Nutrition in Man

Question 1

What is the alimentary canal?

Answer 1

It is a continuous tube: mouth, oesophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (colon, rectum), anus

Question 2

What are associated organs and state them

Answer 2

In digestive system, but not part of alimentary canal

Salivary glands, pancreas, gall bladder and liver

Question 3

What are the five functions of the digestive system?

Answer 3

Ingestion: intake of food at the mouth
Digestion: hydrolysis of large insoluble substances to small soluble substances at mouth oesophagus stomach duodenum jejunum
Absorption: movement of small soluble substances from lumen of small intestine to bloodstream
Assimilation: absorbed food molecules are used to create new protoplasm or used to release energy (growth and repair) at the liver
Egestion: removal of faeces (undigested food) from the rectum at the anus
(ill daisy ate an egg)

Question 4

What happens in the mouth + its other name

Answer 4

Physical digestion: chewing of food by teeth to physically break it down into smaller pieces with a larger SA:V ratio, allowing the enzyme salivary Amal use to digest starch more efficiently/quickly
Chemical digestion: salivary amylase catalyse the breakdown of starch into maltose, optimal conditions of the enzyme is 7.0 and 37°C

buccal cavity

Question 5

What do the salivary glands and tongue do?

Answer 5

The salivary glands secrete saliva which contains salivary amylase
Tongue mixed food with saliva and shapes it into boil (singular: bolus)

Question 6

What is the pharynx and epiglottis and what is its function?

Answer 6

The pharynx is the back of the throat, where both food and inhaled air must pass through (food bolus enters oesophagus, air enters larynx and trachea)
Epiglottis is a flap of tissue that functions to prevent swallowed food from entering the trachea (reject: wide pipe) by closing the opening of the trachea to prevent choking

Question 7

What is peristalsis?

Answer 7

Rhythmic wave-like contractions of the longitudinal and circular muscles that mix and move the contents of the alimentary canal

Question 8

What is the stomach and what happens in there?

What is chyme?

Answer 8

The stomach is a muscular bag that can be stretched or expanded, and it functions in temporary storage of food and digestion occurs here
Physical digestion happens due to peristalsis, breaking the food up into smaller pieces and mixing it with gastric juice
Chyme is food mixed with gastric juice
Chemical digestion occurs due to the gastric juice

Question 9

What is gastric juice composed of and what are its functions

Answer 9

It contains hydrochloric acid and the inactive pepsinogen.
Hydrochloric acid has five functions:
1. Kills bacteria ingested with food
2. Denatures proteins in food and causes them to unfold and lose their 3D conformation, exposing peptide bonds for protein digestion
3. Activates inactive pepsinogen to form active pepsin
4. Creates acidic environment for pepsin (protease enzyme that digests protein)
5. Denatures salivary amylase, stopping starch digestion

Pepsin catalysed the digestion of protein into polypeptides

Question 10

Why must pepsinogen be secreted instead of pepsin?

Answer 10

Pepsin would damage the cells that secrete it

Question 11

What is the small intestine and what does it do?

Answer 11

Digestion and absorption of food occurs here.
Made up of: the duodenum, jejunum, ileum
Most chemical digestion occurs at the duodenum (start), absorption occurs at the ileum (end), a mixture of both occurs at the jejunum (middle)

Question 12

What is secreted by the pancreas?

Answer 12

Pancreatic juice:
Trypsin (protease)
Pancreatic amylase (starch)
Pancreatic lipase (lipids)
Bicarbonate ions (neutralise acidic hcl in chyme, denatures pepsin and trypsin takes over)

Question 13

What are gall stones, and what are the effects of it? What should patients do after surgery to remove it?

Answer 13

Gall stones are solid material that form in the gall bladder, which may result in the bile duct being blocked and unable to secrete bile into the duodenum and jejunum of the small intestine during digestion
Fat digestion is not significantly affected, but no bile storage means it is constantly secreted into the duodenum by the liver and there may be insufficient bile secreted to digest a meal high in fat
Patients should adopt a low fat diet post surgery and eat frequent small meals

Question 14

What are the structural adaptations of the ileum that allow it to carry out absorption efficiently

Answer 14

Small intestine is very long (6m), increased SA for absorption
Small intestine has many folds on its surface
The presence of villus (finger-like projections)
Individual epithelial cells of the vilified contain microvilli
increase the SA:V ratio, enhancing absorption speed
Epithelium of the villi is one cell thick, decreasing diffusion distance and time taken for absorption
Rich network of capillaries, and presence of blood capillaries in lacteal in villi, so absorbed nutrients are quickly transported away from the digestive system, maintaining steep concentration gradient between lumen of the small intestine and its blood supply

Question 15

How are nutrients absorbed?

Answer 15

Via diffusion and active transport
Diffusion: for smaller molecules such as glycerol and fatty acids
Active transport: for larger molecules like glucose and amino acids

Capillaries in the villi combine to form the hepatic portal vein, which transport blood rich in nutrients from the small intestine towards the liver

Question 16

What is coeliac disease?

Answer 16

Autoimmune disease where the body attacks its own cells
The villi are attacked, smaller total surface area available in the small intestine for the absorption of nutrients, reducing small intestine’s ability to absorb nutrients

Symptoms include:
Weight loss
Fatigue
Abdominal pain and bloating
Slow growth in children

Question 17

What happens at the large intestine?

Answer 17

Absorption of water and mineral salts
No digestion
Most of it is absorbed in the small intestine
Faeces (reject: waste), which is undigested food, stored temporarily at the rectum and removed via the anus

Question 18

How do the muscles enable peristalsis?

Answer 18

The antagonistic circular and longitudinal muscles of the alimentary canal
CCC: contraction circular close
Circular inside, longitudinal outside

Question 19

What is the hepatic portal vein?

Answer 19

The blood capillaries in the villi of the small intestine merge to form the hepatic portal vein, which transports blood rich in nutrients from the small intestine to the liver

Question 20

Functions of the liver (assimilation)

Answer 20

1. Blood glucose regulation
   Carbohydrate store, excess glucose in the form of glycogen (insoluble)
2. Deamination of excess amino acids
   Converted into urea and transported dissolved in blood plasma from liver to kidneys and excreted as urine
3. Detoxification of toxins
   Converts toxic to harmless (alcohol into acetaldehyde and then acetate by alcohol dehydrogenase)
4. Fat digestion
   Liver produces bile which emulsifies (physical digestion of) fat
5. Breakdown of red blood cells
   Haemoglobin destroyed in liver (iron stored in liver, bile pigments formed)

Question 21

Effects of excessive consumptions of alcohol

Answer 21

Reduced self-control
Increases reaction time
Depressant
Damage to liver (liver cirrhosis)
Social implications

Question 22

What is the oesophagus and what happens there?

Answer 22

The oesophagus is a muscular tube that connects the pharynx to the stomach
Peristalsis occur in order to move the food bolus from the pharynx to the stomach and mix the contents (food and salivary amylase)
Chemical digestion of starch by salivary amylase (in food bolus) continues to take place at the pharynx and oesophagus

Question 23

What’s the word equation or the hydrolysis of lactose?

Answer 23

Lactose + water —(lactase)—> glucose + galactose (simple sugars)

Question 24

Suggest one impact of severe diarrhoea caused by lactose intolerance on human health

Answer 24

Dehydration and malnutrition

Question 25

Why are lipids the preferred energy storage molecules in the human body?

Answer 25

There is no limit to the amount of lipids that can be stored in the human body
Lipids have a higher energy density compared to carbohydrates
Lipids do not affect the water potential of the surrounding cells

Question 26

Describe the route taken and fate of excess amino acids

Answer 26

They are deaminated in the liver to form urea, and the urea is transported dissolved in the blood plasma from the liver to the kidneys, where urea is excreted from the body in the form of urine

Question 27

What is secreted by the small intestine?

Answer 27

Intestinal juice:
Peptidase (protease)
Maltose (maltose to glucose)
Sucrose (sucrose to glucose)
Lactase (lactose to glucose)
Intestinal lipase (lipids)

Question 28

What is bile and what does it do?

Answer 28

Bile (produced by liver and temporarily stored in gall bladder released via bile duct, not an enzyme):
Emulsifies fats, physical digestion

Question 29

What substances are digested in the mouth, stomach and small intestine?

Answer 29

Mouth: starch to maltose (salivary amylase)
Stomach: proteins (pepsin)
Small intestine:
Starch to maltose (pancreatic amylase)
Lipids (pancreatic and intestinal lipase)
Protein (pancreatic trypsin and intestinal peptidase)
Sucrose, maltose, lactose

Question 30

How are substances transported away from villi?

Answer 30

Glycerol and fatty acids via diffusion, lacteal

Glucose and amino acids via active transport, blood capillaries

Question 31

Difference between hepatic portal vein and hepatic vein

Answer 31

Hepatic portal vein: from ileum to liver, formed by blood vessels of villi merging
Hepatic vein: liver to heart

Question 32

Pathway of food from buccal cavity to anus

Answer 32

Mouth, pharynx, oesophagus, stomach, duodenum, jejunum, ileum, colon, rectum, anus