Nutrition in humans Flashcards
What is physical digestion and where does it take place?
It is the physical breakdown of large pieces of food into smaller pieces.
Locations:
- Mouth through chewing action by teeth
- Oesophagus throguh peristalsis
- Stomach through churning action
- Small intestine throguh emulsification by bile
What is chemical digestion and where does it take place?
It is the process whereby large and complex food substances are broken down into smaller and soluble substances.
Location
- Mouth (Starch)
- Stomach (Proteins)
- Small intestine (Carbohydrates, fats and proteins)
What happens at the mouth?
- Physical digestion
- Food is chewed with the help of teeth
- This increases their surface area to volume ratio and allows enzymes to digest them faster - Chemical digestion
- Starch is digested into maltose by salivary amylase (optimum ph=7)
Chemical equation: Starch -salivary amylase-> maltose
What happens in the oesophagus
- Physical digestion (peristalsis)
- Peristalsis is a rhythmic wave-like contraction of muscles of the wall
- To push the bolus forward - Circular muscles contract
- Longitudinal muscles relax
- Cause gut to be longer and narrower to squeeze the bolus forward
- Near the end of the bolus - Circular muscles relax
- Longitudinal muscles relax
- Cause gut to become shorter and wider which allows the bolus to
What happens in the stomach?
- Physical digestion
- Strong muscular walls and peristaltic action churn the food to break them up further
- Help the food mix with the gastric juice - Chemical digestion
Chemical equation: proteins -pepsin-> polypeptides
What does gastric juice produce and why?
Gastric glands in the walls of the pits secrete gastric juice which consists of hydrochloric acids and pepsin
Purpose of HCl
Kill microorganisms and parasites
Provide optimum pH for enzymes in the stomach
What happens in the pancreas
Chemical digestion (pancreatic juice)
- Transported to the small intestine via the pancreatic duct
- Contains pancreatic amylase, lipase and trypsinogen
- Pancreatic amylase (alkaline pH)
Chemical equation: Starch -amylase-> maltose - Lipase
Chemical equation: Fats → fatty acids + glycerol - Trypsinogen
Chemical equation: Tryopsinogen → trypsin
Chemical equation: Proteins -trypsin-> polypeptides
What happens in the liver?
Physical digestion
- Bile is produced by the liver and stored in the gall bladder
- Transported to the small intestine via the bile duct
- Bile is a substance to break up fat molecules into fat globules through a process known as emulsification
What is emulsification and how is it beneficial?
Emulsification is when fat molecules are broken up into fat globules.
benefit:
it increases the surface area of the fat molecules so they can be digested by lipase faster
What happens at the small intestine?
- Digestion is complete here
- Duodenum is where most of the digestion occurs
Chemical digestion (intestinal juice)
1. Maltase
Chemical equation: Maltose → glucose
2. Lipase
Chemical equation: Fats → fatty acids + glycerol
3. Protease
Chemical equation: Polypeptides → amino acids
What happens in the large intestine?
- Water and mineral salts are absorbed into the body
- Undigested food together with unabsorbed materials form faeces
- Faeces are expelled through the anus by a process called egestion
What are the adaptations and reasons for the absorption of food?
- Very long and folded
- To increase the surface area to volume ratio for efficient absorption to take place rapidly - Presence of villi and microvilli
- These protrusions in the intestinal wall further increase the surface area to volume ratio - Richly supplied with blood vessels to transport sugars and amino acids away from the small intestine
- As the food substances are transported away, a concentration gradient is maintained to facilitate diffusion - Contains lacteal which transports fats away from the small intestine
- A concentration gradient is maintained to facilitate diffusion
How does transportation and assimilation take place?
- After absorption into the bloodstream from the lumen of the small intestine, simple sugars and amino acids are transported to the liver by the hepatic portal vein
- Assimilation is a process where some of the absorbed food materials are converted into new protoplasm or used to provide energy
What happens to amino acids?
- Excess amino acids are broken down in the liver through a process called deamination
- In this process, they are converted into urea which is removed in urine
What are the functions of the liver?
- Metabolism of glucose
- Excess glucose is converted into glycogen - Metabolism of fats
- Liver is responsible for the production of bile which is stored in the gall bladder and released when required for the digestion of fats - Detoxification
- Enzymes in the liver can break down or transform substances like metabolic waste, drugs, alcohol and chemicals so that they can be excreted - Metabolism of proteins
- Excess amino acids undergo deamination to form urea for excretion
- Liver sunthesises plasma proteins from dietary amino acids which include albumins, glubulins and fibrinogen which are essential for blood clotting - Storage
- Liver stores vitamin A, D and K
- Worn out red blood cells are destroyed and their haemoglobin is sent to the liver which breaks down the haemoglobin and stores the iron released in the process
