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Digestive System

Chapter 22 – Day 4

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Large Intestine – DigestionDigestion of Macromolecules Lipids (Fats):

♦Fats are broken up into smaller globules♦Emulsification requires bile♦Fats → Fatty Acids (monoglycerides): needs lipase

Nucleic Acids♦DNA (or RNA) → pentose sugars + nitrogen compounds:

needs nuclease (then they are absorbed)

Small compounds are then ready for absorption♦90% of absorption in S.I. via villi

HOW ARE THEY ABSORBED??

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Large Intestine – Digestion Emulsified fats = Micelles

♦Micelles are absorbed into epithelial cells via simple diffusion♦Inside epithelial cells

•Recombining & repackaging takes place•Fatty acids + monoglycerides = triglycerides•All lipids combine together

◦Triglycerides + cholesterol + phospholipids = coated with a special protein

•Protein package of lipids in the epithelial cells = chylomicron•Enters lacteal (or Peyer’s patches) → lymph → veins →

heart → liver♦Inside liver – chylomicrons are broken down → lipids are released →

next step = solubilization of lipids♦Lipids are attached to Lipoproteins which are then distributed to the

body via the blood stream (HDL)♦These compounds travel through lymph via chylomicron because of

solubility issues

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Large Intestine – Digestion Remaining materials move to large intestine Structural Features

♦Ileum opens into L.I via the ileocecal pshincter → contents enter L.I.

♦First structure in L.I. = cecum (blind pouch)♦Appendix is attached to the surface of the cecum

•Contents of the intestine can enter the appendix

♦contains lymphoid tissue♦Takes care of cellulose digestion in animals

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Large Intestine – Digestion From cecum L.I. extends up = ascending colon Extends horizontally = transverse colon Extends down = descending colon

Fig. 22.22

Turns in = sigmoidal colon Tube goes towards anus =

rectum Anus = opening to release

wastes♦Guarded by a sphincter

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Large Intestine – Digestion Folds of L.I. = haustra (pouches) Histology:

♦Inside = no villi♦Columnar cells with goblet cells

Peristalsis churns food, moves it through the L.I. Thick bands of

longitudinal muscle♦Taeniae coli

Eventually, food

moves into rectum

Fig. 22.23

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Large Intestine – Digestion Chyme remains in L.I. for 3-10 hours Digestion is completed

♦Amino acids are broken down by bacteria♦Carbohydrates are fermented

•Gases are formed:◦ N2, CO2, methane, & H2 = flatus

Absorption is completed♦Large amount of H2O is absorbed

♦Vitamin K & B vitamins are absorbed

Gas accumulation♦= Flatulence♦Smell is due to methane gas

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Large Intestine – Digestion Material not absorbed = semi-solid at the end

♦=FECES

Contains materials that were not absorbed and waste products

Accumulates in rectum Activates pressure-sensitive receptors in rectum

♦Leads to contraction of rectum walls (muscles)♦Shortens rectum, increases pressure

Exit through anus – via sphincter Voluntary control = relaxation of sphincter

♦Aided by abdominal muscles

Fig. 22.24

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Large Intestine – Digestion

Fig. 22.24

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Large Intestine – Common Problems Diarrhea & Constipation Diarrhea: not enough water is absorbed in L.I. Constipation: too much water absorbed in L.I. Diarrhea:

♦Usually caused by bacteria that irritate mucosa

♦Chyme moves too quickly for adequate H2O absorption

Constipation:♦Less H2O or fiber in diet

♦Water is limited so larger % absorbed compared to remaining in feces

♦Need more fluid and fiber in diet

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Large Intestine – Common Problems Diarrhea & Constipation Diarrhea: not enough water is absorbed in L.I. Constipation: too much water absorbed in L.I. Diarrhea:

♦Usually caused by bacteria that irritate mucosa

♦Chyme moves too quickly for adequate H2O absorption

Constipation:♦Less H2O or fiber in diet

♦Water is limited so larger % absorbed compared to remaining in feces

♦Need more fluid and fiber in diet

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Problems in Digestive System Hemorrhoids, Appendicitis, Colon cancer, Ulcers,

Liver problems (hepatitis & cirrhosis) Hemorrhoids:

♦Affects rectum & anus♦Varicose veins in rectal walls♦Damaged valves in veins♦Accumulation of blood – causes blood vessel to protrude♦Damage to valves is caused by pressure against veins:

•Pushing during delivery or during pregnancy (or constipation)

•Can be surgically removed

Fig. 22.22

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Problems in Digestive System Appendicitis:

♦Inflammation of the appendix♦Usually caused by obstruction:

•Foreign body, feces, tumor

♦If not removed it can burst & cause other problems♦Symptoms:

•Waves of abdominal pain on right, then becomes steady

•May experience:◦ Vomiting◦ low-grade fever◦ Increase in WBC count

Fig. 22.22

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Problems in Digestive SystemUlcers Erosion of epithelial lining in the GI tract Forms a lesion → eats through tissue layers Causes

♦Excess acid production•i.e. hypersecretion of gastric juices

♦Reduced mucus secretion•i.e. hyposecretion of alkaline mucus

♦Bacteria or stress•Which enhance hyper- or hyposecretion

Commonly occur in the duodenum or stomach (=gastric ulcer)

Fig. 22.22

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Problems in Digestive SystemUlcers Symptoms

♦Severe pain, usually 1-4 hours after eating♦Weight loss♦Bleeding

Treatment♦Antacids♦Zantac (aluminum coat)♦Surgery♦Lifestyle changes

Fig. 22.22

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Problems in Digestive SystemLiver Problems Cirrhosis

♦Liver cells become inflamed or sever damage, then destroyed

♦Cells cannot regenerate to full extent♦Hepatocyte tissue gets replaced by fibrous tissue♦Causes:

•Damage by:◦ Toxins, Inflammation, Metabolic problems

•Hepatitis can lead to cirrhosis•Most common cause = alcoholism•Bile duct problems

♦Treatment•Depends on cause•Prevent further damage

Fig. 22.22

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Problems in Digestive SystemLiver Problems Hepatitis

♦Caused by a virus – Hepatitis A or Hepatitis B, C & D, E♦Contaminated water with Feces♦Sexual transmission♦Food

Symptoms♦Fever♦Tiredness♦Sore muscles♦Yellowing of the skin = accumulation of bilirubin

Fig. 22.22

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MetabolismColon Cancer Common cancer of the G.I. tract Tumor formation in the large intestine = polyps Polyps may be benign or malignant Usually in the rectum or sigmoidal colon Polyps must be removed and analyzed for cancer

cells – biopsy Symptoms of polyps:

♦Pain, cramps, blood in stool

Detected by colonoscopy♦http://www.mayoclinic.com/health/colonoscopy/MM00010

Fig. 22.22

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Metabolism After digestion & absorption: glucose, lipids etc. Chemical reactions take place in cells

♦Process of cellular metabolism Nutrients in the cell

♦Can either be broken down further by the process of catabolism♦Or they can be joined together to form new larger molecules by the

process of anabolism Catabolic processes – release energy

♦Mitochondria = location for numerous catabolic activities Energy

♦40% ATP, 60% heat (released back into environment) ATP: helps to maintain cellular activities & governs

anabolism (anabolic processes require energy) Big picture: process of metabolism is essential for

homeostasis

Fig. 22.22

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Metabolism

Fig. 23.1

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Metabolism

Fig. 23.2