Ch.7 Nutrition in Humans Flashcards
What are the 5 stages of humans obtaining nutrients and energy from food?
Ingestion -> Digestion -> Absorption -> Assimilation -> Egestion
Ingestion, digestion, absorption and egestion occur in diggerent regions of the digestive tract, also called the __________ _____. Assimilation takes place in all body cells
alimentary canal
(the alimentary canal and several associated glands make up the human digestive system)
The alimentary canal receives digestive juices secreted by _____________________, _____________________, _____________________, _____________________ and _____________________.
salivary glands, gastric glands, the pancreas, the liver and intestinal glands
What is the alimentary canal like?
mouth cavity -> (salivary glands) -> pharynx -> oesophagus -> stomach -> (behind it is the pancres) -> (liver) -> (behind the liver is the gall bladder) -> duodenum -> ileum -> (appendix) -> caecum -> colon -> rectum -> anus
What is ingestion?
The process by which food is taken in through the mouth.
What is mastication?
The process of solid food being chewed and cut into small pieces by teeth.
What are the four types of teeth in humans?
Incisors, canines, premolars and molars
Where are the incisors located?
At the front of the jaw.
Where are the canines located?
Next to the incisors.
Where are the premolars located?
At the sides of each jaw, behind the canine.
Where are the molars located?
At the back of the jaw, behind the premolars.
What are the features of the incisors?
- Chisel-shaped
- With flat sharp edges
- With one root
What are the features of the canines?
- Pointed
- With one root
What are the features of the premolars?
- Broad top with two cusps
- With one or two roots
What are the features of the molars?
- Larger than premolars
- Broad top with four cusps
- With two or three roots
What are the functions of the incisors?
Biting and cutting the food.
What are the functions of the canines?
Tearing food (especially flesh)
What are the functions of the premolars and molars?
Crushing and grinding food.
What is the hardest substance in the human body?
Enamel
What isenamel made up of?
It is made up of mostly calcium salts.
Is enamel living or non-living?
Non-living
The tooth is protected by the _________ from wear during biting and chewing.
Enamel
At the root of the tooth, the enamel is replaced by a thin layer of ___________
Cementum
Cementum fixes the tooth into the jawbone through the ________________________ _____________
periodontal membrane
What are the uses of the periodontal membrane?
This membrane allows the tooth to move slightly and act as a shock absorber during biting.
What is dentine?
Dentine is a bone-like, living layer with numerous small canals containing extensions of cells in the pulp cavity.
What does the pulp cavity contain?
living cells, blood vessels and nerve endings.
What do the living cells in the pulp cavity produce?
dentine
What do the blood vessels in the pulp cavity do?
The blood vessels supply oxyen and nutrients to the living tissues of the tooth, and remove waste products.
What is dentition?
Dentition is a term used to describe the number and arrangement of different types of teeth in a mammal.
How can dentition be expressed?
As a dental formula, which shows the types and numbers of teeth on one side of the upper and lower jaws.
What is the dental formula of a human adult?
i2, c1, pm2, m3
How many sets of teeth do humans have during their lives?
2
When do milk teeth appear?
Between the ages of 6 months and 2.5 years.
What will happen to milk teeth when the child grow older?
Milk teeth gradually fall out and are replaced by permanant teeth between ages of 6 and 12.
___________________ teeth function for most of our lifetime.
Permanent
Can permanent teeth be replaced by new teeth if damaged or lost?
No! 😋
What’s the dental formula for a 4 year-old child?
i2, ,c1, pm0, m2
What is digestion?
The breaking down of food into small and soluble molecules, so that they can be absorbed from the alimentary canal into the blood.
What are the two types of digestion?
- physical digestion
- chemical digestion
Where does digestion begin?
the mouth cavity!!
After food is ingested, the taste of food stimulate _____________ _______ to secrete saliva.
salivary glands
What does the chewing action of teeth do?
- cuts food into smaller pieces
- mixes food with saliva
What type of digestion of food occur in the mouth cavity?
Both chemical and physical
What does physical digestion refer to?
It refers to the breaking up of food into smaller pieces by physical means.
(however, physical digestion does not change the chemical structure of food)
What is the effect of breaking food into smaller pieces by chewing?
Increases the surface area of the food for the action of digestive enzymes.
What does chemical digestion refer to?
It refers to the breakdown of large, complex molecules into small, simple molecules through chemical reactions (hydrolysis).
What are the chemical reactions in chemical digestion catalysed by?
Digestive enzymes
What is saliva?
A digestive juice produced by salivary glands in the mouth.
What do saliva consist?
- water (99.5%),
- salivary amylase,
- mineral salts,
- mucus
What’s the use of salivary amylase?
It catalyses the breakdown of starch into maltose.
What is the use of mineral slats in the saliva?
Mineral salts maintain a slightly alkaline pH (about 7.5) for the optimum action of salivary amylase.
What is the use of water in the saliva?
It moisten and softens food.
What is the use of mucus in the saliva?
Mucus sticks food pieces together and lubricates the food to make it easier to swallow.
After food has been cut and ground by the teeth, mixed with saliva and rolled into a mass called ________ by the tongue, it can be swallowed through the pharynx into the oesophagus.
bolus
The blous is pushed along the oesophagus and the entire alimentary canal by **waves of alternate muscle contractions **called ______________
peristalisis
How is the bolus squeezed forward?
behind the bolus:
circular muscles contract
longitudinal muscles relax
-> lumen narrower
–> squuezes the bolus forward
in front of the bolus:
circular muslces relax
longitudinal muscles contract
-> lumen wider
–> allow bolus move forward
Apart from pushing food forward, peristalisis also helps _________________________________ to speed up digestion.
mix food with digestive juices
what’s the cardiac sphincter?
It’ the entrance to the stomach, which is a circular sphincter muscle. It controls the entry of food and prevents food from going back to the oesophagus.
What’s the pyloric sphincter?
The pyloric sphincter is another circular sphincter muscle, it controls the exit from the stomach to the duodenum.
What are the characteristics of the inner wall of the stomach?
It is folded and elastic.
What will happen to the stomach when it’s filled with food?
When the stomach is filled with food, the folds spread out so that the volume of the stomach increases.
Gastric glands in the inner wall of the stomach secretes _______ juices
gastric
What does grastric juice contain?
It contains
- an enzyme pepsin (a type of protease that catalyses the breakdown of proteins into peptides)
- hydrochloric acid,
1. provides acidic pH (optimum) for the protease to work,
2. denatures proteins in foods (the 3d shapes of protein molecules unfold -> easier to digest)
3. kills most of the bacteria taken in with fod
The stomach wall secretes ________ which covers its inner surface
mucus
What’s the function of mucus?
The mucus forms a physical barrier to prevent the acid and digestive enzymes from damaging the stomach.
Arrival of the bolus stimulates the muscular wall of the stomach to begin rhythmic contractions called _______________
churning
The bolus is thoroughly churned and mixed with gastric juice. The physical and chemical digestion of the bolus results in a semi-liquid paste of partially digested food called ________
chyme
A small/large amount of chyme is then released into the duodenum through the pyloric sphincter at a time.
small
The human small intestine is about six metres long. The _______________ is the first part of the small intestine; ________ forms the rest
duodenum, ileum
What does the duodenum secrete?
intestinal juice
What digestive juices does the duodenum receives?
bile and pancreatic juice
Where is bile produced?
In the liver
What is bile temporarily stored?
In the gall bladder.
What is the bile released through into the duodenum?
bile duct
What is bile like?
A green, alkaline fluid.
Does bile contain digestive enzymes?
no
What does bile contain?
- bile salts
- sodium hydrogencarbonate
- bile pigments
What’s the purpose of bile salts?
Bile salts emulsify lipids i.e. they break fat up into very small oil droplets, this increase the surface area of lipids for the action of the enzym lipase
-> sppeding up the digestion of lipids
What’s the purpose of sodium hydrogencarbonate contained in bile?
It makes the bile alkaline.
Neutralizes the acidic chyme from the stomach and provides an optimum pH of 7.6 to 8.6 for intestinal enzymes.
What are bile pigments contained in bile?
Breakdown products of haemoglobin from red blood cells in the liver.
They give bile its green colour but have no digestive functions
What will happen when fatty food is present in the duodenum?
The gall bladder contracts to release a large amount of bile into the duodenum through the bile duct.
What will happen if the gall bladder is removed?
Bile will flow directly into the duodenum. A small amount of bile may not be sufficient for effective digestion of lipids.
Where is pancreatic juice produced?
the pancreas
How is pancreatic juice released into the duodenum?
through the pancreatic duct
What does pancreatic juice contains?
three types of digestive enzymes:
- pancreatic amylase
(catalyses the breakdown of starch in chyme to maltose)
- lipase
(catalyses the breakdown of lipids into fatty acids and glycerol)
- several protases
(catalyse the breakdown of proteins into peptides and amino acids)
Also contains sodium hydrogencarbonate
-> neautralizes the acidic chyme -> optimum pH for the enzymes
___________ juice is secreted by glands in the wall of the small intestine, especially the duodenum and the first part of the ileum.
intestinal
What does intestinal juice contain?
Water, mucus and sodium hydrogencarbonate.
Enzymes are found within the membranes of _____________ cells of the small intestine.
epithelial
What enzymes are found within the membranes of epithelial cells of the small intestine?
- carbohydrases
(catalyse the breakdown of disaccharides to monosaccharides) - proteases
(catalyse the breakdown of peptides into amino acids)
How does peristalsis of the small intestine helps with digestion?
Peristalsis of the small intestine helps mix food with digestive juices. It also increases the chance of contact of enzymes on epithlial cells with food molecules.
Carbohydrates, lipids and proteins are completely digested in the small intestine. The result is a watery emulsion caled _____________. The _______________ contains monosaccharides, amino acids, fatty acids and glycerol, which can be readily absorbed from the small intestine
chyle
What is absorption?
Absorption is the uptake of the digested food from the lumen of the alimentary canal into the bloodstream.
The small intestine is very long & inner surface is highly folded . It provides large _________________ for absorption.
surface area
The folds on the inner surface of the small intestine bear numerous tiny projections called ______
villi
How is the structure of villi adpated for absorption?
- Villi are finger-like projections. There are numerous projections called microvilli on the surface of epithlial cells of villi. These features greatly increase the surface area for absorption.
- The epithelium of each villus is very thin (one-cell thick). This shortens the distance for transport of food molecules.
- The epithelial cells of villi contain many mitochondria which provide energy for active transport of certain food molecules.
- Each villus has a lymph vessel called lacteal. It is surrounded by a dense network of blood capillaries. The lacteal carries away lipids while the blood capilarries carry away sugars and amino acids. This maintains a steep concentration gradient for rapid absorption.
- the villi are in constant motion due to paristalsis of the muscular wall of the small intestine. This brings the digested food molecules into close contact with villi for rapid absorption
How are small, water-soluble molecules absorbed into the blood?
Small, water-soluble molecules are absorbed through the epithelium of villi into bloodcapillaries by diffusion and active transport.
What is the result for the absorption of digested food into the blood decreasing the water potential of the blood?
Water is drawn into the blood by osmosis. Most of the water from the chyme (~80%) is absorbed in the small intestine.
How do fatty acids and glycerol pass into the epithelial cells of villi?
Diffusion
What hapen inside the epithelial cells when the fatty acids and glycerol pass into the cells?
Inside the cells, the fatty acids and glycerol recombine to form small oil droplets, which are then passed out of the cells end enter the lacteal.
The oil droplets are carried by the lymph in the lymphatic system and eventually enter the bloodstream.
What does the colon do?
The colon absorbs water, minerals and some vitamins from the remaining undigested material.
By the time food material reaches the rectum, all of the digested food and most of the water have been absorbed. The remaining undigested materials form ________.
faeces
What does the faeces contain?
Faeces are usually semi-solid, greenish-brown masses that contain mainly dietary fibre, bile pigments, mucus and dead cells from the lining of the alimentary canal and a large number of bacteria.
Where are faeces temporarily stored?
in the rectum.
At the anus, there are rings of muscle called the ______________________ which control the removal of faeces
anal sphincters
how are faeces expelled through the anus?
When the anal sphincters relax and the muscles of the rectum contract
What’s assimilation?
The uptake and use of absorbed food substances by body cells
After entering the bloodstream in the small intestine, monosaccharides, amino acids and other water-soluble food substances are transported to the liver by the blood through the __________________________
hepatic portal vein
Lipids absorbed from the small intestine are transported by the _________ into the lymphatic system.
lymph
What are the functions of the liver?
- Regulation of blood glucose level
- Deamination of excess amino acids
- Production of bile
- Storage of glycogen, iron and fat soluble vitamins
- detoxification
How does the liver regulate blood glucose level?
After a meal, the liver removes excess glucose from the blood and converts it into glycogen. When the blood glucose level falls below a normal range, glycogen in the liver can be converted back to glucose, which is then released into the bloodstream. In this way, a relatively constant blood glucose level can be maintained.
What happens in the liver during deamination of excess amino acids?
THe nitrogen-containing part (i.e. the amino group) of an amino acid molecule is converted to urea, which is passed to the kidneys for excretion. The remaining part of the amino acid is converted to carbohydrates or lipids.
What’s the use of the liver storing glycogen, iron and fat-soluble vitamins
- The liver stores excess carbohydrates as glycogen which is “short-term” energy reserve
- the liver breaks down old red blood cells and the haemoglobin inside, releasing iron. The stored iron in the liver can be used to make new red blood cells.
- the liver also stores fat-soluble vitamins and carotene. The liver can convert carotene to vitamin A.
What happens during detoxification in the liver?
The liver converts certain toxic substances in the blood into harmless substances. This is called detoxification. The wastes are then formed and then extcreted in urine or bile.
