Gastrointestinal tract V Flashcards
1
Q
Nutrition
A
A nutrient is a substance in food the body uses to promote normal growth, maintenance and repair
- energy value in food is measures in kilocalories
- sometimes values given as or Joules (J)
2
Q
Glycemic Index
A
- Measurement of carbohydrate content in foods according to how they affect blood glucose levels
- carbohydrates with allow GI slow digested, absorbed and metabolised
- cause a lower and slower rise in blood glucose and therefore insulin levels
3
Q
The benefits of carbohydrates
A
- except for milk sugars and a negligible amount of glycogen in meat, all carbohydrates we ingest are derived from plants
- sugars (mono and di) found in grains and vegetables
4
Q
Fibre (poly)
A
- cellulose not digested but provides roughage
- insoluble fibre increases bulk of stool
- soluble fibre e.g pectin in apple and citrus reduces blood cholesterol
5
Q
The benefits of fat
Fat cells work hard
A
- thermal insulator
- produce hormones
- has receptor for insulin, growth hormone and adrenalin
- protect and support organs and bones
- concentrated source of energy
- some nutrients need fat for the body to use them e.g. fat soluble vitamins
- structural elements of a cell
6
Q
Lipid:
A
a compound insoluble in water but soluble in an organic solvent (acetone, chloroform, benzene) –> provide energy
7
Q
Fatty acids: saturated
A
butter, cream, meat fat
8
Q
Fatty acids: trans
A
Created by a process called hydrogenation - behave like saturated fats in the body
e.g. margarine, ready-made meals, snack foods, energy bars
9
Q
Fatty acids: mono
A
vegetable oil, avocado
10
Q
Fatty acids: poly
A
e.g. tuns, salmon, nuts and soys
11
Q
Fatty acids: essential
A
cannot be synthesised by the body, omega-3 and omega-6
12
Q
non-essential fatty acids
A
saturated fatty acids, trans fatty acids, omega-9
13
Q
the benefits of protein
A
- animal products contain the best ratio of essential
- amino acids: eggs, milk, fish, most meats
- plant based best for essential amino acids: soy beans
- plant based amino acid rich: legumes, nuts
14
Q
The four main digestion processes in the GIT
A
enzymes work most efficiently at optimal temperature and optimal pH
15
Q
Carbohydrate digestion
Salivary amylase
Pancreatic amylase
Maltase
A
Salivary amylase: Produced in salivary glands Site of release in mouth pH level is neutral Pancreatic amylase: Produced in pancreas Site of release in small intestine pH level is basic Maltase: Small intestine Small intestine Basic
16
Q
Protein digestion
Pepsin
Trypsin
Peptidases
A
Pepsin: gastric glands stomach acidic Trypsin: pancreas small intestine basic Peptidases: small intestine small intestine basic
17
Q
Nucleic acid digestion
Nuclease
nucleosidases
A
Nuclease and nucleosidases:
pancreas
small intestine
basic
18
Q
Fat digestion
Lipase
A
Pancrease
Small intestine
Basic
19
Q
Digestion of carbohydrates
A
- Starch foods often referred to as carbs = carbohydrates (e.g. bread, pasta, potatoes)
- Starch digestion begins in mouth with salivary amylase, continues in duodenum with pancreatic amylase
- Brush border enzymes in small intestine (maltase, lactase, sucrose) further digest disaccharides into monosaccharides (glucose, galactose, fructose)
20
Q
Absorption of carbohydrates
A
- Only monosaccharides can be absorbed
- Glucose and galactose are absorbed at apical surface of absorptive epithelial via cotransport with Na+
- Fructose passes apical surface of absorptive epithelial via facilitated diffusion
- All monosaccharides leave the epithelial cells via facilitates diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein
21
Q
Digestion of protein
A
- Begins in stomach (pepsinogen converted to pepsin at low pH becomes inactive at high pH of duodenum), continues in small intestine with the help of pancreatic and brush border enzymes
- Proteins are broken into: large polypeptides small polypeptides and small peptides amino acid monomers
- Some peptidases are stores as inactivated zymogens to protect the cells with produce them
22
Q
Source of protein
A
- ingested food
- secretions (mucus, enzymes)
- enterocytes which have sloughed off
23
Q
Absorption of protein
A
- Only amino acids, dipeptides and tripeptides can be absorbed
- Amino acids are co-transported across apical membrane if absorptive epithelial cell via secondary active transport carriers with Na+
- Some dipeptides and tripeptides are absorbed via cotransport with H+ and hydrolysed to amino acids within the cells
- Amino acids leave the epithelial cells across the basolateral membrane by facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein
24
Q
Digestion of lipid
A
-Most lipids are ingested in the form of triglycerides
Triglycerides: glycerol bound to three fatty acids
-Lipids insoluble in water bile salts emulsify lipids and break large fat globules into smaller one
-Pancreatic lipases break down triglycerides into monoglyceride plus two free fatty acids
-Micelle formation” monoglycerid and fatty acids become coated with bile salts and lecithin
25
Absorption of lipid
-Absorption: lipid products leave micelles and cross epithelial membrane via simple diffusion
•Chylomicron formation: monoglycerids and free fatty acids are converted back into triglycerides and packaged with lecithin and lipoproteins
•Chylomicron are exocytosed from basolateral side and enter lymphatic lacteal of villi through pores
•Some short-chain fatty acids are absorbed, move into the capillary blood in the villi by diffusion, and are transported to the liver via the hepatic portal vein
26
Digestion and absorption of nucleic acid
- Nuclei of ingested cells in food contain DNA and RNA
- Pancreatic nucleases hydrolyse nucleic acid to nucleotide monomers
- Brush border enzymes, nucleosidases and phosphatases break nucleotides down into free nitrogenous bases, pentose sugars and phosphate ions
- Breakdown products are actively transported by special carriers in epithelium of villi, then absorbed into capillary blood in the villi
27
Absorption of vitamins
* E.g. vitamin B12 binds with intrinsic factor (produced by parietal cells in stomach) and absorbed by endocytosis in ileum
* Some hydrophobic vitamins (Vit A, D, E and K absorbed with lipids)
* Water-soluble vitamins (C and B) are absorbed by diffusion or by passive or active transporters
28
Absorption of electrolytes
* Most ions are transported actively a long length of small intestine e.g. Na+, Cl-
* K+ diffuses in response to osmotic gradients
* Ca2+ absorption is regulated by vitamin D and parathyroid hormone (PTH)
29
Absorption of water
* 95% is absorbed in the small intestine by osmosis
* Most of rest is absorbed in large intestine
* Water uptake is coupled with solute uptake
30
The large intestine
- about 1.5m long
- residue remains in large intestine 12-24 hours
- important for our comfort, but it is not essential for life
31
Subdivisions of large intestine
Caecum and appendix
Colon: ascending, transverse, descending, sigmoid
Rectum
Anal canal
32
Functions of the large intestine
1. Absorption of water and electrolytes
2. No food breakdown occurs except digestion of some remaining food residues by enteric bacteria
3. Formation and compaction of faeces
4. Haustral churning and propulsion of faeces
5. Storage of faeces
6. Defecation (triggered by rectal distension)
33
Compaction
when food remains in colon for extended periods of time and too much water is absorbed
34
Diarrhoea
watery stools – when large intestine does not have sufficient time to absorb remaining water
35
Histology large intestine
- Thick mucosa of simple columnar epithelium (absorptive cells – water absorption)
- Mucosa is smooth
- Deep crypts with many mucus-producing goblet cells only secretion is mucus
36
The large intestine gross anatomy
Teniae coli: three bands of longitudinal smooth muscle in muscularis
Haustra coli: pocket like sacs caused by tone of teniae coli
Epiploic appendices: fat-filled pouches of visceral pertitoneum
37
Teniae coli
Three bands of longitudinal smooth muscle of the muscularis layer
38
Haustra coli
- Sac-like pouches of the large intestine formed by tone of teniae coli
- Inside semilunar folds caused by contraction of teniae coli
39
Epiploic appendices
- Small fat projections of the serosa attached to the outside of the large bowel
- Also called omental appendices
- Fat-filled pouches of visceral peritoneum
40
Cecum
T-shaped dead-end pouch between small and large intestine
41
Appenix
Worm-like extension from the caecum
| 9cm in length in humans
42
Appendicitis
Acute inflammation of appendix usually due to blockage by faeces that trapped infectious bacteria -> often results in surgical removal of appendix = appendectomy
43
Rectum
three rectal valves stop faeces from being passed with gas
| simple columnar epithelium
44
Anal canal
last Segment of large intestine
opens to body exterior at anus
interior anal sphincter: smooth muscle of muscularis external, involuntary control
external anal sphincter: skeletal muscle of pelvic diaphragm, voluntary control
non-keratinised stratified squamous epithelium
45
bacterial flora
consists of >1000 different types of bacteria
| bacteria outnumber our own cells 10 to 1
46
Metabolic functions of bacterial flora
Fermentation: ferment indigestible carbohydrates and mucin
release irritation acids and gases
Vitamin synthesis: beneficial bacteria outnumber and suppress pathogenic bacteria
Immune system destroys any bacteria that try to breach mucosal barrier
47
Inflammatory diseases of the bowel
Crohn's disease: inflammation of the entire wall of the bowel
caused by combination of genetic and environment factors
Ulcerative colitis: inflammation of the superficial layers of the bowel wall (innermost layer)
