A&P II Chapter 23

Mouth

Where food is ingested, then chewed and mixed with enzyme-coated saliva that begins the process of digestion. (Swallowing process is initiated here.)

Mouth Role in Process

Ingestion, Mechanical (chewing), Propulsion (swallowing), and chemical (salivary amylase)

Mouth Macromolecules Digested

Carbohydrate through the salivary amylase

Esophagus

Transport food from the mouth to the stomach

Esophagus Role in Process

Propulsion (peristalsis) that starts with deglutition (swallowing)

Esophagus Macromolecules Digested

None

Stomach

Temporary food storage tank that starts chemical breakdown of proteins. Essential to life to secrete intrinsic factors for vitamin B12 absorption

Stomach Role in Process

Mechanical breakdown, peristalsis, Chemical digestion (pepsin)

Stomach Macromolecules Digested

Proteins (pepsin)

Liver

Production of bile, metabolism, storage and detoxification

Liver Role in Process

Secrete bile which help with fat digestion (emulsification) and absorption

Liver Macromolecules Digested

Lipids

Pancreas

Supplies most enzymes needed to digest chyme as well as bicarbonate to neutralize stomach acid. Produce pancreatic juice (exocrine function) and secretes insulin and glucagon by pancreatic islet cells (endocrine function)

Pancreas Role in Process

Secretes (proteases, amylase, lipases, and nucleases)

Pancreas Macromolecules Digested

Carbohydrates, proteins, lipids, and nucleases

Gallbladder

Storage of bile that are not immediately needed

Gallbladder Role in Process

Release bile into the small intestine to aid in lipid digestion (emulsification which breaks fat into smaller size to make digestion easier)

Gallbladder Macromolecules Digested

Lipids (through bile emulsification)

Small Intestine

Major organ of digestion and absorption

Small Intestine Role in Process

Digestion and absorption, Peristalsis and Segmentation

When is segmentation done in the small intestine?

when food propels toward the large intestine after meals

When is peristalsis done in the small intestine?

when food is going down toward the large intestine between meals

Small Intestine Macromolecules Digested

Carbohydrates, proteins, lipids

Large Intestine

Absorbs most of the water remaining in the indigestible part of food, temporarily stores indigestible food, eliminates indigestible food in the form of feces (stool), and absorbs metabolites created by bacteria that are part of the normal flora of the large intestine.

Large intestine role in process food/drinks

propulsion, peristalsis, water absorption, defecation, houses bacteria that aid in digestion

Innervation of the GI tract

The enteric nervous system (gut brain), reflex arcs, and parasympathetic and sympathetic inputs

Intrinsic control (short reflexes)

mediated by the ENS and responds to internal stimuli within the GI tract like stretch and chemical changes. It also controls segmentation and peristalsis 

Extrinsic controls (long reflexes)

involves the CNS and response to external stimuli like sight, smell, taste, or thought of food

Parasympathetic (rest and digest)

enhances digestive process due to vagus (X) nerve stimulation digestion

Sympathetic (fight or flight)

inhibits digestion

Peristalsis

major means of food propulsion; alternating waves of smooth muscle contraction and relaxation

Segmentation

local constriction of intestine that mixes food with digestive juices

What organ secretes/creates Salivary amylase

Salivary gland (mouth);

Salivary amylase activation

active upon secretion

Salivary amylase purpose

Begins the digestion of carbohydrates in the mouth

What organ secretes/creates Amylase

Pancreas

Amylase Purpose

begins the breakdown of starch or glycogen

Amylase activation

active upon secretion

What organ secretes/creates Proteases

Pancreas

Why is proteases stored in its inactive form

prevent the pancreas from digesting itself

Proteases purpose

helps to digest protein

Proteases activation

in the Duodenum (small intestine)

What organ secretes/creates Lipases

Pancreas

Lipases activation

active upon secretion

Lipases purpose

helps digest lipids

What organ secretes/creates Bile

Liver

Bile purpose

fat emulsifier (breaks fat into smaller droplets that are easier to digest)

Bile activation

None

What organ secretes/creates Pepsin

Stomach

Pepsin purpose

helps digest proteins

Why is Pepsin stored in its inactive form

due to it breaking down plant cell walls, which kills many bacteria. Pepsinogen (inactive form name) 

Pepsin activation

Hydrochloric acid (HCL) with a pH of 1.5-3.5 

Where is Bicarbonate secreted ( the organ)

Pancreas

Bicarbonate purpose

Neutralize stomach acid

Bicarbonate activation

none needed acts as a buffer

What is the name of the venous portion of the splanchnic circulation

Hepatic portal circulation

Hepatic portal circulation

Drains nutrient-rich blood from digestive organs and Delivers blood to liver for processing before blood returns to right atrium

What are the unique structural modifications that the stomach has?

Mucosa layer and Muscularis externa

Stomach Muscularis Externa (extra layer)

its purpose is to allow the stomach to churn, mix, and move chyme, as well as pummel it, which increases physical breakdown and pushes it into the small intestine

Stomach Mucosa layer

Its surface has rugae, which flatten when the stomach is full. Its purpose is to trap bicarbonate rich fluid later that is beneath it

Small intestine modifications

Circular folds, Villi, and Microvilli (brush border) and their purpose is to increase surface area for maximum nutrient absorption 

Circular fold purpose

forces chyme to slowly spiral through lumen, allows more time for nutrient absorption

Villi purpose

for more absorption due to its dense capillary bed and lymphatic capillary called lacteal

Microvilli purpose

It has brush border that help with the final carbohydrate and protein digestion

What is the Stomach important secretion

Hydrochloric acid (HCl) with pH 1.5-3.5

What is the purpose of Hydrochloric acid (HCl) with pH 1.5-3.5

denatures proteins, activates pepsin, breaks down plant cell walls, kills many bacteria, and has intrinsic factor which is needed for absorption of B12 in small intestine. 

Post-digestion transport of carbohydrates, proteins, and some short chain fatty acid

Hepatic portal vein to the liver

Post-digestion transport of lipids

it enters the bloodstream using the systematic circulation via the lymph in the thoracic duct

Metabolic functions carried by the bacterial flora

Fermentation and vitamin synthesis

Fermentation

Ferment indigestible carbohydrates and mucin; Form short-chain fatty acids (SCFA) that are absorbed by the intestine and can be dispersed to body cells as a fuel source

Vitamin synthesis

Synthesize B complex and some vitamin K needed by liver to produce clotting factors