A&P Exam 2 (Digestive System)

Digestive system

Digestive system

the process by which nutrients become available to the body

Gastrointestinal tract (GI tract)

alimentary canal, continuous/muscular tube that runs through the body, open at both ends

GI tract functions

digest and absorb food

What must occur for food to be absorbed?

food must cross wall of tract to enter internal environment of the body

Accessory digestive organs (3)

teeth, tongue, and gallbladder

Accessory digestive glands (3)

salivary glands, pancreas, and liver

Ducts

connect all accessory organs and glands to the digestive tract and allow their secretion of substances to the tract

Six digestive processes

ingestion, propulsion, mechanical breakdown, chemical digestion, absorption, and defecation

Ingestion

taking food into the tract

Propulsion

moving food through the tract

Propulsion steps

swallowing and peristalsis

Swallowing

initiated voluntarily, ends in involuntarily

Peristalsis

involuntary, alternate waves of contraction/relaxation, squeeze contents forward through tract, major means of movement

Mechanical breakdown

physically changes food in preparation for chemical digestion through chewing, mixing, churning, and segmentation

Segmentation

local constrictions of intestine that results in mixing and facilitates absorption

Chemical digestion

carbohydrates, lipids, and proteins are broken down to chemical building blocks that can be absorbed

Enzymes involved in chemical digestion and where they come from/how they get into the tract

enzymes (bile, salt, mucus + water/electrolytes) produced by exocrine glands and released through neural or hormonal stimulation

Exocrine glands

secrete things though ducts to the outside of the body (i.e. the lumen of the GI tract)

Absorption

movement of molecules from the lumen of the GI tract into either blood or lymph

What molecules are taken in during absorption?

products produced by chemical digestion, water, vitamins, and minterals

Where does almost all absorption occur and how?

the small intestine, molecules must enter cell of organ before being transferred to blood/lymph through passive or active transport

Defecation

elimination of indigestible substances from the body in the form of feces

What three things control digestive activity?

innervation of glands, smooth muscle, or via hormones

How is digestive activity managed through innervation of glands

can activate or inhibit secretion of digestive juices

How is digestive activity managed through innervation of smooth muscle

can activate or inhibit, controls mixing and tract motility

Example of hormones controlling digestive activity

hormones produced and released from the small intestine inhibit the rate of stomach emptying after a fatty meal

Intrinsic control

short reflexes, control is the plexus of nerves within walls of GI tract enteric nervous system; called the gut brain

Extrinsic control

long reflexes, controls exerted from autonomic nervous system in CNS

Parasympathetic effect during extrinsic control

enhance secretory activity and motility

Sympathetic effect during extrinsic control

inhibit digestive activities

Functional anatomy

relating specific structure to specific function

Lips (structure and function)

core of skeletal muscle covered in skin, keep food between teeth when we chew (i.e. mechanical digestion)

Oral cavity

only part of GI tract involved in ingestion, bound by lips/cheeks, palate

Hard palate

bony roof of oral cavity, rigid and rough surface for friction and ease of chewing

Soft palate

muscle that aids in blocking off the nasopharynx during swallowing and sound production

Tongue

muscular organ involved in tasting, breathing, swallowing, and speaking

Phases of deglutition (swallowing)

buccal phase and pharyngeal-esophageal phase

Buccal phase

voluntary; tongue rises against hard palate and contracts, forcing food into oropharynx

Pharyngeal-esophageal phase

involuntary (initially controlled by swallowing center in brain stem); tongue blocks of mouth, soft palate rises to block nasopharynx, larynx rises/epiglottis covers trachea, upper esophageal sphincter relaxes and pharynx/esophageal sphincter contract

Effect of pharynx/esophageal sphincter contraction

esophageal peristalsis, gastro-esophageal (cardiac) sphincter relaxes reflexively to allow food into stomach

When and why does the gastro-esophageal (cardiac) sphincter close?

it closes after food enters to prevent regurgitation

Extrinsic salivary glands

saliva enters into oral cavity by ducts

Examples of extrinsic salivary glands

parotid glands (2), submandibular glands (2), and sublingual glands (2)

Intrinsic salivary glands

scattered throughout oral cavity, secrete a small amount continuously

Examples of intrinsic salivary glands

buccal glands

Saliva

contains water (majority), ions, digestive enzymes, and mucus

Saliva functions (4)

dissolves food so that it can be tasted, moistens food to help in mechanical digestion/bolus formation, begin chemical digestion of starches, and protect from microorganismsW

What type of defenses of saliva have against microorganisms

antibodies, lysozymes, a cyanide compound, and defensins-chemicals that attract WBCs into the mouth

What controls salivary glands (4)?

afferent signals from chemoreceptors, afferent signals from pressoreceptors, sight/smell, sympathetic signals from fight/flight

Example of afferent signal from chemoreceptors for salivary control?

acidic foods/liquids triggering salivary production

Example of afferent signal from pressoreceptors for salivary control?

pressure triggers salvatory nuclei in the brain stem, parasympathetic signals speed up production of serous/enzyme-rich saliva

What happens during sympathetic control to your saliva?

release of mucous like saliva sublingually, strong activation of fight/flight will constrict blood vessels inhibiting production of serous saliva

Teeth function

mechanical digestion of food by chewing, each tooth is modified for specific functions

How do you count teeth?

starting at midline and moving laterally

Types of teeth/number

incisors (2), canine (1), pre-molar (2), molar (3)

How many cusps do pre-molar teeth have?

2

How many cusps do molar teeth have?

4-5

Dental formula

number and relative position of different types of teeth; 2I, 1C, 2PM, 3M (upper/lower)

Deciduous teeth

baby/milk teeth; begin to appear at 6 months, with additional pairs appearing at 1-2 month intervals, fully replaced by 13 years old

First and last teeth to appear

incisors (first) and molars (last)

A complete set of teeth at 2 years old is how many?

20 teeth

Permanent teeth

appear around 6 years old, includes additional sets of molars

A full set of adult teeth (including wisdom teeth) is how many?

32 teeth

Materials in tooth structure (6)

dentin, collagen, pulp, enamel, hydroxyapatites, and cementum

Regions in tooth structure (6)

central pulp cavity, crown, neck, root, periodontal ligament, and root canal

Dentin

bone like material, bulk of tooth; produced throughout lifetime by odontoblasts/laid down rapidly, contain collagen

Pulp

connective tissue, blood vessels, and nerves in central pulp cavity, supplies nutrients to tooth and provides sensation

Crown

exposed part above gum (gingiva) line; dentin covered by enamel

Enamel

hardest substance in the body, densely packed hydroxyapatites, lacks collagen (not flexible, can chip easily)

Once a tooth has erupted, no more enamel forms (t/f)

true

Neck

constriction between crown and rootR

Root

part of tooth embedded in jawbone

Cementum

calcified connective tissue

Periodontal ligament

anchors tooth in jawbone in a fibrous joint (gomphosis)

Root canal

part of pulp cavity in root; open at base for vessels and nerves to pass through

Caries (cavities)

demineralization of enamel and dentin by a certain type of anaerobic bacteria

Series of events that leads to caries

plaque that sticks to teeth is fed on by bacteria that produce acids that dissolve calcium salts

Plaque

film of sugars, bacteria, and mouth debris that sticks to teeth, dietary sucrose increases thickness substantially

The mouth pH is slightly acidic/basic?

acidic

Periodontal disease

95% of people over the age of 35, accounts for 90% of tooth loss

Series of events that leads to periodontal disease

plaque accumulates and calcifies causing separation of gums/teeth, infection of gums causes separation between tooth and bony socket, bacteria invades and dissolves bone

Calculus

“stone,” plaque accumulation that calcified, also called tartar

Gingivitis

gum infection that can cause the separation of the tooth and bony socket

How can periodontal disease increase risk for heart disease?

chronic inflammation promotes atherosclerosis and bacteria can enter blood from infected gums causing clot formation

Pharynx structure and function

upper (pseudostratified ciliated columnar epithelium) and lower (stratified squamous epithelium); common passageway for air and food

Esophagus

muscular tube from pharynx to stomach that transports food down via peristalsis

How is peristalsis triggered in the esophagus?

food expanding walls causes muscles to contract

GERD (gastroesophageal reflux disease)

sphincter into stomach isn’t tight, allowing for acid reflux; can cause esophageal cancer resulting in the stomach being brought into the thoracic cavity

Causes of GERD (4)

overweight, pregnant, overeating, and spicy food

Stomach

muscular sac in superior, left part of abdominal cavity

Functions of the stomach (3)

storage of food, mechanical breakdown, and chemical digestion

Rugae

non-permanent folds that expand to accommodate entering food

Mechanical breakdown in the stomach

food is churned/mixed/broken down, acid causes denaturing

Chemical digestion of the stomach

production of pepsin that digests protein

Small intestine

is the major digestive organ, digestion (mechanical/chemical) is completed and almost all absorption occurs here

Three parts of the small intestine

duodenum, jejunum, and ileum

Duodenum

c-shaped section that curves around the head of pancreas, receives bile form the gallbladder/liver duct and pancreatic juice from a ductW

What two special features does the small intestine have for digestion/absorption?

length and plicae circulares

How long is the small intestine?

almost 21 feet with a 1 inch diameter

Plicae circulares

permanent folds in the lining that slow down movement of chyme through spiraling (increased surface area and time for absorption)