movement of food through GI tract by means of:

ingestion
mastication
deglutition
peristalsis

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Ingestion-

-taking food into mouth

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Mastication–

chewing food & mixing it with saliva

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Deglutition–

swallowing food

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Peristalsis

–rhythmic wave-like contractions that move food through GI tract

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Secretion

Includes release of exocrine & endocrine products into GI tract

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Exocrine secretions include

HCl, H20, HC03-, bile, lipase, pepsin, amylase, trypsin, elastase, & histamine

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Endocrine includes

hormones secreted into stomach & small intestine to help regulate GI system
- E.g. gastrin, secretin, CCK, GIP, GLP-1, guanylin, VIP, & somatostatin

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Digestion

breakdown of food molecules into their smaller subunits

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Absorption

= passage of digested end products into blood or lymph

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Storage and elimination

= Includes temporary storage & subsequent elimination of indigestible components of food

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Digestive System

is composed of

GI tract (alimentary canal) & accessory digestive organs
GI tract is 30 ft long; extends from mouth to anus

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Digestive system Organs include

oral cavity, pharynx, esophagus, stomach, & small & large intestine

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Digestive system Accessory organs include

include teeth, tongue, salivary glands, liver, gallbladder, & pancreas

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Bile is mostly

bile pigment, bile salts, phospholipids, cholesterol, and inorganic ions

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Bile production is between

250 ml/day – 1500 ml/day

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Bile pigment (bilirubin) is produced in

spleen, bone marrow, & liver

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Bile pigment (bilirubin) is derivative of

heme groups (minus iron) from Hb

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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

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

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