Human digestive system Flashcards
Define nutrition
Nutrition is the process by which organisms obtain food and energy for growth, repair and maintenance of the body
Define digestion
Digestion is the process that breaks down complex food substances into simple, soluble molecules that are small enough to be absorbed into body cells
Where does food digestion take place
Alimentary canal
Define physical digestion
Physical digestion is the mechanical breakdown of food into smaller particles to increase surface area to volume ratio for faster rate of chemical digestion
Define chemical digestion
Chemical digestion is the breakdown of large food molecules into small soluble molecules catalysed by digestive enzymes through hydrolytic reactions
What is ingestion
The act of taking food into the mouth
What is the optimum pH in the mouth
6.5-7.5
What glands and enzymes are present in the mouth
Salivary gland
- Salivary amylase
What enzyme actions occur in the mouth
- Starch > Maltose (Amylase)
What is peristalsis
Rhythmic, wave-like, muscular contractions of the oesophagus
What does gastric juice contain
- HCl
- Pepsin
What is the purpose of HCl in the stomach
- Provides acidic medium suitable for stomach enzymes
- Kills bacteria in food
- Denatures salivary amylase
- Converts inactive forms of enzymes to active forms (pepsinogen > pepsin)
What glands and enzymes does the stomach contain
Gastric gland
- Pepsin
What enzyme actions occur in the stomach
Proteins > Polypeptides (Pepsin)
What are the glands and enzymes in the small intestine
Pancreas
- Pancreatic amylase
- Pancreatic lipase
- Trypsin
Intestinal gland
- Maltase
- Sucrase
- Lactase
- Intestinal lipase
- Peptidase
What is the optimal pH in the stomach
2
Are the liver, gall bladder and pancreas part of the alimentary canal
NO
What are the features and functions of bile
- Alkaline greenish-yellow liquid
- Does not contain digestive enzymes
- Emulsifies fats, which physically breaks them down to increase surface area to volume ratio for faster digestion by lipase
- Creates alkaline environment suitable for enzymes
- Contains bile salts
- Contains bile pigments
Describe digestion of food in the stomach
- Stomach is a muscular elastic bag
- Food is churned and mixed with gastric juice by peristaltic stomach contractions
- Partly digested food becomes liquefied, forming chyme
- Chyme passes into small intestine
What does the small intestine consist of
- Duodenum
- Jejunum
- Ileum
What does the liver produce
Bile
What enzyme actions occur in the small intestine
- Starch > Maltose (Amylase)
- Emulsified fats > Fatty acids + Glycerol (Lipase)
- Proteins > Polypeptides (Trypsin)
- Maltose > Glucose (Maltase)
- Sucrose > Glucose+Fructose (Sucrase)
- Lactose > Glucose+Galactose (Lactase)
- Polypeptides > Amino acids (Peptidase)
What is the optimum pH in small intestine
8.5
Describe digestion in the small intestine
- Duodenum receives chyme from stomach and secretions from glands
- Digestion takes place in the duodenum
By the end of digestion, - All carbohydrates digested to monosaccharides
- All fats digested to fatty acids and glycerol
- All proteins digested to amino acids
What enzymes does pancreatic juice contain
- Pancreatic amylase
- Pancreatic lipase
- Trypsin
What enzymes does intestinal juice contain
- Maltase
- Lactase
- Sucrase
- Intestinal lipase
- Peptidase
What are the adaptations of the small intestine for absorption
Long
- Provides sufficient time for absorption of materials
Inner walls have many transverse folds with villi, each villi made up of many microvilli
- Increases SA:V ratio for faster absorption of digested substances by diffusion
Epithelium of villus is one cell thick
- Decrease distance for digested substances to diffuse over, increases rate of absorption
Consists of a dense network of blood capillaries
- Continuous transport of digested substances maintains steep concentration gradient for faster absorption
How are glucose and amino acids absorbed at small intestine
- Glucose and amino acids are absorbed by facilitated diffusion into blood capillaries
- Also absorbed by active transport when blood capillaries have higher concentration of glucose and amino acids than intestinal lumen
- Blood capillaries join to form venules
- Venules join to form the hepatic portal vein, which carries mainly glucose and amino acids to liver to be processed
How are fatty acids and glycerol absorbed at the small intestine
- Fatty acids and glycerol diffuse into epithelial cells
- They then recombine and form minute fat globules before diffusing into lacteal
- fat globules transported away by lacteal
Define assimilation
Assimilation is the utilisation of absorbed nutrients and how the body deals with excess nutrients
Describe assimilation of glucose
- Glucose is a substrate for respiration
- Pancreas produces insulin, which stimulates liver to stimulate conversion of excess glucose to glycogen
- Pancreas produces glucagon when blood glucose levels are low to stimulate conversion of glycogen to glucose
Describe assimilation of amino acids
- Excess amino acids are deaminated in the liver
- Their amino group is removed and converted into urea
- Remaining carbon residue is converted to glucose
Describe assimilation of lipids
- Excess fats are stored in adipose tissue under the skin
- Fat droplets collect in cytoplasm of adipose cells
Describe what happens after absorption in small intestine
- Undigested and unabsorbed matter enters large intestine
- Movement of undigested materials along large intestine is by peristalsis
- Large intestine absorbed most of the water and mineral salts into bloodstream
- Results in the formation of faeces
- Mucus secreted by large intestine binds faeces together
- Faeces temporarily stored in rectum
- Once it accumulates, rectal wall contracts to egest faeces
What are the functions of the liver
- Bile production
- Blood glucose regulation
- Protein synthesis
(Riobosomes in liver synthesise plasma proteins) - Deamination of excess amino acids
- Breakdown of red blood cells
(Liver breaks down haemoglobin and stores released iron) - Detoxification
(Liver produces alcohol dehydrogenase that breaks down alcohol to acetaldehyde, which can be broken down further to glucose)
(Hydrogen peroxide is also broken down into water and oxygen by enzyme catalase in liver)
What are some effects of excessive alcohol consumption
- Depresses motor centre of brain, resulting in longer reaction times
- Affects area of cerebrum, resulting in reduced self-control
- Leads to cirrhosis of liver, where liver cells are destroyed and replaced with fibrous scar tissue, increasing chances of liver failure
