Chapter 5 biology

Nutrition

The process by which organisms obtain food and energy for growth, repair and maintenance of the body

Peristalsis

The rhythmic, wave-like muscular contractions in the wall of the alimentary canal

Process of peristalsis

1. When the circular muscles contract, the longitudinal muscles relax.

2. The gut constricts, making it narrower and longer causing food to be squeezed and pushed forward

3. When the longitudinal muscles contract, the circular muscles relax

4. The gut dilates, becoming wider and shorter which widens the lumen for the food to enter

Digestion

Process whereby large food molecules are broken down into smaller, soluble molecules that can be absorbed into the body cells

Mouth digestion

1. Food in the mouth stimulates the salivary glands to secrete saliva

2. Saliva mixes with the food to soften it

3. Salivary amylase is released which digests starch to maltose and has an optimum temperature of 7

4. Chewing breaks the food up into smaller pieces to increase surface area-to-volume ratio for the salivary amylase to work on

5. The tongue rolls the food into boli to be swallowed and passed down into the oesophagus

6. Peristalsis in the walls of the oesophagus pushes each bolus of food down the stomach

Stomach processes

1. The presence of food in the stomach stimulates the gastric glands to secrete gastric juice into the stomach cavity

2. Peristalsis in the stomach wall churns and breaks up food and mixes the food with gastric juice

3. The mucus layer protects the stomach wall against being digested by the enzyme it produces and moistens the food to allow easy movement within the stomach

4. Food normally remains in the stomach for about three to four hours making it become liquefied, forming chyme

5. Chyme passes in small amounts into the duodenum when the pyloric sphincter relaxes and opens

Gastric juice

• Contains hydrochloric acid

• Stops the action of salivary amylase by denaturing it

• Provides a low pH environment within the stomach for protease to digest proteins optimally

• Kills certain potentially harmful microorganisms in food

• Stomach protease digests proteins polypeptides

Small intestine processes

1. Chyme enters the duodenum which stimulates the pancreas to secrete pancreatic juice

2. The pancreatic juice passes through the pancreatic duct into the duodenum

3. Pancreatic juice contains the enzymes pancreatic amylase, protease and pancreatic lipase

4. Gall bladder releases bile

5. Bile passes through the bile duct into the duodenum

6. Bile does not contain enzymes so it cannot digest food, but bile salts speed up the digestion of fats

7. Epithelial cells in the small intestine produce the enzymes maltease,protease and lipase

Food now comes into contact with pancreatic juice, bile and intestinal juice. The three fluids are alkalis which neutralise the acidic chyme and provides a suitable alkaline medium(ph8) for the action of the pancreatic and intestinal enzymes

Carbohydrate digestion

1. In the mouth, salivary amylase digests starch into maltose. (little starch)

2. No digestion of carbohydrates occurs in the stomach

3. When carbohydrates enter the small intestine, they are fully digested into simple sugars

Protein digestion

1. Protein digestion begins in the stomach where stomach protease digests proteins to polypeptodes

2. The undigested proteins that enter the small intestine are digested by intestinal protease to polypeptides

3. The polypeptides produced are further digested to amino acids by intestinal protease

Fat digestion

1. Bile produced by the liver is released onto the duodenum

2. Bile salts emulsify fats by lowering the surface tension of the fats by reducing the attractive forces between the fat molecules

3. This causes the fat globules to break into tiny fat droplets

4. Emulsification occurs and increases surface area-to-volume ratio of the fats for speeding up rate of digestion by lipase

5. Fats are digested by lipase to fatty acids and glycerol

Absorption

Process whereby digested food substances are absorbed into the body cells

Small Intestine Adaptations

• Inner surface of the ileum is folded extensively and has numerous minute finger-like projections called villi to increase surface area for absorption

• Epithelium is only one cell thick to provide a short diffusion distance for nutrients to pass through

• Cells of the epithelium have many microvilli to further increase the surface area of the small intestine

• Each villus has many microvilli to further increase surface area of the small intestine

• Villus has many blood capillaries that allow the blood to transport the absorbed glucose and amino acids fast in order to maintain a steep diffusion gradient

• Villus contains a lacteal to transport the absorbed fats away and maintain a steep diffusion gradient

• Epithelial cells contain many mitochondria to provide energy for active transport of nutrients into the villi

Absorption in the intestines

• Glucose and amino acids are absorbed by diffusion into the blood capillaries of the villi

• Glucose and amino acids are also absorbed by active transport when there is a lower concentration of digested food substances in the lumen than the blood capillaries

• Glycerol and fatty acids diffuse into the epithelium to form minute fat globules that enter the lacteal

Undigested and unabsorbed food

They are stored temporarily in the rectum before it is discharged as faeces through the anus in a process called egestion

Assimilation

Process whereby some of the absorbed nutrients are converted into new cytoplasm or used to provide energy

Glucose and amino acids transportation and utilisation

1. Glucose is assimilated and then broken down during tissue respiration to release energy for the vital activities of the cells

2. Excess glucose is returned to the liver and stored as glycogen

3. Hormone called insulin which is produced by the islets of Langerhans in the pancreas, stimulates the liver cells to convert excess glucose to glycogen.

4. When the body needs energy, the liver converts the stored glycogen back into glucose and is transported by the blood to the cells

5. Amino acids that enter the cells are converted into new cytoplasm that is used for growth and repair of worn-out parts of the body

6. Excess amino acids are deaminated in the liver

Fats Transportation

1. Fats are absorbed into the lymphatic capillaries and to the lymphatic vessels, that discharges fats into the bloodstream

2. Blood carries the fats to all parts of the body

Fats utilisation

• Under normal conditions when there is a sufficient supply of glucose, fats are not broken down and but used as storage and formation of new protoplasm

• When glucose is in short supply, fats are broken down to provide energy instead

• Excess fats stored as adipose tissues can protect organs by acting as shock absorbers

Deamination

The process by which amino groups are removed from amino acids and converted to urea

Remains of the deaminated amino acids are converted into glucose in the liver and any excess glucose formed is converted to glucagon

Regulation of blood glucose concentration Liver

1. The liver regulates blood glucose concentration through the actions of two hormones secreted by the pancreas: insulin and glucagon produced by the islets of Langerhans.

2. When blood glucose levels are high, such as after a meal, insulin is released and stimulates the liver to convert excess glucose into glycogen for storage, lowering the blood glucose level.

3. When blood glucose levels are low, such as during fasting or after exercise, glucagon is released and stimulates the liver to break down glycogen into glucose, which is then released into the bloodstream, raising the blood glucose level.

4. This hormonal regulation helps maintain a stable internal environment, a process known as homeostasis.

Liver functions

• Breakdown of hormones

• Deamination of amino acids

• Regulation of blood glucose concentration

• Detoxification

• Production of bile

Effects of alcohol consumption

• Liver cirrhosis

• Reduced self-control

• Increased reaction time

• Shrinking of brain

• Violent behaviour

• May neglect work and families