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Digestive system, villi - Coggle Diagram

- - - - shortest segment
        
        most of the digestion and absorption occurs here
      - first segment
    - - second segment
    - - last and longest segment making up about 50% of the small intestine
  - - - the villi expands the surface area that comes in contact with the food
        
        the villi has capillary networks and lymphatic lacteal to absorb digested material
        
        they also have a layer of epithelial cells that secrete digestive enzymes that cover the villi
        
        the epithelial cells themselves have microvilli, facing the lumen of the intestine, forming a brush border
  - - - occurs at the duodenum and jejunum
      - chyme digestion uses digestive enzymes from the pancrease and epithelial cells
      - bile also helps with fat digestion, not a digestive enzyme
    - - this process is enhanced by villi
  - - - polysaccharides are broken down into monosaccharides to be digested
      - digestion is done with amylase, breaking down large polysaccharides into smaller ones and maltose
        
        when the food goes to the stomach, carb digestion stops due to the acidic environment which denatures the salivary amylase
      - in small intestine, the pancreas secretes amylase and bicarbonate ions into the duodenum
        
        the bicarbonate neutralizes the acid from the stomach, allowing amylase to continue with digestion
        
        the amylase only digests the polysaccharide to a disaccharide, so it cannot be absorbed yet
      - enzymes to breakdown each disaccharide
        
        lactase
        
        breakdown of lactose to galactose and glucose
        
        lactose intolerance
        
        inability to make lactase enzyme
        
        causes lactose to stay in digestive tract leading to diarrhea and bacteria feeding on it (which causes bloating, gas and cramps)
        
        maltase
        
        breakdown of maltose to 2 glucose molecules
        
        sucrase
        
        breakdown of sucrose to glucose and fuctose
      - carb absorption
        
        done with a Na+/K+ pump establishing a concentration gradient, powering the Na+/glucose co-transporter (secondary transport)
        
        the concentration of Na+ is high on the outside and low on the inside
        
        this causes 1 glucose inside to diffuse out by facilitated diffusion for every Na+ that moves down the concentration gradient
    - - proteins must be broken down into aa to be absorbed
      - process of digestion
        
        digestion starts in the stomach where inactive pepsinogen is converted to pepsin with HCl
        
        the long chains are digested into smaller polypeptides and passed through the pyloric sphincter into the small intestine
        
        trypsin and chymotrypsin now continue the digestion of proteins
        
        for these proteins to work, they require a neutral pH environment which is done with bicarbonate
        
        at the same time due to the neutral pH, pepsin from the stomach becomes inactivated
        
        proteases (group of enzymes) from the pancreas continue protein digestion in the small intestine
        
        2 classes of protease enzymes
        
        2 more items...
        
        goes to absorption
        
        HCl also uncoils the long and twisted stands of proteins allowing for digestion of long protein chains
      - absorption
        
        done with secondary active transport using a Na+ concentration gradient
        
        this powers a co-transporter, transporting aa into the cell
        
        any remaining peptides are transported inside using endocytosis
    - - The stomach churns to help break up large fat molecules into smaller ones
        
        this churning is called emulsification
        
        there is constant emulsification to keep the broken down lipids from reforming into large droplets, allowing lipid-digesting enzymes to work
        
        these enzymes only work on small fat droplets, not large ones
      - bile is made in the gallbladder where it is stored and concentrated
        
        the bile salts of the bile keep the lipid droplets emulsified so they do not reform into large droplets
        
        colipase from the pancreas is then secreted, allowing the lipase enzyme to reach the lipid inside the fat droplet
        
        this allows the pancreatic lipase to digest the lipid
        
        pancreatic lipase then removes two fatty acid chains, leaving monoglycerides behind, making the fat droplet smaller
        
        micelles (single layer of bile salts surround a small lipid droplet) is formed
        
        the micelles transport the lipid droplets to the intestinal epithelial cells where the lipids are released
      - absorption
        
        fatty acids and monoglycerides free diffuse across the membrane of the epithelial cells
        
        cholesterol needs special active transport transporters to get across the membrane
        
        the bile salts are reabsorbed by a transport system in the ileum to be returned to the liver and reused
        
        absorbed lipids are inside the intestinal epithelial cells where they enter the smooth endoplasmic reticulum and combine with cholesterol
        
        this forms chylomicrons
        
        chylomicrons are packed into vesicles by the golgi, leaving the cell and going to the lacteals of the lymphatic system
        
        last it goes to the circulatory system
    - - lipid soluble vitamins (vitamin A, D, E, K) can freely diffuse through the membrane to be absorbed
      - water soluble vitamin (vitamin B, C, folic acid and Niacin) are absorbed by a Na+ co transport, using a Na+ gradient
    - - about 9 L of water is absorbed by the intestine per day
        
        80 % of water absorbed comes from reabsorption of water in saliva, digestive enzymes, bile and secretions from the intestines
        
        20% of the water absorbed comes from drinking water and food
        
        water absorbed in the small intestines
        
        the duodenum and jejunum together absorbs 44% of water
        
        the ileum absorbed 38% of the water
        
        the large intestines abosrbe 1.5%
        
        the remaining 100 ml is secreted into the feces
        
        when other substances are absorbed in the small intestine, an osmotic gradient is created
        
        there is now a high solute concentration, a low water concentration in the cell
        
        this causes water to flow into the cells by osmosis through the concentration gradient
    - - K+
        
        passively diffuses
        
        passive diffusion is causes by K+ [] increasing in the lumen from water being slowly absorbed
        
        the concentration gradient allows the passive diffusion of K+ into the cells
      - Na+
        
        diffuses using the concentration gradient established by the Na+/K+ pump on the basal lateral surface of the intestinal cells
        
        this causes a high Na+ gradient on outside, but low on inside
        
        Na+ will then diffuse from the lumen to the intestine
        
        Na+ can also be absorbed together along with carbohydrates and amino acids
- - - - neural mechanisms
        
        these mechanisms involve the enteric nervous system (part of the ANS)
        
        for the SNS and PNS to affect the digestive system, the nerve activity in the enteric nervous system must be altered
        
        this affects smooth muscles in the digestive tract, enzyme-secreting cells, endocrine cells and blood vessels in the tract
        
        how the ENS functions using reflex loops
        
        long loop
        
        travels through CNS
        
        uses input from higher brain centers through stimulus of sight or smell
        
        1 more item...
        
        short loop
        
        travels only through the digestive system
        
        the reflex begins with stretching or pH/osmolarity change in the digestive tract
        
        the changes are detected by sensors of the enteric nervous system to initiate a reflex
        
        2 more items...
      - hormonal mechanisms
        
        hormones are released from intestine cells to direct mechanical stimulation in stomach or intestine or in response to neural activation
        
        food causes the release of one/more hormones
        
        hormones release specific digestive enzymes for each specific type of food
        
        the hormones also slow down stomach output to allow for proper digestion and absorption
        
        different hormones used
        
        secretin
        
        released in response to acid in the intestine
        
        prevents emptying from the stomach
        
        cause release of pancreatic bicarbonate and bile from the liver
        
        bicarbonate neutralizes the acid from the stomach, allowing for intestinal digestive enzymes to function optimally
        
        cholecystikinin
        
        released in presence of fats
        
        slows stomach emptying, stimulate release of digestive enzymes from pancreas and gallbladder contraction to release bile
        
        glucose-dependent insulinotropic peptide
        
        secreted in response to glucose and aa
        
        stimulate insulin release from the pancreas which may inhibit stomach emptying
        
        gastric hormones
        
        stomach releases gastrin through the G cells in the antrum of the stomach along with other substances
        
        gastrin is secreted in response to protein, stretch of the tract from food and stimulates the PNS
        
        gastrin causes HCl secretion
        
        HCl causes conversion of pepsinogen to pepsin to digest proteins
  - - - increase gastric motility (increase digestion) and secretion as well as makes watery saliva
        
        the amount of chyme release into the intestine is important to maximize absorption
    - - decrease gastric motility (decrease digestion) and secretion as well as cause a dry mouth with viscous saliva
  - - - they creates a spontaneous basal electrical rhythm (BER)/ slow wave that goes down the digestive tract
        
        these slow waves don't cause muscle contractions as they don't reach threshold and go between smooth muscle cells through gap junctions
        
        The BER in the stomach is 3 waves/ min
        
        the BER in the duodenum is 12 waves / min
        
        to reach threshold there must be stimulus from mechanical, nervous or hormonal inputs
        
        when threshold is reached, the smooth muscles will contract and travels down the intestine
  - - - HCl is release in response to sight, smell, taste and chewing of food
        
        this is an anticipatory response where the ENS is activated through the long loop
        
        a stimulus activates the PNS, which activates the ENS, releasing HCl from the parietal cells and gastrin from G cells
        
        stomach motility also increases
    - - starts after food is swallowed
      - this phase is activated by the presence of aa (from protein breakdown and and food that stretches the walls
        
        this stimuli triggers a short loop reflex which involves the ENS, causing more HCl, gastrin and pepsinogen release
        
        this causes increases gastric motility as well
    - - when the food has left the stomach and entered the intestine
      - HCl release here is caused by the presence of glucose, fat and acidic chyme in the intestine
        
        the intestinal phase decreases motility and inhibit stomach secretions into the intestines
        
        this is done with hormones such as secretin, CCK and glucose-depending insulinotropic peptide
- - - - upper area
    - - aka the pyloric region
      - includes
        
        the pyloric sphincter
        
        empties the stomach into the duodenum (first part of the small intestine)
    - - largest part of the stomach
  - - - the small intestine is where most of the digestion and absorption takes place
        
        chyme is slowly moved through the pyloric sphincter using motility
      - this allows the amount of food entering the intestine to be regulated
  - - - secreted by cells in the body and the antrum to protect the stomach from extreme acidic pH
    - - secreted by cells in stomach body to denature complex protein and connective tissue molecules
      - also kills bacteria and converts the inactive enzyme pepsinogen to pepsin
    - - activated by HCl to pepsin to digest large protein molecules and secreted by cells in the body of the stomach
    - - secreted by cells in the atrum of the stomach which stimulates HCl secretion
    - - helps with absorption of vitamin B12
- - - - food is broken up by saliva and chewing here
      - digestion begins where food is broken down by chewing and is mixed with saliva
        
        this forms a bolus
        
        gets pushed to the back on the mouth by the tongue to initiate the swallowing reflex
        
        the uvula of the soft palate closes over the nasopharynx and the larynx is lifted by the muscles in the neck
        
        the epiglottis bends over the glottis and covers the larynx
        
        the bolus then moves down the esophagus through the cardiac orifice (aka lower esophageal sphincter)
        
        1 more item...
      - saliva
        
        99.5% water
        
        0.5% ions and proteins
        
        secreted by
        
        parotid gland
        
        submandibular gland
        
        sublingual gland
        
        helps to lubricate the bolus of food and digest carbohydrates
        
        digestion of carbohydrates is done here with the enzyme amylase
    - - produces saliva to moisten and digest food
    - - straight muscular tube connecting the mouth and pharynx to the stomach
    - - stores, mixes and digests some food, delivering it to the small intestine
    - - in digestion, it produces and secretes bile
    - - stores and concentrates bile
    - - secretes digestive enzymes, hormones and bicarbonate
    - - allows for digestion and absorption of food
    - - stores and concentrates undigested material while also absorbing salt and water
    - - where the defecation reflex is triggered
  - - - release of digestive fluid into the lumen of the digestive tract
    - - food is broken down into smaller molecules by the digestive enzyme to be taken up later
    - - process where small molecules are taken up by the circulatory system and distributed in the body
- - - - exocrine products go into the long pancreatic duct which merges with the common bile duct before entering the duodenum
    - - secretes many enzymes
        
        amylase
        
        digests carbs
        
        trypsin, chymotrypsin and protease
        
        digests proteins
        
        lipase
        
        digests fats
        
        sodium bicarbonate
        
        secreted into the duodenum to neutralize acid from the stomach
- - - - larger diameter than the small intestine but lacks the many folds and villi of the small intestine
    - - ascending limb
      - longitudinal/transverse limb
      - descending limb
      - sigmoid section
      - rectum
      - anus
  - - - can absorb Na+ by active transport, which causes osmosis afterwards
        
        most absorption happens in the first half of the colon
      - the large intestine secretes mucus to protect its lining from damage and lubricate the forming feces
        
        K+ and bicarbonate are secreted into the colon
        
        secretes K+ and bicarbonate into the colon