Digestive System

Digestive System

1. Function

   • Contribute to homeostasis - providing the body with nutrients and removing waste from body tissue
   • Responsible for breaking down food = molecules so that body cells can access it.

2. Anatomy/Structure

   • Gastrointestinal Tract (GI)
     • Mouth
       • Oral/Buccal cavity
     • Pharynx
     • Oesophagus
     • Stomach
       • Mox saliva, food , gastric juices = chyme
       • act as reservoir before food released to duodenum.
       • Secretes gastric juice to facilitate digestion
       • Minimal absorption of glucose, water, ions, alcohol
       • Anaotmy
         • Oesophageal sphincter
         • Body
         • Pylorus
           • pyloric sphincter connects the stomach - duodenum
         • There are 3 layers of muscle to mix food
         • Stomach Mucoaa
           • Conatains gastric glands = secrete products into lumen
           • Products form Gastric juices +aid in breakdown +absorption
     • Small Intestine
       • Most digestion and absorptio occurs here
       • Has 3 portions = Duodenum,Jejunum,Illeum
       • Mucosa
         • Factor that increase surface area to ++ absorption
           • Circular folds
             • Forcing chyme to go slowly and more time for absorption
           • Villi
             • Figer like projections of mucosa
             • Has blood capillaries and lacteals for fat absorption
           • Microvilli
             • Tiny projections of plasma membrane of the cells on surface of villi
           • Length of small intestine
             • Long = more time and surface are to absorb nutients from the Chyme passing through.
       • Mechanical digestion
         • Peristalsis
           • sequential contractiona and relaction of the smooth muscle to propel the chyme through the tract
           • weaker comapred to the stomach
           • Chyme remains fro 3-5 hours
         • Segementation
           • Contactions of alternative section of the tract to mix chyme. = ++ digestion and absorption
     • Large intestine
       • Complete absorption of water, ions, viamins
       • Production and absorption of vitamin K and some B vitmins
       • Move content of colon to rectum
       • Formation of feaces
       • Removal of feaces
       • Mechanical digestion
         • Haustral Churning
           • Relaxed pouches - filled then contract to move chyme to next haustra
         • Mass Peristalsis
           • Strong peristaltic waves beginning in mid transverse colon = quickly move contects toward rectum
           • Initiated by food in the stomach
       • Formation of feaces
         • More wtare absorbed so chyme = more solid / semisolid = feaces
       • Defecation reflex
         • Reflex actio aided by voluntary contractions of diaphragm and abdominal muscles
         • External anal sphincter can be voluntarily controlled to allow postpone defecation
         • Regulated by ENS and stimulated by presence of chyme
         • GI reflexes regulate GI motility. Increase or decrease the movement of chyme through tract
     • Layers
       • Mucosa
         • Most inner layer
         • secretes enzymes and absorbs nutirents
         • Goblet cells secrete mucus onto surface
         • Cell secrete hormones - control organ function
       • Submucosa
         • Connective tissue
         • Binds Mucosa and Muscularis
         • Contains blood and lymphatic vessels
         • Recieve absorbed food molecules
         • Neurons here control secretion in GI tract
       • Muscularis
         • Smooth muscle
         • Circular and longitudinal
         • Involuntary control
         • involuntary control to propel chyme (called peristalsis)
         • Skeletal Muscle
         • In mouth,pharynx,upper oesophagus and anal sphincter for voluntary ingestion,swallow defacation.
       • Serosa
         • Most outer layer
         • serous membrane
         • secretes serous fluid = reduce friction
         • Covers viscera within abdominal cavity
       • Peritoneum
         • Largest serous membrane
         • Parietal layer
           • lines abdominopelvic cavities
         • Peritoneal cavity
           • contains serous fluid
         • Visceral layer
           • Covers Organs
         • Not a smooth layer that covers heart and lungs, but it has a few folds that weave between organs.
   • Accessory organs
     • Teeth
     • Tongue
       • Skeletal muscle covered with mucous membrane
       • For speech and swallow
       • Gustation, Manipulation , Swallowing , Speech.
       • Hypoglossal CNXII
     • Salivary Glands
       • Secrete saliva into oral cavity
         • Soften, moisten, dissolve food.
         • Cleanses mouth and teeth using the enzymes in it.
         • Homeostasis link?
     • Liver
       • Function
         • Bile production
           • The Heptocytes produce 500-1000ml of Bile a day
           • Needed for emulsifying lipids for absorption
           • Flows out of the liver via bile ducts
           • Some sotred in the gall bladder
           • Remainder secreted into duodenum
           • Pathway
             • Right Hepatic duct + Left Hepatic Duct --> Common hepatic duct from liver --> Cystic duct from gallbladder --> common bile duct --> pancreatic duct frmo pancreas
           • Stimulation
             • Parasympathetic stimulation via Vagus Nerve (X)
             • Presence of Fatty chyme in GI tract
               • More Bile
         • Phagocytosis by Kupffer cells
         • Storage of Fe2+, glycogen, vitamins
         • Formation of blood components
         • Metabolism
         • Heat production through metabolic reactions
       • Liver cells = Heptocytes
         • Contains a lot of RER , SER , Golgi complexes and mitochondria
         • Part of small functional units in liver called Lobules
           • Hexagonal units that makes up the liver. Each lobule the size of sesame seed.
           • Function
             • Filter the nutrient rich blood from the GI tract (The blood that absorbed nutrietn from food
           • Filtration
             • Between hepatocute plates and highly capillaries called sinusoids
             • Blood from Hepatic Artery and Hepatic Portal Vein - percolates through the sinusoids and empties into Central Vein for Venous Return
           • Central Vein empties into Hepatic Veins - leave the luver and drain into Inferior Vena Cava
           • Contains Kupffer cells = remove debris and worn out blood cells as it flows through sinusoids
         • 3 fuction
           • Secretory
           • Metabolic
           • Endocrine
       • Hepatic blood flow
         • Oxygenated blood from hepatic artery and Nutrient rich, deoxygented blood from hepatic portal veing
           • --> Liver sinusoids --> Central Vein --> Hepatic Vein --> Inferior Vena Cava --> Right atrium of heart
     • Gall Bladder
     • Pancreas
       • Function
         • Exocrine
           • Secretion of pancreatic juice = contais essential digestive enzymes
           • Secreted into GI tract
         • Endocrine
           • Secretiotn of hormones - insulin and glucose
           • Secreted into the blood
       • Produce pancreatic juice = flows down pancreatic duct, join with common bile duct before duodenum

3. Nervous system Regulation

   • ENS
     • Functions independetly but influences by ANS
   • Reflexes
     • Gatric Reflex
       • food --> mouth --> stimulates strect receptors --> increased smooth muscle contraction --> increase mixing of stomach contects and stomach emptying
     • Enterogastric Reflex
       • Chyme enters Duodenum --> strecth receptors --> decrease gastric emtyping --> contracts the pyloric sphincter.
       • Protective reflex to prevent overfilling the duodenum
   • Role of ANS
     • Influences the ENS
     • Vagus Nerve (X) supplies parasympathetic fibers to most GI tract.
     • Parasymphathetic stimulation will increase gastric motility and secretions
     • Sympathetic stimulation will decrease gastric motiliy
     • Anger, Fear & Anxiety may inhibit GI function due to sympathetic stimulation

4. Effects of aging

   • Decreased secretion limits digestive function
     • Inadequately digested food = decreased nutrition
   • Decreased motility = loss of smooth muscle tone
     • = delayed passage of chyme and feaces
     • ++ risk of constipation
     • =altered voluntary control of external anal sphincter = feacal incontinence
   • Decreased neural and hormonal control
   • Decreased gustation and olfaction impact on the pleasure associated with food
     • Many older people ahve reduced appetite and require smaller portions due to decreased activity
   • Altered dental function resulting in decreased biting and chewing
     • ++ risk of gum disease if unable to attend to oral hygeine
     • Poorly fitted dentures

5. Processes

   • 1) Ingestion
     • Eating
   • 2) Secretion
     • Water,acid,buffers,enzymes - secreted into the lumen of GI tract
   • 3) Mixing and propulsion
     • Food and secretion through GI tract
     • movement = motility
   • 4) Digestion
     • Mechanical - physical breaking down, moving food
     • Chemical - digestive enzymes break down food = smaller molecules
   • 5) Absorption
     • Molecules through epithelial cells from GI tract into the blood and lymph
   • 6) Defecation
     • Elimination of wastes from the body

6. Nursing Implications

7. 3 stages of swallowing

   • 1) Voluntary movement of food into oropharynx
   • 2) involuntary movement of food into oesophagus
   • 3) Involuntary movement of food into stomach