Chapter Six Flashcards
The digestive system supplies nutrients for the body
Digestion
The process of breaking down carbohydrates, proteins and fat molecules into products small enough to be absorbed into the blood and cells
Mechanical digestion
- The physical breakdown of food particles into smaller pieces to increase surface area
- Increased SA allows for more effective chemical digestion
Chemical digestion
The break down of large complex molecules into smaller more simple molecules, small enough to be absorbed into the blood stream
Alimentary canal
- The continuous tube that runs from the mouth to the anus, together with associated organs make up the digestive system
- The lining of the alimentary canal is where nutrients is absorbed
The mouth
- Mastication
- Bolus is formed
- Swallowing
- Enzyme action
Common name for mastication
Chewing
Bolus
A ball of saliva and food
Salivary glands
- Assists in the creation of the bolus (lubrication)
- Produces enzymes for chemical digestion of carbohydrates
Teeth
- Mechanical digestion
- 4 incisors
- 2 canines
- 4 premolars
- 6 molars
Incisors
Used for biting and cutting
Canines
Used for tearing
Premolars
Used for crushing and grinding
Molars
Used for crushing and grinding
Oesophagus
- Circular and longitudinal muscles
- Peristalsis pushes bolus down the oesophagus into the stomach
Peristalsis
Wave like muscle contractions
Stomach
- Muscular churning (mechanical digestion) to mix food with gastric juice and form chyme
- Circular, longitudinal and oblique muscles to cause these contractions
- Has a protective mucous lining to protect against HCl
Gastric juices
- Released by the gastric glands in the wall of the stomach
- Contains HCl, mucous and enzymes
- Enzymes start chemical digestion
Chyme
Pulpy acidic fluid which passes from the stomach to the small intestine containing gastric juices and partly digested food
Pyloric sphincter
- A circular muscle that prevents food from continuously entering the small intestine
- Every 2-8 hours it opens and allows chyme to be pushed into the duodenum
Absorption in the stomach
- Due to the thick layer of mucus, nutrients are not absorbed in the stomach
- Limited absorption of water, alcohol, glucose and some drugs
Small intestine
- Duodenum : first part of small intestine
- Jejunum : the middle section of the small intestine
- Illeum : the final part of the small intestine
Mechanical digestion in the small intestine
Bile from the liver and gall bladder emulsify fats
Chemical digestion in the small intestine
- Intestinal juice from the lining of the duodenum
- Pancreatic juice from the pancreas
Absorption in the small intestine
- After the nutrients is fully chemically digested it is absorbed through the wall of the SI into the capillaries
- Small intestine is big to increase surface area
- Folded into villi and microvilli to further increase SA
Capillary in the small intestine absorb… and are taken to…
- Simple sugars
- Amino acids
- Water
- Water soluble vitamins
Taken by the hepatic portal vein to the liver
Lacteal
- Lymph capillary inside villus
- Surrounded by network of capillaries
Lacteal in the villus absorbs… and is taken to…
- Fatty acids and glycerol ( which are recommbined with villi to make fats)
These substances are absorbed into the lacteal and transported to the lymph system
Large intestine
- Further absorption of water and some salts
- Bacterial activity (digestion of cellulose)
- May take 18-24 hours for food to pass through the large intestine
Elimination of faeces
Temporary storage in the rectum and then eliminated through the anus
Enzymes
Increase the rate of reaction, without it food would not digest fast enough for ourr needs
Substances involved in digestion
- HCl
- Pepsin
- Pepsinogen
- Salivary amylase
- Pancreatic amylase
- Pancreatic lipase
- Trypsin
- Nuclease
- Peptidase
- Bile
Substances located in the stomach
- HCl
- Pepsin
- Pepsinogen
Substances located in the mouth
Salivary amylase
Substances located in the small intestine
- Peptidase
- Trypsin
- Lipase
- Amylase
- Intestinal juices
- Bile (from the liver/gall-bladder)
Bile
- Produced in the liver, stored in the gall-bladder
- Released from the gall-bladder to the duodenum
- NOT an enzyme
- Mechanical digestion
Digestion in the mouth
- Salivary amylase > Starch/Complex carbohydrates (polysaccharides) > Simple sugars (monosaccharides)
- Teeth crush, grind, tear, cut and bite food into smaller pieces
Digestion in the stomach
- HCl > activated pepsinogen > pepsin > proteins > polypeptides > amino acids
- Churning of the stomach mechanically break down foods
Digestion in the duodenum
- Pancreatic amylase > starch > disaccharides
- Trypsin > proteins > polypeptides
- Pancreatic lipase > lipids > fatty acids + glycerol
- Nucleases > RNA + DNA
Digestion in the small intestine
- Amylases ( maltase, lipase, sucrase) > maltose, sucrose, lactose > glucose
- Lipase > lipids > fatty acids + glycerol
- Peptidase > polypeptides > amino acids
- Bile and peristalsis are forms of mechanical digestion here
Movement of the alimentary canal
- Speed can vary depending on size and contents of a meal
- Large meals cause greater stretching of the stomach and will be pushed into the small intestine quicker
- High protein/fat content slows the movement from the stomach to small intestine
- Alcohol and caffeine stimulate the movements of the stomach
Constipation
- Occurs if the movements of the LI are reduced and the contents remain there for a long period of time
- Contents become drier and harder than usual and defecation becomes difficult and possibly painful
- Caused by roughage (cellulose or insoluble fibre) in the diet
Diarrhoea
- Frequent defecation or watery faeces
- Causes by irritation in the SI or LI which increases peristalsis so contents pass through before there is an adequate amount of water absorbed
- Result of bacteria, virus, parasite, cancer, coeliac disease or lactose intolerance
Bowel cancer
- An uncontrolled growth of cells in the wall of the large intestine
- May be linked to diet, high alcohol consumption + smoking
- A diet high in processed and red meat and low in fibre may increase the risk of bowel developing bowel cancer
Coeliac disease
- Unable to tolerate gluten
- If they eat food containing gluten, their immune system responds by damaging or destroying the villi
- Without healthy villi, nutrients cannot be absorbed and the person becomes malnourished no matter how much food they eat
Bile salts
Bile acids that are conjugated with glycine or taurine
Caecum
Where the small intestine joins the large intestine
Longitudinal muscle
Muscles with fibres that run lengthwise along the body and the circular fibres encircle it
Mucosa
The moist inner lining of some organs and body cavities
Segmentation
Division into seperate parts or sections
Appendix
A small tube attached to the caecum
Colon
The longest part of the large intestine
Three main parts of the colon
- Ascending colon
- Transverse colon
- Descending colon
Ingestion
The process of taking food, drink or another substance into the body by swallowing or absorbing it
Sphincter muscle
Ringlike muscles surrounding and able to contract or close a bodily passage or opening
Exocrine gland
A gland that makes substances such as sweat, tears, saliva and digestive juices and releases them through a duct or opening to a body surface
Emulsification
The process of breaking down complex fat molecules into smaller fat molecules
Fatty acid
A carboxylic acid consisting of a hydrocarbon chain and a terminal carboxyl group
Hepatic portal vein
A blood vessel that carries blood to the liver from the intestines, spleen, pancreas and gallbladder
Central nervous system
The complex of nerve tissues that control the activities od the body
Dietary fibre
The parts of plant foods your body can’t digest or absorb
What are faeces made up of
Water, undigested foods, bacteria, bile and remains of dead cells from the intestinal lining
Involuntary
Done without will or conscious control
Motor nerve
Nerve carrying impulses from the brain or spinal cord to a muscle or gland
Receptors
An organ or cell able to respond to light, heat or other external stimulus and transmit a signal to a sensory nerve
Sensory nerve
Any nerve that conveys impulses from a sense organ to the central nervous system
Stimulus
A thing or event that evokes a specific functional reaction in an organ or tissue
Structure of oesophagus
Mucosa > Submucosa > Muscle layers (circular and longitudinal) > Outer layer fibrous tissue
Intestinal juice
- Peptidase
- Sucrase
- Lactase
- Maltase
- Lipases
What is the pH level in the stomach
2-3
What is the function of the longitudinal layer in the stomach (outer most layer)
It is involved in peristalsis
What is the function of the circular layer in the stomach (middle layer)
It contributes to the pyloric sphincter and helps control the movements of food into the duodenum
What is the function of the oblique layer in the stomach (inner lost layer)
- Unique to the stomach
- Tapers off before duodenum and is important for the churning of food and digestion
What is crohn’s disease
An autoimmune condition which damages the lining of the small intestine
Structure of the small intestine
- Inner lining/mucosa has folds that extend into the interior
- Mucosa has small finger like projections/ folds called villi
- Villi contain microvilli and inside is a lacteal surrounded by blood capillaries
- Villi is the site of nutrient absorption
What does damage to villi mean
- Nutrients won’t be absorbed and no matter how much a person eats they remain malnourished
- SA has decreased
