6.1 Digestion and absorption Flashcards
How many major groups of organs is the digestive system made up of?
Two
What are the two major groups of organs the digestive system is made up of?
The alimentary canal and the accessory organs
What does the ailmentary canal consist of?
Organs where food actually passes
(oesophagus, stomach, small & large intestine)
What do the accessory organs of the digestive system comprise of?
Organs that aid in digestion but do not actually transfer food
(salivary glands, pancreas, liver and gall bladder)
What is the oesophagus?
A hollow tube connecting the oral cavity to the stomach
How is the oesophagus separated from the trachea?
By the epiglottis
What is food mixed with before entering the oesophagus?
Saliva
How is food moved in the oesophagus?
In a bolus via peristalsis
What is the stomach?
A temporary storage tank where food is mixed by churning and protein digestion begins
What is the stomach lined with?
Gastric pits that release digestive juices
What do the digestive juices in the stomach create?
An acidic environment
What is the small intestine?
A long, highly folded tube where usable food substances are absorbed
What are the three sections of the small intestine?
Duodenum
Jejunum
Ileum
What is the large intestine?
The final section of the alimentary canal where water and dissolved minerals are absorbed
What does the large intestine consist of?
Ascending/transverse/descending/sigmoidal colon and the rectum
What are the salivary glands?
Release saliva to moisten food and contains enzymes to initiate starch breakdown
What does the salivary glands include?
The parotid gland, submandibular gland and sublingual gland
What is the pancreas?
Produces a broad spectrum of enzymes that are released into the small intestine via the duodenum
What does the pancreas secrete?
Certain hormones which regulate blood sugar concentrations
What does the liver do?
Takes the raw materials absorbed by the small intestine and uses them to make key chemicals
What are the five roles of the liver?
Detoxification
Storage
Metabolism
Bile production
Haemoglobin breakdown
What does the gall bladder store?
Bile produced by the liver
Where is the bile stored in the gall bladder released?
Into the small intestine via the common bile duct
What are the two ways food can be digested?
Mechanical digestion and chemical digestion
How is food broken down in mechanical digestion?
It is broken down into smaller fragments via the acts of chewing, churning and segmentation
How is food initially broken down?
In the mouth by the grinding action of teeth
What does the tongue do in mechanical digestion?
Pushes the food towards the back of the throat
What does the epiglottis prevent?
The bolus from entering the trachea
What does the uvula prevent?
The bolus from entering the nasal cavity
What do the muscles in the stomach lining do?
Physically squeeze and mix the food with digestive juices
How long is the food digested within the stomach for?
Several hours
Once the food has been digesting in the stomach what does it turn into?
A creamy paste called chyme
Where does the chyme go after the stomach?
Into the small intestine where absorption will occur
What is peristalsis?
The principal mechanism of movement in the oesophagus
Apart from the oesophagus where else does peristalsis occur?
Stomach and the gut
How does peristalsis happen?
Continuous segments of longitudinal smooth muscle rhythmically contract and relax
In what direction is food moved along the alimentary canal?
Unidirectionally in a caudal direction
What does segmentation invlove?
The contraction and relaxation of non-adjacent segments of circular smooth muscle in the intestines
Which direction does segmentation contractions move chyme?
In both directions
What does the fact that segmentation contractions move chyme in both directions allow for?
Greater mixing of food with digestive juices
What is the downside to segmentation?
Its bidirectional propulsion of chyme can slow overall movement
How is food broken down in chemical digestion?
By the action of chemical agents
What is the pH of the stomach?
2
What does the acidic environment of the stomach function to do?
Denature proteins and other macromolecules to aid in their overall digestion
What does the stomach epithelium have to prevent the acids from damaging the gastric lining?
A mucous membrane
What does the alkaline compounds released by the pancreas do?
Neutralise the acids as they enter the intestine
What does the liver produce that is stored in the gall bladder?
Bile
What does the bile contain?
Bile salts
What do bile salts do?
Interact with fat globules and divide them into smaller droplets
What increases the total surface area available for enzyme activity?
The emulsification of fats
What are enzymes?
Biological catalysts which speed up the rate of a chemical reaction
What do enzymes allow digestive processes to occur at?
Body temperatures and sufficient speeds for survival requirements
How does enzymes being specific for a substrate help digestion?
It allows digestion of certain molecules to occur independently in distinct locations
Where are digestive enzymes secreted predominantly from?
The pancreas
What does the type of enzyme secreted and location of secretion depend on?
The specific macromolecule required for hydrolysis
What does carbohydrate digestion begin with?
In the mouth with the release of amylase from the salivary glands
Why is amylase also secreted from the pancreas?
In order to continue carbohydrate digestion in the small intestine
Why is amylase also secreted from the pancreas?
In order to continue carbohydrate digestion in the small intestine
What are immobilised on the epithelial lining of the small intestine, near channel proteins?
Enzymes for disaccharide hydrolysis
Why does cellulose pass through the body undigested?
Humans do not possess an enzyme capable of digesting cellulose
Where does protein digestion begin?
In the stomach with the release of proteases
What breaks the smaller polypeptide chains when they enter the small intestine?
Endopeptidases released by the pancreas
In what type of environment do endopeptidases work optimally in?
Neutral environment
In what type of environment do proteases work optimally in?
An acidic environment
Where does lipid breakdown occur?
In the intestines
What does lipid breakdown begin with?
Emulsification of fat globules by bile released from the gall bladder
What are smaller fat droplets digested by?
Lipases released from the pancreas
What do nucleases digest?
Nuclei acids into smaller nucleosides
What does bicarbonate ions ddo?
Neutralise stomach acid
What are the four main tissue layers of the small intestine?
Serosa
Muscle Layer
Submucosa
Mucosa
What is the serosa?
A protective outer covering composed of a layer of cells reinforced by fibrous connective tissue
What is the muscle layer of the small intestine?
Over layer of longitudinal muscle and inner layer of circular muscle
What is the submucosa?
Composed of connective tissue separating the muscle layer from the innermost mucosa
What is the mucosa?
A highly folded inner layer which absorbs material through its surface epithelium from the intestinal lumen
What is the inner epithelial lining of the intestine highly folded into?
Finger like projections called villi
Where will many villi protruded into?
The intestinal lumen
What does the fact villi protrude into the intestinal lumen greatly increase?
The available surface area for material absorption
What are the six features of villi? (mr slim)
Microvilli
Rich nutrient supply
Single layer epithelium
Lacteals
Intestinal glands
Membrane proteins
Explain the microvilli feature of villi?
Ruffling of the epithelial membrane further increases surface area
Explain the microvilli feature of villi?
Ruffling of the epithelial membrane further increases surface area
Explain the rich blood supply feature of villi?
Dense capillary network rapidly transports absorbed products
Explain the single layer epithelium feature of villi?
Minimises diffusion distance between lumen and blood
Explain the lacteals feature of villi?
Absorbs lipids from the intestine into the lymphatic system
Explain the membrane proteins feature of villi?
Facilitates transport of digested materials into epithelial cells
What are the four structural features of villus epithelium?
Tight junctions
Microvilli
Mitochondria
Pinocytotic vesicles
What are tight junctions?
Occluding associations between the plasma membrane of two adjacent cells, creating an impermeable barrier?
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
What do microvilli have to increase surface area and allow for more absorption to occur?
Microvilli borders
What is the microvilli membrane embedded with to assist in material uptake?
Immobilised digestive enzymes and channel proteins
Why do epithelial cells of the intestinal villi possess large numbers of mitochondria?
To provide ATP for active transport mechanisms
What transport types will ATP help with in the villus epithelium?
Primary active transport
Secondary active transport
Pinocytosis
What is pinocytosis?
The non specific uptake of fluids and dissolved solutes
How do pinocytotic vesicles ingest the materials?
By breaking and reforming the membrane
What must happen during absorption?
Digeste food monomers must pass from the lumen into the epithelial lining of the small intestine
What do tight junctions between epithelial cels occlude?
Any gaps between cells
What are the four different membrane transport mechanisms used in digestion?
Secondary active transport
Facilitated diffusion
Osmosis
Simple diffusion
What is secondary active transport?
A transport protein couples the active translocation of one molecule to the passive movement of another
How are glucose and amino acids transported across the epithelial membrane?
Co transported by the active translocation of sodium ions
What do channel proteins do in digestion?
Help hydrophilic food molecules pass through the hydrophobic portion of the plasma membrane
Where are channel proteins often situated?
Near specific membrane-bound enzymes
What does channel proteins being situated near specific membrane bound enzymes create?
A localised concentration gradient
What is transported by facilitated diffusion?
Vitamins, certain monosaccharides and some minerals
Where does the absorption of water and dissolved ions occur?
In both the small and large intestine
What will water molecules infuse across the membrane in response to?
The movement of ions and hydrophilic monomers
What is simple diffusion?
Hydrophobic materials may freely pass through the hydrophobic portion of the plasma membrane
Once absorbed where will lipids often pass through first instead of being transported via the blood?
Lacteals
What does endocytosis involve?
The invagination of the plasma membrane to create an internal vesicle containing extra cellular material
Why is endocytosis an energy dependent process?
As vesicle formation requires the breaking and reforming of the plasma membrane
In the intestines, what do vesicles commonly form around?
Fluid containing dissolved materials
Why does pinocytosis take less time than shuttling via membrane proteins?
As it allows materials to be ingested en masse
What is starch?
A polysaccharide composed of glucose monomers
What are the two forms starch can exist in?
Linear chains or branched chains
Why does starch digestion not occur in the stomach?
As the pH is unsuitable for amylase activity
What does amylase digest amylose into?
Maltose subunits
What does amylose digest amylopectin into?
Branched chains called dextrins
Where are the enzymes that digest maltose and dextrin fixed to?
The epithelial lining of the small intestine
What does the hydrolysis of maltose/dextrin result in?
The formation of glucose monomers
What can glucose be hydrolysed to produce?
ATP
How is glucose stored in animals as?
The polysaccharide glycogen
What can generate glucose monomers?
The breakdown of other disaccharides
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
What regulates the concentration of glucose in the bloodstream?
Insulin and glucagon
How does insulin affect blood glucose levels?
Lowers them by increasing glycogen synthesis and storage in liver and adipose tissues
How does glucagon affect blood glucose levels?
Increases them by limiting the synthesis and storage of glycogen by liver and adipose tissues
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
What are cell membranes impermeable to?
Large molecules
What can the size specific permeability off cell membranes be modelled using?
Dialysis tubing
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
How is dialysis tubing not like cell membranes?
It is not selectively permeable based on charge
What is dialysis tubing impermeable to?
Amylase and starch
What is dialysis tubing permeable to?
Maltose and water
What are the two experiments to mimic digestion?
Measuring meniscus levels
Measuring maltose diffusion
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
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
