Digestion and Nutrition

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Digestion and Nutrition
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Introduction

• Digestion the mechanical and chemical breakdown
  of foods and the absorption of the resulting
  nutrients by cells
• Digestive System
• alimentary canal (extends 9 meters from mouth to
  anus)
• Accessory organs secrete substances used in the
  process of digestion
• The digestive system is a tube, open at both ends
  which supplies the body cells with nutrients
• alimentary canal (extends 9 meters from mouth to
  anus)
• Accessory organs secrete substances used in the
  process of digestion

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Alimentary Canal
Accessory Organs

• Mouth
• Pharynx
• Esophagus
• Stomach
• Small Intestine
• Large intestine
• Anal canal

Salivary glands Liver Gallbladder Pancreas
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General Characteristics of the Alimentary Canal

• Muscular tube that passes through the bodys
  ventral cavity
• The wall of the alimentary canal consists of four
  distinct layers
• Mucosa
• Submucosa
• Muscular layer
• Serosa (serous layer)

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Mucosa

• Surface epithelium, some connective tissue and a
  small amount of smooth muscle
• Developed into folds and tiny projections in some
  areas which extend into the lumen
• These folds increase the surface area for
  increased absorptive surface
• Contains glands which secrete mucous and
  digestive enzymes
• Serves as a protective layer

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Submucosa

• Contains mostly loose connective tissue
• Glands
• Blood vessels
• Lymphatic vessels
• Nerves
• Function carries away absorbed materials

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Muscular Layer

• Layer which produces movements of the tube
• Two layers of smooth muscle
• Inner layer encircles the tube (contraction
  decreases the diameter of tube)
• Outer layer longitudinal fibers which shorten
  the tube when contracted

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Serosa

• AKA Visceral peritoneum
• Outer covering of the tube
• Secrete serous fluid moisten and lubricate
  outer surface to allow free movement of organs

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Movements of the Tube

• Two types of movements
• Mixing movements occurs when smooth muscles in
  small segments of the tube contract rhythmically
• Propelling movements wavelike motion called
  peristalsis, the wave pushes the contents through
  the tube

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Mouth

• Where food is received
• Begins both mechanical (chewing)and chemical
  (saliva) digestion
• Includes
• Lips, cheeks, tongue, and palate
• Chamber between the palate oral cavity
• Space between the teeth, cheeks and lips -
  vestibule

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Tongue

• Fills most of the oral cavity
• Covered by mucous membrane
• Frenulum connects the midline of tongue to the
  floor of the mouth
• Body of tongue composed of skeletal muscle
• Papillae rough projections on surface provide
  friction and contain taste buds
• Connected at posterior to the hyoid bone

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Palate

• Forms the roof of the oral cavity
• Hard palate anterior
• Soft palate posterior
• Muscular arch connects to uvula
• During swallowing, prevents food from entering
  nasal cavity
• Palatine tonsils and pharyngeal tonsils both
  located at the back of the mouth closely
  associated with the soft palate
• Read Blue Box pg 397, what is tonsillitis, how
  is it treated?

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Teeth

• Two different sets of teeth form during
  development
• Primary teeth (deciduous teeth) 10 in each jaw
• Shed in the same order they appeared
• Roots are resorbed before pressure from new tooth
  pushed tooth out of socket
• Secondary teeth (permanent teeth) 16 in each
  jaw
• Usually appear 6 years of age, finish in late
  teens to 20s

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Tooth Structure

• Read pg 398, summarize structure of teeth
• Draw diagram of a tooth, figure 15.9, pg 399

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Salivary Glands

• Secrete saliva
• Glands contain both serous cells and mucous cells
• Serous cells produce water fluid that contains
  amylase which begins chemical digestion of
  carbohydrates
• Mucous cells secrete thick mucus which binds food
  particles and lubricates during swallowing

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Major Salivary Gland

• Three pairs of major salivary glands (there are
  many other minor ones)
• Parotid
• Submandibular
• Sublingual
• Each secretes varying proportions of serous and
  mucous fluids

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Pharynx and Esophagus

• Do not digest food, but both serve as important
  passageways
• Summarize the steps to swallowing on pg 400-401
• Esophageal hiatus where esophagus penetrates
  the diaphragm
• Lower esophageal sphincter closes the entrance
  of to the stomach preventing regurgitation of
  stomach contents

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Stomach

• J-shaped pouch that lies under the diaphragm
• Capacity of approx. 1 liter or more of food
• Begins protein digestion as food mixes with
  gastric juices
• Four regions cardiac, fundic, body, pyloric
• Pyloric sphincter muscular valve that controls
  gastric emptying

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Gastric Secretions

• Read pg 402-403 and summarize
• Tissues involved in secretion of gastric juices
• Composition and function of gastric secretions

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Regulation of Gastric Secretions

• Gastric juice is continuously produced and is
  controlled by hormones and neural signals (taste,
  smell, sight).
• Signals stimulate release of acetylcholine which
  stimulates gastric glands to secrete gastric
  juice (hydrochloric acid and pepsinogen and
  gastrin a hormone that increases gland secretion)
• In the small intestine, acid triggers inhibition
  of gastric juice secretion while causing the
  intestinal wall to secrete another hormone which
  decreases gastric motility

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Gastric Absorption

• Gastric enzymes begin breaking down proteins, but
  the stomach is not well adapted to absorbing
  nutrients
• The stomach can absorb small quantities of water,
  salts, alcohol and some lipid-soluble drugs.

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Mixing and Emptying Actions

• Chyme semi-fluid paste of food particles and
  gastric juice produced in the stomach
• As the chyme is pushed toward the pyloric
  sphincter, the muscle begins to relax and stomach
  contraction pushed the chyme a little at a time
  into the small intestine
• The rate at which the stomach empties depends on
  the fluidity of the chyme and type of food
  present
• Fatty foods 3-6 hours
• High protein foods faster
• Carbohydrates faster than fats and proteins

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Pancreas

• Endocrine gland that also functions as an
  exocrine gland by secreting digestive juice
  (pancreatic juice)
• Closely associated with the small intestine
• The pancreatic duct connects to the small
  intestine in the same place as the bile duct

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Liver

• Located in the upper right quadrant of the
  abdominal cavity, inferior to diaphragm
• Partially surrounded by ribs
• Reddish-brown color well supplied with blood
  vessels

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Liver Structure

• Connective tissue divides the lobes of the liver
  right (large) and left lobe (smaller)
• Each lobe is separated into tiny hepatic lobules
  (functional units of the liver)
• See diagram on pg 407
• Blood from the digestive tract, which is carried
  in the hepatic portal vein, brings newly absorbed
  nutrients to the hepatic cells
• Bile canals located in the hepatic lobules empty
  into larger ducts which merge into the common
  hepatic duct.

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Liver Function

• Carbohydrate metabolism by maintaining blood
  glucose
• Respond to hormones like insulin and glucagon
• Oxidizes fatty acids to synthesize lipoproteins,
  phospholipids and cholesterol
• Transports fat to adipose tissue for storage
• Protein metabolism synthesizes plasma proteins
  for clotting, forms urea
• Removes toxic substances such as alcohol form
  blood
• Secretes bile

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What is bile?

• Yellowish-green liquid secreted by the hepatic
  cells
• Contains water, bile salts, bile pigments
  (bilirubin and biliverdin), cholesterol, and
  electrolytes
• Bile salts digestive function

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Function of Bile Salts

• Aid digestive enzymes
• Affect fat globules, like soap/detergent
• Emulsification - break down fat globules into
  smaller droplets which aides the enzyme lipase in
  digesting the fat molecules more effectively.
• Aid in the absorption of fatty acids, cholesterol
  and fat-soluble vitamins
• Lack of bile salts results in poor lipid
  absorption and vitamin deficiencies.

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Small Intestine

• Tubular organ, extends form pyloric sphincter to
  the beginning of the large intestine
• Receives secretions form the pancreas and liver
• Completes digestion of nutrients in chyme
• Absorbs the products of digestion
• Transports the residues to the large intestine

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Parts of the Small Intestine

• Consists of three portions
• Duodenum
• About 25 cm long, follows a C-shaped path
• Jejunum
• Mobile and lies free in the peritoneal cavity,
  largest section of the small intestine
• Ileum
• Lowermost portion of the small intestine, not
  distinctly separate from the jujunum, but smaller
  in diameter than the jujunum
• Mesentery membrane of supportive blood vessels,
  nerves, lymphatic vessels

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Structure of the Small Intestine Wall

• Inner wall appears velvety due to many tiny
  projections called intestinal villi,
• Most numerous in the duodenum and the proximal
  portion of the jejunum
• Increase the surface area of the intestinal
  lining aiding in the absorption of digestive
  products

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Secretions of the Small Intestine

• Goblet cells secrete mucus
• Cells in the proximal portion of the duodenum
  secrete large quantities of alkaline mucus
• Enzymes located in the intestinal mucosa include
• Peptidase (digests proteins)
• Sucrase, maltase, lactase (spilt disaccharides
  into monosaccharides like fructose and glactose)
• Lipase (splits fats)
• Summarize the table on pg 414 in your notes

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Lactose Intolerance

• Occurs in people who do not produce enough
  lactase to digest lactose (milk sugar)
• Lactose remains undigested
• Increases the water content in the intestines
• Intestinal bacteria metabolize the undigested
  sugar which produces acids and gases
• Leads to bloating, intestinal cramps and diarrhea

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Absorption in the Small Intestine

• Villi increase the surface area of the intestinal
  mucosa
• The small intestine is extremely efficient at
  absorbing digestive products that very little
  absorbable material reaches the distal end.

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Movements of the Small Intestine

• Like the stomach, the small intestine carries on
  mixing movements and peristalsis
• Chyme moves slowly through the small intestine,
  taking anywhere from 3 to 10 hours to travel its
  length
• At the distal end of the small intestine, the
  ileocecal sphincter joins the small intestine to
  the large intestine

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Large Intestine

• Has a greater diameter than the small intestine
• Begins where the ileum joins the cecum
• Functions
• absorb water and electrolytes form chyme that
  remains in the alimentary canal
• Forms and stores feces

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Parts of the Large Intestine

• Cecum beginning of large intestine, pouch-like
  structure
• Veriform appendix projects downward as a narrow
  tube with a closed end, it has no known digestive
  function, but does contain lymphatic tissue
• Colon four portions
• ascending, transverse, descending and sigmoid
  colon
• Rectum lies next to the sacrum, ends about 5 cm
  below the tip of the coccyx where it becomes the
  anal canal
• Anal Canal last 2.5-4.0 cm of the large
  intestine, open to the outside at the distal end
• Two sphincter muscles
• Internal anal sphincter muscle smooth muscle
• External anal sphincter skeletal muscle

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Function of the Large Intestine

• Contains many tubular glands composed mostly of
  goblet cells which secrete mucus
• Mucus protests the intestinal wall against the
  abrasive action of the matter passing through it
• Absorption takes place in the proximal half of
  the tube, storage occurs in the distal half
• Intestinal flora bacteria that inhabit the
  large intestine and break down some of the
  molecules that are not already digested (ie.
  cellulose, pg 418)