Digestion physiology chapter 26
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Digestion Physiology Chapter 26. Test (Chapters 25 & 26) April 6 th and 7 th (next block day). March 28, 2011. Announcements: Turn in last week’s warm ups to the box Pick up new warm up sheet Practical grades in gradebook Practical make up: Today after school @ 3:15 Tuesday morning 6:45

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Digestion Physiology Chapter 26

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Digestion physiology chapter 26

Digestion PhysiologyChapter 26

Test (Chapters 25 & 26) April 6th and 7th

(next block day)


March 28 2011

March 28, 2011

Announcements:

  • Turn in last week’s warm ups to the box

  • Pick up new warm up sheet

  • Practical grades in gradebook

  • Practical make up:

    • Today after school @ 3:15

    • Tuesday morning 6:45

      Warm Ups:

  • In the large intestine longitudinal muscles are grouped into strips called _______; circular muscles are grouped into rings are form _______.

  • What is produced in the appendix?

  • The two lobes of the liver are connected by the:

  • What are gallstones?

  • Through what two pathways does blood enter the hepatic lobules?


Primary mechanisms of digestive system table 26 1

Primary Mechanisms of Digestive System (Table 26-1)

  • Ingestion – take food in

  • Digestion – break down complex nutrients into simpler nutrients

  • Motility – movement of GI tract; aids in digestion

  • Secretion – enzymes are required for digestion to take place

  • Absorption – movement across GI mucosa into the internal environment

  • Elimination – process of eliminating unabsorbed material


Mechanical digestion

Mechanical Digestion

  • All motility of the digestive tract that cause the following changes:

    • Change in physical state of the food for large particles to smaller particles

    • Churning of the GI lumen to mix particles with digestive juices

    • Propelling food forward ending with elimination


Mastication

Mastication

  • Mastication = chewing

  • Requires tongue, cheek and lips

  • Reduces particle size

  • Mix food with saliva


Deglutition

Deglutition

  • Deglutition = swallowing

  • Oral stage

    • Bolus is formed voluntarily

    • Tongue pushes bolus against the palate and into the oropharynx

    • Soft palate acts as a valve to prevent food from entering the nasopharynx

  • Pharyngeal stage

    • Involuntary reflexes push bolus toward esophagus

    • Epiglottis prevents food from entering trachea

  • Esophageal stage

    • Involuntary reflexes move bolus towards stomach


  • Motility

    Motility

    • Smooth muscle contractions take over in the lower portion of the esophagus

    • Peristalsis – progressive wavelike ripple of the muscle layer of a hollow organ

      • Bolus stretches the GI tract wall  triggers contraction of circular smooth muscle  bolus moves forward


    Motility1

    Motility

    • Segmentation – mixing movement; back and forward movement within a single region

      • Mechanically breakdown food particles

      • Mix food and digestive juices together

      • Facilitate absorption

    • Peristalsis and segmentation can occur in alternating sequence to churn/mix and progress food


    Peristalsis segmentation

    Peristalsis & Segmentation


    Regulation of motility

    Regulation of Motility

    • Gastric Motility

      • Emptying the stomach takes approx 2-6 hours after a meal

      • Food is churned with digestive juices to form chyme

        • Ejection every 20 seconds into the duodenum

        • Controlled by hormonal and nervous mechanisms


    Regulation of motility1

    Regulation of Motility

    • Hormonal Control

      • Fats and nutrients in duodenum cause secretion of gastric inhibitory peptide (GIP) from the intestinal mucosa into the bloodstream

        • Slows peristalsis in stomach; decreasing passage of food into the duodenum


    Regulation of motility2

    Regulation of Motility

    • Nervous Control

      • Nerve receptors in duodenum are sensitive to acid and distention

        • Sensory and motor fibers within the vagus nerve (CN X) cause a reflex inhibition of gastric peristalsis (enterogastric reflex)


    Regulation of motility3

    Regulation of Motility

    • Intestinal Motility

    • Takes approx 5 hours for food to pass through the small intestine

      • Segmentation

        • Mixes chyme and digestive juices from liver, pancreas and intestinal mucosa

        • causes contact with intestinal mucosa to increase absorption

      • Peristalsis

        • Continues in the jejunum to move food into the large intestine

        • Stimulated by the hormone cholecystokinin-pancreozymin (CCK)

          • Secreted by intestinal endocrine cells in the presence of chyme


    Mechanical digestion1

    Mechanical Digestion

    • Summarized in Table 26-2; page 775


    Chemical digestion

    Chemical Digestion

    • Consists of all the changes in the chemical composition of food

    • Result of hydrolysis

      • Compounds combine with water then split into simpler compounds

      • Enzymes catalyze the hydrolysis of foods


    Chemical digestion1

    Chemical Digestion

    • Six main types of chemical substances:

      • Carbohydrates, proteins, fats, vitamins, mineral salts, water

      • Only carbohydrates, proteins and fats must undergo chemical digestion to be absorbed


    Digestive enzymes properties

    Digestive Enzymes Properties

    • Extracellular enzymes

    • Classified as hydrolases

    • Function optimally at a specific pH

      • Ex: amylase vs pepsin

    • Continually destroyed or eliminated

    • Most digestive enzymes are synthesized and secreted as proenzymes

      • Kinases convert proenzymes to active enzymes


    Carbohydrate digestion

    Carbohydrate Digestion

    • Carbohydrates are saccharide compounds

      • Contain one or more saccharide groups

    • Polysaccharides – starches & glycogen

    • Disaccharides – sucrose, lactose and maltose

    • Monosaccharides – glucose, fructose & galactose


    Carbohydrate digestion1

    Carbohydrate Digestion

    • Polysaccharides are hydrolyzed by amylases

      • Present in saliva and pancreatic juice

    • Sucrose, lactose and maltose are hydrolyzed by sucrase, lactase, and maltase

      • Located on epithelial cells lining villi in small intestine

      • End result (usually glucose) is located at site of absorption (“contact digestion”)


    Protein digestion

    Protein Digestion

    • Proteins are large molecules composed of twisted chains of amino acids

    • Proteases catalyze the hydrolysis of proteins into smaller compounds

      • Proteoses  peptides  amino acids

    • Proteins have varying peptide bonds holding amino acids together = increased need for varying proteases


    Protein digestion proteases

    Protein Digestion - Proteases

    • Pepsin – gastric juice

    • Trypsin and chymotrypsin – pancreatic juice

    • Peptidases – intestinal brush border


    Digestion physiology chapter 26 1177417

    Proteoses


    Fat digestion

    Fat Digestion

    • Fats are insoluble in water – must be emulsified prior to digestion

      • Emulsify = dispersed as small droplets

      • Lecithin and bile salts emulsify oils and fats in the small intestine by forming micelles (fig 26-8, page 778)

      • Lecithin mixes with fat to form micelles

    • Fats broken down by mechanical digestion are further broken down by lipase

    • Action of lipase is enhanced by colipase (released from the pancreas)


    Residuals of digestion

    Residuals of Digestion

    • Certain compounds cannot be digested in humans b/c we lack the enzyme required for hydrolysis

    • These compounds are excreted in the feces

    • Cellulose (dietary fiber), connective tissue from meat (collagen), undigested fats combined with calcium and magnesium, bacteria, pigments, water, mucous


    Chemical digestion2

    Chemical Digestion

    • Summarized in Table 26-3, page 779


    Secretion

    Secretion

    • Release of substances from exocrine glands in the GI tract

      • Saliva, gastric juice, bile, pancreatic juice, intestinal juice


    Saliva

    Saliva

    • Secreted from salivary glands

    • Water component helps liquefies food  chyme

      • Allows enzymes to mix with food particles

    • Mucus lubricates food to protect mucosa lining

    • Amylase – chemically digest starch and glycogen

    • Lipase (small amounts) – digest lipids

      • Decreased function when fat are not emulsified

    • Sodium bicarbonate (NaHCO3)

      • Dissociated in water

      • Bicarbonate ions bind with H+ to increase pH


    Control of salivary secretion

    Control of Salivary Secretion

    • Controlled by reflex mechanisms:

      • Olfactory & visual stimuli send impulses to centers in the brainstem  efferent impulses to salivary glands

      • Chemical and mechanical stimuli comes from the presence of food in the mouth


    Gastric juice

    Gastric Juice

    • Secreted by gastric glands surrounds by gastric pits

    • Chief cells – secrete enzymes of digestive juices

      • Pepsin (proenzyme = pepsinogen)

        • Pepsinogen is activated by hydrochloric acid (HCl)

    • Parietal cells

      • Secrete HCl

        • Decreases stomach pH; increases blood pH

      • Secrete intrinsic factor

        • Binds to molecules of vitamin B12 to facilitate absorption in the small intestine


    Control of gastric secretion

    Control of Gastric Secretion

    • Gastric secretion is controlled by 3 phases:

    • Cephalic phase (“psychic phase”)

      • Sight, smell, taste, thought of food activate control centers in medulla oblongata

      • Parasympathetic fibers of the vagus nerve conduct impulses to gastric glands

      • Vagal impulses stimulate production of gastrin

        • Gastrin stimulates gastric secretion


    Control of gastric secretion1

    Control of Gastric Secretion

    2. Gastric phase:

    • Gastrin secretion is further stimulated by the presence of products of protein digestion & distention

    • Gastrin continue to stimulate the secretion of gastric juices (high pepsinogen and HCl content)


    Control of gastric secretion2

    Control of Gastric Secretion

    3. Intestinal phase:

    • Gastric inhibitory peptide (GIP) in secreted in the small intestine in the presence of fats and carbohydrates

      • Decrease gastric motility and secretion

    • Secretin secreted in the small intestine in the presence of acid, digested proteins and fats

      • Inhibit gastric secretion

      • Simulate secretion of pancreatic enzymes

      • Stimulate ejection of bile into small intestine

    • CCK

      • Secreted in the small intestine in the presence of chyme

      • Stimulates ejection of bile from gallbladder

      • Stimulates secretion of pancreatic juices

      • Opposes action of gastrin; raises pH of gastric juice


    Pancreatic juice

    Pancreatic Juice

    • Secreted by exocrine acinar cells of the pancreas

    • Mostly water

    • Enzymes:

      • Trypsin and chymotrypsin (proteases)

      • Lipases

      • Nucelases (RNA and DNA digesting enzymes)

      • Amylase (starch digesting enzyme)

    • Secrete bicarbonate into the GI lumen and H+ into the blood to buffer the effects parietal cell secretion (fig 26-10 and fig 26-11)


    Control of pancreatic secretion

    Control of Pancreatic Secretion

    • Secretin

      • Stimulates the secretion of pancreatic fluid high in bicarbonate to neutralize acidity of chyme in the small intestine

      • See notes under “Control of Gastric Section – Intestinal phase”

    • CCK – see above


    Digestion physiology chapter 26 1177417

    Bile

    • Secreted by liver and stored in gallbladder

    • Lecithin and bile salts

      • Emulsify fats by creating a hydrophilic “shell” around tiny fats droplets

    • Sodium Bicarbonate – increase pH of chyme in small intestine

    • Excretions:

      • Cholesterol, products of detoxification, bilirubin (product of hemolysis)


    Control of bile secretion

    Control of Bile Secretion

    • Controlled by CCK and secretin

    • See Table 26-5, page 782


    Intestinal juice

    Intestinal Juice

    • Mucus – provides lubrication

    • Sodium bicarbonate – increases pH to allow intestinal enzymes to function at optimal level

    • Water – carries mucus and NaHCO3


    Study these tables

    **Study These Tables**

    Table 26-4: Digestive Secretions

    Table 26-5: Actions of Digestive Hormones

    Both on page 782


    Wednesday thursday 3 30 3 31

    Wednesday/Thursday 3/30-3/31

    Warm Up:

    • Name the 5 components of saliva.

    • What is the proenzyme of pepsin? What is needed to activate this proenzyme?

    • Explain the role of bicarbonate in the GI tract.

    • The control of gastric secretion can be broken up into 3 phases. Name these phase and briefly describe each one.

    • Name and give the function of the 5 enzymes found in pancreatic juice.


    Absorption

    Absorption

    • Passage of substances (digested foods, vitamins, salts, water) across the mucosa into the blood

    • Majority of absorption takes place in small intestine where surface area is increased


    Mechanisms of absorption

    Mechanisms of Absorption

    • Some substances (water) are absorbed via diffusion

    • Secondary Active Transport (ex: Sodium)

      • Na+ is actively transported from the basal (backside) of epithelial cells lining the lumen of the small intestine into blood capillaries

      • Creates a low intracellular sodium concentration

      • Na+ ions diffuse passively from the lumen into epithelial cells

      • Fig 26-14, page 785


    Mechanisms of absorption1

    Mechanisms of Absorption

    • Sodium cotransport

      • Glucose is very large and hydrophilic

      • Requires carrier to cross intestinal mucosa

      • Carriers bind sodium and glucose together to passively transport out of lumen

    • Amino Acid absorption

      • Transported by passive carriers on luminal and basal surfaces of absorptive cells

      • Brush border enzymes can also act as carriers

      • Polypeptides can diffuse into absorptive cells, hydrolyze into amino acids, diffuse into blood


    Mechanisms of absorption2

    Mechanisms of Absorption

    • Fatty acid/monoglyceride absorption

      • Bile salts and lecithin form micelles

      • Fat digestion takes place within these tiny spheres

      • At the intestinal brush border, micelle contents can diffuse into absorptive cells

      • Inside triglycerides reform within chylomicrons

      • Water soluble chylomicrons allow fats to be transported through lymph and into bloodstream


    Mechanisms of absorption3

    Mechanisms of Absorption

    • Absorption of vitamins

      • Vitamins A, D, E, K are fat-soluble

        • Depend on bile salts for absorption

      • B Vitamins require carrier-mediated transport

        • Ex: Vit B12 and intrinsic factor


    Summary of absorption

    Summary of Absorption

    • See table 26-6, page 787


    Elimination

    Elimination

    • Expulsion of digestive residuals from the digestive tract in the form of feces

      • Defecation

      • Normally rectum is empty

      • Massive peristalsis of feces into the rectum stimulate receptors and relax the external anal sphincter

      • Voluntary control


    Elimination1

    Elimination

    • Constipation

      • Contents move through large intestine at a slower rate

      • Increased water absorption occurs resulting in hardened feces

    • Diarrhea

      • Result of increased motility of the small intestine

      • Water absorption does not occur


    Gi tract disorders

    GI Tract Disorders

    • Common S/S

      • Gastroenteritis

        • Gastritis – stomach inflammation

        • Enteritis – intestinal inflammation

      • Anorexia: chronic loss of appetite

      • Nausea: feeling of needing to vomit; may progress to vomiting

      • Emesis: vomiting

      • Diarrhea: elimination of liquid feces; abdominal cramps may also be present

      • Constipation: decreased motility of colon; difficulty in defecating


    Gi tract disorders1

    GI Tract Disorders

    • Ulcers

      • In stomach or duodenum

      • Cause pain and may lead to perforation of the wall of the GI tract

      • Bleeding  anemia

      • Causes:

        • Hyperacidity

        • H. phylori bacterium


    Gi tract disorders2

    GI Tract Disorders

    • Stomach cancer

      • Linked to excessive alcohol use, chewing tobacco, eating heavily preserved foods

      • Early signs:

        • Heartburn, belching, nausea

      • Later signs:

        • Chronic indigestion, vomiting, anorexia, stomach pain, blood in feces


    Gi tract disorders3

    GI Tract Disorders

    • Diverticulosis – presence of abnormal sac-like projections on the large intestine (diverticula)

      • When inflamed causes diverticulitis

      • S/S: pain, tenderness, fever


    Gi tract disorders4

    GI Tract Disorders

    • Colitis – inflammation of the large intestine

      • s/s: diarrhea, abdominal cramps, constipation, bleeding, intestinal ulcers

      • Crohn’s Disease: autoimmune colitis

      • Treatment: surgical removal of affected portions of the intestine


    Gi tract disorders5

    GI Tract Disorders

    • Irritable bowel syndrome (IBS)

      • “spastic colon”

      • Noninflammatory condition usually caused by stress

      • Diarrhea or constipation


    Gi tract disorders6

    GI Tract Disorders

    • Colorectal cancer

      • Occurs after 50

      • Associated with low-fiber, high-fat diet

      • Early signs: change in bowel habits, fecal blood, rectal bleeding, abdominal pain, unexplained anemia, weight loss, fatigue


    Liver disorders

    Liver Disorders

    • Hepatitis – inflammation of the liver

      • S/S: jaundice, liver enlargement, anorexia, abdominal discomfort, gray-white feces, dark urine

      • Causes: alcohol or drug abuse; bacterial or viral infection

    • Cirrhosis – degenerative liver condition

      • Tissue can no longer regenerate


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