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 _________________________________________________________
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________________________________ - 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
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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
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Food breakdown begins in the ________________________ (oral cavity)
- Chewing fractures food into tiny pieces and grinding by teeth further increases the surface area for enzymes
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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
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________________________:
- _________________________ - specialized for biting off pieces of food
- _________________________ (cuspids) _ can rip food apart
- _________________________ (bicuspids) – tear apart food
- _________________________ - grind food
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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
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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
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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
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The esophagus pushes the bolus to the stomach by _____________________
- Peristalsis involves rhythmic waves of muscular contractions along the entire length of the digestive system
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__________________________, band-like muscles, are found at junctions in the digestive system
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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
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Opening and closing the sphincter regulates the passage of materials
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_________________________________________________________ (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
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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
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There are three regions:
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___________________________________ (10 inches)
- Closes to the stomach
- The site of most digestion
- ___________________________________ (8.2 feet)
- ___________________________________ (11.5 feet)
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___________________________________ (10 inches)
- The inner wall of the small intestine is folded into finger-like projections, _________________, which increase the absorptive surface
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The villi center contains capillaries and a lacteal, a lymph capillary
- Both engage in transporting nutrients
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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
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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
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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
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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
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Four regions of the large intestine:
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__________________________ 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 __________________________
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__________________________ is a pouch-shaped region from which the appendix projects
- 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
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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
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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
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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
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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
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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
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_____________________ 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
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____________________ 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