Lectures 22-27 HA&P

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4 Major Functions of Digestive System

1. Motility to propel and mix food; 2. Gland secretion to aid in digestion and absorption; 3. Digestion of food into absorable molecules; 4. Nutrient, electrolyte, and H2O absorption into bloodstream.

4 Layers of Digestive Tract

Mucosa, Submucosa, Muscularis, Serosa

Mucosa

contains epithelial tissue, lines lumen, produces mucus

Submucosa

Beneath mucosa, blood &lymphatic vessels, exocrine glands.

Muscularis

Circular muscle & longitudinal muscle

Serosa

Visceral peritoneum forming outer layer of tract

Enteric Plexus

2 networks of nerve fibers between submucosa and muscularis layers

Mesenteries

hold organs in abdominal cavity together, contain 2 layers of serious membranes.

Greater Omentum

Long, double fold of mesentery, creates a pocket where fat accumulates.

Saliva

produced at a rate of ~1L/day by parotid and submandibular glands.

Salivary Amylase

Enzyme; Breaks down starch into disaccharides; does NOT break down cellulose (source of fiber)

Lysozyme

Enzyme; weak antibacterial properties

Mucin

lubricating protien found in saliva

Salivary secretion regulated mostly by __

ANS.

3 phases of deglutination (swallowing)

1. Voluntary Phase 2. Pharyngeal Phase 3. Esophageal phase

Voluntary Phase

Bolus is pushed by toungue into oropharynx

Pharyngeal Phase

Refles initiated when food is detected by mechanoreceptors in oropharynx. 3 Pharyngeal constictor muscles contract in succession and upper esophageal sphincter relaxes, allowing bolus to be pushed into esophagus

Esophageal Phase

Muscular contractions of esophagus, called peristaltic waves, push bolus down into the stomach.

Gastroesophageal Reflux Disease

Heartburn; defined by mucosal damage to the esophagus duw do stomach acid reflux.Complications: Chronic esophagitis, difficulty swallowingCauses: Caffeine, stress, alcohol, fatty food, obesity, smoking, and tight clothing. Acid inhibitor treatment

Stomach

enlarged segment of digestive tract in left superior part of abdomen; contains additional inner oblique muscle layer

Gastric Pits

In stomach; invagination of simple columnar epithelial cells.

4 Cell types of Gastric Pits

Mucus cells(secrete HCO3-, protects stomach from acid), chief cells (secrete pepsin, break down proteins), endocrine cells (secrete gastrin), parietal cells (produce HCL and intrinsic factor, activates Pepsin).

Intrinsic Factor

Binds Vitamin B12 making it more readily absorbed by small intesting. B12 is critical for DNA synthesis and RBC production.

Both __ and __ mechanisms regulate gastric secretion

neural and hormonal

Cephalic stage of Stomach secretion

first stage; anticipatory; taste, smell of food activate parasympathetic NS, stimulating stomach secretions, particulary gastrini which acts on parietal cells for HCL production

Gastric Phase of stomach secretion

greatest gastric secretion; reflex initiated by distention of the stomach

Intestinal phase of stomach secretion

inhibits gastric secretion, presence of chyme in duodenum initiate neural and hormonal resoponses

Neural:

Chemoreceptors in duodenum detect HCl or lipids, sent dignals to medulla to inhibit parasympathetic activity

Peptic Ulcer

Results from erosive and digestive actions of H+ and Pepsin.

Major causative factor of Peptic Ulcers

Helicobactor pylori infection, secretes cutotoxins, damage mucosal layer, secrete enzyme called urease, which alkinalizes the local enviro.

Treatment of Peptic Ulcers

Antibiotics, Proton pump Inhibitors (Block H+ secretion)

Mixing waves

Weak contractions; mix food w. stomach secretions to form chume; push more fluid part toward pyloric sphincter & olid part back toward body

Peristaltic Waves

Stronger contractions; force food toward and through pyloric sph. little bit at a time.

Why must chyme be emptied slowly?

so it can be neutralized by HCO3-

CCK

Decreases stomach secretions, also acts to slow gastric peristaltic waves

small intestine

~6M long, duodenum, jejunum, ileum. Major site of digestion and absorption.

Circular folds

Run perpendicular to length of small intestine (Increase SA)

Villi

projections of mucosal layer (^SA)

Microvilli

cell membrane extensions of individual mucosal eptihelial cells

Mucosa of SI 4 Cell types

Absorptive cells ( have microvilli, produce enzymes & absorb food), Goblet Cells, Granular Cells (protect from bacteria), Endocrine Cells(Produce hormones which stimulate liver and pancreatic secretions)

Digestive Enzymes in Brush Border

Peptidases, Disaccharidases

Lactose Intolerance

Deficiency in disaccharidase, lactase, Can cause asmotic diarhhea.

Segmental contractions

propagated for only short distances and mix intestinal contents

Hepatocytes

Liver cells; process nutrients and detoxify harmful substances from blood

Liver is responsible for

Nutrient storage/release, Nutrient Conversion, Sunthesis of important blood proteins such as albumin, fibrinogen and glouline

Blood supply into and out of liver

Hepatic artery delivers O2 rich blood, Hepatic Portal Vein delivers 02 poor blood containing nutrients absorbed from SI, Hepatic Veins empty into inferior vena cava.

Liver is divided into

lobules by connective tissue septa, have portal triads at corners

Triads

Consist of hepatic portal veins, hepatic arteries, and hepatic ducts.

Bile

produced by liver, secreted into duodenum, contains amphipathic ile salts, which emulsify fats in the duodenum

Bile secreted by

CCk

CCK Response

released by endocrine cells in response to chyme from stomach. cck travels to gallbladder where it causes contraction.

Cirrhosis

refers to damage and death of hepatocytes and replacement by connective scar tissue. Treatment seeks to slow progression

Pancreas

posterior to stomach in left upper quatrant of abdomen. Composed of exocrine and endocrine tissues

endocrine tissue

composed of acinar glands

pancreatic juice

rich in HCO3- which neutralize acidic chyme. contain pancreatic proteases, such as trypsin, pancreatic amylase which breaks down starchinto disaccharides and pancreatic lipase which breaks down lipids into glycerol and fatty acids

pancreatic juice secretions

in response to neural and hormonal activity

Large Intestine

cecum colon rectum anal canal.

cecum

proximal end of LI, SI AND LI meet at ilocecal junction.

colon

longest part of LI consisting of ascendind, transverse, descending and sigmoid segments, mucosal lining contains crypts which contain goblet cells

colon functions

converts chyme into feces, absorbs water& salts, mucus secretion & activity of bacteria.

mass movements

propel feces long distances through the colon, occur every 8-12 hours

defecation reflex

distention of rectal wall, parasympathetic response causes strong peristaltic contractions and relaxation of internal anal sphincter

Irritable bowel syndrom

abdominal pain, twice as common in adult females, highly correlated with stress or depression. treated by stress management, increased fiber, or anxiety drugs.

Types of digestion

Mechanical: breaking food into smaller particles. Chemical: breaking of covalent bonds in nutrients by digestive enzymes

Carbohydrate digestion

begins in oral cavity.

Carbohydrate absorption

Absorbed as monosaccharides. Apical membrane transport; glucose and galactose cotransported with NA; secondary active transport driven by NA, K, ATPase on basal membreane. enter capillaries of intestinal villi and are transported to liver via hepaticportv

Protein digestion

Proteases digest protein and polypeptides into smaller polypeptides. Brush border peptidases break down small polypeptides into absorbable forms, Tripeptides, Dipeptides and amino acids.

Protein absorption

amino acids, dipeptides or tripeptides. apical membrane transport. amino acids cotransported with NA secondary driven by Na, K, ATPase on basal membrane.

Major Ingested Lipids

Triglycerides ( can be saturated or unsaturated), phospholipids ( recall major constituent of cell membrane), steroids (cholesterol and hormones), fat-soluble vitamins such as vitamin E

Lipid Digestion

Emulsification: Amphipathic bile salts break large lipid droplets into much smaller droplets

Absorption of Lipids

Occurs when micelles containing products of lipid digestion feely diffuse across apical surface of intestinal cells

Lipid Digestion

Emulsification: Amphipathic bile salts break large lipid droplets into much smaller droplets

Absorption of Lipids

Occurs when micelles containing products of lipid digestion feely diffuse across apical surface of intestinal cells

Lipoproteins transport

Triglycerides and Cholesterol.

LDL

Low Density Lipoproteins;; transport cholesterol from liver to tissues for use by clls. High cholesterol content and low protein content.

HDL

High Density Lipoproteins transport cholesterol from tissues to liver where its metabolized or excreted in bile.

about __L of H20 enters GItract daily

92% of water absorbed by

7% of water absorbed by

1% of water

lost in feces

water moving across GI Tract

Passive, direction determined by osmotic gradient

Electroltes such as NA, K, Ca are __ across intestinal epithelium

actively transported

Ca2 absorption requires

Vitamin D. Acts on intestinal epithelial cells to increase synthesis of a Ca binding portien called Calbindin.

Diarrhea

Major cause of Death worldwide. responsible for 18% of childhood deaths. Loss of fluid >> loss of extracellular fluid>> low blood volume >> low BP > death.

secretory diarhhea

Vibrio cholerae. cholera toxin released, causes crypt cells to secrete large amounts of fluid>> can be fatal within hours. Easily treated by replacing fluid and electrolytes.

Nutrients

Ingested chemicals.

Major classes of nutrients

carbohydrates, lipids, proteins, vitamins, minerals, water

Essential nutrients

ex: linoleic acid must be ingested. important for blood clotting. Nonessenial are necessary but can be synthesized from esential nutrients.

Benefits of a healthy diet

reduction in heart and chronic diseases

Caloric restriction

Restrict calories by 10-25%. decrease in heart disease, diabetes, and cancer shown (in rats) monkeys less likely to develop Alzheimer's. Increased insulin sensitivity and reduced LDL cholesterol. Humans: lower BP and cholesterol, possibly lifespan.

Glucose

Principal energy source for cells. Glycolysis yeilds ATP. help build DNA and RNA.

When Glycogen stores are full...

The liver converts excess glucose to riglycerides which are exported to adipose tissue for long term storage.

Insulin

Released from Beta cells of pancreas in response to a raise in blood sugar; promotes uptake and storage of glucose as well as fats and proteins.

Insulin uptake & storage

Binds to receptor>intracellular phosphorylation of proteins> insertion of GLUTs in cell membrane > increased glucose Uptake

Glucagon

hormone of starvation. During periods of fasting, raises glucose levels. triggered by low blood glucose levels.

Glucagon release

Breakdown of glycogen> glucose in lover, break down of fats in adipose tissue and breake down of amino acids from muscle; all enter bloodstream.

Gluconeogenesis

Liver can synthesize glucose from other nutrient sources such as amino acids and glycerol in triglycerides

Insulin dependent diabetes mellitus

cause by distruction of beta cells in pancreas so body produces no insulin

Characterization of Type 1 diabetes

hyperglycemia, osmotoic diuresis, bypotension treated by administration of synthetic insulin

non insulin dependent diabetes mellitus (type 2)

caused by increased resistance of target tissues to insulin. assoc. w. obesity. Caloric and cab restriction and drugs

Carb. restriction

Atkins;; Utilization of glycogen stores, gluconeogenisis keeps these people alive

glycemic index

predicts whether absorbed carbs are used for immediate energy needs or sent to long term storage: Low value indicates slower digestion higher = quicker

factors which affect glycemic indes

type of starch, physical entrapment of starch, presence of fat and protein, organic acids such as vinegar

high glycemic index foods

promotes storage as fat; reduces insulin sensitivity

nutrient timing

popular in athletic training; involves significant carb intake during periods before or after intense physical activity. outside of that small window, carb intake is restricted

Fatty acids are classified by..

degree of saturation

saturated

carbon chain has all single bonds. each c atom in chain is saturated with hydrogen atoms

unsaturated

carbon chain has one or more double bonds.

Monounsaturated

unsaturate; one double bond

polyunsaturated

unsaturated; more than 1 double bond

sources of each fatty acid.

Sat: meat, dary, eggs, nutsMono:olive, canola, certain nuts/seedsPolyunsat: fish, safflower, certain nuts/seeds

Homeostasis

maintenence of a relatively stably environment with respect to a given variable

which substances can freely diffuse across CM?

Lipids and other hydrophobic molecules (CO2 and 02 both can) an exception: water CAN freely diffuse

osmosis

diffusion of water across a membrane from high to low concentration

diffusion

movement of molecules across a membrane from high to low concentration

how are substances movs across CM against concentration gradient? classic example?

active transport: proteins.

How is the body able to produce different cell types?

Gene Regulation controls which cells get made my regulating which cells get copied, or transcribed

Action Potential (1)

a Ligand binds to a ligand gated Na+ channel, releasing a bunch of Na+. This floods the cell because of how much more Na is on the outside. This strongly depolarizes the cell. This reaches the threshold potential needed to open the voltage gated Na

AP(2)

Channels, releasing more Na, making the membrane go up to +40mV. Finally, the slower-opening K+ channels open, causing K+ to rush out of the cell, repolarizing it.

Steps of Neurotransmission

current is detected by voltage gated Ca2+ channels, which open allowing Ca2+ to move down its conc. gradient. Ions flow into vessicle and associate with vessicles containing neurotransmitters. vessicles fuse with CM, releasing 10000s of neurotransmitter

Neurotrans (2)

molecules into extracellular space. difuse across synapse and bind specific receptors. leads to channel opening and depolarization of postsynaptic membrane.

how is touch sensation detected and transmited to somatosensory cortex

Skin > spinal cord > thalamus > somatosensory cortex

how brain initiates skeletal muscle movement

planning in premotor area, primary motor cortex initiates signals which result in movement; lower motor neurons project to skeletal muscle fibers;

how brain initiates skeletal muscle movement

planning in premotor area, primary motor cortex initiates signals which result in movement; lower motor neurons project to skeletal muscle fibers;

2 divisions of ANS and functions neurotransmitters released from each

Sympathetic: fight of flight norepiParasympathetic: resorative or vegetative body functions ach

2 divisions of ANS and functions neurotransmitters released from each

Sympathetic: fight of flight norepiParasympathetic: resorative or vegetative body functions ach

motor unit

all muscle fibers a single lower motor neuron innervates.

motor unit

all muscle fibers a single lower motor neuron innervates.

motor unit

all muscle fibers a single lower motor neuron innervates.

intercellular events occuring during muscle contraction and relaxation

release of Ca2+ cells, opens voltage gated Ca channels, in SR, Ca is released into sarcoplasm, allows myosin to bind to actin, myosin binds and unbinds, pulling a little each time and burning one ATP each time. called cross bridge cycling. Ca is pumpedbac

intercellular events occuring during muscle contraction and relaxation

electrical conduction through heart

initiated in SAnode, right A wall, Left A wall, AV node, AV bundle, Ventricles, Purkinje fibers

electrical conduction through heart

initiated in SAnode, right A wall, Left A wall, AV node, AV bundle, Ventricles, Purkinje fibers

Elec activity coordinates atria- ventricle contraction

Slow conduction through AV node

Elec activity coordinates atria- ventricle contraction

Slow conduction through AV node

baroreceptor reflex alters heart function

drop in atrial pressure, less barometric stretch, info sent to cv center; sympathetic response., efferent fibers project to sa node and vent. muscle, release norepi, sa increases HR, ventricles contract more forcefully raising bp, raises arterial pressure

RAAS respons to increase BP

angiotensin causes vasoconstriction, aldosterone increases NA reabsorption causing higher blood volume & thus pressure

breathing

diaphragm contraction causes increase in thorassic pressure, ^ pleural cavity volume, V pleural pressure, expansion of lungs, lowered pressure drives air in. Expiration is natural, lungs have recoil naturally

how 02 and c02 are exchanged in pulmonary and systemic capillaries

partial pressures drive the gasses between alveoli and pulmonary capillaries. hemoglobin in systemic capillaries.

how do kidneys handle Na & main site of reabsorption & how handling relates to blood volume

kidneys can alter serum levels of sodium salts; proximal tubule, more Na, higher BP

Hormone which determines wheter urine is dilute or concentrated by altering water permeability of distal renal tubule

ADH

good fats

Poly and mono unsaturated: Decresase LDL and increase HDL

bad fats

Saturated fats raise LDL and HDL. Really bad fats are transfats, Raise LDL and lower HDL.

1g TG yeilds

as much caloric energy as 2gs FA.