Chapter 05 - Nutrition in Humans Flashcards
Define nutrition
A process by which organisms obtain food and energy for growth, repair and maintenance of the body
What are 5 processes in digestion?
1) Ingestion
2) Digestion
3) Absorption
4) Assimilation
5) Egestion
What is the main function of the digestive system?
Break down large and complex food substances into simpler and smaller food substances
What are the 2 types of digestion?
Physical and chemical
What is physical digestion?
A mechanical breakdown of large pieces of food into smaller pieces, and the identities of food substances remain unchanged, so no new products formed
Why is physical digestion important?
Physical digestion increases surface area to volume ratio
Where does physical digestion occur?
Mouth - chewing
Stomach - churning
Small intestine - emulsification
What is chemical digestion?
It is a process whereby large and complex food substances are broken down into smaller, soluble, simple substances and identities of food substances change, so new products are formed
Why is chemical digestion important?
To allow food substances to enter bloodstream through the intestinal wall
Where does chemical digestion occur?
Mouth - Starch
Stomach - Proteins
Small intestine - Carbohydrates, Proteins, Fats
What is the human digestive system made up of?
Alimentary canal and the associated organs (pancreas, liver, gall bladder)
What are the 3 main actions along the alimentary canal?
1) Peristalsis moves food along gut
2) Mucus along gut acts as a lubricant
3) Digestion takes place outside living cells within the gut
What is the function of associated organs?
Secrete substances involved in digestion
Where is food received into the human body?
The mouth
What is the intake of food known as?
Ingestion
What is ingestion?
The process of taking food and other substances into the body
What glands does the mouth contain?
Salivary glands which produce saliva which consists of salivary amylase which digests starch into maltose
What is a gland?
A gland is a structure that produces and secretes a chemical substance
What does the tongue do?
The tongue mixes food with salivary amylase in the mouth, rolls the food into a bolus and moves the food to the back of the mouth for swallowing
What pH does saliva provide?
Saliva in the mouth provides the optimum pH at 7 (neutral) for salivary amylase to function effectively
What does the teeth do?
Food is chewed by teeth to cut and grind them into smaller pieces to increase surface area to volume ratio allowing enzymes to digest them faster
What connects the buccal cavity to oesophagus and the larynx?
The pharynx. Food travels from the buccal cavity to the oesophagus via the pharynx
What is the structure of the oesophagus?
A narrow muscular tube leading to the stomach
What process occurs to move food from the oesophagus to the stomach?
Peristalsis
What is peristalsis?
Peristalsis is a rhythmic, wave-like contraction of muscles of the wall of the alimentary canal
What muscles do the walls of the oesophagus consists of?
Circular and longitudinal muscles
What kind of muscles are the muscles in the walls of the oesophagus?
Antagonistic muscles, which means that when one contracts, the other relaxes (e.g. when circular muscles contract, longitudinal muscles relax)
What is the purpose of the alternating waves of contraction and relaxation in the muscles of the alimentary canal?
To push food along the canal
What happens to push the bolus forward at one end?
The circular muscles contract while longitudinal muscles relax causing he wall of the alimentary canal to constrict and become longer and narrower to squeeze the bolus forward
What happens near the other end of the bolus?
The circular muscles relax while the longitudinal muscles contract causing the wall of the alimentary to dilate and become shorter and wider, the wider lumen allows the bolus to move to a new position
Stomach acts as a food ____ which can hold food for a few hours
storage
What forms in the stomach after protein digestion?
Protein digestion occurs in the stomach to form chyme, a thin watery liquid consisting of partially digested food
Strong muscular walls and peristalsis ____ the food and brings it into close contact with ____ ____
churns, gastric juices
What does the inner surface of the stomach wall have?
Gastric pits which lead to gastric glands
What do gastric glands secrete?
Gastric glands secrete gastric juices which contains mucus, hydrochloric acid and enzyme pepsin (protease)
What are the 3 functions of the hydrochloric acid in the stomach?
1) Provides an acidic environment (pH=2) in the stomach which is the optimum pH for enzyme protease to function efficiently
2) Hydrochloric acid kills harmful microorganisms in food
3) Hydrochloric acid stops the action of salivary amylase by denaturing it
What are the 2 functions of the mucus in the stomach?
1) Forms a protective barrier that prevents the digestive enzymes produced by the stomach from digesting the stomach wall
2) Moistens food so that it can move through the stomach easily
How long does food remain in the stomach?
3 to 4 hours
What happens to partly digested food in the stomach?
It becomes liquefied to form chyme which passes on into the duodenum
What type of physical digestion happens in the stomach?
Churning caused by peristalsis of the muscular wall breaks up food further into smaller pieces to increase the surface area to volume ratio and mixes food with gastric juices
What enzyme is in the stomach?
Protease which breaks down proteins into polypeptides
What are the 2 parts to the small intestine?
U-shaped duodenum, where most digestion occurs, and the coiled ileum, where absorption of digested food occurs
What are the main three sections in the small intestine?
1) Pancreatic juice secreted by pancreas containing pancreatic amylase, protease and pancreatic lipase
2) Intestinal juice secreted by glands in the lining of the intestinal walls, which contains maltase, protease and lipase
3) Bile produced by liver, stored in gall bladder
When the chyme enters the duodenum, what does it stimulate?
1) The pancreas to secrete pancreatic juice, which passes through the pancreatic duct into the duodenum
2) The glands in the lining of the small intestine to secrete intestinal juice containing maltase, lipase and protease
3) The gall bladder to release bile containing bile salts
Are pancreatic juice, intestinal juice and bile acidic or alkaline?
Alkaline, they help to provide a suitable alkaline medium for optimum enzyme action
What is absorbed into the small intestine?
Water and food substances
What organ produces bile?
Liver
What transports bile into the duodenum?
Bile duct
What process occurs due to bile and what does it do?
Emulsification lowers surface tension of fats by reducing the attractive forces between the fat molecules causing fats to break into tiny fat droplets suspended in water, forming an emulsion. Emulsification is the breaking up of fats into tiny fat droplets
What does emulsification increase?
Emulsification increases surface area to volume ratio of fat molecules to be digested by pancreatic and intestinal lipase faster
What does pancreatic amylase digest?
Starch into maltose
What does lipase in the pancreatic juice digest?
Fats into fatty acids + glycerol
What does protease in the pancreatic juice digest?
Proteins into polypeptides
What does maltase in the intestinal juice digest?
Maltose into glucose
What does lipase in the intestinal juice digest?
Fats into fatty acids + glycerol
What does protease in the intestinal juice digest?
Polypeptides into amino acids
What are the 3 parts the large intestine consist of?
The large intestine has an average length of about 1.5m consisting of the colon, rectum and anus
What does the colon do?
Absorb water and mineral salts from the undigested food into the body
What forms faeces?
Unabsorbed materials and undigested food
Where is faeces stored temporarily?
In the rectum
Where is faeces expelled through and what is the process known as?
Faeces is expelled through the anus by a process known as egestion
Is egestion of faeces considered excretion?
No, faeces is not a metabolic waste product resulting from chemical reactions that occur withing body cells, so its removal from the body is not considered excretion
What are the 3 blood vessels attached to the liver?
1) Hepatic vein
2) Hepatic portal vein
3) Hepatic artery
What do liver cells produce and secrete
An alkaline, greenish-yellow liquid known as bile containing bile salts
Does bile contain enzymes?
No, it does not so no chemical digestion happens in the liver
Which organ stores bile temporarily?
Gall bladder
What happens when the gall bladder contracts?
The gall bladder releases bile into the duodenum via bile duct
What organ is connected to the duodenum by the pancreatic duct?
Pancreas
What does pancreas produce?
Pancreatic juices which contain pancreatic amylase, lipase and protease
What hormones does pancreas secrete?
Insulin and glucagon which are essential in controlling blood glucose level in the body
What is absorption?
The process by which digested food materials are taken into body cells
Which part of the small intestine specifically absorbs digested food?
The villi of the illeum
What does the process of digestion in the illeum produce?
Simple food substances such as simple suars (glucose, fructose, galactose), amino acids, fatty acids, glycerol
What are the folds in the intestinal wall of the illeum called?
Villi
What does villi increase?
Villi increases surface area to volume ratio for faster nutrient aborption
Why are the walls of the villi one cell thick?
Because they are covered by only one layer of epithelial cells which has tinier projections to called microvilli to further increase surface area to volume ratio for faster nutrient absorption and also to reduce diffusion distance for digested food to pass through quicker
Each villus had a lymphatic vessel known as the ____
Lacteal
Each villus has a network _____ _____ ____
Each villus has a network of blood capillaries
What are intestinal walls and villi rich supplied with to transport sugars and amino acids away from the small intestine?
Blood vessels, so that as food substances are transported away, a concentration gradient is maintained to allow for more diffusion
What do lacteals do?
They transport fats away from the small intestine to create a concentration gradient to allow for more diffusion
Why are there many mitochondria in the epithelial cells?
To provide energy for active transport of nutrients into the villi
Simple sugars and amino acids are taken up by the blood capillaries through ____ and sometimes ____ during absorption
Diffusion, active transport
When does active transport occur during absorption?
When the concentration of these food substances in the small intestine is lower than the concentration in the blood capillaries, allowing them to be absorbed against their concentration gradient with the use of energy
When simple food substances are absorbed, they are carried which vein to the liver before being distributed to the rest of the body?
Hepatic portal vein
What is the path of the simple sugars and amino acids?
Diffusion of simple sugars and amino acids through the walls of the villi —> Blood capillaries —> Hepatic portal vein —> Liver
Where do fatty acids and glycerol diffuse into?
The epithelium of the villus, then they recombine to form tiny fat droplets
Where do fat droplets enter?
The lacteals
What do lacteals merge to form?
Larger lymphatic vessels that transport fat droplets away from the small intestine and empty into the bloodstream
Where are fat droplets transported to after lacteals and what happens there?
Fat droplets are transported to the liver where they are further processed for distribution to the rest of the body
After absorption of simple sugars and amino acids from the small intestine lumen, the blood capillaries converge to form which vein?
Hepatic portal vein which carries these nutrients to the liver
What are the 2 conversions happening in the liver?
Excess glucose —> glycogen (stored)
Excess amino acids —> urea (excreted)
The remaining nutrients distributed to body cells
What is assimilation?
Assimilation is a process where some of the absorbed food materials are converted into new cytoplasm or used to provide energy
When glucose molecules leave the liver and are transported to body cells, what happens to the molecules?
They are broken down during tissue respiration to release energy for cellular activities, excess glucose is transported back to the liver for storage as glycogen
What stimulates the conversion of excess glucose into glycogen?
Insulin - a hormone produced by the islets of Langerhans in the pancreas
What happens when the body requires more energy?
The liver converts the glycogen back into glucose
What stimulates the conversion of glycogen into glucose?
Glucagon - a hormone produced in pancreas
What happens to amino acids are transported to the liver from the small intestine by the hepatic portal vein?
They are converted into new cytoplasm used for growth, repair of tissues or form enzymes and hormones
What happens to excess amino acids in the liver?
They are broken down through deamination. Amino groups of excess amino acids are converted into urea, then removed in urine
What happens to the remaining deaminated amino acids?
They are converted into glucose in the liver. When the glucose is excess it converts into glycogen
What are the specialised lymphatic vessels that absorb fats?
Lacteals that join together to form larger lymphatic vessels
What do the larger lymphatic vessels do?
Empty fat droplets into the bloodstream
Where are fats transported to?
Fats are transported throughout the body, including the liver where they are broken down or stored
How are fats used? (3 ways)
1) When there is an adequate supply of glucose, fats are used to build protoplasm
2) When glucose is short in supply, such as during fasting, can be broken down to provide energy for body’s vital functions
3) Excess fats are stored in adipose tissues, which can be found beneath the skin around certain organs (heart, kidneys) to protect them from injury
How does liver help in regulating blood glucose concentration?
The blood glucose concentration is maintained at normal level with the help of hormones insulin and glucagon secreted by the islets of Langerhans in the pancreas
What happens when blood glucose concentration rises above normal?
Pancreas releases hormone insulin to stimulate the liver to convert the glucose into glycogen for storage
What happens when blood glucose concentration falls below normal?
Pancreas releases hormone glucagon to stimulate the liver to convert the glycogen into glucose for release into bloodstream
What does the liver produce?
Bile, which is stored in the gall bladder and released when required for digestion of fats
What happens when deamination occurs in the liver?
Amino groups are removed from the amino acids and converted to urea for removal in urine
Does the liver detoxify substances?
Enzymes in the liver cells can convert harmful substances into harmless substances like metabolic waste, drugs, alcohol and chemicals into harmless substances so that they can be excreted
What happens to hormones after they fulfilled their purpose?
They are broken down in the liver
What harmful effects does excessive alcohol consumption have on the digestive system?
1) Alcohol can increase acid secretion in the stomach leading to high risk of gastric ulcer
2) Cirrhosis, a disease in which the liver cells are destroyed and replaced with fibrous tissue causing liver to gradually lose its ability to function efficiently
What does cirrhosis increase the risk of?
Haemorrhage (heavy bleeding) which leads to liver failure or death
What harmful effect does excessive alcohol consumption have on the nervous system as a depressant?
Alcohol is a depressant as it slows down some brain functions
What harmful effects does excessive alcohol consumption have on the nervous system for reduced self control?
Reduction in self control and become carefree, which can lead to regrettable actions once the effects wear off
What harmful long term effects does excessive alcohol consumption have on the nervous system?
1) A form of dementia caused by brain damage due to alcohol absorbing vitamin B1 in the small intestine which is crucial for breaking down sugar to fuel brain activities
2) Brain volume shrinks affecting memory and reasoning
3) Heavy consumption of alcohol during pregnancy can lead to fetal brain development
What social implications does excessive alcohol consumption have?
1) Absent form work more frequently - affects work performance, reduces productivity
2) Bringing mental health problems to family members (e.g. depression, anxiety)
3) Committing crimes
