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What is the GI tract?
Continuous tube from mouth to anus
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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)
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What are the accessory digestive organs?
teeth, salivary glands, pancreas, liver, gallbladder, tongue
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what is the largest serous membrane in the body?
peritoneum
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pepsin
digestive enzyme released by cheif cells in stomach, made in gastric mucosa (stomach), breaks down proteins into polypeptides
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bile
produced by liver, stored in gallbladder, released into duodeum after fatty meal, helps emulsify fats so they can be broken down easier.
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lingual lipase
in mouth, breaks down triglycerides into fatty acids and diglycerides
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pancreatic amalyse
breaks down starches
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largest gland in body
liver
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four stages of food processing
ingestion, digestion, absoprtion, elimination
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what is deglutition
swallowing
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pancreas
produces secretions (panreatic juices) to aid digestion, had a head, body and tampering tail
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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)
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liver portal triad
hepatic portal vien, hepatic artery, bile duct
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liver functions
- metabolism of carbs, lipids and proteins
- process drugs and hormones
- excrete bilirubin
- synthesise bile salts
- storage
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small intestine
digestion and absorption; contains duodenum, jejunum, ileum
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what connects the small and large intestines?
ileocecal sphincter
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cell types of small intestine
goblet, absorptive, endocrine, paneth
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what do goblet cells secrete?
mucus
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what do absorptive cells do?
absorbs nutrients
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gall bladder
stores and concentrates bile and releases it into the small intestine
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liver, what does it produce
bile, needed fro emulsification and absorptionof lipids in small intestine
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chyme
patially digested food in small intestine
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small intestine function
mix chyme with digestive juices: 90% nutirents and water absorbed here
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large intestine
haustral churning, peristalsis, and mass peristalsis drive contents of colon into rectum
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all blood in digestive system passes through liver before entering the veinous system.
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where are most carbs broken down?
Small intestine by pancreatic amylase
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what are the major regions of the large intestine?
cecum, ascending, transverse, decending, sigmoid, rectum, anal canal, anus
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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
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4 main endocrine hormones for GI tract
- Gastrin
- secretin
- cholecystokinin
- gastric inhibitory peptide
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gastrin
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
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secretin
from s cells in duodenum, responds to acidic juices in stomach, stimulates pancreas to release HCO3
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cholecystokinin
CCK cells in duodenum release CCk in response to fat and high protein, stimulates gallbladder to release bile, pancreas to release digestive enzymes
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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
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what are the 6 main types of nutrients
- water
- carbs
- lipids
- proteins
- minerals
- vitamins
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essential nutrients
cannot be made in sufficient amounts, need to be ingested.
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metabolism
all chemical reaction of the body
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enzymes
catalyze chemical reactions
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anabolic reactions
building reactions, endergonic -energy consuming
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catabolic reactions
decomposition reactions, exergonic - produce energy
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carbs are broken down into
- monosaccharides: glucose, fructose
- these are then used to synthesize ATP, converted to glycogen or used to build trigylcerides
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what can gluose be converted into?
several amino acids
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glycolysis
anaerobic cellular repsiration
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krebs cycle
energy transfer to coenzymes, series of oxidation reduction reactions, aerobic reactions
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Which reactions produce ATP during the complete
catabolism of a molecule of glucose?
Glycolysis, Krebs cycle, electron transport chain
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how many amino acids are there?
20, 10 essential and 10 non essential
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what is a complete protein
provides all 10 essential amino acids
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what is an essential amino acid?
must be in diet, cannot be synthesized by body
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vitamins
organic molecules required in small amounts, 13 essential
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what are the 2 groups of vitamins?
- fat soluble (A,D,E,K)
- water soluble (B and C)
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minerals
simple inorganic nutrients, ie calcium, sodium, copper, potassium, sulfur, chlorine
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undernourishment
result of a diet that consistently supplies less chemical energy than the body requires
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malnourishment
the long term absence from the diet of one or more essential nutrients.
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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
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What are brush border enzymes and what are their
functions?
- Brush border enzymes, synthesised by absorptive
- epithelial cells of the SI, function to digest carbohydrates, proteins and
- nucleotides
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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.
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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.
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The region of the stomach that surrounds the superior opening of the stomach is known as the
cardia
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This major duct carries a fluid rich in bicarbonate ions
pancreatic duct
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This portion of the stomach connects to the duodenum
plyorus
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When blood pH drops then the amount of oxyhemoglobin _______ and oxygen delivery to the tissue cells ________________.
decreases, increases
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Which of the following enzymes digests proteins?
tryspin
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not a function of the large intestine?
Regulation of blood glucose
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