DigestiveDigestive System I Flashcards
1
Q
Four GI Tract layers
A
- Mucosa
- Muscosal epithelium
- Lamina propria
- Muscularis mucosa
- Submucosa
- Muscularis
- Serosa (peritoneum)
2
Q
Mucosa : Epithelium
A
- Protection for: mouth, pharynx, oesophagus, anus
- Columnar epithelium for stomach and intestines
- Microvilli - ⇡ surface area for absorption
- Globlet cells - secrete mucus to lubricate food and protect against erosion
- Enterendocrine cells - secrete hormones into blood
3
Q
Mucosa : Lamina Propria
A
- Connective tissue with blood and lymphatic vessels - absorption of nutrients
- Contains MALT (mucosa associated lymphoid tissue) ⇢ collection of immune cells (lymphoctyes, macrophages)
- in GIT - GALT
- MALT in - tonsils, oesophagus, small intestine, appendix, large intestine
4
Q
GALT
A
- 70% of body’s immune cells
- 25% of intestine mucosal mass
5
Q
Mucosa : Muscularis Mucosa
A
- Smooth muscle
- Creates the villi (smooth folds) - surface area, absorption
6
Q
Submucosa Layer
A
- Connective tissue layer between mucosa and muscularis
- Contains blood and lymph vessels (receive absorbed food molecules)
- Submucosal plexus - network of neurons, ‘brain of the gut’
7
Q
Muscularis Externa
A
- Skeletal muscle for swallowing, defection
- Mouth, pharynx, upper oesophagus, anal sphincter
- Rest of GIT mostly smooth muscle (involuntary - autonomic)
- Mixing of food with digestive juices
- Propelling food (chyme/bolus) along digestive tract (peristalsis)
- Between the 2 layers - nuerons - myenteric plexus
8
Q
Peritoneum
A
- Largest serous membrane in body
- Has blood and lymph vessels
- 2 layers
- Parietal - covers wall of abdomen and pelvic cavity
- Visceral - covers the organs
- Peritoneal cavity - space between the 2 layers, contains lubricating serous fluid
9
Q
Name 2 peritoneal pathologies
A
- Ascites - accumulation of fluid in peritoneal cavity
- Peritonitis - inflammation of peritoneum
10
Q
Great Omentum
A
- Largest fold of the peritoneum
- Drapes over transverse colon and small intestine like apron
- Stores fat, contains adipose tissue
- Lymph nodes - macrophages and plasma cells
11
Q
Lesser Omentum
A
- Peritoneal fold
- Suspends the stomach and duodenum from the liver
- Pathway for blood vessels entering the liver
- Contains hepatic portal vein
12
Q
Enteric nervous system
A
- Brain of the gut from oesophagus to anus
- Independent but regulated by autonomic nervous system
- Parasympathetic - rest and digest
- ⇑ muscular activity (peristalsis ⇢ myenteric plexus)
- ⇑ glandular secretions (submucosal plexus)
- Sympathetic (fight or flight / stress)
- ⇓ muscular activity (peristalsis ⇢ myenteric plexus)
- ⇓ glandular secretions (submucosal plexus)
13
Q
Myenteric plexus
A
Gut motility
14
Q
Submucosal plexus
A
Digestive secretions
15
Q
Portal vein vs liliac veins
A
- Portal vein - lower oesophagus, stomach, pancreas, small and large intestine, upper rectum, spleen
- Iliac vein - lower rectum and anal canal
16
Q
Oral cavity
A
- Hard palate
- Soft palate - arch of muscle
- Uvula - prevents food entering nasal cavity
- Tongue - skeletal muscle
- Papillae - cover tongue, taste buds
17
Q
Functions of oral cavity
A
- Mastication
- Speech
- Taste
- Swallowing
18
Q
Saliva
A
- Produced by parotid glands, submandibular glands, sublingual glands
- Controlled by autonomic nervous system
- Continuous salivation - 1 - 1.5 L per day
- Sympathetic nervous system - reduces salivation
19
Q
Saliva - contents
A
- Water (99.5%)
- Mineral salts (Na, K a, Cl, bicarbonate)
- Enzymes - salivary amylase, lysozymes
- Mucus
- Immunoglobulins (IgA)
- Blood clotting factors
- Mildly acidic (6.35-6.85 pH)
20
Q
Saliva - functions
A
- Digestion
- Lubricating and dissolving food
- Cleansing oral cavity and teeth
- Defense - non-specific IgA
- Taste
- Buffer - for acidic foods
- Waste removal - urea/uric acid
21
Q
Oesophagus
A
- 25 cm muscular tube attached to larynx, passes through diaphragm
- Lined with epithelium, lubricated with mucus
- Peristalsis (muscular contractions) - pass food to stomach
- Epiglottis - prevent food from entering trachea
- Lower oesophageal sphincter - seal on the stomach, prevent reflux
22
Q
4 regions of stomach
A
- Cardia
- Fundus
- Body
- Pyloric
23
Q
2 sphincters in stomach
A
- cardiac
- pyloric
24
Q
Function of stomach goblet cells
A
- Stomach secretes 2-3L of highly acidic gastric juice and mucus per day
- Mucus produced by goblet cells acts as buffer
- Fast turnover of eipthelial cells in stomach - replace lining every 3 days
25
Stomach - 3 types of exocrine cells
1. **Parietal cells**
* _Intrinsic Factor_ (IF) - needed for Vit B12 absorption
* _Hydrochloric acid_ (HCl) - antimicrobial agent; assists in activating bile and pancreatic juice flow
2. **Chief cells**
1. _Pepsinogen_ - protein and lipid digestion
2. _Gastric lipase_ - converts pepsinogen to active enzyme _pepsin_ (digests protein)
3. **Goblet cells** - mucus - protects against acid
26
Stomach - functions
* Mixing chamber
* Storage
* Defence
* Absorption (limited)
* Digestion - mechanical and chemical
* Satiation
27
2 stomach hormones
* Ghrelin - stimulates hunger
* Gastrin - responds to stomach distension, stimulates gastric juice secretion and gastric motility
28
Pancreas
* Accessory organ of digestive system
* Connected to duodenum via **pancreatic duct**
* Exocrine function
* Pancreatic juice ⇢ small intestine
* Sodium bicarbonate and water
* Protease enzymes
* Pancreatic lipase (fats)
* Pancreatic amylase - breaks down sugars
* Endocrine function
* Secrete hormones into blood
* Insulin and glucagon
* Somatostatin (growth-hormone inhibiting hormone)
29
Pancreatic enzymes
* Pancreatic amylase - breaks down starches into sugars
* Pancreatic lipase - lipid / fat digestion
* Trypsin - protein digestion
* Chymotrypsin - protein digestion
* Ribonuclease - digest RNA
* Deoxyribonuclease - digest DNA
30
Gallbladder
* Accessory digestive organ
* Pear shaped sac 7-10 cm
* Bile ducts from gallbladder and liver meet at **common bile duct**
* Bile ducts collect bile produced by **hepatocytes** which pools in gallbladder
* Bile enters small intestine via common bile duct
* When ingest fat - gallbladder contracts to inject bile down the common bile duct into duodenum
* Bile emulsifies fat - breaks lipids into smaller molecules - more surface area for enzymes (**lipase**) to work
31
Bile
* Composed of bile salts, cholesterol and bilirubin
* pH 7.6 - 8.6 9mildly basic)
32
Enterohepatic circulation
Process by which bile is absorbed and transported back to the liver from the ileum
33
What produces bile?
Hepatocytes
34
Small intestine
* Food combines with stomach secretions
* Chyme is pushed through pyloric sphincter into small intestine
* Most **digestion** and **absorption** occurs here
* Villi **maximise surface area**
* Cells - goblet (mucous), endocrine, absorptive
35
3 regions small intestine
1. Duodenum - emulsification, digestion
2. Jejunum - most absorption
3. Vit B12 absorbed
36
Villi and microvilli - purpose
Increase surface area for absorption
Absorbed nutrients ⇒ blood
Absorbed fatty acides ⇒ lymph
37
Brush border enzymes
* Attached to intestinal lining
* **Maltase, sucrase, lactase** - break down sugars
* **Dipeptidase** - breakdown protein into amino acids
* **Nucleosidaases** and **phosphatases** - digest RNA and DNA
38
Cholecystokinin (CCK)
* Peptide hormone secreted by enteroendocrine cells in duodenum (small intestine)
* Released in response to high fat or protein chyme entering duodenum
* Stimulates **pancreas to secrete pancreatic enzymes** (digest fat, carbs, protein)
* Increases hepatic production of **bile and stimulates contraction of gallbladder**
* **Mediates satiety** (feeling of fullness)
39
Small intestine functions
* Movement - peristalsis of food
* Digestion
* Absorption - nutrients and water
* Hunger / satiety
* Immunity - Peyer's patches, bacterial microflora
40
How much of absorption occurs in small intestine?
90%
41
Small intestine absorption
* Carbs, amino acids - capillaries
* Monosaccharides - active/passive transport
* Amino acids - active transport
* Fatty acids, glycerol, cholesterol and fat-soluble vitamins (A,D,E,K)
* Emulsified by bile
* Enter intestinal cells - simple diffusion
* Absorbed into lacteals
* Travel through lymphatic system and enter blood through **subclavian vein**
42
Large Intestine
* Terminal portion of GI tract
* Where final stages of digestions, absorption, some vitamin synthesis (through bacterial activity) and stool formation occurs
* Absorption - water, minerals, vitamins, some drugs
43
Ileocaecal valve
* One-way flow from small to large intestine
* If faulty - large intestine microbes to overpopulate in the small intestine (SIBO)
44
4 regions of large intestine
1. **Caecum** - part of immune system (macrophages, lymphocytes, bacteria), appendix attached
2. **Colon** - ascending, transverse, descending regions
3. **Rectum**
4. **Anal canal -** internal and external sphincter
45
Large intestine - microbes
* Most symbiotic
* Pathogenic species - local pH, poor nutrition, antibiotics
* **Microbial fermentation** - final stage of nutrient extraction
* Bacteria ferment fibre ⇒ short-chain fatty acids (SCFAs) ⇒ support tight junctions
46
Bacterial fermentation produces:
* Hydrogen, CO2, methane (flatulence)
* Fermentation of residual amino acids ⇢ **hydrogen sulfide** - odour
* Toxic products ⇢ liver ⇢ excreted in urine
* **Bilirubin** - decomposed pigments - colour of faeces
* Faeces 50-60% bacteriaa
47
What is needed for B12 absorption and where is it found?
Intrinsic Factor
Produced in **parietal cells** in **stomach**
Absorbed in terminal ileum
48
Liver
* 2nd largest organ (skin largest)
* using 27% of resting metabolism
* Filters 1.4 L of blood every minute
* Heaviest gland in the body
49
Kupffer cells
* Phagocytic cells
* Remove foreign bodies from blood
50
Hepatic first pass
* All blood from GIT is transported to liver via **portal vein**
* Filtered/metabolised before entering systemic circulation
51
Liver - functions
* **Cleansing** blood of microbes
* **Detoxification** - metabolising drugs, toxins, alcohol
* **Bile** production
* **Haemoloysis** (Kupffer cells)
* Other…
52
Liver - Metabolism
* **Carbohydrate** - glucose ⇢ glycogen for storage
* **Fat -** metabolises fat from storage as required
* **Protein** - converts amino acids to non-essential amino acids, breaks down nucleotides to form uric acid to be excreted
53
Liver Detoxification - definition
* **Hepatocytes** convert toxins into **non-toxic metabolites** - **excreted** from the body
54
Liver Detoxification - 2 classifications
1. Hydrophilic - excreted in urine or bile
2. Lipophilic - must be chemically altered into hyrdrophilic compounds
55
Lipophilic to hydrophilic conversion - 2 phases
1. Phase I - **Bio-activation**
1. CYP450 enzymes
2. Converts water-insoluble toxins into water soluble substances to be excreted by kidneys
3. Converts toxins to more reactive substances to be metabolised in Phase II
2. Phase II - **Conjugation**
1. Molecules are attached to toxins to neutralise making stable (non-reactive) and water-soluble to be excreted
2. Glutathione - key anti-oxidant in Phase II
56
Abdominal quadrants
1. Right hypochondrium - Epigastric region - Left Hypochondrium
2. Right flank - Umbilical region - Left flank
3. Right groin - Pubic region - Left groin
57
Dietary Carbohhydrates
1. Monosaccharides - 1 sugar unit - Glucose, Fructose, Galactose
2. Disaccharids - 2 sugar units - Maltose, Sucrose, Lactose
3. Polysaccharides - many sugar units - Starch, Glycogen, Cellulose
58
Dietary Lipids
1. Triglycerides
2. Phospholipids
3. Cholesterol
59
Triglycerides
* Predominant dietary lipid
* Composed of **glycerol and three fatty acid chains**
* Saturated or unsaturated
60
Phospolipids
* 2 fatty acid tails and a phospate head
* Digested to free fatty acids and absorbed
61
Cholesterol
* Steroid particularly in animal foods
* Vital for
* cell membrane integrity
* Vitamin D synthesis
* Sex hormone synthesis
62
Dietary lipids - functions
* Energy - ATP (2nd to carbohydrates)
* Insulation - preserve heat
* Cell membranes
* Hormone production
* Protection of organs
63
Saturated fatty acid
* Molecule containing greatest number of hydrogen atoms
* **No double bonds**
64
Unsaturated fatty acids
One or more double bonds between carbon atoms
65
Cis vs Trans Fatty Acids
* **CIS**
* H atoms are on the **same side** of the double bond
* In nature, nearly all fats have CIS structure
* Body can recognise and use them
* **Trans**
* H atoms are on **separate sides** of the double bond
* Created in labs/industry
* Associated with heart disease
66
Proteins
* Long molecules of amino acids
* Make up 15% of total body mass
* Amino acid chains create 3D structure of each protein which allows it to function
* Amino acids - absorbed in small intestine
67
Protein - functions
* Immunity - immunoglobulin antibodies
* Structures - muscles, collagen
* Enzymes
* Hormones
* Neurotransmitters
* Energy
68
Protease enzymes
* Enzymes that break down proteins
* Proteins must be denatured first (destroy properties of a molecule)
69
Protein structure
* Unique 3D structure
* 'Lock and key' - hormone/enzymes fit into receptor
70
Enzymes
* Biological catalysts
* Speed up chemical reactions
* Highly specific what substrate they react with
* Lock & key structure
* Most end in ‘ase, i.e. ’lactase'
* Those involved in protein digestion end with -in, i.e. ‘pepsin’
* Enzymes can perform same function many times
71
Proteins are easily denatured by:
* pH and temperature changes
