L14 physiology

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Questions and Answers

What is the primary end product of the enzyme lactase?

Amino acids

Maltose

Galactose and glucose (correct)

Fructose

What impact do parasympathetic nerves have on the secretion in the small intestine?

They inhibit secretion.

They increase the secretion. (correct)

They decrease the secretion.

They have no effect on secretion.

What is the primary function of salivary α-amylase?

Digestion of starches (correct)

Digestion of proteins

Digestion of fats

Digestion of sugars

Which enzyme is responsible for breaking down triglycerides into fatty acids?

Intestinal lipase Signup and view all the answers

Which of the following components is NOT found in saliva?

Hydrochloric acid Signup and view all the answers

What is the pH range of the intestinal digestive juices?

7.5 to 8.0 Signup and view all the answers

What is the pH range of saliva?

6 to 7 Signup and view all the answers

Which of the following correctly states the composition of intestinal digestive juices?

Water (99.5%) and solids (0.5%) Signup and view all the answers

Which gastric gland type is primarily located in the body and fundus of the stomach?

Oxyntic or Fundic glands Signup and view all the answers

What is a key function of hydrochloric acid (HCl) in gastric juice?

Activation of pepsinogen Signup and view all the answers

Which of the following is NOT an organic constituent of saliva?

Calcium Signup and view all the answers

Which function of saliva aids in taste sensation?

Solvent action Signup and view all the answers

What percentage of gastric juice is made up of solid constituents?

0.5% Signup and view all the answers

What do G cells secrete?

Gastrin Signup and view all the answers

At what pH is pepsin active?

Between 1.8 and 4.0 Signup and view all the answers

Which enzyme in pancreatic juice is responsible for digesting triglycerides?

Pancreatic lipase Signup and view all the answers

What is the primary component of pancreatic juice?

Water Signup and view all the answers

Which cells secrete somatostatin?

D cells Signup and view all the answers

What is required to activate trypsin?

Enterokinase Signup and view all the answers

Which substrate does pancreatic amylase act on?

Carbohydrates Signup and view all the answers

What do enterochromaffin-like (ECL) cells secrete?

Histamine Signup and view all the answers

What is the main goal of the digestive system?

To break down macromolecules into smaller molecules Signup and view all the answers

Which plexus is responsible for regulating intestinal motility?

Myenteric (Auerbach’s) Plexus Signup and view all the answers

What effect do sympathetic nerve fibers have on the gastrointestinal tract?

They inhibit movements and decrease secretions Signup and view all the answers

What is the voluntary stage of swallowing also known as?

Buccal stage Signup and view all the answers

Where is the submandibular gland located?

At the posterior part of the mouth Signup and view all the answers

How much saliva is typically secreted in a day?

0.8 to 1.5 liters Signup and view all the answers

Which part of the digestive system is primarily responsible for the absorption of digested products?

Small intestine Signup and view all the answers

What regulates local intestinal secretion and absorption?

Submucosal (Meissner’s) Plexus Signup and view all the answers

Which pancreatic secretion is primarily stimulated by cholecystokinin (CCK)?

Pancreatic enzymes Signup and view all the answers

What is the primary function of bile salts?

Aid in the digestion and absorption of fats Signup and view all the answers

Which two bile acids are primarily formed in the liver?

Cholic acid and chenodeoxycholic acid Signup and view all the answers

What is a key role of secretin in pancreatic function?

Increases pancreatic ductal secretion of water and NaHCO3 Signup and view all the answers

Which of the following is NOT a function of bile?

Synthesis of plasma proteins Signup and view all the answers

What condition is characterized by yellow pigmentation of the skin and mucous membranes?

Jaundice Signup and view all the answers

What is the main role of colipase in the digestive process?

Facilitating the action of trypsin Signup and view all the answers

Which of the following best describes the pH and volume of bile produced per day?

Alkaline with a volume of 600-1000 ml/day Signup and view all the answers

Study Notes

GIT Secretions and Absorption

The digestive system's main function is to break down large food molecules (proteins, fats, and carbohydrates) into smaller molecules (amino acids, fatty acids, and glucose) for absorption.
The digestive system includes:
- Ingestion of food into the mouth
- Secretion of enzymes for digestion
- Digestion of food particles
- Absorption of digested products
- Removal of undigested substances

Learning Objectives

Students will need to list the digestive system parts and functions.
Describe the gastrointestinal tract's nerve supply and salivary secretion composition and regulation.
Describe the stomach's functions and secretions.
Understand the roles of bile and pancreatic juice in digestion.
Describe the function and regulation of intestinal secretions.

Digestive System

The main goal is to break down macromolecules into smaller molecules for absorption.

Functions of Digestive System

Ingestion of food
Secretion of digestive enzymes
Digestion of food particles
Absorption of digested products
Removal of waste

Enteric Nervous System

Myenteric (Auerbach's) Plexus: Controls intestinal motility (increased contraction rate).
Submucosal (Meissner's) Plexus: Controls local intestinal secretions and absorption.

Autonomic Control of the GIT

Parasympathetic Nerve Fibers: Increase secretory activities and motility of the GI tract.
Sympathetic Nerve Fibers: Inhibit movements and decrease secretions of the GI tract.

Swallowing (Deglutition)

Swallowing is a coordinated action of the tongue, soft palate, pharynx, esophagus, and muscles.
Stages of swallowing:
- Voluntary (buccal) stage
- Pharyngeal stage (involuntary)
- Esophageal stage (involuntary)

Salivary Glands

Parotid: Located in front of the ear
Submandibular: Located on the posterior part of the mouth
Sublingual: Located anteriorly on the floor of the mouth, under the tongue

Composition of Saliva

Saliva volume: 0.8 to 1.5 liters per day
pH: 6 to 7
Composition:
- 99.5% water
- 0.2% inorganic constituents
- 0.3% organic constituents

Inorganic Constituents of Saliva

NaCl & KCl act as coenzymes for salivary amylase
H₂CO₃, NaHCO₃, & NaHPO₄ act as buffer systems
CaHCO₃ & HPO₄ activate salivary amylase.
Thiocyanate (from protein metabolism) has bactericidal action.

Organic Constituents of Saliva

Ptyalin (α-amylase), lysozyme, & lingual lipase
Albumin, globulins, mucin, traces of urea, uric acid, and lactic acid

Functions of Saliva

Starch digestion (salivary α-amylase, lingual lipase)
Oral hygiene (lysozyme)
Antibody (IgA)
Lubrication and swallowing facilitation
Facilitation of articulation and speech
Iron absorption (lactoferrin)
Taste Facilitates taste sensation (solvent)
Protection against irritants (buffering action) Neutralizes excessive cold and hot food.
Protects mouth from excessive acids and alkalis

Functional Anatomy of the Stomach

Esophagus
Cardiac sphincter
Fundus
Body
Antrum
Pylorus
Pyloric sphincter
Duodenum

Functions of the Stomach

Storage
Mixing/grinding
Gastric emptying
Secretion of hydrochloric acid (HCl)
Kills bacteria with HCl
Activates pepsinogen to pepsin with HCl
Secretes intrinsic factor

Composition of Gastric Juice

Water (99.5%)
Organic components (0.5%):
- Pepsin, Rennin, Lipase, Tributyrase, Gelatinase, Urase, Amylase, Carbonic anhydrase, Mucin, and Intrinsic Factor
Inorganic components (0.5%):
- HCl, Na, K, HCO₃, Cl, PO₄, SO₄, and Mg++

Stomach Glands

Tubular structures in the stomach organized in three types:
- Cardiac glands (cardiac region)
- Oxyntic/Fundic/Gastric glands (body and fundus)
- Pyloric glands (pyloric region)

Pepsinoge-Pepsin

Pepsinogen (MW 42500) is a chief cell product.
Activated to pepsin (MW 3500) by HCl.
Pepsin breaks down protein into peptone, proteases, and polypeptides.
Pepsin's activity is optimal at pH between 1.8 and 4.0.

Pancreatic Juice

Volume: 500 to 1000 ml/day
Highly alkaline with pH of 8 to 8.3
99.5% water, 0.5% solids
Bicarbonate content: 110 to 150 mEq/L

Pancreatic Enzymes

Table of pancreatic enzymes, activators, substrates, and end products presented.

Pancreatic Lipase - Cholesterol Ester Hydrolase - Phospholipases - Colipase

Various enzymes are listed along with their substrates and products.

Regulation of Pancreas Secretion

Acetylcholine (ACh): Parasympathetic stimulation (vagus nerve) increasing acinar cell activity
Cholecystokinin (CCK): Stimulates acinar cell enzymes secretion.
Secretin: Stimulates pancreatic ductal epithelium releasing water and NaHCO3.

Liver Functions

Secretion of bile (bile salts, pigments)
Synthetic function (plasma proteins)
Metabolic functions (carbohydrates, fats, proteins, vitamins)
Excretory function (bile pigments, heavy metals, bacteria)
Hemopoietic function (in the fetus)
Defensive and detoxification function (hormones, drugs)

Bile

Volume: 600-1000 mL/day
pH: 7.8 (alkaline)
Contains water, cholesterol, fatty acids, bile salts, bile pigments, mucins, and electrolytes.
Concentrated in the gallbladder (5-20x)
Important role in fat digestion.
Bile does not contain digestive enzymes.

Bile Function

Fat digestion and absorption
Excretion of heavy metals, toxins, cholesterol, pathogens (typhoid bacteria)
Laxative action
Antiseptic action (inhibits bacterial growth)
Choleretic action (stimulates bile secretion)
Neutralizes acid chyme
Prevent gallstones
Lubrication.
Cholagogue function stimulates bile release from gallbladder

Formation of Bile Salts

Bile salts are Na and K salts of bile acids
Bile acids are synthesized from cholesterol
Primary bile acids in the liver are cholic acid and chenodeoxycholic acid.
In the colon, bacteria further modify these bile acids.

Jaundice (Icterus)

Yellow pigmentation of skin and mucous membranes due to increased serum bilirubin (normal: 0.2-1 mg/dL)
Types:
- Hemolytic (prehepatic)
- Hepatocellular (hepatic)
- Obstructive (posthepatic)

Intestinal Digestive Juices

Volume: 1800 mL/day
pH: 7.5 to 8.0 (alkaline)
Composition: Primarily water (99.5%) and small amount of solids.

Intestinal Enzymes

Table of intestinal enzymes, substrates, and end products is presented.

Regulation of Small Intestine Secretion

Nerve reflexes: initiated by tactile or irritative stimuli.
Parasympathetic: increases secretion
Sympathetic: decreases secretion
Hormones: Secretin and cholecystokinin (CCK)

Learning Resources

Marieb EN, Human Anatomy and Physiology (9th Ed.), ISBN-13: 978-1-2920-2649-7, Chapter 23, pp. 940-952
Powerpoint presentation in the Moodle

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Description

This quiz covers the essential functions of the digestive system, focusing on the process of breaking down food molecules for absorption. Students will explore the parts of the digestive system, the mechanisms of secretion, and the roles of enzymes and digestive juices. Understand how these processes facilitate nutrient absorption and waste removal.