Overview of digestion Flashcards
Describe the five different processes of muscular digestion
- Mastication (chewing)
- Human jaw is the most powerful muscle in the body
- Tooth enamel is hardest substance produced by body
- Tongue plays an important role in manoeuvring food around inside the mouth via actions of:
- Its 8 different muscles, makes it the body’s most flexible striated muscle
- The grippy actions of the rough papillae on the surface
- Several glands (including sublingual, submandibular and parotid) secrete saliva to begin digestion and to provide particles in solution to react with taste buds) - Peristalsis
- When inner circular muscles contract, the tube tightens
- When the outer longitudinal muscles contract, the circular muscles relax and so the tube is loose
- As the circular and longitudinal muscles tighten and relax, the bolus moves ahead of the constriction - Stomach action
- The stomach adds juices to the bolus and grinds it up to a semi-liquid mass called chyme
- The stomach has the thickest walls and the strongest muscles of all the GI tract organs
- Three sets of muscles churn the food (longitudinal, circular and diagonal) for hours, grinding the mouthfuls of food into tiny particles
- Stomach can stretch to hold more than 20 times its empty volume. Rugae (gastric folds) allow the stomach to stretch and accommodate a meal - Segmentation
- Chyme is subjected to localised contractions of circular smooth muscles which constricts the intestines into “segments” in a process called segmentation
- Segmentation mixes the chyme with digestive juices, and brings particles into contact with the wall of the GI tract so that nutrients can adequately be absorbed - Sphincters in the GI tract:
- Function to prevent food from going the wrong way:
- Oesophageal sphincters
- Pyloric sphincter
- Ileocecal valve
- Two sphincters of the anus (extra safety)
Describe the anatomical details of the intestinal cells that facilitate nutrient absorption
Describe the role of the varying pH in the GI tract and how the body defends against acidic environments and secretions
Varying pH of the GI tract
1. Mouth (neutral pH): Saliva enzymes don’t work in the stomach due to the low pH
2. Stomach (low pH): HCl acid is released in when food is detected in the stomach
3. Small intestine (neutral pH):
- Pancreatic juice contains sodium bicarbonate, which is alkaline, and this helps to neutralise the acidic chyme that enters the duodenum. From this point on, chyme remains at a neutral or slightly alkaline pH.
- Bile is also slightly alkaline
Describe the three processes by which nutrients transverse the mucosal cell membrane and how sections of the GI tract are specialised to absorb certain nutrients
- Cell specialisation:
o Mucosal cells at different sites of the small intestine are specialised to absorb certain nutrients
o Nutrients that are quickly digested are generally absorbed higher up in the small intestine
o In the large intestine (colon), water is mainly absorbed
Identify and describe the actions of accessory organs and secretions
> Hydrolysis during digestion:
- Micronutrients require little or no digestive preparation
- Macronutrients need to be broken down to basic units to allow absorption
> Accessory organs and their secretions:
- Salivary glands secrete saliva for carbohydrate digestion
- Gastric glands in stomach - HCL, mucus, enzymes (HCL uncoils protiens, enzymes break down proteins, mucus protects stomach cells)
- Pancreas target small intestine - provide pancreatic juice (bicarbonate and enzymes) - bicarbonate neutralises acidic gastric juices, pancreatic enzymes break down carbohydrates, fats, proteins
- Liver - target organ is gall bladder - bile is stored until needed
- Gall bladder - targets small intestine - secretes bile, emulsifies fat so enzymes can access it and break it down
- Intestinal glands - target small intestine - secrete intestinal juice (enzymes) to break down carbohydrate, fat and protein, mucus protects the intestinal walls
- The stomach’s secretions:
- Major site of protein digestion
- Gastric glands release HCl to create a low pH environment (pH~2)
- The acidic environment functions to:
- Denature proteins aiding in their overall digestion
- Activate the enzyme (pepsin) involved in protein digestion
- Kill harmful bacteria
- The stomach epithelium contains a mucous membrane which prevents the acids from damaging the gastric lining - Small intestine secretions:
> Duodenum: place where most digestion occurs
- Delivery of chyme/HCL
- Liver/gallbladder – delivers bile (emulsifier)
- Pancreas – delivers pancreatic juice (digestive enzymes and bicarbonate)
- Brush border enzymes
> Jejunum – a place where most absorption of nutrients occurs
> Ileum – absorption of some important nutrients (vitamins B12, A, D, E and K)
Briefly describe small intestine structure and Identify which nutrients enter the blood directly and which must first enter the lymph
Small intestine structure:
- Approximately 3-4 metres long with a diameter of 2-3cm
- The microvilli provide the large absorptive surface (equivalent to a tennis court in area)
- Small nutrients become trapped among the microvilli and are absorbed via special nutrient transporters in intestinal cells
- The large surface area allows nutrients to enter mucosal cells and pass into the blood stream or lymphatic vessels (Lacteals)
o Water-soluble nutrients and small products of fat digestion are released into the bloodstream
o Fat-soluble vitamins and larger fats form chylomicrons and are released to the lymphatic system
Explain how nutrients travel in the circulatory systems from the GI tract to the heart
Heart
Arteries
Capillaries (intestines)
Portal Veins - collects blood from the GI tract and delivers it to the capillaries in the liver
Liver
Capillaries (liver)
Hepatic vein - collects blood from the liver and delivers it to the heart
Heart
Describe how bacteria, hormones and nerves influence the health and activities of the GI tract
o The hormonal (or endocrine) system and the nervous system coordinate all digestive and absorptive processes.
o The GI tract stimulates or inhibits secretions of hormones via nerve-pathway ‘feedback mechanisms’
o Pancreatic secretions change based on the content of the diet. A rapid change from one’s usual diet can often result in ‘upset stomach’ due to a lag in pancreatic secretion change
Outline what factors are important for maintaining a healthy GI tract
o A healthy diet promotes a healthy GI tract and optimal nutrient absorption
o Getting ample sleep assists with the maintenance and repair of the GI tract
o Physical activity promotes healthy GI muscle tone
o Relaxed mealtimes maintain physiological controls (hormonal and nervous system) of the GI tract
o In summary: balance, moderation, variety, and adequacy should feature in everyday life
Distinguish between the terms – digestion, absorption and ingestion
Briefly define digestion, absorption and excretion
- Cells require a constant supply of nutrients
- Nutrients are supplied via the blood of the circulatory system
o Digestion involves the mechanical and chemical breakdown of food, extraction of nutrients, and breakdown of macronutrients
o Absorption is the transfer of nutrients from the lumen of the small intestine to blood or lymphatic capillaries surrounding the digestive tract
o Excretion is the process of eliminating any remaining food waste after digestion and absorption are finished
Describe the anatomy of the digestive tract.
- The GI tract is the flexible muscular tube from mouth to anus
- Digestion begins in the mouth, where the salivary glands secrete saliva (starch digesting enzymes) and chewing (mastication) breaks down food
- The epiglottis is a flap in throat that prevents food entering the windpipe
- After swallowing, the food (bolus) heads into the oesophagus, where the oesophageal sphincter control passage from oesophagus –> stomach
- The stomach adds juices and grinds the bolus into chyme (semi liquid)
- The pyloric sphincter regulates the flow of chyme into the small intestine
- The three segments of the small intestine are the duodenum, the jejunum, and the ileum
- The small intestine recieves bile and digestive juices from the gallbladder and the pancreas
- The large intestine (colon) begins at the ileocaecal valve and undigested residues continue through to the rectum (forms stool) and excreted (anus)
- Meal digestion time = three to four hours
Briefly describe the actions in propulsion, mechanical and chemical digestion
- Propulsion
- Swallowing (oropharynx) and peristalsis - Chemical digestion
- Mechanical digestion
- Chewing (mouth)
- Churning (stomach)
- Segmentation (small intestine)
list factors influencing health of GI tract
o Age, diseases and diet can affect its function
o Estimated 10 trillion microbes (bacteria, viruses, protozoa and other microorganisms) live in GI tract
o These flora or microflorae assist in digesting some fibre and protein
o Probiotics are bacteria found in foods such as yoghurt, that can be beneficial to health
o Prebiotics are certain chemical compounds, not absorbed but used as food by intestinal bacteria
