Overview. Physiology 1. The Gastrointestinal Tract. Guyton section XI

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1 Overview Physiology 1 The Gastrointestinal Tract Guyton section XI

2 Basic functions of the GI tract Digestion Secretion Absorption Motility Basic functions of the GI tract Digestion: : Dissolving and breaking down ingested particles Basic functions of the GI tract Digestion: Dissolving and breaking down ingested particles Secretion: : Releasing enzymes, bile and Hydrochloric acid into the lumen of the GI tract Basic functions of the GI tract Digestion: Dissolving and breaking down ingested particles Secretion: Releasing enzymes, bile and Hydrochloric acid into the lumen of the GI tract Absorption: : Moving molecules from the lumen into the blood or lymph

acid into the lumen of the GI tract Absorption: Moving molecules from

3 Basic functions of the GI tract Digestion: Dissolving and breaking down ingested particles Secretion: Releasing enzymes, bile and Hydrochloric acid into the lumen of the GI tract Absorption: Moving molecules from the lumen into the blood or lymph Motility: : Moving food through the GI Tract

4 Structure of the Gastrointestinal Tract Wall

Digestion and Absorption of nutrients Carbohydrate Protein Fat Digestion and Absorption of nutrients Carbohydrate: Body only absorbs monosaccarides (glucose, fructose,

5 Digestion and Absorption of nutrients Carbohydrate Protein Fat Digestion and Absorption of nutrients Carbohydrate: Body only absorbs monosaccarides (glucose, fructose, galactose) Enzymes on luminal membrane break down complex sugars into monosacarides Monosaccarides enter body by facilitated difussion Cellulose (fiber) can not be broken down

6 Digestion and Absorption of nutrients Protein: Free amino acids and short chains can be absorbed. Enzymes Stomach (pepsin) Small intestine (chymotrypsin( chymotrypsin, Trypsin) Pancreas (Carboxypepsidase( Carboxypepsidase) Small intestine epithelium (Aminopepsidase( Aminopepsidase) Digestion and Absorption of nutrients Carbohydrate Protein Fat: must be Emulsified in lumen before absorbed

7 Structure of Bile Salts Emulsification of Fat Fat Digestion/ Lipase

9 Following the pathway of ingested food

11 Secretions from the Stomach Parietal cells secrete acid Chief cells secrete pepsinogen Enterochromaffin- like cells release histamine into the body Conversion of Pepsinogen to Pepsin

12 Regulation of stomach acid secretion

13 Duodenum Jejunum Ileum Small intestine Liver Produces Bile Bile pigments (bilirubin( bilirubin) Has enterohepatic circulation

14 Secretion of Bile is regulated by the hormone Cholecystokinin (CCK)

15 Pancreas Structure of the pancreas Secretes Bicarbonate to neutralize stomach acid Secretes digestive enzymes Trypsin Regulates whole body metabolism via Insulin Glucagon Somatostatin

16 Regulation of the Pancreas Small intestine Acid levels in Small Intestine stimulate pancreatic bicarbonate release (via Secretin) Amino and Fatty acids stimulate enzyme release (via Cholecystokinin,, CCK)

17 Movement of the Small Intestine

18 Physiology 12 Feast or Famine Regulation of systemic Metabolism Everyday the body must shift its metabolism Germann Ch 20 In the fed (absorptive) state Food is being digested or absorbed Energy comes primarily from carbohydrates In the fed (absorptive) state Food is being digested or absorbed Energy comes primarily from carbohydrates Extra carbohydrates are converted to fat (via liver glycogen production)

In the fed (absorptive) state Food is being digested or absorbed Energy comes primarily from carbohydrates Extra carbohydrates are converted to fat (via liver glycogen production) Ingested fatty

19 In the fed (absorptive) state Food is being digested or absorbed Energy comes primarily from carbohydrates Extra carbohydrates are converted to fat (via liver glycogen production) Ingested fatty acids are stored in adipose In the fed (absorptive) state Food is being digested or absorbed Energy comes primarily from carbohydrates Extra carbohydrates are converted to fat (via liver glycogen production) Ingested fatty acids are stored in adipose Excess amino acids are converted to Fat In the Fasted (postabsorptive( postabsorptive) ) state Glycogen and fat production stops

In the Fasted (postabsorptive( postabsorptive) ) state Glycogen and fat production stops Liver releases glucose to maintain blood Glucose levels (brain must have glucose) In the Fasted

20 In the Fasted (postabsorptive( postabsorptive) ) state Glycogen and fat production stops Liver releases glucose to maintain blood Glucose levels (brain must have glucose) In the Fasted (postabsorptive( postabsorptive) ) state Glycogen and fat production stops Liver releases glucose to maintain blood Glucose levels (brain must have glucose) Most energy comes from Fatty acids and Keytones In the Fasted (postabsorptive( postabsorptive) ) state Glycogen and fat production stops Liver releases glucose to maintain blood Glucose levels (brain must have glucose) Most energy comes from Fatty acids and Keytones Muscle breaks down Muscle glycogen for fuel.

21 Feast or famine states are regulated by Pancreatic hormones Insulin Glucagon The endocrine Pancreas

22 Islet of Langerhans

23 Insulin is produced by the Pancreatic islet beta cells, its release is regulated Circulating glucose Circulating amino acids Sympathetic/parasympathetic nerves Other gut hormones (GIP)

24 Glucagon Secreted from the pancreatic islet alpha cells Stimulated by drops in blood sugar

25 Metabolic Rate Whole body metabolism Total energy expenditure per unit time Measured in Kilocalories Varies with activities and inputs

Total regulation of metabolism is a balanced equation Food ingested = total energy expended Total energy expenditure = Work + Heat produced + energy

26 Total regulation of metabolism is a balanced equation Food ingested = total energy expended Total energy expenditure = Work + Heat produced + energy stored Factors affecting Metabolic rate Epinephrine Food Muscle activity Brown adipose tissue activity Hormones Hormones affecting Metabolism Thyroid Thyroxine

27 Thyroxine Hormones affecting Metabolism Thyroid Thyroxine Adrenal cortical hormone Cortisol Hormones affecting Metabolism Thyroid Thyroxine Adrenal cortical hormone Cortisol Leptin

28 Hormonal Regulation of Growth

Physiology 12. Overview. The Gastrointestinal Tract. Germann Ch 19

Physiology 12. Overview. The Gastrointestinal Tract. Germann Ch 19 Physiology 12 The Gastrointestinal Tract Germann Ch 19 Overview 1 Basic functions of the GI tract Digestion Secretion Absorption Motility Basic functions of the GI tract Digestion: : Dissolving and breaking