Digestive

Notes on this page	External links (more links here F	More Links
Nutrition	Book web practice	Bonus video - Entertaining and educational!
Metabolism Functional Anatomy Oral cavity Pharynx & Esophagus Stomach Small Intestine Large Intestine	Fundamental Physiology of the Digestive System	T.W.I.N.K.I.E. Project (or: ain't a college education great!) (This is more of a physics site, but many Twinkies are eaten in the course of the project)
Enzyme Lab Questions Fall 2007	Histology pictures
Handouts and Class Resources	Protein digestion & amino acids
Tour of the Digestive System instructions & Vocab list	Inner body WebAnatomy Practice Digestive System
Digestive System Syllabus	Nutrients and Digestive System Notes
Extra credit projects	Voyage through the digestive tract

Basal Metabolic Rate

Amount of energy needed to sustain the basic processes of life such as respiration, cellular metabolism, circulation, glandular activity, and maintenance of body temperature

Affected by:

§ Surface area à greater surface area requires more energy

§ Gender à males greater BMR than females

§ Body composition à muscle more metabolically active than fat

§ Endocrine gland functionà high thyroid activity increases BMR

§ Age à declines with age

Estimate your BMR

Women: burn 0.9 Kcal / Kg /hr Men: 1.0 Kcal/Kg/hr

1. Convert your weight in Pounds to Kg – divide by 2.2 (2.2 lb/Kg)

2. Multiple weight in Kg by BMR factor above (0.9 Kcal/Kg/hr or 1.0 Kcal/Kg/hr)

3. Multiply Kcal/Kg/hr by 24 hr in a day

4. Example: 140 lb. woman needs 1357.5 Kcal/day

Specific Dynamic Action = Amount of energy used to digest, absorb and process food.
SDA ~ about 10% BMR value

Physical activity effect

Activity level	Examples	Activity effect
Inactive	Driving, office work, sewing	+ 30%
Light	Walking, restaurant work, golf	+ 50%
Moderate	Gardening, walking briskly, skiing, tennis, dancing	+ 75%
Very	Chopping wood, aerobic exercise, basketball, swimming	+100%

Use the following formula to determine your total caloric needs for one day:

BMR + SDA + (BMR X Activity effect) = Total Energy Requirements for one day

Example: 140 lb woman, lightly active

1375 kcal/d + 138 kcal/d + [(0.50)1375 Kcal/d] = 2200 kcal/day

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Body temperature regulation

~ 60% food energy released as heat

must maintian homeostasis

balance between heat production & loss

hypothalamus (ANS) – body thermostat; regulates temp ~ 35-37.8o

1. Mechanisms to protect from heat loss

vasoconstriction of blood vessels – blood routed to deeper tissues

shivering - contractions of voluntary muscles produce heat; when body core drops below ability of skin capillaries to compensate

Consequences of extended heat loss

frostbite - extended loss of blood delivery to skin – ice crystals form - destroy tissue

hypothermia – vital signs decrease; drowsy, comfortable feeling – death

2. Mechanisms to prevent overheating

radiation – blood vessels dilate – skin flushed with blood – heat radiates from body

evaporation – environment warmer than body – evaporation of perspiration from skin surface.

Consequences of overheating

Hyperthermia (Heat stroke) – overheating depresses hypothalamus – positive feedback cycle (bad)
Increases body temp à increases metabolic rate à increases heat, cycle exacerbates problem.
Skin – hot, dry; brain damage

Heat exhaustion –( heat-loss mechanisms still operate) dehydration, low blood pressure, rapid heartbeat, cool clammy skin

Fever = controlled hyperthermia to fight invaders
     Macrophages release pyrogens (chemicals that act on the hypothalamus to set the thermostat higher)
     Vasoconstriction of skin produces chills
     Increasing metabolic rate speeds healing processes, inhibits bacterial growth
     Danger with prolonged high fever– body proteins cannot function optimally; can produce brain damage

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Functional Anatomy of Digestive System

Alimentary canal and accessory organs

Alimentary canal - long tube, open at both ends

Accessory organs - separate from alimentary canal; produce enzymes and chemicals which aid digestion

Structures of the Alimentary Canal	Structures of the Alimentary Canal
	Oral cavity (mouth) Pharynx Esophagus Stomach Small intestine Large intestine Accessory organs Salivary glands Liver Gall bladder Pancreas

6 Processes of Digestion	6 Processes of Digestion
	1. Ingestion Mouth - take in food 2. Mechanical digestion Mouth - chewing (teeth, tongue) Stomach - churn to make chyme Small intestine - segmentation 3. Chemical digestion Mouth - starch Stomach - protein Small intestine - protein, starch, fat 4. Propulsion Pharynx - Swallowing Esophagus - Peristalsis Stomach - Peristalsis Small intestine - Peristalsis Large intestine - Peristalsis 5. Absorption (Stomach) Small intestine Large intestine 6. Defecation Large intestine

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Oral Cavity

Structures	Digestive Processes	Function
Mouth: Lips, cheeks, hard palate, soft palate transverse ridges serve as friction bands for tongue during swallowing	ingestion (suckers or lappers) mechanical digestion	receptacle for food help form bolus
Tongue	mechanical digestion	manipulate food to teeth; help form bolus; taste *
Teeth *	mechanical digestion	masticate (chew) food
Salivary glands *	chemical digestion	salivary amylase breaks down starchesàsugars

F bolus - round moist mass of food formed in the mouth and prepared for swallowing

Human Dental patterns, Tooth structure & function

Humans – 20 deciduous (milk) teeth; 32 permanent teeth

Tooth	Structure	Function
Incisors (4/4)	Chisel shape	cutting & tearing food
Canines (2/2)	cone shape	Holding & tearing
Premolars (4/4)	2 rough cusps	crushing, grinding
Molars (6/6)	large, rough cusps	crushing, grinding

	Enamel	covers crown of tooth
	Dentin	Structural support to tooth
	Pulp	nerves, blood & lymph vessels
	Cementum	fastens tooth to periodontal ligament (borders socket)
	Root canal	passage of vessels & nerves to pulp
	Gingiva	fleshy covering over bony jaw

Salivary glands

3 salivary glands: sublingual, submandibular, parotid (click for diagram)

Produce > 1 quart saliva each day

Functions of saliva

§         cleanses teeth
§         begins starch digestion starch à disaccharides
§         helps form bolus
§         lubricates oral cavity & pharynx
§         dissolves food chemicals à taste *

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Walls of the Alimentary Canal

4 tissue layers (tunics)	Location & structure	Function
Serosa (Visceral peritoneum)	Outermost tunic	Binding and protection
Muscularis externa	Tunic below submucosa Circular & longitudinal layers of smooth muscle*	Segmental contractions and peristalsis
Submucosa	Tunic below mucosa many blood vessels & nerves	Absorption of nutrients and fluids into capillaries
Mucosa	Innermost layer (borders lumen of GI tract) Simple columnar epithelium with goblet cells	Secretion and absorption

Fsmooth muscle - involuntary muscle; cells are spindle-shaped;
distinct from cardiac and skeletal muscle.

Pharynx & Esophagus

Pharynx

· connects mouth to pharynx

· 13 cm (5 in.)

· serves respiratory system & digestive system

Esophagus

· connects pharynx to stomach

· 25 cm (10 in.)

· behind trachea

· 1/3 skeletal muscle; 1/3 skeletal & smooth muscle; 1/3 smooth muscle only

Propulsion: 1. Swallowing

1. Voluntary in mouth. Occurs when bolus forced against soft palate with elevated tongue

2. Involuntary once food enters pharynx & sensors stimulated. Uvula is elevated, sealing off nasal cavity; hyoid bone and larynx elevated so food is less likely to enter trachea; esophagus opened; epiglottis covers trachea as food enters esophagus

3. Bolus or fluid enters esophagus and is transported to stomach by peristalsis

Propulsion: 2. Peristalsis

Contractions of smooth muscle actively move food through alimentary canal (NOT gravity!)

·         Longitudinal & circular contractions in muscularis externa form wave of contractions
·         Circular muscles contract behind bolus (chyme)
·         Longitudinal muscles pushes food further along
·         ~8-9 seconds; stretch receptors in esophagus will initiate further waves if bolus is “stuck”

Transit of food from Mouth to Stomach:
Solid food: 4-8 sec.
Fluid 1-2 sec.

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Stomach

· Storage tank for food as it is
mechanically churned with gastric secretions and
chemically digested with enzymes

· Goal: change bolus à chyme (smooth, creamy)

· 15 – 25 cm long (6 – 10 inches

· Empty – 50 mL

· Full – 4 liter (~1 gallon)

Cardioesophageal sphincter* *(a.k.a. gastroesophageal sphincter)	Entry from the esophagus to stomach What is heartburn?
Muscularis externa: longitudinal, circular, oblique*	“churns” in three directions to produce chyme: longitudinal ô circular Q oblique õø
Rugae of mucosa	Folds of mucosa; expand when stomach fills Contains gastric pits & glands with specialized cells
Lesser curvature	Anchored by lesser omentum
Greater curvature	Outer boundary / body of stomach
Pyloric sphincter	Controls stomach emptying to small intestine Squirts small amounts of chyme into duodenum
Pylorus (pylorus = gatekeeper)	Opening to small intestine

The omentum a.k.a. belly fat

Gastric pits

	Mucous cells	secrete an alkaline mucus that protects the epithelium against acid and erosion
	Parietal cells	secrete hydrochloric acid
	Chief cells	secrete pepsinogen, the precursor to pepsin (protein digesting enzyme)
	G cells	secrete the hormone gastrin which stimulates further gastric juice formation

image from: http://webanatomy.net/anatomy/gastric_pits.jpg

Gastric juice

·         Produced in response to food related stimuli (positive feedback)
·         Produced by cells in gastric pits
·         Contains mucous, HCl, pepsin*

Pepsin

·         Secreted as pepsinogen (inactive form)
·         Activated by HCl (in presence of food) à Pepsin (active form)
·         Breaks bonds between certain amino acids in proteins à shorter chains
(doesn’t completely digest protein)
·         Only activated when food is present (positive feedback)
·         Requires acidic (low) pH

3 Phases of gastric secretion (positive feedback)

1. Cephalic phase
Response to sight, taste, smell, thoughts of food
Parasympathetic NS à initiates secretion of 50-150 ml gastric juice

2. Gastric phase
Food-induced stretching of tunica mucosa, along with chemical breakdown of protein,
Stimulates release of gastrin by G cells à gastric juice

3. Intestinal phase
Chyme entering duodenum stimulates release of cholecystokinin (CCK)
CCK stimulates chief cells à pepsinogen

Why doesn’t the stomach digest itself?

·         protected by thick mucus layer secreted by epithelial cells
·         epithelial cells shed (500,000/minute) continually
·         completely replaces itself in 3 days
·         pepsinogen is inactive when no food present

Click the H. pylori bacteria to learn about ulcers

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Small Intestine

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http://www.medicinenet.com/images/illustrations/pancreas.jpg

Pancreas - chemical digestion

http://www.colorado.edu/kines/Class/IPHY3430-200/image/pancreas.jpg

Connected to small intestine through pancreatic duct

Pancreas produces	Function
Enzymes	Fats – lipase Protein – protease (chymotrypsin, trypsin, carboxyeptidase) Carbohydrates – amylase
Sodium bicarbonate	Neutralize acid in chyme pH 2 à 6-6.5
Hormones (sugar metabolism)	Blood sugar high àinsulin à liver takes up glucose (converts to glycogen) Blood sugar low à glucagons à liver converts glycogen to glucose

Gallbladder- mechanical digestion

·         Connected to liver & small intestine
·         Stores bile produced by liver
·         Releases bile in response to cholecystokinin (food present in stomach)
·         Contracts to send bile through bile ducts into small intestestine

Function of bile

· Breaks fats into smaller droplets to increase access for enzymes to digest
· Enables intake of fat & fat-soluble vitamins

What are gallstones?

Liver - mechanical digestion

·         Beneath diaphragm, right side of body; protected by lungs
·         Largest internal organ: 1.7 Kg (3.5-4.0 pounds) in adult
·         2 main lobes, divided into segments

Liver functions

·         Produces bile for digestion of fats
·         Stores glycogen & regulates blood sugar
·         Produces and stores amino acids, vitamins & minerals
·         Synthesizes blood proteins (albumin) and clotting factors
·         Produces 80% of body’s cholesterol
·         Detoxifies harmful substances, including alcohol