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Chapter 7

 

Chapter 7: Digestive System

 

7.1 The Digestive Tract

  • Its role is to break down foods into their component parts to be reassembled into forms the body can use for generating energy
  • Energy stored in chemical bonds of food is ultimately harvested
  • Food is broken down in the _________________________________________________________

 

  • ________________________________ - breakdown of food into substances useable by the body
    • ___________________________________: crushing, grinding, churning of food; creates smaller pieces thus increases surface area
    • ___________________________________: actions of acids and enzymes

 

  • Digestive tract is composed of five layers surrounding the ______________________

 

  • __________________________________ (mucosa) lines the lumen
  • __________________________________ is the next layer; made of connective tissue, it contains blood vessels and lymph nodes
  • The ______________________________________ surrounds the submucosa; made up of an inner circular muscle that encircles the gut, and an outer longitudinal muscle
  • The outer surface of the tract is the ___________________________, a thin layer of squamous epithelium
    • The serosa secretes fluids that keep the outer intestinal surface moist and helps the abdominal organs to slide against each other

 

  • Food breakdown begins in the ________________________ (oral cavity)
    • Chewing fractures food into tiny pieces and grinding by teeth further increases the surface area for enzymes
  • The palate (roof of the mouth) consists of the anterior __________________________ (contains bones) and the posterior _____________________________ (made of skeletal muscle) which ends in the fleshy _____________________
    • The uvula closes off the nasal cavity during swallowing

 

  • __________________________ cover the tongue surface
  • The tongue is skeletal muscle that helps shape the food into a __________________ that is pushed by the tongue  to the back of the throat
  • _________________________ are lymphoid tissue at the rear of the mouth that help protect against infection

 

  • ________________________:
    • _________________________ - specialized for biting off pieces of food
    • _________________________ (cuspids) _ can rip food apart
    • _________________________ (bicuspids) – tear apart food
    • _________________________ - grind food
  • Children have 20 teeth that begin to emerge around age two
    • Gradually they are replaced by adult teeth
  • Adults have a total of 32 teeth

 

  • Three pair of ________________________________ secrete saliva containing enzymes
    • Parotids are the largest, and are located in the upper cheeks in from of the ears
    • Sublinguals are found beneath the tongue
    • Submandibulars lie beneath the oral cavity floor
      • __________________________ contains salivary amylase (breaks down starch) and lipase (breaks down lipids)
      • Saliva moistens food and kills mouth bacteria

 

  • Swallowing moves food into the _______________________
  • The pharynx branches into the ________________________ (windpipe)
  • The cartilaginous _________________________ keeps swallowed food from entering the trachea

 

  • The esophagus pushes the bolus to the stomach by _____________________
    • Peristalsis involves rhythmic waves of muscular contractions along the entire length of the digestive system
  • __________________________, band-like muscles, are found at junctions in the digestive system
    • Opening and closing the sphincter regulates the passage of materials
      • The gastroesophageal sphincter is at the esophagus/stomach junction; prevents the acidic stomach contents from entering the esophagus
  • _________________________________________________________ (GERD) occurs when stomach acids reflux back into the esophagus, causing irritation
    • Chronic GERD should be treated because ulcers (open sores) may develop

 

  • The _____________________ is on the left side beneath the diaphragm

 

  • The stomach _______________________________________, but does not absorb food, except caffeine, aspirin, and alcohol
  • Food stretches the stomach causing peristalsis in the esophagus
  • Stomach contractions continue the mechanical contraction process resulting in a paste-like product, _________________________

 

  • Glands in the stomach wall secrete _______________________________ (containing hydrochloric acid) to begin chemical digestion
  • Gastric juice kills bacteria and breaks down connective tissue in meats
  • Pepsinogen is modified by HCl to form the enzyme ____________________ (digests proteins)
  • Mucus lines the stomach to protect it from being digested

 

  • HCl that might penetrate the mucus could cause a peptic ulcer
    • Most peptic ulcers are associated with Heliobacter pylori, a bacteria that can be treated with antibiotics

 

  • __________________________, the partially digested food combined with gastric juice, passes through the _______________________________ in order to enter the small intestine
  • The acidic chime is neutralized by pancreatic secretions that protect the intestinal wall

 

  • The _________________________________ (20 feet long) is the main site of chemical digestion and the primary site where nutrients enter the bloodstream
  • There are three regions:
    • ___________________________________ (10 inches)
      • Closes to the stomach
      • The site of most digestion
    • ___________________________________ (8.2 feet)
    • ___________________________________ (11.5 feet)

 

  • The inner wall of the small intestine is folded into finger-like projections, _________________, which increase the absorptive surface
  • The villi center contains capillaries and a lacteal, a lymph capillary
    • Both engage in transporting nutrients

 

  • The villi are covered by ___________________________, which further increases surface area
    • The increased surface area greatly enhances absorption of nutrients
  • Nutrients pass into the circulatory and lymphatic systems, and then into cells where they are used to make cellular structures or are metabolized to produce energy

 

  • Accessory organs make most of the digestive enzymes
  • Small intestine cells make lactase, which hydrolyzes lactose commonly found in milk
    • Lactose intolerance is a genetic deficiency that compromises lactase production, resulting in bacteria metabolizing the lactose and producing lactic acid
    • Lactic acid causes gas, cramps, and diarrhea

 

  • Hormones regulate the secretion of digestive juices

 

  • After eating, the stomach produces the hormone _______________________, which stimulates the production of gastric juices
  • The duodenum secretes _________________________ and ______________________________
    • HCl from the stomach causes secretin release and partially digested fats and proteins stimulate CCK release
  • CCK and secretin in the bloodstream stimulate digestive juice from the pancreas and gallbladder

 

  • The large intestine consists of four regions: the cecum, colon, rectum, and anus
  • The ________________________________ (5 feet) is the next stop for food (chime) in the small intestine
    • Its main function is to absorb water, salts, and some vitamins leaving fecal matter that will later be expelled

 

  • Four regions of the large intestine:
    • __________________________ is a pouch-shaped region from which the appendix projects
      • The appendix may be involved in fighting infections, but may become inflamed and have to be removed
    • __________________________ connects to the cecum and continues as the ascending, transverse, descending, and sigmoid colon before ending at the _________________________________________
    • Fecal matter exits through a sphincter at the end of the rectum, the __________________________

 

  • Undigested fibrous material makes up ____________________________, which collects in the rectum and stimulates nerves in the rectal walls that indicate the urge to defecate

 

7.2 Accessory Organs of the Digestive System

  • The ______________________, __________________________________, and ____________________ lie outside the aliementary canal but produce substances required for digestion
  • These connect to the duodenum via the common hepatic duct, common bile duct, and pancreatic duct

 

  • The ______________________ is on the right side of the abdomen below the diaphragm
  • It is divided into four lobes that are subdivided into __________________________

 

  • Cells of the lobules secrete substances into the blood and filter substances out of the blood
  • These structures are found between lobules
    • Bile duct takes bile from the liver
    • Hepatic artery branch carries oxygen-rich blood
    • Hepatic portal vein branch carries nutrients from the intestines

 

  • The liver produces _____________________
    • Bile contains the pigment _______________________________
    • Bile salts break down fats via emulsification, which prevents fats from clumping and provides exposed surface area to make enzymatic digestion easier
    • Bile passes from the liver to the small intestine through the hepatic ducts

 

  • Hepatic portal veins connect capillary beds in the liver and intestine
  • Fats entering the liver from the intestine are converted into fatty acids and carbohydrates, and then transported by the blood to tissues
  • ___________________________ monomers are joined in the liver to form ______________ when blood glucose levels are high
  • Glycogen is broken down into glucose monomers when blood glucose levels are low

 

  • Blood is filtered by liver ___________________________ cells to remove toxins, dead cells, pathogens, drugs and alcohol
  • Toxins are metabolized and their by-products are secreted into the blood for removal via urine or feces
  • The liver makes cholesterol found in cell membranes, blood plasma proteins, and immune proteins

 

  • The ___________________________ is attached to the liver
  • It stores and concentrates bile, which is released through the common bile duct to the duodenum to help emulsify fats
    • Salts in bile may crystalize to form gallstones that may have to be removed surgically

 

  • The _____________________________ produces and secretes digestive enzymes
    • ________________________________ breaks down starch
    • ___________________________ metabolizes lipids
    • ___________________________ is a protease, which digests proteins
  • Pancreatic cells respond to CCK and secretin by producing digestive enzymes, water and sodium bicarbonate

 

  • _______________________________________ neutralizes chime from the stomach, providing for optimal pancreatic function
  • The pancreas also secretes ________________________ and ___________________________, which regulate blood glucose levels
    • Insulin removes glucose from the blood to help it enter cells
    • Glucagon causes the liver to break down glycogen into glucose when blood levels are low
  • _______________________________________ is the inability to maintain blood glucose homeostasis

 

  • Complex carbohydrates (found in bread, pasta, fruits and vegetables) are hydrolyzed during digestion, releasing glucose into the bloodstream
  • Insulin is required for glucose to enter cells

 

  • _____________________ or _________________________________________ tends to arise in childhood
    • Type 1 diabetes do not produce enough insulin because their own immune system destroys their pancreatic cells
    • Regular injection of insulin is required

 

  • ____________________ or __________________________________________ tends to arise after 40 years of age and is often correlated with obesity
    • Arises either from decreased pancreatic production of insulin or reduced responsiveness in insulin by target cells
    • Target cells become insulin resistant
    • Weight loss may reduce the insulin resistance, otherwise insulin must be used
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