HUMAN DIGESTIVE SYSTEM
Science
INTRODUCTION
The human digestive system is a complex organ system responsible for ingestion, digestion, absorption and elimination of food.
It converts complex food substances into simple, absorbable forms that can be utilized by the body for energy, growth and repair.
The digestive system works in coordination with nervous, endocrine and circulatory systems.
DEFINITION
Digestion is the mechanical and chemical process by which complex food substances are broken down into simpler soluble forms for absorption.
COMPONENTS OF HUMAN DIGESTIVE SYSTEM
The digestive system consists of:
1. Alimentary canal
2. Associated digestive glands
1. ALIMENTARY CANAL
It is a continuous muscular tube extending from mouth to anus, about 8–10 metres long.
Parts of Alimentary Canal:
Mouth → Pharynx → Oesophagus → Stomach → Small intestine → Large intestine → Rectum → Anus
MOUTH
The mouth is the entry point of food into the digestive system.
Functions:
• Ingestion of food
• Mastication (chewing) by teeth
• Mixing of food with saliva
• Initiation of carbohydrate digestion
TEETH
• Adults have 32 teeth
• Types: Incisors, Canines, Premolars, Molars
• Function: Cutting, tearing and grinding food
TONGUE
• Muscular organ attached to the floor of mouth
• Helps in tasting, chewing, swallowing and speech
• Taste buds present on papillae
SALIVARY GLANDS
There are three pairs:
• Parotid
• Submandibular
• Sublingual
Saliva contains:
• Salivary amylase (ptyalin) – digests starch into maltose
• Mucus – lubricates food
• Lysozyme – antibacterial action
PHARYNX
• Common passage for food and air
• Helps in swallowing (deglutition)
OESOPHAGUS
• Muscular tube connecting pharynx to stomach
• Food moves by peristalsis
• No digestion occurs here
STOMACH
• J-shaped muscular organ
• Located in upper left abdomen
• Stores food temporarily
Functions:
• Mechanical churning of food
• Secretion of gastric juice
• Partial digestion of proteins
• Killing of microbes
GASTRIC JUICE CONTAINS:
• Hydrochloric acid (HCl) – kills bacteria, activates pepsin
• Pepsin – protein-digesting enzyme
• Mucus – protects stomach lining
• Rennin (in infants) – digests milk protein
FOOD AFTER STOMACH:
• Semi-digested food called chyme
SMALL INTESTINE
It is the longest part of alimentary canal (about 6 metres).
Divided into:
• Duodenum
• Jejunum
• Ileum
DUODENUM
• Receives bile from liver and pancreatic juice from pancreas
• Neutralizes acidic chyme
JEJUNUM AND ILEUM
• Main site of digestion and absorption
• Inner lining has villi and microvilli to increase surface area
DIGESTIVE JUICES IN SMALL INTESTINE:
BILE (from liver):
• No enzymes
• Emulsifies fats
• Neutralizes acid
PANCREATIC JUICE:
• Amylase – digests starch
• Trypsin – digests proteins
• Lipase – digests fats
INTESTINAL JUICE:
• Maltase, sucrase, lactase – digest carbohydrates
• Peptidase – digests peptides
• Lipase – digests fats
ABSORPTION
• Occurs mainly in small intestine
• Glucose and amino acids absorbed into blood
• Fatty acids absorbed into lymph (lacteals)
LARGE INTESTINE
Consists of:
• Caecum
• Colon
• Rectum
Functions:
• Absorption of water and salts
• Formation of faeces
• Presence of beneficial bacteria (E. coli)
RECTUM AND ANUS
• Rectum stores faeces temporarily
• Anus controls defecation through anal sphincters
2. DIGESTIVE GLANDS
LIVER
• Largest gland in human body
• Produces bile
• Functions:
– Detoxification
– Storage of glycogen, vitamins and iron
– Regulation of metabolism
GALL BLADDER
• Stores and concentrates bile
• Releases bile into duodenum
PANCREAS
• Mixed gland (exocrine + endocrine)
• Exocrine: digestive enzymes
• Endocrine: insulin and glucagon
REGULATION OF DIGESTION
• Controlled by nervous system and hormones
• Hormones involved:
– Gastrin
– Secretin
– Cholecystokinin
COMMON DIGESTIVE DISORDERS
• Indigestion
• Constipation
• Diarrhoea
• Peptic ulcer
• Hepatitis
• Jaundice
IMPORTANCE OF DIGESTIVE SYSTEM
• Provides energy
• Supplies nutrients
• Maintains growth and repair
• Supports immunity
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Subject: Science
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