Digestive system!

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  • Created by: Izzy2807
  • Created on: 17-02-20 15:10
What is high density lipoprotein and low density lipoprotein?
HDL: 'good' cholesterol, takes LDL out of the bloodstream (leads to atheroscelorsis, build up of plaque in BVs)
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What type of fat is 'good' and 'bad' for us?
Saturated and trans fats are bad (high in LDLs, low in HDLs), unsaturated and mono-saturated fats are good (olive oil)
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What is good about fat?
It contains omega 3 and 6 - protect against CVD and lowers blood clots (lowers thrombosis)
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What is good about fibre?
Increased fibre means increased absorption of cholesterole in the gut - has to be soluble fibre though!
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How do antioxidant vitamins A, C and E help health?
They reduce the damage done by free-radicals (associated with cancers and atherosclerosis)
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What are the main layers of the GI tract?
The mesentry connective tissue (elastic, fibres and BVs): the serosa visceral perioteum and muscle!
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What are the 3 muscular layers of the GI tract?
Muscularis externa, submucosa (glands and mucus producing exocrine glands) and mucosa
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What are the 2 intrinsic nerve plexus' of the GI tract?
inner: submucosal nerve plexus. outer: myenteric nerve plexus
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What is the mesentery?
An organs that attaches to the intestines, consists of a double layer peritoneum
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What are the 5 functions of the digestive system?
1) digest food 2) absorb nutrients 3) maintain fluid/biochemical balance in the gut 4) egest waste 5) manage the gut microbiome
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What are the 3 factors that determine transfer of molecules in the GI tract?
SIZE of molecule (has to be small), CHARGE (has to be non-polar), LIPOPHILICITY/HYDROPHOBICITY (has to be lipophilic/hydrophobic)
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What is the general flow of food in the GI tract?
mouth, oesophagus, stomach, small intestine (duodenum, jejunum, ileum) and colon (ascending, transverse, descending and sigmoid)
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What effect does parasympathetic nerve stimulation have on the function of the GIT and secretion of digestive enzymes?
PARA: increases GI activity, increase SM contraction, increase in digestive juices sec., increase blood flow and relaxation of sphincters
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What effect does sympathetic nerve stimulation have on the function of the GI and secretion of digestive enzymes?
SYMP: decreased GI activity, decrease SM contraction, decrease sec. of digestive juices, decreased blood flow and contraction of sphincters
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What does the hormone SECRETIN do?
A peptide hormone that helps regulate pH in the duodenum by INHIBITING release of gastric acid and stimulates release of bicarbonate fluid (neutralises HCL and causes enzyme change)
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What does the hormone GASTRIN do?
Released by G cells (duodenum, pancreas and stomach), stimulates secretion of gastric acid (HCL) which contains enzymes that break down proteins
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What does the hormone cholecystokinin (CCK) do?
Stimulates delivery of digestive enzymes (from digestive juices) into small intestines, acts of sphincters, enables bile ducts to open into duodenum
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What are the 3 main types of mechanical digestion?
Teeth - cutting and chewing. Peristalsis - SM contraction, wave-like motion. Segementation - non-adjacent segements of tract alternatively contract and relax (causes churning and further break down). Churning in stomach
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Where are the 3 places where peristalsis occurs?
Oesophagus, stomach (churning, food mixes with digestive juices) and small intestine
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What are the 3 types of chemical digestion?
Enzyme activity, acids and bile!
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What 3 enzymes are in pancreatic juices?
Amylase (carbs) - carbs to glucose, proteases (pepsin) - proteins to AAs, lipases - fats to FAs and glycerol
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What is the main acid in the GI tract?
Hydrochloric acid - destroys bacteria in the stomach, enzymes work best in an acidic environment
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What does bile do? (released by liver, stored in gall bladder)
Emulsifies fats (separates fat globules into smaller) to form micelles, easier to absorption into lacteal (DOESN'T BREAK THEM DOWN)
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How are mechanical and chemical digestion regulated?
Mechano and chemo-receptors (e.g. stomach distention and pH), stimulates more hormone release or SM contraction
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How is the GI system controlled by nerves?
Enteric nerve plexus (intrinsic), AUTONOMIC NS (parasymp by vagus nerve) and local hormone release (gastrin, CCK and secretin)
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What role does the stomach play in digestion?
Secretes enzymes (pepsin) and HCL, secretes intrinsic factor (B12 abs.), CHURNING in stomach
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How does the stomach regulate gastric activity?
1) cephalic phase - PNS stim by sight/smell/taste of food. 2) gastric phase - activation of chemoreceptors/stretch receptors (vagus nerve), increases gastrin secretion
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What is the intestinal phase of gastric activity?
Partially digested fats and increased acidity stimulates gastrin, enterogastric reflex (inhibit vagal activity, close pyloric sphincter), CCK and secretin hormone released
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What role does the small intestine play in digestion?
mechanical digestion (peristalsis and segmentation), chemical digestion (intestinal and pancreatic enzymes and bile) - received by pancreas and liver
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What are the 2 accessory organs of digestion?
The liver and pancreas
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What does the pancreas do? (accessory organ)
Acinar cells secrete digestive enzymes (amlyase, proteases trypsin and chymotrypsin, lipase). Sec. in repsonse to VAGUS nerve stim, and CKK. Secretes bicarb (stim. secretin) for alkalinity
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What does the liver do? (accessory organ)
Secretes bile (hepatocytes) (emulsifies lipids) in response to vagus nerve stimulation and CCK. DETOXIFIES, synthesizes clotting factors and lipids, involved in gluc. reg, stores vitamines, deamines AAs
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What are the adaptations of the small intestine?
Villi and microvilli, increase SA. Villi 1 epithelial cell thick. Dense lymphatic and circulatory network - hepatic portal vein to liver
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How are liver cells adapted?
Rich blood supply (hepatic portal vein to heart), rich in O2 (hepatic artery)
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What is the function of the large intestine?
Water reabsorption (fluid balance) as well at vitamins and minerals. Contains bacteria: fibre and bile breakdown. Vitamin synthesis
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How does the large intestine ensure defecation?
Haustural contractions (contraction of haustra), gastrocolic reflex (relaxation of ileo-caecal valve)
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Describe defecation!
Food enters stomach, stims colon peri, peptide hormones open ileo-caceal valve, small int contents enter colon, MASS PERISTALSIS, contents into rectum, increase in pressure activates stretch receptors - defecation
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How could damage to the pancreas (pancreatitis) cause digestive issues?
Pancreatic enzymes aren't released (in pancreatic juice), molecules not broken down - diarrhea, malabsorption, oily stools
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Card 3

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Card 4

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Card 5

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