Animal Physiology: Introduction to digestion exam 2

What are the three macronutrients?

carbohydrates, proteins, lipids

What are the five stages of digestion?

Ingestion, digestion, absorption, compaction, defecation

Ingestion

selective intake of food

Digestion

mechanical and chemical breakdown of food into a form usable by the body

absorption

uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood and lymph

compaction

absorbing water and consolidating the indigestible residue into feces

defecation

elimination of feces

Mastication

occurs in the mouth to decrease the food particle size and mixes with saliva, uses tongue to manipulate food

remastication

occurs in the mouth, regurgitation of food particles to further decrease size, important in ruminants that take in large amounts of food in short amount of time

What are the three majored paired glands in the mouth of mammals?

Parotid, mandibular, and sublingual

where is the parotid located

below and front of ear

where is the mandibular located

under the jaw

where is the sublingual located

under the tongue

What are the functions of saliva

lubricate, dissolve some foods, dissolve molecules to stimulate taste buds

what is saliva composed of

water (98-99%), mucus, salivary amylase, sodium, bicarbonate, and phosphate, lingual lipase, lysozymes, immunoglobulin A

What is salivary amylase

begins starch digestion in the mouth, found in humans, horses, swine, and dogs

what is the function of lingual lipase

activated by stomach acid to digest fat after swallowing

lysozymes function

kill bacteria

immunoglobulin A function

inhibits cell growth

Function of the pharynx

passage for air and food, propels food into the esophagus

function of the epiglottis

prevents food from entering trachea

function of the esophagus

muscular tube serving as conduit to move food from the mouth to the stomach, facilitates movement of ingested material through coordinated muscle movements

Peristaltic wave function

used for swallowing by using a ring of contraction to propel food down

upper esophageal region

voluntary control, initiated peristalsis process, skeletal muscle

lower esophageal region

involuntary control, moves food into stomach, smooth muscle

what happens in the oral phase of swallowing

voluntary control, tongue collects food and presses it against palate, food is formed into a bolus by tongue, and the tongue pushes the bolus towards laryngopharynx

what happens in the pharyngeal phase of swallowing

involuntary control, prevents food and drink from re-entering mouth or nasal cavity and lungs, airway and nasal cavity are closed and breathing is suspended, upper esophagus widens, bolus is driven downward by constriction of upper, middle, then lower pharyngeal constrictors

what happens in the esophageal phase of swallowing

involuntary control, peristalsis, when upright food and liquid drop through esophagus by gravity faster than peristalsis can keep up with, when it reaches lower end of esophagus the lower esophageal sphincter relaxes to let food pass into stomach

what is the gastroesophageal sphincter

physiological barrier between the esophagus and stomach, prevents gastric reflux into the esophagus

What is the function of the stomach?

food storage, and mechanical breakdown of food and liquify it, then begin chemical digestion of protein and fat

what is Chyme

soupy or pasty mixture of semi-digested food in the stomach

Stomach anatomy (from top to bottom) of monogastrics

Cardia, fundus, corpus (body), antrum, pylorus

cardia function

adjacent to the esophageal opening and helps to lubricate and protect the stomach from hydrochloric acid, produces mucus

fundus function

gastric secretion: HCL, pepsinogen, mucus

corpus function

food storage and enzyme digestion

antrum

mixing and grinding food

pylorus

regulation of gastric emptying, connects to small intestine

stomach anatomy of ruminants

Rumen, reticulum, omasum, abomasum

rumen function

hold on to hard-to-digest foods like the nitrogen in grass and break them down via fermentation, covered in papillae to increase surface area

reticulum function

guards against the intrusion of any large particles that have slipped past the rumen that need to be broken down more

omasum function

absorbs nutrients as it squeezes waters from feed particles and breaks them down into smaller and smaller particles

abomasum function

true stomach, where acids and digestive juices mingle with the food particles from here, food moves to the small intestine

True stomach anatomy

gastric pits (depressions in the gastric mucosa), lined with simple columnar epithelial cells

stomach cells

mucus cells, regenerative (stem) cells, parietal cells, chief cells, enteroendocrine G cells

Mucus cells function

secrete mucus, located in cardiac and pyloric glands

regenerative cells function

divide rapidly and produce continual supply of new cells to replace dead cells

parietal cells function

secrete hydrochloric acid, intrinsic factor and ghrelin (hunger hormone)

Chief cells function

most numerous, secrete gastric lipase and pepsinogen

enteroendocrine G cells function

secrete hormone and a paracrine messengers that regulate digestion

function of pepsin

protein degrading enzyme, digest dietary proteins into shorter peptides

functions of HCl

activates pepsin and gastric lipase, breaks up connective tissues and plant cell walls (help liquify food to form chyme), converts ingested ferric ions (Fe3+) to ferrous ions (Fe2+), contribute to nonspecific disease resistance by destroying most injected pathogens

what is pepsin

type of enzyme called zymogens which are secreted as inactive proteins and then converted to active enzymes by removing some amino acids by HCl

what is the autocatalytic affect

as some pepsin is formed, it converts more pepsinogen into more pepsin

What is gastric lipase

produced by chief cells, minor role in digesting dietary fat

What are the functions of gastric and pyloric glands

produce chemical messengers

what are the functions of chemical messengers

hormones to enter blood and stimulate distant cells, paracrine secretions that stimulate neighboring cells, peptides produced in the digestive tract and central nervous system

what signals the stomach to relax

swallowing center of the brain

how is the rhythm of peristaltic contractions controlled

pacemaker cells in longitudinal layer of muscularis externa

Steps in the vomiting reflex

relaxation—> stomach and lower esophageal sphincter muscles (pyloric sphincter closes, contraction—> abdominal muscles, expansion—> chest cavity to decrease intrathoracic pressure, relaxation—> upper esophageal sphincter, glottis closes—> protects lungs

True or false: vomiting is not rare in ruminants since they already regurgitate their food

false

True or false: horses are able to vomit because they can relax their lower esophageal sphincter

false

true or false: swine do vomit but it’s not well understood

true

true or false: cats and dogs can vomit

true