Download Digestion1 - MrsGorukhomework

Digestion
Why do we digest our food – 1) macromolecules are too large to pass through
membranes 2) macromolecules are not in the form we need so our body needs to it down
– catabolism and rebuild – anabolism. We need food as monomers. The process of
digestion can be divided into three main activities; physical or mechanical digestion
(breaking down into smaller pieces), chemical digestion and absorption/elimination.
Only small, simple molecules can pass out of the digestive tract and enter cells.
Chemical digestion involves enzymatic hydrolysis. Enzymes are involved everywhere
and require specialized conditions and these conditions vary – need for
compartmentalization.
Carbohydrates must be broken down into disaccharides and then monosaccharide. Fats
are emulsified and broken down into glycerol and fatty acid. Proteins to polypeptides
and then amino acids. Only these forms can pass into the cell.
**Need to draw – including mouth, esophagus, stomach, S.I., L.I. anus, liver, pancreas
and gallbladder. Clearly show interconnections and relative sizes.
Mouth - The digestive tube (gastro-intestinal tract) begins with the mouth and mechanical
breakdown. The saliva lubricates food and contains the digestive enzyme salivary
amylase – begins the breakdown of starches from a polysaccharide to disaccharide called
maltose. Salvia is about pH 7-7.5 to aid enzymes.
*Don’t forget, all steps requires enzymes necessary for catabolism of food to allow it to
occur at body temperature.
Pharynx – esophagus (about 25 cm long) and leads to stomach. To ensure that food
enters the esophagus and not the trachea, the epiglottis is employed – a flap of tissue that
covers the glottis. Food is forced down the esophagus by alternating contractions and
relaxation of muscles called peristalsis. A sphincter muscles (muscle in a ring) controls
the passage of food in and out of the stomach.
Stomach – collapsible bag in folds. The epithelium layer that lines the stomach contains
millions of cells which secrete gastric juices. Function – mixes food with juices,
mechanical digestion through contractions. The gastric juices contain a dilute solution of
HCl, giving the gastric juice a pH of 1-2. Also found in the juice is an enzyme called
pepsinogen. It is included in a group of enzymes called proteases.- protein digesting
enzymes.
HCl kills most bacteria and loosens tough tissue like protein (all the bonds). It also
initiates the conversion of pepsinogen (inactive form) to pepsin. It hydrolyzes proteins
into peptides. Pepsin has an optimum pH of 1-2. Mucus secreted by epithelium cells
protects the stomach.
Stomach cell lining completely replaced every 3 days – chemotherapy
Because the acid and pepsinogen are secreted by different cells, the two don’t mix
until released.
The small intestine – * where most enzymatic hydrolysis occurs and has specific
structures to aid in this function – form = function.. In average adult is 6-7 meters long.
First 30 cm is called the duodenum – where the pancreas and liver, via the gall bladder,
secrete their juices through ducts. The food is mixed with the juices from these organs.
This region is subject to ulcerations due to high acidity
Pancreatic juices – a long, whitish gland lying underneath the stomach. The pH is about
7.5 meaning that buffer bases must be secreted to raise the pH. Its juices are secreted into
the duodenum through pancreatic duct. There are many enzymes in the juices. Has
proteases, which finish off anything pepsin hasn’t done. Pancreatic amylase (important
to distinguish between salivary and pancreatic) digests starches into maltose. Lipase
catalyses the hydrolysis of fats. Fats are a special problem as they are non-polar and tend
to reform in the blood.
If pancreas ruptures enzymes start to auto digest.
Liver – not strictly an organ of digestion but plays a role in fat digestion. Bile is
continuously made by the liver and stored in the gall bladder. (bile will still enter the
duodenum if gall bladder is removed but no so controlled) A hormone stimulates the gall
bladder to release its juices. There are no enzymes in the juices just salts that emulsify
fats to ensure that they don’t reform in the blood. Cholesterol is also part of bile salts.
Emulsification requires ATP and enzymes.
Hepatitis – general term for infection of the liver. Some symptoms – tiredness, poor
appetite, abdominal pains, jaundice.
Bile also contains pigments from Hb. Old Hb is picked up by liver and reused.
Unusable parts are dumped into the bile to be excreted – gives it its brown colour.
We can see this colour when we have a bruise. Jaundice when old RBC stored
under the skin – ultra violet light works – is a condition, not a disease.
*The rest of the small intestine is made up of folds called villi (villus is sing) which will
affect the exchange of material. The villi are further made up of microvilli, which will
greatly increase the surface area. Is very long – about 100 square feet and surrounded by
capillaries. The epithelium cells are only one cell thick and contains a lot of
mitochondria. A lot of channel proteins to aid in facilitated diffusion, dense network of
capillaries to absorb and transport nutrients, large number of mitochondria for active
transport and protein pumps Membrane bound enzymes are incorporated in the
epithelium layer. Be able to recognize. Form = function.
The small intestine contains enzymes that will finish off all digestion so that by the time
it reaches the end, it is in the form of monosaccharide’s, amino acids and fatty acids and
glycerol ready to be absorbed into the blood stream.
Epithelium cells go through mitosis at a great rate as they are constantly being
rubbed off – are affected by cancer drugs as well as stomach.
*when asked for name of enzyme – do NOT say protease as too general. Also don’t
say carbohydrate – instead say starch.
Each villus is richly supplied with blood contained in capillaries. (fits its function) Most
of the transport of food occurs here. Glucose, amino acids, fatty acids and glycerol move
into the capillaries by diffusion. The caps and veins that drain the nutrients away
combine to form the hepatic portal vein, which leads to the liver (about l L/min
which says a lot about the importance of the liver
Large intestine or colon - about 1.5 m, looks like an upside down U. Main function is the
reabsorption of water and the production of vitamin K by bacteria. Some minerals are
also absorbed. The caecum and large intestine are swarming with bacteria, which have
enzymes capable of breaking down some of the food that we cannot. Some of these
bacteria are purely commensal. But some are mutual by releasing wastes that contain
vitamins K and folic acid (a vitamin B).
Some also produce gases and odoriferous wastes. E. coli is one of the bacteria. A wormlike
projection leads from the caecum, the appendix. This may become clogged with decayed
food and become infected- appendicitis. If the infected appendix swells and bursts, the
infection is allowed to spread into the whole body - peritonitis.
What is left contains some water, cellulose, lignin (hard material in cellulose for support),
bile pigments, bacteria and intestinal cells. There could also be some salts if the
concentration is too high in the blood. Cellulose adds bulk, causing receptors in wall of
LI to send message to nervous system - bowl movement. The feces (faeces) pass from the
large intestine into the rectum. Here it remains until 2 sphincter muscles, guarding the
anus, relax and vigorous peristaltic waves expel them in the process of defecation
If not enough roughage - causes feces to stay too long (toxic), might lead to colon problems
and colon cancer. Food residues stay in the large intestine for about 12 to 14 hours.
Sometimes the large intestine becomes irritated and discharges its contents into the rectum
and out the anus before water can be reabsorbed - diarrhea. On the other hand, the large
intestine may retain its contents for an extra long time. The faecal material becomes dried
out and compressed - constipation. Occasionally, harmful bacteria or protozoans can enter
and live in- the large intestine. Typhoid fever, cholera amoebic dysentery are examples..
Hemorrhoids or piles - enlargement of the rectal veins near the opening of the rectum. It
restricts passage, thereby making passage of faecal material very painful) Takes 12-24
hours to leave LI. Castor oil is a laxative - irritates LI lining which stimulates peristalsis.
Mineral oil coats feces, so easier to move. Magnesium sulphate main ingredient in laxativesnot easily absorbed by LI so more water remains which softens feces
Difference between absorption and assimilation – assimilation comes after absorption,
taking the products and building them into complex parts of the body or molecule. See
page 207 and 208 of tiger book. Read ‘Thinking about science’ page 208. Do question
209 #9
Balanced diet - contains all the right nutrients and in right amount - carbohydrates,
proteins, lipids, fibre, (water) vitamins and minerals. Need to satisfy 3 needs - fuel, raw
materials for synthesis and essential nutrients that the body can't make. An equilibrium
between food intake and energy use. Different stages in life require different amounts –
baby, growing child, pregnant women, elderly, sick. Basal metabolic rate (at rest( is
1600 – 1800 kcal/day male and 1300 – 1500 female
Essential nutrients – materials that must be obtained in preassembled form, ie, your cells
can’t make it from raw materials. If your diet is missing one or more essential nutrients
you are said to be malnourished. There are four classes of essential nutrients; amino
acids, fatty acids, vitamins and minerals. Of the 20 amino acids we need, 8 are essential
(and one extra for infants). The fatty acids are unsaturated. Vitamins are organic
compounds needed in small amounts. So far there are 13 essential vitamins, divided into
fat soluble and water soluble vitamins. Minerals are inorganic compounds needed in very
small amounts.