Accessory digestive organs & nutrition

Question 1

Accessory organs of GI tract

Answer 1

Salivary glands
-provide moisture, amylase
* Pancreas
Exocrine pancreas (& endocrine pancreas) Digestive enzymes, HCO3
* Liver & biliary tract-produces and stores bile to aid digestion of fats Stores & converts nutrients
Alters chemicals to aid removal from body

Question 2

Gall bladder

Answer 2

Functions of gall bladder:
* Stores bile from liver
* Concentrates bile up to 10X by
absorbing water from bile
Gall bladder contracts when fat & protein reach duodenum and CCK released

Question 3

Blood flow through the liver

Answer 3

Involves sinusoids = form of very leaky capillaries

Question 4

Liver lobules

Answer 4

Microscopically, liver contains several components
1. Hepatocytes Major functional cells of liver
2. Bile canaliculi (= small canals). Small ducts between hepatocytes that collect bile produced by hepatocytes. Bile canaliculi, join together to exit the liver as
the common hepatic duct.
3. Hepatic sinusoids. Highly permeable blood capillaries between rows of hepatocytes that receive oxygenated blood from hepatic artery and nutrient‐rich deoxygenated blood from hepatic portal vein.
*Hepatic sinusoid stellate reticular endothelial cells also known as Kupffer or macrophage cells destroy worn‐out white and red blood cells, bacteria in venous blood draining from the gastrointestinal tract.

Question 5

Functions of Liver

Answer 5

Secretion of bile and bile salts
* Phagocytosis of bacteria and dead material by stellate reticuloendothelial
cells.
* Carbohydrate metabolism & maintaining normal blood glucose level. When blood glucose high, e.g., after a meal, liver converts glucose to glycogen and triglycerides for storage. –Insulin from the pancreas drives this process
* When blood glucose low, liver breaks down glycogen to glucose and releases it into bloodstream. Liver can convert certain amino acids and lactic acid to glucose.

Question 6

Functions of Liver

Answer 6

Lipid metabolism. Hepatocytes store triglycerides; break down fatty acids to generate ATP; synthesize lipoproteins, which transport fatty acids, triglycerides, and cholesterol to and from body cells; synthesize cholesterol; and use cholesterol to make bile salts.
* Protein metabolism. Hepatocytes remove amino group (–NH2) from amino acids so that amino acids can be used for ATP production or converted to carbohydrates or fats. They also convert the resulting toxic ammonia (NH3) into the much‐less‐toxic urea, which is excreted in urine. Hepatocytes also synthesize most plasma proteins, such as globulins, albumin, prothrombin, and fibrinogen

Question 7

Functions of Liver pt2

Answer 7

Processing of drugs and hormones. Liver detoxifies substances such as alcohol and secretes drugs such as penicillin, into bile. Also inactivates steroid hormones such as oestrogens.
* Excretion of bilirubin. Bilirubin, derived from haem of aged red blood cells, is absorbed by liver from blood and secreted into bile. Most of bilirubin in bile is eliminated in faeces.
* Storage of vitamins and minerals. Liver stores fat-soluble vitamins A, D, E, and K and minerals (iron and copper), which are released from liver when needed elsewhere in body.
* Activation of vitamin D. The skin, liver, and kidneys participate in synthesizing the active form of vitamin D.

Question 8

Source, distribution & use of glucose

Answer 8

Glucose can also be converted to fat & stored in liver or other tissues

Question 9

Carbohydrate metabolism

Answer 9

Glucose enters Krebs cycle and produces ATP, CO2 and water
The lactic acid also enters the Krebs cycle if oxygen is sufficient
If not, lactic acid may enter bloodstream-converted to glucose by liver

Question 10

Sources & uses of amino acids

Answer 10

20 amino acids in proteins, 9 of them are essential, i.e. body cant make them
Excess amino acids in tissues returned to liver via bloodstream –NH2 removed & converted to urea, rest used for energy production or making different amino acid

Question 11

Source, distribution & use of fats

Answer 11

Remember long chain fats absorbed by intestinal villi lacteals transported via lymph into the bloodstream and do not go via the liver.
Liver can make fat from carbohydrate and amino acids

Question 12

Lipid Transport in Blood

Answer 12

Most lipids, such as triglycerides and cholesterol, are not water‐soluble. Need to be made more water soluble by combining them with proteins.
* Such lipoproteins are spherical particles with an outer shell of proteins, phospholipids, and cholesterol molecules surrounding an inner core of triglycerides and other lipids.
* Lipoproteins are transport vehicles: They provide delivery and pickup services for different parts of the body. They are named according to size and density.

Question 13

Lipoproteins in Blood

Answer 13

Named according to size and density.
1. Chylomicrons made in absorptive epithelial cells of small intestine. Transport dietary lipids to fat (adipose) tissue for storage.
2. Very low‐density lipoproteins (VLDLs) transport triglycerides made in liver cells to adipose cells for storage. After depositing some of their triglycerides in adipose cells, VLDLs are converted to LDLs.
3. Low‐density lipoproteins (LDLs) carry 75% of total cholesterol in blood and deliver it to cells throughout body for use in repair of cell membranes and synthesis of steroid hormones and bile salts.
4. High‐density lipoproteins (HDLs) remove excess cholesterol from body cells and transport it to liver for elimination.
Therefore, regarding risk of atheroma development, high levels of LDL are thought of as “bad” cholesterol and HDL as good cholesterol.

Question 14

Fates of the three main energy sources

Answer 14

All three energy sources can be metabolised into the Krebs (Citric acid) cycle
Glucose is bodies first choice to use
If glucose levels insufficient, fats need to be used, liver may get overwhelmed by the amount of Acetyl coenzyme A and cause increased ketones in bloodstream- can smell on breath and positive in urine

Question 15

NUTRIENT ENERGY CONTENT

Answer 15

Carbohydrate 4 kcal/g * Protein 4 kcal/g
* Fat 9 kcal/g
* Alcohol 7 kcal/g

Question 16

Metabolism, anabolism & catabolism

Answer 16

Metabolism is all the chemical reactions of the body.
* Enzymes serve as catalysts to speed up chemical reactions.
* Some enzymes need a specific ion at their active site work e.g., calcium, iron, or zinc.
* Other enzymes work together with coenzymes, which function as temporary carriers of atoms being removed from or added to a substrate during a reaction. Many coenzymes are derived from vitamins. Examples include the coenzyme NAD+, derived from the B vitamin niacin.

Question 17

Metabolism, anabolism & catabolism

Answer 17

The body’s metabolism may be thought of as an energy‐balancing act between anabolic (synthesis) and catabolic (decomposition) reactions.
* Chemical reactions that combine simple substances into more complex molecules are known as anabolism and uses more energy than they produce. The “extra” energy is often derived from ATP conversion to ADP.
* The energy they use is supplied by catabolic reactions, which are used to generate ATP for ADP.

Question 18

Anabolism & catabolism

Answer 18

ATP acts as the energy battery

Question 19

Measuring Heat/energy utilisation

Answer 19

Heat is a form of energy that can be measured as temperature and expressed in units called calories.
* A calorie (cal) is amount of heat required to raise the temperature of 1 gram of water 1°C
* A kilocalorie (kcal) or Calorie (Cal) (always an uppercase C) is 1000 calories.

Question 20

Body Heat Production

Answer 20

Most of the heat produced by body comes from catabolism of food
* The rate at which this heat is produced, the metabolic rate, is measured
in kilocalories.
* The energy usage in a quiet, resting, and fasting condition called
the basal state.
* Basal metabolic rate (BMR). BMR is 1200 to 1800 Calories/day in adults
* The extra calorie requirement for normal activities like digestion and walking, range from 500 Calories for a small, relatively sedentary person to over 3000 Calories for people undertaking extreme exercise.

Question 21

Factors affecting metabolic rate

Answer 21

Exercise. During strenuous exercise metabolic rate increases by as much as 15 to 20 times BMR.
2. Hormones. Thyroid hormones are main regulators of BMR. Testosterone, insulin, and human growth hormone can increase metabolic rate by 5–15%.
3. Nervous system. During exercise or in stressful situation, Release of adrenalin and noradrenalin increases metabolic rate.
4. Body temperature. The higher the body temperature, the higher the metabolic rate. Therefore, energy usage is much higher in patients with fever.
5. Ingestion of food. Ingestion of food, especially proteins, raises metabolic rate 10– 20%.
6. Age. The metabolic rate of a child (on a per Kg basis) is much higher than an elderly person due to the high rates of growth‐related reactions in children.
7. Other factors. Other factors affecting metabolic rate are gender (lower in females, except during pregnancy and lactation), sleep (lower), and malnutrition (lower).

Question 22

Obesity

Answer 22

Common problem in developed countries
* Hormone leptin, produced by fat cells suppresses appetite. Not usually low in obese
individuals.
Complex reasons why obesity occurs. Includes: * Genetic factors,
* Eating habits taught early in life,
* Overeating to relieve tension
* Social customs.
* Energy density of food products
* Reduced energy expenditure
* Body setting of “normal levels” in childhood. * Microbiome may be different.

Question 23

Minerals

Answer 23

• Calcium: bones, teeth
• Phosphorus: bones teeth
• Potassium required for all cells special function in neural conduction, muscle contraction
• Sodium required for driving osmosis
• Iron: vital for haemaglobin
• Iodine: essential for thyroid hormone production
• Zinc: needed for many enzymes & for healin

Question 24

Fat soluble Vitamins

Answer 24

A in egg, milk, cheese, fish oils
- vital for pigment used in retina of eye, Immunity & cell growth
* D: animal fats, fish liver oils
- activated form produced by sunlight on skin and in kidneys: patients with
kidney disease may have bone problems -Increases calcium absorption for bone production
* E: nuts, egg yolks’. Acts as an anti-oxidant protecting lipid membranes.
* K- vegetable oils and green vegetables: important for making clotting factors in blood.

Question 25

Water soluble vitamins

Answer 25

B1 Thiamin
-Needed to allow complete aerobic release of energy from carbohydrates.
-Deficiency seen in people who have diets based on polished rice where husk (site of B1) has been removed Beri Beri
-Severe muscle wasting, nerve and infection problems
* B12 (Cobalamin)
-Mainly in food from animal.
-Absorption requires intrinsic factor to be produced by stomach. Binds to B12 and is adsorbed in last part of small intestine
-Deficiency causes anaemia and nerve injury

Question 26

Water soluble vitamins pt2

Answer 26

Folic acid Leafy vegetable, brown rice, nuts
-Needed for red cell production
-Important for foetus as brain develops folate deficiency increases risk of spina bifida: often prescribe iron & folate supplements in pregnancy
* Vitamin C fresh fruit, lemons oranges green vegetable -Deficiency: scurvy

Question 27

Non-starch polysaccharides (fibre)

Answer 27

Provides bulk to reduce appetite
* Stimulates peristalsis
* Attracts water increasing faecal bulk
* Protects against GI disorders such as diverticulosis and colorectal cancer

Question 28

Protein energy malnutrition

Answer 28

Inadequate intake of proteins, carbohydrates & fat. Marasmus. Starvation combined with long term gut infections
Kwashiokor when body has reduced blood protein levels (due to liver damage) Changes osmotic pressures in tissues and fluid accumulation

Question 29

Jaundice

Answer 29

Yellowing of skin and whites of eye due to inability to excrete bilirubin effectively.
* Caused by problems
* Before liver (Pre-hepatic) e.g., red blood cells are being destroyed quicker
than normal
* Liver injury (intrahepatic jaundice)
* Post-hepatic (drainage blocked) e.g., gallstones

Question 30

Tests of liver function

Answer 30

Blood levels of bilirubin
* Liver transaminase enzymes-hepatocyte damage marker
* Alkaline phosphatase and gamma-glutamyl transferase (gamma GT)- markers of bile duct blockage
* Total protein/albumin-how good the liver cells are at making proteins
* Blot clotting times- in severe injury, clotting factor production is
reduced
* Ultrasound-shows blockages, scarring

Question 31

Hepatitis

Answer 31

Hepatitis is an inflammation of liver caused by viruses, drugs, and chemicals, including alcohol.
Viral hepatitis:
* Hepatitis A caused by hepatitis A virus (HAV), spread via fecal contamination including food. Usually, mild. & no long-lasting effects. Vaccine is available.
* Hepatitis B caused by hepatitis B virus and is mainly spread via blood (passed on from mother to baby), by shared needles, blood transfusion or sexual contact. In some cases, virus survives for many years causing long term injury. Vaccine is available.
* Hepatitis C, caused by hepatitis C virus, is clinically similar to hepatitis B. Hepatitis C can cause cirrhosis and possibly liver cancer. In developed nations, donated blood is screened for the presence of hepatitis B and C.
* Hepatitis D is caused by hepatitis D virus (HDV). It is transmitted like hepatitis B.
* Hepatitis E is caused by hepatitis E virus and is spread like hepatitis A.

Question 32

Hepatitis-chemicals

Answer 32

Paracetamol overdose causes liver injury that is only seen several days after it has been taken
* Liver damage results not from paracetamol itself, but from one of
its metabolites that decreases liver’s glutathione and directly damages cells in the liver.
* Treatment is with acetylcysteine that replenishes depleted glutathione levels in liver. Most effective if given within 8-10 hours of overdose.

Question 33

Cirrhosis

Answer 33

This is long term injury of liver causing scarring and reduced ability of hepatocytes to work
* Viral hepatitis (B & C)
* XS alcohol (long term)
* Autoimmune
* Other less common causes

Question 34

Gall stones

Answer 34

Occur in about 10% of adults
Often cause no symptoms
May cause blockage of bile and pancreatic secretions

Question 35

Pancreatitis

Answer 35

Can be very severe
* Caused by gall stones, viruses, alcohol, unknown * Pancreas starts to digest itself