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human digestion
digestive system structures, functions & common diseases
| Question | Answer |
|---|---|
| Mechanical digestion | Physical breakdown of ingested food into particles. Involves teeth, tongue, roof of mouth & stomach |
| Chemical digestion | Chemical breakdown of ingested food into particles via hydrolytic enzymes. Starts in the mouth with the salivary glands, then the stomach via gastric juice, and is completed in the small intestine. |
| Absorption | the passage of digested nutrients from the gut lumen into the blood or lymph, which distributes them through the body |
| Elimination | the expulsion of indigestible material (ex. cellulose) from the body |
| What directions does food travel through the digestive tract? | Food travels in a one-way path from mouth -> esophagus -> small intestine -> large intestine -> anus |
| Hydrolytic enzymes | Specific digestive enzymes that have an optimal functioning temperature and pH (hydrolytic = add water to break down its substrate) |
| What happens during digestion? | Food is broken down into particles small enough that we can absorb it into our bodies. Carbohydrates -> monosaccharides; proteins -> amino acids; fat -> glycerol & fatty acids; nucleic acids -> nucleotides |
| What type of process is digestion? What type of transport is needed to excrete enzymes out of cells? | Digestion is an extracellular process. Enzymes exit the cell via exocytosis. |
| What is the structure of the mouth? | The mouth is divided into the hard palate and the soft palate. |
| What are the functions of the mouth? | 1. receiving food; 2. mechanical digestion of food; 3. chemical digestion of starch |
| What are the sets of salivary glands and where are they? | 1. Parotid (below ears); 2. sublingual (below tongue); 3. submandibular (below jaw) |
| What is saliva? What does it do? | Saliva is made of water, mucus, and salivary amylase which breaks down starch into maltose. |
| What is chewed food called? | Bolus |
| What is the pharynx? | The region between the mouth and esophagus where swallowing food and air meet |
| What is swallowing? What happens when you swallow? | Swallowing is a reflex action that passes food into the esophagus. To block air passage, the soft palate moves back to cover the nose openings, the uvula covers the internal nares, and the epiglottis covers the trachea |
| What is the structure and function of the esophagus? | The esophagus is long and muscular, lined with mucus membrane. It has circular and longitudinal muscles for peristalsis |
| Peristalsis | Rhymthic contractions of the esophageal muscles to move food towards the stomach |
| Reverse peristalsis | Vomiting |
| Location of cardiac sphincter | Between esophagus and stomach |
| location of pyloric sphincter | Between stomach and duodenum |
| Functions of stomach | Temporary food storage (how long?), mechanical digestion, chemical digestion of proteins |
| Structure of stomach | Rugae - folds that stretch to hold a lot of food, 3 layers of muscles to churn and mix bolus, mucus lining, gastric juice |
| What are hunger pains? | Felt when an empty stomach churns |
| Components of gastric juice | Pepsinogen (turns proteins & water into peptides), HCl (kills bacteria, activates pepsinogen into pepsin by cleaving off a piece, helps digest other molecules) & mucus (prevents HCl from eating stomach wall) |
| What is pepsinogen's active form? Why & when is it stored as inactive? | Pepsin. It is kept as pepsinogen while there is no food in the stomach to save energy and prevent self-digestion |
| What is an ulcer? How does it form? | Open sore in stomach lining, caused by too much gastric juice & not enough mucus; due to stress or illness |
| What is food called after it is digested by the stomach? How long does it take? | After 2-6 hours, depending on the food, it's turned into acid chyme, a very acidic semi-liquid food mass |
| Where does food go after the stomach? | It empties into the duodenum through the pyloric sphincter |
| Functions of small intestine | completing the chemical digestion of proteins, carbs & lipids; absorption of unit molecules into blood (circulatory system) or lymph (lymphatic system) |
| Length of small intestine & sections | ~6 meters; duodenum, jejunum & ilium |
| Duodenum: location, length, functions | 1st part of small intestine connecting stomach & jejunum; 25cm; receives bile & pancreatic juice, major chemical digestion of proteins, carbs & lipids |
| Jejunum & ilium: location, functions | 2nd & 3rd part of small intestine; completion of chemical digestion & absorption of nutrients into blood or lymph |
| Where are interstitial glands? What do they do? | Interstitial glands line the walls of duodenum & small intestine; produce juices containing enzymes that finish digesting proteins & starch |
| Digestive enzymes secreted in small intestine: | peptidase (peptides -> amino acids), maltase (maltose -> glucose), other enzymes for disaccharides (ex. lactase -> lactose, sucrase -> sucrose) |
| Specializations of small intestine & why | Long, convoluted & has villi (each with microvilli), increasing surface area for enzymes. Mitochondria for ATP production (needed for active transport) |
| Villi: what are they; location; structure; function | Finger-like projections lining small intestine; interstitial glands at base of each villus and each has blood & lymphatic vessels; active or passive absorption occurs across walls of villi into the blood or lymph |
| Which nutrients go to the blood or lymph? Why? | Fats (lipids) enter the lymph system bc they aren't soluble in H2O, making it difficult to transport via blood. Lymph is also bigger & nonpolar. Carbs (glucose) & proteins (amino acids) enter the blood through capillaries bc they are H2O soluble and small |
| How are lipids processed by villi? | Fatty acids & glycerol are recombined into fat molecules in cells of villi, then fats move into lacteal of each villus & enter lymphatic system |
| How are proteins & carbs processed by villi? | Blood vessels in villi merge to form the hepatic portal vein which leads to liver |
| Liver functions | 1. keeps blood concentrations of nutrients, hormones, etc. constant; 2. interconversion of nutrients; 3. detoxifies blood; 4. produces bile; 5. destroys old red blood cells; 6. produces urea; 7. makes plasma proteins; 8. makes cholesterol |
| Bile: what is it, location, functions | Bile is a thick, green liquid produced by liver and stored in the gallbladder. It is sent to the duodenum via the bile duct; contains bile salts which break fat into fat droplets (emulsification) |
| Why is it better to break down fat? | Fat droplets increase surface area of fat (substrate) so lipase (enzyme that digests fat) can work on it |
| Pancreas functions | Produces pancreatic juice which enters duodenum thu pancreatic duct |
| Enzymes in pancreatic juice | hydrolytic enzymes: pancreatic amylase (starch + H2O), trypsin (protein + H2O = peptides), lipase (fat + H2O = fatty acids), nuclease (nucleic acid -> nucleotides), nucleosidase (nucleotides -> sugar + PO4 + base), peptidase (peptides -> amino acids) |
| What is in pancreatic juice besides enzymes? | Sodium bicarbonate - with pH 8.5, it neutralizes acid chyme so enzymes can work at optimal pH |
| Large intestine structure | Colon & rectum; opening of rectum is anus; anal sphincter is a circular muscle we learn to control |
| Large intestine functions | Reabsorption of H2O (~95%) from indigestible food & absorption of certain vitamins; rectum stores feces until you poo |
| What is feces made of? | Cellulose (fibre), indigestible food matter, bile pigments, heavy metals & billions of E. Coli |
| What is E. Coli? How does it help us? | E. coli are parasitic bacteria that break down indigestible food & produce vitamin K, amino acids & other growth hormones which the colon absorbs. |
| Why do feces smell? | Hydrogen sulphide produced by E. coli |
| What are farts? | Methane gas produced as by-product of E. coli |
| What is diarrhea? What causes it? | Too much H2O expelled in feces. Common causes: infection or stress (how does stress cause it?). Symptom is a body defence against pathogens (flush it out). Loss of H2O can cause severe dehydration (fatal) |
| What is constipation? What causes it? | Feces are dry, hard & difficult to expel. Caused by a lack of fibre in diet (get fibre thru foods or natural supplements). Most chemical laxatives are irritants - cause increased peristalsis. May weaken intestinal wall until you grow to 'depend' on them |
| Gallstones: what is it?, affected part, signs & symptoms | solid crystal deposit that forms in gallbladder. may contain cholesterol, salt, or cellulose. SYMPTOMS: Most gallstones are 'silent' and don't cause pain - those that do: mostly pain in abdomen, sometimes jaundice, fever & swelling or nausea & vomiting |
| Gallstones: treatments, interesting fact(s) | Most common treatment is laparoscopic abdomen surgery where they remove ur gallbladder. Medications may be prescribed that dissolve gallstones over time (years). Applying heat can temporarily help pain. FACT: 80% of people with gallstones don't know it |
| Colorectal cancer: what is it?, affected part, signs & symptoms | disease where cells of tissues lining colon or rectum grow uncontrollably & form tumours. SYMPTOMS: stomach discomfort, feeling of fullness, gas pain, diarrhea, weight loss etc. |
| Colorectal cancer: treatments, interesting fact(s) | Surgery to remove tumours & part of colon/rectum, radiation therapy, chemotherapy, chemical trials etc. FACTS: very high cure rate if found early but often undiagnosed until late stages. Men have higher risk for developing this cancer. |
| Heartburn: what is it?, affected part | Burning sensation in the chest that can extend to neck, throat & face. Worsened by sitting or lying down. Primary sign of gastroesophageal reflux (stomach acid moves into esophagus due to failure of sphincter), rarely sign of stomach lining inflammation |
| Heartburn: signs & symptoms, treatments, interesting fact(s) | regurgitated stomach contents in mouth, painful swallowing + sore throat, bad breath & gingivitis, greasy foods, pressure on abdomen or lying down after large meals. banana & chamomile or ginger tea relieves it. ~60 mil Americans experience it once/month |
| Crohn's disease: what is it?, affected part | Chronic inflammatory disease of intestines. causes ulcerations in small & large intestine. Starts in small intestine then affects large intestine. |
| Crohn's disease: signs & symptoms | Ulcers in digestive tract, rectal bleeding, blood in stool, chronic diarrhea, abdominal pain/cramps, nausea/vomiting, eye/skin infections, delayed puberty, red spots on skin & many more |
| Crohn's disease: treatments & facts | Limited treatments & unknown prevention, but some can help: Anti-inflammatory drugs, biologic therapies, nutritional supplements, surgery or liquid diets. FACT: ~500k ppl affected in US. 15-30 yrs commonly affected. ppl w/ sibling 30x likelier to develop |
| Appendicitis: what is it?, affected part, signs & symptoms | Appendix becomes bloated & bacteria invades, affecting wall & lumen of appendix. Can push against intestines & cause blockage. SYMPTOMS: vomiting & nausea, loss of appetite, abdominal pain/tenderness, fever, constipation, jaundice |
| Appendicitis: treatments & facts | laparoscopic (keyhole) appendicectomy (surgery removing appendix), otherwise antibiotics to fight infection. FACTS: can cause sepsis if appendix bursts. mainly affects 10-20 yr olds. body could contain infection if appendix ruptures without treatment. |
Created by:
AntBanana
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