The major function of the GI system is absorption of nutrients.. System+Wilson The surface area of the intestine.

The major function of the GI system is absorption of nutrients.

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https://eapbiofield.wikispaces.com/Digestive+System+Wilson

The surface area of the intestine is 300 m3.

Intestinal villi maximizesurface area

The GI tract is not a major site of waste product excretion.

• Fecal material is mostly bacteria that never actually enter the body.

• Major waste products excreted throough the GI tract:– Bilirubin – a breakdown product of

hemoglobin– Cholesterol

Major GI Processes

Major GI Hormones

• Gastrin – stimulates acid secretion and motility of stomach

• Secretin – inhibits acid secretion and motility of stomach i.e. slows gastric emptying, in response to acid in small intestine

• Cholecystokinin (CCK) also inhibits acid secretion and motility of stomach, but in response to amino acids and fatty acids in small intestine.

• Glucose-dependent insulinotropic peptide (GIP) stimulates insulin release in response to glucose and fat in small intestine.

http://www.uoflhealthcare.org/digestivehealth/gerd.htm

http://www.merck.com/media/mmhe2/figures/fg123_1.gif

Barrett’s Esophagus

http://www.barrettsinfo.com/figures/fig3a_4.jpg

http://jama.ama-assn.org/cgi/content/full/294/15/1986

Carbohydrate Digestion

The digestion of carbohydrate. The complex polysaccharide starch is broken down into glucose by the enzymes amylase and maltase (secreted by the small intestine).

(Image © RM)

http://media.tiscali.co.uk/images/feeds/hutchinson/ency/thumbs/0013n025.jpg

Protein Digestion

The digestion of protein. Protein is broken down into amino acids by the enzymes pepsin (secreted by the stomach) and trypsin and peptidase (in the small intestine).

(Image © RM)


Fat Digestion

The digestion of fat. Fat is broken down into fatty acids and glycerol by bile (secreted by the gall bladder) and the enzyme lipase (secreted by the small intestine).

(Image © RM)


Balance of GI inputs and outputs.

Iron absorption is altered in response to changes in iron homeostasis.

Ferritin traps iron andholds it in cells.

When iron levels are low, you produce less ferritin.

When iron levels are high, you produce more ferritin.

http://www.mfi.ku.dk/ppaulev/chapter22/images/22-16.jpg

Consequences of prolonged vomiting

• Dehydration

• Metabolic Alkalosis (due to loss of gastric acid)

• Low serum K+ (due to action of aldosterone, which is released after prolonged dehydration).

• Malnutrition

Diarrhea

• Potential for massive fluid loss, leading to hypotension.

• Can cause acidosis, since intestinal contents are alkaline.

• Can cause hypokalemia (low K+) since intestinal contents are high in K+.

Lactose intolerance results from a lactase insufficiency.

Undigested lactose remains in the intestine, and osmotically draws water intothe intestine, causing diarrhea.

http://www.food-info.net/images/lactase.jpg

Cholera toxin increases the intracellular levels of cAMP. This leads to an increase in chloride secretion into the small intestine. Water follows osmotically.

http://www.surrey.ac.uk/SBMS/ACADEMICS_homepage/mcfadden_johnjoe/img/Cholera%20toxin.jpg

The chloride channel is called “CFTR”, and is defective in people with Cystic fibrosis.

One copy of the CF geneis thought to offer protection against cholera.

The chloride channel is called “CFTR”, and is defective in people with Cystic fibrosis.

One copy of the CF geneis thought to confer protection against cholera.

Celiac Disease

• Results from intolerance to gluten, specifically the gluten breakdown product gliaden.

• Considered to be an autoimmune disease – the person makes antibodies against gliadin, which cross react with proteins in the small intestine.

Consequences of celiac disease

• Pain and diarrhea, inflammation of intestinal villi.

• Malabsorption of nutrients leading to – Osteoporosis (from lack of calcium)– Anemia (from lack of iron)– Short stature (from general malnutrition– Miscarriage, neural tube defects (lack of folic

acid, and other nutrients)

Hemorrhagic Diarrhea

• Infectious diarrhea leading to blood in stools

• Example: recent outbreaks of E. coli 0157:H7

• May be a consequence of factory farming practices – Grows well in corn-fed factory farmed beef– Runoff contaminates vegetable farms

The Pancreas

Pancreatic enzymes are usually released in an inactive form.

Cystic Fibrosis (CF) and the pancreas

• Pancreatic enzyme secretion uses the same CFTR chloride channel we heard about with cholera

• This channel is defective in people with CF, and causes them to have problems with the digestion of food and absorption of nutrients.

Regulation of Pancreatic Function

• Secretin – Stimulates release of bicarbonate• Bicarb release also stimulated by smell and

taste of food, distension of stomach, acid in duodenum, and gastrin.

• CCK - Stimulates release of enzymes• Enzyme release also stimulated by smell and

taste of food, distension of stomach, and presence of peptides and fatty acids.

The Liver

http://www.niaaa.nih.gov/Resources/GraphicsGallery/Liver/214c.htm

http://www.siumed.edu/~dking2/erg/liver.htm

The openings (fenestrations) in the capillaries mean that the hepatocytes are essentially in direct contact with the blood.

Bile duct and sphincter of Oddi

Bile Pigments


When bilirubin metabolism is insufficient, then bile pigments accumulate in the tissues, giving the skin and eyes a jaundiced (yellowish) appearance.


Cirrhosis of the Liver

Cirrhosis occurs when scarring and fibrosis lead to the death of hepatocytes.

Portal hypertension can cause bleeding into the GI tract, as well as congestion of blood in the spleen, leading to

destruction of platelets

http://www.clevelandclinic.org/health/health-info/pictures/tipspre.gif

The yellow coloring of the eye in a patient with jaundice reflects the accumulation of bile pigments in the connective

tissues. Skin also becomes yellowish.

Consequences of Liver Failure

• Portal Hypertension – blood backs up into the GI tract– Blood does not pass through liver, so

nutrients are not absorbed, also loss of immune surveillance

– Varices– Promotes development of ascites– Congestion of blood in spleen, leads to RBC

destruction

Consequences of Liver Failure, (cont.)

• Ascites formation – watery fluid in the abdominal cavity

• Infection

• Generalized edema

• Neurologic disorders (from accumulation of ammonia and other toxins)


• Increased bleeding from – lack of liver-produced clotting factors, – lack of absorption of vitamin K, – hyperactivity of the spleen

• Endocrine disorders– Lack of liver-produced hormone carriers– Inability to degrade estrogen


• Manifestations of decreased bile production– Jaundice (build-up of bile pigments leading to

yellowish color of eyes and skin)– Decreased fat absorption (diarrhea,

steatorrhea, deficiencies of fat-soluble vitamins)


• Problems with glucose metabolism – sometimes hypoglycemia (since liver is site of gluconeogenesis, sometimes hyperglycemia (since blood bypasses liver, glucose is not absorbed from it)

Problems with lipid metabolism – liver is the only place where fatty acid can be converted to ketones, which provide energy during fasting.


• Increased plasma levels of liver enzymes (aminotransferase and alkaline phosphatase) are indicators of liver damage

• Problems with salt and water balance – due to lack of albumin and angiotensinogen.

http://sportsci.org/news/history/beaumont/Wbeaumont.jpg

Dr. William Beaumont with Alexis St. Martin

The major function of the GI system is absorption of nutrients.. System+Wilson The surface area of the intestine.

Documents

malnutrition slide

surface area slide

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fat digestion

digestion of fat

acid secretion

protein digestion

digestion of protein