Davidson Unit 10 Digestive System

functions of digestive system

1. ingestion (taking in food)
2. propulsion (movement of food)
3. digestion + absorption (breaking down food & taking in nutrients)
4. egestion (elimination of waste)

2 sections of digestive system:

alimentary canal (GI tract) & accessory organs

alimentary canal--

mouth, pharynx, esophagus, stomach, small intestine, large intestine

accessory organs--

teeth, tongue, salivary glands, liver, gallbladder, pancreas

layers of alimentary canal (superficial to deep)

serosa, muscularis, submucosa, mucosa

serosa--

(visceral peritoneum) membrane that secretes slippery watery fluid; reduces friction as organs contract + move

muscularis-

layer of muscle extending in 2 directions: circular & longitudinal layer

submucosa-

contains glands, nerve fibers, & blood vessels

mucosa-

1. secreting mucus, digestive enzymes, & hormones
2. absorption of nutrients
3. protection from pathogens (lymphatic tissue)

teeth:

accessory digestive organs, responsible for beginning the mechanical digestion process

types of teeth

incisors (cutting), canines (cuspids; tear & pierce), premolars (bicuspids; crushing), molars (tricuspids; grinding)

anatomy of a tooth:

enamel (hard, protects tooth), dentin (calcified connective tissue), pulp cavity (has blood vessels + nerves), gingivae/gum (seal arnd tooth), cementum (covers dentin in root)

child vs adult teeth

20 teeth @ toddler, adult has 32; incisors come in first (6-8 months) then canines and molars (teens/early twenties)

saliva

99% water, mucus (lubricates food for swallowing), analyse (breaks down starch), lysozymes (kill bacteria), antibodies (mark foreign invaders)

structures in the mouth:

hard palate (bony roof of mouth), soft palate, uvula (prevents swallowed food from entering nasal cavity), & tongue (helps push food towards esophagus)

deglutition

swallowing; has 2 major phases: buccal and pharyngeal-esophageal phase

buccal phase--

after mastication (chewing) + mixed w/ saliva, food lump \= bolus, forced into pharynx by tongue; consciously-controlled process

pharyngeal-esophageal phase--

epiglottis (thin flap of skin) blocks larynx, and uvula blocks nasal cavity, this causes food to go to esophagus instead of into respiratory system, bolus is propelled down by peristalsis

peristalsis:

waves of muscle contractions; involuntary, caused by parasympathetic nervous system rather than gravity

stomach:

muscular sac w/ thick walls, continues process of mechanical + chemical digestion

sphincters:

thick rings of muscle; serve as gatekeepers to allow food to enter & leave at appropriate time

2 sphincters of stomach:

enter cardiac (separates esophagus from stomach) & leave thru pyloric (separates stomach from small intestine)

3 layers that follow outer layer of serosa:

longitudinal muscularis, circular muscularis, and oblique muscularis; help churn food (maceration) + propel to small intestine

rugae:

folds/"wrinkles" of mucosa that stretch when stomach is full

specialized gastric and gland cells in mucosa layer:

mucous, chief, and parietal cells (all make up gastric juices)

mucous cells-

secrete mucus to protect stomach lining

chief cells-

secrete pepsinogen (inactive enzyme)

parietal cells-

secrete HCl to kill microbes in food & convert pepsinogen --\> pepsin (digestive enzyme) which breaks down food proteins

chyme:

soupy mixture from squeezing stomach + gastric juices

small intestine-

location of most digestion + nutrient absorption, 10ft long in adult, 3 sections \= duodenum, jejunum, ileum (joins intestine at ileocecal sphincter)

villi:

tiny finger-like projections in lining of intestine filled w/ blood vessels; help absorb nutrients efficiently

glands in small intestine

many line the small intestine + secrete digestive hormones

mucus-

alkaline mucus from glands & duodenal glands protects from pathogens

secretin-

inhibits release of gastric juices when chyme is very acidic

colecystokinin (CCK)-

cause gall bladder to release bile

maltase, sucrase, lactase-

breakdown enzymes

peptidase & enterokinase-

break down proteiens

in small intestine, chyme must be

slowed down b/c small int needs time to absorb

circular muscles in the intestinal wall cause

segmentation of the chyme

longitudinal muscles in the intestinal wall cause

peristaltic contractions

large intestine-

food from small int --\> large int, 3 major sections \= cecum, colon (ascending, transverse, descending), & rectum

2 major functions of large intestine:

absorption of water back into the body ; removal of waste (feces) thru rectum and anus

bacteria in large int

large amt (abt 3lbs) located here that help produce vitamins B and K (strong doses of antibiotics can disrupt these bacteria & cause vitamin deficiencies)

haustra:

small pouches that give the large intestine its lumpy appearance

haustral contractions:

slow, segmenting movements, last abt 30 min after food moves into large itn

mass movements:

slower & more powerful movements that push waste towards rectum 3-4x a day

rectum collects and stores

undigested waste + bacteria, as it fells pressure is placed on internal anal sphincter causing it to relax, the external anal sphincter needs to be voluntarily relaxed to release built-up feces thru anus

liver-

largest internal organ, 2 major lobes \= L & R, contains hepatic sinusoids (full of blood)

functions of liver cells:

removing bacteria and old RBCs, detoxifying blood from drugs and poisons, storing glycogen and producing fats, manufacturing proteins, storing iron and copper

bile:

greenish fluid responsible for breaking down fat, secreted by liver

gallbladder-

small, green sac attached to liver by bile duct; stores bile b4 sending it to small int to digest fats

gall bladder concentrates bile by

removing water; if too much is removed, gallstones (made of cholesterol crystals) may form [gallbladder may be removed if stones too large/painful]

pancreas-

long, thin gland behind stomach

pancreas functions:

1. secreting digestive enzymes & sodium bicarbonate- a base that neutralizes stomach acid so digestive enzymes are not affected by the lowered pH
2. secreting hormones that regulate blood sugar levels

metabolism:

life-sustaining chemical rxns of body; 2 types \= catabolism & anabolism

catabolism:

breaking down of complex molecules while releasing energy/ATP

anabolism:

formation of complex molecules while using energy

nutrients:

substances that provide the body w energy & can be used for growth

4 macronutrients required by body:

carbs, lipids, protiens, water

2 micronutrients:

vitamins & minerals

carbohydrates-

- sugars/glucose; main source of eneergy
- broken down by: salivary amylase; pancreatic amylase; brush border enzyme (epithelial enzymes of small int)
- broken down in: mouth; small int
- process: cellular respiration (glycolysis, citric acid, ETC); excess sugar \= stored as fat or glycogen

lipids-

- fats; secondary source of energy
- broken down by: bile salts; pancreatic lipase
- broken down in: liver; small int
- process: are insoluble so must be emulsified first; broken into acetic acid --\> metabolized into ATP or stored for later use

proteins-

- make up majority of cellular structures; some used as enzymes
- broken down by: pepsin, pancreatic enzymes, brush border enzymes
- broken down in: stomach (in presence of HCl), small int
- process: polypeptide chains broken into individual amino acids, which r actively pumped into cell

water used for:

chemical rxns, dissolving food for digestion, maintaining blood pH lvls, regulating body temp thru sweat

vitamins:

organic molecules needed in small quantities; can be broken down by heat, acid, or air

minerals:

inorganic molecules needed in small quantities (ex. calcium, chlorine, fluorine, iodine, iron, magnesium, phosphorous, potassium, zinc)

order of anatomical structures involved in the process of digestion from ingestion to excretion of waste

mouth, esophagus, stomach, small intestine, large intestine, rectum and anus & sections within

peptic ulcer

sore that develops on lining of esophagus, stomach, or small intestine

constipation

condition where stools are hard, dry, or lumpy, stools are difficult/painful to pass, or feeling that not all stool has passed

dumping syndrome

group of symptoms, like diarrhea, nausea, light-headed/tired after meals caused by rapid gastric emptying

appendicitis

condition where appendix is inflamed and filled with pus causing pain

Cholecystectomy

surgical removal of gallbladder due to gall stones

Cirrhosis

chronic inflammation where liver is severely damaged, becomes hard + fibrous

Indigestion

Group of symptoms like bloating, pain, burning, feeling full after eating + discomfort

Gastroenteritis

vomiting, diarrhea, fever, headaches, gut infection caused by bacterium/virus

Helicobacter pylori

bacterium associated with development of stomach ulcers

Ulcerative colitis

chronic, inflammatory bowel disease where open sores form in colon, colon is inflamed, small intestine rarely affected

Gastroparesis

affects stomach muscles, prevents proper stomach emptying

diarrhea

loose, watery stools

Crohn’s disease

chronic, inflammatory bowel disease of unknown origin, causing diarrhea, severe abdominal pain, fever, chills, nausea, weight loss

Pancreatitis

serious inflammation of the pancreas because of activation of pancreatic enzymes in pancreatic duct, digests pancreatic tissue and the duct

hiatal hernia

structural abnormality in which superior part of stomach protrudes slightly over diaphragm

Celiac Disease

serious sensitivity to gluten, protein in wheat, causes immune system to attack

hemorrhoids

condition of inflammation and enlargement of the rectal veins

cystic fibrosis

inherited disorder causes damage to lungs, digestive system, and other organs in body, affects cells producing mucus, sweat, digestive juices

gastroesophageal reflux disorder

cardioesophageal sphincter fails to close tightly and gastric juice backs up into esophagus, which has little mucus protection.

irritable bowel disease

disorder affecting colon + rectum, causing bouts of constipation and diarrhea, cramping, bloating, excessive gas