Topic 17 - Digestive System

Question 1

Learning Objectives

Answer 1

1. Describe the anatomy and functions of structures within the digestive system
2. Describe the layers of the gastrointestinal tract and specialised modifications in the stomach and small intestine
3. Describe the digestive enzymes and their activities.
4. Explain the importance of the slow delivery of chyme from the stomach to the small intestine.
5. Analyse the role of different digestive secretions in the processes of protection, chemical digestion, and absorption and predict the potential impacts of inadequate or excess secretion.
6. Understand how nutrients are absorbed for use in the body.
7. Describe the waste products from our digestive system and how these are made

Question 2

Anatomy Overview

Answer 2

• Oral cavity
• Tongue
• Teeth
• Salivary Glands
• Pharynx
• Oesophagus
• Stomach
• Gallbladder
• Pancreas
• Small intestine
• Large intestine
• Rectum
• Anus

Question 3

Layers of Gastrointestinal Tract (GIT)

Answer 3

Outside to Inside:
- Serosa
- Muscularis Externae
- Submucosa
- Mucosa

Question 4

Digestive system overview

Answer 4

Ingestion:
- Food into mouth

Secretion:
- GIT cells and accessory glands
- Acid, Buffers, enzymes, hormones, mucus

Motility:
- Mixing and propulsions of muscle

Digestion:
- Breakdown of food
- Chemical and Mechanical

Absorption:
- Mainly in small intestine
- Molecules into blood or lymph

Protection:
- Mucus and acid fluid against pathogens

Defecation:
- Removal of waste as faeces
- Undigested materal, bacteria, old cells

Question 5

Organic Compounds

Answer 5

Carbohydrates:
- C, H, O
- Monosaccharides (glucose fructose)
- Disaccharides (Sucrose, Lactose, Maltose)
- Polysaccharides (Starch, cellulose, glycogen0

Proteins
- Amino acids
- dipeptides
- polypeptides

Lipids
- Fats, waxes, steroids, fat-soluble vitamines
- Triglycerides
- Fatty acids

Nucleic Acid:
- Nucleotides
- DNA, RNA

Question 6

Digestion

Answer 6

Mechanical:
- Physical breakdown of food into smaller particles

Chemical:- Assisted via enzymes to form absorbable compounds

Question 7

Oral Cavity Anatomy

Answer 7

3 Accessory organs:
- Teeth
- Tongue
- Salivary Gland

Question 8

Major parts of Salivary glands

Answer 8

Parotid
Submandibular
Sublingual

Question 9

Oral cavity functions

Answer 9

Ingestion:
- Location for food to entre body before becoming bolus

Digestion:
- Teeth mechanical
- 2 Ezymes in saliva (Salivary amylase, Lingual lipase)

Secretion:
- Saliva from salivary glands (99% water, 1% salt and protein)
- Mucus lubricates food

Protection
- Saliva contains anti-microbial properties
- Ideal habitat for good microbes

Question 10

Pharynx Anatomy and function

Answer 10

Anatomy:
- Funnel shaped tube of skeletal muscle between oral cavity and oesophagus

Function:
- Shared by digestive and respiratory system
- During swallowing, structures close to ensure bolus moves to oesophagus

Question 11

Oesophagus anatomy

Answer 11

• ~25cm long
• Changes in composition as u=you go down
• Skeletal muscle for voluntary muscle conctractions
• Smooth for invol. peristalsis

Question 12

Oesophagus Function

Answer 12

Motility:
- Propulsion of bolus into stomach via peristalsis

Peristalsis:
- Continuous waves of contraction and relaxation of muscle

Question 13

Stomach Anatomy

Answer 13

• J shaped chamber
• 4 Main regions
• Rugae increases SA:V
• 3 Layers of Muscle
• 2 Sphincters (Gastro-oespogagal & Pyloric)

Question 14

Stomach Function

Answer 14

• Mechanical digestion and motility
• Perstaltic contractions push bolus towards pylorus
• Conctractions strengthen towards pylorus, grinding bolus into chyme
• Specialised cells of the gastic gland secrete gastric juices for chemical digestion, protection and absorption.

Question 15

Stomach unique features

Answer 15

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Question 16

Components of gastric juice

Answer 16

Gastrin:
- hormone that stimulates secretion og HCl and Pepsinogen

Pepsinogen:
- Activated into Pepsin in presence of HCl

Pepsin:
- Chemically targets proteins into peptides in stomach

HCl:
- Denatures proteins, converts pepsinogen into pepsin
- Kills microbes

Bicarbonate-rich mucus:
- Protects stomach wall from protein digestion & HCl corrosion

Gastric Lipase:
- Digest triglycerides

Question 17

Small Intestine Anatomy

Answer 17

• 3-6m long
• Villi & Microvilli for SA:V ratio for absorbtion

3 Regions:
- Duodenum (Closest to stomach)
- Jejunum (middle, longest)
- Ileum (Closest to large intestine)

Joins the large intestine at the ileocecal sphincter

Question 18

Small intestine Function

Answer 18

• Chemical digestion
• Largely occurs in Duodenum
• All forms of organic compounds get digested
• Most digestive enzymes are secreted from pancreas

Question 19

Accessory Organs

Answer 19

Liver:
- Secretes Bile (Bile salts emulsify fats, and fascilitates reabsorbtion of fat)
- Secretes Bilirubin (waste product pigment of RBC breakdown in liver)

Gall Bladder:
- Stores and concentrates bile by absorbing water and ions

Pancrease:
- Endocrine cells release insulin and glucagon
- Exocrine cells release pancreatic juice ( water, bicarbonate, protease, amylase, lipase, nuclease)

Question 20

Small intestine motility and segmentation

Answer 20

• Peristalsis moves chyme though intestinal tract

Segmentation:
- Most common motion in Jejunum
- Promotes mixing and absorbtion of nutrients & water

Question 21

Large intestine Anatomy

Answer 21

4 Major regions:
- Caecum
- Colon
- Rectum
- Anus

Internal Anal sphincter (Involuntary)
External Anal sphincter (Voluntary)

Question 22

Large Intestine Function

Answer 22

Digestion:
- By resident bacteria

Absorption:
- Absorbes remaining water and electrolytes (Na+, Cl-)
- Absorbes vitamines synthesised by bacteria

Motility:
- Haustral contraction ascending and transverse colon
- Peristalsis 3-4 times a day

Defacation:
- Formation of solid/ semi material
- Faecal material stored in rectum until enough accumulated
- Expelled via anus