5 | Nutrition in humans Flashcards
What are the 5 processes in nutrition in humans?
Ingestion
Digestion
Absorption
Assimilation
Egestion
What is ingestion?
Food taken into the body through the mouth
What is digestion?
large, insoluble, indiffusible food molecules are broken down into small, soluble, diffusible molecules that can be absorbed by the body cells.
What are the 2 types of digestion?
Physical digestion
Chemical digestion
What is physical digestion?
mechanical break up of food into smaller pieces to increase surface area to volume ratio to speed up enzyme action
What is chemical digestion?
process which involves the breaking of bonds in molecules which involves enzymes (involves reactions catalysed by digestive enzymes)
What is absorption?
products of digestion such as glucose and amino acids will be taken into the bloodstream through the wall of the ileum of the small intestine by processes active transport and diffusion
What is assimilation?
uptake of absorbed food substances into cells and tissues to be converted into new protoplasm or used to release energy
What is egestion?
Removal of undigested material from the body
Function of mouth in digestion
- Saliva is neutral (pH=7)
- Mucus in saliva lubricates the bolus for swallowing
Chemical digestion in mouth?
- Saliva contains salivary amylase which digests starch into maltose
- Optimum pH of salivary amylase is pH 7 so the saliva is neutral (pH=7)
Physical digestion in mouth?
- Chewing action of teeth breaks up food into small particles
– increase SA2VR - tongue mixes food with saliva
- salivary glands secrete saliva to soften the food.
What is the oesophagus?
Long narrow muscular tube, made up of longitudinal and circular muscles.
What do the longitudinal and circular muscles do?
Both sets of muscles work antagonistically (contract and relax alternately) to produce rhythmic wave-like contractions that push the food down the oesophagus into the stomach and the process is known as peristalsis.
Peristalsis in the oesophagus
To constrict the lumen, Circular muscles Contract, and longitudinal muscles relax
To dilate the lumen, circular muscles relax, and longitudinal muscles contract
Where does peristalsis occur?
Peristalsis occurs in the oesophagus, stomach, small and large intestines and rectum.
Chemical digestion in the oesophagus?
Starch digestion by salivary amylase in the bolus of food continues here and no enzymes are secreted here.
What is the stomach?
Thick muscular bag
Physical digestion in the stomach?
Peristalsis in the stomach churns, breaks up and mixes the food well with gastric juice.
- muscular and elastic stomach churns the food into smaller pieces to increase SA2VR
What does the stomach secrete?
gastric juice
What does gastric juice contain?
Dilute hydrochloric acid, pepsinogen, prorennin
Chemical digestion of stomach?
Pepsinogen –hydrochloric acid–> pepsin
proteins –pepsin–> polypeptides
What is the optimum pH of pepsin?
pH 2
What is the pH of hydrochloric acid?
pH 2
Function of hydrochloric acid?
- Kills harmful microorganisms in food such as bacteria
- Activates pepsinogen into pepsin, prorennin into rennin (to curdle milk for digestion)
- Provide optimum pH/acidic medium for optimal action of gastric enzymes
- denatures salivary amylase
Function of stomach other than digestion?
Storage of food, where the partly digested food particles becomes liquefied chyme
Physical digestion in duodenum
Peristalsis to churn, break up and mix the food well with digestive juices
Parts of small intestine (in order)
duodenum
jejunum
ileum
What does the duodenum receive and secrete?
receives bile and pancreatic juice
Secretes intestinal juice
Where is bile produced and stored?
How does the duodenum receive bile?
bile is produced by liver, and stored in gall bladder
duodenum receives bile via bile duct
What is bile?
- Bile has no enzymes, so it cannot digest food
- Bile salt speeds up fat digestion by lipase by emulsification of fats into small fat globules, which increases SA2VR for lipase to act on
What does intestinal juice contain?
maltose, peptidase, lipase
what does pancreatic juice contain?
pancreatic amylase, lipase, trypsin
pH of duodenum?
pH 8
what colour is bile?
yellowish green
Summary
notes
Functions of liver
BBRD
produces Bile
Breakdown of RBCs
Regulation of blood glucose
Detoxification
Functions of liver – produces bile
- Bile emulsifies fats into small fat globules which increases the SA2VR for lipase to work on
- This happens in the duodenum
- Bile is produced by the liver and temporarily stored in the gallbladder
Functions of liver – regulation of blood glucose
The liver plays a key role in carbohydrate metabolism by keeping the amt of glucose in the blood constant, esp aft a heavy meal or during fasting
How does the liver regulate blood glucose?
- Regulation of blood glucose levels by converting excess glucose into glycogen for storage in the liver or muscles, with the aid of insulin from pancreas
- Regulation of blood glucose levels by converting stored glycogen into glucose to be released into the bloodstream with the aid of glucagon from pancreas.
Functions of liver – detoxification
Liver enzymes detoxify (break down) harmful substances absorbed into the blood into harmless products
- breakdown of alcohol by alcohol dehydrogenase into acetaldehyde (excessive alcohol consumption will lead to liver cirrhosis)
- Acetaldehyde can be further broken down to compounds that can be used in respiration to provide energy for cell activities.
Functions of the liver – deamination
- Metabolism of AA & formation of urea
– deamination of excess AA to form urea - process by which amino groups are removed from AA and converted to urea
- excess AA transported to liver, deaminated and converted to urea and removed from body in urine
Function of liver – breakdown of RBCs
- Breakdown of RBC to form bile pigments from haemoglobin & iron released is stored
Physiological effects of alcohol
- Causes liver cirrhosis (tissue scarring)
- Increased risk of liver cancer
Neurological effects
- CNS depressant: slows some brain functions
- Signs of drunkenness
- Reduced inhibition and self control
- Frequent intake may lead to addiction
Signs of drunkenness
slower reaction time
lack of coordination
loss of balance
drowsiness
vision problems
Function of ileum?
Mainly for absorption
Adaptations of the ileum?
5
See pic in notes
SI –> small intestine
- SI is long and coiled
- Inner surface of the SI has numerous folds and folds have numerous villi
- Presence of microvilli on the epithelial cells
- Epithelium is one cell thick
- Richly supplied with blood capillaries and lacteal
How does long and coiled SI help with absorption?
Provide sufficient time for absorption of digested food substances via diffusion and active transport from the lumen of the SI into the bloodstream
Function of inner surface of the SI having numerous folds and folds having numerous villi / help with absorption?
Increase SA2VR for faster absorption of substances via diffusion and active transport from the lumen of the SI into the bloodstream
Function of presence of microvilli on the epithelial cells / how does it help with absorption?
Further increase SA2VR for faster absorption of digested food substances to take place via diffusion and active transport from the lumen of the SI into the bloodstream
Function of epithelium being one cell thick? / How does it help with absorption?
Provide shorter distance for absorption of digested food via diffusion and active transport from the lumen of the SI into the bloodstream
Function of SI being richly supplied with blood capillaries and lacteal? / How does it help with absorption?
Blood capillaries transport sugars and amino acids away. Lacteal transport fats away.
This continual transport of digested food substances maintains a steeper concentration gradient for faster absorption of digested food substances via diffusion and active transport to take place from the lumen of the SI into the bloodstream
Blood capillaries from the intestines merge to form the ___
hepatic portal vein
Function of hepatic portal vein?
Carries blood rich in absorbed nutrients (glucose and amino acids) from the SI to the liver
Liver in assimilation?
Liver serves as a “checkpoint” before the absorbed nutrients enter the rest of the bloodstream
Uses of glucose in the body?
- Provide energy for aerobic respiration (aka cellular respiration)
- Glucose + oxygen –> carbon dioxide + water+ energy
Uses of amino acids in the body?
- Build new protoplasm (cells)
- Synthesise proteins such as enzymes and hormones
Uses of fats in the body?
- synthesises cell surface membranes
- backup store of energy (2x more than carbohydrates)
What happens to excess fats?
- Form adipose tissues (around organs)
- Fatty deposits around the body
Does digestion take place in the large intestine (colon)?
No digestion takes place
Function of large intestine
Absorbs excess water (SI absorb most of the water, mineral salts and nutrients), vitamins and dissolved mineral salts from the undigested and the remaining undigested matter is known as faeces
Function of rectum?
- Stores faeces temporarily
- Contract to expel faeces through the anus (egestion)
