PSIO Exam 6

Layers of the digestive tract

* mucosa
* submucosa
* muscularis externa
* serosa- produces lubricating fluid

Processes of the digestive system

mastication (chewing)

* mechanical digestion of foodstuff

deglutination (swallowing)

peristalsis

* wavelike contractions that propel food along the GI tract

segmentation

* mixing contractions

chem digestion

* breaking of chem bonds by enzymes

absorption

excretion

Control of Digestive system (Enteric Nervous System)

* mostly controlled by reflexes via the parasympathetic division
* chem and mech receptors are located in organ walls that trigger reflexes

Control of Digestive system: stimuli

stretch of the organ

pH of the contents

presence of breakdown products

Control of Digestive system:

activation or inhibition of glandular secretions

enhanced or reduced smooth muscle activity

Enteric NS

part of the autonomic NS

two plexuses, one between long and circular and the other one is underneath the circular

Phases of Digestive Activity: Cephalic phase

\
anticipation of food stimulates salivation

Phases of Digestive Activity: oral phase

food in the mouth further stimulating salivation gastric phase

phases of digestive activity: gastric phase

food in stomach further stimulates gastric motility and secretion

phases of digestive activity: intestinal phase

* chyme stimulates various digestive secretions
* absorption is occurring

phases of digestive activity: post-absorptive phase

indigestive period

Oral Cavity

teeth

* 32 permanent
* upper and lower arcades

salivary glands

* produce saliva
* water
* mucus
* **salivary amylase**
* **performs chemical digestion of carbs**
* **salivary lipase**
* **first lipid digestion**

tongue

lips and cheeks

Pharynx and Esophagus

* deglutination passes food bolus from mouth down to stomach via pharynx

Pharynx and Esophagus: process 1

food bolus is pushed toward pharynx by tongue

Pharynx and Esophagus: process 2

food bolus touches uvula, stimulating muscular contractions

Pharynx and Esophagus: process 3

food bolus pushes epiglottis over larynx

Pharynx and Esophagus: process 4

food bolus enters esophagus

Pharynx and Esophagus: process 5

food is propelled via peristaltic contractions to the stomach

* the pharyngeal and upper esophageal muscles are skeletal muscle
* the lower portion of esophagus is smooth muscle

Stomach

* j- shaped organ that performs four functions
* food reservoir
* secretes HCl and pepsinogen
* mixes food w/ secretions
* releases food to small intestine in regulated quantities
* no absorption of nutrients occurs across the stomach mucosa
* but, **aspirin and alcohol can be absorbed**
* **gastric rugae - folds in lining of stomach which flatten as it fills**

Control of gastric secretion

* gastric pits contain multiple cell types
* neck cells
* mucus- protects against pepsin, acid, and mech damage
* parietal cells
* hydrochloric acid (HCl)
* Chief cells
* pepsinogen
* G cells
* gastrin

gastric emptying

swallowed food is mechanically and chem digested in stomach

* mixing contractions mix food w/ enzymes and acid, and help reduce the sizes of lipid globules
* converts solid food to chyme
* feedback regulation between pylorus and duodenum meters stomach emptying
* full stomach is normally emptied in average of 4 hours

rippling peristalsis occurs in lower stomach

Gastric emptying: rippling peristalsis occurs in lower stomach

* IF duodenum is empty, then pyloric sphincter will relax
* Then, the next peristaltic contraction will force 1-1.5 ml chyme through pyloric sphincter to intestine
* Chyme in duodenum causes sphincter to close

small intestine

* major digestive organ
* site of absorption
* consists of three segments
* duodenum
* jejunum
* Ileum
* suspended from posterior abdominal wall by mesentery
* \~18 ft long
* **enterocytes line the lumen, participate in digestion and absorption**

duodenum

initiates remainder of chem digestion

jejunum

absorption

ileum

* absorption
* ileocecal sphincter meters passage of intestinal content to large intestine

Small intestine

* acid chyme is neutralized by bicarbonate-rich pancreatic fluid
* sources of enzymes for digestion
* pancreatic enzymes
* brush-border enzymes
* **presence of fats and proteins stimulates bile acid release from gall bladder, and increased bile production by liver (secretin and CCK)**

pancreatic enzymes

* lipases, amylases, peptidases, nucleases
* “coarse” digestion of macro molecules

brush-border enzymes

* carbs- and peptide-digesting enzymes
* completes digestion of molecules to simple forms

Stimulation of the Release of Pancreatic Juice

* Vagus nerve
* Local hormones
* secretin
* cholecystokinin (CCK)
* Acid stimulates __secretin__ release
* pancreas secretes HCO3^- (rich blood)
* **Fat and protein-rich chyme stimulates both secretin and CCK**
* **CCK stimulates secretion of pancreatic enzymes, contraction of gall bladder**
* **secretin stimulates secretion of bile from liver**

Motility of Digestion

* Gut Pacemaker Cells
* interstitial Cells of Cajal (ICC) produce slow wave peristaltic contractions
* 3 per minute in stomach
* 11-12 per minute in duodenum
* 9-10 per minute in ileum
* 3-4 per minute in colon
* autonomic influence
* PSNS increases rates
* SNS decreases rates

Absorption in the Small Intestine

* **water** is absorbed along the length of the small intestine
* end products of digestion
* __most substances (____**water-soluble substances**____) are absorbed by__ __**active transport**__ __through cell membranes.__ __**Lipids are absorbed by diffusion**__
* Substances are transported to the liver by the **hepatic portal vein** or **lymph**

Bile

* Produced by cells in the liver
* Composition
* bile salts
* bile pigment (mostly bilirubin from the breakdown of hemoglobin)
* cholesterol
* phospholipids
* Electrolytes

Functions of the Large intestine

* Absorption of water
* eliminates indigestible food from the body as feces
* does not participate in digestion of food
* Goblet cells produce mucus to act as a lubricant

Food breakdown and Absorption in the large intestine

* No digestive enzymes are produced
* resident (commensal) bacteria digest remaining nutrients
* produce some vitamin K and B
* Release gases (H2, CH4, H2S) and odorous compounds (putrescine, cadaverine, and spermine)
* water and vitamins K and B are absorbed
* remaining materials are eliminated via feces

Propulsion in the Large Intestine

* sluggish peristalsis
* Mass movements
* slow, powerful movements
* occur three to four times per day
* presence of feces in the rectum causes a defecation reflex
* internal anal sphincter is relaxed
* defecation occurs w/ relaxation of the voluntary (external) anal sphincter

Digestive System-associated Metabolic Functions

* glucose handling
* a lot of water is produced as waste
* CO2 is produced as waste
* fat metabolism
* protein metabolism

Metabolic functions of the Liver

Glyco/glucogenesis

glycogenolysis

gluconeogenesis

Glycogenesis (or glucogenesis)

* Glucose molecules are converted to glycogen
* Glycogen molecules are stored in the liver

Glycogenolysis

Glucose is released from the liver after conversion from glycogen

Gluconeogenesis

Glucose is produced from fats and proteins

Fat Metabolism

* Handled mostly by the liver
* use some fats to **make ATP**
* **synthesize lipoproteins,** thromboplastin, and cholesterol
* release breakdown products to the blood
* body cells remove fat and cholesterol to build membranes and steroid hormones

Metabolic functions of the Liver

* fats and fatty acids are picked up by the liver
* Some are oxidized to provide energy for liver cells
* The rest are broken down into simpler compounds and released into the blood
* Requirements: NOT > 30% of total caloric intake

Cholesterol Metabolism

* functions of cholesterol
* serves as a structural basis of steroid hormones and vitamin D
* Is a major building block of plasma membranes
* Most cholesterol is produced in the liver and is not from diet

Cholesterol Transport

* Cholesterol and fatty acids cannot freely circulate in the bloodstream
* they are transported by lipoproteins (lipid-protein complexes)
* low-density lipoproteins (**LDLs*)** transport to body

Protein metabolism

Requirement: 0.8g/kg=60 to 120g/day

Body energy balance

energy intake = total energy output (heat + work + energy storage)

* energy intake is liberated during food oxidation
* energy output
* 60% heat lost (remember: energy in each ATP → 25% work/75% heat)
* storage energy is in the form of fat or glycogen

Regulation of Food In take

Body weight is usually relatively stable

* energy intake and output remain about equal

Mechanisms that may regulate food intake

* levels of **nutrients** in the blood
* **hormones** (leptin, glucagon, insulin)
* **Body temp**
* **psychological factors**

Metabolic Rate and Body Heat Production

* basic metabolic (BMR) - amount of heat produced by the body per unit of time at rest
* factors that influence BMR
* surface area - small body usually has higher BMR
* Gender - males tend to have higher BMR
* 60-72 kcal/hr in 70kg male
* age - children and adolescents have a higher BMR
* the amount of __**thyroxine**__ produced is the most important control factor
* more thyroxine means higher metabolic rate

Total Metabolic Rate (TMR)

* total amount of kilocalories the body must consume to fuel ongoing activities
* TMR increases w/ an increase in body activity
* TMR must equal calories consumed to maintain homeostasis and maintain a constant weight

Body Temperature Regulation

The body has a narrow range of homeostatic temperature

* Must remain between 35.6° to 37.8°C (96° to 100° u)
* The body’s thermostat is in the hypothalamus
* Initiates **heat-loss** or **heat-promoting** mechanisms

heat-loss

heat loss from the skin via radiation and evaporation

* skin blood vessels and capillaries are flushed w/ warm blood
* evaporation of perspiration cools the skin

heat-promoting

vasoconstriction of blood vessels

* blood is rerouted to deeper, more vital body organs

shivering- contraction of muscles produces heat

Hyperthermia

increase in body temp → increase metabolic rate → increase in body temp (positive feedback cycle)

* heat stroke
* no heat loss mechanisms function
* heat exhaustion
* heat loss mechanisms still function
* Pyrogens → fever

The ___________ helps to regulate passage of waste chyme into the large intestine.

ileocecal valve

Nervous control of intestinal contractions and secretions is a product of the

submucosa and myenteric plexus (c**ircular and longitudinal smooth muscle layers)**

_________________ is the process of moving nutrients across the intestinal mucosa and into the lymph or bloodstream for transport to the body's cells.

absorption

Most bile acids are recycled.

true

__________________ is the process of eliminating waste from the body.

excretion

Segmenting and peristaltic contractions are possible due to this intestinal structure.

muscularis externa

Lipid-soluble substances are transported in ________________from the intestine to the liver

chylomicrons

Which of these is not a component of bile?

pancreatic enzymes

Which term means to take in food or liquid to the digestive tract by swallowing (deglutition)?

ingestion

Protein digestion in the stomach requires:

pepsin

gastrin

acidic environment

This is the layer of cells that line the majority of the digestive tract.

mucosa

The substances (chemicals) that our body needs but cannot synthesize and must be obtained through the diet are known as nonessential nutrients.

False: vitamins

This term is used to describe the chemical or mechanical break-down of food stuff.

digestion

Lymph nodes are located throughout the intestinal submucosal space.

true

Where does the chemical digestion of carbohydrate first occur?

in the mouth

Which type of activity serves the function of moving a food bolus further along the intestine?

peristalsis

The plicae can be described as:

The circular folds of the mucosa which give the intestine a "bunched-up" appearance.

In which layer of the intestinal wall would you locate blood and lymphatic capillaries that participate in absorption of nutrients?

submucosa

Which of the following would not be considered a nutrient required by cells?

fiber

These structures increase the surface area available for absorption in the intestinal wall.

villi and microvilli

In which parts of the GI tract would you expect peristaltic contractions to occur?

esophagus

stomach

small intestine

Pepsin continues to break down proteins throughout the small intestine.

false

Which hormone stimulates the release of bile from the gall bladder?

Cholecystokinin

The primary functions(s) of the digestive system can be described as:

breaking down food, absorbing nutrients, and eliminating wastes.

The interstitial cells of Cajal are important for

producing the depolarization needed for peristaltic contractions

The ___________ helps to regulate passage of waste chyme into the large intestine.

ileocecal valve

**What segment of the small intestine is important in detecting break-down products and acid in chyme?**

duodenum

Which of the following is a major stimulator for cholecystokinin secretion?

lipids in the small intestine

During anaerobic metabolism, glucose is converted into pyruvic acid to produce 2 ATP molecules. If oxygen is still not available, muscle will temporarily convert pyruvic acid into _______ to allow the conversion to continue. Excessive levels of this product causes muscle soreness.

lactic acid

A graphic method for demonstrating the quantities of food groups we should take in daily is known as the

Food Pyramid

When we are cold, we shiver. Why?

It is rapid muscle contraction that increases the need for ATP to speed up metabolism and generate heat.

When cold, the body can increase the generation of heat through metabolism and can

decrease loss of heat to the environment.

The average adult takes in about _____ ml of water in food a beverages per day.

2500mL

Why is it recommended that we take in few fats, oils, and sweets?

We take in sufficient quantities in other food groups.

In the small intestine, lipids are absorbed

into lymphatic vessels and passed through the lymphatic system into the bloodstream.

Although dairy products contain protein, vitamins, and minerals, they should not be eaten in large quantities because they also contain

fat

The process by which plants convert solar energy into glucose and oxygen is known as

photosynthesis

Lipid-soluble vitamins are vitamins

A, D, E, and K.

The correct sequence for the layers within the wall of the alimentary canal from inside to outside is

Mucosa, submucosa, muscular layers, serous layer

Peristalsis occurs in the digestive tract

From the pharynx to the anus

The teeth that are best adapted for biting off relatively large pieces of food are the

Incisors

The enzyme called salivary amylase functions to digest

carbs

Gastrin, which is secreted by stomach cells, functions to

Increase the secretion of pepsinogen

The part of the stomach closest to the small intestine is called the

pyloric region

Cholecystokinin (CCK) secretion from the enterocytes is stimulated by the presence of

fat in the small intestine

A relatively new treatment in the management of gastric ulcers is a drug that inhibits the production of HCl in the stomach. If a person took this medication for a long period, the chemical digestion of which of the following would be affected the most?

proteins