Fisiologi Hewan - Fisiologi Pencernaan

• Nutrients obtained by animals are used for egestion, which involves four types of animal ingestion: filter (suspension) feeder, substrate feeder, fluid feeder, and bulk feeder
• Digestion in animals must be contained in specialized compartments, such as:

  • Digestion occurring in individual cells for single-celled organisms like phagocytosis and fusion of lysosomes with the resulting food vacuole
  • Sponges digesting suspended organic material in individual cells
  • Gastrovascular cavity in organisms like Hydra allowing the consumption of larger pieces of food with digestion and circulation of nutrients through one opening
• Platyhelminthes also use a gastrovascular cavity for digestion, while substrate feeders like Annelida take in soil through the mouth
• Annelida have an alimentary canal (AC) where soil enters the pharynx, passes down the esophagus to the crop for moistening and storing food, then continues through specialized compartments for ingestion, digestion, absorption, and egestion
• In Annelida, the crop releases food into the gizzard for mechanical digestion with sand, followed by enzymatic breakdown in the intestines for absorption into the blood, with undigested material egested through the anus
• Chordata, like birds, are bulk feeders ingesting food via the mouth, passing it through the esophagus into the crop for storage, then to the stomach for chemical and mechanical digestion before entering the intestines for absorption into the blood, with undigested material egested through the anus
• The digestive system consists of a long hollow muscular tube called the GastroIntestinal Tract (GIT) and accessory glands like salivary glands, liver, gall bladder, and pancreas
• The main functions of the digestive tract include motility to propel food, secretion of juices for digestion, digestion to break down food, and absorption of nutrients, electrolytes, and water into the bloodstream
• GI motility involves propulsive movement of food forward through peristalsis and mixing movements, like segmentation, to help digestion and absorption
• Peristalsis and segmentation are two main types of motility in the GI tract, with peristalsis producing forward movement of matter and segmentation causing a forward-and-backward movement to break down food particles and facilitate absorption
• The large intestine or colon has motility types like segmentation for continuous mixing, mass movement to propel contents downstream, and defecation involving involuntary and voluntary reflexes for the evacuation of colonic content through the anal canal
• Digestive glands secrete saliva, gastric juice, pancreatic juice, bile, and intestinal juice when food is present in the digestive tract or when it is sensed, smelled, or imagined, with nervous and hormonal mechanisms controlling the flow of digestive juices
• Saliva secretion is reflex-controlled by chemical and mechanical stimuli from the presence of food in the mouth, as well as olfactory and visual stimuli from the smell and sight of food
• The digestive system of an earthworm consists of the salivary glands, gastric juice, and pancreatic secretion

  
• Gastric juice is made up of water, mucus, and digestive enzymes secreted by gastric glands within gastric pits
• The regulation of salivary secretion involves the chloride shift and proton pump to help the stomach become more acidic and the blood more basic
• Pancreatic juice is made up of water and inactive proenzymes, and it has two functions: endocrine functions (secreting insulin and glucagon) and exocrine function (secretion of pancreatic juice)
• Pancreatic enzymes include trypsin, chymotrypsin, lipase, and amylase, essential for the proper digestion and absorption of carbohydrates, fats, and proteins
• Intestinal juice is a basic, mucus solution that buffers and lubricates materials in the intestine
• Absorption in the small intestine occurs through simple diffusion, facilitated diffusion, active transport, endocytosis, and paracellular transport
• Defecation is the expulsion of feces from the digestive tract, occurring as a reflex brought about by stimulation of receptors in the rectal mucosa when the rectum is distended
• The pancreas produces pancreatic juices daily, consisting of a bicarbonate solution containing salts and digestive enzymes
• Salivary glands have three pairs: parotid, sublingual, and submandibular, and their functions include lubricating, cleaning the oral cavity, dissolving chemicals, suppressing bacterial growth, and digesting starch by amylase
• Bile, secreted by the liver and stored in the gallbladder, is stimulated by CCK and contains cholesterol, bile pigments, and products of detoxification for removal through feces
• The large intestine absorbs water, electrolytes, and some vitamins, and feces consist of water, inorganic salts, sloughed-off epithelial cells, bacteria, products of bacterial decomposition, and undigested parts of food