6.1 Digestion and absorption Flashcards
1
Q
How many major groups of organs is the digestive system made up of?
A
Two
2
Q
What are the two major groups of organs the digestive system is made up of?
A
The alimentary canal and the accessory organs
3
Q
What does the ailmentary canal consist of?
A
Organs where food actually passes
(oesophagus, stomach, small & large intestine)
4
Q
What do the accessory organs of the digestive system comprise of?
A
Organs that aid in digestion but do not actually transfer food
(salivary glands, pancreas, liver and gall bladder)
5
Q
What is the oesophagus?
A
A hollow tube connecting the oral cavity to the stomach
6
Q
How is the oesophagus separated from the trachea?
A
By the epiglottis
7
Q
What is food mixed with before entering the oesophagus?
A
Saliva
8
Q
How is food moved in the oesophagus?
A
In a bolus via peristalsis
9
Q
What is the stomach?
A
A temporary storage tank where food is mixed by churning and protein digestion begins
10
Q
What is the stomach lined with?
A
Gastric pits that release digestive juices
11
Q
What do the digestive juices in the stomach create?
A
An acidic environment
12
Q
What is the small intestine?
A
A long, highly folded tube where usable food substances are absorbed
13
Q
What are the three sections of the small intestine?
A
Duodenum
Jejunum
Ileum
14
Q
What is the large intestine?
A
The final section of the alimentary canal where water and dissolved minerals are absorbed
15
Q
What does the large intestine consist of?
A
Ascending/transverse/descending/sigmoidal colon and the rectum
16
Q
What are the salivary glands?
A
Release saliva to moisten food and contains enzymes to initiate starch breakdown
17
Q
What does the salivary glands include?
A
The parotid gland, submandibular gland and sublingual gland
18
Q
What is the pancreas?
A
Produces a broad spectrum of enzymes that are released into the small intestine via the duodenum
19
Q
What does the pancreas secrete?
A
Certain hormones which regulate blood sugar concentrations
20
Q
What does the liver do?
A
Takes the raw materials absorbed by the small intestine and uses them to make key chemicals
21
Q
What are the five roles of the liver?
A
Detoxification
Storage
Metabolism
Bile production
Haemoglobin breakdown
22
Q
What does the gall bladder store?
A
Bile produced by the liver
23
Q
Where is the bile stored in the gall bladder released?
A
Into the small intestine via the common bile duct
24
Q
What are the two ways food can be digested?
A
Mechanical digestion and chemical digestion
25
How is food broken down in mechanical digestion?
It is broken down into smaller fragments via the acts of chewing, churning and segmentation
26
How is food initially broken down?
In the mouth by the grinding action of teeth
27
What does the tongue do in mechanical digestion?
Pushes the food towards the back of the throat
28
What does the epiglottis prevent?
The bolus from entering the trachea
29
What does the uvula prevent?
The bolus from entering the nasal cavity
30
What do the muscles in the stomach lining do?
Physically squeeze and mix the food with digestive juices
31
How long is the food digested within the stomach for?
Several hours
32
Once the food has been digesting in the stomach what does it turn into?
A creamy paste called chyme
33
Where does the chyme go after the stomach?
Into the small intestine where absorption will occur
34
What is peristalsis?
The principal mechanism of movement in the oesophagus
35
Apart from the oesophagus where else does peristalsis occur?
Stomach and the gut
36
How does peristalsis happen?
Continuous segments of longitudinal smooth muscle rhythmically contract and relax
37
In what direction is food moved along the alimentary canal?
Unidirectionally in a caudal direction
38
What does segmentation invlove?
The contraction and relaxation of non-adjacent segments of circular smooth muscle in the intestines
39
Which direction does segmentation contractions move chyme?
In both directions
40
What does the fact that segmentation contractions move chyme in both directions allow for?
Greater mixing of food with digestive juices
41
What is the downside to segmentation?
Its bidirectional propulsion of chyme can slow overall movement
42
How is food broken down in chemical digestion?
By the action of chemical agents
43
What is the pH of the stomach?
2
44
What does the acidic environment of the stomach function to do?
Denature proteins and other macromolecules to aid in their overall digestion
45
What does the stomach epithelium have to prevent the acids from damaging the gastric lining?
A mucous membrane
46
What does the alkaline compounds released by the pancreas do?
Neutralise the acids as they enter the intestine
47
What does the liver produce that is stored in the gall bladder?
Bile
48
What does the bile contain?
Bile salts
49
What do bile salts do?
Interact with fat globules and divide them into smaller droplets
50
What increases the total surface area available for enzyme activity?
The emulsification of fats
51
What are enzymes?
Biological catalysts which speed up the rate of a chemical reaction
52
What do enzymes allow digestive processes to occur at?
Body temperatures and sufficient speeds for survival requirements
53
How does enzymes being specific for a substrate help digestion?
It allows digestion of certain molecules to occur independently in distinct locations
54
Where are digestive enzymes secreted predominantly from?
The pancreas
55
What does the type of enzyme secreted and location of secretion depend on?
The specific macromolecule required for hydrolysis
56
What does carbohydrate digestion begin with?
In the mouth with the release of amylase from the salivary glands
57
Why is amylase also secreted from the pancreas?
In order to continue carbohydrate digestion in the small intestine
58
Why is amylase also secreted from the pancreas?
In order to continue carbohydrate digestion in the small intestine
59
What are immobilised on the epithelial lining of the small intestine, near channel proteins?
Enzymes for disaccharide hydrolysis
60
Why does cellulose pass through the body undigested?
Humans do not possess an enzyme capable of digesting cellulose
61
Where does protein digestion begin?
In the stomach with the release of proteases
62
What breaks the smaller polypeptide chains when they enter the small intestine?
Endopeptidases released by the pancreas
63
In what type of environment do endopeptidases work optimally in?
Neutral environment
64
In what type of environment do proteases work optimally in?
An acidic environment
65
Where does lipid breakdown occur?
In the intestines
66
What does lipid breakdown begin with?
Emulsification of fat globules by bile released from the gall bladder
67
What are smaller fat droplets digested by?
Lipases released from the pancreas
68
What do nucleases digest?
Nuclei acids into smaller nucleosides
69
What does bicarbonate ions ddo?
Neutralise stomach acid
70
What are the four main tissue layers of the small intestine?
Serosa
Muscle Layer
Submucosa
Mucosa
71
What is the serosa?
A protective outer covering composed of a layer of cells reinforced by fibrous connective tissue
72
What is the muscle layer of the small intestine?
Over layer of longitudinal muscle and inner layer of circular muscle
73
What is the submucosa?
Composed of connective tissue separating the muscle layer from the innermost mucosa
74
What is the mucosa?
A highly folded inner layer which absorbs material through its surface epithelium from the intestinal lumen
75
What is the inner epithelial lining of the intestine highly folded into?
Finger like projections called villi
76
Where will many villi protruded into?
The intestinal lumen
77
What does the fact villi protrude into the intestinal lumen greatly increase?
The available surface area for material absorption
78
What are the six features of villi? (mr slim)
Microvilli
Rich nutrient supply
Single layer epithelium
Lacteals
Intestinal glands
Membrane proteins
79
Explain the microvilli feature of villi?
Ruffling of the epithelial membrane further increases surface area
80
Explain the microvilli feature of villi?
Ruffling of the epithelial membrane further increases surface area
81
Explain the rich blood supply feature of villi?
Dense capillary network rapidly transports absorbed products
82
Explain the single layer epithelium feature of villi?
Minimises diffusion distance between lumen and blood
83
Explain the lacteals feature of villi?
Absorbs lipids from the intestine into the lymphatic system
84
Explain the membrane proteins feature of villi?
Facilitates transport of digested materials into epithelial cells
85
What are the four structural features of villus epithelium?
Tight junctions
Microvilli
Mitochondria
Pinocytotic vesicles
86
What are tight junctions?
Occluding associations between the plasma membrane of two adjacent cells, creating an impermeable barrier?
87
What is the function of the tight junctions in villas epithelium?
They keep digestive fluids separated from tissues and maintain a concentration gradient by ensuring one way movement
88
What do microvilli have to increase surface area and allow for more absorption to occur?
Microvilli borders
89
What is the microvilli membrane embedded with to assist in material uptake?
Immobilised digestive enzymes and channel proteins
90
Why do epithelial cells of the intestinal villi possess large numbers of mitochondria?
To provide ATP for active transport mechanisms
91
What transport types will ATP help with in the villus epithelium?
Primary active transport
Secondary active transport
Pinocytosis
92
What is pinocytosis?
The non specific uptake of fluids and dissolved solutes
93
How do pinocytotic vesicles ingest the materials?
By breaking and reforming the membrane
94
What must happen during absorption?
Digeste food monomers must pass from the lumen into the epithelial lining of the small intestine
95
What do tight junctions between epithelial cels occlude?
Any gaps between cells
96
What are the four different membrane transport mechanisms used in digestion?
Secondary active transport
Facilitated diffusion
Osmosis
Simple diffusion
97
What is secondary active transport?
A transport protein couples the active translocation of one molecule to the passive movement of another
98
How are glucose and amino acids transported across the epithelial membrane?
Co transported by the active translocation of sodium ions
99
What do channel proteins do in digestion?
Help hydrophilic food molecules pass through the hydrophobic portion of the plasma membrane
100
Where are channel proteins often situated?
Near specific membrane-bound enzymes
101
What does channel proteins being situated near specific membrane bound enzymes create?
A localised concentration gradient
102
What is transported by facilitated diffusion?
Vitamins, certain monosaccharides and some minerals
103
Where does the absorption of water and dissolved ions occur?
In both the small and large intestine
104
What will water molecules infuse across the membrane in response to?
The movement of ions and hydrophilic monomers
105
What is simple diffusion?
Hydrophobic materials may freely pass through the hydrophobic portion of the plasma membrane
106
Once absorbed where will lipids often pass through first instead of being transported via the blood?
Lacteals
107
What does endocytosis involve?
The invagination of the plasma membrane to create an internal vesicle containing extra cellular material
108
Why is endocytosis an energy dependent process?
As vesicle formation requires the breaking and reforming of the plasma membrane
109
In the intestines, what do vesicles commonly form around?
Fluid containing dissolved materials
110
Why does pinocytosis take less time than shuttling via membrane proteins?
As it allows materials to be ingested en masse
111
What is starch?
A polysaccharide composed of glucose monomers
112
What are the two forms starch can exist in?
Linear chains or branched chains
113
Why does starch digestion not occur in the stomach?
As the pH is unsuitable for amylase activity
114
What does amylase digest amylose into?
Maltose subunits
115
What does amylose digest amylopectin into?
Branched chains called dextrins
116
Where are the enzymes that digest maltose and dextrin fixed to?
The epithelial lining of the small intestine
117
What does the hydrolysis of maltose/dextrin result in?
The formation of glucose monomers
118
What can glucose be hydrolysed to produce?
ATP
119
How is glucose stored in animals as?
The polysaccharide glycogen
120
What can generate glucose monomers?
The breakdown of other disaccharides
121
What are the two functions the pancreas serves in the production of starch?
- produces amylase which is released from exocrine glands into the intestinal tract
- produces insulin and glucagon released from endocrine glands into the blood
122
What regulates the concentration of glucose in the bloodstream?
Insulin and glucagon
123
How does insulin affect blood glucose levels?
Lowers them by increasing glycogen synthesis and storage in liver and adipose tissues
124
How does glucagon affect blood glucose levels?
Increases them by limiting the synthesis and storage of glycogen by liver and adipose tissues
125
What are the two key functions of digestion?
- breaks down insoluble molecules into smaller subunits which can be readily absorbed
- breaks down inert molecules into useable subunits which can be reassembled into new products
126
What are cell membranes impermeable to?
Large molecules
127
What can the size specific permeability off cell membranes be modelled using?
Dialysis tubing
128
Why is dialysis tubing like cell membranes?
Contains small pores and is semi permeable according to molecular size
Large molecules can’t cross but smaller ones can
129
How is dialysis tubing not like cell membranes?
It is not selectively permeable based on charge
130
What is dialysis tubing impermeable to?
Amylase and starch
131
What is dialysis tubing permeable to?
Maltose and water
132
What are the two experiments to mimic digestion?
Measuring meniscus levels
Measuring maltose diffusion
133
What happens in the experiment of measuring meniscus levels?
Dialysis tubing is attached to a thistle funnel and filled with starch solution and a second tube is filled with starch and amylase
Both apparatus are placed in water
Osmosis happens and the tube with amylase will have less solute and the meniscus level should not rise much
134
What happens in the measuring maltose diffusion?
Dialysis tubing is filled with starch solution and suspended in water
A second tube is filled with starch andd amylase solution
Amylase will digest starch into maltose which can diffuse out the tube
Maltose can be detected by Benedict’s reagent or glucose indicator strips
