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ISU / Science / AN S 214 / What are the major parts of the digestive system?

What are the major parts of the digestive system?

What are the major parts of the digestive system?


School: Iowa State University
Department: Science
Course: Domestic Animal Physiology
Professor: Adur
Term: Fall 2016
Tags: animalscience, anatomy, Physiology, digestion, AnS214, and organs
Cost: 25
Name: AnS214-Week 2 Lecture Mon-Fri
Description: Well here it is, everyone! The continuation of the Digestive Tract all the way to completion (lectures Monday, Wednesday and Friday). There will be a visual model that I intend to upload in the next
Uploaded: 09/03/2016
11 Pages 59 Views 1 Unlocks

AnS 214: Digestion Part 2

What are the major parts of the digestive system?

❏ Mechanical

❏ Chemical

­ Microbial: most ruminants

­ Enzymatic: most monogastrics

◼Regulation of the Digestive Tract

❏ Neural Control

­ Muscular activity

­ Secretory activity

❏ Hormones

­ Enzymatic activity

❏ Paracrine Secretion

­ Enzymatic activity

­ Growth & Repair

◼Passage of Food & Parts that Play a Role in Digestion Diagram

What is the regulation of gastric motility?

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◼Stomach (Temporary “Storage Tank”)

❏ Location of Mechanical and Chemical digestion

­ Mechanical and chemical digestion breakdown of protein and fat into chyme.

❏ Minimal absorption of nutrients and water occur in the stomach

­ Mostly proteins, carbs and fats

­ Some lipid­soluble substances with break down in the stomach

e.g. alcohol and aspirin

❏ Gross Anatomy of the Stomach Diagram

What is the meaning of borborygmi?

We also discuss several other topics like What are the layers of the dura mater?

❏ Gastric Gland Secretions

­ 2 to 3 L of gastric juice is produced in a day

­ Components of gastric juice are: H2O, HCl and pepsin

❏ Parietal Cells

­ Intrinsic factor: Glycoproteins and vitamin B12 absorption

­ Hydrochloric Acid helps to break down proteins and kill bacteria → will eventually activate pepsin and lingual lipase release

❏ Chief Cells

­ Pepsinogen (inactive form of enzyme) and lipases

→ pepsin (active form of enzyme)

❏ Enteroendocrine Cells

­ Chemical messengers

➤Paracrine, serotonin, histamines 

➤Hormones, somatostatin, gastrin

◼Regulation of Gastric Secretions

❏ Occurs in 3 Phases:

1. Phase I: Cephalic Phase (has to do with brain function) We also discuss several other topics like What is a musical comedy called?

­ Lasts about a few minutes

­ Phase in which your body begins to prepare itself to receive food

­ Salivation occurs because of sight, smell, taste or thought of food

­ Brain stimulates salivary glands and gastric functions

2. Phase 2: Gastric Phase:

­ Lasts 3 to 4 hours

­ Occurs after food has been chewed, ingested and swallowed

­ Food is transported from the pharynx to the esophagus and then to the stomach → stretch receptors are activated

3.  Phase 3: Intestinal Phase

­ A few hours long

­ The phase in which food begins to digest We also discuss several other topics like Why do cells have semi-permeable membranes?
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­ Food starts to pass through the small and large intestine so nutrients can be absorption

◼Regulation of Gastric Motility

❏ Swallowing chewed food signals the stomach to relax so the food ingested can stretch the stomach until the stretch receptors tell the brain to make our bodies stop (the feeling of being full).

❏ Myenteric pacemaker cells→ signal the longitudinal muscle layer to create three peristalsis waves per minute.

­ Waves of small contractions churns ingested food and mixes it with gastric stomach juices

­ Stronger contractions sends some food into the duodenum (the first section of the small intestine).

­ A standard meal is fully digested within 4 hours on average

­ Borborygmi: stomach rumblings is the result of peristalsis occurring in the stomach and small intestine

­ When your stomach is empty the rumblings are projected to be louder because there is nothing in the stomach to muffle the rumblings

◼Accessory Organs: Liver, Gallbladder and Pancreas

­ All release important secretions into the duodenum via ducts to aid in the continuation of digestion of food.

❏ Each organ plays an important role in digestion

1. Liver

➤Produces bile and secretes it

­ Bile is an alkaline solution containing:

a. Bile Salts​: aid in fat emulsification and absorption

­ Bile salt gets recycled via the enterohepatic circulation

b. Triglycerides and pigments:​ bile pigmentation is called bilirubin

­ Bilirubin​ is formed in the Heme (“Heme” → “Hemoglobin”)

­ The Sterobilin pigment​ is what gives healthy feces the

brown color

c. Cholesterol

d. Phospholipids​ and

e. Electrolytes

2. Gallbladder

➤Stores and excretes bile

only­ then releases when

needed via cystic duct to the

bile duct.

3. Pancreas

➤Endocrine function

­ Secretes insulin and


­ Metabolizes carbohydrates

➤Exocrine function

­ Acini​: clusters of secretory cells

­ Secretes pancreatic juice

­ Zymogen granules​ of Acini contain digestive enzymes

­ Trypsinogen​ (inactive form) and Trypsin​ (active form) are secreted

◼Small Intestine

❏ Duodenum: (1) neutralizes acids and breaks down fats

❏ Jejunum: (2) location where most digestion and absorption

❏ Ileum: (3) connects to that large intestine

­ Peyer’s patches​: keeps bacteria where it is supposed to be (in the intestines) ➤ Maximum Absorption → Structural Mods

­ Increase surface area for nutrient absorption

­ Circular Folds

­ Villi

­ Microvilli

A. Structural Mod. 1: Circular Folds

­ Permanent

­ Forces chyme to slowly spiral through lumen so maximum absorption can occur

B. Structural Mod. 2: Villi

­ Motile fingerlike extensions of the mucosa

­ Villus Epithelium *1 

­ Enterocytes → simple columnar cell → absorption

­ Goblet Cells → secretory → mucus

C. Structural Mod. 3: Microvilli

­ Cytoplasmic projections of absorptive cells → brush border *2 

­ Bear brush border enzymes → complete carbohydrates and protein

digestion in the small intestine

1 Villus Epithelium: the epithelium of the structural modification, villi

2 Brush Border: is the microvilli­covered surface of simple cuboidal epithelium and simple columnar epithelium cells found in certain locations of the body.

◼Intestinal Crypts

❏ Absorptive epithelial cells

❏ Few goblet cells ­ mucus producers

◼Small Intestinal Motility

❏ Mixes chyme with intestinal juice, bile and pancreatic juice

❏ Churns chyme to increase contact with mucosa for absorption and digestion ❏ Moves residue towards large intestine

➤Segmentation: occurs after you eat something

➤Peristalsis: occurs in between eating something

◼Carbohydrate Digestion in The Small Intestine

❏ Salivary amylase stops working in the stomach because most dietary starch is digested already

❏ Pancreatic amylase completes first steps of digestion in the small intestine ❏ Brush border enzymes act upon oligosaccharides, maltose, sucrose, lactose and fructose

❏ Carbohydrate Absorption

­ Sodium­Glucose Transport Proteins​ that are located in the membrane of the small intestine help absorb glucose and galactose

➤These proteins actively transport across the membrane and into cells

­ Fructose absorbed by facilitated diffusion then converted to glucose (sugar) inside the cell

◼Protein Digestion and Absorption in The Small Intestine

❏ Pepsin (the active form of pepsinogen) needs an acidic pH to function (pH 1.5 to pH 3.5) ❏ Pepsin becomes inactive when it reaches the duodenum and mixed with the alkaline pancreatic juices (pH 8).

❏ Fat Digestion and Absorption in the Small Intestine

Important Vocabulary: 

● Micelles​: a group of molecules that have both a polar head and nonpolar tail ● Proteins​: building blocks of DNA; long chains of amino acids that make up the majority all tissues, organs and etc.

● Chylomicrons:​ little droplets of fat that are found in the blood after absorption occurs in the small intestine.

● Exocytosis:​ the release of waste contents of a cell that are collected by the cell’s vacuole organelle.

❏ Fatty acids are mixed with bile salts and form micelles that carry the mixture to the intestinal mucosa

❏ The mixture then leaves the micelle and diffuse into the epithelial cells → combined with proteins and lipids to form Chylomicrons

❏ The chylomicrons are then excreted by the vacuoles of the cells through exocytosis

◼Nucleic Acid Digestion and Absorption in The Small Intestine

❏ The enzymes included in nucleic acid digestion and absorption are:

1. Hydrolyze DNA

2. RNA nucleotides

3. Pancreatic nucleases

❏ The absorption process is carried out by active transport *3 

❏ The nucleic acids are transported to the liver by the Hepatic Portal Vein

◼Vitamin Absorption in the Small Intestine

❏ ­ organic compounds that are essential for nutrition and growth of the body

❏ Vitamins are absorbed as they are­ completely unchanged

❏ Two types of vitamins: fat soluble and water soluble

1. Fat Soluble

a. Vitamins A, D, E and K

2. Water soluble

a. Vitamins B12, B complex and C complex

◼Electrolyte Absorption in The Small Intestine

❏ Mineral or Electrolytes are most actively absorbed by the entire length of the small intestine

◼Water balance in the Intestine

❏ Water is absorbed by osmosis following the ingestion and absorption of salts and organic nutrients

3 Active Transport: the movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy.

❏ ­ when the water is not properly absorbed or balanced by the large intestine

❏ when fecal movements are slow, too much water gets reabsorbed by the large intestine and not enough is left to soften the stool being passed.

◼Large Intestine

❏ Cecum→ Colon→ Rectum

❏ The colon has 3 parts to it:

1. Ascending

2. Transverse

3. Descending

◼Motility of the Large Intestine

❏ Haustral contractions *​ occur every 30 minutes


­ Slow segmenting movements begin

­ Haustra contracts in response to distension *5 

❏ Gastrocolic Reflex

­ Initiated by the presence of food in the stomach

­ Activates 3 or 4 slow but powerful peristaltic waves per day → leads to mass movements which sometimes result in defecation

◼Bacterial Flora and Intestinal Gas

❏ Bacterial flora tends to populate in the large intestine

❏ Responsible for producing flatulence or gas

◼The Appendix

❏ Blind sac extending from the cecum of the large intestine

❏ The lymphoid nodules are the location in which local immune responses occur ❏ Bacterial flora is replenished by the intestinal flora

4 Haustral Contractions: slow segmenting, uncoordinated movements that occur approximately every 25 minutes. 

5 Distension: occurs when substances, such as air (gas) or fluid, accumulate in the abdomen causing its outward expansion beyond the normal girth of the stomach and waist.

◼Rectum and Anus

❏ Rectum

­ Has three rectal valves that stop feces from being passed with gas (helps the  individual to not poop their pants whenever they have to fart)  

❏ Anal Canal

­ The last segment of the large intestine

❏ Sphincters

­ There are 2 main rectal sphincters:

1. Internal anal sphincters

2. External anal sphincters


❏ Mass movements caused by peristaltic waves forces the feces into the rectum where feces adopts its shape

❏ Distension initiates the spinal defecation reflex

❏ Parasympathetic Signals

­ Stimulates the contraction of the colon and rectum and then relaxes the internal anal sphincter so feces can pass comfortably

❏ Voluntary control allows the body to relax the external anal sphincter when needed.


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