Human Physiology - 6.1 Digestion and Absorption Flashcards
the two groups of organs which comprise the human digestive system
- Alimentary canal
- Accessory organs
alimentary canal
consists of organs through which food actually passes
(oesophagus, stomach, small and large intestine)
Accessory organs
aid in digestion but do not actually transfer food
(salivary glands, pancreas, liver, gall bladder)
The role of the: mouth
food is chewed (masticated) and mixed with saliva and swallowed
The role of the: oespohagus
A hollow tube connecting the oral cavity to the stomach (separated from the trachea by the epiglottis),
food is moved in a bolus via the action of peristalsis
The role of the: stomach
both stores food and begins the process of digestion.
churning and digestion of proteins into polypeptides occour
food remains int he stomach for 3-10 hours
muscles that control the entry and exit of materials in the stomach
sphincter muscles
The role of the: small intestine
is long and divided into 3 regions
it is lined with smooth muscles to allow for the mixing and moving of digested food productions
when acidic chyme enters the duodenum it is mixed with pancreatic juice, intestinal juice and bile which digest large molecules
the 3 regions of the small intestine
1) duodenum
2) jejunum
3) longer ileum
The role of the: Pancreas
secretes the enzymes amylase, lipase and an endopeptidase
also secrets certain hormones (insulin, glucagon) which regulate blood sugar concentrations
The role of the: liver
produces bile
role of bile (liver)
bile contains no digestive enzymes but contains salts which acts as a emulsifier and helps in the absorption of fates
bile also contains some wastes of the liver (red blood cell destruction)
The role of the: Gall Bladder
the gall bladder stores the bile produced by the liver (bile salts are used to emulsify fats)
bile stored in the gall bladder is released into the small intestine via the common bile duct
The role of the: large intestine
the indigestible parts of the food, such as cellulose fibre, as well as a large volume of water is passed to the large intestine (colon) water and ions are re-absorved here, leaving solid faeces which passes down the rectum and is ectum and is egested through the anus
what is included in the large intestine
1) ascending/transverse/descending/sigmoidal colon
2) rectum
Mechanical Digestion - understanding
= the contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and movies it along the gut
stats about the digestive system:
= it is about 5 metres long
= takes about 24-72 hours for food to pass through it
Mechanical digestion - chewing
- food is initially broken down in the mouth by the grinding action of teeth (chewing or mastication)
- the tongue pushes the food towards the back of the throat where it then travels down the esophagus as a bolus
what is a bolus?
it is a lump of food
epiglottis’ interaction with the bolus
+
uvula’s interaction with the bolus
- epiglottis prevents the bolus from entering the trachea
- uvula prevents the bolus from entering the nasal cavity
Mechanical Digestion: Peristalsis
= the method of movement in the oesophagus, stomach and small intestine
- smooth muscle rhythmically contract and relax
- food is moved along the alimentary canal from mouth to anus
choaking =
when you eat something too big and peristalsis can not occour
Mechanical Digestion: Segmentation
= involves the contration and relaxation of non-adjacent segments of circular smooth muscle in the intestines
segmentation contractions in the stomach =
move chyme in both directions (ie food can go up and down (eg cows)) = allowing for a greater mixing of food with digestive juices
Chemical digestion - understandings
1) the pancreas secretes enzymes into the lumen of the small intestine
2) enzymes digest most macromolecules in food into monomers in the small intestine
the breakdown of large molecules in the human body
= digestion
some food that humans eat contain substances that are made by other organisms - they must be broken down into their parts (eg amino acids) so that the human body can rebuild them into useful substances
most food molecules are too large to be absorbed through the small intestine into our blood
protein goes through proteases/peptidases to form:
amino acids
polysaccharides and disaccharides goes through amylases to form:
monosaccharides
nucleic acid goes through nucleases to form:
nucleotides
fat goes through fat-digesting enzymes (ie lipides/lipases) to form:
glycerol fatty acids
cellulose/fibre - and NOT being broken down
cellulose remains undigested and is passed from the body in faeces
for details on where chemical digestion can occur in the body (the enzymes, substrates, products and pH)s can be found on PAGES =
4 and 5
What is the: villi in the small intestine
they help in the absorption of nutrients by increasing the surface area for absorption
so that the max amount of substance can be absorbed
consequences of celiac disease for absorption of digested nutrients
celiac disease flattens villi resulting in a lower amount of substances being absorbed and nutrients digested
In chemical digestion, food is broken down by the action of chemical agents, these include
1) enzymes
2) acids
3) bile
digestion of carbohydrates
Carbohydrate digestion begins in the mouth with the release of amylase from the salivary glands (amylase = starch digestion)
Amylase is also secreted by the pancreas in order to continue carbohydrate digestion within the small intestine
Enzymes for disaccharide hydrolysis are often
immobilised on the epithelial lining of the small intestine, near channel proteins
Humans do not possess an enzyme capable of digesting cellulose (cellulase) and hence it passes through the body undigested
digestion of proteins
Protein digestion begins in the stomach with the release of proteases that function optimally in an acidic pH (e.g. pepsin = pH 2)
Smaller polypeptide chains enter the small intestine where they are broken down by endopeptidases released by the pancreas
These endopeptidases work optimally in neutral environments (pH ~ 7) as the pancreas neutralises the acids in the intestine
digestion of lipids
Lipid breakdown occurs in the intestines, beginning with emulsification of fat globules by bile released from the gall bladder
The smaller fat droplets are then digested by lipases released from the pancreas
digestion of nucleic acids
The pancreas also releases nucleases which digest nucleic acids (DNA, RNA) into smaller nucleosides
simplified difference between the small and large intestine
The small intestine absorbs usable food substances (i.e. nutrients – monosaccharides, amino acids, fatty acids, vitamins, etc.)
The large intestine absorbs water and dissolved minerals (i.e. ions) from the indigestible food residues
Features of Villi - MR SLIM
Microvilli – Ruffling of epithelial membrane further increases surface area
Rich blood supply – Dense capillary network rapidly transports absorbed products
Single layer epithelium – Minimises diffusion distance between lumen and blood
Lacteals – Absorbs lipids from the intestine into the lymphatic system
Intestinal glands – Exocrine pits (crypts of Lieberkuhn) release digestive juices
Membrane proteins – Facilitates transport of digested materials into epithelial cells
benifits because of the structure of villus epithelium
1) tight junctions
2) microvilli
3) mitochondria
4) pinocytotic vesicles
DETAILS ON BIONINJA
structure of the small intestine
Serosa – a protective outer covering composed of a layer of cells reinforced by fibrous connective tissue
Muscle layer – outer layer of longitudinal muscle (peristalsis) and inner layer of circular muscle (segmentation)
Submucosa – composed of connective tissue separating the muscle layer from the innermost mucosa
Mucosa – a highly folded inner layer which absorbs material through its surface epithelium from the intestinal lumen
Methods of Membrane Transport Mechanisms
1) Secondary Active Transport
2) Facilitated Diffusion
3) Osmosis
4) Simple Diffusion
Methods of bulk transport mechanisms
Endocytosis
Endocytosis overview
Endocytosis involves the invagination of the plasma membrane to create an internal vesicle containing extracellular material
Vesicle formation requires the breaking and reforming of the phospholipid bilayer and hence is an energy-dependent process
In the intestines, vesicles commonly form around fluid containing dissolved materials (pinocytosis – cell ‘drinking’)
Pinocytosis allows materials to be ingested en masse and hence takes less time than shuttling via membrane proteins
two key functions performed by digestion
It breaks down insoluble molecules into smaller subunits which can be readily absorbed into body tissues
It breaks down inert molecules into usable subunits which can be assimilated by cells and reassembled into new products
starch digestion - role of pancreas
The pancreas serves two functions in the breakdown of starch:
It produces the enzyme amylase which is released from exocrine glands (acinar cells) into the intestinal tract
It produces the hormones insulin and glucagon which are released from endocrine glands (islets of Langerhans) into the blood
The hormones insulin and glucagon regulate the concentration of glucose in the bloodstream (controls availability to cells)
Insulin lowers blood glucose levels by increasing glycogen synthesis and storage in the liver and adipose tissues
Glucagon increases blood glucose levels by limiting the synthesis and storage of glycogen by the liver and adipose tissues
role of villi (2)
-> line the ileum (are “projections”)
1) villi increase the surface area of epithelium over which absorption is carried out
2) villi absobs monomers formed by digestion as well as mineral ions and vitamins
microvilli
- cells of the villi
- increases surface area for absorption
Liquids that pass along ileum…
contain the products OF digestion, minerals and vitamins
==> these are absorbed through the wall of the ileum by the villis into the blood
movement of “stuff” into the liver
the amino acids, glucose, some fatty acids, glycerol, minerals and most vitamins are ABSORBED into the CAPILLARIES and carried via the HEPATIC PORTAL VEIN to the LIVER
lacteal (branch of the lymphatic system) (in the villis)–>
in each villi carries away much of the fatty acids and glycerol
absorbs liquids/lipids from the intestine into the lymphatic system
Rich blood supply =
dense capillary network rapidly transports absorbed products
Single layer epithelium = minimises diffusion distance between lumen and blood =
minimises diffusion distance between lumen and blood
intestial glads =
exocrine pits releases digestive juices
membrane proteins =
facilitates transport of digestied materials into epithelial cells
how is the structure of the villus is related to its role in absorption of the end products of digestion
1) high surface area = rapid absorption of nutrients
2) good blood flow
3) linked to transport lymph vessels -> transport
Methods of membrane transport are required to absorb different nutrients
details + examples on pages 8+9
1) simple diffusion
2) facilitated diffusion
3) active transport
4) endocytosis
5) osmosis
molecules are then distributed and assimilated = it is used by the body to make…
new substances, cells and tissues
Starch digestion in the small intestine ==>
- amylase
- Dextrinase
- Maltase
amylase =
enzyme breaks bonds in chains of 4 or more monomers producing maltose
Dextrinase =
breaks the bonds that amylase cannot deal with forming glucose monomers
maltase =
digests maltose into glucose monomers
Digested glucose is absorbed and then transported to various body tissues by (5) =
1) glucose is co-transported with sodium ions into the epithelial cells (of the villus)
2) glucose moves by facilitated diffusion into the lumen of the villus
3) glose then diffuses a short distance into the adjacent capillaries where it dissolves into the blood plasma
4) blood in the capillaries move to the venules then to the hepatic portal vein which transports the glucose to the liver
5) the liver absorbs excess glucose which it converts to glycogen for storage
peristalsis
the involuntary constriction and relaxation of the muscles of the intestine or another canal, creating wave-like movements that push the contents of the canal forward.
surfactants
a substance which tends to reduce the surface tension of a liquid in which it is dissolved.
that allow for fats/oil to immensafy (mix)
lipase
a pancreatic enzyme that catalyses the breakdown of fats to fatty acids and glycerol or other alcohols + lipids
endopeptidase
an enzyme which breaks peptide bonds other than terminal ones in a peptide chain (breaks down polypeptides)
Mucosa
The moist, inner lining of some organs and body cavities (such as the nose, mouth, lungs, and stomach). Glands in the mucosa make mucus (a thick, slippery fluid). Also called mucous membrane.
lacteal
the lymphatic vessels of the small intestine which absorb digested fats.
dialysis tubing
artificial semi-permeable membrane tubing[1] used in separation techniques, that facilitates the flow of tiny molecules in solution based on differential diffusion
membrane that control the size movement of materials used in osmosis experiments
cellulose
plant sugar used for storage - that cant be broken down
an insoluble substance which is the main constituent of plant cell walls and of vegetable fibres such as cotton. It is a polysaccharide consisting of chains of glucose monomers
macromolecule
a molecule containing a very large number of atoms, such as a protein, nucleic acid, or synthetic polymer.
epithelium
outside layer of cells
the thin tissue forming the outer layer of a body’s surface and lining the alimentary canal and other hollow structures.
the part of the epithelium derived from embryonic ectoderm and endoderm, as distinct from endothelium and mesothelium
lumen
central part of the tube (surrounded by villi)
the central cavity of a tubular or other hollow structure in an organism or cell.
Pancreas
A glandular organ located in the abdomen. It makes pancreatic juices, which contain enzymes that aid in digestion, and it produces several hormones, including insulin. The pancreas is surrounded by the stomach, intestines, and other organs
stomach
the internal organ in which the major part of the digestion of food occurs, being (in humans and many mammals) a pear-shaped enlargement of the alimentary canal linking the oesophagus to the small intestine
colon
the main part of the large intestine, which passes from the caecum to the rectum and absorbs water and electrolytes from food which has remained undigested.
last section of the large intestine
small intestine
the part of the intestine that runs between the stomach and the large intestine; the duodenum, jejunum, and ileum collectively.
liver
for processing food
a large lobed glandular organ in the abdomen of vertebrates, involved in many metabolic processes
gall bladder
a small sac-shaped organ beneath the liver in which bile is stored after secretion by the liver and before release into the intestine.
chyme
the pulpy acidic fluid which passes from the stomach to the small intestine, consisting of gastric juices and partly digested food.
