Topic 17 - Digestive System Flashcards
Learning Objectives
- Describe the anatomy and functions of structures within the digestive system
- Describe the layers of the gastrointestinal tract and specialised modifications in the stomach and small intestine
- Describe the digestive enzymes and their activities.
- Explain the importance of the slow delivery of chyme from the stomach to the small intestine.
- 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.
- Understand how nutrients are absorbed for use in the body.
- Describe the waste products from our digestive system and how these are made
Anatomy Overview
- Oral cavity
- Tongue
- Teeth
- Salivary Glands
- Pharynx
- Oesophagus
- Stomach
- Gallbladder
- Pancreas
- Small intestine
- Large intestine
- Rectum
- Anus
Layers of Gastrointestinal Tract (GIT)
Outside to Inside:
- Serosa
- Muscularis Externae
- Submucosa
- Mucosa
Digestive system overview
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
Organic Compounds
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
Digestion
Mechanical:
- Physical breakdown of food into smaller particles
Chemical:- Assisted via enzymes to form absorbable compounds
Oral Cavity Anatomy
3 Accessory organs:
- Teeth
- Tongue
- Salivary Gland
Major parts of Salivary glands
Parotid
Submandibular
Sublingual
Oral cavity functions
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
Pharynx Anatomy and function
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
Oesophagus anatomy
- ~25cm long
- Changes in composition as u=you go down
- Skeletal muscle for voluntary muscle conctractions
- Smooth for invol. peristalsis
Oesophagus Function
Motility:
- Propulsion of bolus into stomach via peristalsis
Peristalsis:
- Continuous waves of contraction and relaxation of muscle
Stomach Anatomy
- J shaped chamber
- 4 Main regions
- Rugae increases SA:V
- 3 Layers of Muscle
- 2 Sphincters (Gastro-oespogagal & Pyloric)
Stomach Function
- 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.
Stomach unique features
[heft]
Components of gastric juice
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
Small Intestine Anatomy
- 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
Small intestine Function
- Chemical digestion
- Largely occurs in Duodenum
- All forms of organic compounds get digested
- Most digestive enzymes are secreted from pancreas
Accessory Organs
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)
Small intestine motility and segmentation
- Peristalsis moves chyme though intestinal tract
Segmentation:
- Most common motion in Jejunum
- Promotes mixing and absorbtion of nutrients & water
Large intestine Anatomy
4 Major regions:
- Caecum
- Colon
- Rectum
- Anus
Internal Anal sphincter (Involuntary)
External Anal sphincter (Voluntary)
Large Intestine Function
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
