Digestive System II Lecture Notes PDF

ANATOMY & PHYSIOLOGY II Eng Razaz Salih DIGESTIVE SYSTEM II Lecture (5) THE PANCREAS  The pancreas The pancreas is a glandular organ in the digestive system and endocrine system of vertebr...

ANATOMY & PHYSIOLOGY II Eng Razaz Salih DIGESTIVE SYSTEM II Lecture (5) THE PANCREAS  The pancreas The pancreas is a glandular organ in the digestive system and endocrine system of vertebrates. It is located in the abdominal cavity behind the stomach. It is an endocrine gland producing several important hormones, including: − insulin − Glucagon − Somatostatin − pancreatic polypeptide all of which circulate in the blood. Length: 15 cm or 6 inch  Anatomically, the pancreas is Structure divided into: – the head of pancreas, – the neck of pancreas, – the body of pancreas, – and the tail of pancreas. The neck is about 2.5 cm or 1 inch long and lies between the head and the body The body is the largest part of the pancreas and lies behind the pylorus. The tail ends by abutting the spleen.  Function The pancreas is involved in blood sugar control and metabolism within the body. pancreatic islets are present in the pancreas. Within these islets are four main types of cells which are involved in the regulation of blood glucose levels. Each type of cell secretes a different type of hormone: α alpha cells secrete glucagon (increase glucose in blood) β beta cells secrete insulin (decrease glucose in blood) δ delta cells secrete somatostatin (regulates/stops α and β cells) γ (gamma) cells, secrete pancreatic polypeptide. THE LIVER  Liver is a dual organ having both secretory and excretory functions. The liver It is the largest gland in the body, weighing about 1.5 kg in man. It is located in the upper and right side of the abdominal cavity, immediately beneath diaphragm. The liver is a reddish-brown wedge-shaped organ with four lobes of unequal size and shape. weighs 1.44–1.66 kg width -15 cm. It is both the heaviest internal organ and the largest gland in the human body.  Structure The liver is grossly divided into two parts when viewed from above – a right and a left lobe. The falciform ligament, divides the liver into a left and right lobe.  Functions of Liver Synthesis: Proteins produced and secreted by the liver. The liver plays a major role in carbohydrate, protein, amino acid, and lipid metabolism. Breakdown: The liver is responsible for the breakdown of insulin and other hormones. The liver breaks down bilirubin via glucuronidation, facilitating its excretion into bile.  Functions of Liver Other : The liver stores a multitude of substances, including glucose (in the form of glycogen) The liver produces albumin, the most abundant protein in blood serum. Contains phagocytes to destroy damaged erythrocytes and foreign substances, using phagocytosis.  The Gallbladder The gallbladder is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver.  Structure The gallbladder sits in a shallow depression below the right lobe of the liver, that is grey-blue in life. Length-7 to 10 cm or 2.8 to 3.9 inches Diameter -4 cm or 1.6 inch The gallbladder has a capacity of about 50 millilitres The gallbladder is shaped like a pear, with its tip opening into the cystic duct. gallbladder is divided into three sections: o The fundus, o The body, o The neck.  Functions of Gallbladder The main purpose of the gallbladder is to store bile (also called gall) needed for the digestion of fats in food. bile flows through small vessels into the larger hepatic ducts and ultimately though the cystic duct into the gallbladder, where it is stored.  SMALL INTESTINE  Small Intestine Small intestine is the part of gastrointestinal (GI) tract, extending between the pyloric sphincter of stomach and ileocecal valve, which opens into large intestine. It is called small intestine because of its small diameter, compared to that of the large intestine. But it is longer than large intestine. Its length is about 6 meter. Important function of small intestine is absorption. Maximum absorption of digested food products takes place in small intestine.  Portions Of Small Intestine Small intestine consists of three portions: 1. Proximal part known as duodenum 2. Middle part known as jejunum 3. Distal part known as ileum. Wall of the small intestine has all the four layers as in stomach  Portions Of Small Intestine The duodenum : is a short structure ranging from 20 cm to 25 cm in length, and shaped like a "C". The jejunum: is the midsection of the small intestine, connecting the duodenum to the ileum. It is about 2.5 m long. The ileum : is the final section of the small intestine. It is about 3 m long, and contains villi similar to the jejunum.  Functions Of Small Intestine Digestion: The small intestine is where most chemical digestion takes place Many of the digestive enzymes that act in the small intestine are secreted by the pancreas and liver and enter the small intestine via the pancreatic duct. Digestion of proteins & carbohydrate  Functions Of Small Intestine Absorption: Digested food is now able to pass into the blood vessels in the wall of the intestine through either diffusion or active transport. The small intestine is the site where most of the nutrients from ingested food are absorbed. Immunological: The small intestine supports the body's immune system. The presence of gut flora appears to contribute positively to the host's immune system. THE LARGE INTESTINE  The Large Intestine The large intestine, also known as the large bowel or colon, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remaining waste material is stored as feces before being removed by defecation.  Structure The length of male colon is 166 cm and female colon 155 cm The colon consists of five sections: 1. The cecum 2. Ascending colon, 3. The transverse colon, 4. The descending colon, 5. The sigmoid colon 6. The rectum.  Sections of the colon The ascending colon: The ascending colon including the cecum and appendix The transverse colon including the colic flexures and transverse mesocolon The descending colon The sigmoid colon – the s-shaped region of the large intestine 72. The average inner diameter of sections of the colon in centimeters cecum 8.7cm ascending colon 6.6cm transverse colon 5.8cm descending/sigmoid colon 6.3cm and rectum near rectal/sigmoid junction 5.7cm  Sections of the colon The cecum: The cecum is the first section of the colon and involved in the digestion, while the appendix is a structure of the colon, not involved in digestion. The function of the appendix is uncertain, Containing Ileocecal valve The ileocecal valve is a sphincter muscle valve that separates the small intestine and the large intestine.  Sections of the colon The Ascending colon: It is connected to the small intestine by a section of bowel called the cecum. The ascending colon runs upwards through the abdominal cavity toward the transverse colon for approximately eight inches or 20 cm. The unwanted waste material is moved upwards toward the transverse colon by the action of peristalsis. Peristalsis is a radially symmetrical contraction and relaxation of muscles that propagates in a wave down a tube.  Sections of the colon Transverse colon: The transverse colon is the part of the colon from the hepatic flexure to the splenic flexure. Descending colon: The descending colon is the part of the colon from the splenic flexure to the beginning of the sigmoid colon, descending colon is also called the distal gut. One function of the descending colon in the digestive system is to store feces that will be emptied into the rectum.  Sections of the colon Sigmoid colon: The name sigmoid means S-shaped , The sigmoid colon is the part of the large intestine after the descending colon and before the rectum. The walls of the sigmoid colon are muscular, and contract to increase the pressure inside the colon, causing the stool to move into the rectum. Rectum: The rectum is the last section of the large intestine. It holds the formed feces awaiting elimination via defecation.  Sections of the colon The anus: The anus is the external opening of the rectum. Its function is to control the expulsion of feces. Two sphincters control the exit of feces from the body during an act of defecation, These are: The internal anal sphincter The external anal sphincter which are circular muscles that normally maintain constriction of the orifice and which relaxes as required by normal physiological functioning.  FUNCTIONS Of The Large Intestine 1. The large intestine absorbs water and any remaining absorbable nutrients from the food before sending the indigestible matter to the rectum. 2. The colon absorbs vitamins that are created by the colonic bacteria, such as vitamin K. 3. he large intestine houses over 700 species of bacteria that perform a variety of functions. 4. The large intestine absorbs some of the products formed by the bacteria inhabiting this region.  Physiology Of Digestion The mouth is the beginning of the digestive tract. Chewing breaks the food into pieces that are more easily digested, while saliva mixes with food to begin the process of breaking it down into a form your body can absorb and use. From pharynx food travels to the esophagus or swallowing tube. By means of a series of contractions, called peristalsis, the esophagus delivers food to the stomach. The lower esophageal sphincter keep food from passing backwards into the esophagus.  Physiology Of Digestion The stomach secretes acid and powerful enzymes that continue the process of breaking down the food. When it leaves the stomach, food is the consistency of a liquid or paste. From there the food moves to the small intestine. The small intestine continues the process of breaking down food by using enzymes released by the pancreas and bile from the liver. Bile is a compound that aids in the digestion of fat and eliminates waste products from the blood.  Physiology Of Digestion pancreas secretes enzymes into the small intestine. These enzymes break down protein, fat, and carbohydrates from the food we eat. Stool, or waste left over from the digestive process, is passed through the colon by means of peristalsis, first in a liquid state and ultimately in solid form as the water is removed from the stool. A stool is stored in the sigmoid colon until a "mass movement" empties it into the rectum once or twice a day.