Digestive System and Body Metabolism Lecture Guide

2 groups of the digestive anatomy

a. alimentary canal(GI): function: break down food into smaller fragments and absorb into blood

1.mouth, pharynx, esophagus, stomach, small intestine and lg intestine

mouth: mastication and taste, some defense

hard palate: anterior roof, soft : posterior

uvula: fingerlike projection from soft palate

frenulum: fold of mucous mem ties tongue to floor of mouth (tongue tied)

palantine and linguinal tonsils at base of tongue

a. pharynx: longitudinal and circular layers for peristalsis

b. esophagus: through diaphragm to stomach

4 layers of tunics all the way through lg. Intestine

1. mucosa: surface ET of simple columnar, moist membrane little CT

2. submucosa: soft Ct w/blood vessels , nerve endings and lymph vessels

3. muscularis externa: circular inner layer of muscle with outer longitudinal

4. serosa: outermost layer, single layer if flat serous fluid producing cells (visceral peritoneum) continuous with parietal peritoneum which lines abdominopelvic cavity. These are connected by the mesentery

5. layers of 2-4 have a nerve plexus controlled by ANS

c. stomach: cadrioesophageal sphincter: from eso to stomach

1. fundus, body, pylorus (chyme is made here)

2. pyloric sphincter

3. can hold 1 gallon of food

4. rugae: large folds of stomach when empty

5. ommentum (greater: an extension of peritoneum) covers the abdominal organs with lacy network of fat and lymph nodule

6. peritonitis: infection where two membranes stick together

7. smooth lining is covered in gastric pits

gastric juice, HCL acid, mucus and gastrin

d. small intestine: major digestive organ, chemical digestion

from pyloric sphincter to ileocecal valve, 2 m

suspended from posterior abdominal wall by mesentery

pancreatic duct: enz produced by intestinal cells, pancreas

bile duct

hepatopancreatic ampulla to the duodenal papilla and enter the duodenum together

1. duodenum: around pancreas (25 cm)

2. jejunum: 2.5 m

3. ileum 3.6 m joins the lg intestine at the ileocecal valve

ABSORPTION: microvilli (plasma mem), villi (rich capillary bed, lacteal) and surface folds (plicae circulares) all increase surface area

As get closee to lg int. folds decrease and number of peyers patches increase (concentration of bacteria do as well)

e. large intestine 1.5 m

functions: dry out food residue by absorbing water and eliminate waste

1. 1st part cecum: from which hangs the appendix(wormlike)

2. colon

3. anus has external voluntary sphincter and internal involuntary sphincter

4. goblets cells no villi

b. accessory digestive organs

1. Pancreas: from spleen to duodenum, produces wide range of enzymes in alkaline fluid to neutralize chyme, insulin and glucagons

2. liver: largest gland in body, four lobes, suspended from the diaphragm and abdominal wall by the falciform ligament

many function but for digestion: bile leaves lliver at hepatic duct, yellow green water solution with bile salts, bilirubin, cholesterol, phospholipids and electrolytes
bile salts emulsify fat

iii. gallbladder: when food is not digested bile backs up into the cystic duct and enters gallbladder to be stored in cinentrate

iv. gallstones: stored too long or too much water removed

v. back up in hepatic or bile duct due to gallstones causes bile into liver and eventually into blood: jaundiced (also caused by hepatitis or cirrhosis)

3. salivary glands

4. teeth

Functions of the Digestive System: 5 processes controlled by reflexes of the parasympathetic (sebsors fo rreflexes in walls of GI tract: stretch of organ, pH of contents and 3. contents of digestion products0

1. Ingestion

2. food breakdown: mechanical and chemical digestion

hydrolysis of biomolecules

3. food movement: propulsion

a. swallowing

b. peristalsis

4. absorption: food passes from lumen into the mucosal cells by active or passive transport

5. defecation

Activities of Mouth, Pharynx, Esophagus
Food Ingestion and breakdown:
Mechanical and chemical digestion (salivary amylase) , no food absorption
Pharynx and esophagus have no digestive role / Food Movement: Swallowing and Peristalsis
Deglutition (swallowing): 2 phases
1. voluntary buccal phase: mouth makes bolus and forces into pharynx where there is now no control
2. involuntary pharyngeal-esophageal controlled by the ANS. soft palate rises to close off nasal passages, tongue closes mouth, larynx rises so the epiglottis covers respiratory paths
3. longitudinal muscles contract then circular
Activities of the Stomach
Food Breakdown
Gastric juice controlled by hormones and ANS
Presence of food and drop in pH makes gastrin hormone secrete by stomach cells causing more pepsinogens, mucus and HCL
Ulcers: HCL and pepsinogens
Cardioesophageal sphincter: heart burn
Hiatal hernia: superior stomach protrudes above the diaphragm
ACIDIC: converts pepsinogen to pepsin
Rennin which digests milk proteins
No absorption occurs
Physical digestion makes chyme / Food Movement
Only 3 ml or less of liquid chime can squirt through pyloric valve, too big go back
Duodenum gets stretched the enterogastric reflex occurs which inhibits the vagus nerve and slows the emptying of the stomach 4 to 6 hours if high fat to empty stomach
Activities of the Small Intestine
Food breakdown and Absorption
Chemical food digestion (fats start) 4 to 8 hours and absorption
Microvilli enzymes: brush border enzymes breakdown disaccharides to monosaccharides and complete proteindigestion
Mucus in intestinal gland secretion
Pancreatic juice: amylase, (half of protein) trypsin, chymotrypsin, carboxypeptidase and lipases and nucleases
Bicarbonate
Pancreatitis: rare but serious inflammation of the pancreas from activation of enzymes in the duct and leads to nutritional defeiceincies
Chime enters SI stimulates mucosa cells to secrete hormones secretin (causes liver to increase output of bile) & cholecystokinin (stimulates gallbladder) which when combined stimulate pancreatic juice and bile
Bile is necessary for absorption of fats, Vit K,D,A
If bile or pancreatic juice is absent: no fat digestion or absorption occurs = fat bulky stool and often blood clotting since the liver cannot make prothrombin without Vit K
Absorption = mostly by ACTIVE TRANSPORT thru intestinal wall to capillary bed to blood to liver via hepatic portal vein
LIPIDS= diffusion into capillary bed and lacteal
End of ileum all food is digested and absorbed so all that remains is water, indigestible food stuffs and bacteria / Food Movement
Peristalsis
Local irritation of stomach or SI (ie. Food poisoning) can activate the emetic center in the medulla causing vomiting (reverse peristalsis)
Activities of the Large Intestine
Food Breakdown and Absorption
Colon produces no enzymes
Resident bacteria metabolize left overs and make gas and vit K and B
Absorption of water, these vit and some ions
Feces: contain undigested food, water and bacteria and mucus / Movement of the residue and defecation
Colon peristalsis is sluggish and contributes little to propulsion
Mass movements: long slow moving and powerful contractions 3 to 4 times a day forcing towards the rectum
Fiber: strengthens colon and softens stool
No fiber: colon narrows, circular muscles contract harder encouraging formation of diverticula in which the mucosa protrudes through colon wall and come inflamed and if rupture are life threatening
Rectum is empty until rushed in by mass movements = defecation reflex causing sigmoid colon and rectum to contract while relaxing anal sphincters
Diarrhea: rushes food through LI
Constipation: food remains too long in LI

II. NUTRITION AND METABOLISM

Food > metabolic fuels> oxidized into ATP

Kilocalories

Nutrition

Nutrient: substance to promote growth, maintenance and repair (carbs, lipids, proteins, vitamins and minerals and water)

Carbohydrates: milk and glycogen in meat, most come from plants as sugar

Lipids: meat and dairy: triglycerides, cholesterol (eggs, milk and meat) and phospholipids, unsaturated fats: seeds, nuts and vegetables

Proteins: animal products

Eggs, milk and meat: ost complete proteins meeting all amino acid requirements

Legumes, nuts and cereals are incomplete proteins missing > one eaa

Vitamins: coenzymes

Minerals: (ca, P, K, S, Na, Cl, Mg) are rich in vegetables, legumes, milk, some meats

Metabolism: cll chemical reactions necessary for maintaining life catabolism and anabolism

Carbs = ATP

Fat = membranes, myelin sheath, storage for ATP

Proteins = tend to be hoarded by cells

Liver: central role in metabolism

Die within 24 hours without it

Role in digestion = make bile

Detoxify drugs, makes cholesterol, blood proteins, albumin and clotting proteins and lipoproteins

Hepatic portal circulation : brings nutrient rich blood

Liver is the major metabolic organ, liver removes amino acids, fatty acids and glucose and phagocytic cells remove /destroy bacteria

Vital to glucose balance 100mg/100 ml of blood

Glycogenesis: glucose to glycogen

Glycogenolysis: opposite

Fats and faa are used to make some ATP and acetic acid and released into the blood or used to make blood proteins

Albumin; most abundant: holds fluids in bloodstream too low then edema results

Clotting proteins

Lipoproteins: HDL and LDL circulate lipids in blood because fats are not water soluble

LDL; transport cholesterol and other lipids to body cells if too high then atherosclerosis is high possibility

HDL: transport cholesterol from body cells to liver to bile

Carbohydrate Metabolism:

Glucose: cellular respiration into ATP , CO and water

Hyperglycemia: too high glucose (glycogen in liver an dmuscle then turn to fat)

Hypoglycemia: blood sugar too low

Fat Metabolism: mostly in liver

Fat in blood gets used to make cell membranes, myelin sheaths and fat around organs for insulation

For energy: fat must be broken into acetic acid and then oxidized to CO , water and ATP

Fat oxidation is fast and incomplete leaving products such as acetoacetic acid in the blood = acidosis or ketosis (breath takes on fruity flavor) common in diets

Cholesterol is never used for energy

Protein Metabolism

Make up bulk of cellular features

Amino acids in blood used by cells for themselves: enzymes , membranes, spindle fibers, muscle fproteins, mucus. Hormones etc…)

ACTIVE TRANSPORT to get aa inside cells need all 20 amm 8 of which are essential cannot be made

Metabolize for energy when not enough carbs and fats unavailable

Oxidize aa for energy lose their amine group =ammonia and the rest enters krebs cycle

Liver combines CO with ammonia as urea so it is not toxic to nerves

Body energy Balance

Intake = outflow energy lost as heat

Basal Metabolic Rate

Total Metabolic Rate

Body Temperature regulation Heat loss mechanisms

Hypothalamus Vasodilation

Heat promoting mechanisms Sweating

Shivering

Hypothermia vs hyperthermia (heat stroke, heat exhaustion and fever)