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What is the GI tract?
Continuous tube from mouth to anus
What are the 4 layers of the GI tract?
- Mucosa (epithelium, lamina propria, muscularis mucosae)
- Submucosa (lymph & blood vessels)
- Muscularis (inner circular layer, outer longtitudinal layer)
- Serosa (epithelium, arelora connective tissue)
What are the accessory digestive organs?
teeth, salivary glands, pancreas, liver, gallbladder, tongue
what is the largest serous membrane in the body?
digestive enzyme released by cheif cells in stomach, made in gastric mucosa (stomach), breaks down proteins into polypeptides
produced by liver, stored in gallbladder, released into duodeum after fatty meal, helps emulsify fats so they can be broken down easier.
in mouth, breaks down triglycerides into fatty acids and diglycerides
breaks down starches
largest gland in body
four stages of food processing
ingestion, digestion, absoprtion, elimination
what is deglutition
produces secretions (panreatic juices) to aid digestion, had a head, body and tampering tail
dual functions of pancreas
- exocrine: secreates digestive juices (acinar cells) to buffer pH in gastric juices; stops pepsin working in stomach; digestive enzymes
- endocrine: releases hormones (islet cells)
liver portal triad
hepatic portal vien, hepatic artery, bile duct
- metabolism of carbs, lipids and proteins
- process drugs and hormones
- excrete bilirubin
- synthesise bile salts
digestion and absorption; contains duodenum, jejunum, ileum
what connects the small and large intestines?
cell types of small intestine
goblet, absorptive, endocrine, paneth
what do goblet cells secrete?
what do absorptive cells do?
stores and concentrates bile and releases it into the small intestine
liver, what does it produce
bile, needed fro emulsification and absorptionof lipids in small intestine
patially digested food in small intestine
small intestine function
mix chyme with digestive juices: 90% nutirents and water absorbed here
haustral churning, peristalsis, and mass peristalsis drive contents of colon into rectum
all blood in digestive system passes through liver before entering the veinous system.
where are most carbs broken down?
Small intestine by pancreatic amylase
what are the major regions of the large intestine?
cecum, ascending, transverse, decending, sigmoid, rectum, anal canal, anus
3 phases of digestion
cephalic phase: sight and smell of food, system gets ready; gastric phase, pH rises which triggers action in stomach; Intestinal Phase, food into small intestine
4 main endocrine hormones for GI tract
- gastric inhibitory peptide
released into blood by g cells in stomach in response to stomach distention, or activation of vagus nerve to stimulate pearietal cells in stomach to make HCL and intrincis factor
from s cells in duodenum, responds to acidic juices in stomach, stimulates pancreas to release HCO3
CCK cells in duodenum release CCk in response to fat and high protein, stimulates gallbladder to release bile, pancreas to release digestive enzymes
gastric inhibitory peptide
k cells in duodenum release GIP in response to fat adn carbs; slows entry to small intestine, stimulates insulin release from pancreas
what are the 6 main types of nutrients
cannot be made in sufficient amounts, need to be ingested.
all chemical reaction of the body
catalyze chemical reactions
building reactions, endergonic -energy consuming
decomposition reactions, exergonic - produce energy
carbs are broken down into
- monosaccharides: glucose, fructose
- these are then used to synthesize ATP, converted to glycogen or used to build trigylcerides
what can gluose be converted into?
several amino acids
anaerobic cellular repsiration
energy transfer to coenzymes, series of oxidation reduction reactions, aerobic reactions
Which reactions produce ATP during the complete
catabolism of a molecule of glucose?
Glycolysis, Krebs cycle, electron transport chain
how many amino acids are there?
20, 10 essential and 10 non essential
what is a complete protein
provides all 10 essential amino acids
what is an essential amino acid?
must be in diet, cannot be synthesized by body
organic molecules required in small amounts, 13 essential
what are the 2 groups of vitamins?
- fat soluble (A,D,E,K)
- water soluble (B and C)
simple inorganic nutrients, ie calcium, sodium, copper, potassium, sulfur, chlorine
result of a diet that consistently supplies less chemical energy than the body requires
the long term absence from the diet of one or more essential nutrients.
What are the functions of segmentation and
peristalsis in the small intestine?
Segmentation- mixes chime with digestive juices and brings the chime into contact with the mucosa for absorption
Peristalsis- pushes intestinal contents along the intestine
What are brush border enzymes and what are their
- Brush border enzymes, synthesised by absorptive
- epithelial cells of the SI, function to digest carbohydrates, proteins and
Describe the digestion of carbohydrates that occurs in the small intestine.
Pancreatic amylase acts on glycogen and starches, then a brush border enzyme alpha-dextrinase continues enzymatic breakdown of carbohydrate by clipping off one glucose unit at a time.
Other brush border enzymes digest disaccharides to monosaccharides; Sucrase digests sucrose into glucose and fructose, Lactase digests lactose into glucose and galactose; Maltase digests maltose into 2 glucose molecules.
Why are bile salts needed for lipid digestion?
- Bile salts emulsify large lipid globules into smaller
- lipid globules which increases the surface area for pancreatic lipase to effectively digest triglycerides.
The region of the stomach that surrounds the superior opening of the stomach is known as the
This major duct carries a fluid rich in bicarbonate ions
This portion of the stomach connects to the duodenum
When blood pH drops then the amount of oxyhemoglobin _______ and oxygen delivery to the tissue cells ________________.
Which of the following enzymes digests proteins?
not a function of the large intestine?
Regulation of blood glucose