A&P 2 - Digestive system

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Describe the general function(s) of the digestive system

- primary route for intake of water, nutrients (CHO, proteins, lipids, nucleic acids, minerals, vitamins) required for cellular metabolism
- Principle route for deliver of meds and drugs
route for excretion of bilirubin and other toxins/metabolites
- minor route for elimination of water in feces
synthesis of vitamin K - needed by liver for production of clotting factors

Identify and describe the five stages of action carried out by the digestive system.

1) ingestion - intake of food
2) digestion - mechanical and chemical breakdown of food
3) absorption - uptake of nutrient molecules into digestive tract, then into blood/lymph
4) Excretion - secretion of bile allowing for removal unwanted substances
5) Elimination/Defecation - rectum eliminates of feces (undigestible substances, anything found in bile, anything produced in colon by flora that isn't absorbed, additional water that hasn't been absorbed)

Compare and contrast the processes of mechanical digestion and chemical digestion.

- Mechanical - physical breakdown of food; done through cutting and grinding of teeth, churning of small intestines and stomach, HCl release exposing food to enzymes, starting chemical digestion
- Chemical - series of hydrolysis reactions that breakdown macromolecules into monomers; carried out by digestive enzymes from salivary glands, stomach, pancreas and small intestines

Describe the 5 principal actions of the digestive system.

1) Motility - smooth muscle activity producing activities of churning, peristalsis, movement
2) Secretion - secretion of digestive enzymes, mucus, bile, hormones
3) Enzymatic Digestion
4) Absorption - uptake of nutrient molecules into digestive tract, then into blood/lymph
5) Excretion - function of liver removing toxins through bile

List all the primary organs of the digestive system and list their movement action.

- Mouth - masticating
- Pharynx - swallowing
- Esophagus - peristalsis (contraction (behind bolus) and relaxation (before bolus) of muscularis externa around bolus)
- Stomach - mixing/churning
- Small Intestine - peristalsis/segmentation
- Colon - Mass movement
- Rectum - elimination
- Anal Canal/Anus - elimination

List all the secondary organs of the digestive system and list their movement

- Teeth - grinding, biting, tearing
- Tongue/palate - taste, forming of bolus
- Salivary glands - Secrete digestive enzymes
- Lips/Cheeks
- Liver - secretion of bile to SI
- Gallbladder - stores and concentrates bile eventually going to SI
- Pancreas - secretes digestive enzymes and endocrine hormones to SI; secretes HCO₃- that helps w/ pH regulation - acts as buffer by combining w/ H+, neutralizing pH

List all the sphincters/valves that regulate the digestive tract and the organs that it separates

- Upper esophageal sphincter - separates pharynx and esophagus
- Lower Esophageal Sphincter (cardiac sphincter) - separates esophagus and stomach
- pyloric sphincter - separates stomach and SI
- Ileocecal valve - separates SI and LI
- Internal anal sphincter - smooth muscle that controls outflow of stool
- External anal sphincter - skeletal muscle that controls outflow of stool

Name the substance as it passes through each part of the digestive tract

- Food - input into oral cavity
- Bolus - forms in oral cavity and moves through pharynx, esophagus into stomach
- Chyme - moves through stomach, SI
- Feces (stool) - begins in LI, moves through rectum and excreted out anal canal

List the hormones secreted by each organs of the digestive system and the function of that hormone

- Gastrin - secreted by stomach stimulating activity of the stomach
- CCK - secreted by SI stimulating secretion of pancreatic enzymes; contraction of gallbladder and pyloric sphincter and inhibitory effects on stomach
- Secretin - secreted by SI if material entering SI is acidic, triggering secretion of HCO₃-
- Insulin - produced by beta-cells of pancreas and
stimulates storage of glucose in liver and muscle tissue and reuptake of glucose when blood-sugar is high, lowering blood sugar
- Glucagon - produced by alpha-cells of pancreas and
stimulates release of glucose from liver when blood-sugar is low, raising blood sugar

Describe the function of the pharynx

- epiglottis ensures that food doesn't move into lungs
- oropharynx initiates SC reflex, relaxing constrictor muscles of pharynx, pushing food down pharynx, continuing to move food down into esophagus

Describe the function of the esophagus

- secretes mucus to help w/ lubrication, allowing food to continue moving down esophagus

Describe the structure and function of the stomach

- contains 3 layer of muscles - additional oblique muscle layer allows stomach to twist
- secretes HCl enzyme - help breakdown chyme
- secretes many other digestive enzymes
- produces mucus that provides barrier b/t stomach and walls of stomach to prevent HCl from acting on walls of stomach

Describe the structure and function of the Small Intestine (SI)

- contains brush border - folded mucosal tissue (villi) that enhance absorption
- Brush border contains "brush border enzymes" - final stage of chemical digestion in digestive tract

Describe the function of the large intestine (colon)

- Contains intestinal flora bacteria and moves food toward rectum

Describe the importance of fiber in the diet

- Fiber in diet is important b/c it can't be digested and has a tendency to absorb water, helping w/ colonic transit

List the salivary glands and the digestive enzymes that they excrete

- parotid glands
- submandibular glands
- sublingual glands
- Secrete saliva though duct that contain A-antibodies, digestive enzymes (salivary lipase - digests fats, salivary amylase - digests CHO), mucus, lysozyme

List the digestive enzymes of the stomach and describe the function of each enzyme

- Pepsin(ogen) enzyme - breaks down proteins; pepsinogen becomes pepsin once comes in contact w/ HCl. Pepsin is enzyme that actually breaks down chyme
- Gastric lipase enzyme - breaks down fats
- Intrinsic factor - facilities absorption of Vitamin-B12 (necessary for cell mitosis)

List the cells of the stomach and the enzyme that each secretes

- Parietal cell - HCl, intrinsic factor
- Chief cells - pepsinogen, gastric lipase
- G-cells - gastrin

List the digestive enzymes that the brush border of the small intestines secrete and describe the function of each enzyme

- enterokinase - activates trypsin and chymotrypsin
- aminopeptidase - breaks down protein
- dipeptidase - breaks down protein
dextrinase - breaks down CHO
glucoamylase - breaks down CHO
maltase - breaks down CHO
sucrase - breaks down CHO
lactase - breaks down CHO

List the digestive enzymes that pancreas secretes and describe the function of each enzyme

- Pancreatic amylase - breaks down CHO
- Pancreatic lipase - breaks down fats
- Trypsinogen and chymotrypsinogen - break down proteins
- DNAase and RNAase - breaks down nucleic acids
- Procarboxypeptidase - breaks down from carboxy end of protein
secretes HCO3- - helps w/ pH regulation - acts as buffer by combining w/ H+, neutralizing pH

List the 4 layers that comprise the wall of the organs of the digestive tract

- Mucosa
- Submucosa
- Muscularis Externa
- Serosa

Describe the composition of the mucosa layer of the digestive tract

-Line lumen of digestive tract
Conatins:
- inner epithelium - columnar cells that allow for absorption
- lamina propria - connective tissue
- muscularis mucosae - smooth muscle tenses mucosa, enhancing surface area and contact w/ food

Describe the composition of the submucosa of the digestive tract

- Thicker layer of loose connective tissue
- Contains submucosal plexus
- contains blood vessels, lymphatic vessels, nerve plexus, glands

Describe the composition of the muscularis externa of the digestive tract

- 2 layers of muscle that run entire length of digestive tract
- inner layer - encircle track; thickens in some places forming sphincters ensuring food substance doesn't move backwards in tract
- outer layer - runs longitudinal; mechanism that propels food through tract

Describe the composition of the Serosa that lines the digestive tract

- Lower 3 - 4 cm of esophagus to rectum
- composed of areolar tissue and mesothelium

Describe the components of the enteric nervous system that allows local control and regulation of many activities of the digestive system.

1) submucosal plexus
- located between the muscularis mucosae and submucosal layers
- monitors chemical composition of contents in the lumen
2) myenteric plexus
- located between the inner circular layer and outer longitudinal layer of the muscularis externa
- regulates peristalsis and other mass movements of the muscularis externa

Describe the gastrocolic reflex

- Short reflex where stomach communicates to colon that stuff is coming, forcing colon to get rid of existing materials to rectum

Describe the defecation reflex

- Long reflex b/t rectum and sacral spinal nerves, stimulating Internal anal sphincter

Identify which division of the autonomic nervous system (ANS) provides neural input from the central nervous system to the digestive system.

- Vagus nerve (cranial nerve X) stimulates structures in mouth, pharynx, esophagus, stomach, SI, and parts of LI
- Sacral spinal nerves stimulates anus

Describe the steps and enzymes involved in the intestinal digestion and absorption of
carbohydrates

Digestion:
- broken down into carb monomers (glucose, fructose, galactose) until small enough to be absorbed into bloodstream, going to liver
- Broken down by -amylase enzymes, brush border enzymes
Absorption:
- absorbed into bloodstream via ICF in villi of SI
- Glucose, galactose, and fructose use facilitated diffusion to move into capillaries in core villus, eventually moving to liver

Describe the steps and enzymes involved in the intestinal digestion and absorption of proteins.

Digestion:
- broken down into amino acids until small enough be absorbed into bloodstream going to liver
- broken down by pepsin, -trypsin enzymes, -peptidase enzymes into single amino acid
Absorption:
-absorbed into bloodstream via ICF in villi of SI
- single amino-acid diffuses from villi of SI into epithelial cell lining SI, and eventually into bloodstream via capillaries in core villus

Describe the steps and enzymes involved in the intestinal digestion and absorption of lipids.

Digestion:
- broken down in fatty acids, glycerol, cholesterol until small enough to be absorbed into lymph; Glycerol and fatty acids get reassembled into TG and stored
broken down by -lipase enzymes
- bile (produced by liver) released via CCK when lipids present in SI
- bile acids and lecithin (both contain hydrophobic and hydrophilic) break down fat into smaller globules that have water soluble outer layer
- hydrophilic sides interact w/ water; hydrophobic sides interact with fat
- pancreatic lipase breaks down fat into fatty acids, giving FFA, monoglycerides (glycerol w/ on FA), then broken down into miceles
Absorption:
- absorbed into lymphatics, bypass liver
miceles (smaller droplets of fat) still to big to enter bloodstream to they enter lympatics via lacteal in the lymphatic capillary
- flows with lymph into thoracic duct, eventually entering bloodstream
- bypassing of liver allows us to directly store fat in adipose tissue to be used for energy after glucose has been depleted

Describe the steps involved in the intestinal digestion and absorption of nucleic acids.

Digestion:
- broken down into nucleotides
- broken down by DNAase and RNAase enzymes
Absorption:
- absorbed into bloodstream via ICF in villi of

Describe the steps involved in the intestinal absorption of vitamins.

Digestion:
- Not broken down chemically, but released from the food and absorbed
Absorption:
- absorbed into bloodstream via ICF in villi

Describe the intestinal absorption of minerals, such as Na+, Cl-, K+, Fe2+ and Ca2+.

Digestion:
- not broken down chemically, but released from food and absorbed
Absorption:
- absorbed into bloodstream via ICF in villi

Describe the intestinal absorption of water.

Water moves through intracellular gaps out of SI into bloodstream via osmosis

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