The Digestive System Flashcards
List the main functions of the digestive system
-ingestion (taking food into alimentary tract like eating and drinking)
-propulsion (mixes contents and moves them along alimentary tract)
-digestion (mechanical breakdown of food mastication (chewing), chemical digestion of food into small molecules
-absoption (process by which the products of digestion pass through the walls)
-elimination (food cannot be digested and is then excreted from the alimentary canal in faeces by the process of defecation)
Describe the structure and functions of the organs of the digestive system
Gut:
-external surface
-purpose: absorb water, excrete cholesterol and synthesise some vitamins
Peritoneum:
-serious membrane sac on the abdomen
-it encases the abdominal organs to: provide structure and hold organs in place, contain any developing infections to stop them spreading e.g. appendcitis and reduces friction: the two layers of the peritoneum (parietal and visceral) have serious fluid between them, making them slippery: friction is bad because it causes inflammation
Alimentary canal (GI tract):
-long tube which food passes through
-starts at the mouth and terminates at anus
-parts are: mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anal canal
-contractions of these muscle layers: peristalsis (moves forward), segmentation (back and forth- mixes), mass movements (rapid movement forward)
Mouth:
-physical breakdown of food mastication (chewing)
-hard palate made of bone (anterior)
-soft palate made of muscle (posterior)
-initial digestive enzymes released
-infection control
Pharynx:
-3 sections: naso-, pro-, laryngo-pharynx
-food goes from oral cavity to oesophagus via the pharynx
Oesophagus:
-rapid transport of bolus to stomach through thorax
-around 25cm long tube from pharynx to stomach
Sphincters:
-thickened rings of circular muscle
-they keep the GI tract a ‘one way system’ to prevent backflow
Tongue:
-voluntary muscle covered by mucous membrane. Needed for deglutition (swallowing)
-anchored to floor of mouth by the frenulum
-covered in papillae which contain taste buds
-functions: chewing (mastication), swallowing (deglutition), swallowing (deglutition), speech, taste
Teeth:
-incisors and canine teeth are cutting teeth- bites food pieces
-premolar and molar are flat surfaces- used for grinding or chewing food
Salivary glands:
-3 main glands: parotid glands, submandibular glands and sublingual glands
-role of saliva: chemical digestion of polysaccharides- amylase enzyme breakdown of complex sugars, lubrication of food (bolus) - dry food is moistened, non specific defence- antibodies present combat the invading microbes, taste - dry food only stimulates a taste after mixing with the saliva, oral hygiene: prevent tooth decay
Stomach:
-storage facility
-mechanical breakdown (3 smooth muscle layers allow the food to churn, gastric juice liquefy the ‘chyme’)
-physical breakdown
-chemical breakdown (pepsin)
-mucous membrane- thrown into folds (rugae) enabling it to stretch when full. Gastric glands release the constituents of gastric juice
-limited absorption
-non specific defence against microbes-through hydrochloric acid in gastric juice so vomiting happens
-secretion or hormone gastric
-preparation of iron for absoption
-production and secretion of intrinsic factors
-regulation of the passage of gastric contents into the duodenum
-stomach produces gastric juice: unravels proteins, activates enzymes: pepsinogen -> pepsin, disinfects stomach contents
-stuff leaving stomach is called chyme: partially digested, acidic (hydrochloric), very concentrated
Duodenum: (jejunum, ileum- small intestine)
-start of small intestine
-c-shaped curve around the pancreas
-pancreases and liver join gut tube here
-acidic chyme is neutralised here
-water enters duodenum through gut walls (dilutes chyme)
-digestive enzymes enter here
Liver:
-see separate flash card
Gallbladder:
-connected to live above and duodenum below
-stores and concentrates bile (which comes from liver)
-connects to GI tract through a system of tubes (biliary tree)
-contracts when fat is detected in the duodenum - release bile into duodenum
Bile:
-contains bile salts- these help emulsify fats into small droplets, makes it possible to absorb cholesterol and fatty acids and fat-soluble vitamins
-contains bilirubin
-when red cells die bilirubin is released and needs to be excreted from body- it gives stool their colour, if bilirubin is not excreted it can lead to jaundice
Pancreas:
-endocrine function (small bit of pancreas): produces insulin/glucagon
-exocrine function (most of the pancreas): produces pancreatic juice- contains active enzymes for digestion e.g. amylase and lipase and inactive enzymes e.g. trypsinogen which is activated on arrival
Jejunum and ileum:
-jejunum-next section of small intestine, following from the duodenum, middle section, around 2 metres long
-ileum- last section of small intestine, around 3 meters long
-secretes alkaline intestinal juice: final digestion, nutrient absorption (mainly jejunum)
-water/electrolyte absorption (mainly ileum)
Small intestine:
-the mucous membrane needs a high surface area
-has small circular folds called ‘plicae’. Under the rugae of the stomach, they do not smooth out
-has villi: 1mm long projections, covered by enterocytes, cells which complete the chemical digestion of proteins, carbohydrates and fats as they contain peptidase, sucrose, lipase, lactase, and lactase
-enterocytes have microvilli: even smaller projections to increase nutrient absorption
Large intestine:
-made up of the caecum, colon (ascending, transverse, descending, sigmoid), rectum, and anal canal
-role: final water and electrolyte absorption, temporary storage, secretes mucus to lubricate food waste moving along
-caecum: wide pouch that acts as a reservoir, once full, food moves the large intestine
-rectum/anus: absorption, microbial activity, mass movement and defecation
List the main functions of the liver
-mainly composed of cells called hepatocytes
-produces bile
-synthesises proteins like albumin/clotting factors
-detoxifies blood
-energy storage (glycogen)
Describe the functions of the liver, with reference to bile secretion, and the metabolism of carbohydrates, proteins and lipids
Carbohydrates metabolism:
-liver maintains the plasma glucose levels
-after the levels rise and glucose is converted to glycogen for storage under the influence of the hormone insulin
-after the levels fall glucagon stimulates conversion to glycogen into glucose again to maintain levels
Lipid digestion:
-stored fat can be converted to a forming which it can be used by the tissues to provide energy
Protein metabolism:
1. Deamination of the amino acids
-removes nitrogenous portion from excess amino acids- this is where urea is formed and excreted as urine
-breaks down the nucleic acid to form uric acids- this is excreted in the urine
- Transamination:
-removes the nitrogenous portion of amino acids and attaches to other carbohydrate molecules and forms other new non- essential amino acids - Synthesis of plasma proteins:
-liver produces 90% of plasma proteins contained in blood stream, including albumins, globulins and blood clotting factors
Bile secretion:
-the hepatocytes synthesis the constitutes of bile from the mixed arterial and venous blood in the sinusoids- including bile salts, bile pigments and cholesterol
Describe the structure of carbohydrates, proteins and fats and their function in the body
Carbohydrates:
-carbon, hydrogen, oxygen
-long chains of sugars (starch) in rice, and shorter chains of sugars like lactose in milk
-broken down by enzymes
-turns into small sugar units called monosaccharides
-and the function is short term energy
Proteins:
-composed of amino acids
-primary, secondary, tertiary, quaternary
-long chains of amino acids (polypeptides)
-broken down by protease (enzyme)
-the function is growth and repair (helps tomato new cells)
Fats:
-glycerol and three fatty acids
-digest fat you need bile and enzymes (lipase)
-functions include: energy storage, insulation, transport of proteins in blood and cell membrane structure
Describe the digestion of carbohydrates, proteins and fats with reference to relevant organs and enzymes
-carbohydrate digestion begins in the mouth through the action of salivary amylase. Amylase breaks down complex carbohydrates into smaller fragments, producing a mixture primarily composed of disaccharides (two simple sugars) and trisaccharides (three simple sugars)
-salivary amylase continues to digest the starches and glycogen in the meal for an hour or two before stomach acids render it inactive
-in the duodenum, the remaining complex carbohydrates are broken down through the action of pancreatic amylase
-before diasaccharides and trisaccharides are absorbed, they are fragmented into simple sugars (monosaccharides) by brush boarder enzymes found on the surfaces of the intestinal microvilli
-trypsin, a protease, a type of enzyme that catalyses the digestion of proteins in to smaller peptide, which can then be broken down further into amino acids by other proteases. Trypsin is produced in the pancreas and released in pancreatic juice. The amino acids are absorbed into the cells lining the digestive system and then absorbed into the bloodstream
-need bile and enzymes
-bile-breaks the fat up into smaller droplets (emulsify)
-lipases (enzymes) then break the gut molecules into smaller units
Describe the metabolism of proteins
-enzymes involved are called transaminases
-digestion breaks down dietary proteins into amino acids in prep for absorption into blood capillaries of villi in small intestine
-amino acids are first in the portal circulation to liver and then to general circulation and then available to all body cells and tissues
-different cells choose specific ones required to build their specific tissues and for synthesising their secretions
Describe the metabolism of carbohydrates
-digested carbohydrates is absorbed into the blood capillaries of the villi of the small intestine, its transported to the liver where:
-glucose = oxidised to provide chemical energy (ATP)- important for metabolic activity that takes place in the liver
-some glucose circulate blood to maintain blood glucose around 3.5-8
-other glucose if too much converted to a hormone called insulin
-carbohydrate in excess of that required to maintain blood glucose level and glycogen stores in the tissues is converted to fat and stored in the fat depots
Describe the metabolism of lipids
-lipid metabolism- regulates circulating levels of triglycerides, fatty acids and cholesterol
-role of fatty acids and triglycerides in lipid metabolism:
-fatty acids and glycerol circulating the blood are used by cells to provide energy and synthesise secretions
-in live- provides energy and heat and some recombined to form triglycerides
-when required, triglycerides are converted back to fatty acids and glycerol and used to provide energy
-when body tissues are deprived of glucose (starvation, strenuous exercise)- body uses alternative energy storage, fatty acids may be converted to acetyl coenzyme A
-role of phospholipid in lipid metabolism:
-essential for the abosorbtion, transport and storage of lipids
-role of cholesterol in lipid metabolism
-allows the body to produce bile acids -> which are needed to help breakdown fats in the digestive tract so that it can be absorbed into the body
What is the role of insulin and glucagon in carbohydrate metabolism?
-role of insulin: insulin works to keep the glucose levels in the blood at a normal range, and if the glucose levels are in excess then it will be converted in the hormone insulin to be given to the insoluble polysaccharide, glycogen, in the liver and the skeletal muscles
-role of glucagon: glucagon instructs the liver to convert glucogen to glucose, making glucose more available in the bloodstream. It also stimulated hepatic glucose output
Define glycolysis
A metabolic process that breaks down carbohydrates and sugars through a series of reactions to either pyruvic acid or lactic acid and release energy for the body in the form of ATP
Define glycogenesis
Formation of glycogen from glucose
Define gluconeogenesis
The making of glucose from a non carbohydrate source such as amino acids or glycerol
Describe excretion of waste to include the physiology of defaecation
-rectum is normally empty- but as mass movement forces the contents of the sigmoid colon into the rectum and the nerve endings of the wall are all stimulated by stretch
-after a couple of years, humans have voluntary control so the brain can inhibit the relax until it is convenient to defecate
-excretion is the process by which metabolic wastes are eliminated from the body
-defecation- the elimination of body waste formed in the intestine, as faeces, from the rectum
Describe the constitutes of a healthy diet with reference to food groups
