Nutrition in Humans Flashcards
what is nutrition
intake of food and processes that convert food substances into living matter
describe the 5 processes in human nutrition
- ingestion: intake of food into body
- digestion: breaking down of large food molecules into smaller soluble and diffusible molecules that can be absorbed into body cells
- absorption: taking up of small molecules (e.g. simple sugars/amino acids) by body cells from digestive tract
- assimilation: conversion of absorbed food molecules to new protoplasm/used to provide energy
- egestion: undigested food removed from body
describe chewing in the mouth (3 points)
- teeth cut and grind to break up food for easier swallowing and increasing surface-area-to-volume ratio for digestive juices containing enzymes to act efficiently
- presence of food in mouth triggers a reflex, causing salivary glands to secrete saliva
- tongue tastes food and manipulates it during chewing, shapes food into a ball (bolus), during swallowing, tongue pushes bolus back into pharynx
what does saliva contain (4 points)
- salivary amylase: starch > maltose (optimum pH 7)
- mucin: protects soft lining of mouth from abrasions, lubricates food for easier swallowing
- buffers: prevent tooth decay by neutralising acid in mouth
- antibacterial agents: kill bacteria that enter mouth with food
what is peristalsis
rhythmic, wave-like contractions by smooth muscles in wall of alimentary canal
what is the function of the oesophagus
conducts food form pharynx down to stomach by peristalsis
describe the antagonistic relationship between the walls of the oesophagus (2 points)
- circular contracts, longitudinal relaxes — wall contricts, becomes narrower and longer
- longitudinal contracts, circular relaxes — wall dilates, becomes wider and shorter
what does gastric juice contain (2 points, 4/2 subpoints)
- dilute solution of HCl
- stops action of salivary amylase by denaturation
- kills most bacteria swallowed with food
- provides acidic environment for gastric enzymes to work
- converts inactive forms of enzymes into active forms (pepsinogen to pepsin, prorennin into rennin)
- pepsin (optimum pH 2)
- protease that breaks down protein into polypeptides
- released into lumen as pepsinogen
briefly describe digestion in the stomach
churning action (peristalsis) by smooth muscles of stomach wall mixes food with gastric juice into chyme
what does pancreatic juice contain (3 points)
- pancreatic amylase (starch > maltose)
- pancreatic lipase (fats > fatty acids + glycerol)
- pancreatic protease (trypsin) (protein > polypeptides)
what is secreted OR released into the duodenum (4 points)
- intestinal juice
- pancreatic juice
- bile
- chyme
what does intestinal juice contain (3 points)
- intestinal carbohydrase (maltase) (maltose > glucose)
- intestinal protease (polypeptides > amino acids)
- intestinal lipase (fats > fatty acids + glycerol)
what does bile contain (2 points)
- bile salts: emulsifies and break up big fat globules into tiny fat droplets that form stable emulsion in water (emulsification)
*emulsification greatly increases surface-area-to-volume ratio of fats for digestion by pancreatic and intestinal lipase
- bile pigments: by-product of red blood cell destruction in liver, removed with faeces
what are 6 adaptations of the small intestine
1) inner surface has numerous finger-like projections (villi)
- increases surface area for absorption
2) epithelium of villus is one-cell thick
- provides short diffusion distance for nutrients to pass through
3) cells of epithelium has many microvilli
- further increases surface area for absorption
4) each villus has many blood capillaries
- capillaries allow blood to transport absorbed glucose & amino acids away to maintain diffusion gradient
5) each villus contains a lacteal
- allows transport of absorbed fats away to maintain steep diffusion gradient
6) epithelial cells contain many mitochondria
- mitochondria provide energy for active transport of nutrients into villi
how are digested food absorbed (2 points)
- glucose & amino acids — diffusion + active transport into blood capillaries of villi
- glycerol & fatty acids — diffuse into epithelium, combines to form minute fat globules that enter lacteals
how is glucose assimilated (3 points)
- most are converted into glycogen and stored in the liver
- some transported by blood leaving liver, distributed around body to be used for energy during cell respiration
- excess glucose then transported back to liver and stored as glycogen for future use
how are amino acids assimilated (3 points)
- those that enter cells are converted into new cytoplasm used for growth and repair of worn-out parts of the body
- used to form enzymes and hormones
- excess AAs’ amino groups are removed and converted into urea in liver (deamination)
*urea removed from body in urine
*remains of deaminated AAs converted into glucose in liver
how are fats assimilated (5 points)
- absorbed into lymphatic capillaries (lacteal) which join to form larger lymphatic vessels, which discharge fats into bloodstream
- blood carries fats to all parts of body, especially liver
- enough glucose: fats not broken down and used to build protoplasm like cell membranes
- not enough glucose: fats broken down to provide energy for vital activities in body
- excess stored in adipose tissues (protects body as shock absorbers) beneath skin and around heart and kidneys
what are functions of the liver
- produces bile (fat digestion)
- deamination of amino acids
- regulates blood glucose concentration (insulin + glucagon)
- breakdown of hormones (after they serve their purpose)
- detoxification (e.g. alcohol, food preservatives)
what is a hormone
chemical substance produced in very small quantities by an endocrine gland
how is blood glucose concentration regulated (2 points, 4/3 subpoints)
high conc.:
- pancreas detects this and produces insulin
- transported in blood to liver and muscle cells
- makes cell membranes more permeable to glucose for more diffusion
- stimulates liver/muscle cells to convert excess glucose into glycogen for more respiration
low conc.:
- pancreas detects this and produces glucagon
- transported in blood to liver
- stimulates conversion of glycogen into glucose
how does alcohol affect the digestive system (2 points)
- alcohol stimulates acid secretion in stomach, excess increases risk of gastric ulcers
- cirrhosis, where liver cells are destroyed and replaced with fibrous tissue, makes liver less able to function and may lead to haemorrhage in liver, liver failure, and death
what are the impacts of alcohol on the nervous system (3 points)
- depressant (slows down brain functions, effects vary from person to person)
- reduced self-control
- slower/increased reaction time, slurred speech, blurred vision, poor muscular coordination
what are 2 long-term impacts of alcohol on the brain
1) wet brain
- type of dementia caused by brain damage
2) shrinkage of brain volume
- brain shrinks smaller than normal, especially region associated with memory and reasoning
*overconsumption can also affect foetus’ brain development
what are some social implications of alcohol overconsumption
- neglect their work and families
- exhibit violent behaviour, especially towards family members
- higher risk of committing crimes
*may lead to addiction as well
