Section 8: Digestive System Flashcards
(207 cards)
1
Q
Gut - structure
A
A soft muscular tube
~5m long
2
Q
Gut - function
A
Where food is stored, broken down and absorbed
3
Q
Glands associated with gut tube
A
Pancreas
Liver
4
Q
Tooth: Enamel
A
Crystalline rods/prisms of calcium phosphate and carbonate
No cells –> difficult to replace
No sensation
5
Q
What is the hardest tissue of the body
A
Enamel of teeth
6
Q
Tooth: Dentin
A
Similar to bone, but cells (odontoblasts) are localised at junction between dentin and pulp instead of scattered
7
Q
Tooth: Pulp
A
Core of tooth
Soft tissue
BVs, nerves, lymphatics
8
Q
Tooth: Cementum
A
Calcified CT surrounding dentin in root region
9
Q
Tooth: Periodontal ligament
A
Collagen fibres linking alveolar bone to cementum
Rapid turnover
10
Q
Tooth: Alveolar bone
A
Bone of the socket
11
Q
Tooth: Enamel - what does it cover
A
Covers dentin in the crown region
12
Q
Tooth: Periodontal ligament - size
A
Short in terms of distance, but has large X-sectional area
So distance between cementum and alveolar bone is v short
13
Q
Tooth: Periodontal ligament - mechanoreceptors - functions
A
Protection, e.g. biting a fork
Force transducers, e.g. braces
14
Q
Tooth: Periodontal ligament - rapid turnover
A
Lots of collagen synthesis
Vit C is crucial for this, so a poor vit C supply –> scurvy –> teeth can fall out
15
Q
Tooth: Why is it important to remove infections in the pulp
A
Because there’s a blood supply there –> bacteria can travel into blood vessel
16
Q
How many roots do most teeth have
A
3-4
17
Q
Tongue has both _____ and ______ muscles
A
Intrinsic
Extrinsic
18
Q
Tongue: Intrinsic muscles
A
Longitudinal - along length of tongue
Vertical
Horizontal/transverse
19
Q
Tongue: Intrinsic muscles - contraction
A
Longitudinal - shortens tongue
Vertical - flattens tongue
Horizontal/transverse - narrows tongue
20
Q
Tongue: Papillae
A
Projections towards surface of tongue
21
Q
Tongue: Papillae - types
A
Filiform
Fungiform
Vallate
22
Q
Tongue: Papillae - filiform
A
Sharp-like
No taste buds
Flexible
23
Q
Tongue: What is the most common form of papillae
A
Filiform
24
Q
Tongue: Papillae - fungiform
A
Mushroom-like projections
Some have taste buds but not many
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Tongue: Papillae - vallate
Most important for taste buds
| Surrounded by a groove like a moat - protection
26
Tongue: Papillae - different regions
Depending on the region of tongue, have diff frequencies of types of papillae
27
Salivary glands - major types
Parotid - serous only
Sublingual - mixed, mostly mucous
Submandibular - mixed
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Salivary glands: Types of cells
```
Serous cells (watery)
Mucous cells (viscous)
```
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Salivary glands: Serous cells
Contribute a watery component towards saliva that is enzyme-rich
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Salivary glands: Serous cells - enzymes
Amylase
| Lysozyme
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Salivary glands: Enzymes - amylase
Breaks down carbohydrate/starchy debris around teeth
Contained within zymogen granules and released in batches when you chew food to make sure there's not abundant starch for bacterial growth
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Salivary glands: Enzymes - lysozyme
Antibacterial properties
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Salivary glands: Mucous cells
Viscous/sticky
Good for lubricating
Contain mucin granules
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Salivary glands: Types of cells - staining
Serous cells = quite dark-staining
| Mucous cells = quite light-staining
35
Salivary glands: Parotid glands - location
In front of ears
36
Digestive system - functions
Digestion
Absorption
Secretion
Transport
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Digestive system: Functions - digestion
Chemical breakdown of ingested food into absorbable molecules
Requires secretion
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Digestive system: Functions - absorption
Movement of nutrients, water and electrolytes through epithelial lining of gut into blood or lymph
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Digestive system: Functions - secretion
Saliva - enzymes and mucous
40
Gaining surface area - methods
Gross convolutions
Luminal folds/wrinkles
Projections towards lumen = evagination
Projections away from lumen = glands
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Gaining surface area: Luminal folds - examples
Circular in small intestine = plicae circulares
| Longitudinal, e.g. stomach = rugae
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Gaining surface area: Evagination - examples
Villus/villi, small intestine
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Gaining surface area: Glands - examples
Stomach and small intestine
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Gaining surface area - must take what into account?
Time
45
Tunics of gut tube - what are they
Mucosa (mucous membrane)
Submucosa
Muscularis externa (external smooth muscle)
Serosa
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Tunics of gut tube: Mucosa - components
Epithelium
Lamina propria
Muscularis mucosae
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Tunics of gut tube: Mucosa - epithelium
Specialised for protection, absorption, secretion, or combination of all 3
Physical barrier between outside world and internal systems
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What happens if there's a breach of the epithelium
Results in ulceration
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Tunics of gut tube: Mucosa - lamina propria
Soft fibrous bed of loose CT where the epithelium rests
Carries nerves and blood capillaries
Populated with defense cells and collagen
Support
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Tunics of gut tube: Mucosa - lamina propria - lymphocytes
Scattered throughout gut to control pathogens / harmful agents coming through
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Tunics of gut tube: Mucosa - muscularis mucosae
2 thin layers of smooth muscle; inner circular and outer longitudinal
Provides mucosa with some movement independent of external muscle coat
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Tunics of gut tube: Submucosa
Thick bed of loose CT carrying larger BVs, lymphatic vessels and nerves (submucosal plexus)
Connects mucosa to external muscle coat, but allows some movement between them
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Tunics of gut tube: Muscularis externa
2 layers to produce peristalsis (transport)
| Inner circular layer and outer longitudinal layer
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Tunics of gut tube: Muscularis externa - myenteric nerve plexus
Occurs between the two layers of the muscularis externa
| Responsible for coordinating the 2 layers
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Enteric nervous system is made up of...
Submucosal nerve plexus + myenteric nerve plexus
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Enteric nervous system: SNS and PNS
PNS excites/stimulates enteric NS
| SNS inhibits function of enteric NS
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Enteric nervous system and ANS
Enteric NS is thought of as a separate entity, but has many interactions with ANS
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Tunics of gut tube: Serosa
A slippery outer covering for gut tube (except oesophagus)
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Tunics of gut tube: Serosa - layers
Two layered;
Outer mesothelial boundary
CT layer
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Tunics of gut tube: Serosa - AKA...
Visceral peritoneum
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Tunics of gut tube: Serosa - adventia
Where a structure is not in contact with the body cavity, the outermost CT layer is referred to as the adventitia
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Mesothelial cells secrete...
Serous fluid
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Oesophagus - structure
Muscular tube
Extends from pharynx to stomach
Normally empty with lumen collapsed, and expands to accommodate food/water
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Oesophagus - functions
*Transport* (fast travel time, due to peristalsis)
Protection
No absorption or digestion, little secretion
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Oesophagus: Epithelium
Thick, stratified squamous, with sacrificial outer layers for protection against abrasive fragments of food
Protects against friction and abrasion
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Oesophagus: Epithelium - how are cells replaced
By division in basal layers at BM, then slow migration outwards
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Oesophagus: The entire epithelium is renewed every ______
7 days
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What is the most variable throughout the gut tube
Epithelium
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Serosa vs adventitia
Serosa: when an organ is not in contact with a neighbouring organ, and instead is in contact with a body cavity
Adventitia: glues one organ to its adjacent organs
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Omentum
A fatty apron-like structure that hangs off the transverse colon
Must cut this away to expose underlying organs
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Fatty tissue - function
Protection
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Omentum - lymphatic tissue
Helps control localised infection by migrating to quarantine the infection
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Swallowing food - pathway
Food is pushed backwards by tongue --> oropharynx --> laryngopharynx --> oesophagus
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Swallowing food - epiglottis
Bolus comes in contact with epiglottis, pushing it backward to seal off the glottis (opening to trachea)
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Adventitia between trachea and cartilage
Loose because it needs to move/expand
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Oesophagus - luminal surface
Many layers of stratified squamous epithelium
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Tunics of gut tube: Mucosa - lamina propria - blood vessels
Supply epithelium with nutrients and O2, and take waste away from epithelium
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Oesophagus: External muscle (Muscularis externa)
Contains additional skeletal muscle in upper third of oesophagus to allow rapid contraction and voluntary control of swallowing
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Oesophagus: Serosa
Majority of oesophagus doesn't lie in a body cavity so lacks a serosa
Instead is mostly covered with a fibrous adventitia
Only when it passes the diaphragm into abdominal cavity where it starts to have serosa
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Bolus of food travels down the oesophagus by _____
Peristalsis
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Oesophagus: Peristalsis
Involves coordinated contraction of inner circular and outer longitudinal muscle layers (muscularis externa)
Inner = narrows tube
Outer = shortens tube --> squeezing motion
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Stomach - structure
J-shaped bag on left side
| Enlargement of gut tube
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Stomach - capacity
~1.5L
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Stomach - primary function
Storage, since food is eaten quicker than its digested and absorbed
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Stomach - regions
Cardia
Fundus
Body
Pylorus
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Stomach - rugae
Transient structures - only when empty, it's lined with longitudinal folds called rugae
When stomach is full, wrinkles flatten
Increases SA
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Stomach: Pyloric sphincter
Well-developed muscular sphincter at outlet
| Controls rate of chyme flow into duodenum
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Stomach: Pyloric sphincter is a thickening of...
Inner circular layer of muscles
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Stomach: Sphincter at inlet
Less developed
| If not well-developed enough, can result in gastric reflux
90
Stomach: Epithelium
Forms many pits lined with mucus-secreting cells
| Gastric glands open into pits
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Stomach: External muscle / Muscularis externa
Additional layer (3 in total) with addition of innermost oblique layer - gives churning motion --> mixing waves
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Stomach: Functions
```
Storage
Secretion of acids, enzymes, mucous
Digestion of proteins by pepsin
Absorption of water, ions, some drugs
Protection
Transport (mixing waves)
```
93
Chyme = ?
Food + gastric juice
94
Mucosa of stomach: Gastric pits
Pores
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Mucosa of stomach: Gastric glands
Increase SA
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Mucosa of stomach: Parietal cells
Pumps out H+ and Cl- separately, which recombine in lumen instead of killing the cell - kills microbes and living cells
Secretes intrinsic factor
97
Autodigestion
When a cell makes pure HCl - we don't want this!
98
Mucosa of stomach: Parietal cells - what is HCl important for
Sterilisation of food
| Acidifying environment --> indirectly helps with digestion
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Mucosa of stomach: Parietal cells - intrinsic factor
Important for B12 absorption, which is critical for haematopoiesis / RBC formation
100
Lack of RBCs leads to...
Anaemia
101
Mucosa of stomach: Chief cells
Secrete pepsinogen into lumen --> travels up past the acidic environment by parietal cells and become activated into pepsin --> digests luminal contents
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Mucosa of stomach: Chief cells - structure
Have apical granules in their cytoplasm which contain pepsinogen
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Mucosa of stomach: Chief cells - what is pepsin
A protein-splitting enzyme
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Mucosa of stomach: Surface mucous cells
Secrete insoluble alkaline mucus which protects the mucosa from acid and pepsin, i.e. protects stomach from digesting itself
But some cells will still die
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Mucosa of stomach: Undifferentiated cells
Stem cells dividing to generate new epithelium
| Migrate upwards to replace superficial cells which died
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Mucosa of stomach: Mucous neck cells
Secrete soluble acid mucus at mealtimes
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Mucosa of stomach: Enteroendocrine cells
Secretes gastrin (hormone) into bloodstream
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Mucosa of stomach: Enteroendocrine cells - stimuli
When you eat food:
- stomach becomes distended/stretched
- pH of stomach changes
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Mucosa of stomach: Enteroendocrine cells - what does gastrin stimulate
Secretion of acid and pepsinogen
Muscular contractions of stomach
Relaxes pyloric sphincter
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Mucosa of stomach: Enteroendocrine cells - structure
Granules are basolaterally located
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Liver is made of...
Epithelial cells called hepatocytes
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Liver - hepatocytes
Multi-talented cells, performing many metabolic functions
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Liver: Every hepatocyte requires...
Access to:
- nutrient-laden blood drained from intestinal wall
- oxygenated blood from systemic circuit
- ducts which drain bile to gall bladder
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Liver: Hepatocytes - structure
Stacked up like a wall with canals passing through them
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Liver: Hepatocytes - Bile canaliculus
Little canals that carry bile
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Liver: Hepatocytes - capillaries
Hepatocytes are flat either side by capillaries, which are v leaky
Thick enough to let through lymph, but exclude RBCs
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Liver: Hepatocytes - microvilli
Increases SA available for transport proteins to be embedded in membrane to allow substrate to be absorbed into mepatocyte
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Liver: Hepatocytes - sinusoid
Can accommodate more than 1 RBC
| Wide and leaky (fenestrated)
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Liver: Hepatocytes - sinusoid fenestration
Allow passage of lymph but exclude RBCs
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Lymph
Watery part of blood
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Liver lobules
Formed by plates of hepatocytes stacked tgt
| Hexagonal in X-section
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Liver lobules: Portal triads
Found at the edges of each lobule
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Liver lobules: Hepatic portal vein
Carries nutrient-rich but oxygen-poor blood to feed into lobule
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Liver lobules: Hepatic artery
Carries systemic oxygen-rich blood to supply hepatocytes
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Liver lobules: Blood in sinusoids
Mixed; both nutrient and O2 rich, which is consumed by hepatocytes until eventually drained by central vein away from liver --> IVC --> heart
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Liver lobules: Where is bile carried
In canaliculi between adjacent hepatocytes
| Transported through ductules that connect canaliculi and feed into bile duct
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Liver lobules: Triad - components
Hepatic portal vein
Hepatic artery
A branch of the bile duct
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Liver lobules: Bile - direction
Opposite direction to blood
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Sinusoids - leakiness
More leaky than typical capillary because have fenestrations - allows more watery components of blood to pass through to hepatocytes
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Bile ductules
Combine into a bile duct which converge and feed into gallbladder
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Bile - functions
Helps emulsify fats --> increases SA for things to act on them, e.g. pancreatic enzymes
Once pancreatic enzymes have digested smaller fat globules, bile helps absorb the fats
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Emulsification
Breaking down large fat globules into smaller ones
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Where is bile released and stored
Released from liver and transported and stored in gallbladder
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When/where is bile released during a meal
Into duodenum (small intestine)
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Pancreas
Dual-function organ
| Both endocrine and exocrine
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Pancreas: Exocrine gland
Manufactures precursors of digestive enzymes and secrete them as alkaline 'pancreatic juice' via duct system leading to duodenum
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Pancreas: Exocrine - why are enzymes released as precursors
To prevent autodigestion
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Pancreas: Exocrine gland - when are precursors converted to their active form
Once they arrive in duodenum
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Most food substances are digested by...
Pancreatic enzymes
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Pancreas - tree
Leaf = acinus
Twigs and branches = duct system
Trunk = main pancreatic duct
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What organ makes bile and what happens to the bile
Liver makes bile, can either be stored in gallbladder or ejected directly through common bile duct into duodenum
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Stomach: Chyme - where does it go
Travels through lumen of duodenum
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Pancreas - inputs
3 inputs;
Liver - bile
Stomach - chyme
Pancreas - pancreatic juice / enzyme precursors
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Pancreas - secretory unit
Acinus
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Pancreas: What does the secretory cell contain
Lots of mitochondria and organelles - helps with production
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Pancreas: What type of cell is the secretory cell
Serous type
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Pancreas: Secretory cell - cytoplasm
Has secretory granules / acinar cells containing enzyme precursors, which travel through out of acinus --> ducts --> converge and feed into bigger ducts
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Small intestine - parts
Duodenum (shortest)
Jejunum
Ileum
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Small intestine - size
3cm diameter
| 3m long
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Where does most digestion and absorption occur
Small intestine
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What does the small intestine receive exocrine secretions from
Liver (bile) and pancreas (pancreatic juice)
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Small intestine: Duodenum
```
Shortest part of SI
C-shaped
Not suspended by mesentery
Receives biliary and pancreatic ducts
Close to gallbladder, stomach, pancreas
```
153
Small intestine: Jejunum
Longer ~1m long
| Coiled
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Small intestine: Ileum
Longer ~2m long
| Coiled
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Small intestine: Mucosa
Specialised to increase SA available for secretion and absorption
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Small intestine: Submucosa
Just downstream of pyloric sphincter contains mucous glands / Brunner glands
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Small intestine: Submucosa - Brunner/mucous glands
Acidic chyme from stomach (mixed with HCl, so pH 1-2)
Secretes HCO3- rich mucous that helps buffer against acidic content coming in
Simultaneously changes pH to optimise environment in duodenum for pancreatic enzymes
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Small intestine: Increasing SA - methods
Gross convolutions (coiled)
Plicae circularis
Villi
Microvilli
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Small intestine: Increasing SA - Plicae circularis
Circular folds
Each is covered with mucosa and has a core of submucosa
Permanent structures
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Small intestine: Increasing SA - villi
Mini finger-like projections / evaginations
| Covering is epithelium, core is lamina propria
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Small intestine: Increasing SA - microvilli
Microscopic projections
Form a brush border on surface of individual absorptive cells
Each is covered with cell membrane and filled with cytoplasm
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Small intestine: Increasing SA - size
Gross convolutions = largest, visible with naked eye
Plicae = visible for naked eye
Villi = much smaller, visible with naked eye
Microvilli = microscopic, can't see with naked eye
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Small intestine: Nutrient-laden blood in veins goes back to...
The liver
164
Small intestine: Lacteals
Lymph vessel within each villus
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Small intestine: Lacteals - function
Absorb broken-down products from lumen of SI
Lymph is 'milked' along lacteal by contraction of smooth muscle fibres in lamina propria which shorten the villus
Products transported in blood system back to CVS
Fibres arise from muscularis mucosae
166
Small intestine: Lacteals - passive
No smooth muscles, so depend on external source of squeezing - muscularis mucosae
167
Small intestine: Muscularis mucosae - smooth muscle fibres
Some extend into lamina propria core of villus
| When contract --> squeezing motion --> milk lacteals
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Small intestine: Mucosa - columnar absorptive cells (enterocytes)
Absorb small molecules resulting from digestion
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Small intestine: Mucosa - Where are the microvillus projections located
Columnar absorptive cells (enterocytes)
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Small intestine: Mucosa - goblet cells
Embedded among enterocytes
Secrete mucus - provides lubrication to help with movement of substances, absorption and to mix things
Eventually die so need to be replaced
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Small intestine: Mucosa - undifferentiated cells
Stem cells dividing to generate new epithelium / diff cells to replace dying cells
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Small intestine: Mucosa - paneth cells
Secrete bactericidal enzyme lysozyme - localised immune control
Phagocytic
Apical zymogen granules
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Small intestine: Mucosa - Enteroendocrine cells - stimuli
Stimulated by acid from chyme and amino acid fragments (since pepsin has initiated breakdown of proteins)
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Small intestine: Mucosa - Enteroendocrine cells - where is secretin secreted
Secreted into capillaries of lamina propria
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Small intestine: Mucosa - Enteroendocrine cells - what does secretin stimulate
Release of pancreatic juice and bile
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Small intestine: Mucosa - epithelium
Short-lived
Cell division occurs deep in glands and migrates
Entire journey lasts ~5 days
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Large intestine - functions
Absorption of salts and water
Conversion of chyme into feces; bacteria ferment remaining carbohydrates
Bacteria produce vitamins (B and K) which are absorbed
Secretion of mucus to lubricate feces
Defecation
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Large intestine - main function
Absorption of water
179
Large intestine: Parts
Caecum --> asc colon --> transverse colon --> desc colon --> sigmoidal colon --> rectum --> anus
180
Large intestine: Mucous secretion
As colon is reabsorbing water, contents of lumen become more compact/dehydrated
Mucous is secreted to provide lubrication to make sure there's enough flow
181
Large intestine: Appendix
Not a vital organ
Enriched with lymphatic tissue - monitors activity in LI
Vermiform - worm-shaped
182
Large intestine: Appendix - inflammation
Appendicitis - acute condition
| Could eventually burst --> content would go into peritoneum and infect surrounding organs in abdominal cavity
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Large intestine: Ileocecal valve
Controls intermittent flow of chyme from ileum into caecum
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Large intestine: Caecum
A dilated pouch
| Bacteria (not enzymes) are responsible for digestion
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Large intestine: What do faeces contain
Bacteria 30%
Undigested dietary fibre 30%
Cells shed from intestinal lining
Mucous
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Large intestine: External muscle
Outer longitudinal muscle is thickened in three strips = teniae coli, which contract to pull intestinal tube into sac-like pockets (haustra coli)
187
Large intestine: External muscle - Haustra coli
Changes shape and position
| Allows diff segments of colon to process things at diff rates
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Large intestine: Mucosa - villi
No villi, but many intestinal glands
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Large intestine: Mucosa - no of goblet cells
From asc --> transverse --> desc colon, have an increasing no of goblet cells because content becomes more dehydrated so need more lubrication
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Large intestine: Mucosa - goblet cells
Secrete mucus for lubrication
| Die so need to be replaced by undifferentiated cells
191
Large intestine: Mucosa - does it contain paneth cells
No, have WBCs instead
192
Large intestine: Mucosa - WBCs
Help control environment since lots of bacteria in large intestine
193
Large intestine: Mucosa - Entire epithelium is replaced every...
4-5 days
194
Large intestine: Mucosa - lymphocytes (WBCs)
Mostly lymphocytes
| Lots in lamina propria - large bacterial content of colon
195
Large intestine: Mucosa - columnar absorptive cells (enterocytes)
Similar to those in small intestine
| Absorb mostly water
196
Rectum: Anal canal
Last 2cm of rectum = anal canal
197
Rectum: Anal canal - sphincters
Closed by 2 sphincters;
Inner = involuntary smooth-muscle sphincter
Outer = partial-voluntary skeletal-muscle sphincter
198
Rectum: Urge to defecate
Felt when rectum fills ~25% of capacity
Stretching of rectal wall initiates reflex contraction of teniae coli --> increases pressure in rectum --> internal anal sphincter relaxes/opens (reflex)
199
Rectum: External sphincter
If time is convenient, it relaxes voluntarily
| If not, it's maintained in contracted state and defecation reflex subsides
200
Rectum: Children
Takes some time to learn how to control external sphincter
201
Rectum - epithelium
At anal region (rectum and anus), epithelium changes from glandular secretory epithelium to stratified squamous to protect from friction
202
Small intestine: Venules in submucosa are tributaries of...
Hepatic portal vein
203
Stomach - villi
No villi
204
Stomach - goblet cells
No goblet cells
205
Gastric juice - pH
Very low pH
206
Simple columnar epithelium
Specialised for absorption
207
Tooth is fixed in socket by the...
Periodontal membrane
