Functions of Digestive Apparatus Reception food & drink. Mechanical & chemical digestion. Absorption of food & drink. Elimination of unabsorbed residues (e.g. Eliminate solid waste from the body).
Overview of the Digestive System Organs are divided into two groups The alimentary canal (gastrointestinal (GI)tract) Mouth, pharynx, and esophagus Stomach, small intestine, and large intestine (colon), anus Open at both ends to the outside of the body Accessory digestive organs Teeth and tongue Gallbladder, salivary glands, liver, and pancreas Secrete saliva, bile, digestive enzymes
Digestive System Muscular, hollow tube (= “digestive tract”) + Various accessory organs consists of:
Function ingestion mechanical digestion chemical and enzymatic digestion secretion absorption compaction excretion and elimination The function of the system as a whole is processing food in such a way that high energy molecules can be absorbed and residues eliminated. Individual parts function in:
Propulsion Movement of food through the GI tract Swallowing Peristalsis - Major means of propulsion Adjacent segments of the alimentary canal relax and contract
Digestion - Mechanical Mechanical digestion – physically prepares food for chemical digestion. – Chewing – Churning of food – Segmentation - Rhythmic local contractions of the intestine Mixes food with digestive juices to help increase the efficiency of nutrient absorption
Digestion - Chemical Series of steps in which complex food molecules (carbohydrates, proteins and lipids) are broken down to their chemical building blocks (simple sugars, amino acids, fatty acids, and glycerol) Digestive enzymes are released in the lumen of the GI tract
Digestive Processes - continued Absorption – transport of digested end products from the lumen of the GI tract into the blood and lymph capillaries located in the walls of the tract Defecation – elimination of indigestible substances from the body as feces
Muscularis externa Histological Organization Tube made up of four layers. Modifications along its length as needed. 1 2 3 4
The Mouth : entered between the lips & continues into pharynx. Structure : 1.Cavity & its wall. 2.Accessory structures (teeth, tongue). 3. Salivary glands. Function: Prehension, Mastication & insalivation of food. The form of lips varies with feeding habits. -A wide gap is necessary in species that use their teeth to seize prey or in fight as in the Dog.
The Mouth It is divide to : 1-Vestibule : Is the cavity laying outside the teeth and the gum and inside the lips and cheeks 2-Mouth (oral) Cavity : Is bounded dorsally by the hard palate and ventrally by the tongue and craniolateral by the dental arches and caudoventral by the palatogloossal arch,
The lips of the dog are extensive but thin. Lips posture is an important factor in communication in the dog & can signal aggressive or submission. It composed of : 1. Muscle. 2. Tendon. 3.glands. 4. Oral mucosa. The salivary glands are scattered between two lips. The lower lip of the dog its rather loose but fixed to the lower jaw. In the upper lip in the dog sometimes occur a modified skin around the nostrils ( It divided by median groove (philtrum) ).
The Salivary Glands Their secretion “saliva”: 1. Keeps the interior of the mouth moist. 2. Facilitate mastication when mixed with food. 3. Lubricate the passage of food when dog is swallowing the food. 4. Excretion of certain substances, some of which may accumulate as a deposit (tartar) on teeth.
The Salivary Glands The salivary glands in the dog are : 1.Parotid gland : it is small & confined to the vacinity of the ear cartilage its duct is short &open to opposite of fourth upper premolar - its secretion important in moistening & softening the food. 2. Mandibular gland :it is moderately large, very regular ovoid shape. It produce mucous & serous secretion.
3. Sublingual gland : composed of compact part - its fits over the rostral extremity of the mandibular gland. 4. Zygomatic gland.
The Tongue Highly muscular organ capable of both vigorous & precise movements. Occupies the greater part of the oral cavity. It attachment at its root &body, but free apex. Used to prehension, lapping, grooming
The Tongue The surface is covered by a variety of papillae. The ventral part of the tongue contains a prominent fibrous condensation. The “lyssa” easily recognized on palpation. The lingual branch of mandibular nerve is responsible for general sensation over the rostral two third of the tongue.
The Teeth Function to tear and grind food Deciduous teeth – 28 teeth Permanent teeth – 38 teeth
Structure of Teeth Crown - exposed surface of tooth Neck - boundary between root and crown Enamel - outer surface Dentin – bone-like, but noncellular Pulp cavity - hollow with blood vessels and nerves
Dental formula – shorthand Way to indicate number and position of teeth The largest teeth in the dog are : the last premolar & the first lower molar. The lower canine engages in front of the upper canine filling the space between this & the third incisor. Temporary: upper jaw: I3-C1-P3 Lower jaw: I3-C1-P3 permanent: upper jaw: I3-C1-P4-M2 Lower jaw: I3-C1-P4-M3
The Pharynx Lies behind the mouth & continues into the esophagus. Pathway of food as well as air. It is provided by soft palate. In response it lies on the tongue, but in swallowing it raised into horizontal position
The esophagus Convey food from pharynx to stomach. It consist of cervical, thoracic & abdominal portions. Dorsal to the cricoid cartilage of the larynx, & follows the trachea down the neck The first flexure to the left but regaining a median position above the trachea before or shortly after entering the thorax. It runs in mediastinum & continuing beyond the tracheal bifurcation
The esophagus It passes over the heart before penerating the esophageal hiatus of the diaphragm It then makes its way over the dorsal border of the liver to join the stomach at the cardia. The outer coat is a loose connective tissue in the neck, largely replaced by serosa in thorax & abdomen.
The esophagus *Its wall contain of 3 layers: 1. Mucosa. 2. 2 layers of muscle:a. longitudinal(outer). b. circular (inner). 3. Outer loose connective tissue. *Thin stratified squamous with the degree of keratinization reflecting the relative harshness of the dog habitual diet. *Many mucus-secreting tubuloacinar glands present in the submucosa of the canine esophagus. *Its innervation from sympathetic & vagus nerves.
The stomach It is organ which process of digestion is initiated. It received food from esophagus & retain it before discharging it into small intestine. Its parts are : cardiac part, fundus, body, & pyloric part. These parts form a great & lesser curvature.
The stomach of the dog : The concentrated diet of carnivores is most easily digested & the dog has a simple stomach & relatively short & uncomplicated intestine. The stomach of the dog has a relatively modest capacity ranging from 0.5-6.0 L according to breed.
The intestine Commences at the pylorus & continues to the anus. It divided into proximal small intestine & distal large intestine. Small intestine consist of : 1. duodenum 2. Jejunum 3. Ilium. *Which are carried by the great mesentery. Large intestine consist of : 1. Cecum 2. Colon (ascending, transverse,descending ) 3. Rectum (it is reteroperitoneal).
The small intestine: The more constant relation of dog’s duodenum are to the liver at its origin. The luminal surface of the intestine has villi, these shape like finger in the dog. To increase the area for absorption. The large intestine: villi are lacking in large intestine. Rectum is straight but often this part of the bowel is deflected to one side by pressure from the distended bladder. -It is most dorsal of the pelvic viscera & lies above the reproductive organ, bladder & urethra.